Spectroscopic analysis on structure–affinity relationship in the interactions of different oleanane‐type triterpenoids with bovine serum albumin

Oleanane‐type triterpenoids serve as an important group of plant secondary metabolites with a variety of biological activities and the C‐3 position substitution pattern is a significant structural feature for their biological activities. Three selected oleanane‐type triterpenoids (glycyrrhizin, glycyrrhetinic acid, and carbenoxolone) bearing different substituents (glucuronic acid dimer, hydroxyl, and succinyl groups) at the C‐3 position were studied for their affinities to bind bovine serum albumin (BSA) by steady‐state fluorescence, synchronous, three‐dimensional fluorescence and ultraviolet–visible (UV–vis) absorption spectra. The binding mechanism of the triterpenoids to BSA is due to the formation of the triterpenoids–BSA complex and the binding affinity is strongest for carbenoxolone and ranked in the order carbenoxolone > glycyrrhetinic acid > glycyrrhizin. The thermodynamic parameters calculated at different temperatures showed that triterpenoids binding to BSA primarily depended on hydrophobic interaction and hydrogen bonding. The distance between the bound triterpenoid and BSA was determined on the basis of the Förster's energy transfer theory. Displacement experiments using phenylbutazone and ibuprofen showed the binding site of triterpenoids on BSA at subdomain IIA (Sudlow's site I). The effect of triterpenoids on BSA conformation was analyzed by UV–vis absorption, and synchronous and three‐dimensional fluorescence spectra. These results revealed that the C‐3 position substitution pattern significantly affects the structure–affinity relationships of oleanane‐type triterpenoid binding to BSA and further affects the bioavailability of triterpenoids in the blood circulatory system. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of Cu2+ on interaction between flavonoids with different C-ring substituents and bovine serum albumin: structure-affinity relationship aspect

Four flavonoids quercetin (QU), luteolin (LU), taxifolin (TA) and (+)-catechin (CA) with the same A- and B-rings but different C-ring substituents have been investigated for their binding to bovine serum albumin (BSA) in the absence and presence of Cu²⁺ by means of various spectroscopic methods such as fluorescence, UV-visible and circular dichroism (CD). The results indicated that hydroxyl group at 3-position increased the binding affinities between flavonoids and BSA. The values of the binding affinities were in the order: QU > CA > TA > LU. The presence of Cu²⁺ affected the interactions of flavonoids with BSA significantly. The binding affinities of QU and TA for BSA were decreased about 6.7% and 13.2%. However, the binding affinities of LU and CA for BSA were increased about 43.0% and 20.7%. The formation of Cu²⁺-flavonoid complex and steric hindrance together influenced the binding affinities of QU, LU and TA for BSA, while the conformational change of BSA may be the main reason for the increased binding affinity of CA for BSA. However, the quenching mechanism for QU, LU, TA and CA to BSA was based on static quenching combined with non-radiative energy transfer irrespective of the absence or presence of Cu²⁺. The UV-visible results showed the change in BSA conformation and the formation of flavonoid-Cu²⁺ complex. The CD results also explained the conformational changes of BSA on binding with flavonoids.     

Investigations of interaction mechanism and conformational variation of serum albumin affected by artemisinin and dihydroartemisinin

In this work, binding interactions of artemisinin (ART) and dihydroartemisinin (DHA) with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated thoroughly to illustrate the conformational variation of serum albumin. Experimental results indicated that ART and DHA bound strongly with the site I of serum albumins via hydrogen bond (H-bond) and van der Waals force and subsequently statically quenched the intrinsic fluorescence of serum albumins through concentration-dependent manner. The quenching abilities of two drugs on the intrinsic fluorescence of HSA were much higher than the quenching abilities of two drugs on the intrinsic fluorescence of BSA. Both ART and DHA, especially DHA, caused the conformational variation of serum albumins and reduced the α-helix structure content of serum albumins. DHA with hydrophilic hydroxyl group bound with HSA more strongly, suggesting the important roles of the chemical polarity and the hydrophilicity during the binding interactions of two drugs with serum albumins. These results reveal the molecular understanding of binding interactions between ART derivatives and serum albumins, providing vital information for the future application of ART derivatives in biological and clinical areas.     

