Fluorescence Intensity Of Bovine Serum Albumin Research Articles

The Inhibition Mechanisms of Three Structurally Different Salvianolic Acids on the Non-Enzymatic Glycation of Bovine Serum Albumin.

The antiglycation mechanisms of three structurally different salvianolic acids (Sals) including salvianolic acid A (Sal-A), salvianolic acid B (Sal-B) and salvianolic acid C (Sal-C) were investigated using the bovine serum albumin (BSA)-fructose model. The results showed that the three compounds could inhibit the formation of glycation products, maintain protein structural stability, mitigate the development of amyloid fibrils and scavenge radicals. Notably, Sal-A possessed the highest anti-glycated activity compared with Sal-B and Sal-C. This may be related to the fact that Sal-A contained the most molecules of caffeic acid (Sal-A, Sal-B, and Sal-C possessing two, one, and zero caffeic acid units, respectively), and caffeic acid played a leading role in the antiglycation properties relative to Danshensu. Moreover, these compounds quenched the intrinsic fluorescence intensity of BSA in a static mode, with the binding constants in the order of Sal-A > Sal-B > Sal-C. Obviously, Sal-A possessed the strongest binding affinity among these compounds, which may be one of the reasons why it exhibited the optimal antiglycation capability. Furthermore, molecular docking demonstrated that the three Sals exerted protective effects on BSA by preventing glycation modification of lysine and arginine residues. These findings would provide valuable insights into the potential application of Sals for alleviating non-enzymatic glycation of protein.

Probing binding mode between sodium acid pyrophosphate and albumin: multi-spectroscopic and molecular docking analysis

Sodium acid pyrophosphate (SAPP) food additive is widely used as a preservative, bulking agent, chelating agent, emulsifier and pH regulator. It is also used as an improver of color and water retention capacity in the processing of various types of seafood, canned food, cooked meat and flour products. For the first time, we evaluated the SAPP interaction with bovine serum albumin (BSA) using spectroscopic methods including UV-Vis absorption, fluorescence spectroscopy, and surface plasmon resonance, and docking analysis to understand the mechanisms of complex formation and binding. The fluorescence intensity of BSA reduces when titrated with various concentrations of SAPP by forming a complex with BSA via a static quenching mechanism. The binding constant between BSA and SAPP decreased from 123,300 to 15,800 (M−1) with rising temperature, which indicates a decrement in complex formation owing to the interaction of SAPP with BSA. A negative ΔG° value means that SAPP binds spontaneously to BSA at all temperatures, and both ΔH° and ΔS° negative values indicate that hydrogen bonds (H-bonding) and van der Waals forces are the primary forces involved in the binding processes. The UV-Vis spectrum of BSA reduced upon increasing SAPP concentrations due to forming a new ground state complex between SAPP and BSA. Molecular docking study shows that residues Arg256, Ser259, Ser286, Ile 289 and Ala 290 play an important role in SAPP binding process to site I (subdomain IIA) of BSA through H-bonding and van der Waals forces, which is supported by the thermodynamic study. Communicated by Ramaswamy H. Sarma

Probing the interaction of uranyl(VI) complex with bovine serum albumin via in-depth experimental and computational perspectives

Interaction aspects of uranyl(VI) complexes as well as the coordinated ONNO-donor ligand with bovine serum albumin (BSA) were investigated by the fluorescence spectroscopy and computational insights. Under optimal physiological condition, it was observed that there was significant decrease in fluorescence intensity of BSA upon interaction with uranyl(VI) complexes as well as the ligand. The mechanism of interaction between the uranyl(VI) complex and BSA protein was examined by fluorescence measurement. The Stern-Volmer constant, binding affinity, binding constant, standard free energy, and fluorescence lifetime decay profile of BSA in the absence as well as in the presence of uranyl(VI) complex were determined. Furthermore, the conformational binding of uranyl(VI) complexes with BSA protein was explored via molecular docking studies, and confirmed that there is a strong affinity between the Trp-213 residue in the binding pocket of sub-domain IIA and uranyl(VI) complex.

