Study of the Interaction between <Emphasis Type="Italic">Trans</Emphasis>-resveratrol and BSA by the Multi-spectroscopic Method

The interaction of trans-resveratrol and BSA was investigated by means of fluorescence quenching, resonance light scattering, ultraviolet spectroscopy and Fourier Transform Infrared Spectroscopy. Binding of trans-resveratrol to BSA quenches the BSA fluorescence and both static and dynamic quenching occur with complex formation. The apparent binding constants of trans-resveratrol and BSA at 20, 30 and 40?°C are 1.95×10⁶, 1.70×10⁶ and 1.65×10⁶ L?mol^?1, respectively. The binding site values are (1.25±0.02). According to the Förster theory of non-radiation energy transfer, the binding distances between trans-resveratrol and BSA are 3.47, 3.73 and 3.99 nm at 20, 30 and 40?°C, respectively. The negative enthalpy change and positive entropy change indicated that the interaction of trans-resveratrol and BSA was driven mainly by electrostatic forces. The process of binding was spontaneous whereby the Gibbs energy change was negative.     

Crystal structures,Hirshfeld analysis,and energy framework analysis of two differently 3′-substituted 4-methylchalcones: 3′-(N=CHC6H4-p-CH3)-4-methylchalcone and 3′-(NHCOCH3)-4-methylchalcone

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a p-methyl substitution on the 3-Ring, but differ with respect to the m-substitution on the 1-Ring. Their systematic names are (2E)-3-(4-methylphenyl)-1-(3-{[(4-methylphenyl)methylidene]amino}phenyl)prop-2-en-1-one (C₂₄H₂₁NO) and N-{3-[(2E)-3-(4-methylphenyl)prop-2-enoyl]phenyl}acetamide (C₁₈H₁₇NO₂), which are abbreviated as 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone and 3′-(NHCOCH₃)-4-methylchalcone, respectively. Both chalcones represent the first reported acetamide-substituted and imino-substituted chalcone crystal structures, adding to the robust library of chalcone structures within the Cambridge Structural Database. The crystal structure of 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone exhibits close contacts between the enone O atom and the substituent arene ring, in addition to C…C interactions between the substituent arene rings. The structure of 3′-(NHCOCH₃)-4-methylchalcone exhibits a unique interaction between the enone O atom and the 1-Ring substituent, contributing to its antiparallel crystal packing. In addition, both structures exhibit π-stacking, which occurs between the 1-Ring and R-Ring for 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone, and between the 1-Ring and 3-Ring for 3′-(NHCOCH₃)-4-methylchalcone.     

A generic rotamer model to explain the temperature dependence of BSA protein fluorescence

Protein fluorescence signals essential information about the conformational dynamics of proteins. Different types of intrinsic fluorophores reflect different protein local or global structural changes. Bovine Serum Albumin (BSA) is a transport protein that contains two intrinsic fluorophores: Tryptophan134 (Trp134) and Tryptophan213 (Trp213). This protein displays an interesting temperature dependence of the tryptophan fluorescence. However, the molecular mechanism of the temperature dependence is still unclear. In this work, we propose a generic rotamer model to explain this phenomenon. The model assumes the presence of rotamer-specific fluorescence lifetimes. The fluorescence temperature dependence is caused by the population shifts between different rotamers due to thermal effects. As a proof of concept, we show that the tryptophan's two fluorescence lifetimes (𝜏₁ = 0.4–0.5 ns and 𝜏₂ = 2-4 ns) are sufficient to qualitatively explain the fluorescence intensity change at different temperatures, both in buffer solution (water) and in the protein. To computationally verify our rotamer hypothesis, we use an all-atom molecular dynamics simulation to study the effects of temperature on the two tryptophans' rotamer dynamics. The simulations show that Trp134 is more sensitive to temperature, consistent with experimental observations. Overall, the results support that the temperature dependence of fluorescence in the protein BSA is due to local conformational changes at the residue level. This work sheds light on the relationship between tryptophan's rotamer dynamics and its ability to fluorescence.     

