Fluorometric investigation of the interaction between methylene blue and human serum albumin

Study of Amiloride Binding to Human Serum Albumin: Insights from Thermodynamic, Spectroscopic, and Molecular Docking Investigations

This study was undertaken to investigate the interaction between the sodium channel blocker amiloride (AML) and human serum albumin (HSA). A combination of multi-spectroscopic techniques and computational methods were employed to identify the AML binding site on HSA and the forces responsible for the formation of the HSA-AML complex. Our findings revealed that AML specifically binds to Sudlow's site II, located in subdomain IIIA of HSA, and that the complex formed is stabilized using van der Waals hydrogen-bonding and hydrophobic interactions. FRET analysis showed that the distance between AML and Trp214 was optimal for efficient quenching. UV-Vis spectroscopy and circular dichroism indicated minor changes in the structure of HSA after AML binding, and molecular dynamics simulations (MDS) conducted over 100 ns provided additional evidence of stable HSA-AML-complex formation. This study enhances understanding of the interaction between AML and HSA and the mechanism responsible.

Shield, Anchor, and Adhesive Roles of Methylene Blue in Tyrosinase Adsorbed on Carbon Felt for a Flow Injection Amperometric Enzyme Biosensor for Phenolic Substrates and Inhibitors

Methylene blue (MB) acted as a stabilizer for preventing surface-induced denaturation of tyrosinase (TYR) adsorbed on a carbon felt (CF) surface, which is based on shield and anchor roles preventing the unfavorable conformational change of TYR on the hydrophobic CF surface. Furthermore, MB acted as an effective adhesive for TYR immobilization on CF. The resulting TYR and MB coadsorbed CF (TYR/MB-CF) worked as an excellent working electrode unit in an electrochemical detector in a flow injection amperometric biosensor, which allowed highly sensitive consecutive determination of not only TYR substrates but also competitive inhibitors. Simultaneous adsorption of TYR and MB from their mixed solution was much useful as compared with step-wise separated adsorption of TYR on the MB-adsorbed CF, which suggests that the binding interaction of MB with TYR in the solution phase is important for this phenomenon. Fluorescence and UV-vis spectroscopy revealed that not only electrostatic forces between the cationic MB and anionic amino acid residues of TYR but also hydrophobic interactions via the phenothiazine ring of MB play a principal binding driving force of MB with TYR at the surface of the TYR molecules. Synchronous fluorescence, three-dimensional fluorescence, and circular dichroism (CD) spectroscopy clarified that the conformation and the secondary structure of TYR slightly changed upon the MB binding, implying that MB binding leads to the modification of the original intramolecular bonding in part.

Antioxidant and Antivenom Potential of an Essential Oil, 4-(2-Oxo-propyl)-cyclopentane-1,3-dione, and Allantoin Derived from the Polyherbal Combination of Aristolochia indica L. and Piper nigrum L

The goal of this study was to identify new compounds from a methanol extract of a polyherbal combination of Aristolochia indica L. and Piper nigrum L. (MECAIPN), two traditional medicinal plants used to cure envenomation, as well as to assess their antioxidant and antivenom properties. MECAIPN yielded EA1 (an essential oil), AA2 (4-(2-oxo-propyl)-cyclopentane-1,3-dione), and W3 ((2,5-dioxo-imidazolidin-4-yl)-urea) (Allantoin). Although EA1 had stronger radical scavenging activity, AA2 had higher DPPH and ferric ion radical scavenging activity, and W3 had higher molybdenum ion radical scavenging activity due to being a single molecule, the binding investigation revealed that EA1 has a greater Stern–Volmer quenching constant (Ksv) than AA2 and W3. Synchronous measurements indicated that EA1, AA2, and W3 bind to tryptophan and tyrosine residues in venom, causing denaturation of the secondary structure of the residue. Finally, the current study concludes that EA1 has more therapeutic antivenom potential, which could be related to the synergism of chemicals found in it. When it came to single compounds, AA2 had stronger antioxidant and antivenom capabilities than W3. To understand the mechanism of action and manufacture the green antivenom medication, more testing of the EA1 and compounds remains required.

Study of interaction of methylene blue with DNA and albumin

The interaction of thiazine dye methylene blue (MB) with Calf thymus DNA and human blood serum albumin (HSA) has been studied. MB was revealed to stabilize the native structure of DNA and HSA, since the melting temperature of the complexes is shifted to higher values in relation to that of both macromolecules in pure state. It was also revealed that the absorption and fluorescence spectra of the MB-DNA complexes change significantly, while those of MB-albumin complexes do not change noticeably. Analysis of the obtained data allows to conclude that MB binds to DNA by two modes, including intercalation and electrostatic mechanisms. In the case of HSA, the main binding mode of MB, conditioning the stabilization of the protein native structure, is the electrostatic mechanism.Communicated by Ramaswamy H. Sarma.

