光谱法研究两种抗菌类药物对牛血清白蛋白结构变化的影响

利用荧光猝灭光谱、同步荧光光谱、三维荧光光谱、紫外-可见吸收光谱及圆二色谱法研究了磺胺甲恶唑(Sulfamethoxazole,SMX)、磺胺二甲嘧啶(Sulfamethazine,SMZ)对牛血清白蛋白(Bovine serum albumin,BSA)结构的影响。荧光猝灭实验结果表明SMX和SMZ可以使BSA发生荧光猝灭;通过同步荧光光谱、三维荧光光谱和紫外-可见光谱实验数据定性的证实了SMX和SMZ的加入会使BSA的构象发生变化,并且通过紫外-可见光谱的实验结果可知SMX和SMZ与BSA之间的作用机理为静态猝灭。此外,由圆二色谱法得到的定量结果可知:当SMX或SMZ与BSA之间的摩尔浓度比为4∶1时,SMX可使BSA的α-螺旋结构含量由53.77%降低到51.82%;SMZ可使BSA的α-螺旋结构含量由53.77%降低到47.59%。     

烷基咪唑型离子液体与牛血清白蛋白的相互作用研究

应用荧光光谱、紫外吸收光谱、傅立叶变换红外光谱和核磁共振波谱研究了烷基咪唑型离子液体[bmim][PF6]及其前体物质[bmim]Cl与牛血清白蛋白(BSA)分子间的相互作用.研究表明:在生理pH值条件下,[ bmim][ PF5]和[bmim] Cl均对BSA的内源性荧光产生猝灭,其猝灭程度[bmim][ PF6]＞...     

1,4-二甲基-6,8-二甲氧基-9,10-蒽醌的合成及其与牛血清白蛋白和DNA的相互作用

合成了大黄素类蒽醌衍生物1,4-二甲基-6,8-二甲氧基-9,10-蒽醌(1)并应用紫外光谱、荧光光谱、圆二色谱等方法研究了其与牛血清白蛋白(BSA)和小牛胸腺DNA(ct-DNA)的相互作用.荧光光谱结果表明,化合物1与BSA的相互作用主要以静态猝灭方式使BSA的内源性荧光发生猝灭;圆二色谱表明,化合物1通过疏水作用及形成氢键破坏了α-螺旋结构,导致BSA分子中的α-螺旋含量下降.在pH 7.4时固定DNA的浓度,加入化合物1后,紫外光谱的最大吸收峰发生红移且吸光度加大.荧光光谱表明,化合物1与DNA-4S green NC的结合为竞争性抑制,并可使溶液体系荧光猝灭;圆二色谱表明,随着化合物1的加入,DNA碱基间作用能迅速减弱,表明化合物1与DNA之间为嵌插作用.此外,MTT方法的结果表明,化合物1对结肠癌细胞株HCT116增殖有明显的抑制作用.     

1,4-二甲基-6,8-二甲氧基-9,10-蒽醌的合成及其与BSA和ct-DNA的相互作用

合成了大黄素类蒽醌衍生物1,4-二甲基-6,8-二甲氧基-9,10-蒽醌(1)并应用紫外光谱、荧光光谱、圆二色谱等方法研究了其与牛血清白蛋白(BSA)和小牛胸腺DNA(ct-DNA)的相互作用。荧光光谱结果表明,化合物1与BSA的相互作用主要以静态猝灭方式使BSA的内源性荧光发生猝灭;圆二色谱表明,化合物1通过疏水作用及形成氢键破坏了α-螺旋结构,导致BSA分子中的α-螺旋含量下降。在p H 7.4时固定DNA的浓度,加入化合物1后,紫外光谱的最大吸收峰发生红移且吸光度加大。荧光光谱表明,化合物1与DNA-4S green NC的结合为竞争性抑制,并可使溶液体系荧光猝灭;圆二色谱表明,随着化合物1的加入,DNA碱基间作用能迅速减弱,表明化合物1与DNA之间为嵌插作用。此外,MTT方法的结果表明,化合物1对结肠癌细胞株HCT116增殖有明显的抑制作用。     

