To see the other types of publications on this topic, follow the link: ZBC Radio.
Journal articles on the topic 'ZBC Radio'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 18 journal articles for your research on the topic 'ZBC Radio.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Smith, Jacob. "Travels with Jack." Resonance 1, no. 1 (2020): 94–115. http://dx.doi.org/10.1525/res.2020.1.1.94.
Full textAbstract:
Nonprofit arts organization the ZBS Foundation began as a “media commune” in the early 1970s and continues to the present day: a period that spans dramatic changes in American radio culture and audio technology. The key creative figure at ZBS is the writer and producer Thomas Lopez, whose work serves as a case study in a “post-network” style of radio drama, one shaped by multitrack editing, field recording, and the ethos of the 1960s counterculture. The ZBS aesthetic comes into sharpest focus in the Jack Flanders adventure series, which demonstrates how ZBS adapted a “theater of the mind” approach to radio drama to create a “theater of the mind-body” that re-accentuated earlier conventions of the radio adventure serial for a countercultural audience. Lopez’s increasing use of field recordings to structure his narratives established a formal tension between the inner exploration of the hero’s psyche and an encounter with different cultures. I chart the development of this formal tension in ZBS’s theater of the mind-body and argue that Lopez’s work with ZBS is a bridge across multiple eras of radio, an archive of enduring characters and distinctive styles of storytelling, and a sonic laboratory for the fostering of cultural dialogue through sound.
2
BAEK, JANG-HYUN, KYUNG-HEE KIM, and DOUGLAS C. SICKER. "MODELING AND OPTIMIZATION OF ZONE-BASED REGISTRATION FOR MOBILE COMMUNICATION NETWORK." Asia-Pacific Journal of Operational Research 24, no. 05 (October 2007): 667–85. http://dx.doi.org/10.1142/s0217595907001449.
Full textAbstract:
An efficient mobility management for mobile stations plays an important role in mobile communication networks. Two basic operations of mobility management are location registration and paging. A zone-based registration (ZBR) is implemented in most of the mobile communication networks and we consider the mobility management scheme that combines a zone-based registration and a selective paging (SP). We propose a new analytical model that can reflect the characteristics of the ZBR smoothly where location areas of the ZBR are set up so that regions such as roads, bridges, rivers and mountains, where there is relatively little traffic, will constitute their boundaries. We adopt a revised 2-dimensional random walk mobility model to consider such characteristics. In addition, we propose a more efficient division scheme of location area for 2-step selective paging. We evaluate the performance of the mobility management scheme using our mobility model to determine the optimal size of a location area that will result in the minimum signaling traffic on radio channels. Numerical results are provided to demonstrate that our mobility model is useful to evaluate the ZBR more exactly. The results of this study can be used effectively in analyzing and comparing the performances of various mobility management schemes.
3
Nyssens, Lucas, Martin Rack, and Jean-Pierre Raskin. "Effective resistivity extraction of low-loss silicon substrates at millimeter-wave frequencies." International Journal of Microwave and Wireless Technologies 12, no. 7 (June 23, 2020): 615–28. http://dx.doi.org/10.1017/s175907872000077x.
Full textAbstract:
AbstractThe effective resistivity (ρeff) is a figure of merit commonly used to assess the radio-frequency performance of a substrate from the measurements of coplanar waveguide lines. For highly resistive substrates, such as the trap-rich (TR) substrate, the extracted ρeff decreases by several orders of magnitude at millimeter-wave frequencies. The explanation for this decay is twofold. First, the imaginary part of the characteristic impedance ${\rm \lpar \Im }\lpar Z_c\rpar \rpar$ is not well extracted, which leads to an incorrect separation of the total losses among the metal and substrate losses. Second, the original expression of ρeff does not include dielectric losses, which might become non-negligible at millimeter-wave frequencies. This paper solves both issues by presenting a new procedure to extract ρeff and the dielectric losses simultaneously, and by introducing a novel method to correct ${\rm \Im }\lpar {Z_c} \rpar$. Furthermore, it is shown that this extraction method enables the correct extraction of substrate parameters up to 220 GHz of TR and high-resistivity silicon substrates. Finally, the origin of the large extracted value of dielectric loss is discussed in the potential presence of surface roughness and surface wave radiation. Both phenomena are discounted thanks to measurements of an additional reflective structure and a standard impedance substrate.
