Non-covalent binding analysis of sulfamethoxazole to human serum albumin: Fluorescence spectroscopy, UV-vis, FT-IR, voltammetric and molecular modeling

Modeling antimicrobial fate in the circular food system

The livestock sector plays a critical role in the circular food production system, but excessive use of antimicrobials (AMs) in livestock farming can lead to AM residue contamination in human food. CirFSafe, a model framework was developed to predict the fate of five different AMs in a primary circular food production system, comprising mixed farms with arable (maize) and animal (bovine) components. Two bovine exposure scenarios to AMs were simulated: annual constant exposure and a one-off exposure in the first year of circularity. Over a 5-year timeframe, model predictions suggest that fertilizing soil with animal manure and feeding animals with maize grown in the same soil are unlikely to cause AM residues in milk or meat exceeding European regulatory limits. Nevertheless, the distinct residual patterns of different AMs across the system underscore the need for precautionary monitoring, particularly for the routine use of flumequine (FLU) and doxycycline (DOX), which exhibits a greater tendency to transfer into food products.

Novel Spectroscopic Studies of the Interaction of Three Different Types of Iron Oxide Nanoparticles with Albumin

In the present work, we studied the interactions of three types of iron oxide nanoparticles (IONPs) with human serum albumin (HSA) by fluorescence and UV-Vis spectroscopy. The determined binding parameters of the reactions and the thermodynamic parameters, including ΔHo, ΔSo, and ΔGo indicated that electrostatic forces play a major role in the interaction of IONPs with HSA. These measurements indicate a fluorescent quenching mechanism based on IONPs-HSA static complex formation. Our study shows that the interaction between HSA and IONPs depends on the nanoparticle structure. The interaction between IONPs and HSA was found to be spontaneous, exothermic, and entropy-driven. HSA was shown to interact moderately with IONPs obtained with plant extracts of Uncaria tomentosa L. (IONP@UT) and Clinopodium vulgare L. (IONP@CV), and firmly with IONPs prepared with Ganoderma lingzhi (Reishi) extract (IONP@GL), via ground-state association. Analysis by modified Stern-Volmer approximation indicates that the quenching mechanism is static. Our study significantly improves our understanding of the mechanisms of interaction, distribution, and transport involved in the interaction between proteins and IONPs. It provides crucial insights into the functional perturbations of albumin binding capacity and the effects of IONPs on the stability and structural modifications of plasma carrier proteins.

Profiling the Interaction between Human Serum Albumin and Clinically Relevant HIV Reverse Transcriptase Inhibitors

Tenofovir (TFV) is the active form of the prodrugs tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF), both clinically prescribed as HIV reverse transcriptase inhibitors. The biophysical interactions between these compounds and human serum albumin (HSA), the primary carrier of exogenous compounds in the human bloodstream, have not yet been thoroughly characterized. Thus, the present study reports the interaction profile between HSA and TFV, TDF, and TAF via UV-Vis, steady-state, and time-resolved fluorescence techniques combined with isothermal titration calorimetry (ITC) and in silico calculations. A spontaneous interaction in the ground state, which does not perturb the microenvironment close to the Trp-214 residue, is classified as weak. In the case of HSA/TFV and HSA/TDF, the binding is both enthalpically and entropically driven, while for HSA/TAF, the binding is only entropically dominated. The binding constant (Ka) and thermodynamic parameters obtained via ITC assays agree with those obtained using steady-state fluorescence quenching measurements, reinforcing the reliability of the data. The small internal cavity known as site I is probably the main binding pocket for TFV due to the low steric volume of the drug. In contrast, most external sites (II and III) can better accommodate TAF due to the high steric volume of this prodrug. The cross-docking approach corroborated experimental drug-displacement assays, indicating that the binding affinity of TFV and TAF might be impacted by the presence of different compounds bound to albumin. Overall, the weak binding capacity of albumin to TFV, TDF, and TAF is one of the main factors for the low residence time of these antiretrovirals in the human bloodstream; however, positive cooperativity for TAF and TDF was detected in the presence of some drugs, which might improve their residence time (pharmacokinetic profile).

