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Journal articles on the topic 'Covalent radius'

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Published: 4 June 2021
Last updated: 10 February 2022

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1

Natapoff, M. "The radius of an atom in covalent compounds." Chemical Physics Letters 233, no. 5-6 (February 1995): 653–57. http://dx.doi.org/10.1016/0009-2614(94)01512-t.

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2

Gillespie, Ronald J., and Edward A. Robinson. "Bond lengths in covalent fluorides. A new value for the covalent radius of fluorine." Inorganic Chemistry 31, no. 10 (May 1992): 1960–63. http://dx.doi.org/10.1021/ic00036a045.

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3

GILLESPIE, R. J., and E. A. ROBINSON. "ChemInform Abstract: Bond Lengths in Covalent Fluorides. A New Value for the Covalent Radius of Fluorine." ChemInform 23, no. 33 (August 21, 2010): no. http://dx.doi.org/10.1002/chin.199233003.

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4

Apátiga, Jorge Luis, Roxana Mitzayé del Castillo, Luis Felipe del Castillo, Alipio G. Calles, Raúl Espejel-Morales, José F. Favela, and Vicente Compañ. "Non-Covalent Interactions on Polymer-Graphene Nanocomposites and Their Effects on the Electrical Conductivity." Polymers 13, no. 11 (May 24, 2021): 1714. http://dx.doi.org/10.3390/polym13111714.

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It is well known that a small number of graphene nanoparticles embedded in polymers enhance the electrical conductivity; the polymer changes from being an insulator to a conductor. The graphene nanoparticles induce several quantum effects, non-covalent interactions, so the percolation threshold is accelerated. We studied five of the most widely used polymers embedded with graphene nanoparticles: polystyrene, polyethylene-terephthalate, polyether-ketone, polypropylene, and polyurethane. The polymers with aromatic rings are affected mainly by the graphene nanoparticles due to the π-π stacking, and the long-range terms of the dispersion corrections are predominant. The polymers with linear structure have a CH-π stacking, and the short-range terms of the dispersion corrections are the important ones. We used the action radius as a measuring tool to quantify the non-covalent interactions. This action radius was the main parameter used in the Monte-Carlo simulation to obtain the conductivity at room temperature (300 K). The action radius was the key tool to describe how the percolation transition works from the fundamental quantum levels and connect the microscopic study with macroscopic properties. In the Monte-Carlo simulation, it was observed that the non-covalent interactions affect the electronic transmission, inducing a higher mean-free path that promotes the efficiency in the transmission.
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5

Zhang, Yonghe. "Covalent Radii and New Applications." International Journal of Chemoinformatics and Chemical Engineering 7, no. 1 (January 2018): 42–51. http://dx.doi.org/10.4018/ijcce.2018010103.

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Ionocovalency theory is defined “…everything exists in ionocovalency, the harmony of ionic energy with the covalent environment.” The authors have succeeded in thoroughly studying ionic energy part of the ionocovalent theory, and will now focus target on the covalent environment part of the theory. The essence of chemical reactions and chemical bonds is the overlap of atomic orbitals, the electron density or the ionocovalent potential. The covalent radius rc is the unique parameter that can be considered as an atomic property derived from molecules for data reduction and can be assigned to the atoms interacting in molecules. In the present study, A new application view of covalent radii of multidimensional world is revealed by the ionocovalency theory which can quantitatively describe the chemical phenomena and qualitatively correlates to the universal observations.
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6

Al Nakeeb, Nischang, and Schmidt. "Tannic Acid-Mediated Aggregate Stabilization of Poly(N-vinylpyrrolidone)-b-poly(oligo (ethylene glycol) methyl ether methacrylate) Double Hydrophilic Block Copolymers." Nanomaterials 9, no. 5 (April 26, 2019): 662. http://dx.doi.org/10.3390/nano9050662.

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The self-assembly of block copolymers in aqueous solution is an important field in modern polymer science that has been extended to double hydrophilic block copolymers (DHBC) in recent years. In here, a significant improvement of the self-assembly process of DHBC in aqueous solution by utilizing a linear-brush macromolecular architecture is presented. The improved self-assembly behavior of poly(N-vinylpyrrolidone)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PVP-b-P(OEGMA)) and its concentration dependency is investigated via dynamic light scattering (DLS) (apparent hydrodynamic radii ≈ 100–120 nm). Moreover, the DHBC assemblies can be non-covalently crosslinked with tannic acid via hydrogen bonding, which leads to the formation of small aggregates as well (apparent hydrodynamic radius ≈ 15 nm). Non-covalent crosslinking improves the self-assembly and stabilizes the aggregates upon dilution, reducing the concentration dependency of aggregate self-assembly. Additionally, the non-covalent aggregates can be disassembled in basic media. The presence of aggregates was studied via cryogenic scanning electron microscopy (cryo-SEM) and DLS before and after non-covalent crosslinking. Furthermore, analytical ultracentrifugation of the formed aggregate structures was performed, clearly showing the existence of polymer assemblies, particularly after non-covalent crosslinking. In summary, we report on the completely hydrophilic self-assembled structures in solution formed from fully biocompatible building entities in water.
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7

Uchida, Etsuo, Motoki Murasugi, and Shuichi Okuda. "Simultaneous Partitioning of Divalent Metal Ions between Alabandite and 1 mol/L (Ni, Mg, Co, Zn, Fe)Cl2 Aqueous Solutions under Supercritical Conditions." Minerals 10, no. 8 (August 5, 2020): 696. http://dx.doi.org/10.3390/min10080696.

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To clarify the element partitioning behavior between minerals and aqueous chloride solutions, we conducted experiments to investigate simultaneous partitioning of Ni2+, Mg2+, Co2+, Zn2+, Fe2+, and Mn2+ ions between alabandite (MnS) and 1 mol/L (Ni, Mg, Co, Zn, Fe)Cl2 aqueous solutions at 500–800 °C and 100 MPa. The bulk partition coefficients calculated using the following equation were in the order of Fe2+ > Co2+ > Ni2+ ≈ Zn2+ > Mn2+ >> Mg2+; KPN = (xMeS/mMeaq)/(xMnS/mMnaq). A partition coefficient-ionic radius (PC-IR) curve was plotted with the logarithmic value of the partition coefficient on the y-axis and the ionic radius at the six-fold coordinated site on the x-axis. The peak of this curve was located near the ionic radius of Fe2+ and not near the ionic radius of Mn2+. Zn2+ showed a slight negative partitioning anomaly, which increased in the order of sulfide minerals < arsenic sulfide minerals < arsenide minerals as the covalent bond became stronger. Ni2+ showed a positive partitioning anomaly, which indicated that it preferred an octahedral structure. The width of the PC-IR curve decreased in the order of sulfide minerals > arsenic sulfide minerals > arsenide minerals as the covalent bond became stronger, that is, the ion selectivity became stronger.
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8

Ghanty, Tapan K., and Swapan K. Ghosh. "Simple Density Functional Approach to Polarizability, Hardness, and Covalent Radius of Atomic Systems." Journal of Physical Chemistry 98, no. 37 (September 1994): 9197–201. http://dx.doi.org/10.1021/j100088a018.

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9

Al-Zafeeri, Ajeel F. A. "The Effect of the Radius of Covalent Bond on Melting Temperature of Organic Compounds." IOSR Journal of Engineering 4, no. 7 (July 2014): 05–08. http://dx.doi.org/10.9790/3021-04710508.