4
Lin, Cun, Takashi Kadono, Kazuharu Yoshizuka, Takuya Furuichi, and Tomonori Kawano. "Effects of Fifteen Rare-Earth Metals on Ca2+ Influx in Tobacco Cells." Zeitschrift für Naturforschung C 61, no. 1-2 (February 1, 2006): 74–80. http://dx.doi.org/10.1515/znc-2006-1-214.
Full textAbstract:
Abstract Effects of naturally existing rare-earth metals (REMs; atomic numbers, 39, 57D60, 62D71; Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), added as chloride salts, on Ca2+ influx induced by two different stimuli, namely hypoosmotic shock and hydrogen peroxide, were examined in a suspension-cultured transgenic cell line of BY-2 tobacco cells expressing aequorin, a Ca2+-sensitive luminescent protein in cytosol. Most REM salts used here showed inhibitory effect against Ca2+ influx. Especially NdCl3, SmCl3, EuCl3, GdCl3 and TbCl3 showed the most robust inhibitory action. In contrast, LuCl3, YbCl3, ErCl3 and YCl3 were shown to be poor inhibitors of Ca2+ influx. Since REMs tested here form a sequential range of ionic radii from 86.1 to 103.2 pm and the optimal range of ionic radii required for blocking the flux of Ca2+ was determined for each stimulus. The hydrogen peroxideinduced Ca2+ influx was optimally blocked by REMs with a broad range of ionic radii (93.8D 101 pm) which is slightly smaller than or similar to that of Ca2+ (100 pm), while the hypoosmotically induced flux of Ca2+ was inhibited optimally by few REMs with a narrower range of relatively smaller ionic radii around that of Gd3+ (93.8 pm) a well known inhibitor of stretch-activated channels. Possible applications of such series of channel blockers in elucidation of plant signal transduction pathways are encouraged
5
Stoicheva, Natalia, Iana Tsoneva, and Dimiter S. Dimitrov. "Protoplast Dielectrophoresis in Axisymmetric Fields." Zeitschrift für Naturforschung C 40, no. 9-10 (August 1, 1985): 735–39. http://dx.doi.org/10.1515/znc-1985-9-1026.
Full textAbstract:
Abstract Pea protoplasts dielectrophoretic coefficients were measured in alternating electric fields of frequency 1 M Hz and voltage 5 V applied between two concentric cylindrical metal electrodes of outer and inner radii 0.24 mm and 1 mm, respectively. They do not vary significantly with solution osmolarity, but show a clear expressed maximum in isotonic conditions; the values in 0.4 ᴍ, 0.5 ᴍ, 0.6 ᴍ and 0.7 ᴍ manitol solutions are (6.5, 10.2, 8.8 and 5.6) × 10−24 A2s4/Kg, pectively. The average cell radii in those conditions are 14.2 µm, 14.6 µm, 13.8 µm and 13.6 µm. The radii of cell-to-electrode contacts follow the same dependence on the osmolarity as the dielectrophoretic coefficients; they do not depend on the applied voltages up to 18V. The times of cell approach near to the electrode were too short to be explained by the action only of the dielectrophoretic force; consequently an attractive force appeared at very close approach. These results may be of use in future studies of membrane adhesion and fusion.
6
Rusin, Pawel, Anna Walczak, Anita Zwierzchlejska, Jurek Olszewski, Alina Morawiec-Bajda, Dariusz Kaczmarczyk, Krzysztof Kusmierczyk, et al. "DNA Damage and Repair of Head and Neck Cancer Cells after Radio- and Chemotherapy." Zeitschrift für Naturforschung C 64, no. 7-8 (August 1, 2009): 601–10. http://dx.doi.org/10.1515/znc-2009-7-821.
Full textAbstract:
DNA repair is critical for successful chemo- and radiotherapy of human tumours, because their genotoxic sensitivity may vary in different types of cancer cells. In this study we have compared DNA damage and the efficiency of its repair after genotoxic treatment with hydrogen peroxide, cisplatin and γ-radiation of head and neck squamous cell carcinoma (HNSCC). Lymphocytes and tissue cells from biopsies of 37 cancer patients and 35 healthy donors as well as the HTB-43 larynx cancer cell line were employed. The cell sensitivity to genotoxic treatment was estimated by the MTT survival assay. The extent of DNA damage and efficiency of its repair was examined by the alkaline comet assay. Among the examined treatments, we found that HNSCC cells were the most sensitive to γ-radiation and displayed impaired DNA repair. In particular, DNA damage was repaired less effectively in cells from HNSCC metastasis than healthy controls. In conclusion, our results suggest that the different genotoxic sensitivity of HNSCC cells may depend on their DNA repair capacity what in turn may be connected with the effectiveness of head and neck cancer therapy.