桑色素与血清白蛋白相互作用热力学行为

利用荧光光谱、紫外-可见吸收光谱、圆二色谱、分子模拟等方法,在近似生理条件下,以牛血清白蛋白(BSA)为模式蛋白质,研究了桑色素(Morin)和血清白蛋白相互作用的热力学行为及其特征。荧光光谱结果表明:Morin能有效猝灭BSA的内源荧光,猝灭机制为静态猝灭;通过van’t Hoff方程,获取了BSA与Morin结合的热力学参数(?H?、?S?、?G?等),发现Morin与BSA两者之间的相互作用是一个吉布斯自由能降低的自发过程,且氢键和范德华力是二者结合的驱动力。通过分子模拟方法,发现Morin结合在BSA分子亚结构域IIIA的疏水腔内位点II,荧光共振能量转移结果表明Morin和与BSA的两个色氨酸残基的平均距离为3.09nm。圆二色谱结果表明Morin分子的结合会引起BSA分子α-螺旋含量降低。     

荧光法研究偏钒酸钠与牛血清白蛋白的相互作用

本文用荧光光谱和紫外可见吸收光谱研究了在模拟人体生理条件下，偏钒酸钠与牛血清白蛋白(BSA)结合反应的特征，研究了紫外灯(253.7 nm)照射对偏钒酸钠与BSA结合的影响。紫外吸收光谱显示，加入偏钒酸钠后，牛血清白蛋白的紫外吸收降低，表明偏钒酸钠与BSA形成了缔合物。荧光猝灭光谱显示偏钒酸钠对牛血清白蛋白有较强的荧光猝灭作用，荧光猝灭机理符合静态机制。缔合物的稳定常数分别为：K_s=0.357×10⁴(25 ℃)，K_{s相似文献}   

光谱法研究牛血清白蛋白与磷钼酸的相互作用

运用UV-Vis光谱、荧光光谱、同步荧光光谱、FT-IR光谱等手段,研究了在模拟人体生理条件下,牛血清白蛋白(BSA)与磷钼酸的相互作用。UV-Vis光谱显示,加入磷钼酸后,BSA的紫外吸收降低且吸收峰红移,表明磷钼酸与BSA形成了复合物;荧光猝灭光谱显示磷钼酸对BSA有荧光猝灭作用,且其荧光猝灭机理符合静态机制,磷钼酸与BSA结合的结合常数为:Ks=2.539×104L·mol-1;探针实验表明磷钼酸与BSA在结合位点I发生结合;Fster偶极-偶极非辐射能量转移机理确定了磷钼酸在BSA中与第214位色氨酸残基之间的距离r=1.93nm;FT-IR光谱显示磷钼酸诱导BSA的二级结构发生了变化,α-螺旋含量降低。     

光谱法研究萘酰亚胺类衍生物与牛血清白蛋白的相互作用

采用荧光光谱、紫外-可见吸收光谱、红外光谱和圆二色光谱研究了3-氨基-4-二甲氨基-N-丁基-1.8-萘酰亚胺(ADBN)与牛血清白蛋白(BSA)结合反应的特征。荧光光谱与紫外-可见吸收光谱表明,ADBN使BSA荧光猝灭的机理为静态猝灭。根据热力学参数判断ADBN与BSA主要是通过氢键和范德华力结合,结合距离为4.08 nm。同步荧光光谱、圆二色光谱以及红外光谱表明,结合过程中BSA的构象发生了变化。     

铜(Ⅱ)离子与神经红蛋白的相互作用

利用紫外可见吸收光谱、荧光光谱、同步荧光光谱及圆二色(CD)光谱研究了铜髤离子与神经红蛋白(NGB)的相互作用。结果表明,Cu2+离子使NGB在280nm处的紫外吸收增强,说明Cu2+与NGB发生了相互作用;Cu2+使NGB内源性荧光发生猝灭,其猝灭机制为静态猝灭;同步荧光光谱表明,Cu2+使色氨酸微环境的疏水性有所降低,Cu2+对NGB的作用位点更接近于色氨酸;CD光谱显示Cu2+没有引起NGB二级结构明显的变化。     