Molecular spectroscopic and docking analysis of the interaction of fluorescent thiadicarbocyanine dye with biomolecule bovine serum albumin

Binding studies of the water-soluble thiadicarbocyanine dye 3,3’-diethylthiadicarbocyanine acetate (DTC) with bovine serum albumin (BSA) were examined under physiological conditions using spectroscopic techniques like fluorescence, UV-Visible, circular dichroism (CD), FT-IR and molecular docking methods. Compiled experimental results envisage that DTC quench the fluorescence intensity of BSA. The increasing binding constants (K) were found to be in the order of 103 Mol−1 as a function of temperature, as calculated from the fluorescence quenching data. The quenching mechanism, thermodynamic parameters (ΔH0, ΔS0 and ΔG0) and the number of binding sites have been explored. CD values showed that the secondary structure of the BSA has been altered upon binding to DTC. Displacement experiments were carried out with different site probes to find out the binding site of DTC on BSA and it was found that binding interaction at site II of sub-domain IIIA. The interference of common metal ions on the interaction of DTC with BSA has also been studied. The experimental data exhibit that DTC interacts with BSA by hydrophobic forces. The experimental findings from BSA binding studies were validated by using in silico molecular docking technique. The results of the investigations were accurately supported by studies on molecular docking. The optimal shape of the molecular probe demonstrated the affinity as a free binding energy release of −7.37 Kcal/mol. The present research report endeavors to the approachable nature of water-soluble DTC dye and paves way for targeted biological interactions. Communicated by Ramaswamy H. Sarma

Effect of glycation of bovine serum albumin on the interaction with xanthine oxidase inhibitor allopurinol: Spectroscopic studies and molecular modeling

Serum albumin is glycated in diabetic or hyperglycemic conditions. For in vitro experiments bovine serum albumin (BSA) is employed as a transport protein. So, in this work, we aim to study the impact of monosaccharide mediated glycation of BSA (gBSA) on the binding of allopurinol. The glycation causes a reduction in the fluorescence intensity of BSA. The Ksv and kb values calculated using the Stern-Volmer and binding plots were lower for glycated BSA in comparison to native BSA. The structural changes in native and glycated BSA after interaction with allopurinol were studied using fluorescence, UV–Visible, CD, FTIR, 3D and synchronous fluorescence. The molecular docking study reveals that glucose, fructose, and allopurinol bind to common sites, which explains the lower affinity of glycated BSA for allopurinol.

Spectroscopic analysis to identify the binding site for Rifampicin on Bovine Serum Albumin

This article reports the interaction of rifampicin, one of the important antituberculosis drugs, with Bovine Serum Albumin (BSA). Herein, we have monitored the fluorescence properties of tryptophan (Trp) residue in BSA to understand the interactions between protein and rifampicin. Fluorescence intensity of BSA was quenched tremendously upon interacting with the drug. Using steady state and time-resolved spectroscopic tools the static and dynamic nature of quenching have been characterised. Time correlated single photon counting technique confirmed that out of two lifetime components ∼6.2 ns and ∼2.8 ns of BSA, the rifampicin has affected only the shorter lifetime component a lot that was assigned to Trp-213 residue. Hence, it was thought that the drug must have been located near to the amino acid residue. Molecular docking studies have revealed the structural information of drug-protein complex which supported the above conjecture, confirming the nearest tryptophan as Trp-213 to the complexing rifampicin molecule.

