Studies on the interaction of salvianolic acid B with human hemoglobin by multi-spectroscopic techniques

The interaction between salvianolic acid B (Sal B) and human hemoglobin (HHb) under physiological conditions was investigated by UV-vis absorption, fluorescence, synchronous fluorescence and circular dichroism spectroscopic techniques. The experimental results indicate that the quenching mechanism of fluorescence of HHb by Sal B is a static quenching procedure, the binding reaction is spontaneous, and the hydrophobic interactions play a major role in binding of Sal B to HHb. Based on F?rster's theory of non-radiative energy transfer, the binding distance between Sal B and the inner tryptophan residues of HHb was determined to be 2.64 nm. The synchronous fluorescence experiment revealed that Sal B can not lead to the microenvironmental changes around the Tyr and Trp residues of HHb, and the binding site of Sal B on HHb is located at α(1)β(2) interface of HHb. Furthermore, the CD spectroscopy indicated the secondary structure of HHb is not changed in the presence of Sal B.     

Influence of the methyl position on the binding of 5-epi-taiwaniaquinone G to HHb investigated by spectrofluorimetry and molecular modelling

The interactions of human haemoglobin (HHb) with 5-epi-taiwaniaquinone G (G1) and one structural analogue of 5-epi-taiwaniaquinone G (G2) systematically by UV–vis absorption spectroscopy and fluorescence spectroscopy in combination with molecular modelling are studied in this paper. They caused the fluorescence quenching of HHb by the formation of complex. The binding constants and thermodynamic parameters were obtained. The hydrophobic and electrostatic interactions were the predominant intermolecular forces to stabilise these complexes. Results of thermodynamic analysis and molecular modelling showed that G2 was the stronger quencher and bound to HHb with higher affinity. The result of molecular modelling is close to that obtained by experimental methods.     

Investigation of the interaction between human hemoglobin and five antioxidants by fluorescence spectroscopy and molecular modeling

L-ascorbic acid, α-tocopherol, procyanidin B3, β-carotene, and astaxanthin are five classic dietary antioxidants. In this study, the interaction between the five antioxidants and human hemoglobin (HHb) was investigated by fluorescence spectroscopy and molecular modeling. The quenching mechanisms of HHb by the five antioxidants are all static quenching. The downward curvature of the Stern–Volmer plots for HHb–procyanidin B3 system at higher concentrations of procyanidin B3 come from the reason for the variation in the number of accessible tryptophan (Trp) residues toward HHb. The upward curvature of the Stern–Volmer plots for HHb–β-carotene system at higher concentrations of β-carotene predominantly by the “sphere of action” quenching mechanism. The binding constants of HHb with the five antioxidants are in the following order as: astaxanthin > L-ascorbic acid > β-carotene > α-tocopherol > procyanidin B3 at 298 K. The binding processes of the five antioxidants to HHb are all entropy process. Thermodynamic analysis and molecular modeling suggest that the hydrophobic forces are the main interaction force in the binding of the five antioxidants to HHb and hydrogen bond interactions between HHb and L-ascorbic acid/α-tocopherol/procyanidin B3/astaxanthin should be also considered. The fluorescence experimental results are in agreement with the results obtained by molecular modeling study.     

Fluorescence Quenching and Binding Interaction of l0-Methylacridinium Iodide to Nucleic Acids

Interaction of 10‐methylacridinium iodide (MAI) as fluorescence probe with nucleobases, nucleosides and nucleic acids has been studied by UV‐visible absorption and fluorescence spectroscopy. It was found that fluorescence of MAI is strongly quenched by the nucleobases, nucleosides and nucleic acids, respectively. The quenching follows the Stern‐Volmer linear equation. The fluorescence quenching rate constant (k_q) was measured to be 10^9‐10¹⁰ (L/mol)/s within the range of diffusion‐controlled rate limit, indicating that the interaction between MAI and nucleic acid and their precursors is characteristic of electron transfer mechanism. In addition, the binding interaction model of MAI to calf thymus DNA (ct‐DNA) was further investigated. Apparent hypochromism in the absorption spectra of MAI was observed when MAI binds to ct‐DNA. Three spectroscopic methods, which include (1) UV spectroscopy, (2) fluorescence quenching of MAI, (3) competitive dual‐probe method of MAI and ethidium bromide (EB), were utilized to determine the affinity binding constants (K) of MAI and ct‐DNA. The binding constants K obtained from the above methods gave consistent data in the same range (1.0–5.5) × 10⁴L/mol, which lend credibility to these measurements. The binding site number was determined to be 1.9. The influence of thermal denaturation and phosphate concentration on the binding was examined. The binding model of MAI to ct‐DNA including intercalation and outside binding was investigated.     

