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Journal articles on the topic 'Keto-enol Tautomer'

Author: Grafiati

Published: 5 June 2025

Last updated: 2 August 2025

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1

Oziminski, Wojciech P., and Agata Wójtowicz. "New theoretical insights on tautomerism of hyperforin—a prenylated phloroglucinol derivative which may be responsible for St. John’s wort ( Hypericum perforatum ) antidepressant activity." Structural Chemistry 31, no. 2 (2019): 657–66. http://dx.doi.org/10.1007/s11224-019-01434-6.

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AbstractThe thermodynamic aspects of keto-enol tautomerism of hyperforin were investigated theoretically using density functional theory methods. At the B3LYP/aug-cc-pVTZ//B3LYP/aug-cc-pVDZ level of theory the enol tautomer dominates the tautomeric mixture and the second enol tautomer 1OH-HB has Gibbs free energy higher by 1.2 kcal/mol, despite possessing an intramolecular hydrogen bond. The purely keto tautomer is less stable by 3.3 kcal/mol compared with the 1OH tautomer, which means that the percentage of the keto tautomer in the tautomeric mixture is only about 0.4%. This is a different pi

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2

CHARIF, I. E., S. M. MEKELLECHE, and D. VILLEMIN. "SOLVENT EFFECTS ON THE KETO-ENOL TAUTOMERIC EQUILIBRIUM OF TETRONIC AND ETHYL ACETOACETATE CARBON ACIDS: A THEORETICAL STUDY." Journal of Theoretical and Computational Chemistry 09, no. 06 (2010): 1021–32. http://dx.doi.org/10.1142/s0219633610006171.

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The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA) and tetronic acid (TA) are theoretically investigated. The present study shows that the most stable keto tautomer of EAA corresponds to the trans diketo, E, Z form; while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. Our calculations also put in evidence that the keto tautomer of TA prefers the trans diketo, E, E form, while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl

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3

Cysewski, Piotr. "Theoretical Studies on the Tautomeric Properties of Diamino-5-formamidopyrimidines." Zeitschrift für Naturforschung C 53, no. 11-12 (1998): 1027–36. http://dx.doi.org/10.1515/znc-1998-11-1214.

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Abstract The results of theoretical geometry prediction of formamidopyrimidine(fapy)-adenine and fapy-guanine tautomers are presented. Among 54 potential tautomeric structures of fapy-adenine the most stable structure corresponds to the diamino-keto isomer. The solvent effect has insignificant influence on the fapy-adenine tautomers succession. The fapy-guanine has 172 potential isomers. There are three most stable tautomers of this guanine derivative, which may exchange the order depending on the polarity of the environment. In vapour the most probable is the 4-enol-6-keto-diamino tautomer, w

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4

Hureau, Matthieu, Alain Moissette, and Konstantin Smirnov. "A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites." Molecules 24, no. 4 (2019): 795. http://dx.doi.org/10.3390/molecules24040795.

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Salicylideneaniline (SA) sorbed in cation-exchanged M-ZSM-5 (M = H+, Li+, Na+, K+, Rb+, Cs+ and Zn2+) zeolites was studied by spectroscopic techniques assisted by quantum-chemical calculations. The nature of extra-framework cations present in the zeolite void was found to affect the spectral signature of the sorbed SA molecule that points to the shift of tautomeric equilibrium between the enol and keto forms. Small size cations, such as H+ and Li+, stabilize a cis-keto SA tautomer along with a enol one in the zeolite structure. The calculations indicate that the sorbed cis-keto tautomer may ha

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5

Hush, NS, MK Livett, JB Peel, and GD Willett. "Variable-Temperature Ultraviolet Photoelectron-Spectroscopy of the Keto-Enol Tautomers of Pentane-2,4-Dione." Australian Journal of Chemistry 40, no. 3 (1987): 599. http://dx.doi.org/10.1071/ch9870599.

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The HeI photoelectron spectra of pentane-2,4-dione measured at various temperatures have been subjected to a spectrum-stripping technique to enable isolation of the complete HeI photoelectron spectra of the keto and enol tautomers. The resulting spectrum-stripping coefficients allow evaluation of the enolization equilibrium constant at each temperature and subsequently the enthalpy of enolization. Interpretation of the photoelectron spectra is achieved with the use of ab initio molecular orbital calculations. Photoionization of non-bonding oxygen, and π -type electrons, contribute to the low i

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6

Hall, Victoria M., Jeffery A. Bertke, and Jennifer A. Swift. "Two tautomeric forms of 2-amino-5,6-dimethylpyrimidin-4-one." Acta Crystallographica Section C Structural Chemistry 72, no. 6 (2016): 460–64. http://dx.doi.org/10.1107/s2053229616007403.