Increasing the bioactivity of kynurenine by ultraviolet irradiation via resonance energy transfer in vitro

Kynurenine (Kyn) is involved in a variety of physiological/pathological reactions via activating aryl hydrocarbon receptor (Ahr). However, how to activate Ahr by Kyn under physiological/pathological conditions is still unclear. Here, we presented that Kyn (8 μM, a concentration less than the dose of Kyn-induced Ahr activation) significantly induced the nuclear transfer of Ahr and the expression of cytochrome P450 1A1 (CYP1A1, a classic biomarker for Ahr activation) when co-administered with ultraviolet (UV) irradiation in 95D cells, which were transfected transiently with siRNA against indoleamine 2,3-dioxygenase 1 (IDO 1) and cultured in cell medium supplemented with bovine serum containing bovine serum albumin (BSA), in vitro. Additionally, we found that the fluorescence intensity of BSA was attenuated by Kyn (2, 4, 6, 8, 10, 12 and 14 μM) mainly through quenching the fluorescence of tryptophan (Trp) residues in the pattern of dynamic quenching related to molecular diffusion. More important, resonance energy transfer from excited-state BSA to Kyn was confirmed, leading to the generation “energetic” Kyn that might be ability of hyperactivity according to the theory of photochemical reaction. These data indicate that UV irradiation is contributable for Kyn to function, and present a novel pattern of altering the activity of biomolecules to some degree.

Alleviation of Ultrafiltration Membrane Fouling by ClO2 Pre-Oxidation: Fouling Mechanism and Interface Characteristics.

In order to alleviate membrane fouling and improve removal efficiency, a series of pretreatment technologies were applied to the ultrafiltration process. In this study, ClO2 was used as a pre-oxidation strategy for the ultrafiltration (UF) process. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were used as three typical organic model foulants, and the mixture of the three substances was used as a representation of simulated natural water. The dosages of ClO2 were 0.5, 1, 2, 4, and 8 mg/L, with 90 min pre-oxidation. The results showed that ClO2 pre-oxidation at low doses (1–2 mg/L) could alleviate the membrane flux decline caused by humus, polysaccharides, and simulated natural water, but had a limited alleviating effect on the irreversible resistance of the membrane. The interfacial free energy analysis showed that the interaction force between the membrane and the simulated natural water was also repulsive after the pre-oxidation, indicating that ClO2 pre-oxidation was an effective way to alleviate cake layer fouling by reducing the interaction between the foulant and the membrane. In addition, ClO2 oxidation activated the hidden functional groups in the raw water, resulting in an increase in the fluorescence value of humic analogs, but had a good removal effect on the fluorescence intensity of BSA. Furthermore, the membrane fouling fitting model showed that ClO2, at a low dose (1 mg/L), could change the mechanism of membrane fouling induced by simulated natural water from standard blocking and cake layer blocking to critical blocking. Overall, ClO2 pre-oxidation was an efficient pretreatment strategy for UF membrane fouling alleviation, especially for the fouling control of HA and SA at low dosages.

On the Effect of pH, Temperature, and Surfactant Structure on Bovine Serum Albumin-Cationic/Anionic/Nonionic Surfactants Interactions in Cacodylate Buffer-Fluorescence Quenching Studies Supported by UV Spectrophotometry and CD Spectroscopy.

Due to the fact that surfactant molecules are known to alter the structure (and consequently the function) of a protein, protein–surfactant interactions are very important in the biological, pharmaceutical, and cosmetic industries. Although there are numerous studies on the interactions of albumins with surfactants, the investigations are often performed at fixed environmental conditions and limited to separate surface-active agents and consequently do not present an appropriate comparison between their different types and structures. In the present paper, the interactions between selected cationic, anionic, and nonionic surfactants, namely hexadecylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene glycol sorbitan monolaurate, monopalmitate, and monooleate (TWEEN 20, TWEEN 40, and TWEEN 80, respectively) with bovine serum albumin (BSA) were studied qualitatively and quantitatively in an aqueous solution (10 mM cacodylate buffer; pH 5.0 and 7.0) by steady-state fluorescence spectroscopy supported by UV spectrophotometry and CD spectroscopy. Since in the case of all studied systems, the fluorescence intensity of BSA decreased regularly and significantly under the action of the surfactants added, the fluorescence quenching mechanism was analyzed thoroughly with the use of the Stern–Volmer equation (and its modification) and attributed to the formation of BSA–surfactant complexes. The binding efficiency and mode of interactions were evaluated among others by the determination, comparison, and discussion of the values of binding (association) constants of the newly formed complexes and the corresponding thermodynamic parameters (ΔG, ΔH, ΔS). Furthermore, the influence of the structure of the chosen surfactants (charge of hydrophilic head and length of hydrophobic chain) as well as different environmental conditions (pH, temperature) on the binding mode and the strength of the interaction has been investigated and elucidated.

