A Computational Study On Excited States Of Luciferin Analogues And Intermolecular Interactions Of N-heterocyclic And Chloride Anions

1. Bioluminescence of firefly has attracted the attention ofmany scientists, and has bceome a ubiquitous tool for tagging andobserving gene expression, disease progression, and constructingrecombinant whole-cell biosensors. In this paper, we theoreticallystudy ground state and excited state properties of luciferinanalogue using density functional theory (DFT) and time-dependentdensity functional theory (TDDFT). We focus on the assessment ofvalidity of TDDFT in the study on the excites states of luciferinanalogue. The main results are outlined as follows:(1) The impact of basis set effects for absorption and emissionspectra of luciferin analogueis very limited. The basis set withpolarization and diffuse functions,6-31+G(d), is proved to bereliable in this work.(2) The spectra of luciferin analogueis are very sensitive to thechoice of XC functional. B3LYP, mPW3PBE, B3PW91can providesatisfying results, with RMS errors and standard deviation (SD)within0.40eV, and0.27eV for the absorption spectra and0.24eV,0.17eV for the emission spectra. 2. Intermolecuar interactions play important roles in chemistry,physics, biology, and so on. In this paper we discuss the interactionbetween20N-heterocyclic aromatics and chloride anions F-, Cl-, Br-by means of MP2method. The main results are outlined as follows:(1) In all of the stable isomers of these complexs, F-favors formingstrong covalent σ bond with N-heterocyclics, but Cl-and Br-favorsforming hydrogen bond. In addition, Cl-and Br-also form a few ofanionic-π type complexs with N-heterocyclics.(2) With the number of N atoms of N-heterocyclic increase, theinteractions between halide anions and the N-heterocyclicschange more negative, the complexes become more stable. Thesubstitution of β-site C atoms by N atoms has more contribution tothe interactions than α sites C atoms.(3) In the complexes of N-heterocyclics and halide anions, thestrong, covalent σ interaction significantly affects the frontiermolecular orbitals (FMOs) of N-heterocyclic, resulting in the changeof the constituent and energy level order of FMOs. The hydrogenbond and anion-π interaction have rather small effects on FMOs ofN-heterocyclic, favoring to slightly increase the nπ*energy gap anddecrease the ππ*energy gap.