6-乙基-4-乙氧羰基-2-(4-氰基苯基)喹啉与BSA相互作用研究

合成了一种新型喹啉类化合物6-乙基-4-乙氧羰基-2-(4-氰基苯基)喹啉(EECCPQ),用核磁氢谱(~1H NM R)、碳谱(~(13)C NM R)以及傅里叶红外光谱(FTIR)对其进行了表征。采用荧光光谱(FL)、紫外可见光谱(UV)、时间分辨光谱(TRF)、圆二色光谱(CD)和分子模拟法研究了EECCPQ与牛血清白蛋白(BSA)的相互作用。由紫外吸收光谱和Stern-Volmer方程推断EECCPQ与BSA形成复合物,导致BSA内源荧光降低;依所测荧光寿命数据得出荧光猝灭机理主要为静态猝灭;根据双对数方程计算出不同温度下EECCPQ与BSA的结合常数和结合位点。热力学分析得出ΔH0,△S0和△G0,表明体系是熵增加、Gibbs自由能降低的自发分子间作用过程,氢键和范德华力起着重要的内驱力作用;据Frster非辐射能量转移理论得EECCPQ与BSA的结合距离r=3.19 nm(299 K);同步荧光光谱显示EECCPQ的加入影响了BSA所处的微环境;CD光谱揭示BSA二级结构从α-螺旋向无规则卷曲转变;分子对接表明EECCPQ作用于BSA中亚域ⅡA的疏水腔区域(位点Ⅰ)。     

室温下Kelvin探针力显微镜分析离子液体的界面

研究离子液体阳离子和阴离子在界面的排列具有意义,因为它们能够影响离子液体在界面的表面结构和属性。作为一种扫描探针显微技术,Kelvin探针力显微镜（KPFM）在本文中被用于室温下离子液体界面性质的研究。离子液体氯化（1-丁基-3-甲基咪唑）（[Bmim]Cl）在本文中被用作研究对象。实验中,[Bmim]Cl被选择性地固定在亲液的化学修饰表面,形成超薄的固态吸附层和液滴。由于表面电势能够用于直接指示表面偶极子,因而对于检测分子的取向十分有用。利用KPFM获得的表面电势图表明[Bmim]Cl离子液体在气液界面（当离子液体以液滴形式存在）和气固界面（当离子液体以固态吸附层形式存在）呈现出不同的分子排列。我们的研究表明Kelvin探针力显微镜能够用于表征离子液体在界面的分子排列。     

血红蛋白在Span 80/PEG 400/H2O囊泡体系中的结构性质

通过紫外-可见吸收光谱、荧光光谱、动态光散射、圆二色谱、负染-透射电镜(NS-TEM)和冷冻蚀刻-透射电镜(FE-TEM)等实验方法研究了血红蛋白(Hb)与Span 80/PEG 400/H₂O囊泡间的相互作用及其结构特性. 结果表明: Hb易于吸附在囊泡表面, 使得囊泡的表观半径稍有增大; Hb的肽链在囊泡表面能够逐渐伸开, 特征荧光峰强度显著增强, 部分氨基酸残基进一步暴露, α-螺旋结构含量减少, β-折叠和β-转角结构含量增加, 无规卷曲结构含量基本不变. 囊泡体系中Hb的稳定性与囊泡的稳定性有关.     

Interactions between a surface active imidazolium ionic liquid and BSA

The interactions between a surface active imidazolium ionic liquid (IL), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr) and bovine serum albumin (BSA) were studied. To investigate the structure changes of BSA induced by addition of C₁₄mimBr, this system was studied by surface tension, isothermal titration microcalorimetry, far-UV circular dichroism (CD) and fluorescence spectra. The surface tension measurement shows the formation of C₁₄mimBr/BSA complex and the effect of the complex on surface tension. Furthermore, it reveals the interaction type. The enthalpy change in the whole interaction process between C₁₄mimBr and BSA was obtained by isothermal titration microcalorimetry, and the results prove the alteration of the BSA structure. To realize the structure alteration position more definitely, far-UV CD was used to obtain the contents of α-helix and random coil. Changes of these contents reveal that the secondary structure of BSA changes with addition of C₁₄mimBr. Fluorescence spectra are used to prove that the alteration of the secondary structure is due to the interactions of C₁₄mimBr molecules and amino acid residues. They show that tryptophan (Trp) residues, one of the intrinsic fluorophores in BSA, are exposed to a hydrophobic microenvironment with the addition of C₁₄mimBr.     