Interactions of linagliptin, rabeprazole sodium, and their formed complex with bovine serum albumin: Computational docking and fluorescence spectroscopic methods.

The foremost aim of this thermodynamic study was to evaluate the pharmacokinetics (PK) and pharmacodynamics (PD) profiles of linagliptin (LG), rabeprazole sodium (RS), and their 1:1 formed complex by interacting with bovine serum albumin (BSA) at physiological pH 7.4. The molecular interactions of these ligands with the desired biomolecule were substantiated by the spectral quelling of fluorescence intensity of BSA. The fluorescent test and molecular docking revealed that the quenching mechanism was a spontaneous and exothermic static process, and the protein gained its secondary structure due to the interactions. The spectroscopic method was exercised to determine the thermodynamic factors that supported the interactions mediated by van der Waals forces and hydrogen bonds. The activation energy of the formed complex was higher than its precursor drugs while interacting with BSA, and the energy transformation profiles were studied by UV-fluorescence overlaid curves according to Förster resonance energy transfer (FRET) theory. The double log plot verified that these ligands bound with protein at a 1:1 ratio, which was confirmed by the approximately estimated values of the binding parameters. The drastically lower value of the binding constant of the formed complex suggested the lower half-life as well as its triggered elimination rate from the cardiovascular system, which may be an initial indicator of the reduced hypoglycemic property of linagliptin. Moreover, the UV-vis and synchronous fluorescence spectroscopic methods affirmed the conformational changes of the BSA due to drug-protein complexation and polarity alterations in the microenvironment of disparate chromophores of the biomolecule.

Binding process evaluation of bovine serum albumin and Lawsonia inermis (henna) through spectroscopic and molecular docking approaches

Lawsonia inermis L. (Henna) has been widely used in cosmetic, medicine and pharmacy industries. Henna is one of the ancient used plants and it can be absorbed into the blood and interact with plasma serum albumin. In this article, we investigated the interaction between henna and bovine serum albumin (BSA) through several spectroscopic techniques, which accompanied with molecular docking approach. According to the results, fluorescence intensity of BSA were decreased upon addition of different concentrations of henna and variation of the intensity illustrates the interaction between henna and BSA. Stern-Volmer quenching analysis along with bimolecular quenching rate results suggested that henna quenched the intensity of BSA through hybrid quenching mechanism, which was confirmed via UV–Vis measurement. As the temperature increase, values of binding constant increased from 5.17 × 102 to 6.17× 102 (M−1) demonstrating that the stability of henna–BSA complex increased with temperature rising. Thermodynamic investigations revealed that the henna molecule bind to BSA via hydrophobic bonds spontaneously. Furthermore, the molecular docking analysis demonstrated that henna has high affinity to bind a cavity in Site II (Domain III, subdomain IIIA) on BSA with binding energy score - 11.37 kcal/mol. Finally, it should be stated that distribution of the henna in the blood circulatory system can be done via BSA, which would accompany us to understand the different medicinal aspects of this natural product especially in drug delivery.

Heparin Accelerates the Protein Aggregation via the Downhill Polymerization Mechanism: Multi-Spectroscopic Studies to Delineate the Implications on Proteinopathies.

