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Izomery porfiryny : podobieństwa i różnice

Waluk Jacek

Wiadomości Chemiczne

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2021

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[Z] 75, 5-6

631--652

EN

Porphyrins, “pigments of life”, are extremely popular objects of fundamental research and as candidates for diverse applications. The prerequisite for a successful application is the understanding of the electronic structure. For that purpose, it is instructive to compare the properties of porphyrin with those of its isomers. To date, six such isomers have been synthesized. In this work, we compare the characteristics of all “nitrogen-in”, N-confused- and neo-confused porphyrin isomers, including three structures that have not yet been obtained. We discuss the electronic spectra, intramolecular hydrogen bonding, and tautomerism. Analysis of the energy pattern of frontier orbitals allows predicting the redox properties, as well as the pattern of electronic absorption and magnetic circular dichroism (MCD) spectra. In turn, the geometry of the inner cavity is the factor that determines the strength of hydrogen bonds and, in consequence, the kinetics of tautomerization.

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Molecular Perspective Review of Biochemical Role of Nucleobases Modified by Oxidative Stress

Cysewski P.

Computational Methods in Science and Technology

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2010

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Vol. 16, No. 1

51-72

EN

Numerous damages to cellular DNA are imposed by oxidative stress. Formation of stable products resulting from oxidation of nucleobases is one of many observed consequences. The oxidized species constitute a class of heterocyclic compounds with great diversities of physicochemical properties. Modified nucleosides significantly differ from their canonical protoplasts by tautomeric equilibriums, protolytic properties in the gas phase and water solution, they have altered oxidative susceptibility and N-glycosidic bond stabilities. However, what is most important, they have overwhelmingly altered pairing properties, which are directly responsible for observed cytotoxic properties of these lesions. Besides, since many analogues are structurally different with respect to canonical bases their presence in DNA must impose many energetic, structural and dynamic modifications. These aspect are reviewed as fruits of project no 39 supported by computational grant in Poznań Supercomputing and Networking Center (PSNC, Poland).

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Tautomeric Equilibria in Solutions of 1-Phenacylpyridazin-1-ium and 1-(o-Fluorophenacyl)pyridin-1-ium Cations. DFT and NMR Studies

Gawinecki R., Dobosz R., Ośmiałowski B., Zakrzewska A.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 9

1623-1628

EN

Although 1-(2-oxo-2-phenylethyl)pyridazin-1-ium and 1-[2-oxo-2-(o- fluoro phenyl - ethyl)]pyridin-1-ium cations may equilibriate with the respective enol and enaminone tautomeric forms, both experimental NMR data and results of ab in itio calculations show the keto forms to be the only species present in DMSO solution. Intramolecular hydrogen bonds and pi electron delocalization seem to have negligible effect on stabilization of the tautomers. On the other hand, electrostatic repulsions between the onium nitrogen and hydroxy oxygen atoms in the compounds studied are considered to be responsible for the in stability of the enol and enaminone tautomeric forms.

4

Alfa-Pyridoin Tautomerism - Reducing Difference Infrared Spectral Analysis

Chapkanov A., Zareva S.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 3

467-476

EN

The existence of diol and oxidized diketoforms in chloroform of -pyridoin was established using reducing-difference IR-spectral analysis for non-polarized spectra interpretation. The linear-dichroic IR-spectral analysis of the compound, studied in nematic liquid crystal solution, showed stabilization of the diolic tautomer. Detailed vibrational assignment of the corresponding modes was carried out using reduced-difference procedure for polarized spectra interpretation. The experimental results were completed and enlarged with theoretical ab initio calculations.

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Adenine and Some of Its Analogues in DMSO-d6 Solution: an NMR and GIAO-DFT Study

Dybiec K., Molchanov S., Gryff-Keller A.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 5

857-868

EN

The results of GIAO-DFT calculations [at B3LYP/6-311++G(2d,p) PCM and PBE1PBE/6-311+G(2fd,p) PCM levels] of 13C NMR and 15N NMR parameters have been employed to reinvestigate tautomerism of adenine in DMSO solution. The separate 13C NMR sig nals of N7-H and N9-H adenine tautomers have been observed for the first time. The ex erimental 13C chemical shifts, 3J(C,H) coupling constants and 15N chemical shifts of adenine and three of its methyl derivatives (9MeA, 7MeA and 3MeA) have been quantitatively analyzed using the calculated parameter values. This procedure has provided the solution populations of the predominant adenine tautomers being in agreement with the available literature data. The apparent dependence between the amino group geometry and the chemical shift of the adjacent carbon in 2-aminopyridine system has also been discussed.