Investigation of the mechanism of beta-amyloid fibril formation by kinetic and thermodynamic analyses

Extracellular beta-amyloid (A beta) deposit is considered as one of the primary factors that induce Alzheimer's disease (AD). The effects of various environmental factors, including temperature, ionic strength, and pH, on A beta (1-40) aggregation mechanisms were investigated in this study by spectrometry, isothermal titration calorimetry (ITC), and hydrophobic fluorescence assay. In the aggregation process, the secondary structure of A beta (1-40) transforms to the beta-sheet conformation, which could be described as a two-state model. As the temperature and ionic strength increase, the conformation of A beta converts to the beta-sheet structure with an increased rate. Results of circular dichroism monitoring demonstrate that the rate constant of nucleation is smaller than that of elongation, and the nucleation is the rate-determining step during the overall A beta aggregation. The beta-sheet structure was stabilized by hydrophobic forces, as revealed by the ITC measurements. The different structural aggregates and forming pathways could be identified and discriminated at high and low ionic strengths, resulting in distinctive fibril conformations. Furthermore, the thermodynamic analysis shows that hydrophobic interaction is the major driving force in the nucleation step. Our study provides an insight into the discriminative mechanisms of beta-amyloid aggregation via kinetics and thermodynamics, especially the first reported thermodynamics information obtained by ITC.     

Binding of organophosphate insecticides with serum albumin: multispectroscopic and molecular modelling investigations

The interaction between two organophosphate insecticides (monocrotophos and phosphamidon) and bovine serum albumin (BSA) under physiological conditions is investigated by UV-Vis, fluorescence (steady state, synchronous and three-dimensional) and circular dichroism spectroscopy. The UV-Vis and fluorescence spectral studies indicate the formation of complex between BSA and the insecticides. The complex formation is a spontaneous process as evidenced by negative free energy changes. The positive values of entropy changes reveal that hydrophobic forces played the major role in the interaction process, which is well supported by the molecular docking studies. Synchronous and three-dimensional fluorescence investigations suggest that there is no significant change in the conformation of BSA upon binding with the insecticides, which is strongly supported by the results of circular dichroism spectral studies.     

Thermodynamic studies on the interaction of folic acid with bovine serum albumin

Binding of the vitamin folic acid with bovine serum albumin (BSA) has been studied using isothermal titration calorimetry (ITC) in combination with fluorescence and circular dichroism spectroscopies. The thermodynamic parameters of binding have been evaluated as a function of temperature, ionic strength, in the presence of nonionic surfactants triton X-100, tetrabutylammonium bromide, and sucrose. The values of the van’t Hoff enthalpy calculated from the temperature dependence of the binding constant agree with the calorimetric enthalpies indicating that the binding of folic acid to the BSA is a two state process without involving intermediates. These observations are supported by the intrinsic fluorescence and circular dichroism spectroscopic measurements. With increase in the ionic strength, reduction in the binding affinity of folic acid to BSA is observed suggesting predominance of electrostatic interactions in the binding. The contribution of hydrophobic interactions in the binding is also demonstrated by decrease in the binding affinity in the presence of tetrabutylammonium bromide (TBAB). The value of binding affinity in the presence of sucrose indicates that hydrogen bonding also plays a significant contribution in the complexation process. The calorimetric and spectroscopic results provide quantitative information on the binding of folic acid to BSA and suggest that the binding is dominated by electrostatic interactions with contribution from hydrogen bonding.     

Binding of naproxen and amitriptyline to bovine serum albumin: biophysical aspects