Heparin is one of the members of the glycosaminoglycan (GAG) family, which has been associated with protein aggregation diseases including Alzheimer’s disease, Parkinson’s disease, and prion diseases. Here, we investigate heparin-induced aggregation of bovine serum albumin (BSA) using different spectroscopic techniques [absorption, 8-anilino-1-naphthalene sulfonic acid (ANS) and thioflavin T (ThT) fluorescence binding, and far- and near-UV circular dichroism]. Kinetic measurements revealed that heparin is involved in the significant enhancement of aggregation of BSA. The outcomes showed dearth of the lag phase and a considerable change in rate constant, which provides conclusive evidence, that is, heparin-induced BSA aggregation involves the pathway of the downhill polymerization mechanism. Heparin also causes enhancement of fluorescence intensity of BSA significantly. Moreover, heparin was observed to form amyloids and amorphous aggregates of BSA which were confirmed by ThT and ANS fluorescence, respectively. Circular dichroism measurements exhibit a considerable change in the secondary and tertiary structure of the protein due to heparin. In addition, binding studies of heparin with BSA to know the cause of aggregation, isothermal titration calorimetry measurements were exploited, from which heparin was observed to promote the aggregation of BSA by virtue of electrostatic interactions between positively charged amino acid residues of protein and negatively charged groups of GAG. The nature of binding of heparin with BSA is very much apparent with an appreciable heat of interaction and is largely exothermic in nature. Moreover, the Gibbs free energy change (ΔG) is negative, which indicates spontaneous nature of binding, and the enthalpy change (ΔH) and entropy change (ΔS) are also largely negative, which suggest that the interaction is driven by hydrogen bonding.

Synthesis, molecular structure and BSA-binding properties of a new binuclear Cd(II) complex based on 2-(1H-tetrazol-1-methyl)-1H-imidazole-4,5-dicarboxylic acid

Abstract A new binuclear Cd(II) complex, [Cd2(H2tmidc)4(H2O)2]·6H2O (1) based on 2-(1H-tetrazol-1-methyl)-1H-imidazole-4,5-dicarboxylic acid (H3tmidc) has been synthesized and structurally characterized. The single-crystal X-ray diffraction analysis has revealed that there are two crystallographically distinct H2tmidc– anions in complex 1, one of which is coordinated to Cd(II) ion in a terminal fashion, while the other acts as a bis-connector linking two Cd(II) cations to form the dinuclear structure. The dimeric units are stabilized by intra-molecular O–H···O hydrogen bonds and π-π stacking interactions and are further connected into a three-dimensional supramolecular architecture through inter-molecular hydrogen bonds and π-π stacking interactions. The interactions of complex 1 with bovine serum albumin (BSA) were analyzed by fluorescence measurements under physiological conditions. The results have indicated that the fluorescence intensity of BSA was decreased considerably upon the addition of complex 1 through a static quenching mechanism. The synchronous fluorescence spectrum suggested that the interaction of complex 1 with BSA affects the conformations of tryptophan and tyrosine residues and thereby has an influence on the conformation of BSA.

Synthesis, crystal structure, and BSA binding studies of new Co(II) and Ni(II) complexes of 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylate

Two new complexes [Co(H3hmIDC)2(H2O)2]·3H2O (1) and [Ni(H3hmIDC)2(H2O)2] (2), where H4hmIDC = 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid, have been synthesized and characterized by analytical and spectral techniques. X-ray single crystal diffraction shows that both complexes possess mononuclear structure, but the detail structures are different. Complex 1 belongs to triclinic space group P-1, while 2 belongs to the monoclinic space group P21/c. The mechanism of interaction between the complexes and bovine serum albumin (BSA) were examined by fluorescence emission spectra. The results indicated that the fluorescence intensity of BSA was decreased considerably upon the addition of the complexes through a static quenching mechanism with formation of one binding site. The associated changes in enthalpy and entropy indicating that hydrogen bonding and van der Waals forces were the dominant intermolecular forces for BSA-complex 1 binding system, and hydrophobic interactions was the dominant intermolecular forces for BSA-complex 2 binding system. Furthermore, the effects of the complexes upon the conformation of BSA were analyzed using synchronous fluorescence spectrum and the results showed that the interaction of complex 1 or 2 with BSA affected the conformation of tryptophan residue and then affected the conformation of BSA.