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10

Kozlov, Georgii V., and Igor V. Dolbin. "STRUCTURAL MODEL OF EFFICIENCY OF COVALENT FUNCTIONALIZATION OF CARBON NANOTUBES." IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENII KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 62, no. 10 (October 29, 2019): 118–23. http://dx.doi.org/10.6060/ivkkt.20196210.5962.

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Functionalization of carbon nanotubes (covalent and noncovalent ones) is effective and often applied method of enhancement of their interaction with polymer matrix of nanocomposites. In present work the treatment is proposed, for the first time allowing quantitative estimation of efficiency (quality) of this nanofiller functionalization. For this purpose proposed earlier generalized model was used, taking into consideration characteristics of matrix polymer and nanofiller and also type of the last. Application of the indicated model allows to obtain quantitative characteristic of functionalization efficiency and also elucidation of interconnection of the indicated efficiency with structure of carbon nanotubes in polymer matrix of nanocomposite, namely, with radius of their annular structures. It has been found that the same method of functionalization from the chemical point of view can be changed its efficiency in 20 times that is dependent upon structure (radius) of annular formations of carbon nanotubes. Their specific surface is the more precise characteristic of these formations. This surface serves as indicator of intensity of contact of polymer matrix and surface of nanotubes, which in the end forms mechanical and other properties of the considered nanocomposites. The equation has been obtained, showing the dependence of functionalization efficiency on two parameters: effective specific surface and content of carbon nanotubes. The sharp discrete reduction of functionalization occurs at reaching of percolation threshold of nanofiller. This means that functionalization of local structures of carbon nanotubes is more effective than functionalization of uninterrupted structures of this nanofiller. The most important mechanical property of polymer nanocomposites, namely, the reinforcement degree, is defined unequivocally by efficiency of functionalization. This approach allows making structural prediction of mechanical properties of nanocomposites polymer/carbon nanotube depending of efficiency of nanofiller functionalization.
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11

ZHANG, MING-BO, DONG-XIA ZHAO, and ZHONG-ZHI YANG. "THE CHARACTERISTIC BOUNDARY RADII OF ATOMS." Journal of Theoretical and Computational Chemistry 04, no. 01 (March 2005): 281–88. http://dx.doi.org/10.1142/s0219633605001568.

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The characteristic boundary radius of an atom has been defined as the distance from the classical turning point of electronic motion to the nucleus of the atom. With the ab initio method, the atomic boundary radii for elements from H through Xe are calculated. For the atoms in the same group, the radii defined in this way are of good linear relationship with the empirical radii commonly accepted, such as the van der Waals and covalent atomic radii determined by experimental data.
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12

Du, Lifei, Peng Zhang, Lianli Wang, and Huiling Du. "Effect of different RE site ionic radii on the electronic structures and elastic properties of Ba2RENbO6: A first-principles study." International Journal of Modern Physics B 31, no. 23 (September 14, 2017): 1750165. http://dx.doi.org/10.1142/s021797921750165x.

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RE site ionic radius has a critical influence on the properties of double perovskite oxide Ba2RENbO6. In this paper, the electronic structures and elastic properties of Ba2RENbO6 (RE = Ho, Er, Yb) have been calculated by using the plane-wave pseudopotential density functional theory, and the effect of the different RE site ions on the structures and properties of Ba2RENbO6 is discussed. Results indicate that Ba2RENbO6 (RE = Ho, Er, Yb) are all direct bandgap semiconductors with a bandgap of 0.95 eV, 1.26 eV and 2.36 eV, respectively. With the decrease of the RE site ionic radius of Ba2RENbO6 (RE = Ho, Er, Yb), RE–O and Nb–O covalent bonds are enhanced, and the elastic constants ([Formula: see text], [Formula: see text], [Formula: see text]), elastic modulus ([Formula: see text], [Formula: see text], [Formula: see text]), [Formula: see text], Poisson’s ratio ([Formula: see text]), the Debye temperature [Formula: see text], Gruneisen parameters [Formula: see text] all show a trend of increase. The elastic and thermodynamic properties are all improved with the decreasing radius of RE site ion.
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13

Ghanty, Tapan K., and Swapan K. Ghosh. "A Frontier Orbital Density Functional Approach to Polarizability, Hardness, Electronegativity, and Covalent Radius of Atomic Systems." Journal of the American Chemical Society 116, no. 19 (September 1994): 8801–2. http://dx.doi.org/10.1021/ja00098a046.

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14

Sun, Xiaomin, Dacheng Feng, Zhengting Cai, and Wensheng Bian. "An ab initio study of the potential energy surfaces for the collision between a Cs atom and an I2 molecule." Canadian Journal of Chemistry 82, no. 7 (July 1, 2004): 1216–22. http://dx.doi.org/10.1139/v04-025.

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For the Cs + I2 collision system, a systematic theoretical study is first reported using the ab initio method. Three of eight possible channels are considered. The nonadiabatic coupling between the covalent state and the ionic one is calculated from different angles, especially the T-shape collision. The complete ion-pair formation potential energy surfaces of the T-shape collision in two electronic states (ionic 2B2 state and covalent 2A1 state) and the reactive surface of the linear collision are constructed at the QCISD(T)/SDD level. The main features of potential energy surfaces, such as the minimum energy reaction path, the crossing radius (Rc), and energy minimum geometries, are analyzed. The cross section of this titled system is calculated based on the harpoon mechanism and compared with the available experimental data and those obtained for the M + I2 (M = Li, Na) systems.Key words: ab initio two-state potential energy surfaces, nonadiabatic coupling, ion-pair formation, cross section.
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15

Robinson, E. A. "The duodecet rule: Part 3. Fluoro species of the third period elements." Canadian Journal of Chemistry 70, no. 6 (June 1, 1992): 1696–705. http://dx.doi.org/10.1139/v92-213.

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On the basis of the suggested new value of 54 pm for the single bond covalent radius of fluorine, the previously established duodecetrule for period 3 elements in molecular species with highly electronegative ligands is extended to fluorides. It is shown, for species such as SiF4, (F3Si)2O, F3SiNH2, F3PO, and PF5, that the observed bond lengths are consistent with significant partial double bonding involving all the ligands, including fluorine, and with a total of six electron pairs in the valence shell of the central atom. Empirical rules based on d/d1, the ratio of an observed bond length to the corresponding single bond length calculated from the sum of covalent radii, are developed as a simple approximate guide to the extent of partial double bonding in bonds to third period elements. It is also shown that bond lengths in species such as Al2F5, AlO45−, and Al(NH2)4− are consistent with a duodecet rule.
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16

Zhang, Haopeng, Wenbin Liu, Tingting Lin, Wenhong Wang, and Guodong Liu. "Phase Stability and Magnetic Properties of Mn3Z (Z = Al, Ga, In, Tl, Ge, Sn, Pb) Heusler Alloys." Applied Sciences 9, no. 5 (March 7, 2019): 964. http://dx.doi.org/10.3390/app9050964.

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The structural stability and magnetic properties of the cubic and tetragonal phases of Mn3Z (Z = Ga, In, Tl, Ge, Sn, Pb) Heusler alloys are studied by using first-principles calculations. It is found that with the increasing of the atomic radius of Z atom, the more stable phase varies from the cubic to the tetragonal structure. With increasing tetragonal distortion, the magnetic moments of Mn (A/C and B) atoms change in a regular way, which can be traced back to the change of the relative distance and the covalent hybridization between the atoms.
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17

Chattaraj, Pratim K., Andrés Cedillo, and Robert G. Parr. "Fukui function from a gradient expansion formula, and estimate of hardness and covalent radius for an atom." Journal of Chemical Physics 103, no. 24 (December 22, 1995): 10621–26. http://dx.doi.org/10.1063/1.469847.

