Investigation on the interaction of pyrene with bovine serum albumin using spectroscopic methods

Investigating the protein modification and degradation under the influence of petrol and kerosene

During any crime scene investigation, forensic experts gather a variety of evidence in various forms, often degraded, contaminated, or fragmentary in nature. Arson-associated suicide or homicidal cases often result in partial or complete burning of this evidence, making the acquisition of crucial information more challenging. Proteins found in biological samples serve as crucial sources of evidence in criminal investigations due to their abundance within the body and greater stability than another biological macromolecule. Protein based technologies are gaining momentum for investigating wide range of forensic cases. In the present study, we probed different modifications in chicken protein subjecting after burning with petrol and kerosene individually. Structural changes and modifications in burnt chicken meat protein samples were analyzed by various biophysical techniques, such as absorption and fluorescence spectroscopy. Gel-based method such as electrophoresis was performed which showed different degradation patterns under the influence of petrol and kerosene. Our results showed that petrol-exposed meat sample caused higher rate of protein degradation than kerosene exposed samples, over a period of 12 days. Prevalent oxidative modifications, including increased carbonylation and decreased thiol levels were observed in both petrol and kerosene treated sample attributing oxidative stress environment caused by burning. Present study highlights that petrol is more potent in causing damage and protein modification than kerosene. Furthermore, this study elucidates the application of protein-based methods in forensic science, which can serve as a corroborative approach in ascertaining the cause of death in cases of burning, particularly where fuel has been utilized.

Interaction mechanism of Cu+/Cu2+ on bovine serum albumin: Vitro simulation experiments by spectroscopic methods

Copper (Cu) is an essential trace element for organisms, while excessive concentration of Cu is toxic. In order to assess the toxicity risk of copper in different valences, FTIR, fluorescence, and UV-vis absorption techniques were conducted to study the interactions between either Cu⁺ or Cu²⁺ and bovine serum albumin (BSA) under vitro simulated physiological condition. The spectroscopic analysis demonstrated that the intrinsic fluorescence emitted by BSA could be quenched by Cu⁺/Cu²⁺ via static quenching with binding sites 0.88 and 1.12 for Cu⁺ and Cu²⁺, respectively. On the other hand, the constants of Cu⁺ and Cu²⁺ are 1.14 × 10³ L/mol and 2.08 × 10⁴ L/mol respectively. ΔH is negative whereas ΔS is positive, showing that the interaction between BSA and Cu⁺/Cu²⁺ was mainly driven by electrostatic force. In accordance with Föster's energy transfer theory, the binding distance r showed that the transition of energy from BSA to Cu⁺/Cu²⁺ is highly likely to happen. BSA conformation analyses indicated that the interactions between Cu⁺/Cu²⁺ and BSA could alter the secondary structure of proteins. Current study provides more information of the interaction between Cu⁺/Cu²⁺ and BSA, and reveals the potential toxicological effect of different speciation of copper at molecular level.

Hydrophobization of a TIP60 Protein Nanocage for the Encapsulation of Hydrophobic Compounds

Encapsulation of hydrophobic molecules in protein-based nanocages is a promising approach for dispersing these molecules in water. Here, we report a chemical modification approach to produce a protein nanocage with a hydrophobic interior surface based on our previously developed nanocage, TIP60. The large pores of TIP60 act as tunnels for small molecules, allowing modification of the interior surface by hydrophobic compounds without nanocage disassembly. We used four different hydrophobic compounds for modification. The largest modification group tested, pyrene, resulted in a modified TIP60 that could encapsulate aromatic photosensitizer zinc phthalocyanine (ZnPC) more efficiently than the other modification compounds. The encapsulated ZnPC generated singlet oxygen upon light activation in the aqueous phase, whereas ZnPC alone formed inert aggregates under the same experimental conditions. Given that chemical modification allows a wider diversity of modifications than mutagenesis, this approach could be used to develop more suitable nanocages for encapsulating hydrophobic molecules of interest.