Interaction between a water-soluble anionic porphyrin and human serum albumin unexpectedly stimulates the aggregation of the photosensitizer at the surface of the albumin

The 5,10,15,20-tetrakis(2,6-difluoro-3-sulfophenyl)porphyrin (TDFPPS4) was reported as a potential photosensitizer for photodynamic therapy. The capacity of the photosensitizers to be carried in the human bloodstream is predominantly determined by its extension of binding, binding location, and binding mechanism to human serum albumin (HSA), influencing its biodistribution and ultimately its photodynamic therapy efficacy in vivo. Thus, the present work reports a biophysical characterization on the interaction between the anionic porphyrin TDFPPS4 and HSA by UV-visible absorption, circular dichroism, steady-state, time-resolved, and synchronous fluorescence techniques under physiological conditions, combined with molecular docking calculations and molecular dynamics simulations. The interaction HSA:TDFPPS4 is spontaneous (ΔG° < 0), strong, and enthalpically driven (ΔH° = -70.1 ± 3.3 kJ mol-1) into subdomain IIA (site I). Curiously, despite the porphyrin binding into an internal pocket, about 50 % of TDFPPS4 structure is still accessible to the solvent, making aggregation in the bloodstream possible. In silico calculations were reinforced by spectroscopic data indicating porphyrin aggregation between bound and unbound porphyrins. This results in an adverse scenario for anionic porphyrins to achieve their therapeutical potential as photosensitizers and control of effective dosages. Finally, a trend of anionic porphyrins to have a combination of quenching mechanisms (static and dynamic) was noticed.

Stimuli-responsive ultra-small vanadate prodrug nanoparticles with NIR photothermal properties to precisely inhibit Na/K-ATPase for enhanced cancer therapy

Inhibition of Na/K-ATPase is a promising cancer treatment owing to the essential role of Na/K-ATPase in maintaining various cellular functions. The potent Na/K-ATPase inhibitor, vanadate(V) (termed as V(V)), has exhibited efficient anticancer effects. However, nonspecific inhibition using V(V) results in serious side effects, which hinder its clinical application. Here, bovine serum albumin (BSA)-modified ultra-small vanadate prodrug nanoparticles (V(IV) NPs) were synthesized via a combined reduction-coordination strategy with a natural polyphenol tannic acid (TA). A lower systemic toxicity of V(IV) NPs is achieved by strong metal-polyphenol coordination interactions. An efficient V(V) activation is realized by reactive oxygen species (ROS) at the tumor site. Furthermore, V(IV) NPs show excellent photothermal properties in the near-infrared (NIR) region. By NIR irradiation at the tumor site for mild hyperthermia, selective enhancement of the interactions between V(V) and Na/K-ATPase achieves stronger inhibition of Na/K-ATPase for robust cell killing effect. Altogether, V(IV) NPs specifically inhibit Na/K-ATPase in cancer cells with negligible toxicity to normal tissues, thus making them a promising candidate for clinical applications of Na/K-ATPase inhibition.

Novel Bovine Serum Albumin-Decorated-Nanostructured Lipid Carriers Able to Modulate Apoptosis and Cell-Cycle Response in Ovarian, Breast, and Colon Tumoral Cells

A novel nanoscale approach was developed for the improved cellular internalization of hybrid bovine serum albumin-lipid nanocarriers loaded with piperine (NLC-Pip-BSA) in different tumor cells. The effect of the BSA-targeted-NLC-Pip and untargeted-NLC-Pip on the viability, proliferation, and levels of cell-cycle damage and apoptosis in the colon (LoVo), ovarian (SKOV3) and breast (MCF7) adenocarcinoma cell lines was comparatively discussed. NLCs were characterized concerning particle size, morphology, zeta potential, phytochemical encapsulation efficiency, ATR-FTIR, and fluorescence spectroscopy. The results showed that NLC-Pip-BSA showed a mean size below 140 nm, a zeta potential of -60 mV, and an entrapment efficiency of 81.94% for NLC-Pip and 80.45% for NLC-Pip-BSA. Fluorescence spectroscopy confirmed the coating of the NLC with the albumin. By MTS and RTCA assays, NLC-Pip-BSA showed a more pronounced response against the LoVo colon cell line and MCF-7 breast tumor cell lines than against the ovarian SKOV-3 cell line. Flow cytometry assay demonstrated that the targeted NLC-Pip had more cytotoxicity and improved apoptosis than the untargeted ones in MCF-7 tumor cells (p < 0.05). NLC-Pip caused a significant increase in MCF-7 breast tumor cell apoptosis of ~8X, while NLC-Pip-BSA has shown an 11-fold increase in apoptosis.