Exogenous genistein in late gestation: effects on fetal development and sow and piglet performance

Due to their functional similarity to estradiol, phytoestrogens could prove to be beneficial in late gestating sows. The goal of this study was to determine the impact of providing the phytoestrogen genistein during late pregnancy on the performance of sows and their litters. In total, 56 gilts were equally divided into the two following groups on day 90 of gestation: (1) controls (CTL); and (2) two daily i.m. injections of 220 mg of genistein (GEN). Treatments were carried out until farrowing. Jugular blood samples were collected from 16 gilts/treatment on days 89 and 110 of gestation, and on days 3 and 21 of lactation. Milk samples were also obtained from those sows on day 3 of lactation. A male piglet from 16 CTL and 15 GEN litters was slaughtered at 24 h postpartum and a blood sample was obtained. The liver, heart and visceral organs were weighed and the semitendinosus (ST) muscle was collected and carcass composition was determined. The treatment increased (P<0.05) the concentrations of genistein and daidzein in the plasma of gilts on day 110 of gestation and of genistein in the plasma of piglets at 24 h postpartum. It also increased IGF1 concentrations in gilts at the end of the treatment period (P<0.05). Genistein had no impact (P>0.1) on weight or backfat loss of sows during lactation, milk composition or weights of piglets. The pre-weaning mortality rate of piglets was very low (<7%), yet the odds ratio comparing CTL with GEN sows indicated almost twice as many chances of pre-weaning deaths occurring in litters from CTL than GEN sows. Weights of the piglet carcasses were similar for both treatments, as well as weights of the various organs and of the ST muscle (P>0.1). However, carcasses from GEN litters contained more fat than those from CTL litters (9.63% v. 8.34%, P<0.05). None of the biochemical properties of the ST muscle differed between groups (P>0.1). In conclusion, injecting gilts with 440 mg/day of genistein in late gestation increased IGF1 concentrations in gilts and carcass fat in neonatal piglets, but had minimal effect on muscle development of piglets at birth and on the performance of lactating sows and their litters.     

Spectroscopy and molecular docking study on the interaction of daidzein and genistein with pepsin

The interaction of pepsin with daidzein (Dai) or genistein (Gen) was investigated using spectroscopic techniques under simulated physiological conditions. Dai and Gen can quench the fluorescence of pepsin and the quenching mechanism was a static process. The binding site number n and apparent binding constant K were measured at different temperatures. The thermodynamic parameters ΔΗ, ΔG and ΔS were calculated. The results indicated that van der Waals forces and hydrogen bond formation played major roles in the interaction of Dai or Gen with pepsin. The binding distance between pepsin and Dai or Gen was calculated according to energy transfer theory. The results of synchronous fluorescence spectra showed that the microenvironment and conformation of pepsin were changed. UV absorption and 3D fluorescence spectra showed that the binding interaction disturbed the microenvironment of amino acid residues and induced conformational changes in pepsin. Molecular docking results showed that Dai and Gen entered into the hydrophobic cavity of pepsin and two hydrogen bonds formed between Dai or Gen and pepsin. The results demonstrated that the interaction behavior between Dai and Gen with pepsin was slightly different, which denoted that the 5‐hydroxyl group of Gen, to a certain extent, had an effect on ligand binding to proteins. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental,computational and chemometrics studies of BSA-vitamin B6 interaction by UV–Vis,FT-IR,fluorescence spectroscopy,molecular dynamics simulation and hard-soft modeling methods

The interaction of pyridoxine (Vitamin B6) with bovine serum albumin (BSA) is investigated under pseudo-physiological conditions by UV–Vis, fluorescence and FTIR spectroscopy. The intrinsic fluorescence of BSA was quenched by VB6, which was rationalized in terms of the static quenching mechanism. According to fluorescence quenching calculations, the bimolecular quenching constant (k_q), dynamic quenching (K_SV) and static quenching (K_LB) at 310 K were obtained. The efficiency of energy transfer and the distance between the donor (BSA) and the acceptor (VB6) were calculated by Foster’s non-radiative energy transfer theory and were equal to 41.1% and 2.11 nm.The collected UV–Vis and fluorescence spectra were combined into a row-and column-wise augmented matrix and resolved by multivariate curve resolution-alternating least squares (MCR-ALS). MCR-ALS helped to estimate the stoichiometry of interactions, concentration profiles and pure spectra for three species (BSA, VB6 and VB6-BSA complex) existed in the interaction procedure. Based on the MCR-ALS results, using mass balance equations, a model was developed and binding constant of complex was calculated using non-linear least squares curve fitting. FT-IR spectra showed that the conformation of proteins was altered in presence of VB6. Finally, the combined docking and molecular dynamics (MD) simulations were used to estimate the binding affinity of VB6 to BSA. Five-nanosecond MD simulations were performed on bovine serum albumin (BSA) to study the conformational features of its ligand binding site. From MD results, eleven BSA snapshots were extracted, at every 0.5 ns, to explore the binding affinity (GOLD score) of VB6 using a docking procedure. MD simulations indicated that there is a considerable flexibility in the structure of protein that affected ligand recognition. Structural analyses and docking simulations indicated that VB6 binds to site I and GOLD score values depend on the conformations of both BSA and ligand. Molecular modeling results showed that VB6–BSA complex formed not only on the basis of electrostatic forces, but also on the basis of π–π staking and hydrogen bond. There was an excellent agreement between the experimental and computational results. The results presented in this paper, will offer a reference for detailed and systematic studies on the biological effects and action mechanism of small molecules with proteins.     

