Binding of rare earth metal complexes with an ofloxacin derivative to bovine serum albumin and its effect on the conformation of protein

The water-soluble Pr (Ⅲ) and Nd (Ⅲ) complexes with an ofloxacin derivative have been prepared and characterized. The single-crystal X-ray diffraction showed that the Pr (III) and Nd (III) complexes have the similar molecular structure. Under physiological pH condition, the effects of [PrL(NO₃)₂(CH₃OH)](NO₃) and [NdL(NO₃)₂(CH₃OH)](NO₃) on bovine serum albumin (BSA) were examined using fluorescence spectroscopy in combination with UV-vis absorbance and circular dichroism (CD) spectra. The result reveals that the quenching mechanism of fluorescence of BSA by two complexes is a static quenching process and the number of binding sites is about 1 for both. The thermodynamic parameters (ΔH=−14.52 kJ mol⁻¹, ΔS=56.54 J mol⁻¹ K⁻¹ for [PrL(NO₃)₂(CH₃OH)](NO₃) and ΔH=−24.63 kJ mol⁻¹, ΔS=22.07 J mol⁻¹ K⁻¹ for [NdL(NO₃)₂(CH₃OH)](NO₃)) indicate that hydrophobic and electrostatic interactions are the main binding force in the complexes-BSA system. The binding average distance between complexes and BSA was obtained on the basis of Förster's theory. In addition, it was proved by the CD spectra that the BSA secondary structure was changed in the presence of complexes in an aqueous solution.     

Probing the interaction of flower-like CdSe nanostructure particles targeted to bovine serum albumin using spectroscopic techniques

The interaction between flower-like CdSe nanostructure particles (CdSe NP) and bovine serum albumin (BSA) was investigated from a spectroscopic angle under simulative physiological conditions. Under pH 7.4, CdSe NP could effectively quench the intrinsic fluorescence of BSA via static quenching. The binding constant (K_A) was 6.38, 3.27, and 1.90×10⁴ M⁻¹ at 298, 304, and 310 K, respectively and the number of binding sites was 1.20. According to the Van't Hoff equation, the thermodynamic parameters (ΔH°=−77.48 kJ mol⁻¹, ΔS°=−168.17 J mol⁻¹ K⁻¹) indicated that hydrogen bonds and van der Waals forces played a major role in stabilizing the BSA−CdSe complex. Besides, UV-vis and circular dichroism (CD) results showed that the addition of CdSe NP changed the secondary structure of BSA and led to a decrease in α-helix. These results suggested that BSA underwent substantial conformational changes induced by flower-like CdSe nanostructure particles.     

Study on the interaction between promethazine hydrochloride and bovine serum albumin by fluorescence spectroscopy

The interaction between promethazine hydrochloride (PMT) and bovine serum albumin (BSA) in vitro was investigated by means of fluorescence spectroscopy and absorption spectroscopy. The fluorescence of BSA was quenched remarkably by PMT and the quenching mechanism was considered as static quenching by forming a complex. The association constants K_a and the number of binding sites n were calculated at different temperatures. The BSA-PMT binding distance was determined to be less than 8 nm, suggesting that energy transfer from BSA to PMT may occur. The thermodynamic parameters of the interaction between PMT and BSA were measured according to the van’t Hoff equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be −23.62 kJ mol⁻¹ and −0.10 J mol⁻¹ K⁻¹, respectively, which indicated that the interaction of PMT with BSA was driven mainly by van der Waals forces and hydrogen bonds. The binding process was a spontaneous process in which Gibbs free energy change (ΔG) was negative. In addition, the results of synchronous fluorescence spectra and three-dimensional fluorescence spectra showed that binding of PMT with BSA can induce conformational changes in BSA.     