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Derivatives of 4-hydroxypyrimidine are an important class of biomolecules. These compounds can undergo keto–enol tautomerization in solution, though a search of the Cambridge Structural Database shows a strong bias toward the 3H-keto tautomer in the solid state. Recrystallization of 2-amino-5,6-dimethyl-4-hydroxypyrimidine, C6H9N3O, from aqueous solution yielded triclinic crystals of the 1H-keto tautomer, denoted form (I). Though not apparent in the X-ray data, the IR spectrum suggests that small amounts of the 4-hydroxy tautomer are also present in the crystal. Monoclinic crystals of form (II

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7

Pasca, Roxana-Diana, Atena Moldovan, Ossi Horovitz, and Alexandru Lupan. "On the thermodynamics of triazines. A DFT and topological study." International Journal of Computational Physics Series 1, no. 1 (2018): 12. http://dx.doi.org/10.29167/a1i1p12.

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Tautomerism is the relation between isomeric organic compounds, which readily interconvert, usually by relocation of a proton. It plays an important role in the biological activity of compounds. In the series of tautomeric triazines (monoxime and dioxime derivatives) energy computations have been performed. The results have shown that for the monoxime, the amino keto tautomer is favored by 10.9 kJ/mol vs. the enol form; for the dioxime tautomer, the imino keto form is 17.6 kJ/mol lower in energy in comparison with the most stable amino keto tautomer. Topological aspects have been considered. C

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8

Oziminski, Wojciech Piotr, and Igor Wiśniewski. "Quantum-chemical study on the relative stability of sildenafil tautomers." Structural Chemistry 32, no. 5 (2021): 1733–43. http://dx.doi.org/10.1007/s11224-021-01818-7.

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AbstractThe tautomeric equilibrium of sildenafil molecule was theoretically studied using B3LYP and M06-2X density functional theory (DFT) methods in connection with aug-cc-pVDZ correlation consistent basis set. Calculations were performed for gas phase and water solution conditions modelled by polarizable continuum model (PCM). Three tautomeric forms are possible. Two keto forms: A — where the tautomeric proton in more distant from carbonyl group and B — where it is closer, and one enol form denoted, C. Both DFT methods qualitatively give similar tautomer stability order: B > A > C. The

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9

Venkatachalam, T. K., Gregory K. Pierens, and David Reutens. "Synthesis and Characterization of Anils Exhibiting Thermochromism." Australian Journal of Chemistry 63, no. 8 (2010): 1272. http://dx.doi.org/10.1071/ch09579.

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Several Schiff bases containing a hydroxy naphthyl moiety and substituted pyridyl groups were synthesized. The pyridyl substituted Schiff bases were isolated as a single stable tautomer at room temperature. High-resolution proton and carbon NMR spectroscopy showed that these compounds exist as keto tautomers. The Schiff bases showed extraordinary stability and did not convert to the enol tautomer, even at high temperatures. Most of the compounds exhibited thermochromic properties.

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10

Ruaysap, Makabodee, Stuart R. Kennedy, Collin M. Mayhan, et al. "Novel keto–enol tautomerism in 1,3,5-trihydroxybenzene systems." Chemical Communications 56, no. 85 (2020): 12985–88. http://dx.doi.org/10.1039/d0cc03639k.

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We report a new synthesis of the water-soluble compound 1,3,5-trihydroxy-2,4,6-trimethylsulfonic acid (1), which exists in two tautomeric forms (60 : 40::enol%:keto%), and its lanthanide complexes. Relative tautomer stability is influenced by intramolecular H-bonding and competing implicit solvent effects.

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11

Raczyńska, Ewa D. "Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution." Symmetry 13, no. 3 (2021): 497. http://dx.doi.org/10.3390/sym13030497.

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Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been

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12

Akerman, Kate J., and Orde Q. Munro. "An X-ray crystallographic and density functional theory study of (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one." Acta Crystallographica Section C Crystal Structure Communications 69, no. 3 (2013): 258–62. http://dx.doi.org/10.1107/s0108270113002369.

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The Schiff base enaminones (3Z)-4-(5-ethylsulfonyl-2-hydroxyanilino)pent-3-en-2-one, C13H17NO4S, (I), and (3Z)-4-(5-tert-butyl-2-hydroxyanilino)pent-3-en-2-one, C15H21NO2, (II), were studied by X-ray crystallography and density functional theory (DFT). Although the keto tautomer of these compounds is dominant, the O=C—C=C—N bond lengths are consistent with some electron delocalization and partial enol character. Both (I) and (II) are nonplanar, with the amino–phenol group canted relative to the rest of the molecule; the twist about the N(enamine)—C(aryl) bond leads to dihedral angles of 40.5 (

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13

Sıdır, İsa, Yadigar Gülseven Sıdır, Halil Berber, Maria L. Ramos, Licínia L. G. Justino, and Rui Fausto. "Reversal in Solvatochromism, enol-imine/keto-amine Tautomerism and (E)-(Z) Photoisomerizations in a Benzylidene Aniline Schiff Base Derivative in Different Solvents." Molecules 30, no. 3 (2025): 745. https://doi.org/10.3390/molecules30030745.