Deciphering binding mechanism between bovine serum albumin and new pyrazoline compound K4

The binding mechanism of a new and possible drug candidate pyrazoline derivative compound K4 and bovine serum albumin (BSA) was investigated in buffer solution (pH 7.4) using ultraviolet-visible light absorption and steady-state and synchronous fluorescence techniques. The fluorescence intensity of BSA was quenched in the presence of K4. The quenching process between BSA and K4 was examined at four different temperatures. Decrease of the quenching constants calculated using the Stern-Volmer equation and at increasing temperature suggested that the interaction BSA-K4 was realized through a static quenching mechanism. Synchronous fluorescence measurements suggested that K4 bounded to BSA at the tryptophan region. Fourier transform infrared spectroscopy results showed that there was no significant change in polarity around the tryptophan residue The forces responsible for the BSA-K4 interaction were examined using thermodynamic parameters. In this study, the calculated negative value of ΔG, the negative value of ΔH and the positive value of ΔS pointed to the interaction being through spontaneous and electrostatic interactions that were dominant for our cases. This study provides a very useful in vitro model to researchers by mimicking in vivo conditions to estimate interactions between a possible drug candidate or a drug and body proteins.

The noncovalent conjugations of bovine serum albumin with three structurally different phytosterols exerted antiglycation effects: A study with AGEs-inhibition, multispectral, and docking investigations.

The antiglycation effects of three structurally different phytosterols (PS) including stigmasterol, β-sitosterol, and γ-oryzanol on bovine serum albumin (BSA) were deeply studied in a BSA-glucose model by measuring the glycoxidation-based products, SDS-PAGE intensity, free lysine, and their fluorescence microscopy clicks. For the first time, the underlying mechanisms of the antiglycation effects of PS were wholly elucidated by measuring their interaction ability with BSA and their antiradical activity during the glycation reactions. The results showed that PS could partially inhibit the formation of advance glycation end products, block some of the lysyl residues of BSA (Lys127, 357, 434, and 524), prevent the glucose-BAS bonding, and their disaggregation effects on the glycated BSA. Throughout the underlying mechanism behind the antiglycation activity, PS were found to structurally quench the fluorescence intensity of BSA in a static mode, leading to fluctuations in its Z-average size, UV-vis spectrum, and secondary structure. Additionally, PS mitigated the formation the advanced glycation end products by scavenging the radicals produced during the glycation reactions. Overall, these results unleash that PS prevent the glycation reactions and their subsequent changes through shielding the NH2 groups via H-bonding with their OH-groups and pi-pi interaction of the steroid core, besides the antiradical activity of PS on the free radicals generating during the glycation reactions.

Interaction of repaglinide with bovine serum albumin: Spectroscopic and molecular docking approaches

Repaglinide (RPG) regulates the amount of glucose by stimulating the pancreas to release insulin in the blood. In view of its biological importance, we have examined the interaction between RPG and a model protein, bovine serum albumin (BSA) employing various spectroscopic, electrochemical and molecular docking methods. Fluorescence spectra of BSA were recorded in the presence and absence of RPG in phosphate buffer of pH 7.4. Fluorescence intensity of BSA was decreased upon the addition of increased concentrations of RPG, indicating the interaction between RPG and BSA. Stern-Volmer quenching analysis results revealed that RPG quenched the intensity of BSA through dynamic quenching mechanism. This was further confirmed from the time-resolved fluorescence measurements. The binding constant as calculated from the spectroscopic and voltammetric results was observed to be in the order of 104 M−1 at 298 K, suggesting the moderate binding affinity between RPG and BSA. Competitive experimental results revealed that the primary binding site for RPG on BSA was site II. Absorption and circular dichroism studies indicated the changes in the secondary structure of BSA upon its interaction with RPG. Molecular simulation studies pointed out that RPG was bound to BSA in the hydrophobic pocket of site II.