Molecular interactions between bovine serum albumin (BSA) and trihalophenol: Insights from spectroscopic, calorimetric and molecular modeling studies

The issue of disinfection byproducts (DBPs) in the water has received critical attention due to the health effects on humans. In the water environment, interactions between bovine serum albumins (BSA), the most abundant water-soluble protein, and DBPs unavoidably occur. In this study, comparative binding interactions of two aromatic DBPs - 2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP) with BSA were investigated systematically utilizing fluorescence spectrometry, UV absorption spectrometry, isothermal titration calorimetry and molecular docking approach. The fluorescence quenching results indicated that TCP/TBP could quench the endogenous fluorescence of BSA through static quenching mechanisms, and TBP showed a more substantial quenching effect. The binding constants were determined for TCP-BSA (3.638 × 10⁵ L/mol, 303 K) and TBP-BSA (6.394 × 10⁵ L/mol, 303 K) complexes, with TBP showing higher binding affinity than TCP. The thermodynamic study and docking analysis suggested that hydrogen bonding and van der Waals forces were the primary interaction forces. Both of TCP and TBP were located in the subdomain IIIA of BSA, and TBP could form more stable complex than TCP. The results of the present study contributed valuable information on the environmental behaviors of halophenols in water environment from perspectives of binding with BSA.

Enhancement of thioethers removal by pre-oxidation-coagulation: Effects of background organic matter

Swampy/septic odor caused by thioethers has become the main taste and odor (T&O) problem in drinking water of China. Improving its removal performance by commonly traditional water treatment process is significant. In our study, we have found that pre-oxidation could modify the background dissolved organic matter (DOM) properties and thus improve the coagulation performance of thioethers, increasing the coagulation removal rates by 1.5-3 times. Particularly, after pre-ozonation only protein-like substances remained, and thioethers removal was 1.5 times higher than that after pre-chlorination (only coagulation not including oxidation). Compared with humic acid (HA), the thioethers compounds removal efficiencies under bovine serum albumin (BSA) as background DOM was increased by 0.3-3 times. Through Freundlich model analysis, the binding strength of BSA (K_F = 20.712, at 298 K) to dimethyl disulfide (DMDS) was enhanced by 60 % compared to HA (K_F = 12.778, at 298 K). According to thermodynamic parameters, the binding effect between HA/BSA and thioethers compounds was mainly van der Waals forces and hydrogen bond. BSA with more amino structure and oxygen groups was more easily to adsorb DMDS through hydrogen bond and thus achieved better coagulation performance. Therefore, pre-ozonation combined with coagulation was suggested to be more suitable for thioethers compounds control.

A novel heterometallic ruthenium-silver complex as potential antitumor agent: Studies on its synthesis, in vitro assays and interactions with biomolecular targets

Certain ruthenium compounds are found to be potent growth inhibitors for cancer cells. In the current study, a novel ruthenium-triphenylphosphine (PPh₃) cation and silver-2-mercapto nicotinate acid (H₂mna) anion complex (RSC) was synthesized, and its molecular structure was determined by IR, NMR and X-ray crystallography. Biological assays revealed that RSC strongly inhibited the viability of MCF-7 and MDA-MB-231 cells with IC₅₀ values of 9.6±1.1 and 7.5±0.8 µM, respectively, and significantly blocked their migration rates. Ultraviolet spectroscopy and fluorescence emission experiments demonstrated that RSC interacted with BSA, but not DNA. Further studies on [Ag₆(Hmna)₂(mna)₄]^4- binding with BSA and DNA found the anion did not interact with these biomolecules, indicating that RSC exerted its biological functions through its ruthenium-PPh₃ complex (RTC) moiety, and molecular docking provided additional evidence supporting this result. Fluorescence resonance energy transfer showed that the number of binding sites (n) and binding constant of RTC-BSA complex were 1 and 8.60 × 10⁴ M^-1 at 310K, suggesting a strong interaction between RTC and BSA. The thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ of the binding were calculated, and it was demonstrated that the binding of RTC with BSA was enthalpy-driven, and the main forces between RTC and BSA were electrostatic force and hydrogen bonding. Molecular docking showed that the binding site of BSA with RSC was located on the interface between the domains IIA and IIB of the protein. The present study sheds light on that a ruthenium mono-coordinated with PPh₃ complex could help to design and develop a new class of antitumor drugs.