Protein-enabled detection of ibuprofen and sulfamethoxazole using solid-state nanopores

Enabled by proteins, we present an all-electrical method for rapid detection of small pharmaceuticals (ibuprofen and sulfamethoxazole [SMZ]) in aqueous media using silicon nitride pores. Specifically, we use carrier proteins, bovine serum albumin (BSA), and take advantage of their interactions with two small drug molecules to form BSA-drug complexes which can be detected by nm-diameter pores, thereby confirming the presence of small pharmaceuticals. We demonstrate detection of ibuprofen and SMZ at concentrations down to 100 nM (∼21 μg/L) and 48.5 nM (12 μg/L), respectively. We observe changes in electrical signal characteristics (reflected in event durations, rates, current magnitudes, and estimated particle diameters) of BSA-drug complexes compared to BSA-only, and differences between these two small pharmaceuticals, possibly paving a path toward developing selective sensors by identifying "electrical fingerprints" of these molecules in the future. These distinct electrical signals are likely a combined result of diffusion, electrophoretic and electroosmotic effects, interactions between the pore and particles, which depend on pore diameters, pH, and the resulting surface charges. The use of single-molecule-counting nanopores allows sensing of small pharmaceuticals, studies of protein conformational changes, and may aid in efforts to evaluate the impact of small drug molecules on aquatic and human life.

Interaction of pharmaceutical metabolites with blood proteins and membrane lipids in the view of bioconcentration: A preliminary study based on in vitro assessment

Pharmaceuticals pose a real threat to the environment, which has been proven in many studies to date. However, still little is known about the transformation products (TPs) of these compounds, which can also interact with organisms, causing adverse effects like noticeable toxicity or bioconcentration. Many recent works confirm that metabolites of pharmaceuticals are present in the environment, and preliminary studies suggest that they may be equally dangerous to or even more so than their parent compounds. Additionally, it has been proven that some of them have high hydrolytic stability, thus they may be persistent in the environment. This property also increases the likelihood that these compounds will be uptaken and accumulated in the tissues of organisms. Therefore, the aim of the present study was to preliminarily estimate the affinity of the transformation products of selected drugs for blood proteins and cell membrane-forming lipids, considered as important sorption phases during distribution in a living organism. In this study, it was shown that although the examined metabolites do not have a strong affinity for membrane lipids, they exhibit relatively strong binding to proteins, which may considerably affect the distribution of TPs in an organism and may indicate a non-classical process of bioconcentration. The results obtained confirm that the TPs of pharmaceuticals should be given much more attention and their potential for bioconcentration should be further determined.

Binding mechanism of 4-octylphenol with human serum albumin: Spectroscopic investigations, molecular docking and dynamics simulation

4-Octylphenol (OP) is an environmental estrogen that can enter organisms through the food chain and cause various toxic effects. Here, the interaction between OP and human serum albumin (HSA) was explored through multipectral, molecular docking and dynamics simulation. The results showed that OP and HSA formed a ground state complex through a static quenching mechanism, and the interaction was spontaneously driven by hydrogen bonds and hydrophobic interaction forces. The binding constant at different temperatures was measured to be on the order of 10⁵ L mol^-1. Site competition experiments suggested that OP interacted with amino acid residues Lys195, Cy245 and Cys246 located at the Sudlow site I of HSA, resulting in a more stretched protein peptide. The presence of OP increased the surface hydrophobicity of HSA, and reduced the content of α-helix in HSA by 3.4%. FT-IR spectra showed that OP interacted with the C=O and C-H groups of the polypeptide backbone. Molecular docking demonstrated that OP mainly bound to Site I of HSA and hydrogen bonds participated in the interaction. In addition, molecular dynamics simulations further explored the stability and dynamic behavior of the OP-HSA complex through RMSD, RMSF, SASA and Rg.