Investigation of the Interaction between Nitrite Ion and Bovine Serum Albumin Using Spectroscopic and Molecular Docking Techniques

The interaction between nitrite ion and bovine serum albumin (BSA), in an aqueous environment, was studied using spectroscopic methods, including fluorescence quenching technique, synchronous fluorescence, UV? Vis spectrophotometry and Resonance Rayleigh Scattering (RRS), and molecular docking technique. The experimental results showed that nitrite ion effectively quenched the intrinsic fluorescence of BSA with the static quenching. The ion‐BSA binding constant was determined to be 3.69×10³ L mol^?1. As the results showed the stoichiometry of binding nitrite ion to BSA was 1 : 1. Furthermore the thermodynamic parameters and nature of the binding force were calculated. The negative ΔH^o and ΔS^o values of reaction between nitrite ion and BSA indicated the predominant forces in the ion‐BSA interactions are hydrogen bonding interactions. Based on the Förster’s theory of non‐radiative energy transfer, the binding distance between nitrite ion and the inner tyrosine and tryptophan residue of BSA were determined to be 2.16 nm. Furthermore binding site of this ion on BSA was carried out by molecular docking technique.     

2,4-二硝基苯胺与牛血清白蛋白相互作用的研究

通过荧光和紫外光谱法研究了2,4-二硝基苯胺同牛血清白蛋白(BSA)的相互作用. 2,4-二硝基苯胺对牛血清白蛋白的内源荧光具有强烈的猝灭作用. 二者之间形成不发荧光的复合物是导致荧光猝灭的主要原因. 计算了其结合常数和结合位点数. 紫外光谱法进一步证明了其猝灭机理为静态猝灭. 根据能量转移理论计算了作用距离(3.13 nm). 同步荧光的结果表明2,4-二硝基苯胺的存在改变了牛血清白蛋白的分子构象.     

Exploring the binding mechanism of dihydropyrimidinones to human serum albumin: spectroscopic and molecular modeling techniques

The binding mechanism of molecular interaction between 5-(ethoxycarbonyl)-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (a dihydropyrimidinones derivative, EMPD) and human serum albumin (HSA) was studied using spectroscopic methods and modeling technique. The quenching mechanism was investigated in terms of the binding constants and the basic thermodynamic parameters. The results of spectroscopic measurements suggested that EMPD have a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. The drug-protein complex was stabilized by hydrophobic forces and hydrogen bonding as indicated from the thermodynamic parameters and synchronous fluorescence spectra, which was consistent with the results of molecular docking and accessible surface area calculation. Competitive experiments indicated that a displacement of warfarin by EMPD, which revealed that the binding site of EMPD to HSA was located at the subdomains IIA. The distance between the donor and the acceptor was 4.85nm as estimated according to F?rster's theory of non-radiation energy transfer. The effect of metal ions on the binding constants was also investigated. The results indicated that the binding constants between EMPD and HSA increased in the presence of common metal ions.     

岩白菜素与牛血清蛋白相互作用的荧光光谱研究

应用荧光光谱研究了岩白菜素与牛血清白蛋白(BSA)分子间的相互作用.结果表明,岩白菜素对BSA内源荧光的猝灭机制属于形成化合物所引起的静态猝灭,猝灭常数Ksv为1.905×104L.mol-1;岩白菜素与BSA反应的结合常数为2.083×104,结合位点数为1.由热力学参数确定了岩白菜素与牛血清白蛋白的结合作用主要为静电作用.实验还发现随着岩白菜素的加入,BSA的猝灭值与岩白菜素浓度在1.5×10-5~1.5×10-4mol.L-1的范围内呈良好的线性关系,检出限2.0×10-6mol.L-1,可用于岩白菜素的测定.     