Lipid Nanosystems and Serum Protein as Biomimetic Interfaces: Predicting the Biodistribution of a Caffeic Acid-Based Antioxidant

Purpose

AntiOxCIN₃ is a novel mitochondriotropic antioxidant developed to minimize the effects of oxidative stress on neurodegenerative diseases. Prior to an investment in pre-clinical in vivo studies, it is important to apply in silico and biophysical cell-free in vitro studies to predict AntiOxCIN₃ biodistribution profile, respecting the need to preserve animal health in accordance with the EU principles (Directive 2010/63/EU). Accordingly, we propose an innovative toolbox of biophysical studies and mimetic models of biological interfaces, such as nanosystems with different compositions mimicking distinct membrane barriers and human serum albumin (HSA).

Methods

Intestinal and cell membrane permeation of AntiOxCIN₃ was predicted using derivative spectrophotometry. AntiOxCIN₃ –HSA binding was evaluated by intrinsic fluorescence quenching, synchronous fluorescence, and dynamic/electrophoretic light scattering. Steady-state and time-resolved fluorescence quenching was used to predict AntiOxCIN₃-membrane orientation. Fluorescence anisotropy, synchrotron small- and wide-angle X-ray scattering were used to predict lipid membrane biophysical impairment caused by AntiOxCIN₃ distribution.

Results and Discussion

We found that AntiOxCIN₃ has the potential to permeate the gastrointestinal tract. However, its biodistribution and elimination from the body might be affected by its affinity to HSA (>90%) and by its steady-state volume of distribution (VD_SS=1.89± 0.48 L∙Kg⁻¹). AntiOxCIN₃ is expected to locate parallel to the membrane phospholipids, causing a bilayer stiffness effect. AntiOxCIN₃ is also predicted to permeate through blood-brain barrier and reach its therapeutic target – the brain.

Conclusion

Drug interactions with biological interfaces may be evaluated using membrane model systems and serum proteins. This knowledge is important for the characterization of drug partitioning, positioning and orientation of drugs in membranes, their effect on membrane biophysical properties and the study of serum protein binding. The analysis of these interactions makes it possible to collect valuable knowledge on the transport, distribution, accumulation and, eventually, therapeutic impact of drugs which may aid the drug development process.

[Determination of thermodynamic binding parameters and type of interaction between the А/Bangkok/1/1979 (Н3N2) influenza virus hemagglutinin and phosphatidylcholine liposome]

The study of interaction between surface viral proteins and model phospholipids is important for learning more details about the mechanisms of viral penetration into cells during infection. In this context, liposomes represent suitable systems for modeling a cell membrane. The binding of hemagglutinin (HA) of influenza virus with phosphatidylcholine liposomes was studied by equilibrium adsorption. It was interesting elucidate changes occurring in the structure of a protein during its translocation from the surface into the interior part of the membrane. In this work, we have studied characteristics of the protein-lipid interaction during HA complex formation with phospholipids including adsorption of HA on a phospholipid bilayer. Using the Scatchard equation and the Gibbs-Helmholtz equation at pH 4.0 and pH 6.0 thermodynamic parameters were determined. The results concluded the hydrophobic type of interaction between viral protein and liposomes. The additional confirmation of hydrophobic protein-lipid interaction presence was determination of HA distribution constants in two-phase systems: dextran-polyethylene glycol (K1) and dextran-polyethylene glycol esterified with palmitic acid (K2). The presence of hydrophobic interaction between HA and the liposome membrane was also confirmed using the quenching method of intrinsic protein fluorescence by a neutral quencher with acrylamide. At pH 4.0, an increase in the Stern-Volmer quenching constant was observed for the HA+liposome from phosphatidylcholine system, which is caused by structural changes in HA upon incorporation into the liposome bilayer. The fluorescence quenching rate constants calculated using the Stern-Volmer equation indicate a static quenching mechanism in which the quencher interacts with fluophors of a stationary protein molecule. The obtained results are interesting for not only studying virus and cell fusion theoretically, but also have practical applications. Using values of the protein-bilayer binding constant and free energy constant, it is possible to select the optimal phospholipid composition of liposomes or virosomes to obtain a stronger complex with various viral proteins. With two-phase systems, it is possible to determine the presence of hydrophobic sites on the viral protein surface, which can be used for evaluation both protein-lipid and protein-protein interaction.