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A novel Schiff base, (E)-4-acetyl-N-(4-hydroxy-3-methoxybenzylidene)aniline (abbreviated as ANHMA), was synthesized and characterized using infrared and 1H- and 13C-NMR spectroscopies. Optical properties in different solvents were evaluated using UV-vis absorption spectroscopy. The compound is shown to exhibit both positive and negative solvatochromism with reversal occurring for solvents with ET(30)~45 (e.g., DMSO). The solvatochromic behavior of the compound was found to be strongly dependent on the hydrogen bond abilities and polarizability of the solvent, the observed reversal in solvatoch

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14

Rode, Michał F., Daniela Nedeltcheva-Antonova, and Liudmil Antonov. "Long-Range Proton Transfer in 7-Hydroxy-Quinoline-Based Azomethine Dyes: A Hidden Reason for the Low Efficiency." Molecules 27, no. 23 (2022): 8225. http://dx.doi.org/10.3390/molecules27238225.

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In the tautomeric Schiff bases, derived from 7-hydroxyquinoline, two competitive channels are possible upon excitation of the enol tautomer, namely proton transfer (PT) through intramolecular hydrogen bonding to the corresponding keto form and trans–cis isomerization around the azomethine double bond. The former leads to switching, based on twist-assisted excited state intramolecular PT, where the long-range proton transfer can occur as a targeted process. The latter, determined by the flexibility of the crane part, reduces the efficiency of the main targeted process. In previously studied mol

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15

Hamidian, Kourosh, Mohsen Irandoust, Ezzat Rafiee, and Mohammad Joshaghani. "Synthesis, Characterization, and Tautomeric Properties of Some Azo-azomethine Compounds." Zeitschrift für Naturforschung B 67, no. 2 (2012): 159–64. http://dx.doi.org/10.1515/znb-2012-0208.

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The primary azo compound 1-(3-formyl-4-hydroxyphenylazo)-4-nitrobenzene reacts with some aliphatic and aromatic diamines and yields the corresponding azo-azomethine compounds. These compounds were characterized by elemental analysis, IR, UV/Vis, and NMR spectroscopy. The primary azo compound exists entirely in the azo form in solution as well as in the solid phase. The tautomeric structure of azo-azomethine compounds heavily depends on the solvent and the substituents. Aliphatic diamine-based compounds favor the enol-imine tautomer while aromatic diamine-based compounds have structures that li

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16

Tivendale, Nathan D., Noel W. Davies, James Horne, John J. Ross, and Jason A. Smith. "Analysis of the Enol–Keto Tautomers of Indole-3-pyruvic Acid." Australian Journal of Chemistry 68, no. 2 (2015): 345. http://dx.doi.org/10.1071/ch14343.

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Indole-3-pyruvic acid (IPyA) is an important naturally occurring biosynthetic intermediate whose quantitation by standard analytic techniques can be complicated as it can exist as either the keto or enol tautomer. Here, we present a detailed analysis of the tautomerism of IPyA and provide further evidence that the two tautomers of IPyA may be readily separated by ultra high-performance liquid chromatography and that the relative proportions of each form may be controlled using temperature and pH.

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17

Nedeltcheva-Antonova, Daniela, and Liudmil Antonov. "Ground-State Tautomerism and Excited-State Proton Transfer in 7-Hydroxy-4-methyl-8-((phenylimino)methyl)-2H-chromen-2-one as a Potential Proton Crane." Physchem 4, no. 1 (2024): 91–105. http://dx.doi.org/10.3390/physchem4010007.

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The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isome

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18

Silber, Vincent, Christophe Gourlaouen, and Romain Ruppert. "Keto–enol equilibrium: stable tautomers of ortho-, meta-, and para-hydroquinones in large aromatics." RSC Advances 14, no. 17 (2024): 11969–76. http://dx.doi.org/10.1039/d4ra02202e.

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Keto–enol tautomerism of hydroquinones was studied for fused aromatic compounds. For larger fused aromatic compounds the dione tautomer was the stable form. These experimental results were corroborated by calculations.

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19

Tsuchiya, Yuko, Teruhiko Tamura, Masaaki Fujii, and Mitsuo Ito. "Keto-enol tautomer of uracil and thymine." Journal of Physical Chemistry 92, no. 7 (1988): 1760–65. http://dx.doi.org/10.1021/j100318a013.

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20

Babiker, Musa E. Mohamed, Ahmed A. Alzharani, and Ayyob M. Bakry. "Computational Study of the Keto-Enol Tautomerism of 3-Phenyl-2,4-Pentanedione in the Gaseous Phase and Solvents Using DFT Methods." Oriental Journal Of Chemistry 39, no. 1 (2023): 40–46. http://dx.doi.org/10.13005/ojc/390105.