Spectroscopic studies on binding of 1-phenyl-3-(coumarin-6-yl)sulfonylurea to bovine serum albumin

The interaction of 1-phenyl-3-(coumarin-6-yl)sulfonylurea (SU22) with bovine serum albumin (BSA) has been investigated by fluorescence quenching spectroscopy combined with UV-absorption, circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy techniques under simulative physiological conditions for the first time. Fluorescence data and UV-absorption spectra revealed that the quenching mechanism of fluorescence of BSA by SU22 was a static quenching process and the number of binding sites was about 0.8858; the thermodynamic parameters (DeltaG=-29.23 kJ mol(-1), DeltaH=-47.48 kJ mol(-1), and DeltaS=-61.24 J mol(-1)K(-1)) explained that hydrogen bond and Van der Waals interaction were the main binding force stabilizing the complex. The binding average distance between SU22 and BSA was obtained (3.20 nm) on the basis of the F?rster's theory. In addition, The CD spectra and FT-IR spectra have proved that BSA secondary structure changed in the presence of SU22 in aqueous solution.     

茉莉酸甲酯和超氧化物歧化酶相互作用的光谱法研究

通过荧光光谱法和紫外吸收光谱法研究了超氧化物歧化酶和茉莉酸甲酯之间的相互作用。经过荧光光谱法的研究表明,超氧化物歧化酶和茉莉酸甲酯的相互作用是一个静态猝灭的过程,它们之间是以氢键和范德华力结合的,同时得到超氧化物歧化酶和茉莉酸甲酯的结合位点数n,表观结合常数K和热力学参数ΔH,ΔG,ΔS。而根据非放射性能量转移的F rster理论和同步荧光光谱证明茉莉酸甲酯和超氧化物歧化酶的相互作用位点同时接近超氧化物歧化酶色氨酸(Trp)和酪氨酸(Tyr)残基。     

核黄素与牛血清白蛋白相互作用的荧光光谱研究

采用荧光猝灭光谱、同步荧光光谱研究了核黄素与牛血清白蛋白(BSA)相互作用的光谱行为。结果发现,在温度为293 K和310 K时核黄素与BSA的结合常数(Kb)分别为4.879×105L.mol-1和1.880×105L.mol-1,结合热力学方程计算得到了对应温度下的热力学参数。结果表明核黄素对BSA有较强的荧光猝灭作用,其荧光猝灭过程属于动态猝灭机制,二者主要靠疏水作用力结合。采用同步荧光光谱探讨了核黄素对BSA构象的影响。     

UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

碱性橙与蛋白间的特异性与非特异性作用荧光光谱比较

将碱性橙与抗体的作用、碱性橙与牛血清白蛋白(BSA)间的作用分别作为特异性作用和非特异性作用模型,采用荧光光谱法固定激发波长为280 nm,扫描不同温度下碱性橙与抗体和牛血清白蛋白两种相互作用,在300～600 nm的发射波长,比较了两种相互作用的差异.结果表明,碱性橙与抗体结合为单一的静态猝灭过程,二者之间的作用力主要为静电作用力;在溶液中,二者以摩尔比1∶1结合,结合常数为3.88×104 L/mol(25.C),3.73×104 L/mol(37.C)和2.35×104 L/mol (45.C);碱性橙距抗体分子色氨酸残基最短距离(r)为5.52 nm.碱性橙与BSA的结合也为静态猝灭,作用力为静电作用力.但碱性橙与抗体作用过程中形成了激基复合物,与BSA则不形成激基复合物.     