7
Tamba, M. "Role of Thiols in Radioprotection: Radiation Chemical Aspects." Zeitschrift für Naturforschung C 44, no. 9-10 (October 1, 1989): 857–62. http://dx.doi.org/10.1515/znc-1989-9-1027.
Full textAbstract:
Using the technique of pulse radiolysis, it has been demonstrated that thiyl radicals (RS˙) derived from glutathione (GSH), cysteine (CYSH), penicillamine (PnSH) and 2-m ercaptoethanol (M E) interact with oxygen at a high rate. The resulting transient absorption, with a maximum around 540-560 nm, is characteristic of the sulphur peroxyl radical (RSOO˙). The yield and the kinetic of formation of RSOO˙ further support our previous suggestion that thiyl/O2 reaction is an equilibrium. The redox properties of RSOO˙ are discussed on the basis of the interaction with reductants. Studies on the radio-induced enzyme inactivation in the presence of thiols seem to suggest a damaging role for RSOO˙ radicals.
8
Schuch, Ricardo, and Kumar D. Mukherjee. "Radiochemical Methods for Studying Lipase-Catalyzed Interesterification of Lipids." Zeitschrift für Naturforschung C 42, no. 11-12 (December 1, 1987): 1285–90. http://dx.doi.org/10.1515/znc-1987-11-1223.
Full textAbstract:
Reactions involving lipase-catalyzed interesterification of lipids, which are of commendable interest in biotechnology, have been monitored and assayed by radiochemical methods using 14C-labeled substrates. Medium chain (C12 plus Cu) triacylglycerols were reacted in the presence of an immobilized lipase from Mucor miehei and hexane at 45 °C with methyl [1-14C]oleate. [1-14C]oleic acid, [carboxyl-14C]trioleoylglycerol. [1-14C)octadecenyl alcohol, and [U-14C)glycerol, each of known specific activity. The reactions were monitored and the rate of interesterification determined by radio thin layer chromatography from the incorporation of radioactivity into acyl moieties of triacylglycerols (from methyl oleate, oleic acid, and trioleoylglycerol), alkyl moieties of wax esters (from octadecenyl alcohol), and into glycerol backbone of monoacylglycerols and diacylglycerols (from glycerol).
9
Zhang, Zheng-Zheng, Dong Tian, Ji-Ning Gao, Xue-Mei Qin, and Zhen-Yu Li. "Evaluation of the water soluble extractive of astragali radix with different growth patterns using 1H-NMR spectroscopy." Zeitschrift für Naturforschung C 70, no. 9-10 (September 1, 2015): 257–63. http://dx.doi.org/10.1515/znc-2015-5018.
Full textAbstract:
Abstract Astragali radix (AR), known in China as huangqi, is commonly used in traditional Chinese medicine. Water soluble extractive (WSE) values play an important role in the quality evaluation of herbal drugs. In this study, WSE of wild and cultivated AR were compared systematically. The WSE value of cultivated AR was significantly higher than that of the wild AR, and their UV-absorbance in the range of 250–400 nm was also different. The chemical compositions of different WSE were further compared by 1H NMR spectroscopy combined with multivariate analysis. Results from the principal component analysis and the hierarchical cluster analysis showed a clear separation between the WSEs of wild and cultivated AR. The differential metabolites responsible for the separation were identified by orthogonal projections to latent structures discriminant analysis and recursive support vector machine. The WSE of wild AR contained more arginine, valine, threonine, asparagine, succinate, and glutamine, while the cultivated AR contained more sucrose. Thus, the WSE can be used as a simple and reliable method for discrimination of wild and cultivated ARs, and the results obtained in this study extend the potential use of WSE in the quality evaluation of herbal drugs.
10
Sabaawy, Hatem E., Lisa J. Embree, Mizuki Azuma, and Dennis D. Hickstein. "Transplantation of Hematopoietic and Endothelial Stem Cell Progenitors in Transgenic Zebrafish." Blood 108, no. 11 (November 16, 2006): 337. http://dx.doi.org/10.1182/blood.v108.11.337.337.