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Crystal Structure of a Schiff Base, 2-Hydroxynaphthylidene-(8-aminoquinoline) - In Search of Two Tautomeric Forms

Lipkowski J., Fita P., Grabowska A.

Polish Journal of Chemistry

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2008

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Vol. 82, nr 10

2009-2016

EN

Crystal structure of a Schiff base, 2-hydroxynaphthylidene-(8-aminoquinoline) (HNAQ) has been determined at 4 different temperaturs in the range of 100-400 K. While spectral studies would indicate the coexistence of two different tautomeric forms in thermal equilibrium, no statistically significant structural effects have been observed as the pre umed evidence for the presence of the enol form in the solid. HNAQ crystallizes in the monoclinic space group Pc with unit cell parameters a = 10.3400(7) Capital A, b = 5.8870(19) Capital A, c = 14.2960(21) Capital A, beta = 125.844(10) graduate, V = 705.41(27) Capital A 3 and Z = 2 (at 100 K). Crystallographic data for HNAQ have been compared to previously known structures of its metalo-organic complexes. This showed only minor changes due to complexation. In all the cases the mol e cules in the crys tal are al most pla nar and the presence of the metal atom affects only the bonds in the chelate ring.

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NMR Studies of Tautomerism and Protonation Patterns in Bis(6-purinyl) Disulfide and Ionic Forms of 6-Mercaptopurine

Pazderski L., Toušek J., Sitkowski J., Kozerski L., Szłyk E

Polish Journal of Chemistry

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2007

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Vol. 81, nr 2

193-210

EN

1H-13C and 1H-15N HMBC-NMR spectroscopy was applied to study tautomerism and the protonation patterns in 6-mercaptopurine (6mpH) derivatives: bis(6-purinyl) disulfide ((6puS)2), 6-mercaptopurinium cation (6mpH2 + ) and purine-6-thiolate anions (6mp–, 6mp-deH2–). 1H, 13C, 15N resonances were assigned and the respective delta 1H, delta 13C, delta 15N chemical shifts as well as JHC, JHN coupling constants determined. Quantum-chemical NMR calculations by GIAO method (B3LYP/6-31G**//RHF/6-31G*) allowed to evaluate the ratio of N(1), N(3), N(7), N(9)H : N(1), N(3), N(7)H, N(9) tautomeric forms for the DMSO-solvated (6puS)2 molecules as ca. 9:1. The existence of “semi-protonated” 6mpHźH3O+ species, intermediate between 6mpH and 6mpH2 + , and readily oxidized to (6puS)2 was suggested in the DMSO-d6 + HCl solution. Further hydrolysis and oxidation of the formed disulfide lead to the derivatives of purine-6-sulfenic and purine-6-sulfinic acid.

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Analysis of Electron Density in trans-N,N'-Bis-(R-salicylidene)-1,2-cyclohexanediamines

Dziembowska T., Majerz I.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 5-6

911-920

EN

The hydrogen bonds in three tautomeric forms of trans-N,N-bis-(R-salicylidene)- 1,2-cyclohexanediamine (R = H, 5-NO2, 4,6-di-OCH3 and 3,5-di-Cl) have been studied by DFT calculations and topology of density charge function according to Bader’s AIM theory. Comparison of the CP values at the H…N and H…O bond critical points (BCP) for the compounds studied has revealed the effect of substituents on the hydrogen bonds strengths in the two chelate rings of trans-N,N-bis-(R-salicylidene)-1,2-cyclohexanediamines.

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Spectroscopic 1H NMR, 13C NMR and Theoretical DFT Study of Isoguanine and 8-Oxoadenine in Water and DMSO-d6 Solutions

Dybiec K., Gryff-Keller A.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 11

1831-1843

EN

1Hand 13CNMRspectra of isoguanine (2-hydroxyadenine) and 8-oxoadenine inH2Oand DMSO-d6 solutions of various acidity have been interpreted using arguments based on the results of several 1D and 2D NMR experiments and theoretical DFT-based calculations. The collected data for H2O solutions can serve for identification of these compounds in body fluids during medical analysis. The 1H and 13C NMR spectra of the investigated compounds in DMSO-d6 solutions have provided information on their tautomeric forms and the mobility of their exchangeable protons.

10

On n-pi Elektron Distribution in Simple Keto-Enol tautomeric Systems: H3C-C(R)=O==H2C=C(R)-OH and RH@C-CH=O==RHC=CH-OH

Raczyńska E.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 4

749-758

EN

Variations of the n- electron distribution during the tautomeric interconversion and substituent effects were analysed for simple keto-enol tautomeric systems of general formulae H3C-C(R)=O H2C=C(R)-OH and RH2C-CH=O RHC=CH-OH using the geometry-based HOMA index.

