Laura Soccorsi

A STUDY OF THE DONOR PROPERTIES OF THE CARBONYL GROUP OF PYRIDONES

Abstract The donor properties of the CO group of pyridones have been examined by studying the IR spectra of their complexes with mercury-(II)-chloride and with hydroquinone. The complexes with mercury chloride are formed by a weak O⋯Hg donor-acceptor bond, while the others have the character of strongly H-bonded salts of hydroxypyridinium cations. The dipole moment of N-methyl-3-pyridone, not reported so far, has also been measured, (7·2 D). These results, and the agreement between the theoretical and the experimental dipole moments, support the prediction that the donor properties of the CO group are very similar for the three isomers.

Isomeric methoxypyridine-1-oxides and 1-methoxypyridones electronic spectra and structure

Abstract The electronic spectra of the isomeric forms of hydroxypyridine-1-oxides and 1-hydroxypyridones were calculated by the CNDO/CI method. Transition energies, intensities and assignments were compared with the u.v. spectra recorded for the first time on all the methyl-substituted isomers under similar conditions in non-aqueous solvents. Ground state properties of the same compounds were calculated after a full geometry optimization using the CNDO/2 and MINDO/3 approximations.

494—Apparent equilibrium constants for self-stacking: Calorimetric study of 5′AMP in aqueous solutions

Abstract Data available in the literature show that the numerical values of the apparent equilibrium constants, K st , of self-association of nucleotides and nucleobases differ by up to an order of magnitude, for the same compound. In addition to the known influence of the salts present in water solution it would also appear that the experimental technique used may influence the numerical values of K st . With regard to this last point, we report here a study of the self-association of 5′AMP using microcalorimetry. The thermodynamic parameter values obtained confirm their dependence on the experimental techniques utilized.

390 - Quantitative study of donor-acceptor interactions with biological relevance. I. C-T complexes between substituted pyridinium ions and phenolic structures

Abstract The apparent association constants and enthalpies of various C–T complexes between substituted pyridinium ions and phenolic structures have been determined by U.V. absorption spectroscopy. All the complexes are 1:1 with apparent association constants in the range 0.2–1.0 M−1. The ΔHo of the reactions are of the order of 10 kJ mol−1. As expected the presence of the OH groups in the donor molecule is the main structural feature influencing the interaction; while their relative position (o, m, p) is irrelevant in this respect.

Effect of C(5) methylation on self- and heteroassociation of cytidine in aqueous solution

Abstract The stacking self-association in aqueous solution of 2′-deoxycytidine and 5-methyl-2′-deoxycytidine has been studied by microcalorimetry; the apparent equilibrium constants and association enthalpy have been determined on the assumption of the isodesmic model of self-association. The relative ionization potential of 5-methyl-2′-deoxycytidine has been determined through the analysis of the ultraviolet absorption spectra of its hetero-associate with N -methyl-nicotinamide cation.

Regioselective reactions in heteroaromatic systems. Rules for methyl migration and nucleophilic substitution in methyl cyanurates and thiocyanurates

A comparative analysis carried out on 19 methyl cyanurates and thiocyanurates (some of which reported for the first time) allowed the following general conclusions to be drawn about their reactivity in nucleophilic substitution and thermal isomerisation reactions. The nucleophilic substitution of the methylthio-groups by methoxide anions is always possible, but requires different experimental conditions which are specific for the molecular region in which the methylthio is located; the thermal isomerisation reaction of the methoxy-derivatives into the corresponding S- or N-methyl isomers requires temperature conditions which are also largely dependent upon the molecular site of the methoxy-group. In both reactions the reactivity is enhanced by local asymmetry of substitution at the ring carbon atom to which the XMe (X = S or O) group is bound.

On the interactions of catecholamines with N-methylnicotinamide cation: a UV spectral study

Abstract The associations between catecholamines and an appropriate aromatic π-electron acceptor ( N -methylnicotinamide cation) have been studied as models allowing, through stacking interactions, understanding of the contribution of the catechol moieties to the drug affinity to receptor sites. Apparent association constants and enthalpies of various complexes have been determined by UV absorption spectroscopy. The experimental results suggest that catechol rings significantly and specifically contribute to the receptor affinity of catecholamines.

UV spectral study of ion-ligand interactions: alkali and alkaline earth cation binding to N-methyl-8-quinolone

The electronic absorption spectra of N-methyl-8- quinolone in acetonitrile and in acetonitrile containing Li(I) and Mg(II) ions (from perchlorates) provide evidences for the base—hard acids interaction and the consequent perturbations induced by the ion binding to the electronic structure of the ligand itself. More than one chromophore has been detected in the studied systems; the direct cation—ligand binding seems to involve a significant amount of charge- transfer from the ligand to the ion. The role of water, generally present in the used systems, is also discussed in relation to the structure of the associates.