Spectroscopic characterization of effective components anthraquinones in Chinese medicinal herbs binding with serum albumins

Efficient detection of aklomide/nitromide based on a sensor of MPA capped CdTe QDs using fluorescence quenching method

Based on the fluorescence sensor of 3-Mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs), two novel detection methods for aklomide and nitromide were developed. The MPA-CdTe QDs were synthesized and characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), ultraviolet visible (UV-vis) and fluorescence (FL). The quenchings were all static. The binding constants (Ka) at different temperatures were obtained. Electrostatic forces were the main forces for the two bindings. For the detection of aklomide and nitromide, under the optimal conditions, the effects of some metal ions, glucose, bovine serum albumin (BSA) and congeneric drug on the determination were explored. The standard equations were established and the limits of detection (LOD) were 0.0215 and 0.0388 μg mL-1 (3S0/S), repectively. The methods were applied to analyse the samples of chicken and duck, the recoveries were 99.41 % - 101.24 % with RSDs of 0.29 % - 1.19 % (n = 5).

Study on the toxicity prediction model ofacetolactate synthase inhibitor herbicides based on human serum albumin and superoxide dismutase binding information

Toxicity significantly influences the successful development of drugs. Based on the toxicity prediction method (carrier protein binding information-toxicity relationship) previously established by the our group, this paper introduces information on the interaction between pesticides and environmental markers (SOD) into the model for the first time, so that the toxicity prediction model can not only predict the toxicity of pesticides to humans and animals, but also predict the toxicity of pesticides to the environment. Firstly, the interaction of acetolactate synthase inhibitor herbicides (ALS inhibitor herbicides) with human serum albumin (HSA) and superoxide dismutase (SOD) was investigated systematically from theory combined with experiments by spectroscopy methods and molecular docking, and important fluorescence parameters were obtained. Then, the fluorescence parameters, pesticides acute toxicity LD50 and structural splitting information were used to construct predictive modeling of ALS inhibitor herbicides based on the carrier protein binding information (R2 = 0.977) and the predictive modeling of drug acute toxicity based on carrier protein binding information and conformational relationship (R2 = 0.991), which had effectively predicted pesticides toxicity in humans and animals. To predict potential environmental toxicity, the predictive modeling of drug acute toxicity based on superoxide dismutase binding information was established (R2 = 0.883) by ALS inhibitor herbicides-SOD binding information, which has a good predictive ability in the potential toxicity of pesticides to the environment. This study lays the foundation for developing low toxicity pesticides.

A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone

A method was established for detecting the content of nitrofurazone (NFZ) by fluorescence quenching of N-Acetyl-L-Cysteine (NAC) coated cadmium telluride quantum dots (CdTe QDs). By means of transmission electron microscopy (TEM) and multispectral methods such as fluorescence and ultraviolet visible spectra (UV-vis), the synthesized CdTe QDs were characterized. The quantum yield (φ) of CdTe QDs was measured as 0.33 by reference method. The CdTe QDs had a better stability, the RSD of fluorescence intensity was 1.51% in three months. NFZ quenching the emission light of CdTe QDs was observed. The analyses of Stern-Volmer and time-resolved fluorescence suggested the quenching was static. The binding constants (K_a) between NFZ and CdTe QDs were 1.14 × 10⁴ (293 K), 0.74 × 10⁴ (303 K) and 0.51 × 10⁴ (313 K) L mol^-1. The hydrogen bond or van der Waals force was the dominated binding force between NFZ and CdTe QDs. The interaction was further characterized by UV-vis absorption as well as Fourier transform infrared spectra (FT-IR). Using fluorescence quenching effect, a quantitative determination of NFZ was carried out. The optimal experimental conditions were studied and determined as following: pH was 7 and contact time was 10 min. The effects of reagent addition sequence, temperature and the foreign substances including some metals (Mg²⁺; Zn²⁺; Ca²⁺; K⁺; Cu²⁺), glucose, bovine serum albumin (BSA) and furazolidone on the determination were studied. There was a high correlation between the concentration of NFZ (0.40 - 39.63 μg mL^-1) and F₀/F with the standard curve F₀/F = 0.0262c + 0.9910 (r = 0.9994). The detection limit (LOD) reached 0.04 μg mL^-1 (3S₀/S). The contents of NFZ in beef and bacteriostatic liquid were detected. The recovery of NFZ was 95.13% - 103.03% and RSD was 0.66% - 1.37% (n = 5).