Investigation of the interaction between trazodone hydrochloride and bovine serum albumin

In this paper, the binding of trazodone hydrochloride (TZH) to bovine serum albumin (BSA) was investigated by spectroscopic (fluorescence, spectrophotometry and circular dichroism) techniques under simulative physiological conditions. A strong fluorescence quenching reaction of TZH to BSA was observed and the quenching mechanism was suggested as dynamic quenching according to the Stern-Volmer equation. The binding constants of TZH with BSA at 288, 302 and 309 K were calculated as (1.56±0.003)×10⁴, (2.31±0.002)×10⁴ and (5.44±0.004)×10⁴ M⁻¹, respectively. The thermodynamic parameters, ΔH⁰ and ΔS⁰ were obtained to be 39.86±0.008 kJ mol⁻¹ and 217.89±0.011 J mol⁻¹ K⁻¹, respectively, which indicated the presence of hydrophobic forces between TZH and BSA. The spectral results observed showed that the binding of TZH to BSA induced conformational changes in BSA. Based on the Förster's theory of non-radiation energy transfer, the binding average distance, r between donor (BSA) and acceptor (TZH) was found to be 2.4 nm. The effect of common ions on binding of TZH to BSA was also examined.     

Probing the binding of vitexin to human serum albumin by multispectroscopic techniques

The interaction between vitexin and human serum albumin (HSA) has been studied by using different spectroscopic techniques viz., fluorescence, UV-vis absorption, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy under simulated physiological conditions. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of vitexin to HSA. The binding constants (K_a) between vitexin and HSA were obtained according to the modified Stern-Volmer equation. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were calculated to be -57.29 kJ mol⁻¹ and -99.01 J mol⁻¹ K⁻¹ via the van't Hoff equation, which indicated that the interaction of vitexin with HSA was driven mainly by hydrogen bond and van der Waals forces. Fluorescence anisotropy data showed that warfarin and vitexin shared a common binding site I corresponding to the subdomain IIA of HSA. The binding distance (r) between the donor (HSA) and the acceptor (vitexin) was 4.16 nm based on the Förster theory of non-radioactive energy transfer. In addition, the results of synchronous fluorescence, CD and FT-IR spectra demonstrated that the microenvironment and the secondary structure of HSA were changed in the presence of vitexin.     

Characterization of the interaction between human lactoferrin and lomefloxacin at physiological condition: Multi-spectroscopic and modeling description

The interaction between lomefloxacin (LMF) and human lactoferrin (Hlf) was studied by using fluorescence, circular dichroism (CD) spectroscopic and molecular modeling measurements. By the fluorescence quenching results, it was found that the binding constant K_A=8.69×10⁵ L mol⁻¹, and number of binding sites n=1.75 at physiological condition. Experimental results observed showed that the binding of LMF to Hlf induced conformational changes of Hlf. The participation of tyrosyl and tryptophanyl residues of protein was also estimated in the drug-Hlf complex by synchronous fluorescence. The quantitative analysis data of far-UV CD spectra from that of the α-helix 37.4% in free Hlf to 30.2% in the LMF-Hlf complex further confirmed that secondary structure of the protein was changed by LMF. Near-UV CD showed perturbations around tryptophan and tyrosine residues which involves perturbations of tertiary structure. The thermodynamic parameters like, ΔH° and ΔS°, have been calculated to be 63.411 kJ mol⁻¹ and 231.104 J mol⁻¹ K⁻¹, respectively. Thermodynamic analysis showed that hydrophobic interactions were the main force in the binding site but the hydrogen bonding and electrostatic interaction could not be excluded which in agreement with the result of molecular docking study. The distance r between donor and acceptor was obtained according to fluorescence resonance energy transfer (FRET) and found to be 1.78 nm. The interaction between LMF and Hlf has been verified as consistent with the static quenching procedure and the quenching mechanism is related to the energy transfer. Furthermore, the study of molecular modeling that LMF could bind to the α-helixes between Pro145-Asn152 and Phe167-Gln172 regions and hydrophobic interaction was the major acting force for the binding site, which was in agreement with the thermodynamic analysis.     

