Voltammetric and spectroscopic studies on the interaction of anti-cancer herbal drug rutin with an anti-tuberculosis agent rifampicin

In this paper, the interaction of rutin (Rt) with rifampicin (RIF) has been investigated using voltammetric and spectroscopic techniques. With the addition of RIF into the Rt solution, both the reduction and oxidation currents of rutin decrease with few changes in the peak potentials and no new peaks appeared. The binding of Rt with RIF forms a kind of supramolecular complex Rt-RIF, which is electrochemically non-active. The experimental data showed that the formation of supramolecular complex is due to the electrostatic attraction of Rt with RIF. The binding reaction resulted in the decrease of the concentration of free Rt in the solution, and the decrease of the cathodic peak current of Rt. The stoichiometry of the Rt-RIF biocomplex was determinated to be 1: 1 by means of voltammetric data. The effect of pH on the binding reaction has been also studied. Based on the peak current values of Rt in the presence and absence of RIF, the binding constants of Rt-RIF at pHs 4, 7 and 9 were calculated as 0.72 × 10⁴ M⁻¹, 1.28 × 10⁴ M⁻¹ and 0.19 × 10⁴ M⁻¹, respectively. The experimental results indicate that there is a strength interaction between Rt and RIF in neutral pH. This binding reaction was supported by UV-Vis. and IR spectroscopy techniques.     

Chromatographic Framework to Determine the Memantine Binding Mechanism on Human Serum Albumin Surface

In this work, the interaction of memantine with human serum albumin (HSA) immobilized on porous silica particles was studied using a biochromatographic approach. The determination of the enthalpy change at different pH values suggested that the protonated group in the memantine–HSA complex exhibits a heat protonation with a magnitude around 65 kJ mol^?1. This value agrees with the protonation of a guanidinium group, and confirmed that an arginine group may become protonated in the memantine–HSA complex formation. The thermodynamic data showed that memantine–HSA binding, for low temperature (<293 K), is dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge–charge interactions contribute to the memantine–HSA complex formation. Above 293 K, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface. The temperature dependence of the free energy of binding is weak because of the enthalpy–entropy compensation caused by a large heat capacity change, ΔC _p = ? 3.79 kJ mol^?1 K^?1 at pH = 7. These results were used to determine the potential binding site of this drug on HSA.     

Study on the interaction mechanism between aromatic amino acids and quercetin

In this paper, we selected quercetin and aromatic amino acids (tryptophan, tyrosine, phenylalanine) as the research objects to investigate the change rules in the reaction process. The thermodynamic functions (Ka, ΔG, and ΔS) of the interactions between quercetin and aromatic amino acids (tryptophan, tyrosine, phenylalanine) were measured by isothermal titration calorimetry. The values of binding constant (Ka) reached maximum at 25°C; the entropies and Gibbs free energies were both negative at different temperatures. The kinetic parameters of quercetin and amino acids in the interaction process was determined by microcalorimetry. The results inferred that the driving force of the reaction was hydrogen bond or van der Waals force.     

Identification of pyrazosulfuron-ethyl binding affinity and binding site subdomain IIA in human serum albumin by spectroscopic methods

Pyrazosulfuron-ethyl (PY) is a sulfonylurea herbicide developed by DuPont which has been widely used for weed control in cereals. The determination of PY binding affinity and binding site in human serum albumin (HSA) by spectroscopic methods is the subject of this work. From the fluorescence emission, circular dichroism and three-dimensional fluorescence results, the interaction of PY with HSA caused secondary structure changes in the protein. Fluorescence data demonstrated that the quenching of HSA fluorescence by PY was the result of the formation of HSA–PY complex at 1:1 molar ratio, a static mechanism was confirmed to lead to the fluorescence quenching. Hydrophobic probe 8-anilino-1-naphthalenesulfonic acid (ANS) displacement results show that hydrophobic patches are the major sites for PY binding on HSA. The thermodynamic parameters ΔH° and ΔS° were calculated to be ?36.32 kJ mol^?1 and ?35.91 J mol^?1 K^?1, which illustrated van der Waals forces and hydrogen bonds interactions were the dominant intermolecular force in stabilizing the complex. Also, site marker competitive experiments showed that the binding of PY to HSA took place primarily in subdomain IIA (Sudlow's site I). What presented in this paper binding research enriches our knowledge of the interaction between sulfonylurea herbicides and the physiologically important protein HSA.     