Exploring the interactions of acenaphthene with bovine serum albumin: Spectroscopic methods, molecular modeling and chemometric approaches

The interaction of acenaphthene (ACN), a widespread environmental pollutant, with bovine serum albumin (BSA) was explored using spectroscopic methods, molecular modeling and chemometric approaches. The multivariate curve resolution-alternating least squares (MCR-ALS) analysis decomposed the overlapped excitation-emission matrix (EEM) spectra of mixture of ACN and BSA successfully and extracted spectral profiles of pure BSA, ACN and BSA-ACN complex. Based on fluorescence quenching analysis, ACN quenched the inherent fluorescence of BSA remarkably via a static mechanism. The obtained value of binding constant (K_b = 3.82 × 10⁵ L mol^-1) revealed a high binding affinity of ACN to BSA which facilitates its distribution by blood circulation system. Furthermore, the binding parameters values revealed that one binding site in BSA was involved in BSA-ACN complex. FT-IR, UV-Vis and CD spectra showed that the conformation of BSA was altered in presence of ACN slightly. Molecular docking simulation suggested that ACN was located in the IA region of BSA and the main interactions between ACN and BSA, are van der Waals forces. The obtained results provide some insight into interactions between ACN and serum albumins at the molecular level.

Probing the biological toxicity of pyrene to the earthworm Eisenia fetida and the toxicity pathways of oxidative damage: A systematic study at the animal and molecular levels

Pyrene (Pyr), a widely used tetracyclic aromatic hydrocarbon, enters soil in large quantities and causes environmental pollution due to its production and mining. In order to systematically study the biotoxicity of pyrene to model organisms Eisenia fetida in soil, experiments were carried out from four dimensions: animal, tissue, cell and molecule. Experimental results proved that the mortality rate increased with increasing concentration and time of exposure to pyrene, while the mean body weight and spawning rate decreased. Meanwhile, when the pyrene concentration reached 900 mg/kg, the seminal vesicle and longitudinal muscle of the earthworm showed obvious atrophy. Experimental results at the cellular level showed that pyrene induced cell membrane damage and Ca²⁺ influx triggered mitochondrial membrane depolarization and a surge in ROS levels. Oxidative stress causes damage to proteins and lipids and DNA inside cells. When the mortality rate was 91.67 %, the Olive Tail Movement (OTM) of the comet experiment reached 15. The results of molecular level tests showed that pyrene inhibited the activity of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) mainly by changing the microenvironment and secondary structure of amino acid Tyr 108. The weakened function of direct antioxidant enzymes may be the root cause of the excessive increase of reactive oxygen species (ROS) in cells. The systematic approach used in this study enriches the network of toxic pathways in toxicological studies, and basic data on the biological toxicity of pyrene can provide support for future soil contamination detection.

Evaluation of the interaction of novel tyrosine kinase inhibitor apatinib mesylate with bovine serum albumin using spectroscopies and theoretical calculation approaches

Apatinib mesylate (APM), a novel tyrosine kinase inhibitor, has been applied in treating various cancers. In the present study, the binding mechanism of APM with bovine serum albumin (BSA) was studied by making use of various spectroscopic and theoretical calculation approaches to provide theoretical support for further studying its pharmacokinetics and metabolism. The results from fluorescence experiments showed that the quenching mechanism of BSA induced by APM was static quenching and the APM-BSA complex with the stoichiometry of 1:1 was formed during binding reaction. Moreover, the findings also showed that the binding process of APM to BSA was spontaneous and enthalpy-driven, and the mainly driving forces were hydrogen bonding, van der Waals as well as hydrophobic interactions. From the outcomes of the competitive experiments, it can be found that the binding site was primarily nestled in sub-domain IIIA of BSA (site II) which was in line with the results of molecular docking. An appreciable decline in α-helix content of BSA can be observed from the FT-IR data, meaning that the conformational change of BSA occurred after binding with APM, this phenomenon can be corroborated by the results of UV-vis, synchronous fluorescence and 3D fluorescence studies. Furthermore, the effect of some metal ions (e.g. K⁺, Co²⁺, Ni²⁺, Fe³⁺) on the binding constant of APM to BSA was explored.Communicated by Ramaswamy H. Sarma.