Modulation of DNA intercalation by resveratrol and genistein

Time correlated Single Photon Counting study (TCSPC) was performed for the first time to evaluate the effect of resveratrol (RES) and genistein (GEN) at 10–100 μM and 10–150 μM respectively, in modulating the DNA conformation and the variation induced due to intercalation by the dyes, ethidium bromide (EtBr) and acridine orange (AO). It is demonstrated using UV-absorption and fluorescence spectroscopy that RES and GEN, at 50 μM and 100 μM respectively can bind to DNA resulting in significant de-intercalation of the dyes, preventing their further intercalation within DNA. Hyperchromicity with red/blue shifts in DNA when bound to dyes was reduced upon addition of RES and GEN. DNA-dependent fluorescence of EtBr and AO was quenched in the presence of RES by 87.97% and 79.13% respectively, while similar quenching effect was observed for these when interacted with GEN (85.52% and 83.85%). It is found from TCSPC analysis that the higher lifetime component or constituent of intercalated dyes (τ₂, A ₂) decreased with the subsequent increase in smaller component or constituent of free dye (τ₁, A ₁) after the interaction of drugs with the intercalated DNA. Thus these findings signify that RES and GEN can play an important role in modulating DNA intercalation, leading to the reduction in DNA-directed toxicity.     

Differential binding of tetracyclines with serum albumin and induced structural alterations in drug-bound protein

Interaction of tetracycline (TC) derivatives viz. oxytetracycline, doxycycline, demeclocycline and chlorotetracycline with bovine serum albumin (BSA) and concomitant changes in protein conformation were studied using fluorescence quenching and circular dichroism measurements. Fluorescence data revealed the presence of one to three binding sites on BSA for different TC derivatives. Binding studies with the marker ligands, warfarin and bilirubin, elucidated site-I as a primary binding site for TCs on albumin. Scatchard analysis revealed the binding affinity (K_a) and capacity (n) for these derivatives vary in the range from 0.8 to 3.2×10⁶ l/mole and 1.3–3.4, respectively. Significant reduction (60–45%) in secondary structure (-helical content) of BSA was noticed upon interaction with different TC derivatives in presence of Cu (II) ions. High affinity binding of TCs with BSA signifies drug stability. However, excessive binding at higher TC concentrations in combination with Cu (II) induces conformational change in protein structure, which may exert detrimental effect on cellular protein.     

Study of the interaction between 8-azaguanine and bovine serum albumin using optical spectroscopy and molecular modeling methods

The interaction between 8-azaguanine (8-Azan) and bovine serum albumin (BSA) in Tris-HCl buffer solutions at pH 7.4 was investigated by means of fluorescence and ultraviolet-visible (UV-Vis) spectroscopy. At 298 K and 310 K, at a wavelength of excitation (λ _ex) of 282 nm, the fluorescence intensity decreased significantly with increasing concentrations of 8-Azan. Fluorescence static quenching was observed for BSA, which was attributed to the formation of a complex between 8-Azan and BSA during the binding reaction. This was illuminated further by the UV-Vis absorption spectra and the decomposition of the fluorescence spectra. The thermodynamic parameters ∆G, ∆H, ∆S were calculated. The results showed that the forces acting between 8-Azan and BSA were typical hydrophobic forces, and that the interaction process was spontaneous. The interaction distance r between 8-Azan and BSA, evaluated according to fluorescence resonance energy transfer theory, suggested that there is a high possibility of energy transfer from BSA to 8-Azan. Theoretical investigations based on homology modeling and molecular docking suggested that binding between 8-Azan and BSA is dominated by hydrophilic forces and hydrogen bonding. The theoretical investigations provided a good structural basis to explain the phenomenon of fluorescence quenching between 8-Azan and BSA.     