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The study of tautomerics equilibria is of vital importance as tautomeric compounds reactivity highly depends on the proportion of each tautomer. Herein, the tautomeric equilibrium of the 3-phenyl-2,4-pentanedione was studied theoretically by the b3lyp/6-31+g(d)methods. The effect of four solvents was considered (water, methanol, carbon tetrachloride and Cyclohexane).The tautomeric equilibrium takes place through four-membered ring transition state. The barrier heights energies of the tautomerics equilibria reaction of the transition state with reference to Keto were found to be 31.26, 31.23, 3

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21

Zaharieva, Lidia, Ivan Angelov, and Liudmil Antonov. "Stationary External Electric Field—Mimicking the Solvent Effect on the Ground-State Tautomerism and Excited-State Proton Transfer in 8-(Benzo[d]thiazol-2-yl)quinolin-7-ol." Molecules 29, no. 15 (2024): 3506. http://dx.doi.org/10.3390/molecules29153506.

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The effect of the external electric field on the ground-state tautomerism in 8-(benzo[d]thiazol-2-yl)quinolin-7-ol has been studied by using density functional theory. The compound exists as an enol tautomer (off state) and under the influence of the external electric field a long-range intramolecular proton transfer can occur, placing the tautomeric proton at the quinolyl nitrogen atom (on state). This is a result of the much higher dipole moment of the end keto tautomer and indicates that the external electric field can be used to mimic the implicit solvent effect in tautomeric systems. In t

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22

Georgiev, Anton, and Liudmil Antonov. "8-(Pyridin-2-yl)quinolin-7-ol as a Platform for Conjugated Proton Cranes: A DFT Structural Design." Micromachines 11, no. 10 (2020): 901. http://dx.doi.org/10.3390/mi11100901.

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Theoretical design of conjugated proton cranes, based on 7-hydroxyquinoline as a tautomeric sub-unit, has been attempted by using ground and excited state density functional theory (DFT) calculations in various environments. The proton crane action request existence of a single enol tautomer in ground state, which under excitation goes to the excited keto tautomer through a series of consecutive excited-state intramolecular proton transfer (ESIPT) steps with the participation of the crane sub-unit. A series of substituted pyridines was used as crane sub-units and the corresponding donor-accept

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23

Jiang, Jian, Ronald Y. Dong, and Mark J. MacLachlan. "Lyotropic liquid crystallinity in mixed-tautomer Schiff-base macrocycles." Chemical Communications 51, no. 90 (2015): 16205–8. http://dx.doi.org/10.1039/c5cc06253e.

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New Schiff-base macrocycles that combine keto-enamine and enol-imine tautomers are reported. As well as forming host–guest complexes with organic cations, these macrocycles form a lyotropic liquid crystal in organic solvents.

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24

Abraham, Raymond J., M. Ashley Cooper, Amin Aghamohammadi, Kamyar Afarinkia, and Xiangli Liu. "The Use of MM/QM Calculations of 13C Chemical Shifts in the Analysis of Edaravone Tautomers." Journal of Solution Chemistry 51, no. 9 (2022): 1162–67. http://dx.doi.org/10.1007/s10953-022-01186-8.

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AbstractThe 13C NMR chemical shifts of the three Edaravone tautomers (keto, enol, and amine) were calculated using a combined molecular mechanics (Pcmod 9.1/MMFF94) and ab initio (GIAO (B3LYP/DFT, 6–31 + G(d)) model. This method gave such good agreement with experiment that the assignment of the complex spectrum of Edaravone in solution, which is a mixture of the three tautomers could be made. This has been attempted previously by various methods with diverse results. In CDCl3 solution, the observed spectra show only one form, the keto tautomer, and this is also the case with acetonitrile solv

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25

Deneva, Vera, Georgi Dobrikov, Aurelien Crochet, Daniela Nedeltcheva, Katharina M. Fromm, and Liudmil Antonov. "Tautomerism as primary signaling mechanism in metal sensing: the case of amide group." Beilstein Journal of Organic Chemistry 15 (August 8, 2019): 1898–906. http://dx.doi.org/10.3762/bjoc.15.185.

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The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hydroxy group and the nitrogen atom from the amide group) could stabilize the pure enol form in some solvents, the keto tautomer is also observed. This is a result from the formation of intramolecular associates in some solvents. Strong bathochromic an

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26

Talmaci, Natalia, Diana Dragancea, Elena Gorincioi, Paulina Bourosh, and Victor Kravtsov. "Crystal structure and NMR spectroscopic characterization of 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide." Chemistry Journal of Moldova 18, no. 2 (2023): 53–60. http://dx.doi.org/10.19261/cjm.2023.1074.