Monosaccharides interact weakly with human serum albumin. Insights for the functional perturbations on the binding capacity of albumin

Monosaccharides, e.g. fructose, glucose, and arabinose are present in most foods consumed daily, whether, in natural or industrialized forms, and their concentration in the human bloodstream can impact the formation of advanced glycation end-products (AGEs, prevalent in people with diabetes) impacting the profile of Human Serum Albumin (HSA) in biodistribution of endogenous and exogenous compounds. Multiple spectroscopic techniques (UV-vis, circular dichroism, steady-state, and time-resolved fluorescence) combined with molecular docking showed that carbohydrates interact weakly and spontaneously via a ground-state association with HSA. The binding is enthalpically and entropically driven in the subdomain IIA (site I) and perturb weakly the secondary structure of the albumin. Hydrogen bonding and van der Waals forces are the main intermolecular interactions involved in the ligand binding, as well as hydrophobic effects related to the release of hydration shell upon ligand binding. Overall, the results indicated that an increase in glucose, fructose or arabinose level in the human bloodstream may cause functional perturbation on the binding capacity of albumin. Therefore, there is the necessity of carbohydrate level control in the bloodstream to not compromise the interaction and distribution of exogenous and endogenous compounds by HSA.

Interactions and effects of food additive dye Allura red on pepsin structure and protease activity; experimental and computational supports

Background and purpose:

Today, color additives such as Allura red (AR) are widely used in different kinds of food products. Pepsin is a globular protein that is secreted as a digestive protease from the main cells in the stomach. Because of the important role of pepsin in protein digestion and because of its importance in digestive diseases the study of the interactions of pepsin with chemical food additives is important.

Experimental approach:

In this study, the interactions between AR and pepsin were investigated by different computational and experimental approaches such as ultraviolet and fluorescence spectroscopy along with computational molecular modeling.

Findings/Results:

The experimental results of fluorescence indicated that AR can strongly quench the fluorescence of pepsin through a static quenching. Thermodynamic analysis of the binding phenomena suggests that van der Waals forces and hydrogen bonding played a major role in the complex formation. The results of synchronous fluorescence spectra and furrier transformed infra-red (FTIR) experiments showed that there are no significant structural changes in the protein conformation. Also, examined pepsin protease activity revealed that the activity of pepsin was increased upon ligand binding. In agreement with the experimental results, the computational results showed that hydrogen bonding and van der Waals interactions occurred between AR and binding sites.

Conclusion and implications:

From the pharmaceutical point of view, this interaction can help us to get a deeper understanding of the effect of this synthetic dye on food digestion.

Fluorescent pyrene moiety in fluorinated C6F5-corroles increases the interaction with HSA and CT-DNA

Two fluorinated meso-C6F5-corroles (5,15-bis(pentafluorophenyl)-10-(phenyl)corrole and 5,15-bis(pentafluorophenyl)-10-(1-pyrenyl)corrole) were biologically evaluated in terms of binding affinity to human serum albumin (HSA) and calf-thymus DNA (CT-DNA) via multiple spectroscopic techniques under physiological conditions combined with molecular docking calculations. The HSA:corrole interaction is spontaneous and moderate via static binding, disturbing both secondary and tertiary albumin structures at high fluorinated corrole concentrations. The competitive binding studies indicated positive cooperativity or allosteric activation, while molecular docking calculations suggested that both fluorinated corroles bind preferentially inside subdomains IIA and IB (sites I and III, respectively). The experimental CT-DNA binding assays indicated that fluorinated corroles interact spontaneously by non-classical modes in the minor groove of the CT-DNA strands via static fluorescence quenching mechanism. Molecular docking results also showed the minor groove as the main binding site for CT-DNA. Overall, the pyrene moiety increased the interaction with HSA and CT-DNA, which is probably due to the planarity and volume that favors the pyrene unit to be buried inside the biomacromolecule pockets.

Effect of quercetin on the amiloride-bovine serum albumin interaction using spectroscopic methods, molecular docking and chemometric approaches

The effect of quercetin flavonoid (QUE), on the binding interaction of antihypertensive drug, amiloride (AMI) with bovine serum albumin (BSA) was investigated in this study. Spectroscopic methods such as steady-state, synchronous, three-dimensional fluorescence, and circular dichroism spectroscopy were employed to study the interaction. Fluorescence data were analyzed using the Stern-Volmer equation and a static quenching process was found to be involved in the formation of AMI-BSA and QUE-BSA complexes and were in good agreement with the thermodynamic study. The thermodynamic parameters illustrated that the process is spontaneous and enthalpy driven. Hydrophobicity is acting as the primary force in the binding interaction. Fluorescence spectral data were resolved using a multivariate curve resolution-alternating least squares method (MCR-ALS). Site marker and molecular docking studies confirmed the binding site of AMI on BSA, i.e. site II. The binding distance between amino acid of BSA and AMI was calculated and found to be 2.18 nm which indicated that energy transfer has occurred from an amino acid of BSA to AMI. The binding affinity of AMI to BSA was found to be reduced in the presence of QUE, which may lead to the poor distribution of AMI at the desired site.