Different spectroscopic and molecular modeling studies on the interaction between cyanidin‐3‐O‐glucoside and bovine serum albumin

Anthocyanin is one of the flavonoid phytopigments that shows strong antioxidant activity. The cyanidin‐3‐O‐glucoside (C3G) is one of the principal types of anthocyanins. To understand the interaction between C3G and bovine serum albumin (BSA), fluorescence spectroscopy, ultraviolet–visible absorption, Fourier transform infrared spectroscopy, circular dichroism and molecular modeling techniques were used. Binding constant (K_a) and the number of binding sites (n) were calculated. The quenching mechanism of fluorescence of BSA by C3G was discussed. The results studied by Fourier transform infrared spectroscopy and circular dichroism experiments indicate that the secondary structures of the protein have been changed by the interaction of C3G with BSA. The result of molecular modeling confirmed that the C3G bound to the site I (sub‐domain IIA) of BSA, and that the hydroxyl groups in the B ring of C3G took part in the binding with BSA. Copyright © 2013 John Wiley & Sons, Ltd.     

Combined experimental/computational aspects for the molecular interaction of empagliflozin with bovine serum albumin: Quantification and application to human plasma

Empagliflozin (EMP) is an oral antihyperglycemic agent for type 2 diabetic patients. The molecular binding of EMP to bovine serum albumin (BSA) was elucidated by a combined experimental/computational approach to fulfil the pharmacokinetics and pharmacodynamics gaps of the cited drug for further development. Fluorescence, synchronous, and three-dimensional fluorescence spectroscopy verified that EMP quenched BSA native fluorescence through a dual static/dynamic mechanism that was further supported by Fӧrster resonance energy transfer and ultraviolet absorption spectroscopy. Fourier transform infrared spectroscopy revealed the conformational variations in BSA secondary structure induced by EMP. Thermodynamic properties of the BSA–EMP complex were also investigated, and the hydrophobic interactions' role in the binding process was demonstrated by the computed enthalpy (ΔH = 6.558 kJ mol⁻¹) and entropy (ΔS = 69.333 J mol⁻¹ K⁻¹). Gibbs free energy (ΔG) values were negative at three distinct temperatures, illuminating the spontaneity of this interaction. In addition, molecular docking studies depicted the optimal fitting of EMP to BSA on Site I (sub-domain IIA) through three hydrogen bonds. Additionally, and based on the quenching effect of EMP on BSA fluorescence, this study suggests a simple validated spectrofluorometric method for the quantitation of the studied drug in bulk form and human plasma samples with reasonable recoveries (96.99–103.10%).     

Contributions of active site residues to cofactor binding and catalysis of 3α-hydroxysteroid dehydrogenase/carbonyl reductase

3α-Hydroxysteroid dehydrogenase/carbonyl reductase reversely catalyzes the oxidation of androsterone with NAD⁺ to form androstanedione and NADH. In this study, we investigated the function of active site residues N86, Y155, and K159 in NADH binding and catalysis in the reduction of androstanedione, using site-directed mutagenesis, steady-state kinetics, fluorescence quenching, and anisotropy measurements. The N86A, Y155F, and K159A mutant enzymes decreased the catalytic constant by 37- to 220-fold and increased the dissociation constant by 3- to 75-fold, respectively. Binding of NADH with wild-type and mutant enzymes caused different levels of fluorescence resonance energy transfer, implying a different orientation of nicotinamide ring versus W173. In addition, the enzyme-bound NADH decreased the fluorescence anisotropy value in the order WT > N86A > Y155F > K159A, indicating an increase in the mobility of the bound NADH for the mutants. Data suggest that hydrogen bonding with the hydroxyl group of nicotinamide ribose by K159 and Y155 is important to maintain the orientation of NADH and contributes greatly to the transition-state binding energy to facilitate the catalysis. N86 is important for stabilizing the position of K159. Substitution of alanine for N86 has a minor effect on NADH binding through K159, resulting in a slight increase in the mobility of the bound NADH and decreases in affinity and catalytic constant.     