Insight into interaction mechanism between theaflavin-3-gallate and α-glucosidase using spectroscopy and molecular docking analysis

To elucidate the α-glucosidase (α-GC) inhibitory mechanism of theaflavin-3-gallate (TF-3-G), their interaction mechanism was investigated using spectroscopy and molecular docking analysis. The inhibition ratio of TF-3-G against α-GC was determined to be 92.3%. Steady fluorescence spectroscopy showed that TF-3-G effectively quenched the intrinsic fluorescence of α-GC through static quenching, forming a stable complex through hydrophobic interactions. Formation of the TF-3-G/α-GC complex was also confirmed by resonance light scattering spectroscopy. Synchronous fluorescence spectroscopy and circular dichroism spectroscopy indicated that the secondary structure of α-GC was changed by TF-3-G. Molecular docking was used to simulate TF-3-G/α-GC complex formation, showing that TF-3-G might be inserted into the hydrophobic region around the active site of ɑ-GC, and bind with the catalytic Asp215 and Asp352 residues. The ɑ-GC inhibitory mechanism of TF-3-G was mainly attributed to the change in ɑ-GC secondary structure caused by the complex formation. PRACTICAL APPLICATIONS: α-Glucosidase (α-GC) can hydrolyze the glycosidic bonds of starch and oligosaccharides in food and release glucose. Therefore, the inhibition of α-GC activity has been used to treat postprandial hyperglycemia and type 2 diabetes mellitus. Theaflavin-3-gallate (TF-3-G), a flavonoid found in the fermentation products of black tea, exhibits strong inhibition of α-GC activity. However, the α-GC inhibitory mechanism of TF-3-G is unclear. This study aids understanding of this mechanism, and proposed a possibly basic theory for improving the medicinal value of TF-3-G in diabetes therapy.

Spectroscopic and cytotoxicity studies on the combined interaction of (-)-epigallocatechin-3-gallate and anthracycline drugs with human serum albumin

The interactions of (-)-epigallocatechin-3-Gallate (EGCG) and anthracycline drugs (doxorubicin, DOX and epirubicin, EPI) alone or in combination with human serum albumin (HSA) under physiological condition were studied by fluorescence spectroscopy, UV-vis absorption spectroscopy, circular dichroism (CD) spectroscopy, and dynamic light scattering (DLS). The cytotoxic activity of the single drug, combined drugs, and their complexes with HSA against human cervical cancer HeLa cell line was determined by MTT assay. Fluorescence quenching result and difference spectra of UV absorption revealed the formation of static complex between EGCG, DOX, or EPI and HSA. The binding of EGCG with HSA was driven by both enthalpy and entropy while the binding of DOX or EPI was mainly entropy driven. The nature of binding was expounded based on the effect of sodium chloride, tetrabutylammonium bromide, and sucrose which interfere in electrostatic, hydrophobic, and hydrogen bonding interactions, respectively. Site marker competitive experiments combined with synchronous fluorescence spectra showed that these three ligands mainly bound to subdomain IIA of HSA and were closer to tryptophan residues. In EGCG + DOX/EPI + HSA ternary system, the effect of one drug on the binding ability of another drug was discussed. The influences of the individual and combined binding of EGCG and DOX/EPI on the secondary structure and particle size of HSA were investigated by CD spectroscopy and DLS, respectively. Moreover, the synergistic cytotoxicity of EGCG and DOX/EPI as well as their complexes with HSA were discussed. Obtained results would provide beneficial information on the combination of EGCG and anthracyclines in clinic.

Emissive Enhancement of the Singlet Oxygen Chemiluminescence Probe after Binding to Bovine Serum Albumin

A chemiluminescence probe for singlet oxygen ¹O₂ (SOCL) was investigated in phosphate buffer saline (PBS), either in the absence of proteins or containing bovine serum albumin (BSA). In the protein-free PBS, the reactivity of SOCL for methylene blue (MB)-photosensitized ¹O₂ was found to be moderate or low. The reaction yield increased with temperature and/or concentration of dissolved molecular oxygen. Unexpectedly, the presence of BSA boosted both the emissive nature and the thermal stability of the phenoxy-dioxetane intermediate formed in the chemiexcitation pathway. Isothermal titration calorimetry showed that SOCL has a moderate binding affinity for BSA and that entropy forces drive the formation of the SOCL-BSA complex. A model with two identical and independent binding sites was used to fit the binding isotherm data. Co-operative binding was observed when MB was present. Local viscosity factors and/or conformational restrictions of the BSA-bound SOCL phenoxy-dioxetane were proposed to contribute to the formation of the highly emissive benzoate ester during the chemically initiated electron exchange luminescence (CIEEL) process. These results led us to conclude that hydrophobic interactions of the SOCL with proteins can modify the emissive nature of its phenoxy-dioxetane, which should be taken into account when using SOCL or its cell-penetrating peptide derivative in living cells.