Co(III) and VO(IV) complexes with a new bidentate Schiff base: Interaction with BSA and antimicrobial studies

A Schiff base ligand L was prepared from the condensation of 2-amino-3-benzyloxypyridine and 5-chlorosalicylaldehyde. The ligand forms complexes with Co(III) and VO(IV) in good yield. Design, synthesized and characterization of cobalt(III) and oxidovanadium(IV) with (E)-2-((3-(benzyloxypyridinylimino) methyl)-4-chlorophenol (L) are described. The prepared complexes were characterized by different analytical techniques elemental analysis, molar conductance, infrared spectra, 1H and 13C NMR, mass, electronic absorption and TGA. The coordination geometry is octahedral in C1 and C2, while complexes C3 and C4 show a square-pyramidal geometry. Numerous biological studies have been conducted on L and Co(III) and VO(IV) complexes. The results of antimicrobial studies indicated that all compounds had antimicrobial activity against bacteria and fungi. The binding of metal complexes with BSA (bovine serum albumin) was reported. The results of these indicated that Co(III) and VO(IV) are significantly quenching fluorescence intensity of BSA, that results in changing its conformation and results in a static quenching.

Characterization of the binding and conformational changes of bovine serum albumin upon interaction with antihypertensive olmesartan medoxomil

The interaction of bovine serum albumin (BSA) with the olmesartan medoxomil (OLM) was investigated by different spectroscopic and linear sweep voltammetric techniques under experimentally optimised physiological conditions. The alteration of functional properties of BSA when quenched by OLM was illustrated by the continuous decrease of the fluorescence intensity of BSA upon addition of OLM. The quenching constants (Ksv) obtained were 0.71 × 104, 1.3 × 104 and 2.1 × 104 Lmol−1 at 288, 298 and 308 K respectively. The binding mechanism was dynamic type quenching. The value of K is of the order of 104, indicating that a long-lasting interaction exists between OLM and BSA. The positive values of ΔH0 and ΔS0 suggested the hydrophobic interactions play the major roles in the binding reaction. The conformational change of BSA after binding with OLM was demonstrated by the synchronous, FTIR and 3-D fluorescence spectral results. The effects of some common metal ions and site probes on binding of BSA– OLM were also investigated.

Generation of a Diligand Complex of Bovine Serum Albumin with Quercetin and Carbon Nanotubes for the Protection of Bioactive Quercetin and Reduction of Cytotoxicity.

The interactions between proteins and bioactive ligands (such as flavonoids and nanomaterials) are vital to the design of effective protein carriers for the protection of bioactive molecules and reduction of the cytotoxicity of nanotubes. Bovine serum albumin (BSA) can bind various bioactive components and subsequently form protein-ligand complexes. Herein, the binding of BSA to quercetin and single-walled carbon nanotubes (SWCNTs) was investigated by using experimental and molecular-docking methods. The fluorescence intensity of BSA was decreased by both quercetin and SWCNTs in static quenching mode (i.e., compound formation), which was authenticated by Stern-Volmer calculations. Although quercetin showed a higher affinity for BSA than SWCNTs, the binding of both components to BSA was located in site I (subdomain IIA). BSA-diligand complexes were successfully generated when SWCNTs and quercetin, in that sequence, were added. The cytotoxicity of SWCNTs and the formation of reactive oxygen species in endothelial cells were decreased with the BSA-diligand complexes relative to those of SWCNTs or BSA-SWCNT corona, whereas the stability problems of quercetin were ameliorated in the BSA-diligand complex relative to in the free flavonoid. The BSA-diligand complex showed a better inhibitive effect on the cytotoxicity of SWCNTs than the BSA-SWCNT complex, and thus the coexistence of quercetin played a crucial role. These data demonstrate the advantages and possibility of designing BSA carriers for the protection of bioactive ligands and reduction of the cytotoxicity of nanotubes in functional-food and biomedical applications.