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The solid-state structure of a symmetrical carbohydrazone, namely 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide was determined by X-ray single crystal diffraction method. Compound 1 crystallizes in the monoclinic space group P21/n with unit cell parameters a= 10.1198(6), b= 22.7847(11), c= 15.1738(10) Å, β= 100.458(6)°, Z= 4, V= 3440.6(3) Å3, R1= 0.0540. Crystal structure of 1 is defined by two crystallographic independent molecules, which are bonded via N–H···O hydrogen bond. The organic molecules are as keto tautomers with respect to the carbamide fragment, and adopt the anti confo

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27

Kudrya, V. Yu, V. M. Yashchuk, A. P. Naumenko, Y. Mely, and Ya O. Gumenyuk. "Low-Temperature Luminescent Studies of Emissive Guanine Substitute for the Detection of Biopolymers." Ukrainian Journal of Physics 65, no. 4 (2020): 317. http://dx.doi.org/10.15407/ujpe65.4.317.

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The optical absorption at 300 K and the fluorescence and phosphorescence at 78 K of the emissive guanine substitute, deoxythienoguanosine, (dthG) were investigated in aqueous and TRIS-HCl-buffer solutions. Two optical absorption and fluorescence centers at room temperature were attributed to two keto-enol tautomers of dthG, which confirms previously obtained results. In contrast to room temperature, only one emission band was observed at 78 K in fluorescence spectra that was close to the long-wave fluorescence band at room temperature and could be associated with the tautomer with long-wave ab

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28

Deneva, Vera, Sofia Slavova, Alina Kumanova, Nikolay Vassilev, Daniela Nedeltcheva-Antonova, and Luidmil Antonov. "Favipiravir—Tautomeric and Complexation Properties in Solution." Pharmaceuticals 16, no. 1 (2022): 45. http://dx.doi.org/10.3390/ph16010045.

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The tautomeric properties of favipiravir were investigated experimentally for the first time by using molecular spectroscopy (UV–Vis absorption, fluorescence and NMR), as well as DFT quantum–chemical calculations. According to the obtained results, the enol tautomer is substantially more stable in most of the organic solvents. In the presence of water, a keto form appears to be favored due to the specific solute–solvent interactions. Upon the addition of alkaline-earth-metal ions, deprotonation and complexation occurred simultaneously, giving the formation of 2 : 1 ligand : metal complexes. Ac

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29

Solea, Atena B., Ivan Cornu, Vera Deneva, et al. "Tautomerism and Self-Association in the Solution of New Pinene-Bipyridine and Pinene-Phenanthroline Derivatives." Molecules 25, no. 2 (2020): 298. http://dx.doi.org/10.3390/molecules25020298.

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Two novel pinene-type ligands have been synthesized and their tautomeric and self-associating behavior studied in solution and in the solid state. The first ligand, an acetylated derivative of 5,6-pinene-bipyridine, displays keto-enol tautomerism in solution. This tautomeric equilibrium was studied by NMR and UV-Vis spectroscopy in various solvents, and the results were compared with the ones obtained through DFT calculations. The second ligand was obtained by an unusual oxidation of the phenanthroline unit of a pinene-phenanthroline derivative. This compound exists as a single tautomer in sol

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30

L., Krishnakumar K., Mathew Paul Ukken та Manju R. "A STUDY ON EFFECT OF INDOLE AS A SUBSTITUENT ON A KETO-ENOL TAUTOMER: A SYNTHETIC APPROACH ON β-DIKETONE". International Journal of Pharmacy and Pharmaceutical Sciences 9, № 8 (2017): 219. http://dx.doi.org/10.22159/ijpps.2017v9i8.19576.

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Objective: The existence of keto-enol tautomerism in β-diketones can typically study by a choice of analytical technique. The position of the keto-enol equilibrium depends on a number of factors like solvent, temperature, and substituents. Here an attempt was made to examine the effect of indole, a heterocyclic moiety with the moderately high polar surface area to examine its effect on ketonisation of β-diketone.Methods: The β-diketone studied and synthesized is a structural analog of magical drug curcumin. The structural influence of indole on ketonisation of β-diketone is studied to give a h

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31

MACIEJEWSKA, Agnieszka M., Katarzyna D. LICHOTA, and Jarosław T. KUŚMIEREK. "Neighbouring bases in template influence base-pairing of isoguanine." Biochemical Journal 369, no. 3 (2003): 611–18. http://dx.doi.org/10.1042/bj20020922.

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Assuming that the efficiency of the incorporation of 5-methyl-2′-deoxyisocytosine-5′ triphosphate (dMiCTP) and dTTP opposite isoguanine (iG) is a measure of the proportion of the keto and enol tautomers of iG in the Thermus aquaticus DNA polymerase active centre, we studied the influence of temperature and iG-neighbouring bases in the template on base-pairing of iG. On the basis of experiments with four sequences (3′-TXT-5′, 3′-GXG-5′, 3′-CXC-5′, 3′-CXT-5′, where X = iG) at 37, 50, 65 and 80°C, we found that 3′-neighbours decrease the fraction of the keto tautomer in the order C>GT, wherea

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32

Zaharieva, Lidia, Daniela Nedeltcheva-Antonova, and Liudmil Antonov. "8-(Pyridin-2-yl)quinolin-7-ol and Beyond: Theoretical Design of Tautomeric Molecular Switches with Pyridine as a Proton Crane Unit." Chemistry 6, no. 6 (2024): 1608–21. https://doi.org/10.3390/chemistry6060097.