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On n-pi Electron Distribution in Simple Acyclic Tetrad and Pentad Tautomeric Systems

Raczyńska E.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 6

1003-1013

EN

Variations of the n-pi electron distribution during the tautomeric interconversion were analysed for simple acyclic tetrad and pentad tautomeric systems using the geometry- based HOMA index. Internal effects such as Y-conjugation, push-pull effect and intramolecular H-bonding were discussed.

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Creatinine and Creatininium Cation in Water Solution. Tautomerism and Quantitative Interpretation of the Solution Acidity Effect on 1H, 13C and 14 N NMR Chemical Shifts

Kotsyubynskyy D., Molchanov S., Gryff-Keller A.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 2

239-248

EN

1H, 13C and 14N NMR chemical shifts for creatinine in water solutions of various acidity have been measured. Analysis of these data enabled determination of the acidity constant of creatininium cation and the chemical shifts of the neutral and protonated forms of creatinine. Molecular energies and carbon and nitrogen magnetic shielding constants for various tautomeric structures of the investigated species have been calculated using the quantum chemistry method GIAO DFT B3LYP/6-311++G(2d,p). Compilation of the available experimental and theoretical results has provided additional information on the problem of tautomerism of this important biological molecule.

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Predominance of (E)-1,2-Di(pyridin-2-yl)ethene-1,2-diol over 2-Hydroxy-1,2-di(pyridin-2-yl)ethanone in Solution

Gawinecki R., Ośmiałowski B., Kolehmainen E.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1411-1417

EN

1H, 13C and 15N NMR spectra, supported by the GIAO/DFT calculated (B3LYP/6- 311G//RHF/3-21G) 13C and 15N (B3LYP/6-31++G**//RHF/3-21G) NMR chemical shifts, show that (E)-1,2-di(pyridin-2-yl)ethene-1,2-diol (OO3) is the only tautomer present in chloroform solution. MP2/6-31G**//RHF/6-31G** and MP2/6-31G** ab initio calculations confirm that this perfectly planar form is really more stable than 2-hydroxy-1,2-di(pyridin-2-yl)ethanone (OK1, OK2 and OK3) and other isomeric dimers of pyridine-2-carboxaldehyde. The strong intramolecular hydrogen bonds are responsible for high stability of (E)-1,2-di(pyridin-2-yl)ethene-1,2-diol (the conjugation in the molecule is of minor importance).

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A Theoretical Study of the cis-syn Cytosine-containing Pyrimidine Dimers in the Gase Phase and a Water Cluster and a Tautomer-Bypass Mechanism for the Origin of UV-induced Mutations

Danilov V., Leś A., Alderfer J. L.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 7

1039-1049

EN

A quantum mechanical study of cis-syn cyclobutane cytosine-containing photodimers including the normal and rare tautomeric forms of bases has been performed using the ab initio method at HF/6-31G(d,p), MP2(fc)//HF/6-31G(d,p) and MP2(fc)/6-31G(d,p) levels. It is predicted that in the gas phase all photodimers containing the rare imino form of cytosine are more stable than those containing its normal form. The Monte Carlo study of the hydration for cytosine-consisting dimers showed that the dimer containing the imino form of cytosine is stabilized by water cluster more than that containing its amino forms. As a result, the imino form of cytosine in the cytosine-containing dimer directs the incorporation of adenine in the complementary strand during replicative bypass. Data obtained point to the cytosine tautomerism as a possible mechanism for the origin of UV-induced mutation.

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Isotope effects on chemical shift in tautomeric systems with double proton transfer. Citrinin

Hansen P.E., Langgard M., Bolvig S.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 2

269-276

EN

Primary and secondary deuterium isotope effects on 1H and 13C chemical shifts are measured in citrinin, a tautomeric compound with an unusual doubly intramolecularly hydrogen bonded structure. The isotope effects are to a large extent dominated by equilibrium contributions and deuteration leads to more of the deuterated enol forms rather than the deuterated acid form. 1H, 13C and 17O nuclear shieldings are calculated using density functional ab initio methods. A very good correlation between calculated nuclear shieldings and experimental 1H and 13C chemical shifts is obtained. The tautomeric equilibrium can be analyzed based on the isotope effects on C-6 and C-8 carbons and shows an increase in the o-quinone form on lowering the temperature. Furthermore, upon deuteration the largest equilibrium shift is found for deuteration at OH-8 and the shift in the tautomeric equilibrium upon deuteration is increasing at lower temperature.