Spectroscopic and molecular docking studies for characterizing binding mechanism and conformational changes of human serum albumin upon interaction with Telmisartan

Human serum albumin (HSA), one of the most copious plasma proteins is responsible for binding and transportation of many exogenous and endogenous ligands including drugs. In this study, we intended to explore the extent and types of binding interaction present between HSA and the antihypertensive drug, telmisartan (TLM). The conformational changes in HSA due to this binding were also studied using different spectroscopic and molecular docking techniques. The spectral shifting and intensity variations upon interaction with TLM were studied using FT-IR spectroscopy. Binding constant and the change in absorption of HSA at its λ_max was analyzed using absorption spectroscopy. Eventually, the types and extent of binding interactions were confirmed using molecular docking technique. Results have shown that TLM significantly interacts with the binding site-1 of HSA utilizing strong hydrogen bonding with Glu292, and Lys195 residues. The UV-absorption intensities were found to be decreased serially as the drug concentration increased with a binding constant of 1.01 × 10³ M⁻¹. The secondary structure analysis using FT-IR spectroscopy also revealed a marked reduction in the α-helix (56%) component of HSA on interaction. This study gives critical insights into the interaction of TLM with HSA protein which eventually affects the concentration of TLM reaching the site of action and ultimately its therapeutic profile.

Probing the interaction of a coumarin-di(2-picolyl)amine hybrid drug-like molecular entity with human serum albumin: Multiple spectroscopic and molecular modeling techniques

HSA is an important plasma protein responsible for transport of drug molecules. Coumarin derivatives play critical role as anticancer, antidiabetic and antiparkinson agents. In our lab we have synthesized coumarin-based pharmacophore, di(2-picolyl)amine-3(bromoacetyl) coumarin (ligand-L) endowed with anticancer activity. Anticancer agents binding mode of HSA provides valuable pharmacological information and is a structural guidance in synthesizing new drugs with greater efficacy. Thus, binding mechanism of ligand-L with HSA was explored using spectroscopic and molecular docking techniques. UV-Vis spectroscopy demonstrates hyperchromism in the absorbance spectra of HSA on addition of ligand-L suggesting interaction of ligand-L with HSA. Fluorescence spectroscopy indicates quenching in the fluorescence of HSA in the presence of ligand-L confirming the complex formation and this binding follows static mechanism. Steady state fluorescence spectroscopy revealed high binding affinity between ligand-L and HSA with a 1:1 stoichiometry. Thermodynamic parameters obtained by ITC suggest that the interaction between ligand-L and HSA is mainly driven by van der Waals forces and hydrogen bonds, and the negative value of ΔG is an indication of spontaneous binding process. Competitive binding and molecular docking experiments showed that the binding site of ligand-L mainly resides in sub-domain IIA of HSA. CD experiments revealed no significant conformational changes in the secondary structure of HSA on binding of ligand-L. We also found that esterase-like activity of HSA was not affected by ligand-L. In conclusion, this study demonstrates binding mechanism of ligand-L with HSA, and the binding did not induce conformational changes in HSA. This study is likely to provide better understanding of transport and delivery of ligand-L via HSA. Overall, it will provide insights into pharmacokinetic properties of ligand-L and designing new ligand-L based derivatives with greater efficacy.

β-lactoglobulin-irinotecan inclusion complex as a new targeted nanocarrier for colorectal cancer cells

Beta-lactoglobulin (β-LG) is a lipocalin family member whose general function appears to be solubilizing and transport of hydrophobic molecules. Some properties such as avalability, ease of purification, and peculiar resistance to acidic environments can make β-LG as a carrier for hydrophobic and acid labile drugs for oral administration. In this protein vehicle, drug could be protected in acidic environment of stomach and then released within the basic small intestine. In this study, the potential of β-LG as a nanocarrier for oral delivery of a potent agent in colorectal cancer treatment, irinotecan, was evaluated. The nanoparticle was prepared by the physical inclusion complex method. Size, drug loading, encapsulation efficiency, and in vitro drug release at various pH values were investigated. The optimum formulation showed a narrow size distribution with an average diameter of 139.86 ± 13.75 nm and drug loading about 84.33 ± 5.03%. Based on the results obtained from docking simulation of irinotecan-complex, there are two distinct binding sites in this nanocarrier. Cytotoxicity of this nanocarrier on the HT-29 cancer cell line and AGS was measured by MTT assay. The cytotoxicity experiment showed that the drug-loaded nanocarrier was more effective than free drug. The higher release percent of drug from the β-LG complex at pH 7.4 compared to pH 1.2 indicated that the proposed nanocarrier could be introduced as a suitable nanovehicle for labile drugs in acidic medium targeted for colorectal segment.