Role of anthraquinones in Cassia occidentalis induced hepato-myo-encephalopathy

ETHNOPHARMACOLOGICAL RELEVANCE

The different plant parts of Cassia occidentalis Linn, (CO) such as root, leaves, seeds and pods have traditionally been used in multifarious medicines for the treatment of dysentery, diarrhea, constipation, fever, eczema, cancer and venereal diseases.

MATERIALS AND METHODS

A systematic search of literature has been done in books and scientific databases like Science Direct, Pubmed, Google Scholar and Scopus etc. These sources were used to compile, analyze and review the information regarding the phytochemistry, toxicology and mechanism of toxicity of CO. The various references on this subject are cited in our review ranging from 1956 to 2019.

RESULTS

Unintentional exposure of CO causes serious pathological condition in children, known as hepato-myo-encephalopathy (HME). The toxicity after CO consumption is associated with the presence of anthraquinones (AQs), a class of secondary plant metabolites. These AQs at high concentrations are known to cause detrimental effects on essential vital organs such as liver, kidney, spleen, brain, muscle and reproductive organs. The animal studies in rodent models as well as clinical investigations have clearly revealed that CO toxicity is associated with enhanced hepatotoxicity serum markers (ALT, AST, and LDH) and presence of necrotic lesions in liver. Furthermore, CO also causes vacuolization in muscle tissue and increases the level of CPK which is a prominent muscle damage marker. Apart from these target organs, CO consumption also causes neuronal damage via disturbing the levels of different proteins such as (GFAP and b-tubulin III). The mechanistic studies show that AQs present in CO have the potential to disturb the cellular homeostasis via binding to DNA, increasing the production ROS and showing inhibitory effects on essential enzymes etc. Therefore, AQs have been observed to be the primary culprit agents contributing to the toxicity of CO in children and animals.

CONCLUSION

Despite its therapeutic potential, CO consumption can be detrimental if consumed in high amounts. A thorough analysis of literature reveals that AQs are the primary factors contributing to toxicity of CO seeds. Exposure to CO seeds causes HME, which is a serious life threatening condition for the malnourished children from lower strata. Multiple mechanisms are involved in the CO induced HME in patients. Lack of appropriate diagnostic measures and a poor understanding of the CO toxicity mechanism in humans and animals complicate the clinical management of CO poisoning subjects. Therefore, development of point of care diagnostic kits shall help in early diagnosis & suitable management of CO poisoning.

Multispectral and molecular modeling investigations on the binding behaviors of two anticoccidials with serum albumins

The interaction properties of monensin/clopidol with bovine/human serum albumin (BSA/HSA) were determined via multispectral together with molecular modeling techniques in the report. Fluorescence quenching spectra at different temperatures and fluorescence lifetime determination demonstrated that the fluorescence quenching belonged to a static quenching type. In the case of monensin-BSA, clopidol-BSA, monensin-HSA and clopidol-HSA, the binding constants K_a (291 K) were 5.42 × 10⁴, 4.96 × 10⁴, 3.22 × 10⁴ and 2.99 × 10⁴ M^-1, respectively; the binding distances r₀ were 1.88, 2.53, 2.19 and 2.02 nm, respectively. Monensin and clopidol bound strongly with BSA/HSA with binding free energies equal to -26.37/-25.11 and -26.11/-24.93 kJ mol^-1, respectively. The spontaneous binding process was dominated by hydrogen bonds and van der Waals forces as reflected in thermodynamic parameters analyses. Synchronous, CD, FTIR and UV-vis spectra assays confirmed that serum albumins conformations were altered. Using competitive experiment, monensin/clopidol was observed to bind at site I of serum albumins, which were reconfirmed by the results of molecular modeling.Communicated by Ramaswamy H. Sarma.

Assessment on the binding characteristics of residual marbofloxacin in animal-derived food to bovine/human serum albumin by spectroscopy and molecular modelling

To assess the toxicity of residual marbofloxacin from animal-derived food, the interaction characteristics of marbofloxacin to bovine/human serum albumins (BSA/HSA) were explored using spectroscopic methods combined with molecular modelling. According to fluorescence spectra and time-resolved fluorescence spectra measurements, quenching of BSA/HSA fluorescence induced by marbofloxacin was characterized as static quenching. A 1:1 ground-state complex of marbofloxacin to BSA/HSA was formed with binding constant (K_a ) 1.66 × 10⁴ /9.74 × 10³ M^-1 at 291 K. The location of marbofloxacin binding at site I within BSA/HSA was clarified by site marker competitive experiments. Molecular modelling demonstrated that the binding region for marbofloxacin to BSA and HSA were at site I with the lowest binding free energies of -22.86 and -21.60 kJ mol^-1 , respectively. Hydrogen bonds and van der Waals forces were dominantly involved in the spontaneous binding. Nonradiation energy transferred from BSA and HSA to marbofloxacin, due to the close distance (r₀ ) between marbofloxacin and Trp residues of BSA (4.28 nm) and HSA (3.34 nm). As explained by circular dichroism (CD) spectra, an increased BSA/HSA α-helix structure was observed after binding to marbofloxacin. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectra suggested that conformation of the two proteins was altered by marbofloxacin.

