Calculos de propriedades moleculares atraves do metodo semi-empirico HAM/3 : aplicação em espectroscopia de fotoeletron molecular de moleculas biologicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

D. Dougherty et al. published photoelectron spectra of molecules of biological interest, in which a few bands were assigned. We used the semiempirical HAM/3 method to analyze these spectra, calculating Ionizations Potencials. Our purpose is to extend the studies about these spectra. The reasons why the HAM/3 method was chosen for these calculations are: the rapidity in its execution and the small errors expected. With the help of the HAM/3 calculations together with comparison among photoelectron spectra of standard molecules (or analogous), we could assign almost all the observed photoelectron spectra of the molecules. Both the semiempirical MNDO and AM1 method were used to calculate molecular geometries. The results of the two methods were compared. The two methods reproduced experimentaly determined geometries equally well. No significant difference was observed between MNDO and AM1. Electron affinities were aIso calculated by the HAM/3 method. We studied the effect of the substituents for the ionization potencials as well as the electron affinities. We verified that some occupied molecular orbitals are affected significantly with the substituents. Some of ionization potentials of molecules vary sensibly depending on whether the substituents are electron donor or acceptor. On the other hand, electron affinities or the molecules vary little. They are not affected with substituents. The studied molecules possess biological activity: nicotinic acid, nicotinamide, nicotinic acid methyl esther, N,N-diethylnicotinamide, formic acid, methyl formate, formamide, N,N-dimethylformamide, pyridine.

ASSUNTO(S)

espectroscopia fotoeletronica moleculas fisico-quimica

ACESSO AO ARTIGO

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