Photophysical and Photobiological Properties of Coordination Polymers of Hypocrellin B Complexes Containing Magnesium and Zinc

Abstract

Hypocrellin B(HB) can chelate with Mg~(2+) and Zn~(2+) ions to form the coordination complexes Mg~(2+)-HB and Zn~(2+)-HB,which consist of 5-22 repeat units.The structures of these two complexes are characterized by ultraviolet-visible(UV-Vis) spectroscopy,Fourier transform infrared(FTIR) spectroscopy, and ~1H nuclear magnetic resonance(~1H NMR).The relative quantum yields of singlet oxygen(~1O_2) for Mg~(2+)-HB and Zn~(2+)-HB are 1.2 and 0.42 times as high as that of HB,respectively.Transient absorption spectra results indicate that O_2is able to quench the triplet excited state of Mg~(2+)-HB and Zn~(2+)-HB with an efficiency higher than 96%.The intersystem crossing efficiency(φ_T) and the fraction of triplet states quenched by O_2 that yield ~1O_2(f_△~T) are considered to be essential for the singlet oxygen quantum yields of HB and its complexes.Electron paramagnetic resonance(EPR) results suggest that Mg~(2+)-HB and Zn~(2+)-HB have a weak ability to generate a semiquinone anion radical,which reduces the generation of the superoxide anion radical(O_2~(·-)) by Mg~(2+)-HB and Zn~(2+)-HB.The results of the UV-Vis spectra and the deoxyribonucleic acid(DNA) melting temperature experiments indicate that Mg~(2+)-HB and Zn~(2+)-HB bind with calf thymus(CT) DNA in an electrostatic interaction mode.Under aerobic conditions,the efficiencies of photoinduced damage to CT DNA by Mg~(2+)-HB,HB,and Zn~(2+)-HB are found to be 32%,25%,and 22%, respectively.The reactive oxygen quencher experiments indicate that singlet oxygen is the main component generated by Mg~(2+)-HB that damages CT DNA.