Molecular Assessment of the Toxic Mechanism of the Latest Neonicotinoid Dinotefuran with Glutathione Peroxidase 6 from Arabidopsis thaliana

With widespread applications of the latest neonicotinoid in agriculture, dinotefuran has gradually become a hazardous contaminant for plants through the generation of excessive reactive oxygen species. However, the potential toxic mechanisms of oxidative damages to plants induced by dinotefuran are still unknown. As a core component of the glutathione antioxidant enzyme system, glutathione peroxidases have been used as biomarkers to reflect excessive oxidative stress. In this study, the hazardous effects of dinotefuran on AtGPX6 were investigated at the molecular level. The intrinsic fluorescence intensity of AtGPX6 was quenched using the static quenching mechanism upon binding with dinotefuran. Moreover, a single binding site was predicted for AtGPX6 toward dinotefuran, and the complex formation was presumed to be driven by hydrogen bonds or van der Waals forces, which conformed with the molecular docking results. In addition, AtGPX6 exhibited moderate binding affinity with dinotefuran based on the bio-layer interferometry assay. In addition, the loosening and unfolding of the protein skeleton of AtGPX6 with the addition of dinotefuran were explored along with the increase of hydrophobicity around tryptophan residues. Lastly, the toxic effects of dinotefuran on the root growth of Arabidopsis seedlings were also examined. The exploration of the binding mechanism of dinotefuran with AtGPX6 at the molecular level would provide the toxicity assessment of dinotefuran on plants.

Biophysical Characterization and Anticancer Activities of Photosensitive Phytoanthraquinones Represented by Hypericin and Its Model Compounds

Photosensitive compounds found in herbs have been reported in recent years as having a variety of interesting medicinal and biological activities. In this review, we focus on photosensitizers such as hypericin and its model compounds emodin, quinizarin, and danthron, which have antiviral, antifungal, antineoplastic, and antitumor effects. They can be utilized as potential agents in photodynamic therapy, especially in photodynamic therapy (PDT) for cancer. We aimed to give a comprehensive summary of the physical and chemical properties of these interesting molecules, emphasizing their mechanism of action in relation to their different interactions with biomacromolecules, specifically with DNA.

Molecular complexes of calf thymus DNA with various bioactive compounds: Formation and characterization

The interaction between biomacromolecules and ligands has attracted great interest because of their biological properties. Calf thymus DNA (ctDNA) can interact with bioactive compounds to form complexes. Here, ctDNA-ligand complexes were studied using fluorescence, absorption, and infrared spectroscopy, circular dichroism, ABTS assay and competitive displacement. The binding constants of bioactive compounds at the intercalative site of ctDNA ranked in order kaempferol > apigenin > quercetin > curcumin > riboflavin, while the binding constants at minor groove sites ranked quercetin > kaempferol > naringenin ~ apigenin > hesperetin > curcumin ~ resveratrol ~ riboflavin > caffeic acid. CtDNA maintained stable B-form with an enhancement of base stacking and a decrease of right-handed helicity in the presence of these bioactive compounds, except for hesperetin and caffeic acid. Bioactive compounds preferentially bound to guanine bases and tended to transfer into a more hydrophobic environment upon complexation with ctDNA. The DNA complexation did not affect the ABTS·⁺ scavenging capacity of quercetin, kaempferol, resveratrol and apigenin but increased the ones of naringenin, caffeic acid, curcumin, hesperetin and riboflavin. The data gathered here should be useful to understand the binding modes of DNA with ligands for their potential application in pharmaceutical and food industries.