Determination of the specific interaction between palmatine and bovine serum albumin

The binding of palmatine to bovine serum albumin (BSA) was studied under physiological conditions (pH = 7.40) by molecular spectroscopic approach. It was proved that the fluorescence quenching of BSA by palmatine is a result of the formation of palmatine–BSA complex. Binding parameters were determined using the modified Stern–Volmer equation and Scatchard equation, to measure the specific binding between palmatine and BSA. The thermodynamic parameters calculated, ∆G°, ∆H° and ∆S° indicate that the electrostatic interactions play a major role in the palmatine–BSA association. Site marker competitive displacement experiments demonstrated that palmatine binds with specific affinity to site II (subdomain IIIA) of BSA. Furthermore, the specific binding distance r (3.36 nm) was obtained according to fluorescence resonance energy transfer. The results of synchronous fluorescence spectra and UV–Visible absorption spectra show that the conformation of bovine serum albumin has been changed.     

New insight into the stereoselective interactions of quinine and quinidine,with bovine serum albumin

Quinine (QN) and quinidine (QD), the chief quinoline alkaloids of various species of cinchona bark, are stereoisomers to each other. In this study, a series of appropriate and efficient methods have been applied to compare the binding modes of QN and QD with bovine serum albumin (BSA). The isothermal titration calorimetry and room temperature phosphorescence results show that both QN and QD can interact with BSA at one binding site to form drug–protein complexes, mainly through enthalpic driving force with the binding affinity order: QN > QD. The fluorescence resonance energy transfer and time‐resolved fluorescence spectroscopy exhibits that QN has a larger energy transfer and more intensified binding capacity for BSA than QD. Data of dynamic light scattering reveal that the aggregate state of BSA is changed during this binding process, and the particle size distribution of QN‐BSA bioconjugate is larger than that of QD. Nuclear magnetic resonance analysis indicates that aromatic protons make more contribution during ligand‐protein complexation than that of aliphatic protons. The circular dichroism spectra exhibit different degrees of changes in BSA secondary structures in the presence of QN and QD, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic insight into the interaction of bovine serum albumin with imidazolium‐based ionic liquids in aqueous solution

The study of protein–ionic liquid interactions is very important because of the widespread use of ionic liquids as protein stabilizer in the recent years. In this work, the interaction of bovine serum albumin (BSA) with different imidazolium‐based ionic liquids (ILs) such as [1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate (EmimESO₄), 1‐ethyl‐3‐methyl‐imidazolium chloride (EmimCl) and 1‐butyl‐3‐methyl‐imidazolium chloride (BmimCl)] has been investigated using different spectroscopic techniques. The intrinsic fluorescence of BSA is quenched by ILs by the dynamic mechanism. The thermodynamic analysis demonstrates that very weak interactions exist between BSA and ILs. 8‐Anilino‐1‐naphthalenesulfonic acid (ANS) fluorescence and lifetime measurements reveal the formation of the compact structure of BSA in IL medium. The conformational changes of BSA were monitored by CD analysis. Temperature‐dependent ultraviolet (UV) measurements were done to study the thermal stability of BSA. The thermal stability of BSA in the presence of ILs follows the trend EmimESO₄ > EmimCl > BmimCl and in the presence of more hydrophobic IL, destabilization increases rapidly as a function of concentration.     

Quasi‐spherical silver nanoparticles with high dispersity and uniform sizes: preparation,characterization and bioactivity in their interaction with bovine serum albumin

A stepwise seeded growth route for the preparation of silver nanoparticles (AgNPs) is reported. In the process, silver nitrate was used as a precursor, with sodium borohydride as a reducing agent and trisodium citrate as both a reductant and stabilizer. The AgNPs were characterized using several methods, including UV–vis spectroscopy, X‐ray diffraction and transmission electron microscopy. The prepared AgNPs were quasi‐spherical and crystalline, with an average diameter of 21 nm. Interactions between the AgNPs and bovine serum albumin (BSA) were investigated using UV–vis, fluorescence spectroscopy and synchronous fluorescence spectroscopy (SFS). It was proved that the quenching mechanism is a static process. The binding constants and number of binding sites were calculated. The thermodynamic parameters implied that the binding process was spontaneous and the main driving force of the interaction was electrostatic. The results of the SFS indicated that the conformational change of BSA was induced by AgNPs. Copyright © 2016 John Wiley & Sons, Ltd.     

