Abstract:
The methods of spectroscopy and quantum chemistry were used to investigate the nature of absorption spectra and charge distribution of benzylpenicillins. The assumed spatial structure of the complex of benzylpenicillin sodium salt anion with water of composition 1 : 3 has been optimized. It was found that the absorption in the long-wave and middle regions of the spectrum is associated with the penam of the benzylpenicillin molecule. The intensity of the short-wave part of the spectrum is mainly formed by electronic transitions of the benzene part of the molecule. The distribution of effective charges on benzylpenicillin fragments was calculated and analyzed using quantum chemistry methods. The proton-acceptor power of all fragments was determined in benzylpenicillin anion and their complexes with water. The transfer of effective charge was calculated during the transition from a neutral benzylpenicillin molecule to its anion, as well as during complex formation. In the neutral molecule of benzylpenicillin, the donor properties of the penam significantly exceed those of the benzyl fragment, and the side chain has a higher acceptor ability than the carboxyl group. The formation of hydrogen bonds in the benzylpenicillin molecule markedly reduces both the donor properties unit of the penam and the acceptor properties of the side chain. The changes on the benzyl and carboxyl moieties are less significant. Data analysis has established that in the benzylpenicillin anionic form the donor and acceptor properties of fragments change sharply in comparison with the neutral form. The main difference of the charged form is that the penam system becomes practically neutral, and the proton-acceptor center becomes the CCO group in the anionic form.
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