Interaction between Glyoxal-bis-(2-hydroxyanil) and Bovine Serum Albumin in Solution

The interaction between glyoxal-bis-(2-hydroxyanil) (GBH) and bovine serum albumin (BSA) was studied by spectroscopic methods including fluorescence spectroscopy, circular dichroism (CD) and UV–visible absorption spectra. The mechanism for quenching the fluorescence of BSA by GBH is discussed. The number of binding sites n and observed binding constant K _b were measured by the fluorescence quenching method. The thermodynamic parameters ΔH ^θ , ΔG ^θ , and ΔS ^θ were calculated at different temperatures and the results indicate that hydrogen bonding and van der Waals forces played major roles in the reaction. The distance r between the donor (BSA) and acceptor (GBH) molecules was obtained according to Förster’s theory of non-radiation energy transfer. Synchronous fluorescence and three-dimensional fluorescence spectra were used to investigate the structural change of BSA molecules that occur upon addition of GBH, and these results indicate that the secondary structure of BSA molecules is changed by the presence of GBH.     

Interaction Between Plumbagin and Human Serum Albumin by Fluorescence Spectroscopy

The interaction of plumbagin (PLU) with human serum albumin (HSA) in physiological buffer (pH=7.4) was studied by fluorescence spectroscopy. Results obtained from analysis of the fluorescence spectra indicated that PLU has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. Fluorescence quenching data revealed that the quenching constants (K) are 4.43×10⁴, 3.26×10⁴ and 1.69×10⁴ L?mol^?1 at 293, 303 and 313 K, respectively. The thermodynamic parameters ΔH° and ΔS° were calculated to be ?36.63 kJ?mol^?1, and ?35.702 J?mol^?1?K^?1 respectively, which suggested that van der Waals interactions and hydrogen bonds play a major role in the interaction of PLU with HSA. The distance between donor (HSA) and acceptor (PLU) was calculated to be 3.76 nm based on Förster’s non-radiative energy transfer theory. The results of synchronous fluorescence spectra showed that binding of PLU to HSA can induce conformational changes in HSA.     

Study of the interactions between fluoroquinolones and human serum albumin by affinity capillary electrophoresis and fluorescence method

The interactions between fluoroquinolones and human serum albumin (HSA) were investigated by affinity capillary electrophoresis (ACE) and fluorescence quenching technique. Based on the efficient separation of several fluoroquinolones using a simple phosphate buffer, the binding constants of fluoroquinolones with HSA were determined simultaneously during one set of electrophoresis by ACE method. The thermodynamic parameters were obtained from data at different temperatures, and the negative ΔH and ΔS values showed that both hydrogen bonds and van der Waals interaction played major roles in the binding of fluoroquinolones to HSA. The interactions were also studied by fluorescence quenching technique. The results of fluorescence titration revealed that fluoroquinolones had the strong ability to quenching the intrinsic fluorescence of HSA through the static quenching procedure. The binding site number n, apparent binding constant K_b and the Stern-Volmer quenching constant K_sv were determined. The thermodynamic parameters were also studied by fluorescence method, and the results were consonant with that of ACE.     

表皮生长因子受体和抑制剂之间分子对接的研究

研究了表皮生长因子受体(EGFR)和4-苯胺喹唑啉类抑制剂之间的相互作用模式，表皮生长因子受体的三维结构通过同源蛋白模建的方法得到，而抑制剂和靶酶结合复合物结构则通过分子力学和分子动力学结合的方法计算得到。从模拟结果得到的抑制剂和靶酶之间的相互作用模式表明范德华相互作用、疏水相互作用以及氢键相互作用对抑制剂的活性都有重要的影响，抑制剂的苯胺部分位于活性口袋的底部，能够与受体残基的非极性侧链产生很强的范德华和疏水相互作用，抑制剂双环上的取代基团也能和活性口袋外部的部分残基形成一定的范德华和疏水性相互作用，而抑制剂喹唑啉环上的氮原子能和周围的残基形成较强的氢键相互作用，对抑制剂的活性有较大的影响，计算得到抑制剂和靶酶之间的非键相互作用能以及抑制剂和靶酶之间的相互作用信息能够很好地解释抑制剂活性和结构的关系，为全新抑制剂的设计提供了重要的结构信息。     

Study of caffeine binding to human serum albumin using optical spectroscopic methods

The binding of caffeine to human serum albumin (HSA) under physiological conditions has been studied by the methods of fluorescence, UV-vis absorbance and circular dichroism (CD) spectroscopy. The mechanism of quenching of HSA fluorescence by caffeine was shown to involve a dynamic quenching procedure. The number of binding sites n and apparent binding constant K _b were measured by the fluorescence quenching method and the thermodynamic parameters ΔH, ΔG, ΔS were calculated. The results indicate that the binding is mainly enthalpy-driven, with van der Waals interactions and hydrogen bonding playing major roles in the reaction. The distance r between donor (HSA) and acceptor (caffeine) was obtained according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD and three-dimensional fluorescence spectroscopy showed that the microenvironment and conformation of HSA were altered during the reaction.     

