Antibacterial effects of a monoporphyrinato ytterbium(III) complex and its free components on Staphylococcus aureus as determined by stop-flow microcalorimetry.

The antibacterial effect of Yb3+, the free porphyrin base 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (H2TMP; 1), and the corresponding Yb3+ porphyrinato complex [Yb(III)(TMP)(H2O)3]+ Cl- (Yb(TMP); 2) towards Staphylococcus aureus was investigated by stop-flow microcalorimetry. By analyzing the obtained metabolic thermogenic curves, crucial parameters such as rate constant of bacterial growth (k), half inhibitory concentration (IC50), and generation time (t(G)) were determined. The antibacterial activities of the three compounds tested was 2>1>Yb3+, with an IC50 value of 273 mg/l for complex 2. The Yb3+ porphyrinato complex is proposed to benefit from synergetic effects of Yb3+ and the free porphyrin 1.

Microcalorimetric and spectroscopic investigation of the antibacterial properties of cationic ytterbium(III)-porphyrin complexes lacking charged peripheral groups.

The antibacterial activities towards Escherichia coli of two cationic Yb(III)-monoporphyrin complexes, [Yb(III)(TMP)(H2O)3]Cl (1) and [Yb(III)(TTP)(H2O)3]Cl (2), were investigated at the cellular and sub-cellular levels. The biological effects of the complexes on the growth of E. coli were evaluated by microcalorimetry and by analysis of the resulting metabolic thermogenic curves, from which IC50 values and metabolic parameters such as growth rate and generation time were derived. At the subcellular level, DNA-binding experiments were performed by means of UV/VIS- and fluorescence-titration experiments, as well as by near-infrared (NIR) emission, which revealed that 1 and 2 strongly bind to herring-sperm DNA (HS-DNA), though by different binding modes.

Fluorometric investigation of the interaction of bovine serum albumin with surfactants and 6-mercaptopurine.

Fluorescence quenching in solutions of bovine serum albumin has been investigated in the presence of 6-mercaptopurine and ionic surfactants. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of bovine serum albumin by 6-mercaptopurine was dynamic quenching mechanism. The Stern-Volmer quenching model has been successfully applied, and the activation energy of the interaction between 6-mercaptopurine and bovine serum albumin as much as 4.26 kJ mol(-1) was calculated. The distance r between donor (bovine serum albumin) and acceptor (6-mercaptopurine) was obtained according to fluorescence resonance energy transfer (FRET). The result of synchronous fluorescence spectra shows that the conformation of bovine serum albumin has been changed at the present of 6-mercaptopurine.

Fluorometric investigation of the interaction between methylene blue and human serum albumin.

The interaction between methylene blue (MB) and human serum albumin (HSA) was investigated by fluorescence spectroscopy and UV-vis absorbance spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by MB is a result of the formation of MB-HSA complex and electrostatic interactions play a major role in stabilizing the complex. The Stern-Volmer quenching constant K(SV) and corresponding thermodynamic parameters DeltaH, DeltaG and DeltaS were calculated. Binding studies concerning the number of binding sites n and apparent binding constant Kb were performed by fluorescence quenching method. The distance r between the donor (HSA) and the acceptor (MB) was obtained according to fluorescence resonance energy transfer (FRET). Wavelength shifts in synchronous fluorescence spectra showed the conformation of HSA molecules is changed in the presence of MB.

Interaction of colchicine with human serum albumin investigated by spectroscopic methods.

We investigated the interaction between colchicine and human serum albumin (HSA) by fluorescence and UV-vis absorption spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of HSA by colchicine is a result of the formation of colchicines-HSA complex; van der Waals interactions and hydrogen bonds play a major role in stabilizing the complex. The modified Stern-Volmer quenching constant K(a) and corresponding thermodynamic parameters deltaH, deltaG, deltaS at different temperatures were calculated. The distance r between donor (Trp214) and acceptor (colchicine) was obtained according to fluorescence resonance energy transfer (FRET).

[Thermochemical studies on the binding reaction of perseleno diphenyl 2,2'-diformic acid with bovine serum albumin].

The binding of newly compounded perseleno diphenyl 2,2'-diformic acid to bovine serum albumin(BSA) was studied at different temperatures using fluorescence spectrum and UV spectrum. The fluorescence quenching data was analyzed according to Stern-Volmer equation and Lineweaver-Burk double-reciprocal equation. It was showed that this quenching complies better with the charactristic of static fluorescence quenching. The binding constant, thermodynamic parameters, and the binding spot of the compound with certain structure, coming from perseleno diphenyl 2,2'-diformic acid and bovine serum albumin, were obtained. Besides, themechanism of static fluorescence quenching and the quality of binding power were both discussed. The information of the binding mode, the mechanism of its transportation, and some medical theories in human body were offered.

Study of the interaction between monoammonium glycyrrhizinate and bovine serum albumin.