新型水溶性咪唑基硅量子点制备及用于果蔬中痕量铜的荧光检测

硅量子点因其极佳的亲生物性和光学性能成为纳米材料新宠,但传统硅量子点水溶性差限制了它的广泛应用。本实验以三甲基硅咪唑为硅前驱体采用水热法制备水溶性咪唑基硅量子点。相对于硼氢化钠、抗坏血酸、牛血清蛋白、半胱氨酸和柠檬酸,柠檬酸钠作为还原剂和稳定剂制得的硅量子点荧光发射最强。合成反应于220℃下可在2 h内完成,所制备的硅量子点水溶性好,平均粒径为2.6 nm,红外分析证实其表面存在游离的咪唑基。研究表明,硅量子点能与铜离子相互作用导致荧光强度的明显下降。考察不同温度下Cu2+对硅量子点荧光的猝灭行为,发现荧光猝灭程度随温度升高而增大。这说明荧光下降属于静态猝灭,即Cu2+与硅量子点上的咪唑基作用形成稳定配合物。此外,共振光散射分析还揭示荧光猝灭过程伴随着粒子团聚。基于硅量子点的荧光猝灭行为,建立了痕量铜的荧光检测方法。当Cu2+浓度在0.04~2400μmol/L之间,硅量子点的荧光强度随Cu2+浓度的增加而线性下降,检出限(S/N=3)达1.29×10-8 mol/L。本方法具有高的灵敏度、选择性和重现性,已应用于果蔬中痕量铜的荧光检测。     

Synthesis and interaction studies of benzimidazole derivative with human serum albumin

A benzimidazole derivative, 1-(2-picolyl)-3-(2-picolyl) benzimidazole iodide (PPB), was synthesized. Fourier transform infrared spectroscopy (FT-IR), UV–visible, three-dimensional (3D) fluorescence, synchronous fluorescence (SF) and fluorescence spectroscopic methods were used to determine the PPB binding mode and the effects of PPB on protein stability and secondary structure. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of PPB to human serum albumin (HSA). The binding constants between PPB and HSA were obtained according to Scatchard equation. The number of binding sites, the binding constants and the thermodynamic parameters were measured. The results showed a spontaneous binding of PPB to HSA through hydrogen bonds and van der Waals forces. In addition, the distance between PPB and the Trp 214 was estimated via employing the Förster's non-radiative energy transfer theory, and was found to be 3.49 nm, which indicated that PPB can bind to HSA with high probability. Site marker competitive experiments indicated that the binding of PPB to HSA primarily took place in subdomain IIA.     

磁性纳米氧化铁与CdTe量子点相互作用的光谱学研究

采用荧光光谱及紫外-可见吸收光谱研究了不同条件下磁性纳米氧化铁(MION)与CdTe量子点的相互作用, 发现MION对CdTe量子点荧光有猝灭作用. 由Stern-Volmer方程分析得到MION与CdTe量子点结合反应的荧光猝灭速率常数K_q值为7.68×10¹⁵ mol•L^－1•s^－1, 结合紫外-可见吸收光谱进一步证实此过程为静态猝灭过程. 并由Lineweaver-Burk方程得到MION与CdTe量子点结合的热力学焓变(?H^?)值为21.6 kJ•mol^－1、熵变(?S^?)值为210.3 J• mol^－1•K^－1和自由能变(?G^?)值为－41.1 kJ•mol^－1 (298 K). 对其相互作用机理进行探讨, 结果表明MION对CdTe量子点作用为自发过程, 主要存在静电作用.     

Mechanism and conformational studies of farrerol binding to bovine serum albumin by spectroscopic methods

The mechanism and conformational changes of farrerol binding to bovine serum albumin (BSA) were studied by spectroscopic methods including fluorescence quenching technique, UV–vis absorption, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy under simulative physiological conditions. The results of fluorescence titration revealed that farrerol could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The thermodynamic parameters enthalpy change and entropy change for the binding were calculated to be −29.92 kJ mol⁻¹ and 5.06 J mol⁻¹ K⁻¹ according to the van’t Hoff equation, which suggested that the both hydrophobic interactions and hydrogen bonds play major role in the binding of farrerol to BSA. The binding distance r deduced from the efficiency of energy transfer was 3.11 nm for farrerol–BSA system. The displacement experiments of site markers and the results of fluorescence anisotropy showed that warfarin and farrerol shared a common binding site I corresponding to the subdomain IIA of BSA. Furthermore, the studies of synchronous fluorescence, CD and FT-IR spectroscopy showed that the binding of farrerol to BSA induced conformational changes in BSA.     

