Theoretical Study on UV Spectrum and Active Site of Penicillin

Abstract The research of frontier orbit and active site of penicillin molecule has theoretical and practical significance to better understand the physical and chemical properties of penicillin molecule, to synthesize penicillin molecule and to develop its new pharmacological properties. In this paper, based on density functional theory, the spatial structure of penicillin molecules was firstly constructed by using Gaussian View 6.0 software, and the configuration optimization and frequency calculation of penicillin molecules were performed by using Gaussian09 software at the B3LYP/ 6-311g (D, P) basis set level. On the basis of structural optimization, based on time-dependent density functional theory, 25 excited states of penicillin molecules in aqueous solution were calculated, and then the frontier orbitals and active sites of penicillin molecules were analyzed by Multiwfn3.6 software, Fukui function method and frontier orbital theory method. The UV spectrum was plotted with Origin2017 software. The results show that the highest occupied molecular orbital (HOMO) and the lowest unoccpied molecular orbital (LUMO) of penicillin molecule are the 88th and 89th electron orbital, respectively. The maximum absorption peak of penicillin molecule UV spectrum is at 220.89nm, and its absorption mole coefficient is 6960.18L/mol/cm. It is mainly formed by the transition from the ground state S0 of the electronic state to the excited state S2, S4, S9, S11 and S12 of the electronic state, and the transition from S0 to the excited state S4 is the biggest contributor to the UV spectrum. The nucleophile site of penicillin molecule is C35 and the potentiophile site is S25.