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18

Lundquist, Eric G., Kirsten Folting, John C. Huffman, and Kenneth G. Caulton. "A single bond covalent radius for IrIII: Crystal and molecular structure of fac-Ir(CH3)3(PMe2Ph)3." Polyhedron 7, no. 21 (January 1988): 2171–73. http://dx.doi.org/10.1016/s0277-5387(00)81798-2.

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19

Индейцев, Д. А., and Е. В. Осипова. "Анализ водородоустойчивости алюминиевых сплавов." Письма в журнал технической физики 47, no. 4 (2021): 15. http://dx.doi.org/10.21883/pjtf.2021.04.50638.18562.

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It was established by the methods of quantum chemistry that tungsten W and rhenium Re are the most effective additives that increase the hydrogen resistance of aluminum Al. It is shown that W and Re strongly compress aluminum, but at the same time have a rather large covalent radius. In addition, each W and Re atom form stable chemical bonds with 12 Al atoms. As a result, the W and Re atoms strongly bind Al atoms significantly increasing the energy of vacancy formation and slowing down the process of hydrogen embrittlement. All basic physical and mechanical properties of the most hydrogen-resistant aluminum compound WReAl24 have been calculated using density functional theory.
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20

Chen, Zhihua, Abaid ur Rehman Virk, Mustafa Habib, Tariq Javed Zia, Imran Ahmed, Ce Shi, and Waqas Nazeer. "Irregularity Indices of Dendrimer Structures Used as Molecular Disrupter in QSAR Study." Journal of Chemistry 2019 (December 4, 2019): 1–21. http://dx.doi.org/10.1155/2019/5371254.

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Dendrimers are rising polymeric structures known for their flexibility in medication conveyance and high usefulness, whose properties are same biomolecules. These nanostructured macromolecules have shown potential capacities in capturing as well as conjugating the high subatomic weight hydrophilic/hydrophobic substances by host-visitor collaborations and covalent holding (prodrug approach) individually. In quantitative structure-property relationships (QSPR), topological indices are utilized to gather properties of dendrimers. Topological indices catch symmetry of dendrimer structures and give it a logical reasoning to predict properties, for instance, viscosity, boiling points, the radius of gyrations, etc. In this report, we intend to examine dendrimers through irregularity indices that are valuable in QSPR studies. We studied sixteen irregularity indices if diverse dendrimer structures.
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21

Tan, Xin, Zhixin Liu, Xuejie Liu, Yuan Ren, Shiyang Sun, and Huiling Jia. "Ab initio study of structural stability and electronic properties of GeV in diamond." International Journal of Modern Physics B 34, no. 06 (February 27, 2020): 2050036. http://dx.doi.org/10.1142/s0217979220500368.

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A complete theory is the guide and explanation of the experiment. According to the first principle, the stable structure of Ge vacancy color center (GeV) is the double vacancy center structure by using the constructed GeV color center supercell. The covalent radius and bond angle of GeV are explored by analyzing the microstructures. The electronic structure of GeV color center is calculated, and the charge transfers of GeV color center are explained, thereby demonstrating the existence of stable bonds. The principle of the energy-level transition of the GeV color center in terms of light emission is described. The effect of each element and energy level orbital is illustrated by the density-of-states diagram.
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22

Ringuet, Michel, Denis Girard, and Camille Chapados. "Vibrational and electronic spectra of new liposoluble metalloporphyrins in a nonpolar noncoordinating solvent." Canadian Journal of Chemistry 69, no. 7 (July 1, 1991): 1070–79. http://dx.doi.org/10.1139/v91-159.

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A new liposoluble porphyrin, 2,7,12,17-tetrahexyl-3,8,13,18-tetramethylporphin(THTMP), and its complexes with divalent (Mg, Co, Ni, Cu, Zn, Cd, Hg) and trivalent (Mn, Fe) metals have been synthesized. The electronic, infrared, and far-infrared spectra of these compounds were obtained in the same nonpolar, noncoordinating solvent, CCl4. After comparison with the experimental data and the results of normal coordinate analyses from the literature, the assignment of the vibrational bands of THTMP and its complexes is made. Some correlations between the shifts of the metal sensitive bands in the diffferent regions and the structural characteristics of the porphyrin complexes are reported. Some emphasis is made on the magnesium complex in relation to chlorophyll. Key words: Metalloporphyrin, porphyrin, infrared spectroscopy, far-infrared spectroscopy, electronic spectroscopy, nitrogen-metal bond, covalent radius, reduced mass.
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23

Melník, Milan, and Peter Mikuš. "Variable combinations of organophosphines in PtP3X derivatives: Structural aspects." Main Group Metal Chemistry 44, no. 1 (January 1, 2021): 12–21. http://dx.doi.org/10.1515/mgmc-2021-0003.

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Abstract This review covers over fifty Pt (II) complexes of the compositions PtP3X (X = H, OL, NL, BL, Cl, SL, Br, or I). These complexes crystallized in three crystal classes: monoclinic (23 examples) triclinic (17 examples) and orthorhombic (11 examples). The PtP3Cl is most common with 23 examples. There are variable combinations of organophosphines monodentate – P; bidentate- P,P; P,N; P,B; and tridentate – P,P,P; P,O,P; P,N,P; and P,S,P. The structural parameters (Pt–L, L–Pt–L) are analyzed and discussed with an attention to the distortion of a square-planar geometry about the Pt (II) atoms as well as of trans-influence. The sums of Pt–L (x4) bond distances growing with covalent radius of the X-atoms.
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24

Morishita, Kohei, Kazuo Nakajima, Takashi Fujii, and Masakazu Shiinoki. "Near-Net Shaping of Silicon for Optical Lens by One-Shot Pressing at Temperature just below Silicon Melting Point and Improvement of Infrared Transmittance by Primary Recrystallization." Materials Science Forum 783-786 (May 2014): 2474–79. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.2474.

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Silicon is brittle and easily cracks even under a small load. The difficulty in shaping silicon has prevented breakthroughs in the mass production of silicon lenses for terahertz and infrared technology. We developed a novel method of deforming bulk single-crystal silicon into the required shape by one-shot pressing at a temperature just below the melting point of silicon, despite its brittleness and covalent nature, and realized the near-net shaping of the material into the plano-convex shape with the curvature radius R=7.5 mm for a infrared transmission lens. The crystallographic quality of the obtained lens could be improved by primary recrystallization. The simple method of 'pressing' will enable the mass production of not only silicon lenses but also lenses with a complex shape, such as aspherical lenses, and lens arrays by using dies with desired shape.
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25

O’Neill, H. St C. "The influence of next nearest neighbours on cation radii in spinels: the example of the Co3O4-CoCr2O4solid solution." Mineralogical Magazine 67, no. 3 (June 2003): 547–54. http://dx.doi.org/10.1180/0026461036730116.

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AbstractLattice parameters and crystal structures of the synthetic spinels Co3O4, CoCr2O4, and solid solutions in the binary join Co3O4-CoCr2O4, have been determined by powder X-ray diffraction structural refinements. In all these spinels the cation distribution is completely normal at room temperature, and the tetrahedrally coordinated cation site is occupied only by Co2+. The ionic radius of Co2+(tet) increases from 0.556(3) in Co3O4to 0.599(4) in CoCr2O4. In the spinel structure, the interatomic distance between the tetrahedral cations and oxygen are geometrically independent of those between the octahedral cations and oxygen; thus the variation in effective ionic radii is ascribed to next-nearest neighbour effects, induced by covalent tendencies in the low-spin Co3+-O bond. The results demonstrate that the assumption of constant ionic radii even within an isomorphic group such as the oxide spinels needs to be made with caution.
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26

Iwanowski, R. J. "Tetrahedral covalent radius of Mn in AII1−xMnxBVI and AIII1−xMnxBV compounds – Supplement to the paper: Chem. Phys. Lett. 350 (2001) 577." Chemical Physics Letters 359, no. 5-6 (June 2002): 516–19. http://dx.doi.org/10.1016/s0009-2614(02)00717-0.