Binding of model polycyclic aromatic hydrocarbons and carbamate-pesticides to DNA, BSA, micelles and liposomes

The binding to biosubstrates and micellar systems of pollutants as the polycyclic aromatic hydrocarbon (PAH) derivatives 1-aminopyrene (1-PyNH₂) and 1-hydroxymethylpyrene (1-PyMeOH) and the carbamate-pesticides 1-naphthyl-N-methylcarbamate (carbaryl, CA) and methyl benzimidazol-2-ylcarbamate (carbendazim, CBZ) was analysed through an integrated strategy combining spectroscopy and quantum chemistry. As biosubstrates, natural DNA and bovine serum albumin (BSA) were taken into account for a thermodynamic analysis of the binding features through spectrophotometric and spectrofluorometric techniques. In all cases, a strong DNA interaction is present and intercalation is supposed as the major binding mode. For the PAH derivatives, DNA binding is found to be favoured under high salt conditions and BSA static quenching and binding with 1:1 stoichiometry occurs. The molecular structure and optical properties of 1-PyNH₂, CA and CBZ together with their intercalated adducts in DNA were studied also by means of quantum chemical approach. The (TD)DFT calculations on intercalated dye/DNA adducts quantitatively reproduce the experimentally observed spectroscopic changes, thus confirming the intercalation hypothesis. The theoretical approach also provides information on the adducts' geometries and on the amount of charge transfer with DNA. Moreover, ultrafiltration tests in the presence of anionic (SDS), cationic (DTAC) and neutral (Triton X) micellar aggregates and liposomes provided insights into lipophilicity and cellular membrane affinity. PAH derivatives show high retention coefficient in all cases, whereas in the case of carbamate-pesticides micellar retention might be significantly reduced and is very limited in the case of liposomes.

Spectroscopic methodologies and molecular docking studies on the interaction of antimalarial drug piperaquine and its metabolites with human serum albumin

Artemisinin-based combination therapy is widely used for the treatment of uncomplicated Plasmodium falciparum malaria, and piperaquine (PQ) is one of the important partner drugs. During the biotransformation of PQ, M1 (N-oxidation product), M2 (N-oxidation product), M3 (carboxylic acid product), M4 (N-dealkylation product), and M5 (N-oxidated product of M4) are formed by cytochrome P450 pathways. Despite decades of clinical use, the interactions between PQ and its main metabolites (PQs) with human serum albumin (HSA) have not been reported. In the present study, the binding of PQs with HSA under physiological conditions was investigated systematically through fluorescence, circular dichroism (CD) spectroscopy, and molecular docking methods. The experimental results show that the intrinsic fluorescence quenching of HSA was induced by those compounds resulting from the formation of stable HSA-compound complexes. The main forces involved in the interactions between PQ, M1, and M2 which bind to HSA were hydrogen s and van der Waals forces, while the interactions of M3, M4, and M5 were driven by hydrophobic forces. The main binding sites of the compounds to HSA were also examined by classical fluorescent marker experiments and molecular docking studies. Binding constants (K_b) revealed that the affinities of the PQ, M1, M2, M3, and M4 to HSA were stronger than that of M5. Additionally, the binding rates of PQs with HSA were determined by ultrafiltration methods. Consistent with the binding constant results, the binding rate of M5 was lower than the binding rates of PQ, M1, M2, M3, and M4. Furthermore, PQs binding to HSA led to conformational and structural alterations of HSA, as revealed by multi-spectroscopic studies. In order to investigate one possible mechanism by which PQs inhibit the growth of malaria-causing Plasmodium parasites, ¹H NMR spectroscopy was performed to investigate the interaction of the PQs with heme. This study is beneficial to enhance our understanding of the ecotoxicology and environmental behaviors of PQ and its metabolites.