Spectroscopic studies on the binding of barbital to bovine serum albumin

In this paper, the interaction between barbital and bovine serum albumin (BSA) was investigated by the method of fluorescence spectroscopy under simulative physiological conditions. Fluorescence data revealed that the fluorescence quenching of BSA by barbital was the result of the formation of BSA-barbital complex, and the effective quenching constants (K_a) were 1.468×10⁴, 1.445×10⁴ and 1.403×10⁴ M⁻¹ at 297, 303 and 310 K, respectively. The thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS) for the reaction were calculated to be −2.679 kJ mol⁻¹ and 70.76 J mol⁻¹ K⁻¹, respectively, according to the van’t Hoff equation. The results indicated that hydrophobic and electrostatic interactions were the dominant intermolecular force in stabilizing the complex. The results of synchronous fluorescence spectra showed that binding of barbital with BSA can induce conformational changes in BSA. In addition, the effects of Cu²⁺ and Zn²⁺ on the constants of BSA-barbital complex were also discussed.     

Study on the interaction between methyl blue and human serum albumin by fluorescence spectrometry

The interaction of methyl blue (MB) with human serum albumin (HSA) was studied by fluorescence and absorption spectroscopy. The intrinsic fluorescence of HSA was quenched by MB, which was rationalized in terms of the static quenching mechanism. The number of binding sites and the apparent binding constants at different temperatures were obtained from the Stern-Volmer analysis of the fluorescence quenching data. The thermodynamic parameters determined by the van’t Hoff analysis of the binding constants (ΔH°=39.8 kJ mol⁻¹ and ΔS°=239 J mol⁻¹ K⁻¹) clearly indicate that binding is absolutely entropy-driven and enthalpically disfavored The efficiency of energy transfer and the distance between the donor (HSA) and the acceptor (MB) were calculated as 60% and 2.06 nm from the Förster theory of non-radiation energy transfer.     

Interaction of nobiletin with human serum albumin studied using optical spectroscopy and molecular modeling methods

The binding of nobiletin to human serum albumin (HSA) was investigated by fluorescence, UV-vis, FT-IR, CD, and molecular modeling. Fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K) at four different temperatures (289, 296, 303 and 310 K) were 4.054, 4.769, 5.646 and 7.044×10⁴ M⁻¹, respectively. The enthalpy change (ΔH⁰) and the entropy changes (ΔS⁰) were calculated to be 1.938 kJ mol⁻¹ and 155.195 J mol⁻¹ K⁻¹ according to the Van’t Hoff equation. The binding average distance, r, between the donor (HSA) and the acceptor (nobiletin) was evaluated and found to be 2.33 nm according to the Förster's theory of non-radiation energy transfer. Changes in the CD and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. Computational mapping of the possible binding sites of nobiletin revealed the molecule to be bound in the large hydrophobic cavity of subdomain IIA.     

Characterize the interaction between naringenin and bovine serum albumin using spectroscopic approach

Naringenin, a flavanone compound highly enriched in grapefruits, has been identified as a possible inhibitor of cell proliferation; and thus has the potential to act as an antitumorigenic agent. In this study, the binding of naringenin to bovine serum albumin (BSA) was studied at the physiological conditions (pH=7.40) by fluorescence and UV-vis spectroscopy. Naringenin strongly quenches the intrinsic fluorescence of BSA, and a decrease in the fluorescence quenching constant was observed together with an increase in temperature, which indicates that the fluorescence quenching of BSA by naringenin is a result of the formation of naringenin-BSA complex. Binding parameters calculating from Stern-Volmer method and Scatchard method showed that naringenin bind to BSA with the binding affinities of the order 10⁴ L mol⁻¹. Thermodynamic parameters such as ΔG, ΔH and ΔS, were calculated at different temperatures, showing that electrostatic interactions were mostly responsible for the binding of naringenin to BSA. Site marker competitive displacement experiments demonstrating that naringenin bind with high affinity to site I (subdomain IIA) of BSA. Furthermore, the effect of metal ions to naringenin-BSA system was studied, and the specific binding distance r (3.30 nm) between donor (Trp-212) and acceptor (naringenin) was obtained according to fluorescence resonance energy transfer (FRET).     