2,5-di-[2-(3,5-bis(2-pyridylmethyl)amine -4-hydroxy-phenyl) ethylene] pyrazine zinc complex as fluorescent probe for labeling proteins

The binding characteristics between 2,5-di-[2-(3,5-bis(2-pyridylmethyl)amine -4-hydroxy-phenyl) ethylene] pyrazine (1) or its complex (1-Zn) and serum albumins were studied by fluorescence spectroscopy in pH 7.4 aqueous solution. 1-Zn emitted weak fluorescence at 580 nm in a pH 7.4 Tris-HCl buffer solution when excited at 435 nm, however, the fluorescence intensity increased upon addition of serum albumins with the blue shift of emission peak to 524 nm. The binding constants were estimated as 8.40 x 10(7) and 3.03 x 10(6)mol(-1)L for bovine serum albumin (BSA) and human serum albumin (HSA) respectively, and the number of binding sites was 1 for each. The quenching mechanism of fluorescence of serum albumins by 1-Zn was considered as a static quenching process. The binding distance between 1-Zn and serum albumins and the energy transfer efficiency were obtained based on the theory of F?rester spectroscopy energy transfer. The effect of 1-Zn on the conformation of serum albumins was further analyzed using synchronous fluorescence spectrometry. The experiment results clearly showed that 1-Zn is a highly sensitive protein sensor.     

Synthesis and characterization of polymer eight-coordinate (enH2)[YIII(pdta)(H2O)](2)·10H2O as well as the interaction of [YIII(pdta)(H2O)]2(2-) with BSA

The eight-coordinate (enH2)[YIII(pdta)(H2O)](2)·10H2O (en=ethylenediamine and H4pdta=1,3-propylenediamine-N,N,N',N'-tetraacetic acid) was synthesized, meanwhile its molecular and crystal structures were determined by single-crystal X-ray diffraction technology. The interaction between [Y(III)(pdta)(H2O)]2(2-) and bovine serum albumin (BSA) was investigated by UV-vis and fluorescence spectra. The results indicate that [YIII(pdta)(H2O)]2(2-) quenched effectively the intrinsic fluorescence of BSA via a static quenching process with the binding constant (Ka) of the order of 10(4). Meanwhile, the binding and damaging sites to BSA molecules were also estimated by synchronous fluorescence. Results indicate that the hydrophobic environments around Trp and Tyr residues were all slightly changed. The thermodynamic parameters (ΔG=-25.20 kJ mol(-1), ΔH=-26.57 kJ mol(-1) and ΔS=-4.58 J mol(-1) K(-1)) showed that the reaction was spontaneous and exothermic. What is more, both ΔH and ΔS were negative values indicated that hydrogen bond and Van der Waals forces were the predominant intermolecular forces between [YIII(pdta)(H2O)]2(2-) and BSA.     

Chlorobenzylidine-herring sperm DNA interaction: binding mode and thermodynamic studies

The interaction of chlorobenzylidine with herring sperm DNA has been investigated by fluorescence, absorption, DNA melting experiment and differential scanning calorimetry (DSC). When bound to DNA, chlorobenzylidine shows hypochromism and red shift in absorption spectra, fluorescence quenching and polarization increasing in fluorescence spectra and increasing in DNA melting temperature. These spectral characteristics strongly support intercalation of chlorobenzylidine into herring sperm DNA. Scatchard plots constructed from fluorescence titration data give a binding constant of 3.2 x 10(4) M(-1) and a binding site size of six base pairs per bound drug molecule. The intercalative interaction is exothermic with a van't Hoff enthalpy of -30.6 kJ mol(-1). This result is obtained from DSC experiment. In addition, DeltaG degrees =-28.5 kJ mol(-1), and DeltaS degrees =-7.1 J mol(-1) K(-1). These results show that the binding of chlorobenzylidine to herring sperm DNA is exothermic.