Study on the binding of sulfaclozine sodium monohydrate with bovine and human serum albumins using multi-spectroscopy and molecular docking

The interactions of sulfaclozine sodium monohydrate (SSM) with bovine and human serum albumins (BSA and HSA) were studied by multi-spectroscopy and molecular docking technique. Stern-Volmer analysis and fluorescence lifetime measurements suggested the quenching processes were static. According to the Fluorescence resonance energy transfer (FRET) theory, the binding distances were obtained indicating SSM interacted with BSA/HSA along with non-radiation energy conversion. Electrostatic attraction was the main force in keeping the stability of the compound based on thermodynamic parameters. Circular dichroism (CD), synchronous fluorescence and Fourier Transform infrared (FT-IR) spectra embodied the secondary structures of serum albumins were transformed by SSM. The site marker competitive and molecular docking measurements testified SSM bound to BSA/HSA at site I. In conclusion, the secondary structures of BSA/HSA were changed by SSM in the static fluorescence quenching processes with the non-radiation energy conversion. The binding sites were all located at site I and electrostatic attraction was the main force for the new compound. Communicated by Ramaswamy H. Sarma.

Separation of Protein-Binding Anthraquinones from Semen Cassiae Using Two-Stage Foam Fractionation

Anthraquinones are compounds of high medicinal value in many plants. Based on their good protein binding affinity, foam fractionation was attempted to separate them using proteins in the aqueous extract of Semen Cassiae as collectors. Firstly, the interaction between anthraquinones and Semen Cassiae proteins has been analyzed by the Stem–Volmer equation with physcion as a standard. The results show that physcion had good interaction with the proteins via hydrophobic forces. More importantly, the proteins effectively assisted the foam fractionation of several anthraquinones including aurantio-obtusifolin, aloe-emodin, rhein, emodin, chrysophanol, and physcion. On this basis, a two-stage foam fractionation technology was developed for process intensification using a foam fractionation with vertical sieve trays (VSTs). VSTs, initial feed concentration of total anthraquinones, temperature, volumetric air flow rate and pore diameter of gas distributor had significant effects on enrichment ratio and recovery yield of anthraquinones. Under suitable conditions, the enrichment ratio of total anthraquinones reached 47.0 ± 4.5 with a concentration of 939 ± 94 mg/L in the foamate while their total recovery percentage reached more than 47.7%. In addition, foam fractionation also increased the purity and hydroxyl radical scavenging activity of total anthraquinones. The results had significant implications for the separation of anthraquinones from Semen Cassiae.

Multispectral and molecular docking investigations on the interaction of primethamine/trimethoprim with BSA/HSA

Primethamine (PMA) and trimethoprim (TMP) were investigated as traditional coccidiostats on the binding of bovine serum albumin (BSA) and human serum albumin (HSA) by multispectral and molecular docking techniques. The Stern-Volmer plots and time-resolved fluorescence measurement declared that PMA/TMP quenching the intrinsic fluorescence of BSA/HSA was static quenching process. The binding constants (K_a) and binding sites (n) were calculated at different temperatures. Meanwhile, thermodynamic parameters showed electrostatic forces played a leading role in the interaction of PMA/TMP with BSA/HSA. Some metal ions such as K⁺, Mg²⁺, Cu²⁺, Ca²⁺, Zn²⁺ and Fe³⁺ had no effects on the binding system. The UV-vis absorption spectra confirmed that the interaction between PMA/TMP and BSA/HSA did happen. The analyses of synchronous fluorescence, FT-IR and circular dichroism spectra illustrated that PMA/TMP changed the secondary structures of BSA/HSA. According to Förster non-radiative energy transfer theory, the binding distance between PMA/TMP and BSA/HSA was calculated. The binding location of PMA/TMP to BSA/HSA was identified as sub-domain IIA, which was further confirmed by molecular docking.Communicated by Ramaswamy H. Sarma.

Micronomicin/tobramycin binding with DNA: fluorescence studies using of ethidium bromide as a probe and molecular docking analysis

Two aminoglycosides, micronomicin (MN), and tobramycin (TB), binding with DNA were studied using various spectroscopic techniques including fluorescence, UV-Vis, FT-IR, and CD spectroscopy coupled with relative viscosity and molecular docking. Studies of fluorescence quenching and time-resolved fluorescence spectroscopy all revealed that MN/TB quenching the fluorescence of DNA-EB belonged to static quenching. The binding constants and binding sites were obtained. The values of ΔH, ΔS, and ΔG suggested that van der Waals force or hydrogen bond might be the main binding force. FT-IR and CD spectroscopy revealed that the binding of MN/TB with DNA had an effect on the secondary structure of DNA. Binding mode of MN/TB with DNA was groove binding which was ascertained by viscosity measurements, CD spectroscopy, ionic strength, melting temperature (T_m), contrast experiments with single stranded (ssDNA), and double stranded DNA (dsDNA). Molecular docking analysis further confirmed that the groove binding was more acceptable result.

