Computational study on macro biological active molecules

Abstract

The halonium heterocyclic compounds are a group of unique compounds which possess various kinds of biological activities. Quantum mechanical calculation is carried out to characterize the molecular structure, molecular electronic properties, vibrational spectra and excited states, as well as to investigate the biological reaction mechanism.Comprehensive investigations of molecular structures and electronic properties on bioactive 3,7--dinitrodibenzobromolium cation was carried out using ab initio calculation. The calculated molecular structure agrees very well with X-ray diffraction data. The agreement between the calculated IR and Raman frequencies and experimental frequencies is excellent, except for the symmetric and asymmetric vibration frequencies of the nitro group which show relatively larger discrepancies, but this has been improved when the DFT methods are hired.Besides the cationic form considered in the HF and DFT studies, the structure of the 3,7-dinitrodibenzobromonium chloride is optimized. A strong ionic bond is formed between the chloride anion and the 3,7-dinitrodibenzobromonium cation, with a Br-Cl bond length of 2.606 C?. The excited state of the 3,7-dinitrodibenzobromonium cation were investigate with Configuration Interaction (CI) singlet method. Among the predicted excited state, the excitation at 3.3345 eV and 4.4467 eV are found to match the experimental observations. It was found that the electron excitation for the state at 4.4476 eV occurs mostly on the benzoid carbon atoms, while the electron excitation for the state at 3.3345 eV involves charge transfer only on one nitro group. As the charge transfer in the excited state at 3.3345 eV is quite significant that the electron distribution change quite a lot for the whole molecule.A series of iodonium heterocyclic compounds are studied using DFT method. The reaction mechanism of these compounds with the DNA strands was proposed and verified by the correlation of the calculated electrostatic potential value on the surface defined by 0.002 e/bohr3 electron density with their prohibition rate for DNA replication in cancer cells.