Marı́a Eugenia Costas

Density functional study of neutral allopurinol tautomeric forms

Optimized structures and total molecular energy density functional theory calculations for the 14 possible neutral allopurinol tautomers give the decreasing stability order

Density functional study of the anionic hypoxanthine tautomeric forms

\hbox{\underbar{N}(1)-H/\underbar{N}(5)-H} > \hbox{\underbar{N}(2)-H/\underbar{N}(5)-H} > \hbox{cis-enolic/\underbar{N}(1)-H}

Density functional study of the monocationic hypoxanthine tautomers

for the three most stable forms. Several molecular and electronic structure properties, the stabilities in oxidation and reduction processes, the tautomeric equilibrium constants, and the IR vibrational spectra were obtained for these. Those properties corresponding to the ketonic

Density functional study of the dicationic hypoxanthine tautomeric forms

\hbox{\underbar{N}(5)-H}

Density functional study of three-protonated hypoxanthine3+ isomeric forms

forms are discussed and compared with the theoretical ones for the two most stable species of the isomer hypoxanthine. A noticeable agreement is found between the predicted properties and the experimental behavior known up to date for both isomers. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 200–206, 1999

Density functional study of anionic allopurinol tautomers

Abstract Chemical and physicochemical properties of certain purine derivatives and isomers have been studied for several years. One of these heterocycles, hypoxanthine (hyp), has focused our attention under systematically modified protonation levels and tautomeric and isomeric forms. In the study reported here, we have carried out the Density Functional Theory calculations for all the possible tautomeric forms of monoanionic and dianionic hypoxanthine. For these, we have obtained: (i) the total molecular energies; (ii) several molecular and electronic structure properties; (iii) the Δ G values associated with heterocyclic tautomeric equilibria and monoprotonation processes; and (iv) the IR vibrational spectra. From the study, the relationship between the theoretical properties and both the anionic state and tautomeric forms arise. Among the results obtained, we found that the N (1)– H ketonic form is the comparatively most stable hypoxanthine 1− species. Considering previous theoretical calculations, the suggested descending sequence of π-type reductor character is: hyp 2− >hyp 1− >hyp 0 >hyp 1+ >hyp 2+ >hyp 3+ . Also, the suggested descending sequence of σ-type basicity is: N (1)> N (9)≈ N (7)> N (3)>0. The theoretical study supports both the N (1)– H predominance in hyp 1− aqueous solutions and the experimental reactivity of anionic hypoxanthine. All the suggested trends are in very good concordance with the experimental physicochemical and chemical behavior of hypoxanthine in different protonation states.

Spectral and magnetic studies of the polynuclear compound [Cu(II)(hypoxanthine2−)(H2O)2]n

Abstract The chemical and physicochemical properties of the purine derivative hypoxanthine have been the subject of study for several years from different points of view. In this article, the density functional theory study of the hypoxanthine monocationic state was carried out; the relative energetic stabilities, the structural parameters, several electronic structure properties, the tautomeric equilibrium constants and the IR vibrational spectra of the first five energetically most stable hypoxanthine1+ tautomers were calculated. Additionally, we obtained the Δ G for certain heterocyclic protonic transfer processes. The theoretical properties of the comparatively most stable 179 ketonic tautomer are discussed and successfully employed to analyze some features of the experimental physicochemical and chemical behavior of this hypoxanthine1+ predominant tautomer, as inferred from the studies on hypoxanthine–Lewis acid chemical interactions both in solution and in solid state.

Density Functional Theory Study of Hypoxanthine Tautomerism in Both the Isolated State and a Modeled-Ideal Aqueous Solution at Several Heterocyclic Protonation Levels

Abstract The study of the chemical and physicochemical properties of purine derivatives and isomers has received heightened attention for several years. Accordingly, the Density Functional Theory study of the dicationic state of purine derivative hypoxanthine was performed. In this study, the relative energetic stabilities, several molecular and electronic structure properties and the IR vibrational spectra of the four energetically most stable dicationic hypoxanthine tautomers were calculated. Additionally, we calculated Δ G for the heterocyclic protonic transfer processes and the constants of the tautomeric equilibria. The theoretical properties of the comparatively most stable K1379 ketonic form are discussed and compared with those for the energetically most stable hypoxanthine tautomers and isomers in different protonation levels. The results obtained are employed to analyze some features of the experimental physicochemical and chemical behavior of both the predominantly dicationic tautomer and hypoxanthine in diverse heterocyclic protonation states.

Density functional study of the monocationic allopurinol tautomers

Abstract The chemical and physicochemical properties of purine derivatives and isomers have received special attention for several years. The Density Functional Theory study of three-protonated hypoxanthine 3+ is presented here. Total molecular energies, relative energetic stabilities, several molecular and electronic structure properties, Δ G values of the heterocyclic protonic transfer processes, the isomeric equilibrium constant and the IR vibrational spectra for the two possible enolic isomeric forms of tricationic hypoxanthine were calculated. The theoretical properties are discussed and compared with those homologues for the most stable tautomers showing lower protonation levels. The resulting theoretical trends for several properties are then employed successfully to analyze some features of the experimental physicochemical and chemical behavior of hypoxanthine, thus leading to postulate some factors associated with the remarkable instability of hypoxantine 3+ .

Density functional study of the di-protonated allopurinol2+ tautomers

Abstract The chemical and physicochemical properties of the purine isomer allopurinol have been the subject of study from experimental and theoretical points of view. To gain insight into the knowledge of these properties, a density functional theory study of the allopurinol anionic forms was carried out. Full geometry optimization and total molecular energy theoretical calculations of the six possible monoanionic tautomers and allopurinol2− were performed by employing two different functionals and basis sets. For the first three most stable allopurinol1− tautomers and allopurinol2−, several molecular and electronic structure properties were calculated. Also, thermodynamic properties concerning heterocyclic protonic transfer and tautomeric processes and the IR vibrational spectra were obtained. Among other theoretical results, we can consider N(1)–H species as the energetically most stable allopurinol1− tautomer in gas phase with the comparatively higher stabilization of N(5)–H species in allopurinol1− aqueous solutions. Several of the molecular and electronic structure properties are strongly sensitive to tautomerism and allopurinol anionic state. The heterocycle shows an increase of its π-type Lewis basicity and also a decrease of its π-type Lewis acidity upon ascending the anionic state. The identity of the atoms proposed to be favored in electronic charge density donating processes is suggested to be independent of both the tautomerism and anionic state. Comparative σ-type Lewis basicities are suggested for the electron donor sites of the heterocycle, the lowest one corresponding to the exocyclic O site. Several IR spectral features characterize allopurinoln−, one of these corresponding to the energy decrease of the νC O vibrational mode with the increase of the anionic state. A number of theoretical properties are in overall concordance with the experimental behavior shown by allopurinol in the condensed phase. These show correspondence with those shown by the purine derivative hypoxanthinen−.