Full textAbstract:
Abstract The zebrafish has emerged as an excellent vertebrate model for analysis of hematopoietic and leukemogenic development. Blood production in adult zebrafish occurs in the kidney marrow (KM), within the peritubular kidney interstitium, while kidney tubules support renal functions. To study the molecular mechanisms of stem cell specification and fate decision, we developed transgenic zebrafish expressing EGFP either at distinct hematopoietic levels using the zebrafish SCL/TAL1, RAG2, and FLI1 promoters, or in all tissues using the zebrafish β-actin promoter. KM progenitor cells from the SCL-EGFP, FLI1-EGFP, RAG2-EGFP, and ZBA-EGFP transgenic zebrafish were separated by FACS based on previously described method. The kinetics of KM progenitor cell transplantation from transgenic zebrafish into adult and embryonic recipients was analyzed. Visualization of donor cells in embryonic and adult recipients allowed us to detect trafficking and multilineage reconstitution in transplanted recipients in real-time. Transplantation of whole KM to unconditioned adult recipients resulted in the disappearance of donor-derived cells within 3 weeks. Thus, efficient engraftment of donor cells required host conditioning using β radiation or busulfan. Dose response experiments indicated that the minimum lethal dose of radiation averaged between 38 and 54 Gy, and was strain-dependent since hematolymphoid ablation of the Ek strain required higher radiation doses compared to the AB* strain. Sublethal irradiation doses of 25 Gy predominantly ablated lymphocytes and permitted transplantation of lethal TEL-AML1-induced pre B-cell leukemia. All irradiated animals not receiving transplants showed 10–50 fold decrease in all hematopoietic lineages at one week, and then died by 3 weeks post-radiation. In contrast, 60% of animals that received a transplant survived for at least 3 months. FACS analysis indicated that the frequency of EGFP-positive KM progenitors from the ZBA-EGFP (Common progenitors), the FLI1-EGFP (Hematopoietic-endothelial progenitors), and the RAG2-EGFP (Lymphoid progenitors) averaged 7%, 0.6%, and 4%, respectively. FACS-sorted EGFP+ donor cells were transplanted into adult wild-type irradiated recipients or blastula stage embryos. Transplantation of donor ZBA-EGFP KM cells resulted in engraftment and detection of donor-derived hematopoietic cells of all lineages within 2–3 weeks. No overt signs of graft-versus-host disease or graft rejection were detected. Transplantation of KM endothelial progenitors or angioblasts from the FLI1-EGFP transgenic fish resulted in endothelial homing and appearance of donor-derived intersegmental vessels in recipient fish 3–4 weeks post-transplant. These data demonstrate that marrow-derived angioblasts reconstitute endothelium of adult zebrafish, and represent, to our knowledge, the first evidence for a marrow derived hematopoietic-endothelial precursor homing to the vasculature of a transplanted vertebrate. Embryonic transplantation of 2×103 to 3×103 cells to blastula stage embryos resulted in dose-dependent lineage-faithful contribution of the transplanted cells to the developed embryos. We are investigating whether single transplanted progenitor cells sorted from SCL-EGFP KM engraft wild-type and SCL-depleted recipients, and provide long-term survival when transplanted to GATA1−/− and RUNX1−/− mutants. Transplantation of KM progenitors in zebrafish is sufficient for radio- and chemoprotection, and provides an excellent system to analyze oncogenic transformation, stem cell engraftment and immune cell function.
11
Verostek, Mary Fran, Lee E. Bartholomew, and Peter Weber. "Isolation and Characterization of a Polysaccharide Antigen from Propionibacterium acnes Released by a Glycine-Specific Chemical Protein Degradation Procedure." Zeitschrift für Naturforschung C 45, no. 7-8 (August 1, 1990): 797–804. http://dx.doi.org/10.1515/znc-1990-7-809.