Spectroscopic studies on the interaction between disperse blue SBL and bovine serum albumin

The interaction of disperse blue SBL (DBSBL) with bovine serum albumin (BSA) was investigated using fluorescence, UV-visible and far-UV circular dichroism (CD) spectroscopy. The results showed that the fluorescence of BSA was quenched by DBSBL through static quenching after correcting for the inner filter effects (IFE). The binding constant K_b of DBSBL with BSA at 288, 298 and 303 K were 0.116×10⁶, 3.18×10⁶ and 12.3×10⁶ L mol⁻¹, respectively. The thermodynamic parameters, standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰), for the reaction were evaluated to be 227.2 kJ mol⁻¹ and 886 J mol⁻¹ K⁻¹ according to the van’t Hoff equation. The above data suggested that the forces acting between DBSBL and BSA were predominantly hydrophobic interactions. The results of UV-visible absorption and far-UV CD spectroscopy also revealed that the conformation and microenvironment of BSA molecule were changed after DBSBL binding to BSA. At 288 K one binding site was present but at higher temperatures a second binding site was detected between DBSBL and the BSA molecule. The lower bound for the distance between the bound dye and the Trp residue is 2.35 nm as calculated from Forster energy transfer.     

Spectrofluorimetric study on the interaction between antimicrobial drug sulfamethazine and bovine serum albumin

The interaction between the antimicrobial drug sulfamethazine (STM) and bovine serum albumin (BSA) has been studied using steady state and synchronous fluorescence spectroscopy. Fluorescence emission data revealed that BSA (2×10⁻⁶ M) fluorescence was statically quenched by STM at various concentrations, which implies that STM-BSA complex has been formed. The fluorescence emission data was analyzed via applying the Stern-Volmer analysis in combination with thermodynamic investigation, where obtained results revealed that quenching is static with quenching constants of 2.371, 1.658, and 0.916×10⁵ M⁻¹ at 298, 304, and 310 K, respectively. Binding constants and number of binding sites at different temperatures were also determined by applying the Scatchard method, which in turn were used to construct the van't Hoff plot in order to estimate the enthalpy (ΔH) and entropy changes (ΔS) for the complexation process. An average of 1.00±0.17 was estimated for the number of sites of BSA, which indicated that STM binds to BSA with stoichiometric ratio of 1:1. The values that were estimated from the van't Hoff plot for ΔH and (ΔS) were −36.8 kJ mol⁻¹ and −14.9 J mol⁻¹ K⁻¹, respectively, which indicate that the STM-BSA complex is stabilized with hydrogen bonds and van der Waals interactions. Synchronous fluorescence data was obtained at Δλ of 15 and 60 nm, where obtained results confirmed that STM binds to BSA at the tryptophan residue (Trp. 213). In addition, the distance between STM and the Trp. 213 was estimated via employing the Förster's non-radiative energy-transfer theory, and was found to be 2.73 nm, which in turn indicated that STM can bind to BSA with high probability.     

Static quenching of bovine serum albumin conjugated with small size CdS nanocrystalline quantum dots

The author reports on a strong fluorescence quenching of a model transport protein, bovine serum albumin BSA, when bioconjugated with CdS quantum dots QDs. The 4.4 nm size CdS QDs were synthesized using wet chemistry method and were characterized using UV-vis spectroscopy, scanning electron microscopy SEM and X-ray diffraction XRD techniques. It was found that the BSA fluorescence quenching increases linearly with increasing the CdS QDs concentrations in the range of 3×10⁻⁷-2.0×10⁻⁶ mol L⁻¹. This quenching is explained in terms of Stern-Volmer equation and is ascribed to static quenching with quenching constant 1.321×10⁴ L mol⁻¹ at 300 K.     