盐酸表阿霉素与牛血清白蛋白的相互作用和伏安分析

应用线性扫描技术研究盐酸表阿霉素的电化学行为.结果表明,在pH 6.80的Tris-HCl缓冲溶液中,盐酸表阿霉素有一较灵敏的还原峰,Epc=-0.34 V(vs.SCE).加入牛血清白蛋白(BSA)后,盐酸表阿霉素的还原峰电流明显下降.据此,建立了BSA的电化学测定法.在最佳实验条件下,1.0×10-9～1.0×10-6 mol.L-1范围内,BSA浓度与盐酸表阿霉素的峰电流下降值△ip呈线性关系(R=0.9973),BSA检出限达8.05×10-10 mol.L-1.盐酸表阿霉素与BSA的结合比为1,结合常数β为3.04×106 L.mol-1.     

Kinetic Study of Bovine Serum Albumin (BSA) Released from Alginate-Ca2+/PNIPAAm Hydrogels

Summary: In this work the releasing of Bovine Serum Albumin (BSA) from thermosensitive hydrogels of alginate-Ca²⁺/PNIPAAm was investigated. The hydrogels are constituted of PNPAAm network interpenetrated in alginate-Ca²⁺ network, so the hydrogels are IPN-typed. The PNIPAAm network was synthesized in the first step in which the sodium alginate remained soluble. The alginate-Ca²⁺ network was formed in the second step by immersion the membrane obtained on the first step in aqueous calcium chloride. It was changed the amount of NIPAAm in the feed solution of the first step. The fractions of BSA released as a function of time were treated according to the mathematical model recently published by our lab [J. Coll. Interf. Sci. 2007 , 310, 128] that allows predicting the whole profile of solute released from polymer networks. This mathematical model is based in the partition phenomena. The amount of BSA released from alginate-Ca²⁺/PNIPAAm hydrogels changes inversely to both amount of PNIPAAm and temperature. Thus, the IPN-typed matrixes of alginate-Ca²⁺/PNIPAAm may be considered as smart hydrogels for release the BSA because the amount and rate of released BSA can be tailored by the amount of PNIPAAm in the hydrogel and by the control of temperature. Finally, the whole profile of released BSA can be adequately fitted by the model based in the partition phenomenon. From that model the kinetic parameter t_1/2 and rate constant of releasing, k_R, were calculated for the different hydrogels investigated in this work.     

Characterization of Interaction Between Raltitrexed and Bovine Serum Albumin by Optical Spectroscopic Techniques

The interaction of raltitrexed(RTX) with bovine serum albumin(BSA) was investigated by steady state/lifetime fluorescence spectroscopy and circular dichroism(CD) spectroscopy under the simulative physiological conditions. The results of fluorescence titration reveal that RTX could strongly quench the intrinsic fluorescence of BSA via a static quenching procedure. The obtained binding constant K_A of RTX with BSA was 478630 and 44259 L/mol at 298 and 310 K, respectively. According to van’t Hoff equation, the thermodynamic parameters ΔH, ΔG and ΔS were calculated, indicating that hydrophobic forces were the predominant intermolecular forces in stabilizing the complex. The binding process was a spontaneous process, in which Gibbs free energy change was negative. According to Förster’s non-radioactive energy transfer theory, the distance r between donor(BSA) and acceptor(RTX) was 3.82 nm, suggesting that the energy transfer from BSA to RTX occurred with high probability. Displacement experiment and the number of binding sites calculation confirmed that RTX could bind to the site-I of BSA. Furthermore, the effects of pH and some metal ions on the interaction of RTX with BSA were also investigated. The results of synchronous fluorescence and CD spectra show that the RTX-BSA binding induced conformational changes in BSA.     

大黄酸铜(Ⅱ)配合物与血清白蛋白的相互作用

采用荧光光谱法和紫外光谱法研究了大黄酸铜配合物与牛血清白蛋白之间的相互作用.大黄酸铜配合物能显著猝灭牛血清白蛋白的内源荧光并以静态猝灭为主;计算了298 K和309 K温度下结合常数、结合位点,根据热力学参数判断大黄酸铜配合物与牛血清白蛋白之间具有较强的疏水作用力;依据F?rster的偶极-偶极非辐射能量转移理论,计算出大黄酸铜在蛋白质中结合位置与色氨酸残基间的距离为3.21 nm, 表明大黄酸铜的部分片段能够插入蛋白质分子内部;用同步荧光光谱和圆二色光谱技术探讨了大黄酸铜对牛血清白蛋白构象的影响.     