Study of Methylene Blue Interaction with Human Serum Albumin

The thiosine dye methylene blue (MB) interaction with human serum albumin (HSA) has been studied. MB was revealed to stabilize the native structure of HSA, since the denaturation temperature of the complexes is shifted to higher values in relation to that of the pure protein. It was also revealed that the absorption spectra of the complexes do not change noticeably, while in the fluorescence spectra the maximal intensity of MB decreases with the albumin concentration enhancement. Analysis of the obtained data allows to conclude that the main binding mode of MB to HSA, providing the stabilization of the protein native structure, is the electrostatic mechanism.

Photochemical behavior of biosupramolecular assemblies of photosensitizers, cucurbit[n]urils and albumins

Biosupramolecular assemblies combining cucurbit[n]urils (CB[n]s) and proteins for the targeted delivery of drugs have the potential to improve the photoactivity of photosensitizers used in the photodynamic therapy of cancer. Understanding the complexity of these systems and how it affects the properties of photosensitizers is the focus of this work. We used acridine orange (AO⁺) as a model photosensitizer and compared it with methylene blue (MB⁺) and a cationic porphyrin (TMPyP⁴⁺). Encapsulation of the photosensitizers into CB[n]s (n = 7, 8) modified their photoactivity. In particular, for AO⁺, the photo-oxidation of HSA was enhanced in the presence of CB[7]; meanwhile it was decreased when included into CB[8]. Accordingly, peroxide generation and protein fragmentation were also increased when AO⁺ was encapsulated into CB[7]. The triplet excited state lifetimes of all the photosensitizers were lengthened by their encapsulation into CB[n]s, while the singlet oxygen quantum yield was enhanced only for AO⁺ and TMPyP⁴⁺, but it decreased for MB⁺. The results obtained in this work prompt the necessity of further investigating these kinds of hybrid assemblies as drug delivery systems because of their possible applications in biomedicine.

Stabilization of bovine lactoperoxidase in the presence of ectoine

Lactoperoxidase (LPO) is a heme peroxidase with various applications in industry and medicine. In this study, the effects of ectoine, as a compatible solute, on the structure, thermal stability, thermodynamic parameters, activity, and stability of LPO have been investigated. The results showed that the catalytic activity of LPO was improved by increasing ectoine concentration. The UV-visible absorption spectroscopy and FTIR spectra studies indicated that ectoine could bind to the LPO spontaneously. Moreover, ectoine increased the enzyme Tm and Gibbs free energy. The fluorescence measurements showed that LPO fluorescence was quenched in the presence of ectoine. The quenching mechanism was probably a static quenching by forming a ground state complex. The thermodynamic parameters indicated that hydrogen bonding and Vander Waals forces played a key role in the LPO-ectoine interaction process. The findings suggest that ectoine could be used as a lactoperoxidase stabilizing agent for industrial or medical purposes.

Biophysical influence of coumarin 35 on bovine serum albumin: Spectroscopic study

The binding mechanism and protein-fluorescence probe interactions between bovine serum albumin (BSA) and coumarin 35 (C35) was investigated by using UV-Vis absorption and fluorescence spectroscopies since they remain major research topics in biophysics. The spectroscopic data indicated that a fluorescence quenching process for BSA-C35 system was occurred. The fluorescence quenching processes were analyzed using Stern-Volmer method. In this regard, Stern-Volmer quenching constants (K_SV) and binding constants were calculated at different temperatures. The distance r between BSA (donor) and C35 (acceptor) was determined by exploiting fluorescence resonance energy transfer (FRET) method. Synchronous fluorescence spectra were also studied to observe information about conformational changes. Moreover, thermodynamics parameters were calculated for better understanding of interactions and conformational changes of the system.