Spectroscopic study on the interaction of Bacillus subtilis α-amylase with cetyltrimethylammonium bromide

The interaction between α‐amylase from Bacillus subtilis and cetyltrimethylammonium bromide (CTAB) has been investigated at various temperature conditions using fluorescence and circular dichroism (CD) spectroscopic methods. Fluorescence data revealed that the fluorescence quenching of α‐amylase by CTAB is the result of complex formation between CTAB and α‐amylase. The thermodynamic analysis on the binding interaction data shows that the interactions are strongly exothermic (ΔH°=−17.92 kJ mol⁻¹) accompanied with increase in entropy (ΔS° between 109 to 135 J mol⁻¹ K⁻¹). Thus the binding of CTAB to α-amylase is both enthalpic and entropic driven, which represent the predominate role of both electrostatic and hydrophobic interactions in complex formation process. The values of 2.17×10⁻³ M⁻¹ and 1.30 have been obtained from associative binding constant (K_a) and stoichiometry of binding number (n), from analysis of fluorescence data, respectively. Circular dichroism spectra showed the substantial conformational changes in secondary structure of α‐amylase due to binding of CTAB, which represents the complete destruction of both secondary and tertiary structure of α-amylase by CTAB.     

Binding study of diprophylline with lysozyme by spectroscopic methods

The binding properties of diprophylline (DPP) to lysozyme (Lys) were investigated using fluorescence spectroscopy in combination with UV-vis absorption techniques under simulative physiological conditions. Results of fluorescence measurement indicated that the intrinsic fluorescence of Lys was strongly quenched by DPP. The binding constants and the number of binding sites at different temperatures (298, 310, and 318 K) calculated with the data obtained from fluorescence quenching experiments via the modified Stern-Volmer equation were 8.61×10⁴ L mol⁻¹ and 1.34; 10.36×10⁴ L mol⁻¹ and 1.22; 12.85×10⁴ L mol⁻¹ and 1.11, respectively. Positive values of ΔH⁰ and ΔS⁰ obtained according to the Van’t Hoff equation for the formation of the DPP-Lys complex implied that typical hydrophobic interactions might play a significant role during the binding process. Furthermore, the effect of DPP on the conformation change of Lys was analyzed using synchronous fluorescence measurement. The effects of common co-ions on the interaction of DPP with Lys were also discussed.     

Complexes between C.I. Acid Orange 6 and human serum albumin, a multi-spectroscopic approach to investigate the binding behavior

The interaction mechanism of Acid Orange 6 (AO6) with human serum albumin (HSA) was investigated firstly by using fluorescence quenching technique, UV absorbance, circular dichroism (CD), Fourier transform infrared (FT-IR), three-dimensional fluorescence spectroscopy in combination with molecular modeling method under simulative physiological conditions. Fluorescence data indicated that there is a single class of binding sites between AO6 and HSA, and the alterations of HSA secondary structure in the presence of AO6 was confirmed by synchronous fluorescence, UV, CD, FT-IR and three-dimensional fluorescence spectra. The efficiency of fluorescence resonance energy transfer provided the binding distance (r) of 2.83 nm for AO6-HSA system. Furthermore, the thermodynamic parameters enthalpy change (ΔH⁰) and entropy change (ΔS⁰) for the reaction were calculated to be −5.77 kJ mol⁻¹ and 109.42 J mol⁻¹ K⁻¹, respectively, according to Van't Hoff equation, these data suggested that both hydrophobic forces and hydrogen bonding play a major role in the binding of AO6 to HSA, which agrees well with the results of molecular modeling study. Experimental results showed that the interaction between AO6 and HSA induced a conformational change of HSA, which was proved by the qualitative and quantitative analysis data of different spectroscopic techniques under simulative physiological conditions.     

Interaction of the docetaxel with human serum albumin using optical spectroscopy methods

Docetaxel is a semi-synthetic product derived from the needles of the European yew. It is an antineoplastic agent belonging to the taxoid family. The interaction between docetaxel and human serum albumin (HSA) has been investigated systematically by the fluorescence quenching technique, synchronous fluorescence spectroscopy, ultraviolet (UV)-vis absorption spectroscopy, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) under physiological conditions. Our fluorescence data showed that HSA had only one docetaxel binding site and the binding process was a static quenching procedure. According to the Van’t Hoff equation, the thermodynamic parameters standard enthalpy (ΔH⁰) and standard entropy (ΔS⁰) were calculated to be −41.07 KJ mol⁻¹ and −49.72 J mol⁻¹ K⁻¹. These results suggested that hydrogen bond was the predominant intermolecular force stabling the docetaxel-HSA complex. The data from the CD, FT-IR and UV-vis spectroscopy supported the change in the secondary structure of protein caused by the interaction of docetaxel with HSA.     

