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The interaction between 20(S)-protopanaxatriol (PPT) and bovine serum albumin ( BSA) was studied with fluorescence quenching technique and ultra-violet absorption spectroscopy. The results indicated that PPT led to the intrinsic fluorescence quenching of BSA through a static quenching process .The binding constants of PPT with BSA obtained with fluorescence quenching method were calculated as 0.926 3×10(3) (298 K), 0.618 2×10(3) (308 K), 0.414 4×10(3) L·mol(-1)(318 K), respectively; while the number binding sites n were close to unity. The results showed that the driving force of the interaction between PPT and BSA was hydrogen bond and Van der Waals force. The result of synchronous fluorescence spectra showed that binding of PPT with BSA could induce conformational changes in BSA, that the part of tryptophan became more closely. According to Föster fluorescence resonance energy transfer theory, the binding distance r and energy-transfer efficiency E were respectively 26.2 nm and 0.32.

A new ligand N, N-bis[(diphenylphosphino)methyl]-2-pyridinylamine (L) and its luminescent dinuclear copper(I) complex [CuBrL]1 (1) were synthesized and characterized by mass spectrometry, elemental analysis, NMR and electronic spectroscopies. The structure of complex 1 was determined by X-ray crystal analysis to be a dinuclear complex with a pseudo-tetrahedral geometry. The complex 1 crystallizes in a triclinic space group P-1 and has two copper(I ) centers bridged by two halogen ligands to form the dinuclear structure with a four-membered Cu2 Br2 ring. The Cu-Cu distance in complex 1 is 0.306 0 nm which is longer than a sum of Van der Waals radius of two copper( I ) atoms. Therefore there is no substantial interaction between the two copper(I) centers in complex 1. DFT calculations indicate that the electron density of HOMO is distributed mainly over the copper, bromine and phosphorus atoms, while that of LUMO is localized on the ligand. Our work shows that there are two mechanisms to form the the lowest excited state of complex 1, i.e. the metal-to-ligand charge transfer (MLCT) and halogen-to-ligand charge transfer (XLCT).

The molecular geometries of four 2,4-dimethyl-7-amino-1,8-naphthyridine derivatives were optimized with B3LYP/6-31G(d) method. The energies of their frontier molecular orbitals and the molecular structures were investigated theoretically. The theoretical electronic spectra were calculated with TD-DFT in gas phase, PCM-TD-B3LYP/6-31 + G(d) and semiempirical ZINDO in CH2 Cl2 solution. The influences of solvent model and calculation methods on the electronic absorption spectra were also probed. The calculated results show that delocalized pi bonds exist in the four 1,8-naphthyridine derivatives, and their energy gaps (deltaE) between HOMO and LUMO are relatively small. The variation in their deltaE values gives a consistent trend with that of their electronic absorption with lambda(max). Theoretical spectra achieved prove that their absorptions are red-shifted when the delocalization of pi electrons is enhanced or the capability to donate electron by a substituted group is increased. The maximum absorption peaks of the four derivatives originate from pi (HOMO) --> pi * (LUMO) transition. The spectra calculated at the PCM-B3LYP/6-31 + G(d) level have little difference from experimental results: the differences in wavelength are 2.6, 10.3, 5.3 and 6.9 nm, whereas those in energies are 0.03, 0.09, 0.04 and 0.08 eV, respectively. The obtained results suggest that electronic spectra calculated by TD-DFT on the bases of geometries optimized with B3LYP/6-31(d) are in agreement with experimental ones, and can account for the different spectroscopic properties of the four 1,8-naphthyridine derivatives.