Synthesis and study on the binding of thiazol-2(3H)-ylidine derivative with human serum albumin using spectroscopic and molecular docking methods

In this article, a facile and convenient synthesis of thiazol-2(3H)-ylidine derivatives of fatty acid (3a-c) is described. The binding of N'-(4,5-dimethyl-3-penylthiazol-2(3H)-ylidine)octadec-9-enehydrazide (3a) with human serum albumin (HSA) is explored using various spectral methods and molecular docking. Fluorescence quenching results show that 3a induces conformational changes in HSA and the polarity around the tryptophan residues is increased. Stern-Volmer quenching plots at different temperatures (298, 305 and 312 K) show that the fluorescence quenching mechanism is static quenching. Synchronous fluorescence, 3D fluorescence spectra, circular dichroism and Fourier transform infrared spectroscopy are used to determine the structural change in HSA on interaction with 3a. Förster resonance energy transfer analysis shows that the binding distance (r₀  = 2.78 nm) between HSA (Trp214) and 3a is within the of range 2-8 nm for quenching to occur. The molecular docking study also confirms that 3a is located in subdomain IIA (site I) of HSA and is stabilized by hydrogen bonding and hydrophobic forces.

Bile salt induced solubilization of methylene blue: Study on methylene blue fluorescence properties and molecular mechanics calculation

Methylene blue (MB) is a hydrophobic drug molecule, having importance both as a staining reagent and pharmaceutical agent. MB is strongly fluorescent, with an emission peak at 686 nm (λ_ex 665 nm). In the study, the possibility of MB as an extrinsic fluorophore to study the micellization behavior of bile salts (BSs) was carried out. Since BSs are drug delivery systems, the solubilization of hydrophobic MB drug molecule by BSs was achieved and the nature of association of MB with BS media, namely sodium cholate (NaC) and sodium deoxycholate (NaDC) was evaluated. Change in the photophysical properties of MB is monitored through fluorescence intensity and fluorescence anisotropy at emission peak, 686 nm of MB. Molecular mechanics calculations were carried out to evaluate the MB–BS association. The estimated heat of formation, ΔH_f values are –625.19 kcal/mol for MB–NaC and –757.48 kcal/mol for MB–NaDC. The photophysical study also revealed that MB reports the step-wise aggregation pattern of BSs media, as an extrinsic fluorescence probe.

Measuring the bioactivity and molecular conformation of typically globular proteins with phenothiazine-derived methylene blue in solid and in solution: A comparative study using photochemistry and computational chemistry

Methylene blue is a phenothiazine agent, that possesses a diversity of biomedical and biological therapeutic purpose, and it has also become the lead compound for the exploitation of other pharmaceuticals such as chlorpromazine and the tricyclic antidepressants. However, the U.S. Food and Drug Administration has acquired cases of detrimental effects of methylene blue toxicities such as hemolytic anemia, methemoglobinemia and phototoxicity. In this work, the molecular recognition of methylene blue by two globular proteins, hemoglobin and lysozyme was characterized by employing fluorescence, circular dichroism (CD) along with molecular modeling at the molecular scale. The recognition of methylene blue with proteins appears fluorescence quenching via static type, this phenomenon does cohere with time-resolved fluorescence lifetime decay that nonfluorescent protein-drug conjugate formation has a strength of 10(4)M(-1), and the primary noncovalent bonds, that is hydrogen bonds, π-conjugated effects and hydrophobic interactions were operated and remained adduct stable. Meantime, the results of far-UV CD and synchronous fluorescence suggest that the α-helix of hemoglobin/lysozyme decreases from 78.2%/34.7% (free) to 58.7%/23.8% (complex), this elucidation agrees well with the elaborate description of three-dimensional fluorescence showing the polypeptide chain of proteins partially destabilized upon conjugation with methylene blue. Furthermore, both extrinsic fluorescent indicator and molecular modeling clearly exhibit methylene blue is situated within the cavity constituted by α1, β2 and α2 subunits of hemoglobin, while it was located at the deep fissure on the lysozyme surface and Trp-62 and Trp-63 residues are nearby. With the aid of computational analyses and combining the wet experiments, it can evidently be found that the recognition ability of proteins for methylene blue is patterned upon the following sequence: lysozyme<hemoglobin<albumin. Basically, the distinction originates from different spatial structures of proteins and noncovalent interactions between proteins and methylene blue. In addition, biological relevance of the biorecognition of methylene blue with proteins was briefly discussed. We hope that this study could provide further standpoint so that one explore the biological activity of methylene blue and also phenothiazines.