Multi-Spectroscopic Characterization of Human Serum Albumin Binding with Cyclobenzaprine Hydrochloride: Insights from Biophysical and In Silico Approaches

Cyclobenzaprine hydrochloride (CBH) is a well-known muscle relaxant that is widely used to relieve muscle spasms and other pain associated with acute musculoskeletal conditions. In this study, we elucidated the binding characteristics of this muscle relaxant to human serum albumin (HSA). From a pharmaceutical and biochemical viewpoint, insight into the structure, functions, dynamics, and features of HSA-CBH complex holds great importance. The binding of CBH with this major circulatory transport protein was studied using a combination of biophysical approaches such as UV-VIS absorption, fluorescence quenching, and circular dichroism (CD) spectroscopy. Various in silico techniques, molecular docking and molecular dynamics, were also used to gain deeper insight into the binding. A reduction in the fluorescence intensities of HSA-CBH complex with a constant increase in temperature, revealed the static mode of protein fluorescence quenching upon CBH addition, which confirmed the formation of the HSA-CBH ground state complex. The alteration in the UV-VIS and far-UV CD spectrum indicated changes in both secondary and tertiary structures of HSA upon binding of CBH, further proving CBH binding to HSA. The analysis of thermodynamic parameters ∆H° and ∆S° showed that binding of CBH to HSA was dominated by intermolecular hydrophobic forces. The results of the molecular docking and molecular dynamics simulation studies also confirmed the stability of the complex and supported the experimental results.

Physicochemical characterization of carbamylated human serum albumin: an in vitro study

Carbamylation is an ubiquitous process in which cyanate (OCN⁻) reacts with the N-terminal amino or ε-amino moiety and generates α-carbamyl amino acids and ε-carbamyl-lysine (homocitrulline).

Site-specific binding of a water molecule to the sulfa drugs sulfamethoxazole and sulfisoxazole: a laser-desorption isomer-specific UV and IR study

Using isomer-specific IR spectroscopy, we show that sulfamethoxazole and sulfisoxazole exhibit distinct site specificities for binding a water molecule.

Spectroscopic Studies on the Interaction between Tilorone and Human Serum Albumin

Under physiological conditions, in vitro interaction between the antiviral drug 2,7-bis[2-(diethylamino)ethoxy]-9-fluorenone dihydrochloride (Tilorone, TIL) and human serum albumin (HSA) was investigated at excitation wavelength 280 nm and at different temperatures (298 K and 313 K) by fluorescence emission spectroscopy. TIL showed a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant is estimated as KA =7.19× 104L·mol-1 at 298 K. The enthalpy change (ΔHº) and entropy change (ΔSº) were derived to be negative values. A value of 1.63 nm for the average distance r between TIL (acceptor) and tryptophan residues of HSA (donor) was derived from the fluorescence resonance energy transfer.

Study on the interaction of 6-(2-morpholin-4-yl-ethyl)-6H-indolo [2,3-b]quinoxaline hydrochloride with human serum albumin by fluorescence spectroscopy

Under physiological conditions, in vitro interaction between the bio-active substance 6-(2-morpholin-4-yl-ethyl)-6H-indolo[2,3-b]quinoxaline hydrochloride (MIQ) and human serum albumin (HSA) was investigated at an excitation wavelength 260 nm and at different temperatures (298 K, 308 K and 313 K) by fluorescence emission spectroscopy. From spectral analysis, MIQ showed a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant is estimated asK _A   =  2.55  ×  10^-4 l · mol^-1 at 298 K. Based on the thermodynamic parameters evaluated from the van 't Hoff equation, the enthalpy change (ΔH°) and entropy change (ΔS°) were derived to be negative values. A value of 2.37 nm for the average distance r between MIQ (acceptor) and tryptophan residues of HSA (donor) was derived from the fluorescence resonance energy transfer. UV/vis absorption spectra were used to confirm the quenching mechanism.