Full textAbstract:
Abstract An acid-labile antigenic polysaccharide has been isolated from both cell walls and culture media of Propionibacterium acnes using a new chemical degradation procedure which liberates protein-bound or associated carbohydrate. Lyophilized cells and culture media were treated with a suspension of mercuric oxide in a solution of alkaline mercuric cyanide for several hours at room temperature liberating water-soluble polysaccharide material. The antigenic polysac- charide was freed of reaction products by alcohol extraction and purified by anion exchange chromatography and gel filtration, resulting in three distinct fractions of acidic polysaccha- rides of apparent molecular weights between 15 - 50 kDa. Sugar analysis showed the polysac- charides to contain fucose, galactose, glucose, mannose, galactosamine. glucosamine, and 2,3- diamino-2.3-dideoxy-D-glucuronic acid. The three fractions also contained amino acids, predominantly glutamic acid, alanine, and glycine, known to be components of P. acnes cell wall peptidoglycan. All three molecular weight fractions reacted with rabbit antisera raised against whole P. acnes cells, with the highest titer for both cell and media-derived polysaccharide material consistently in the high molecular weight fraction. This procedure was also capable of releasing antigenic polysaccharide from tissues of rats administered P. acnes cells or radio- labeled cell wall fragments.
12
Hacker-Klom, Ursula, Eva-Maria Meier, and Wolfgang Göhde. "Säugetierspermatogenese als biologischer Indikator für ionisierende Strahlung / Mammalian Spermatogenesis as a Biological Indicator for Ionizing Radiation." Zeitschrift für Naturforschung C 40, no. 11-12 (October 1, 1985): 898–907. http://dx.doi.org/10.1515/znc-1985-11-1225.
Full textAbstract:
Abstract We have analysed spermatogenetic cells by flow cytometry to quantify effects of ionizing radiation. The radiation-induced reductions of testicular DNA-synthesizing cells, primary spermatocytes, haploid round and elongated spermatids as well as the increases of numerical chromo some aberrations (abnormal diploid spermatids and aneuploidies) in NMRI inbred mice are described. Testicular weights were determined as a parameter of germ cell decrease, and histologic cross sections of the testes were analysed. Since even an exposure of 0.05 Gy (= 5 rad) may be detected by a reduction of DNA-synthesizing cells (Acta Radiol. Oncol. Radiat. Phys. Biol. 21, 349-351 (1982) [1]), the use of the in vivo system “spermatogenesis” as a biological dosimeter to monitor low dose effects and to determine RBE values of different radiation qual ities is suggested.
13
Cserháti, Tibor, and Mária Szögyi. "Hydrophilic Interactions between Charged Amino Acids and the Effect of Ions on the Strength of Interaction." Zeitschrift für Naturforschung C 45, no. 1-2 (February 1, 1990): 79–83. http://dx.doi.org/10.1515/znc-1990-1-214.
Full textAbstract:
The interaction between oppositely charged amino acids was studied by charge-transfer reversed- phase thin-layer chromatography. The dependence of the lipophilicity of Arg, Lys and Orn on the concentration of G lu , Asp, Gln and Asn in the eluent was considered to be related to the strength of interaction. The interaction of dibasic amino acids with Glu and Asp was stronger than with Gln and Asn. Mono- (Li+, Na+, K+, Rb+ and Cs+) and divalent (Mg2+ and Ca2+) cation s decreased the strength of interaction suggesting the electrostatic character of the interaction. Their inhibitory effect mainly depended on their concentration and to a lesser extent on the ion charge and hydrated ion radii. Stepwise regression analysis proved that the strength of interaction depends on the polarity parameters of amino acids and is independent of their chemical structure.
14
Sarapuk, Janusz, Halina Kleszczyńska, Juliusz Pernak, Joanna Kalewska, and Bożenna Różycka-Roszak. "Influence of Counterions on the Interaction of Pyridinium Salts with Model Membranes." Zeitschrift für Naturforschung C 54, no. 11 (November 1, 1999): 952–55. http://dx.doi.org/10.1515/znc-1999-1116.
Full textAbstract:
Abstract The interaction of pyridinium salts (PS) with red blood cells and planar lipid membranes was studied. The aim of the work was to find whether certain cationic surfactant counterion influence its possible biological activity. The counterions studied were Cl- , Br-, I-, ClO4-, BF4- and NO3-. The model membranes used were erythrocyte and planar lipid membranes (BLM). At high concentration the salts caused 100% erythrocyte hemolysis (C 100) or broke BLMs (CC). Both parameters describe mechanical properties of model membranes. It was found that the efficiency of the surfactant to destabilize model membranes depended to some degree on its counterion. In both, erythrocyte and BLM experiments, the highest efficiency was observed for Br-, the lowest for NO3-. The influence of all other anions on surfactant efficiency changed between these two extremities; that of chloride and perchlorate ions was similar. Some differences were found in the case o f BF4- ion. Its influence on hemolytic possibilities of PS was significant while BLM destruction required relatively high concentration of this anion. Apparently, the influence of various anions on the destructive action of PS on the model membrane used may be attributed to different mobilities and radii of hydrated ions and hence, to different possibilities of particular anions to modify the surface potential of model membranes. This can lead to a differentiated interaction of PS with modified bilayers. Moreover, the effect of anions on the water structure must be taken into account. It is important whether the anions can be classified as water ordering kosmotropes that hold the first hydration shell tightly or water disordering chaotropes that hold water molecules in that shell loosely.