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Long-range proton transfer in several conjugated proton cranes, originating from 7-hydroxy quinoline as a proton transfer platform, has been investigated theoretically by means of DFT and TD-DFT methodology. Major emphasis was given to their applicability to provide clean switching upon irradiation. The border conditions require the existence of a single enol tautomer in the ground state, which under excitation through a series of consecutive exited and ground state intramolecular proton transfer steps is transferred to the keto tautomer. It was shown that the most suitable candidates are base

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33

Jung, Hunmin, Michael A. Hawkins, and Seongmin Lee. "Structural insights into the bypass of the major deaminated purines by translesion synthesis DNA polymerase." Biochemical Journal 477, no. 24 (2020): 4797–810. http://dx.doi.org/10.1042/bcj20200800.

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The exocyclic amines of nucleobases can undergo deamination by various DNA damaging agents such as reactive oxygen species, nitric oxide, and water. The deamination of guanine and adenine generates the promutagenic xanthine and hypoxanthine, respectively. The exocyclic amines of bases in DNA are hydrogen bond donors, while the carbonyl moiety generated by the base deamination acts as hydrogen bond acceptors, which can alter base pairing properties of the purines. Xanthine is known to base pair with both cytosine and thymine, while hypoxanthine predominantly pairs with cytosine to promote A to

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Blanco, Carlos A., та Michael J. Hynes. "Catalysis of the deprotonation of β-diketones during formation of the 1:1 metal complexes". Canadian Journal of Chemistry 70, № 8 (1992): 2285–89. http://dx.doi.org/10.1139/v92-287.

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Catalytic effects on the deprotonation rate constants of β-diketones were observed during kinetic studies of the formation reactions of the 1:1 complexes of these ligands. When vanadium(IV), chromium(III), iron(III), cobalt(II), nickel(II), copper(II), and uranium(VI) react with pentane-2,4-dione, heptane-3,5-dione, 1,1,1-trifluoropentane-2,4-dione, 4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dione, 1-phenylbutane-1,3-dione, and 2-acetylcyclohexanone a significant catalytic effect on the rate of ionization of the keto tautomer of the ligand was observed. A considerable enhancement of the rate of

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35

De, Soumi, Manisha Ray, Anusooya Y. Pati, and Puspendu K. Das. "Base Triggered Enhancement of First Hyperpolarizability of a Keto–Enol Tautomer." Journal of Physical Chemistry B 117, no. 48 (2013): 15086–92. http://dx.doi.org/10.1021/jp410368z.

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Xie, Bin-Bin, Ke-Xin Wang, Pei-Ke Jia, Xiang-Yang Liu, and Ganglong Cui. "Excited-state double proton transfer of 1,8-dihydroxy-2-naphthaldehyde: A MS-CASPT2//CASSCF study." Chinese Journal of Chemical Physics 35, no. 3 (2022): 422–30. http://dx.doi.org/10.1063/1674-0068/cjcp2109163.

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Excited-state double proton transfer (ESDPT) is a controversial issue which has long been plagued with theoretical and experimental communities. Herein, we took 1,8-dihydroxy-2-naphthaldehyde (DHNA) as a prototype and used combined complete active space self-consistent field (CASSCF) and multi-state complete active-space second-order perturbation (MS-CASPT2) methods to investigate ES-DPT and excited-state deactivation pathways of DHNA. Three different tautomer minima of S1-ENOL, S1-KETO-1, and S1-KETO-2 and two crucial conical intersections of S1S0-KETO-1 and S1S0-KETO-2 in.and between the S0

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37

Bacsa, John, Maurice Okello, Pankaj Singh, and Vasu Nair. "Solid-state tautomeric structure and invariom refinement of a novel and potent HIV integrase inhibitor." Acta Crystallographica Section C Crystal Structure Communications 69, no. 3 (2013): 285–88. http://dx.doi.org/10.1107/s0108270113003806.

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The conformation and tautomeric structure of (Z)-4-[5-(2,6-difluorobenzyl)-1-(2-fluorobenzyl)-2-oxo-1,2-dihydropyridin-3-yl]-4-hydroxy-2-oxo-N-(2-oxopyrrolidin-1-yl)but-3-enamide, C27H22F3N3O5, in the solid state has been resolved by single-crystal X-ray crystallography. The electron distribution in the molecule was evaluated by refinements with invarioms, aspherical scattering factors by the method of Dittrichet al.[Acta Cryst.(2005), A61, 314–320] that are based on the Hansen–Coppens multipole model [Hansen & Coppens (1978).Acta Cryst.A34, 909–921]. The β-diketo portion of the molecule e

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38

Kokornaczyk, Artur K., Simone Thum, Constantin G. Daniliuc, Anna Junker, and Bernhard Wünsch. "Molecular structure of a brominated 2-benzazepinone – a crucial intermediate in the synthesis of novel chemokine CCR2 receptor antagonists." Zeitschrift für Naturforschung B 72, no. 6 (2017): 421–24. http://dx.doi.org/10.1515/znb-2017-0030.