Fluorescent Polyvinylphosphonate Bioconjugates for Selective Cellular Delivery

To date, many poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAAm) biomolecule conjugates have been described, but they often show long response times, are not bio-inert, or lose function in biological fluids. Herein, we present a modular synthetic approach to generate polyvinylphosphonate biomolecule conjugates. These conjugates exhibit a sharp phase transition temperature even under physiological conditions where few other examples with this property have been described to date. Furthermore, it was feasible to add biological functions to the polymers via the conjugation step. The polyvinylphosphonate cholesterol constructs are attached to the cellular membrane and the folic acid anchored polymers are shuttled into the cells. This is an exceptional finding through a straightforward synthetic approach.

Study on the interaction of chromate with bovine serum albumin by spectroscopic method

The interaction between two chromates [sodium chromate (Na₂CrO₄) and potassium chromate K₂CrO₄)] and bovine serum albumin (BSA) in physiological buffer (pH 7.4) was investigated by the fluorescence quenching technique. The results of fluorescence titration revealed that two chromates could strongly quench the intrinsic fluorescence of BSA through a static quenching procedure. The apparent binding constants K and number of binding sites n of chromate with BSA were obtained by the fluorescence quenching method. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) were negative, indicating that the interaction of two chromates with BSA was driven mainly by van der Waals forces and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative. The distance r between donor (BSA) and acceptor (chromate) was calculated based on Forster's non-radiative energy transfer theory. The results of UV-Vis absorption, synchronous fluorescence, three-dimensional fluorescence and circular dichroism (CD) spectra showed that two chromates induced conformational changes of BSA.

Thermal stability of the complex formed between carotenoids from sea buckthorn (Hippophae rhamnoides L.) and bovine β-lactoglobulin

Sea buckthorn has gained importance as a versatile nutraceutical, due to its high nutritive value in terms of carotenoids content. β-Lactoglobulin (β-LG) is a natural carrier for various bioactive compounds. In this study, the effect of thermal treatment in the temperature range of 25 to 100°C for 15min on the complex formed by β-LG and carotenoids from sea buckthorn was reported, based on fluorescence spectroscopy, molecular docking and molecular dynamics simulation results. Also, the berries extracts were analyzed for their carotenoids content. The chromatographic profile of the sea buckthorn extracts revealed the presence of zeaxanthin and β-carotene, as major compounds. The Stern-Volmer constants and binding parameters between β-LG and β-carotene were estimated based on quenching experiments. When thermally treating the β-LG-carotenoids mixtures, an increase in intrinsic and extrinsic fluorescence intensity up to 90°C was observed, together with blue-shifts in maximum emission in the lower temperature range and red-shifts at higher temperature. Based on fluorescence spectroscopy results, the unfolding of the protein molecules at high temperature was suggested. Detailed information obtained at atomic level revealed that events taking place in the complex heated at high temperature caused important changes in the β-carotene binding site, therefore leading to a more thermodynamically stable assembly. This study can be used to understand the changes occurring at molecular level that could help food operators to design new ingredients and functional foods, and to optimize the processing methods in order to obtain healthier food products.

Analysis of binding ability of two tetramethylpyridylporphyrins to albumin and its complex with bilirubin