Large-scale synthesis of soluble graphitic hollow carbon nanorods with tunable photoluminescence for the selective fluorescent detection of DNA

A high-yield synthesis of water-soluble photoluminescent carbon nanorods is described. The wsCNRs were used for the selective determination of DNA molecules via a fluorescent turn-off/turn-on mechanism.

Thermodynamic and conformational changes of protein toward interaction with nanoparticles: a spectroscopic overview

Nanoparticles (NPs) in different forms have been widely used in medicine and pharmaceutics for diagnosis and drug delivery.

Enhancement of the binding affinity of methylene blue to site I in human serum albumin by cupric and ferric ions

In this work, the binding characteristics of methylene blue (MB) to human serum albumin (HSA) and the influence of Cu(2+) and Fe(3+) on the binding affinity of MB to HSA were investigated using fluorescence, absorption, circular dichroism (CD) spectroscopy and molecular modelling. The results of competitive binding experiments using the site probes ketoprofen and ibuprofen as specific markers suggested that MB was located in site I within sub-domain IIA of HSA. The molecular modelling results agreed with the results of competitive site marker experiments and the results of CD spectra indicated that the interaction between MB and HSA caused the conformational changes in HSA. The binding affinity of MB to HSA was enhanced but to a different extent in the presence of Cu(2+) and Fe(3+), respectively, which indicated that the influence of different metal ions varied. Enhancement of the binding affinity of MB to HSA in the presence of Cu(2+) is due to the formation of Cu(2+)-HSA complex leading to the conformational changes in HSA, whereas in the presence of Fe(3+), enhancement of the binding affinity is due to the greater stability of the Fe(3+)-HSA-MB complex compared with the MB-HSA complex.

Elucidating the interaction of limonene with bovine serum albumin: a multi-technique approach

Mechanistic insight into the BSA–limonene interaction: biophysical and molecular docking approach.

Exploring the binding mechanism of Guaijaverin to human serum albumin: fluorescence spectroscopy and computational approach

The Guaijaverin (Gua) is a polyphenolic substance which exhibits some pharmacological activities such as antibacterial and antioxidant activities. Here we have investigated the binding of Gua with human serum albumin (HSA) at physiological pH 7.0. In this study, the fluorescence spectroscopy, ab initio and molecular modeling calculations were applied. The Stern-Volmer quenching constant (K(SV)) and its modified form (K(a)) were calculated at 298, 303 and 308 K, with the corresponding thermodynamic parameters ΔH, ΔG and ΔS as well. The fluorescence quenching method was used to determine the number of binding sites (n) and binding constants (K(b)) values at 298, 303 and 308 K. The distance between donor (HSA) and acceptor (Gua) was estimated according to fluorescence resonance energy transfer. The geometry optimization of Gua was performed in its ground state by using ab initio DFT/B3LYP functional with a 6-31G(d,p) basis set used in calculations. Molecular modeling calculation indicated that the Gua is located within the hydrophobic pocket of the subdomain IIA of HSA. The theoretical results obtained by molecular modeling were corroborated by fluorescence spectroscopy data.

Fluorescence spectroscopy of osthole binding to human serum albumin

The interaction of human serum albumin (HSA) with osthole was investigated by fluorescence spectroscopy. Osthole can quench the fluorescence of HSA and the quenching mechanism is a static process. The binding site number n and apparent binding constant K were measured at different temperatures. The thermodynamic parameters ΔH⁰, ΔG⁰ and ΔS⁰ were calculated at different temperatures. The results indicated that electrostatic forces played a major role in the interaction of osthole with HSA. Results of osthole synchronous fluorescence and UV absorption spectra showed that the microenvironment and conformation of HSA were changed.

Fluorescence studies of interaction between flavonol p-coumaroylglucoside tiliroside and bovine serum albumin

In this paper, the interaction between flavonol p-coumaroylglucoside tiliroside and BSA was investigated by fluorescence quenching spectra, synchronous fluorescence spectra, and three-dimensional fluorescence spectra under simulative physiological conditions. It was proved that the fluorescence quenching of BSA by tiliroside was mainly a result of the formation of a tiliroside-BSA complex. The modified Stern-Volmer quenching constant and the corresponding thermodynamic parameters DeltaH, DeltaG and DeltaS at different temperatures were calculated. The results indicated that electrostatic interactions were the predominant intermolecular forces in stabilizing the complex. The distance r=3.95 nm between the donor (BSA) and acceptor (tiliroside) was obtained according to Förster's nonradioactive energy transfer theory. The synchronous fluorescence and three-dimensional fluorescence spectra results showed the microenvironment and conformation of BSA were changed in the binding reaction.