Zhifen Li

Partial molal volume of DMSO and Me2CO in the mixture of water and t-butyl alcohol (TBA) at 278.15, 288.15 and 298.15 K

Abstract Volume measurement can be used in the evaluation of the molecular interaction in solution. The apparent molal volumes V a of DMSO and Me 2 CO in the concentration range 0.2–1.4 mol per kg of solvent in mixed solvents of TBA and water were calculated from density data. The apparent molal volume of DMSO and Me 2 CO at infinite dilution − V o was determined by extrapolation. The variation of − V o with the composition of binary mixed solvent was indicated in plots. The contribution of molecular interaction and structure to solution volumes was discussed.

Interactions of calf thymus DNA with short chain oligoamides

In order to detect the biological activity of new synthetic short chain oligoamides, the present work gives the results of studies on the interaction between calf thymus DNA and short chain oligoamides: PyPyPy-g-Dp (ligand 1) and PyPyPyPy-g-Dp (ligand 2). In the circular dichroism (CD) spectra of the mixing solution of DNA with ligands a specific peak appears in the region of 300‐380 nm wavelength, which indicates that both ligands 1 and 2 can bind calf thymus DNA specifically. 1 H NMR spectra show that aromatic ring protons of ligand 1 appear as an obvious down-field shift, while those protons in ligand 2 disappear since ligand 2 owns a higher binding affinity with DNA than that of ligand 1. Investigations of DNA transition by differential scanning calorimetry (DSC) reveal that DNA melting temperature rises due to binding with ligands, and that ligand 2 alters the DNA transition process more significantly. At the same time, the molar binding enthalpies of ligands with DNA are measured at 293 K. The difference between the binding affinity of ligand 1 and 2 with DNA implies that increasing the number of N-methylpyrrole increases both the binding site size and the binding affinity. # 2002 Elsevier Science B.V. All rights reserved.

Urease conformational change induced by transplatin: A comparison on the interaction of urease with transplatin and cisplatin

Abstract The interaction between transplatin and urease was studied by microcalorimetry, DSC, circular dichroism (CD) spectrum and fluorescence spectrum. Transplatin can render urease inactive as is indicated by the experimental results of microcalorimetry. Thermal denaturation experiments of urease by DSC show that transplatin generally reduces urease thermal stability since urease T m decreases dramatically. From the features of urease CD and fluorescence spectra, transplatin leads to urease conformational change at lower concentrations than in case of cisplatin. The interaction of transplatin with urease is stronger than that of cisplatin and the binding site of urease with transplatin may be different from that with cisplatin.

DSC Studies of the Effects of Cisplatin and Transplatin on G-Actin

The effects of cisplatin and its trans isomer transplatin on the thermal denaturation of G-actin were studied with a Micro DSC-III differential scanning calorimeter. The denaturation enthalpy of G-actin was found to be 12 J g−1, and the denaturation temperature was 328 K. The thermal denaturation curve showed that increasing cisplatin concentration decreased the enthalpy change. However, after the ratio of cisplatin to G-actin attained 8:1 (mol:mol), the denaturation enthalpy no longer decreased. Transplatin decreased the enthalpy change more rapidly. In contrast with cisplatin, the denaturation peak at 328 K disappeared, and a strong exothermic peak appeared at 341 K when the ratio of transplatin to G-actin was 8:1 (mol:mol). The enthalpy change was 75 J g−1, which is far in excess of the range of weak interactions. This strong exothermic phenomenon probably reflects the agglutination of protein. The effects of cisplatin and transplatin on the number of the free thiol groups of G-actin are discussed.