The biological effects of rare-earth metal ions on the organism have been studied using La3

The water-soluble quaternary ammonium salt of chitosan was synthesized by reaction of chitosan with glycidyl trimethylammonium chloride. It was characterized by Fourier transform infrared and carbon-13 magnetic resonance spectra. Its microbiostatic effects against Staphylococcus aureus, Escherichia coli and Candid albicans were explored by microcalorimetry. The antimicrobial activity of the quaternized chitosan was stronger in alkaline condition than that in weak acidic condition.

The interaction between monoammonium glycyrrhizinate (MAG) and bovine serum albumin (BSA) were studied by fluorescence and absorption spectroscopy. The quenching mechanism of fluorescence of bovine serum albumin by monoammonium glycyrrhizinate was discussed. The binding sites number n and apparent binding constant K were measured by fluorescence quenching method. The thermodynamic parameters [1]H◦, [1]G◦, [1]S◦ at different temperatures were calculated. The distance r etween donor (bovine serum albumin) and acceptor (monoammonium glycyrrhizinate) was obtained according to F˝orster theory of non-radiation energy transfer. The results of synchronous fluorescence spectra and UV－vis absorption spectra show that the conformation of bovine serum albumin has been changed.

The binding of Schiff base selenide, (2-hydroxy-benzimido)ethyl-n-hexylselenide, to bovine serum albumin (BSA) was studied using fluorescence spectroscopy. The measurement was performed in Tris-HCl buffer aqueous medium at pH 7.4. Stern-Volmer graphs were plotted and quenching constants were estimated. The quenching constant at 303 K was (1.639-0.046)1013 L mol-1 s-1. Decreased quenching was observed as temperature increased, but at the temperature range of 303-313 K, the association of Schiff base selenide to BSA was not significantly different. The static quenching presented in the system of Schiff base selenide and BSA. A complex was possibly formed between Schiff base selenide and BSA, which was responsible for the quenching of the fluorescence of BSA. This fact was also confirmed by differences in the absorption spectra of BSA before and after Schiff base selenide addition. The hydrophobic interaction was found to play a main role in the binding according to the thermodynamic parameters, enthalpy change (H) and entropy change (S) of reaction. Schiff base selenide most likely binds to the hydrophobic pockets within sub domain IIA of BSA, which can be proved by competition experiments for sodium dodecyl sulfate. By constant-wavelength synchronous fluorescence spectra, the influence of (2-hydroxy-benzimido)-ethyl-n-hexylselenide on the surrounding environment of tyrosine and tryptophan residues in BSA was also investigated. The red shift of the fluorescence peak of tryptophan residues indicated that the hydrophobic amino acid structure surrounding tryptophan residues in BSA collapsed slightly after the addition of (2-hydroxy-benzimido)ethyl-n-hexylselenide.

An on-line solution-reaction isoperibol calorimeter has been constructed. The performance of the apparatus was evaluated by measuring the molar enthalpy of solution of KCl inwater at 298.15 K. The uncertainty and the inaccurary of the experimental results were within±0.3% compared with the recommended reference data. Using the calorimeter, the molar enthalpies of reaction for the following two reactions: LaCl3-7H2O(s)+2Hhq(s)+NaAc(s)=La(hq)2Ac(s)+NaCl(s)+2HCl(g)+7H2O(l) and PrCl3-6H2O(s)+2Hhq(s)+NaAc(s)= Pr(hq)2Ac(s)+NaCl(s)+2HCl(g)+6H2O(l), were determined at T=298.15 K, as−(78.3±0.6) and−(97.3±0.5) kJ mol−l, respectively. From the above molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of La(hq)2Ac and Pr(hq)2Ac, at T=298.15 K, have been derived to be−(1535.5±0.7) and−(1536.7±0.6) kJ mol−l, respectively