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27

Cotton, F. Albert, and Kenneth J. Wiesinger. "Structures of Mo2(CH3)4(PR3)4 molecules: constancy of covalent radius of molybdenum in these and other Mo2X4(PR3)4 molecules." Inorganic Chemistry 29, no. 14 (July 1990): 2594–99. http://dx.doi.org/10.1021/ic00339a014.

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28

Iwanowski, R. J. "Comment on the covalent radius of Mn [to the papers Chem. Phys. Lett. 283 (1998) 313 and Chem. Phys. Lett. 336 (2001) 226]." Chemical Physics Letters 350, no. 5-6 (December 2001): 577–80. http://dx.doi.org/10.1016/s0009-2614(01)01267-2.

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29

Wong-Ng, W., J. A. Kaduk, G. Tan, Y. Yan, and X. Tang. "X-ray powder reference patterns of the Fe(Sb2+xTe1−x) skutterudites for thermoelectric applications." Powder Diffraction 29, no. 3 (May 7, 2014): 260–64. http://dx.doi.org/10.1017/s0885715614000347.

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The crystal structure and powder X-ray diffraction (XRD) patterns for three skutterudite samples, Fe(Sb2+xTe1−x), x = 0.05, 0.10, 0.20, have been determined. These compounds crystallize in the cubic space group $Im\bar 3$. Te was found to randomly substitute in the Sb site. Because of the fact the covalent radius of Sb is greater than that of Te, a trend of increasing lattice parameter has been observed as the x value in Fe(Sb2+xTe1−x) increases [cell parameters range from 9.10432(4) to 9.11120(3) Å for x = 0.0 to 0.2, respectively]. The Fe–Sb/Te bond distance also increases progressively [from 2.5358(4) to 2.5388(4) Å] as the Te content decreases. While average Sb/Te–Sb/Te distances in the four-membered rings are similar in these three compounds, the average Sb/Te–Sb/Te edge distances in the octahedral framework increase progressively from 3.5845(12) to 3.5900(13) Å. Reference XRD patterns of these three phases have been prepared to be included in the Powder Diffraction File (PDF).
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30

Gil, Gabriel, and Augusto González. "Regularized perturbative series for the ionization potential of atomic ions." Canadian Journal of Physics 95, no. 2 (February 2017): 184–89. http://dx.doi.org/10.1139/cjp-2016-0255.

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We study N-electron atoms with nuclear charge Z. It is well known that, in the cationic (Z > N) large-Z region, the atom behaves as a weakly interacting system. The anionic (Z < N) regime, on the other hand, is characterized by an instability threshold at [Formula: see text], below which the atom spontaneously emits an electron. We construct a regularized perturbative series (RPS) for the ionization potential that is based on the behaviors for large Z and Z near Zc. The large-Z expansion coefficients are analytically computed from perturbation theory, whereas the slope of the energy curve at Z = N − 1 is computed from a kind of zero-range forces theory that uses as input the electron affinity and the covalent radius of the neutral atom with N − 1 electrons. Relativistic effects in the one-particle Hamiltonian are considered at the level of first-order perturbation theory. Our RPS formula is to be used to check the consistency of the ionization potential values for atomic ions contained in the NIST database.
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31

Harvey, Miguel Angel, Sebastián Suarez, Fabio Doctorovich, and Ricardo Baggio. "Two isomorphous transition metal complexes displaying a coordinated tetrathionate unit: bis(4,4′-dimethyl-2,2′-bipyridine-κ2N,N′)(tetrathionato-κ2S,S′)cadmium(II) dimethylformamide disolvate and the zinc(II) analogue." Acta Crystallographica Section C Crystal Structure Communications 69, no. 7 (June 25, 2013): 745–49. http://dx.doi.org/10.1107/s0108270113016521.

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The isomorphous title compounds, [Tr(S4O6)(C12H12N2)2]·2C3H7NO (Tr = CdIIand ZnII), consist of metal centres to which one tetrathionate and two 4,4′-dimethyl-2,2′-bipyridine chelating ligands bind. The structures are completed by two symmetry-related dimethylformamide solvent molecules. Each metal-centred complex is bisected by a twofold axis running through the metal centre and halving the chelating tetrathionate dianion through the central S—S bond. The ancillary symmetry-related 4,4′-dimethyl-2,2′-bipyridine ligands act as chelates. This results in a distorted six-coordinate geometry, with similar Tr—O/N distances but central angles differing substantially from 90 and 180°. Both ligands are basically featureless from a geometric point of view, with torsion angles in both coordinated tetrathionate groups suggesting a trend linking metal size (covalent radius) and ligand `openness'. Packing is directed by (C—H)aromatic...O bridges and π–π offset stacked interactions defining chains along [001], further linked by weaker (C—H)methyl...O bridges, some of them mediated by the dimethylformamide solvent molecules.
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32

Ivanciuc, Ovidiu, Teodora Ivanciuc, and Alexandru T. Balaban. "Design of Topological Indices. Part 10. Parameters Based on Electronegativity and Covalent Radius for the Computation of Molecular Graph Descriptors for Heteroatom-Containing Molecules." Journal of Chemical Information and Computer Sciences 38, no. 3 (February 28, 1998): 395–401. http://dx.doi.org/10.1021/ci970021l.

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33

Matienko, Ludmila, Mil Elena Mickhailovna, Binyukov Vladimir Ivanovich, and Goloshchapov Alexandr Nikolaevich. "AFM Research in Catalysis and Medicine." Current Organocatalysis 7, no. 3 (November 30, 2020): 248–55. http://dx.doi.org/10.2174/2213337207999200717171645.

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Background: In this study, we show that the AFM method not only allows monitoring the morphological changes in biological structures fixed on the surface due to H-bonds, but also makes it possible to study the self-organization of metal complexes by simulating the active center of enzymes due to intermolecular H-bonds into stable nanostructures; the sizes of which are much smaller than the studied biological objects. The possible role of intermolecular hydrogen bonds in the formation of stable supramolecular metal complexes, which are effective catalysts for the oxidation of alkyl arenes to hydroperoxides by molecular oxygen and mimic the selective active sites of enzymes, was first studied by AFM. Methods and Results: The formation of supramolecular structures due to intermolecular hydrogen bonds and, possibly, other non-covalent interactions, based on homogenous catalysts and models of active centers enzymes, heteroligand nickel and iron complexes, was proven by AFM-technique. AFM studies of supramolecular structures were carried out using NSG30 cantilever with a radius of curvature of 2 nm, in the tapping mode. To form nanostructures on the surface of a hydrophobic, chemically modified silicon surface as a substrate, the sample was prepared using a spin-coating process from solutions of the nickel and iron complexes. The composition and the structure of the complex Ni2(acac)(OAc)3·NMP·2H2O were determined in earlier works using various methods: mass spectrometry, UV- and IR-spectroscopy, elemental analysis, and polarography. Self-assembly of supramolecular structures is due to intermolecular interactions with a certain coordination of these interactions, which may be a consequence of the properties of the components themselves, the participation of hydrogen bonds and other non-covalent interactions, as well as the balance of the interaction of these components with the surface. Using AFM, approaches have been developed for fixing on the surface and quantifying parameters of cells. Conclusion: This study summarizes the authors' achievements in using the atomic force microscopy (AFM) method to study the role of intermolecular hydrogen bonds (and other non-covalent interactions) and supramolecular structures in the mechanisms of catalysis. The data obtained from AFM based on nickel and iron complexes, which are effective catalysts and models of active sites of enzymes, indicate a high probability of the formation of supramolecular structures in real conditions of catalytic oxidation, and can bring us closer to understanding enzymes activity. With a sensitive AFM method, it is possible to observe the self-organization of model systems into stable nanostructures due to H-bonds and possibly other non-covalent interactions, which can be considered as a step towards modeling the active sites of enzymes. Methodical approaches of atomic force microscopy for the study of morphological changes of cells have been developed.
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34