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AbstractChemokines (chemoattractant cytokines) together with their receptors represent key players in inflammatory processes. In order to develop novel chemokine CCR2 and CCR5 receptor antagonists, 2-benz-azepin-1-one 5 was prepared, which showed promising CCR2 affinity. During the synthesis, regioisomeric bromo substituted β-keto esters 4a and 4b had to be separated. A crystal structure determination of the regioisomer 4b displayed unequivocally the bromine atom in the 7-position and the existence of 4b as the enol ester tautomer. Although the 7-membered azepine ring is rather flat, it is dis

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39

Wang, Jia, Andrew M. Turner, Joshua H. Marks, et al. "Preparation of Acetylenediol (HOCCOH) and Glyoxal (HCOCHO) in Interstellar Analog Ices of Carbon Monoxide and Water." Astrophysical Journal 967, no. 2 (2024): 79. http://dx.doi.org/10.3847/1538-4357/ad3c3e.

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Abstract Enols—tautomers of ketones or aldehydes—are considered key intermediates in the formation of prebiotic sugars and sugar acids. Although laboratory simulation experiments suggest that enols should be ubiquitous in the interstellar medium, the underlying formation mechanisms of enols in interstellar environments are largely elusive. Here, we present the laboratory experiments on the formation of glyoxal (HCOCHO) along with its ynol tautomer acetylenediol (HOCCOH) in interstellar ice analogs composed of carbon monoxide (CO) and water (H2O) upon exposure to energetic electrons as a proxy

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40

Karton, Amir. "Thermochemistry of Guanine Tautomers Re-Examined by Means of High-Level CCSD(T) Composite Ab Initio Methods." Australian Journal of Chemistry 72, no. 8 (2019): 607. http://dx.doi.org/10.1071/ch19276.

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We obtained accurate gas-phase tautomerization energies for a set of 14 guanine tautomers by means of high-level thermochemical procedures approximating the CCSD(T) energy at the complete basis set (CBS) limit. For the five low-lying tautomers, we use the computationally demanding W1-F12 composite method for obtaining the tautomerization energies. The relative W1-F12 tautomerization enthalpies at 298K are: 0.00 (1), 2.37 (2), 2.63 (3), 4.03 (3′), and 14.31 (4) kJmol−1. Thus, as many as four tautomers are found within a small energy window of less than 1.0kcalmol−1 (1kcalmol−1=4.184kJmol−1). We

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41

Vittal, Jagadese J., and Christopher J. Willis. "Coordination-induced keto–enol tautomerization in the formation of Ni2+ and Cu2+complexes of a fluorinated keto-diol." Canadian Journal of Chemistry 71, no. 7 (1993): 1051–56. http://dx.doi.org/10.1139/v93-140.

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The fluorinated keto-diol (CF3)2C(OH)CH2C(=O)CH2C(CF3)2OH forms stable, neutral, 1:1 complexes of Ni2+ (6a) and Cu2+ (6b) with tetramethylethylenediamine (TMED) as coligand. The structure of each complex has been determined crystallographically; they are isomorphous and isostructural, monoclinic with space group Cc (No. 9). Complex 6a, C15H20F12N2NiO3, has a = 11.495(2), b = 15.516(2), c = 12.323(2) Å, β = 99.88(1)°, V = 2165.4(6) Å3Z = 4. Complex 6b, C15H20CuF12N2O3, has a = 11.603(2) b = 15.661(2), c = 12.276(2) Å, β = 99.75(2)°, V = 2198.5(6) Å Z = 4. In each, the metal is in square-planar

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42

Irrera, Simona, and Nora H. de Leeuw. "A density functional theory study of the adsorption of uracil on the Au(100) surface." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, no. 2131 (2011): 1959–69. http://dx.doi.org/10.1098/rspa.2010.0657.

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We have used plane-wave density functional theory methods to explore the adsorption modes and configurations of uracil molecules on a gold surface to gain insight into the rational design of surface functionalization. We have investigated at the molecular level, the interactions of the RNA pyrimidine base uracil molecule isolated on the single crystal (100) surface of the gold substrate to determine the structure of uracil and orientation. Our calculations have shown that the most stable adsorbate structure is the enol tautomer of uracil, which adsorbs flat onto the gold surface through one of

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43

Zielinski, Theresa Julia, and Alexander Grushow. "Hydrogen Bonding Using NMR: A New Look at the 2,4-Pentanedione Keto-Enol Tautomer Experiment." Journal of Chemical Education 79, no. 6 (2002): 707. http://dx.doi.org/10.1021/ed079p707.