Arginine Side Chains as a Dispersant for Individual Single‐Wall Carbon Nanotubes

Charged peptides and proteins disperse single‐wall carbon nanotubes (SWCNTs) in aqueous solutions. However, little is known about the role of their side chains in their interactions with SWCNTs. Homopolypeptide–SWCNT systems are ideal for investigating the mechanisms of such interactions. In this study, we demonstrate that SWCNTs are individually dispersed by poly‐L ‐arginine (PLA). The debundled SWCNTs exhibited a distinct fluorescence. The dispersibility of SWCNTs with PLA was greater than that of SWCNTs with poly‐L ‐lysine (PLL). Molecular dynamics simulations suggest that the side chains of PLA have stronger interactions with the sidewalls of SWCNTs compared with those of PLL. The guanidinium group at the end of the side chain of an arginine residue plays an important role in the interaction with SWCNTs, likely through hydrophobic, van der Waals, and π–π interactions. PLA can be useful as a tool for the dispersion of SWCNTs and can be used to non‐covalently anchor materials to SWCNTs with strong binding.     

Studies of the Interaction Between Ronidazole and Human Serum Albumin by Spectroscopic and Molecular Docking Methods

Ronidazole (RNZ) is widely used for the therapeutic treatment of farmed animals and is suspected of being a human carcinogen and mutagen. The interaction between RNZ and human serum albumin (HSA) was investigated systematically by fluorescence spectroscopy, synchronous fluorescence, three-dimensional fluorescence, CD spectroscopy, UV–vis absorption spectroscopy and a molecular docking study. The results indicate that the probable quenching mechanism of HSA by RNZ is dynamic quenching. The corresponding thermodynamic parameters, such as ΔH, ΔS and ΔG, etc., were calculated according to the van’t Hoff equation. The results indicate that the forces acting between RNZ and HSA are mainly hydrogen bonds and van der Waals forces. The conformational changes in the interaction were studied by synchronous fluorescence, CD spectroscopy and three-dimensional fluorescence spectra. The results reveal that the microenvironment and conformation of HSA has been changed. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.     

Investigation on the interaction between a heterocyclic aminal derivative, SBDC, and human serum albumin

The interaction between a novel promising drug (spiro[(2R,3R,4S)-4-benzyloxy-2,3-isopropylidene-dioxy-1-oxa-cyclopentane-5,5′-(2-benzoylmethylene-1,3-diaza-cyclohexane)] (SBDC)) and human serum albumin (HSA) under physiological conditions has been investigated by using fluorescence, absorption, and circular dichroism (CD) spectroscopic techniques in combination with protein–ligand docking study. It was observed that SBDC has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The association constants of SBDC with HSA were determined at different temperatures based on fluorescence quenching results. The negative ΔH and positive ΔS values in case of SBDC–HSA complex showed that apart from an initial hydrophobic association, both van der Waals interactions and hydrogen bonding play a vital role in the binding of SBDC to HSA. The quantitative analysis data of CD spectra showed that the binding of SBDC to HSA induced conformational changes in HSA and the α-helix of 52.1% in free HSA increased to 55.7% in HSA–SBDC complex. The distance between donor (HSA) and acceptor (SBDC) was obtained according to the Förster's theory of non-radiation energy transfer. Data obtained by spectroscopic techniques and protein–ligand docking study suggested that SBDC binds to residues located in subdomain IIA of HSA.     

Uncovering the interactions driving carotenoid binding in light-harvesting complexes

Carotenoids are essential constituents of plant light-harvesting complexes (LHCs), being involved in protein stability, light harvesting, and photoprotection. Unlike chlorophylls, whose binding to LHCs is known to require coordination of the central magnesium, carotenoid binding relies on weaker intermolecular interactions (such as hydrogen bonds and van der Waals forces), whose character is far more elusive. Here we addressed the key interactions responsible for carotenoid binding to LHCs by combining molecular dynamics simulations and polarizable quantum mechanics/molecular mechanics calculations on the major LHC, LHCII. We found that carotenoid binding is mainly stabilized by van der Waals interactions with the surrounding chlorophyll macrocycles rather than by hydrogen bonds to the protein, the latter being more labile than predicted from structural data. Furthermore, the interaction network in the binding pockets is relatively insensitive to the chemical structure of the embedded carotenoid. Our results are consistent with a number of experimental data and challenge the role played by specific interactions in the assembly of pigment-protein complexes.