KOCH, J. T., B. D. KAY, and G. L. LANGE. "SURFACE STRENGTH OF A WATER-SATURATED BED OF GLASS BEADS WHEN POLYACRYLIC ACID IS COVALENTLY BONDED TO THE BEADS." Canadian Journal of Soil Science 69, no. 3 (August 1, 1989): 579–86. http://dx.doi.org/10.4141/cjss89-058.

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According to Emerson's model of the soil aggregate, a large soure of physical weakness exists at the surface of sand particles within the aggregate, particularly when wet. The aim of this study was to simulate sand particles with glass beads and to test the hypothesis that a bed of glass beads can resist large compressive forces in water when a polymer is bonded to the bead surfaces using chemicals and conditions that produce hydrolytically stable, covalent bonding. Because carboxyl and amine functional groups can react to form the amide bond and silanes can bond to a silanol surface (e.g., sand or glass), polyacrylic acid (PAA: FW ≈ 50 000), amines, and silanes were used to test the hypothesis for glass beads (53-μm mean diameter). The pressure at which the bed surface of the glass beads (when water-saturated) was penetrated with a flat probe (radius = 1.37 mm) served as an index of strength imparted by various chemicals when these were introduced into the system individually and in various combinations. A dramatic increase in the strength of the bed surface occurred only when all the theoretical requirements were met for both covalent bonding between the polymer and the silane and silanol coupling between the silane and the glass surface. We conclude that the hypothesis is confirmed for a simple system of glass beads and that large increases in the efficiency of soil conditioners may be potentially realized in soil aggregates if the weak links between inorganic particulates (sand, silt, and clay particles) and organic polymeric materials (natural or synthetic) are augmented with, or replaced by, strong and water-resistant links. Key words: Soil structure, soil conditioners, polymers, coupling agents, soil aggregates
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35

Wang, Fengqi, Wei Cai, Chunlin Fu, Rongli Gao, Gang Chen, Xiaoling Deng, Zhenhua Wang, and Chaoyang Zhang. "The electronic structure and optical properties of Ca3(Mn1−xTix)2O7from first-principle calculations." Journal of Advanced Dielectrics 09, no. 01 (February 2019): 1950007. http://dx.doi.org/10.1142/s2010135x19500073.

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The electronic structure and optical properties of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 ([Formula: see text], 1/8, 2/8, 3/8, 4/8) were studied by first-principle calculations within the generalized gradient approximation approaches (GGA). The lattice constants of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 increase with the increase of Ti[Formula: see text] content caused by the substitution of Ti[Formula: see text] with larger ionic radius for Mn[Formula: see text]. Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 is a direct band gap semiconductor, and the band gap ([Formula: see text]) increases with the increase of Ti[Formula: see text] content. From the density of states, the introduction of Ti-3[Formula: see text] states can weaken the effects of Mn-3[Formula: see text] states on the bottom of conduction band and has little influence on O-2[Formula: see text] states on the top of valence band. The introduction of nonmagnetic Ti[Formula: see text] ions can weaken the magnetism of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7. According to the Mulliken population analysis, it is found that the introduction of Ti[Formula: see text] enhances the electronic accepting capacity of oxygen ions and enhances the electronic losing capacity of manganese ions. The bond strength of Ti–O covalent bond is stronger than that of Mn–O covalent bond. Furthermore, the optical properties of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 was calculated. As Ti[Formula: see text] content increases, the absorption edge of Ca3(Mn[Formula: see text]Ti[Formula: see text]O7 has a blue shift, the static refractive index [Formula: see text] decreases, the static dielectric constant [Formula: see text](0) decreases, the position of loss peak moves to higher energy.
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36

Wright, J. Fraser. "Coating of AAV Vectors with Human Albumin Blocks Antibody Binding and Enables Transduction of Human Hepatocytes in the Presence of Neutralizing Antibodies." Blood 112, no. 11 (November 16, 2008): 3542. http://dx.doi.org/10.1182/blood.v112.11.3542.3542.

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Abstract Neutralization of recombinant adeno-associated virus (AAV) gene transfer vectors by pre-existing antibodies is a significant barrier to clinical gene transfer using systemic administration. In a recent clinical trial for hemophilia B, while efficient gene transfer and therapeutic levels of hFIX were achieved in a human subject with low pre-existing antibodies to AAV2, no gene transfer was observed in a subject with a modest pre-existing AAV2 antibody titer of 1:17 who received the same dose (Manno et al. Nature Med.2006;12:342–347). With the objective to achieve consistent and efficient transduction in the presence of AAV antibodies, ‘humanized’ AAV vectors were generated by covalent attachment of human albumin (HSA) to the surface of purified AAV2 by cross linking the single free thiol (Cys34) of HSA to lysine residues on the vector surface using suflosuccinimidyl 4 [N-maleimidomethyl] cyclohexane-1-caboxylate (Sulfo-SMCC). Variable levels of HSA substitution up to 65 HSA molecules per virion were achieved, corresponding to a maximum of approximately one HSA molecule per virion capsid protein. Analysis by SDS-PAGE of the modified vector revealed the presence of a 130kDA polypeptide species in the conjugated vector, not observed in the unmodified vector, that was consistent with predicted molecular weight obtained by covalent attachment of HSA with AAV capsid protein VP3. Dynamic light scattering demonstrated an average radius of 16.6 nm for the HSA-conjugated vector compared with 11.6 nm for unconjugated vector, consistent with coating of the vector surface with HSA. Analysis by flow cytometry demonstrated that the binding of AAV2-specific monoclonal antibody A20 to unmodified vectors was progressively reduced to background levels in HSA-conjugated vectors with increasing HSA substitution. Quantitative analysis by Biacore indicated that the association rate and available sites per virion for antibody binding were reduced > 10- fold in HSA-conjugated vectors. The conjugated vectors were significantly more resistant than unmodified vectors to neutralization by AAV antibody, demonstrating comparable transduction in the presence of 16-fold higher concentration of MAb A20 following transduction of cultured human hepatocytes (HepG2). In conclusion, covalent coupling of HSA to the surface of recombinant AAV2 is demonstrated as a feasible method to modify AAV vectors to increase their resistance to neutralizing antibodies. ‘Humanized’ AAV vectors such as HSA-coated AAV that effectively mask viral epitopes recognized by antibodies and display human epitopes may enable more consistent transduction following systemic administration in vivo, and enable vector readministration.
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37

Rondeau, J. J., N. McNicoll, E. Escher, S. Meloche, H. Ong, and A. De Léan. "Hydrodynamic properties of the angiotensin II receptor from bovine adrenal zona glomerulosa." Biochemical Journal 268, no. 2 (June 1, 1990): 443–48. http://dx.doi.org/10.1042/bj2680443.

