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Spectroscopic investigations and hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine: a theoretical study.
MedLine Citation:
PMID:  23315214     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The structure, spectral properties and the hydrogen bond interactions of 8-aza analogues of xanthine, theophylline and caffeine have been studied by using quantum chemical methods. The time-dependent density functional theory (TD-DFT) and the singly excited configuration interaction (CIS) methods are employed to optimize the excited state geometries of isolated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine in both the gas and solvent phases. The solvent phase calculations are performed using the polarizable continuum model (PCM). The absorption and emission spectra are calculated using the time-dependent density functional theory (TD-DFT) method. The results from the TD-DFT calculations reveal that the excitation spectra are red shifted relative to absorption in aqueous medium. These changes in the transition energies are qualitatively comparable to the experimental data. The examination of molecular orbital reveals that the molecules with a small H→L energy gap possess maximum absorption and emission wavelength. The relative stability and hydrogen bonded interactions of mono and heptahydrated 8-azaxanthine, 8-azatheophylline tautomers and 8-azacaffeine have been studied using the density functional theory (DFT) and Møller Plesset perturbation theory (MP2) implementing the 6-311++G(d,p) basis set. The formation of strong N-H…O bond has resulted in the highest interaction energy among the monohydrates. Hydration does not show any significant impact on the stability of heptahydrated complexes. The atoms in molecule (AIM) and natural bonding orbital (NBO) analyses have been performed to elucidate the nature of the hydrogen bond interactions in these complexes.
Authors:
Mylsamy Karthika; Ramasamy Kanakaraju; Lakshmipathi Senthilkumar
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-1-15
Journal Detail:
Title:  Journal of molecular modeling     Volume:  -     ISSN:  0948-5023     ISO Abbreviation:  J Mol Model     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-1-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9806569     Medline TA:  J Mol Model     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Department of Physics, NGM College, Pollachi, 642 001, India.
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