Carotenoids are essential constituents of plant light-harvesting complexes. This in silico study shows that carotenoid binding is mainly driven by van der Waals interactions with the surrounding chlorophylls rather than hydrogen bonds to the protein.     

Spectroscopic studies on in vitro binding of cefixime and tolcapone drugs with serum albumin

The interaction between cefixime (antibacterial) and tolcapone (Parkinson’s disease) drugs with bovine serum albumin (BSA) was investigated using several spectroscopic techniques viz. UV–Vis, fluorescence and circular dichroism. The thermodynamic parameters of the interactions were calculated, which indicated that the binding processes are spontaneous and H-bonding and van der Waals forces play a major role in BSA–cefixime interaction and hydrophobic interactions dominate BSA–tolcapone complexation. Cefixime quenches the intrinsic fluorescence of BSA by dynamic process while tolcapone through static process. The binding constant of the BSA–tolcapone complex (10⁷ L mol^?1) is found to be relatively higher than that of BSA–cefixime complex (10⁴ L mol^?1). The binding distance between BSA and cefixime and tolcapone is calculated to be 3.3 and 4.2 nm, respectively. Both fluorescence and circular dichrosim spectral studies confirmed conformational changes in BSA upon binding with these drugs. Molecular docking studies suggest the possible binding sites in the protein molecule.'     

CEPA calculations of potential energy surfaces for open-shell systems.: III. Van der Waals interaction between O(3P) and He(1S)

Quantum-chemical ab initio calculations have been performed for the van der Waals interaction between helium and oxygen atoms in their respective ground states: He(¹S)+ O(³P). As long as fine-structure effects are neglected, there are two low-lying electronic states, ³Σ^? and ³Π resulting from the degeneracy of the O(³P) ground state. Both states are purely repulsive at the SCF level, after inclusion of electronic correlation by the CEPA method they exhibit shallow van der Waals (dispersion) minima at large interatomic separation: R_? = 3.61 Å, ? = 1.0 meV (³Σ^?) and R_? = 3.05 Å, ? = 2.3 meV (³Π). The analysis of the results shows the very slow convergence of the dispersion interaction with increasing basis size, while SCF repulsion and the repulsion due to the change of the intra-atomic correlation are obtained reasonably accurately with moderate basis stes. Van der Waals coefficients C₆, C₈, C₁₀, potential curves of the type HFD (i.e. Hartree-Fock plus damped dispersion) and the influence of fine-structure effects (mainly spin-orbit coupling) on the shape of the adiabatic potential curves are discussed as well.     

Copper Mediated Affinity of Amyloid β to Chondroitin Sulfates

Aβ is a major component of the senile plaques characteristic of Alzheimer disease (AD) and sulfated GAGs such as chondroitin sulfates (CS) have been found in all types of amyloidosis. In this paper, a biochromatographic approach was developed to measure for the first time changes in enthalpy, heat capacity change and copper effect for the binding of Aβ to CS in a wide temperature range. For this, CS was immobilized on a chromatographic support. It was established that this novel CS column was stable during an extended period of time. The thermodynamic data showed that Aβ–CS binding, for low temperature (<10 °C), is enthalpically unfavourable and being dominated by a positive entropy change. This result suggested that dehydration at the binding interface and charge–charge interactions contribute to the Aβ–CS complex formation and a large heat capacity change, ΔC _p = ?2.32 kJ mol^?1 K^?1, was determined. Above 10 °C, the thermodynamic data ΔH and ΔS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface confirming strong Aβ–CS hydrogen bond networks. Also, for a copper concentration in the range 20–160 μM, it was shown that an increase of the Cu²⁺ concentration in the medium led an increase of this association classically attributed to salt effect (i.e. hydrophobic bonds) and to ion pair formations between the Cu²⁺ cation and Aβ to bind to chondroitin sulfate and could thus improve the Aβ aggregation by copper.     

Thermodynamics of the formation of nickel(II) complexes with L-histidine in aqueous solutions

The heat effects of the formation of Ni(II) complexes with L-histidine in an aqueous solution are determined via direct calorimetry at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO₃). The standard thermodynamic characteristics (Δ_r H ^○, Δ_r G ^○, Δ_r S ^○) of complex formation in the investigated system are calculated. It is concluded that the resulting values are consistent with the results from studying the structure of L-histidine complexes with Ni²⁺ ions by various spectral methods.     