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The bovine adrenal angiotensin II receptor was solubilized with the non-ionic detergent octyl β-D-glucoside following its binding with the high-affinity antagonist 125I-labelled [Sar1,Ile8]angiotensin II. The complex was sufficiently stable to allow the determination of its hydrodynamic properties. The solubilized receptor migrated on a Superose 6 column as a single peak with a Stokes radius of 5.29 nm. Comparison of sedimentation behaviour through a sucrose density gradient in H2O and 2H2O lead to a partial specific volume of 0.751 ml/g and a sedimentation coefficient (S20,w) of 5.17 S. Combination of gel filtration and sedimentation data indicated that the labelled protein-detergent complex has an Mr of 124,000 and a frictional ratio of 1.42. The Mr of the angiotensin II receptor was estimated as 104,000 kDa after correction for the bound detergent. Photoaffinity cross-linking of 125I-[Sar1, (4-N3)Phe8]angiotension II with bovine adrenal membrane receptor followed by SDS/PAGE under reducing and non-reducing conditions yielded a broad band of Mr 54,000. This suggests that the angiotensin II receptor is a non-covalent dimer in which the two subunits have a similar Mr.
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38

Li, Yingying, Xuxin Yang, Zihao Wang, Yonghong Hu, Caixia Mao, Juntao Wang, Huailin Li, and Yunyi Wu. "First-principles study of hydrogen incorporation into the Ti3SiC2/Zr heterojunction." Modern Physics Letters B 34, no. 01 (December 3, 2019): 2050014. http://dx.doi.org/10.1142/s0217984920500141.

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The geometric structure, energy barrier and electronic properties of H-incorporated [Formula: see text] heterojunctions were investigated by first-principles calculations. Hydrogen atom settles in [Formula: see text] as interstitial impurity due to its small radius. Through calculating and analyzing the total energies of H-incorporated [Formula: see text] heterojunction, a much higher potential barrier (1.75 eV) was found when H atom diffuses from the interface into the [Formula: see text] material than that (0.25 eV) into the Zr metal. The encountered potential barriers of H atom diffusing from vacuum into the [Formula: see text] and Zr metal are also calculated, and they are both positive. These findings indicate that [Formula: see text] is a suitable coating material to prevent the hydrogen embrittlement and corrosion in Zr metal. The electronic properties and valence bond properties of H-incorporated [Formula: see text] were analyzed based on the band structure, electronic density of states and Mulliken distribution. The calculated results show that all the H-incorporated [Formula: see text] heterojunctions exhibit metallic, covalent and ionic properties. These investigations may provide new insight into the underlying mechanisms of hydrogen diffusion in the [Formula: see text] heterojunction.
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39

GIL, GABRIEL, and AUGUSTO GONZALEZ. "ATOMS IN THE ANIONIC DOMAIN, Z < N." Modern Physics Letters B 27, no. 24 (September 11, 2013): 1350178. http://dx.doi.org/10.1142/s0217984913501789.

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We study atoms with N electrons, and nuclear charge Z. It is well known that the cationic regime, Z > N, is qualitatively described by Thomas–Fermi theory. The anionic regime, Z < N, on the other hand, is characterized by an instability threshold at Zc ≲ N-1, below which the atom spontaneously emits an electron. We compute the slope of the energy curve at Z = N - 1 by means of a simple model that depends on the electron affinity and the covalent radius of the neutral atom with N - 1 electrons. This slope is used in order to estimate Zc, which is compared with previous numerical results. Extrapolation of the linear behavior in the opposite direction, up to Z = N, allows us to estimate the ionization potential of the atom with N electrons. The fact that the obtained ionization potentials are qualitatively correct is an indication that, with regard to certain properties, neutral atoms are closer to the anionic instability threshold than they are to the Thomas–Fermi, large Z, region. A regularized series is written for the ionization potential that fits both, the large Z and Z → Zc limits.
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40

Lobo, Luís Sousa, and Sónia A. C. Carabineiro. "Mechanisms of Carbon Nanotubes and Graphene Growth: Kinetics versus Thermodynamics." C 6, no. 4 (October 27, 2020): 67. http://dx.doi.org/10.3390/c6040067.

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Thermodynamics must be favorable for the growth of carbon nanotubes (CNTs) and graphene to take place, but a kinetic study is required to find the operating mechanism. In fact, thermodynamics indicates whether a reaction is possible; however, the route prevailing is not necessarily the most thermodynamically favorable, but the fastest one. Detailed kinetic studies state that there are three alternative routes operating under different temperature and pressure rates. The modes and rates of diffusion of carbon (C) atoms and noble metals have been known since the 1930s, but proof of C bulk diffusion operating in CNT growth came from detailed kinetic studies performed in the early 1970s, when reversible versus irreversible C formation was discussed with examples. The reason for interstitial C bulk diffusion in transition metals is evidenced based on the values of covalent radius. The reason for operating under steady-state conditions (linearity of the weight versus time) when searching for the operating mechanism is discussed herein. The steady-state C formation process operates sometimes with two different solid phases at each side of the catalyst particle (e.g., Ni and Ni3C), with thicknesses proportional to 1/D of the respective C bulk diffusivities when the carbon bulk diffusion step is the rate-determining one.
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41

Fedorenko, Leonid, and Arthur Medvid. "Laser-Induced Nano-Structuring of Semiconductors and Metals in near Surface Layers by Nanosecond Pulses." Advanced Materials Research 1117 (July 2015): 9–14. http://dx.doi.org/10.4028/www.scientific.net/amr.1117.9.

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It was established that irradiation of a semiconductor by nanosecond laser leads to drift of the impurity atoms. The direction of the drift depends on relation between covalent radius of the impurity and of the basic substance atoms. This effect was shown for a wide class of semiconductors, such as: Si, Ge, InSb, GaAs, CdTe, CdxZn1-xTe. This is due to a laser thermal shock effect connected with action of high temperature and pressure gradients formed by strong absorbed nanosecond laser pulse. A new concept was proposed, and the technology has been developed of laser-induced (YAG: Nd +3, wavelength l= 0.532 mm, pulse duration τp = 10 ns) nano-fragmentation of metal film, for example, Au with an average size of fragments <δ> = 80 nm, and the concentration on the surface <n> = 2.5×109 cm-2. The fragmentation is realized by the self organization of surface plasmon-polariton subsystem excited by high power laser pulses at a surface plasmon-polariton resonance. It was shown that the proposed method provides by laser-assisted fragmentation of the metal film (Au) in conditions of the resonance, decomposition of the nanofragments from the substrate, their transfer through an air gap, and implantation in a polymer layer on a separate surface at the same laser pulse.
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42

Zhou, Xin, Haifang Cai, Chunwei Hu, Jiao Shi, Zongli Li, and Kun Cai. "Analogous Diamondene Nanotube Structure Prediction Based on Molecular Dynamics and First-Principle Calculations." Nanomaterials 10, no. 5 (April 28, 2020): 846. http://dx.doi.org/10.3390/nano10050846.