An interaction between 5,10,15,20-tetrakis-(N-methyl-x-pyridyl)porphyrins, x=2; 4 (TMPyPs) with bovine serum albumin (BSA) and its bilirubin (BR) complex was investigated by UV-Viz and fluorescence spectroscopy under imitated physiological conditions involving molecular docking studies. The parameters of forming intermolecular complexes (binding constants, quenching rate constants, quenching sphere radius etc.) were determined. It was showed that the interaction between proteins and TMPyPs occurs via static quenching of protein fluorescence and has predominantly hydrophobic and electrostatic character. It was revealed that obtained complexes are relatively stable, but in the case of TMPyP4 binding with proteins occurs better than TMPyP2. Nevertheless, both TMPyPs have better binding ability with free protein compared to BRBSA at the same time. The influence of TMPyPs on the conformational changes in protein molecules was studied using synchronous fluorescence spectroscopy. It was found that there is no competition of BR with TMPyPs for binging sites on protein molecule and BR displacement does not occur. Molecular docking calculations have showed that TMPyPs can bind with albumin via tryptophan residue in the hydrophilic binding site of protein molecule but it is not one possible interaction way.

A novel bioaccessibility prediction method for PAHs in soil: Composite extraction with hydroxypropyl-β-cyclodextrin and extracellular polymer substances

Hydroxypropyl-β-cyclodextrin (HPCD) extraction has been widely used to estimate bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in soil, but it often underestimates the actual risk due to lack of information regarding the exogenous active substances, such as extracellular polymer substance (EPS) secreted by microorganisms. In this study, a novel technique, composite extraction of HPCD each with rhamnolipid (RL), bovine serum albumin (BSA) and alginate sodium (AS), models of lipopolysaccharide, proteins and polysaccharides, was developed to assess PAHs bioaccessibility to earthworms. In addition, comparisons were conducted with accelerated solvent extraction (ASE) and individual HPCD extraction. The results demonstrated that all chemical extractions were linearly correlated with earthworm accumulation, and individual HPCD extraction underestimated PAH bioaccessibility by about two times. However, the overall performances of the three composite chemical extractions (HPCD/AS, HPCD/RL, HPCD/BSA) were better than individual HPCD extraction, among which, HPCD/AS was best at estimating the earthworm accumulation (considering both correlation coefficient and fitted linear slope). Therefore, all observations implied that HPCD/AS extraction could be used as a fast and reliable method to predict PAH bioaccessibility to earthworms in contaminated soils.

Binding interaction of phosphorus heterocycles with bovine serum albumin: A biochemical study

Interaction between bovine serum albumin (BSA) and phosphorus heterocycles (PHs) was studied using multi-spectroscopic techniques. The results indicated the high binding affinity of PHs to BSA as it quenches the intrinsic fluorescence of BSA. The experimental data suggested the fluorescence quenching mechanism between PHs and BSA as a dynamic quenching. From the UV–vis studies, the apparent association constant (K_app) was found to be 9.25×10², 1.27×10⁴ and 9.01×10² L/mol for the interaction of BSA with PH-1, PH-2 and PH-3 respectively. According to the Förster's non-radiation energy transfer (FRET) theory, the binding distances between BSA and PHs were calculated. The binding distances (r) of PH-1, PH-2 and PH-3 were found to be 2.86, 3.03, and 5.12 nm, respectively, indicating energy transfer occurs between BSA and PHs. The binding constants of the PHs obtained from the fluorescence quenching data were found to be decreased with increase of temperature. The negative values of the thermodynamic parameters ΔH, ΔS and ΔG at different temperatures revealed that the binding process is spontaneous; hydrogen bonds and van der Waals interaction were the main force to stabilize the complex. The microenvironment of the protein-binding site was studied by synchronous fluorescence and circular dichroism (CD) techniques and data indicated that the conformation of BSA changed in the presence of PHs. Finally, we studied the BSA-PHs docking using Autodock and results suggest that PHs is located in the cleft between the domains of BSA.

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The interaction between BSA and PHs by spectroscopic methods.

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The fluorescence quenching mechanism is dynamic.

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Van der Waals force and hydrogen bond are the main force for BSA-PHs interaction.

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Docking of PHs-BSA interaction.

Interactions of 1-hydroxypyrene with bovine serum albumin: insights from multi-spectroscopy, docking and molecular dynamics simulation methods

Combining multi-spectroscopy, docking with MD simulations, the interactions of 1-hydroxypyrene with BSA and the adverse effects on BSA were investigated.