Binding of the drugs naproxen (which is an anti-inflammatory) and amitriptyline (which is an anti-depressant) to bovine serum albumin (BSA) has been studied using isothermal titration calorimetry (ITC), in combination with fluorescence and circular dichroism spectroscopies. Naproxen is observed to bind more strongly to BSA than amitriptyline. The temperature-dependent ITC results indicate the interaction of one molecule of naproxen with more than one protein molecule. On the other hand, amitriptyline binds to BSA with a reaction stoichiometry that varies from 1:1.2 to 1:2.9. The van't Hoff enthalpy, which is calculated from the temperature dependence of the binding constant, agrees well with the calorimetric enthalpy in the case of naproxen binding to BSA, indicating adherence to a two-state binding process. However, their disagreement in the case of amitriptyline indicates conformational changes in the protein upon ligand binding, as well as with the rise in temperature. The spectroscopic results did not suggest appreciable conformational changes as a result of binding; hence, the discrepancy could be attributed to the temperature-induced conformational changes. With increases in the ionic strength, a reduction in the binding affinity of naproxen to BSA is observed. This suggests the prevailing electrostatic interactions in the complexation process. The preponderance of the hydrophobic interactions in the binding of amitriptyline to BSA is indicated by the absence of any dependence of the ionic strength. A predominance of electrostatic interactions in the case of naproxen binding to BSA and that of hydrophobic interactions in the case of amitriptyline binding to BSA is further strengthened by the results of the binding experiments performed in the presence of ionic and nonionic surfactants. The binding parameters indicate that Triton X-100 blocks the hydrophobic binding sites on BSA, thereby altering the binding affinity of amitriptyline toward BSA. A partial overlap of the binding sites for these drugs is indicated by the binding parameters obtained in the titration of naproxen to the amitriptyline-BSA complex and vice versa. Thus, the results provide a quantitative understanding of the binding of naproxen and amitriptyline to BSA, which is important in understanding their effect as therapeutic agents individually and in combination therapy.     

Interaction of water-soluble amino acid Schiff base complexes with bovine serum albumin: fluorescence and circular dichroism studies

Fluorescence spectroscopy in combination with circular dichroism (CD) spectroscopy were used to investigate the interaction of water-soluble amino acid Schiff base complexes, [Zn(L1,2)(phen)] where phen is 1,10-phenanthroline and H2L1,2 is amino acid Schiff base ligands, with bovine serum albumin (BSA) under the physiological conditions in phosphate buffer solution adjusted to pH 7.0. The quenching mechanism of fluorescence was suggested as static quenching according to the Stern-Volmer equation. Quenching constants were determined using the Stern-Volmer equation to provide a measure of the binding affinity between amino acid Schiff base complexes and BSA. The thermodynamic parameters DeltaG, DeltaH and DeltaS at different temperatures (298, 310 and 318K) were calculated. The results indicate that the hydrophobic and hydrogen bonding interactions play a major role in [Zn(L1)(phen)]-BSA association, whereas hydrophobic and electrostatic interactions participate a main role in [Zn(L2)(phen)]-BSA binding process. Binding studies concerning the number of binding sites and apparent binding constant Kb were performed by fluorescence quenching method. The distance R between the donor (BSA) and acceptor (amino acid Schiff base complexes) has been obtained utilizing fluorescence resonant energy transfer (FRET). Furthermore, CD spectra were used to investigate the structural changes of the BSA molecule with the addition of amino acid Schiff base complexes. The results indicate that the interaction of amino acid Schiff base complexes with BSA leads to changes in the secondary structure of the protein. Fractional contents of the secondary structure of BSA (f(alpha), f(beta), f(turn) and f(random)) were calculated with and without amino acid Schiff base complexes utilizing circular dichroism spectroscopy. Our results clarified that amino acid Schiff base complexes could bind to BSA and be effectively transported and eliminated in the body, which could be a useful guideline for further drug design.     

Effect of Cyclodextrins on the Interaction Between BSA and Sodium Dodecyl Benzene Sulfonate

Cyclodextrins offer the potential of modulating protein–surfactant interactions. In our work, the effect of cyclodextrin (CD) on the interaction between bovine serum albumin (BSA) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) has been studied by isothermal titration calorimetry (ITC), fluorescence spectra and circular dichroism measurements. The presences of cyclodextrin can slightly hinder the strong interactions between BSA and SDBS by the combination of electrostatic and hydrophobic interactions between BSA and SDBS. Furthermore, the effectiveness of α-CD is lower than that of β-CD, due to the lower association constant between α-CD and surfactant. The presence of both α- and β-CD totally hinders the nonspecific interactions between BSA and SDBS, because the hydrophobic interaction between cyclodextrin and surfactant is stronger than that between BSA and surfactant.     

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.