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A concentric twin tube (CTT) can be built by placing a carbon nanotube (CNT) in another identical CNT. Different from diamondene nanotubes, a stable CTT has no inter-shell covalent bond. As a prestressed double-walled nanotube, CTT has a lower structural stability at a finite temperature. According to the molecular dynamics and first-principle calculations, (a) CTTs have three types of relaxed configurations. In a type III CTT, the inner tube buckles to produce a V-shaped cross-section, and the outer tube may be convex or concave. (b) The minimal radii of relaxed zigzag and armchair CTTs with concave outer tubes were found. (c) After relaxation, the circumferences and areas of the two tubes in a type III CTT are different from those of the corresponding ideal CNT. The area change rate (A-CR) and circumference change rate (C-CR) of the outer tube are the first-order Gaussian function of the radius of the ideal CNT (which forms the CTT), and tends to be 73.3% of A-CR or 95.3% of C-CR, respectively. For the inner tube of a CTT, the A-CR is between 29.3% and 37.0%, and the C-CR is close to 95.8%. (d) The temperature slightly influences the findings given above.
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43

Sjöberg, B., S. Pap, S. E. Järnberg, and K. Mortensen. "Kinetics of the urea-induced dissociation of human plasma α2-macroglobulin as measured by small-angle neutron scattering." Biochemical Journal 278, no. 2 (September 1, 1991): 325–28. http://dx.doi.org/10.1042/bj2780325.

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The kinetics of the urea-induced dissociation of human plasma alpha 2-macroglobulin into two half-molecular fragments was investigated at 21.0 degrees C by using small-angle neutron scattering. The relative change in molecular mass that occurs upon dissociation was monitored by recording the forward scattering of neutrons as a function of time. All these kinetic data can be explained by a reaction that is first-order with respect to the concentration of undissociated alpha 2-macroglobulin. The velocity constant is a function of urea concentration and it varies within wide limits. For instance, the half-life of the reaction at the lowest concentration of [2H]urea studied (2.70 M) is 328 h, whereas the same value at the highest concentration of [2H]urea (6.24 M) is only 8 min. Measurements were made both with [1H]urea in 1H2O and with [2H]urea in 99% 2H2O, and it was found that there is a pronounced kinetic isotope effect, i.e. the dissociation is 4 times faster in the 1H-containing medium as compared with the 2H-containing medium at the same molar concentration of urea. From the angular dependence of the neutron scattering it can be concluded that the dissociation is associated with a drastic change in structure. This is directly shown by the radius of gyration, which increases from about 7.4 nm immediately after the addition of urea up to about 9.4 nm when the protein is fully dissociated. A structural analysis shows that the scattering curve of urea-dissociated alpha 2-macroglobulin can best be explained by that of a Gaussian coil with a radius of gyration equal to 9.44 nm. These data indicate that the so-called non-covalent interaction of alpha 2-macroglobulin probably is more complicated than just a pure hydrophobic interaction. Finally, it is also shown that the dissociation is accompanied by a loss in trypsin-binding activity, which is directly related to the fraction of dissociated protein.
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44

SALHANY, James M., Karen A. CORDES, and Renee L. SLOAN. "Mechanism of band 3 dimer dissociation during incubation of erythrocyte membranes at 37 °C." Biochemical Journal 345, no. 1 (December 17, 1999): 33–41. http://dx.doi.org/10.1042/bj3450033.

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The mechanism of dissociation of the stable dimer of band 3 was investigated during the incubation of isolated erythrocyte membranes or resealed ghosts at 37 °C. The kinetics of changes in the structural and functional integrity of the membrane domain of band 3 (MDB3) were measured and correlated with the change in the Stokes radius of band 3. MDB3 integrity was determined as follows: (1) by measuring the fluorescence emission spectrum of 4,4ʹ-di-isothiocyanostilbene-2,2ʹ-disulphonate (DIDS) bound covalently to MDB3; (2) by measuring the number of DIDS covalent binding sites present after incubation of unlabelled resealed ghosts; and (3) by measuring the anion transport Vmax by using the same resealed ghosts. Incubation of membranes at 37 °C caused the dissociation of band 3 dimers to monomers but only after a lag period lasting approx. 50 h. The observation of such a lag implies that dissociation involves a sequence of molecular events beginning with some type of initial process. We have discovered that this initial process involves a conformation change in MDB3. There was a shift in the fluorescence spectrum for DIDS-labelled band 3 and a decrease in the DIDS binding capacity and transport activity of the unlabelled protein. Incubation of membranes at 4 °C inhibited the conformational change in MDB3 and the dissociation of dimers. Furthermore, no conformational change in MDB3 was observed when erythrocytes were incubated at 37 °C. We suggest that MDB3 unfolding is the molecular event responsible for the subsequent dissociation of stable dimers of band 3 to monomers during the incubation of erythrocyte membranes at 37 °C. The monomers so generated are either not functional in anion exchange or they have an attenuated functionality. The absence of a conformational change for band 3 in erythrocytes might imply that haemolysis perturbs the membrane structure and somehow predisposes band 3 to the conformational change that occurs during incubation at 37 °C.
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45

Persson, Ingmar. "Hydrated metal ions in aqueous solution: How regular are their structures?" Pure and Applied Chemistry 82, no. 10 (August 6, 2010): 1901–17. http://dx.doi.org/10.1351/pac-con-09-10-22.

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The hydration reaction is defined as the transfer of an ion or neutral chemical species from the gaseous phase into water, Mn+(g) → Mn+(aq). In this process, water molecules bind to metal ions through ion-dipole bonds of mainly electrostatic character. The hydration reaction is always strongly exothermic with increasing heat of hydration with increasing charge density of the ion. The structures of the hydrated metal ions in aqueous solution display a variety of configurations depending on the size and electronic properties of the metal ion. The basic configurations of hydrated metal ions in aqueous solution are tetrahedral, octahedral, square antiprismatic, and tricapped trigonal prismatic. This paper gives an overview of the structures of hydrated metal ions in aqueous solution with special emphasis on those with a non-regular coordination figure. Metal ions without d-electrons in the valance shell form regular aqua complexes with a coordination figure, allowing a maximum number of water molecules to be clustered around the metal ion. This number is dependent on the ratio of the metal ion radius to the atomic radius of oxygen in a coordinated water molecule (1.34 Å). The lighter lanthanoid(III) ions have a regular tricapped trigonal prismatic configuration with the M–O distance to the capping water molecules somewhat longer than to the prismatic ones. However, with increasing atomic number of the lanthanoid(III) ions, an increasing distortion of the capping water molecules is observed, resulting in a partial loss of water molecules in the capping positions for the heaviest lanthanoids. Metal ions with d4 and d9 valance shell electron configuration, as chromium(II) and copper(II), respectively, have Jahn–Teller distorted aqua complexes. Metal ions with low charge and ability to form strong covalent bonds, as silver(I), mercury(II), palladium(II), and platinum(II), often display distorted coordination figures due to the second-order Jahn–Teller effect. Metal ions with d10s2 valence shell electron configuration may have a stereochemically active lone electron pair (hemi-directed complexes) or an inactive one (holo-directed). The hydrated tin(II), lead(II), and thallium(I) ions are hemi-directed in aqueous solution, while the hydrated bismuth(III) ion is holo-directed. The structures of the hydrated cationic oxo-metal ions are reported as well.
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46

Oliveira, Ana Rita, António Alberto Correia, and Maria Graça Rasteiro. "Heavy Metals Removal from Aqueous Solutions by Multiwall Carbon Nanotubes: Effect of MWCNTs Dispersion." Nanomaterials 11, no. 8 (August 17, 2021): 2082. http://dx.doi.org/10.3390/nano11082082.