Ionic liquid-coated Fe3O4/APTES/graphene oxide nanocomposites: synthesis, characterization and evaluation in protein extraction processes

A magnetic solid-phase extraction (MSPE) procedure with ionic liquid (IL) coated 3-aminopropyltriethoxysilane (APTES)-Fe₃O₄ grafted graphene oxide (GO) nanocomposite (Fe₃O₄/APTES/GO/IL) as adsorbent has been developed for protein extraction.

Study on the binding interaction of chromium(VI) with humic acid using UV-vis, fluorescence spectroscopy and molecular modeling

In this report, the binding interaction of chromium(VI), as Cr2O7(2-), with humic acid was studied by using UV-visible absorption, fluorescence spectroscopy, and molecular modeling method. The fluorescence spectral data indicated that the binding interaction existed between Cr2O7(2-) and humic acid and the order of magnitude of binding constants were 10(3). The rise in temperature caused a decrease in the values of the binding constant of humic acid with Cr2O7(2-). Thermodynamic analysis presented that multi-intermolecular forces including hydrogen bonding, hydrophobic, and electrostatic forces were involved in the binding process at pH 6.5. The spectral data also indicated that Cr2O7(2-) affected the aromatic ring structures in humic acid. Furthermore, the molecular modeling analysis indicated that a lot of reactive groups and binding cavities in HA played a key role in its binding with Cr2O7(2-).

Interaction mechanisms between organic UV filters and bovine serum albumin as determined by comprehensive spectroscopy exploration and molecular docking

Organic UV filters are a group of emerging PPCP (pharmaceuticals and personal care products) contaminants. Current information is insufficient to understand the in vivo processes and health risks of organic UV filters in humans. The interaction mechanism of UV filters with serum albumin provides critical information for the health risk assessment of these active ingredients in sunscreen products. This study investigates the interaction mechanisms of five commonly used UV filters (2-hydroxy-4-methoxybenzophenone, BP-3; 2-ethylhexyl 4-methoxycinnamate, EHMC; 4-methylbenzylidene camphor, 4-MBC; methoxydibenzoylmethane, BDM; homosalate, HMS) with bovine serum albumin (BSA) by spectroscopic measurements of fluorescence, circular dichroism (CD), competitive binding experiments and molecular docking. Our results indicated that the fluorescence of BSA was quenched by these UV filters through a static quenching mechanism. The values of the binding constant (Ka) ranged from (0.78±0.02)×10(3) to (1.29±0.01)×10(5) L mol(-1). Further exploration by synchronous fluorescence and CD showed that the conformation of BSA was demonstrably changed in the presence of these organic UV filters. It was confirmed that the UV filters can disrupt the α-helical stability of BSA. Moreover, the results of molecular docking revealed that the UV filter molecule is located in site II (sub-domain IIIA) of BSA, which was further confirmed by the results of competitive binding experiments. In addition, binding occurred mainly through hydrogen bonding and hydrophobic interaction. This study raises critical concerns regarding the transportation, distribution and toxicity effects of organic UV filters in human body.

Intrinsic tryptophan fluorescence in the detection and analysis of proteins: a focus on Förster resonance energy transfer techniques

Förster resonance energy transfer (FRET) occurs when the distance between a donor fluorophore and an acceptor is within 10 nm, and its application often necessitates fluorescent labeling of biological targets. However, covalent modification of biomolecules can inadvertently give rise to conformational and/or functional changes. This review describes the application of intrinsic protein fluorescence, predominantly derived from tryptophan (λ EX ≈ 280 nm, λ EM ≈ 350 nm), in protein-related research and mainly focuses on label-free FRET techniques. In terms of wavelength and intensity, tryptophan fluorescence is strongly influenced by its (or the proteinlocal environment, which, in addition to fluorescence quenching, has been applied to study protein conformational changes. Intrinsic Förster resonance energy transfer (iFRET), a recently developed technique, utilizes the intrinsic fluorescence of tryptophan in conjunction with target-specific fluorescent probes as FRET donors and acceptors, respectively, for real time detection of native proteins.