Studies on the interaction between benzophenone and bovine serum albumin by spectroscopic methods

The interaction between benzophenone (BP) and bovine serum albumin (BSA) was investigated by the methods of fluorescence spectroscopy combined with UV–Vis absorption and circular dichroism (CD) measurements under simulative physiological conditions. The experiment results showed that the fluorescence quenching of BSA by BP was resulted from the formation of a BP–BSA complex and the corresponding association constants (K _a) between BP and BSA at four different temperatures had been determined using the modified Stern–Volmer equation. The enthalpy change (ΔH) and entropy change (ΔS) were calculated to be –43.73 kJ mol⁻¹ and −53.05 J mol⁻¹ K⁻¹, respectively, which suggested that hydrogen bond and van der Waals force played major roles in stabilizing the BP–BSA complex. Site marker competitive experiments indicated that the binding of BP to BSA primarily took place in site I (sub-domain IIA). The conformational investigation showed that the presence of BP decreased the α-helical content of BSA and induced the slight unfolding of the polypeptides of protein, which confirmed some micro-environmental and conformational changes of BSA molecules.     

Binding of teicoplanin and vancomycin to bovine serum albumin in vitro: a multispectroscopic approach and molecular modeling

In this paper, the binding properties of teicoplanin and vancomycin to bovine serum albumin (BSA) were investigated using fluorescence quenching, synchronous fluorescence, Fourier transform infrared (FTIR), circular dichroism (CD) and UV–vis spectroscopic techniques and molecular docking under simulative physiological conditions. The results obtained from fluorescence quenching data revealed that the drug–BSA interaction altered the conformational structure of BSA. Meanwhile, the 3D fluorescence, CD, FTIR and UV–vis data demonstrated that the conformation of BSA was slightly altered in the presence of teicoplanin and vancomycin, with different reduced α‐helical contents. The binding distances for the drug–BSA system were provided by the efficiency of fluorescence resonance energy transfer (FRET). Furthermore, the thermodynamic analysis implied that hydrogen bond and van der Waals' forces were the main interaction for the drug–BSA systems, which agreed well with the results from the molecular modeling study. The results obtained herein will be of biological significance in future toxicological and pharmacological investigation. Copyright © 2013 John Wiley & Sons, Ltd.     

The investigation of the interaction between ribavirin and bovine serum albumin by spectroscopic methods

The interaction between ribavirin (RIB) with bovine serum albumin (BSA) has been investigated by fluorescence quenching technique in combination with UV–vis absorption and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The quenching of BSA fluorescence by RIB was found to be a result of the formation of RIB–BSA complex. The binding constants and the number of binding sites were calculated at three different temperatures. The values of thermodynamic parameters ?H, ?S, ?G at different temperatures indicate that hydrophobic and hydrogen bonds played important roles for RIB–BSA association. The binding distance r was obtained according to the theory of FÖrster’s non–radiation energy transfer. The displacement experiments was performed for identifying the location of the binding site of RIB on BSA. The effects of common ions on the binding constant of RIB and BSA were also examined. Finally, the conformational changes of BSA in the presence of RIB were also analyzed by CD spectra and Synchronous fluorescence spectra.     

Synthesis and interaction of bovine serum albumin with p‐hydroxybenzoic acid derivatives

Three novel p‐hydroxybenzoic acid derivatives (HSOP, HSOX, HSCP) were synthesized from p‐hydroxybenzoic acid and sulfonamides (sulfamonomethoxine sodium, sulfamethoxazole and sulfachloropyridazine sodium) and characterized by elemental analysis, HNMR and MS. Interactions between derivatives and bovine serum albumin (BSA) were studied by fluorescence quenching spectra, UV–vis absorption spectra and time‐resolved fluorescence spectra. Based on fluorescence quenching calculation and Förster's non‐radioactive energy transfer theory, the values of the binding constants, basic thermodynamic parameters and binding distances were obtained. Experimental results indicated that the three derivatives had a strong ability to quench fluorescence from BSA and that the binding reactions of the derivatives with BSA were a static quenching process. Thermodynamic parameters showed that binding reactions were spontaneous and exothermic and hydrogen bond and van der Waals force were predominant intermolecular forces between the derivatives and BSA. Synchronous fluorescence spectra suggested that HSOX and HSCP had little effect on the microenvironment and conformation of BSA in the binding reactions but the microenvironments around tyrosine residues were disturbed and polarity around tyrosine residues increased in the presence of HSOP. Copyright © 2012 John Wiley & Sons, Ltd.