Spectroscopic Investigation of the Interactions of Cryptotanshinone and Icariin with Two Serum Albumins

The interactions of two drugs, cryptotanshinone (CTS) and icariin, with bovine serum albumin (BSA) and human serum albumin (HSA) have been investigated using multiple spectroscopic techniques under imitated physiological conditions. CTS and icariin can quench the fluorescence intensity of BSA/HSA by a static quenching mechanism with complex formation. The binding constants of CTS–BSA, CTS–HSA, icariin–BSA and icariin–HSA complexes were observed to be 1.67 × 10⁴, 4.04 × 10⁴, 4.52 × 10⁵ and 4.20 × 10⁵ L·mol^?1, respectively at 298.15 K. The displacement experiments suggested icariin/CTS are primarily bound to tryptophan residues of the proteins within site I and site II. The thermodynamic parameters calculated on the basis of the temperature dependence of the binding constants revealed that the binding of CTS–BSA/HSA mainly depends on van der Waals interaction and hydrogen bonds, and yet the binding of icariin–HSA/BSA strongly relies on the hydrophobic interactions. The binding distances between BSA/HSA and CTS/icariin were evaluated by the Föster non-radiative energy transfer theory. The results of synchronous fluorescence, 3D fluorescence, FT-IR and CD spectra indicates that the conformations of proteins were altered with the addition of CTS or icariin. In addition, the effects of some common ions on the binding constants of CTS/icariin to proteins are also discussed.     

两种组氨酸酰胺衍生物的合成及其与人血清白蛋白的结合

L-组氨酸对生物有机体有着良好的亲和能力,通过修饰其化学结构以期寻找药理活性和生物利用度高的衍生物。本文将L-组氨酸分别与反式肉桂酸和对甲氧基肉桂酸反应,合成了两种组氨酸酰胺类衍生物,利用傅里叶变换红外光谱、质谱、氢谱/碳谱核磁共振谱进行了结构表征。采用分子操作环境(MOE)软件分子对接技术、荧光光谱法、同步荧光光谱法(SFS)、紫外-可见光谱法(UV-Vis),共同研究了两种衍生物分别和人血清白蛋白(HSA)相结合的机理。MOE对接结果显示,这两种衍生物与HSA的模拟结合能分别为-13.82和-16.25 kcal/mol,主要是通过范德华力和疏水作用结合在HSA亚结构域ⅡA(即siteⅠ)的疏水腔内。荧光猝灭数据表明,衍生物与HSA相互作用并形成了新的基态配合物,荧光猝灭过程为静态猝灭;不同温度(300、305和310 K)下衍生物与HSA相互作用的结合常数分别为1.773×104、6.354×10~3、1.260×10~3和5.314×10~4、4.614×10~3、1.420×10~3;由热力学参数得到衍生物与HSA的结合过程是由范德华力驱动;SFS表明,衍生物使得HSA的二级结构发生了变化。结合UV-Vis的结果可以确定,在体外生理条件下,组氨酸酰胺类衍生物均可以通过范德华力与HSA结合,并对HSA内源荧光产生静态猝灭及构象影响,这与分子对接结果一致,从而为组氨酸酰胺类衍生物药物的进一步开发提供了参考。     

Competitive binding of small molecules with biopolymers: a fluorescence spectroscopy and chemometrics study of the interaction of aspirin and ibuprofen with BSA

The interaction of aspirin and ibuprofen with bovine serum albumin (BSA) was studied by spectrofluorimetry under simulated physiological conditions. Both aspirin and ibuprofen quenched the intrinsic fluorescence of BSA and the binding ratios obtained were 2 : 1 for aspirin-BSA and 3 : 1 for ibuprofen-BSA interactions, respectively. The thermodynamic parameters (ΔH, ΔS and ΔG) obtained from the fluorescence spectroscopy data showed that the binding of aspirin to BSA involved van der Waals interactions and hydrogen bonds. Competitive experiments using warfarin and diazepam as site markers indicated that aspirin was mainly located in the hydrophobic pocket of site II of the protein as well as to a small extent in site I. Furthermore, the competitive interaction of the aspirin and ibuprofen with BSA, which was studied with the use of the three-way excitation-emission fluorescence spectra and a parallel factor analysis (PARAFAC) chemometrics method, showed that the competitive effect of ibuprofen was stronger than that of aspirin, i.e. the former molecule replaced the aspirin from the aspirin-BSA complex.