All valence-electrons calculations of the biological purines and pyrimidines

A calculation of the electronic structure of the bases of DNA has been performed by an SCF procedure including simultaneously all the valence electrons. The results are analyzed and compared to those of previous calculations made in the electron approximation.

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Zusammenfassung Die Elektronenstrukturen der DNA-Basen werden mit einer SCF-Methode unter Einschluß aller Valenzelektronen untersucht. Die Ergebnisse werden mit denen reiner -Rechnungen verglichen.

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Résumé Un calcul de la structure électronique des bases de l'acide déoxyribonucléique a été effectué par un procédé self-consistent traitant tous les électrons de valence simultanément. Les résultats sont analysés et comparés à ceux de calculs antérieurs faits dans l'approximation de la séparation -.

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This work was supported by grant no. 67-00-532 of the Délégation Générale à la Recherche Scientifique et Technique (Comité de Biologie Moléculaire).     

PPP calculations of the absorption spectra of purines and pyrimidines

A mechanism of the synthesis of cyclooctatetraene is discussed in which a temporary transfer of the multiplicity from the Ni²⁺ ion to the four acetylene molecules takes place.     

Laser Raman spectroscopy of irradiated purines and pyrimidines

The laser Raman spectra of irradiated crystalline uracil and guanine show changes compared to that of the unirradiated compounds which are believed to be due to the production of ionic species. The Raman spectrum crystalline guanine is presented for the first time.     

Solid phase synthesis of purines from pyrimidines

In this paper the solid phase synthesis of various substituted purines is described starting from 4,6-dichloro-5-nitropyrimidine. The 4,6-dichloro-5-nitropyrimidine was coupled to Rink amide resin followed by displacement of the second chloride by an amino compound. Reduction of the nitro compound proved to be problematic but was achieved using lithium aluminum hydride/aluminum trichloride. The diamines (13) were then elaborated to purines by three different routes.     

SCF Deformation densities and electrostatic potentials of purines and pyrimidines

4-31G wave functions have been computed for five purines and pyrimidines. The calculated deformation densities have been partitioned into atomic fragments, which were integrated to yield atomic multipole moments. The transferability of atomic fragments between related molecules was verified by constructing model maps for uracil and guanine from appropriate fragments of cytosine and adenine. Model electrostatic potentials calculated from the moments of model atoms are similar to the corresponding 4-31G potentials. Comparison of 4-31G and 4-31G** deformation densities of cytosine provides simple rules for estimating the effects of polarization functions on the atomic multipole moments of most atom types occurring in the purines and pyrimidines. These rules were applied to the other molecules and yielded reasonable approximations for their molecular dipole moments. Substituting CH₃ for H has little effect on the deformation density beyond the substitution center.     

Theoretical study of the electronic properties of biological purines and pyrimidines

In view of a study of the atypical bases of the nucleic acids, the integral values appropriate for the methyl substituent have been determined in the SCF approximation previously described [1]. Both the inductive and the hyperconjugation effects have been introduced. An application to thymine is described.     

Determination of purines and pyrimidines in beer samples by capillary zone electrophoresis

Ten purine and pyrimidine bases were separated using capillary zone electrophoresis (CZE) with direct UV detection at 254 nm as well as mass spectrometric (MS) detection using an electrospray ionization (ESI) interface. For this purpose a carrier electrolyte composition compatible with both methods of detection containing 300 mM diethylamine (DEA) was selected. Limits of detection were in the range between 0.1 and 0.3 mg l⁻¹ and calibration plots were found to be linear over at least two orders of magnitude. The applicability of the developed method for the analysis of real samples was demonstrated for some beer samples. A series of “Lager” beer samples from different breweries in Europe as well as a number of completely different types of beers were investigated with respect to their content in the selected purine and pyrimidine bases using the developed CE method with UV detection at 254 nm.     

Analysis of purines and pyrimidines by mixed partition-adsorption normal-phase high-performance liquid chromatography

This paper summarizes the results in the development of mixed partition-adsorption (MPA) normal-phase high-performance liquid chromatography published in the last 10 years. The MPA normal-phase systems are an alternative approach not only to the adsorption normal-phase mode but also to the most widely used reversed-phase mode in the separation area of purine and pyrimidine derivatives. It is shown that the MPA systems are applicable in analytical practice.     

Fluorimetric determination of dissociation constants and ph-controlled fluorescence analysis of purines and pyrimidines

Fluorimetrically determined pH-titration curves have been obtained for twelve purines and pyrimidines at room temperature, in aqueous solution. The pK(a) values for these compounds have been determined fluorimetrically and potentiometrically. Except for 6-mercaptopurine and uric acid, there is close agreement between the two sets of pK(a) values, but a large difference for the corresponding excited singlet-state values, pK(S1)(a), which were calculated previously. This indicates that the excited singlet-state proton-transfer rate is much slower than the fluorescence-decay rate of purines and pyrimidines in our experimental conditions. A direct, simple, pH-controlled fluorimetric method is proposed for the determination of purines and pyrimidines. The limits of detection vary between 60 ng ml and 5.4 mug ml .     

Analysis of mixtures of purines and pyrimidines by first- and second-derivative ultraviolet spectrometry

Zero-order, first-derivative and second-derivative ultraviolet absorption spectra of a series of purines, pyrimidines and their binary mixtures in aqueous solution have been recorded at 298 K. It is shown that second-derivative spectra can be used for the identification of eight mixtures of purines and pyrimidines. Several graphical procedures are tested for evaluating derivative spectra in quantitative measurements of single compounds and mixtures. Linear log-log calibration plots are obtained with correlation coefficients generally larger than 0.99. Second-derivative spectra appear to provide a precise and simple method for determination of purines and pyrimidines, at concentrations ranging between 5 x 10(-6) and 5 x 10(-4)M.