15
Yadav, Ram P., and Ajay Singh. "Toxic Effects of Crotocaudin Extracted from the Medicinal Plant Croton tiglium." Zeitschrift für Naturforschung C 65, no. 5-6 (June 1, 2010): 327–36. http://dx.doi.org/10.1515/znc-2010-5-604.
Full textAbstract:
The compound crotocaudin extracted from the stem bark of the medicinal plant Croton tiglium Linn. was administered for 24 h or 96 h to the freshwater vector snail Lymnaea (Radix) acuminata Lamarck in order to test its toxicity. L. acuminata is the intermediate host of Fasciola hepatica and Fasciola gigantica which cause immense harm to man and his domestic animals. It was observed that the molluscicidal activity of crotocaudin against L. acuminata is time- as well as dose-dependent. There was a significant negative correlation among LC50 values and exposure periods, i.e. increasing the exposure time, the LC50 value of crotocaudin decreased from 5.37 μM (24 h) > 2.08 μM (48 h) > 1.36 μM (72 h) to 1.01 μM (96 h), respectively, against L. acuminata. The toxicological experiments to proof for environmental toxicity, if any, have also been carried out on the non-target freshwater fish Channa punctatus (Bloch) [Channidae (Ophicephalidae)], which shares the habitat with L. acuminata. The sublethal doses of crotocaudin (40% and 80% of LC50) administered over 24 h caused significant changes in the carbohydrate and nitrogenous metabolisms in nervous, hepatopancreas, and ovotestis tissues of Lymnaea acuminata. Channa punctatus was also exposed to sublethal doses of crotocaudin (40% and 80% of 24-h LC50 of L. acuminata) for 96 h which showed significant alterations in the metabolism in muscle, liver, and gonad tissues. After withdrawal of crotocaudin the snail tissues recovered in part after 7 days and the fish tissues completely.
16
Róźycka-Roszak, Boźenna, Romuald Żyłka, and Janusz Sarapuk. "Hydration of Alkylammonium Salt Micelles - Influence of Bromide and Chloride Counterions." Zeitschrift für Naturforschung C 55, no. 5-6 (June 1, 2000): 413–17. http://dx.doi.org/10.1515/znc-2000-5-617.
Full textAbstract:
The micellization process of dodecyltrimethylammonium chloride (DTAC) and bromide (DTAB) was studied. Nuclear magnetic resonance method was used. The 1H NM R and 13C NM R spectra were taken at higher and lower concentrations than the critical micelle concentrations (CMC) of the compounds studied. Chemical shifts were analysed. The studies performed were prompted by earlier calorimetric measurements which showed that there were significant qualitative and quantitative differences in the micellization process of the compounds studied. Namely, DTAB micelle dissociation was found to be an endothermic process while that of DTAC was exothermic. The differences found must be the result of differentiated influence of bromide and chloride counterions on the micellization process, including the phenomenon of micelle hydration. The objective of the work was to check whether cationic surfactant counterions can influence the micelle hydration process. Indeed, DTAB and DTAC, as monomers, exhibit similar hydrophobic hydration, but DTAB micelles are more hydrated than DTAC ones. It seems that the differences found in micellization of both salts studied may be attributed to different physicochemical properties of bromide and chloride ions, such as their mobilities and radii of their hydrated forms. Moreover, the effect of anions on the water structure must be taken into account. It is important whether the anions can be classified as water ordering kosmotropes, that hold the first hydration shell tightly, or water disordering chaotropes, that hold water molecules in that shell loosely.