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Carbon nanotubes (CNTs) are one of the most studied nanoparticles due to their physical, chemical and electronic properties. However, strong Van der Waals bonds, which promote CNTs aggregation are usually present, affecting their unique properties. Avoiding CNTs aggregation is one of the main difficulties when using these nanoparticles. Regarding the adsorption capacity of CNTs, the tendency of CNTs to aggregate decreases the surface area available to retain contaminants. One way to overcome this issue is by changing the surface energy of CNTs through chemical (covalent and noncovalent methods) or mechanical stabilization, but there is not yet a unique solution to solve this problem. In this work, a chemical noncovalent method (addition of surfactants) combined with mechanical energy (ultrasounds) was applied for CNTs stabilization, and the influence in heavy metal ions removal, Pb (II), Cu (II), Ni (II) and Zn (II), an area of high environmental relevance, was evaluated. It was proved that high amounts of metals could be removed from water during the first eighteen hours. Competitive adsorption between heavy metals, during adsorption tests with the simultaneous presence of all ions, was also studied and it was possible to prove that the electronegativity and atomic radius of cations influence their removal. Pb (II) and Cu (II) were the metals removed in higher percentages, and Ni (II) and Zn (II) were the metals less removed during competitive adsorption. Finally, the results obtained show that MWCNTs, if adequately dispersed, present a good solution for the treatment of water contaminated with highly toxic heavy metals, even when using very low concentrations of Multiwall Carbon Nanotubes (MWCNTs).
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47

Zhao, Jian, Xinzhan Qin, Jiamin Wang, and Manchao He. "Effect of Mg(II) and Na(I) Doping on the Electronic Structure and Mechanical Properties of Kaolinite." Minerals 10, no. 4 (April 20, 2020): 368. http://dx.doi.org/10.3390/min10040368.

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Because kaolinite has multiple defects, it is very important to study the effect of different doped cations on the electronic structure and mechanical properties of kaolinite (Al4Si4O18H8) from the microscopic point of view with the first-principle calculation method. The results exhibited that the doping of Mg(II) and Na(I) makes the ion bond and layer spacing of kaolinite crystal change, and the bond length of the chemical bond between the doped and O atom is positively related to the atomic radius of the doped cations. Compared with undoped kaolinite crystal, the band gap width of the Mg-doped and Na-doped kaolinite crystal was larger, but the typical insulator characteristics were still maintained. Compared with undoped kaolinite crystal, Mg-doped and Na-doped kaolinite crystal had more electron transfer to O, while the Mg–O bond and Na–O bond had more ionic bond properties and less covalent bond composition than the Al–O bond. Finally, the elastic properties of undoped, Mg-doped, and Na-doped kaolinite crystal were further analyzed by calculating the elastic constant matrix. The influence of doping Mg(II) and Na(I) on C11 and C22 was greater than that on C33, indicating that doping had a greater influence on the stiffness in the direction of the parallel crystal plane. The doping of Mg(II) and Na(I) weakened the rigidity of kaolinite crystal materials and improved the plasticity and ductility of the materials. The atom-scale information provided a basis for explaining the mechanical behavior of kaolinite and is expected to provide guidance for solving the deformation problems in soft rock roadways.
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48

Gavrielides, Andreas, Thomas Duguet, Maëlenn Aufray, and Corinne Lacaze-Dufaure. "Model of the DGEBA-EDA Epoxy Polymer: Experiments and Simulation Using Classical Molecular Dynamics." International Journal of Polymer Science 2019 (February 13, 2019): 1–9. http://dx.doi.org/10.1155/2019/9604714.

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Polyepoxy samples are synthesized from diglycidylether of bisphenol A (DGEBA) and ethylene diamine (EDA) monomers at a stoichiometric ratio of 2 DGEBA : 1 EDA in model conditions in order to promote a high degree of polymerization and a low density of defects and to try to approach the ideal models obtained by simulation. A slow polymerization (>24 h at ambient temperature) and a postcuring achieved in an inert atmosphere lead to a conversion degree of 92±2% and a midpoint glass transition temperature of 391±1 K. In parallel, a model is created with a multistep cross-linking procedure. In this work, all-atom molecular dynamics (MD) simulations are performed with LAMMPS and the GAFF 1.8 force field. In the initial liquid mixture of reactants (600 molecules), proper mixing is demonstrated by the calculation of the partial radial distribution functions (RDF), which show a minimum intermolecular distance of 2.8 Å and similar distributions for EDA-EDA, DGEBA-DGEBA, and DGEBA-EDA molecules in the simulation boxes. Then, in alternation with MD equilibrations, cross-linking is performed on frozen configurations by creating covalent bonds between reactive pairs within a reaction radius of 3 Å. The resulting boxes show conversion rates of 90-93% and densities close to the experimental value. Finally, a cooling ramp from 700 K to 25 K is applied in order to monitor the specific volume and the coefficient of volumetric thermal expansion (CVTE) of the polymer and to derive the glass transition temperature. Experimental thermomechanical analyses (TMA) compares well with simulations for both the specific volume and the CVTE evolutions with temperature. Whereas the uncertainty remains high with the fitting procedure used, we calculate a glass transition temperature of 390±8 K which compares very well with the experimental values (391±1 K from DSC and 380 K from TMA).
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49

Gawęda, Weronika, Marek Pruszyński, Edyta Cędrowska, Magdalena Rodak, Agnieszka Majkowska-Pilip, Damian Gaweł, Frank Bruchertseifer, Alfred Morgenstern, and Aleksander Bilewicz. "Trastuzumab Modified Barium Ferrite Magnetic Nanoparticles Labeled with Radium-223: A New Potential Radiobioconjugate for Alpha Radioimmunotherapy." Nanomaterials 10, no. 10 (October 20, 2020): 2067. http://dx.doi.org/10.3390/nano10102067.

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Barium ferrite nanoparticles (BaFeNPs) were investigated as vehicles for 223Ra radionuclide in targeted α-therapy. BaFe nanoparticles were labeled using a hydrothermal Ba2+ cations replacement by 223Ra with yield reaching 61.3 ± 1.8%. Radiolabeled nanoparticles were functionalized with 3-phosphonopropionic acid (CEPA) linker followed by covalent conjugation to trastuzumab (Herceptin®). Thermogravimetric analysis and radiometric method with the use of [131I]-labeled trastuzumab revealed that on average 19–21 molecules of trastuzumab are attached to the surface of one BaFe–CEPA nanoparticle. The hydrodynamic diameter of BaFe–CEPA–trastuzumab conjugate is 99.9 ± 3.0 nm in water and increases to 218.3 ± 3.7 nm in PBS buffer, and the zeta potential varies from +27.2 ± 0.7 mV in water to −8.8 ± 0.7 in PBS buffer. The [223Ra]BaFe–CEPA–trastuzumab radiobioconjugate almost quantitatively retained 223Ra (>98%) and about 96% of 211Bi and 94% of 211Pb over 30 days. The obtained radiobioconjugate exhibited high affinity, cell internalization and cytotoxicity towards the human ovarian adenocarcinoma SKOV-3 cells overexpressing HER2 receptor. Confocal studies indicated that [223Ra]BaFe–CEPA–trastuzumab was located in peri-nuclear space. High cytotoxicity of the [223Ra]BaFe–CEPA–trastuzumab bioconjugate was confirmed by radiotoxicity studies on SKOV-3 cell monolayers and 3D-spheroids. In addition, the magnetic properties of the radiobioconjugate should allow for its use in guide drug delivery driven by magnetic field gradient.
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50

Sharma, Ishu, and Sruthi Sunder. "Analysis of glass forming ability using percolation concept and tunability of physical parameters of a-Ge12Se76 - xAs12Bix glassy semiconductors." Materials Science-Poland 36, no. 2 (June 25, 2018): 242–54. http://dx.doi.org/10.1515/msp-2018-0006.

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AbstractGlass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L > 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76-xAs12Bixlone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.
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