Spectroscopic studies on the interaction and sonodynamic damage of neutral red (NR) to bovine serum albumin (BSA)

In this paper, the interaction of neutral red (NR) with bovine serum albumin (BSA) and the sonodynamic damage to BSA under ultrasonic irradiation was studied by means of ultraviolet-visible (UV-vis) and fluorescence spectra. The quenching constant (K_SV=5.749×10⁴ L/mol), binding constant (K_A=3.19×10⁴ L/mol) and binding site number (n=0.9462) were measured. The binding distance (r=2.47 nm) between NR and BSA was obtained according to Föster’s non-radiative energy transfer theory. The damage process of BSA molecules was detected by the hyperchromic effect of UV-vis spectra and quenching of intrinsic fluorescence spectra. In addition, the influencing factors such as ultrasonic irradiation time and NR concentration on the damage to BSA molecules were also considered. The results showed that the damage degree is enhanced with the increase of ultrasonic irradiation time and NR concentration. The possible mechanism of sonodynamic damage to BSA molecules was mainly mediated by singlet oxygen (¹O₂). Otherwise, the binding and damaging sites to BSA molecules were also estimated by synchronous fluorescence. The results indicated that the NR is more vicinal to tryptophan (Trp) residue than to tyrosine (Tyr) residue and the damage site is also mainly at Trp residues. The research result will bring a certain significance to use sonosensitive drugs in the fields of tumor treatment.     

Study of interaction of butyl p-hydroxybenzoate with human serum albumin by molecular modeling and multi-spectroscopic method

Study of the interaction between butyl p-hydroxybenzoate (butoben) and human serum albumin (HSA) has been performed by molecular modeling and multi-spectroscopic method. The interaction mechanism was predicted through molecular modeling first, then the binding parameters were confirmed using a series of spectroscopic methods, including fluorescence spectroscopy, UV-visible absorbance spectroscopy, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The thermodynamic parameters of the reaction, standard enthalpy ΔH⁰ and entropy ΔS⁰, have been calculated to be −29.52 kJ mol⁻¹ and −24.23 J mol⁻¹ K⁻¹, respectively, according to the Van’t Hoff equation, which suggests the van der Waals force and hydrogen bonds are the predominant intermolecular forces in stabilizing the butoben-HSA complex. Results obtained by spectroscopic methods are consistent with that of the molecular modeling study. In addition, alteration of secondary structure of HSA in the presence of butoben was evaluated using the data obtained from UV-visible absorbance, CD and FT-IR spectroscopies.     

Spectroscopic and voltammetric characterizations of the interaction of two local anesthetics with bovine serum albumin

The interactions of bovine serum albumin (BSA) with two local anesthetics, procaine hydrochloride (PCH) and tetracaine hydrochloride (TCH) were studied using spectroscopic methods such as fluorescence and ultraviolet visible (UV-vis), and electrochemical techniques including cyclic voltammetry (CV) and differential pulsed stripping voltammetry (DPSV). The results obtained from these techniques turned out that both PCH and TCH could bind to BSA. The binding constants (K_A) and the number of binding sites (n) of the two drugs with BSA at different temperatures were determined, respectively. At 291 K, K_A was found as 2.40×10⁴ and 1.42×10⁴ L mol⁻¹ and n was 1.03 and 0.99 for PCH-BSA and TCH-BSA, respectively. According to van’t Hoff equation, the thermodynamic parameters, ΔG, ΔH and ΔS, were obtained, showing the involvement of hydrophobic and electrostatic force in these interactions. Based on the theory of the Förster energy transference, the distance between the acceptor (PCH or TCH) and the donor (BSA) were determined as 2.32 and 3.62 nm for PCH and TCH, respectively. The effects of Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺ and Ca²⁺ on the binding of PCH or TCH to BSA were also evaluated.