17
Deeble, David J., Eberhard Bothe, Heinz-Peter Schuchmann, Barry J. Parsons, Glyn O. Phillips, and Clemens von Sonntag. "The Kinetics of Hydroxyl-Radical-Induced Strand Breakage of Hyaluronic Acid. A Pulse Radiolysis Study Using Conductometry and Laser-Light-Scattering." Zeitschrift für Naturforschung C 45, no. 9-10 (October 1, 1990): 1031–43. http://dx.doi.org/10.1515/znc-1990-9-1016.
Full textAbstract:
Abstract Hydroxyl radicals were generated radiolytically in N2O -and N2O / O2(4: 1)-saturated aqueous solutions of hyaluronic acid. The hydroxyl radicals react rapidly with hyaluronic acid mainly by abstracting carbon-bound H atom s. As a consequence of subsequent free-radical reactions, chain breakage occurs the kinetics of which has been followed using the pulse radio lysis technique. In the absence of oxygen, strand breakage was followed by the change in conductivity in duced by the release of cationic counterions condensed at the surface of hyaluronic acid which is a polyanion consisting of subunits of glucuronic acid alternating with N-acetyl-glucosamine. It appears that strand breakage is not due to one single first-order process, however, the con tributions of the different com ponents cannot be adequately resolved. At pH7 the overall half-life is 1.4 ms, in both acid and basic solutions the rate of free-radical induced strand breakage is accelerated (at pH 4.8, t1/2 = 0.6 ms; at pH 10, t1/2 = 0.18 ms). In the absence of oxygen there is no effect of dose rate on the kinetics of strand breakage. In the presence of oxygen in addition to conductom etric detection, strand breakage was also followed by changes in low-angle laser light-scattering. These two techniques are complementary in that in this system the conductometry requires high doses per pulse while the light-scat tering technique is best operated in the low -dose range. In the presence of oxygen a pro nounced dose-rate effect is observed, e.g. at pH 9.7 after a dose of 9.4 Gy the overall half-time is approx. 0.5 s, while after a dose of 6.6 Gy the half-time is approx. 0.23 s. Both the yield and the rate of strand breakage increase with increasing pH, e.g. at pH 7 G(strand breaks) = 0.7 × 10-7 mol J-1 and at pH 10.4, 4.8 × 10-7 mol J-7. The radiolytic yields of CO2, H2O2, organic hydroperoxides, O2·- and oxygen consum ption have been determined in y-irradiated N2O/ 0 2(4: 1)-saturated solutions of both hyaluronic acid and β-cyclodextrin.
18
"Chloroacetamide Mode of Action, I: Inhibition of Very Long Chain Fatty Acid Synthesis in Scenedesmus acutus." Zeitschrift für Naturforschung C 53, no. 11-12 (December 1, 1998): 995–1003. http://dx.doi.org/10.1515/znc-1998-11-1210.
Full textAbstract:
Abstract Herbicidal chloroacetamides cause a very sensitive inhibition of fatty acid incorporation into an insoluble cell wall fraction of Scenedesmus acutus. The molecular basis was investigated in more detail. After incubation of the algae with [14C]oleic acid and saponification, the remaining pellet was solubilized and fractionated consecutively with chloroform / methanol, phosphate buffer, amylase, pronase, and finally with dioxane/HCl. By acid hydrolysis in dioxane a part of the cell wall residue was solubilized showing inhibition of exogenously applied oleic acid and other labelled precursors such as stearic acid, palmitic acid, and acetate. After extraction of this dioxane-soluble subfraction with hexane, HPLC could separate labelled metabolites less polar than oleic acid. T heir formation was completely inhibited by chloroacetam ides, e.g. 1 μᴍ metazachlor. This effect was also observed with the herbicidally active 5-enantiomer of metolachlor while the inactive R-enantiomer had no influence. These strongly inhibited metabolites could be characterized by radio-HPLC /MS as very long chain fatty acids (VLCFAs) with a carbon chain between 20 and 26. Incubating am etazachlor-resistant cell line of S. acutus (Mz-1) with [14C]oleic acid, V LCFA s could not be detected in the dioxane/ HCl-subfraction. Furthermore, comparing the presence of endogenous fatty acids in wildtype and mutant Mz-1 the VLCFA content of the mutant is very low, while the content of long chain fatty acids (C16 -18) is increased, particularly oleic acid. Obviously, the phytotoxicity of chloroacetam ides in S. acutus is due to inhibition of VLCFA synthesis. The resistance of the mutant to metazachlor has a bearing on the higher amount of long chain fatty acids replacing the missing VLCFAs in essential membranes or cell wall components.