邻菲啰啉和氨三乙酸钴配合物与牛血清白蛋白相互作用的荧光分析

利用溶液法合成了邻菲啰啉(phen)和氨三乙酸(H₃nta)钴配合物Co(phen)₂Cl₂(1), Na[Co(nta)]·H₂O(2), [Co(phen)₂(H₂O)₂][Co(nta)(phen)]₂·12H₂O(3), 对配合物3进行了X射线单晶衍射表征, 结果表明: 该配合物属三斜晶系, P1空间群, a=1.2448(2) nm, b=1.5898(3) nm, c=1.7412(3) nm, α=91.746(3)°, β=97.807(3)°, γ=103.745(3)°, V=3.309(1) nm³. 利用荧光光谱法研究了室温下这3种配合物与牛血清白蛋白(BSA)的相互作用, 并测定了不同温度下这3种配合物与BSA相互作用的荧光强度变化, 确定配合物1和3对BSA的荧光猝灭方式均为静态猝灭; 分析了配合物1和3与BSA相互作用时的结合常数、 结合位点数以及热力学函数与温度之间的关系, 进一步讨论了这2种配合物分别与BSA相互作用时的作用位点、 作用力的类型以及两者之间的距离.     

含磷三足体稀土铕(Ⅲ)配合物与牛血清白蛋白的作用机理

在pH=7.3的Tris-HCl缓冲溶液(模拟生理条件)中, 采用荧光光谱、 循环伏安曲线和紫外光谱研究了N-二(苯-二氨基甲酰基)甲基磷酸铕(Ⅲ)配合物[Eu(pic)₃L]与牛血清白蛋白(BSA)的相互作用. 实验结果表明: 配合物与BSA可以形成1∶1结合型无荧光复合物Eu(pic)₃L-BSA, Eu(pic)₃L对 BSA 内源荧光的猝灭类型为静态猝灭. 根据双对数回归方程计算出二者在不同温度下的结合常数K及结合位点数n, 通过热力学参数得出配合物与 BSA 之间以氢键和范德华力为主. 根据Foster的偶极-偶极无辐射能量转移机理可知配合物与BSA之间可能以偶极-偶极无辐射能量转移方式进行能量传递. 分别考察了Fe³⁺和Cu²⁺对配合物与BSA结合作用的影响, 推测Fe³⁺和Cu²⁺可能在配合物与BSA间起“离子架桥”作用, 使Eu(pic)₃L-BSA复合物的稳定性增强. 循环伏安法研究结果表明配合物与BSA相互作用形成无电活性的Eu(pic)₃L-BSA复合物, 使得溶液中游离的配合物浓度降低.     

Interaction of Mixed Porphyrin-polypyridyl Ru(II) Complex with Bovine Serum Albumin

The interactions of mixed porphyrin-polypyridyl Ru(II) complexes [m(Py-3′)TPP-Ru(phen) 2 Cl] + (1) and its derivatives [Nim(Py-3′)TPP-Ru(phen) 2 Cl] + (2) and [Cum(Py-3′)TPP-Ru(phen) 2 Cl] + (3)(phen=1,10-phenanthroline; m(Py-3′)TPP=5-(3′-pyridyl)-10,15,20-triphenylporphyrin) with bovine serum albumin(BSA) were investigated by fluorescence, UV-Vis and circular dichroism(CD) spectroscopies. The UV-Vis and CD spectral experiments indicated that the secondary structures of the protein were perturbed in the presence of the porphyrin Ru(II) complex and the perturbation was enhanced under the irradiation with ultra-violet light. The fluorescence quenching mechanism of BSA by the three complexes was determined to be a static process, and the apparent binding constant K values for complexes 1, 2 and 3 measured by fluorescence quenching method were (3.86±0.03)×10 3 L/mol(n=0.94±0.04), (5.69±0.04)×10 3 L/mol(n=1.03±0.06), and (6.54±0.02)×10 3 L/mol(n=1.03±0.05), respectively.