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44

Cysewski, Piotr, and Ryszard Oliński. "Theoretical Description of the Coding Potential of Diamino-5-formamidopyrimidines." Zeitschrift für Naturforschung C 54, no. 3-4 (1999): 239–45. http://dx.doi.org/10.1515/znc-1999-3-414.

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Abstract The results of geometry optimisation of possible Watson-Crick-like pairs o f 2,6-diamino-4-oxy-5-formamidopyrimidine (fapy-adenine) or 4,6-diamino-5-formamidopyrimidine (fapy-guanine) were presented. In the absence of the external field the fapy-adenine is able to form pairs with all four canonical nucleic acid bases. However, pairs with guanine, cytosine and thymine the most stable are. Thus, the potential miscoding abilities may be observed. In contrast, in the presence of the external field the mispairing abilities of fapy-adenine become insignificant since the most stable dimers a

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45

Uchimaru, Tadafumi, Seiji Tsuzuki, Kazutoshi Tanabe, Kensuke Furukawa, and Kazunari Taira. "Ab InitioCalculations on Keto/Enol Tautomers of Pterins. On the Significance of the Enol Tautomer of Pterin Ring in the Enzymatic Reduction of Dihydrofolate by DHFR." Chemistry Letters 18, no. 7 (1989): 1223–26. http://dx.doi.org/10.1246/cl.1989.1223.

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46

Fita, P., E. Luzina, T. Dziembowska, et al. "Keto–enol tautomerism of two structurally related Schiff bases: Direct and indirect way of creation of the excited keto tautomer." Chemical Physics Letters 416, no. 4-6 (2005): 305–10. http://dx.doi.org/10.1016/j.cplett.2005.09.069.

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47

Berenbeim, Jacob A., Natalie G. K. Wong, Martin C. R. Cockett, et al. "Unravelling the Keto–Enol Tautomer Dependent Photochemistry and Degradation Pathways of the Protonated UVA Filter Avobenzone." Journal of Physical Chemistry A 124, no. 15 (2020): 2919–30. http://dx.doi.org/10.1021/acs.jpca.0c01295.

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48

Ravikumar, Krishnan, Balasubramanian Sridhar, Jagadeesh Babu Nanubolu, Venkatasubramanian Hariharakrishnan, and Awadesh Narain Singh. "Structures of benzoxazine-fused triazoles as potential diuretic agents." Acta Crystallographica Section C Crystal Structure Communications 68, no. 8 (2012): o302—o307. http://dx.doi.org/10.1107/s0108270112029800.

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6,8-Dinitro-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]oxazin-1-one, C9H5N5O6, (I), a potential diuretic, and its acetylacetone derivative (E)-2-(2-hydroxy-4-oxopent-2-en-3-yl)-6,8-dinitro-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]oxazin-1-one, C14H11N5O8, (II), both crystallize from methanol but in centrosymmetric and noncentrosymmetric space groups, respectively. To the best of our knowledge, this is the first report of crystal structures of benzoxazine–triazole fused systems. The acetylacetone group in (II) exists as the keto–enol tautomer and is oriented perpendicular to the

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Trivedi, Mahendra Kumar, Snehasis Jana, Sambhu Charan Mondal, Mayank Gangwar, Kalyan Kumar Sethi, and Parthasarathi Panda. "Solid and liquid state characterization of tetrahydrocurcumin using XRPD, FT-IR, DSC, TGA, LC-MS, GC-MS, NMR and its biological activities." Journal of Pharmaceutical Analysis 10, no. 4 (2020): 334–45. https://doi.org/10.1016/j.jpha.2020.02.005.

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Tetrahydrocurcumin (THC) is one of the major metabolites of curcumin (CUR), an ancient bioactivenatural polyphenolic compound. This research article describes both the solid and liquid state characterizationof THC using advanced spectroscopic and thermo-analytical techniques. Anti-inflammatory,anti-oxidant, and neuroprotective activities of THC were investigated using in vitro cell lines. Liquidchromatography-mass spectrometry analysis revealed that our sample comprised 95.15% THC, 0.51%tetrahydrodemethoxycurcumin (THDC), 3.40% hexahydrocurcumin, and 0.94% octahydrocurcumin. Gaschromatography-

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Terwingen, Steven van, and Ulli Englert. "Argentophilic Interactions in Two AgI Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand." Crystals 9, no. 8 (2019): 414. http://dx.doi.org/10.3390/cryst9080414.

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Reactions of 3-(2-(pyridin-4-yl)ethyl)pentane-2,4-dione (HacacPyen) with AgPF6 and AgBF4 afforded cationic silver complexes [Ag(HacacPyen)2]+ with essentially linear coordination of the Ag I cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF6- salt 1 adopt the diketo form, in contrast to the uncoordinated HacacPyen molecule, whereas the corresponding BF4- salt 2 and the majority of 3-substituted acetylacetones crystallizes as the enol tautomer. In both compounds 1 and 2, complex cations aggregate via short Ag...Ag interactions to pairs. These contacts amount t

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