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 DeltaH degrees , DeltaG degrees , DeltaS degrees at different temperatures were calculated. The distance r between donor (bovine serum albumin) and acceptor (monoammonium glycyrrhizinate) was obtained according to Forster 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.

Thermodynamics of binding of cadmium to bovine serum albumin.

The binding isotherm of Cd2+ ion to bovine serum albumin (BSA) has been investigated by microcalorimetry at 310.15 K and pH 7.0. The thermodynamic parameters of the binding reaction have been determined, and the stoichiometry of the complex is 2:1, indicating that there exist two identical binding sites of BSA with Cd2+ ion. The value of deltarHthetam is -28.4+/-1.7 kJ mol(-1), the free energy of binding deltarGthetam is -25.2 kJ mol(-1), and the entropy of binding deltarSthetam is -10.3 J mol(-1) K(-1). The negative deltarHthetam and deltarSthetam values are observed for the binding reaction of Cd2+ ion and BSA, suggesting that the binding reaction is mainly enthalpy-driven and the entropy is unfavorable for it.

Microcalorimetric studies of the action of Na2SeO3 on the growth of Halobacterium halobium R1.

The effect of Na2SeO3 on the growth of Halobacterium halobium R1 was investigated by means of microcalorimetry at 37 degrees C. The biological response to toxicants is observed as the inhibition of the rate constant of growth of living cells. A low concentration of Na2SeO3 stimulated the growth of H. halobium R1, and a high concentration of Na2SeO3 inhibited the growth of H. halobium R1. Toxicity may be expressed as the half-inhibition concentration (IC50). The rate constants of growth (k) and the concentrations of Na2SeO3 (c) shows a linear relationship: k = 1.790 x 10(-6) -- 2.27 x 10(-3) c. The value of IC50 obtained from the accompanying figure of I-c is 679 microg/mL.

[Study on thermodynamics of binding reaction of dipyridamole with bovine serum albumin].

The binding feature of dipyridamole with bovine serum albumin (BSA) was studied using fluorescence spectroscopy. It was shown that this compound has a powerful ability to quench the BSA fluorescence via a nonradiative energy transfer mechanism. The fluorescence quenching data were analyzed according to stern-volmer equation and double-reciprocal equation, and the binding constant and the thermodynamic parameters were obtained.

Interaction of cromolyn sodium with human serum albumin: a fluorescence quenching study.

The interaction between cromolyn sodium (CS) and human serum albumin (HSA) was investigated using tryptophan fluorescence quenching. In the discussion of the mechanism, it was proved that the fluorescence quenching of HSA by CS is a result of the formation of a CS-HSA complex. Quenching constants were determined using the Sterns-Volmer equation to provide a measure of the binding affinity between CS and HSA. The thermodynamic parameters DeltaG, DeltaH, and DeltaS at different temperatures were calculated. The distance r between donor (Trp214) and acceptor (CS) was obtained according to fluorescence resonance energy transfer (FRET). Furthermore, synchronous fluorescence spectroscopy data and UV-vis absorbance spectra have suggested that the association between CS and HSA changed the molecular conformation of HSA and the electrostatic interactions play a major role in CS-HSA association.

Thermodynamics and kinetics of the cleavage of DNA catalyzed by bleomycin A5.

Microcalorimetry and UV-vis spectroscopy were used to conduct thermodynamic and kinetic investigations of the scission of calf thymus DNA catalyzed by bleomycin A5 (BLM-A5) in the presence of ferrous ion and oxygen. The molar reaction enthalpy for the cleavage, the Michaelis-Menten constant for calf thymus DNA and the turnover number of BLM-A5 were calculated by a novel thermokinetic method for an enzyme-catalyzed reaction to be -577 +/- 19 kJ.mol-1, 20.4 +/- 3.8 microm and 2.28 +/- 0.49 x 10-2 s-1, respectively, at 37.0 degrees C. This DNA cleavage was a largely exothermic reaction. The catalytic efficiency of BLM-A5 is of the same order of magnitude as that of lysozyme but several orders of magnitude lower than those of TaqI restriction endonuclease, NaeI endonuclease and BamHI endonuclease. By comparing the molar enthalpy change for the cleavage of calf thymus DNA induced by BLM-A5 with those for the scission of calf thymus DNA mediated by adriamycin and by (1,10-phenanthroline)-copper, it was found that BLM-A5 possessed the highest DNA cleavage efficiency among these DNA-damaging agents. These results suggest that BLM-A5 is not as efficient as a DNA-cleaving enzyme although the cleavage of DNA by BLM-A5 follows Michaelis-Menten kinetics. Binding of BLM-A5 to calf thymus DNA is driven by a favorable entropy increase with a less favorable enthalpy decrease, in line with a partial intercalation mode involved in BLM-catalyzed breakage of DNA.