Extracellular polymeric substances affect the responses of multi-species biofilms in the presence of sulfamethizole

The occurrence and transportation of antibiotics in biofilms from natural and engineered sources have attracted increasing interests. Nevertheless, the effects of extracellular polymeric substances (EPS) on the responses of biofilms to the exposure to antibiotics are not clear. In this study, the effects of EPS on the sorption and biological responses to one representative antibiotic, sulfamethizole (STZ), in model biofilms were investigated. Proteins dominated the interactions between the EPS and the STZ and the EPS from a moving bed biofilm reactor exhibited the strongest interaction with the STZ. The EPS served as important reservoirs for the STZ and the tested biofilms all showed reduced sorption capacities for the STZ after the EPS were extracted. The respiratory rates and typical enzymatic activities were reduced after the EPS were extracted. High-throughput 16S rRNA gene sequencing results confirmed that the bacterial community in the biofilm without the EPS was more vulnerable to antibiotic shock as indicated by the community diversity and richness indices. A greater increase in the abundance of susceptible species was observed in the natural biofilm. The results comprehensively suggested that the EPS played important role in biosorption of STZ and alleviated the direct damage of the antibiotic to the cells; in addition the extent of the bacterial community response was associated with the origins of the biofilms. Our study provided details on the responses of multi-species biofilms to the exposure to an antibiotic and highlighted the role of the EPS in interacting with the antibiotic, thereby providing a deeper understanding of the bioremediation of antibiotics in real-life natural and engineered biofilm systems.

Safety of hydroxyanthracene derivatives for use in food

The Panel on Food Additives and Nutrient Sources added to Food (ANS) was asked to deliver a scientific opinion on the safety of hydroxyanthracene derivatives and to provide advice on a daily intake that does not give rise to concerns about harmful effects to health. Hydroxyanthracene derivatives are a class of chemical substances naturally occurring in different botanical species and used in food to improve bowel function. The ANS Panel reviewed the available scientific data on a possible relationship between hydroxyanthracene derivatives exposure and genotoxic and carcinogenic effects. On the basis of the data currently available, the Panel noted that emodin, aloe-emodin and the structurally related substance danthron have shown evidence of in vitro genotoxicity. Aloe extracts have also been shown to be genotoxic in vitro possibly due to the presence of hydroxyanthracene derivatives in the extract. Furthermore, aloe-emodin was shown to be genotoxic in vivo and the whole-leaf aloe extract and the structural analogue danthron were shown to be carcinogenic. Epidemiological data suggested an increased risk for colorectal cancer associated with the general use of laxatives, several of which contain hydroxyanthracene derivatives. Considering the possible presence of aloe-emodin and emodin in extracts, the Panel concluded that hydroxyanthracene derivatives should be considered as genotoxic and carcinogenic unless there are specific data to the contrary, such as for rhein, and that there is a safety concern for extracts containing hydroxyanthracene derivatives although uncertainty persists. The Panel was unable to provide advice on a daily intake of hydroxyanthracene derivatives that does not give rise to concerns about harmful effects to health.

Characterization of the binding of neomycin/paromomycin sulfate with DNA using acridine orange as fluorescence probe and molecular docking technique

The binding of neomycin sulfate (NS)/paromomycin sulfate (PS) with DNA was investigated by fluorescence quenching using acridine orange (AO) as a fluorescence probe. Fluorescence lifetime, FT-IR, circular dichroism (CD), relative viscosity, ionic strength, DNA melting temperature, and molecular docking were performed to explore the binding mechanism. The binding constant of NS/PS and DNA was 6.70 × 10³/1.44 × 10³ L mol^-1 at 291 K. The values of ΔH^θ, ΔS^θ, and ΔG^θ suggested that van der Waals force or hydrogen bond might be the main binding force between NS/PS and DNA. The results of Stern-Volmer plots and fluorescence lifetime measurements all revealed that NS/PS quenching the fluorescence of DNA-AO was static in nature. FT-IR indicated that the interaction between DNA and NS/PS did occur. The relative viscosity and melting temperature of DNA were almost unchanged when NS/PS was introduced to the solution. The fluorescence intensity of NS/PS-DNA-AO was decreased with the increase in the ionic strength. For CD spectra of DNA, the intensity of positive band at nearly 275 nm was decreased and that of negative band at nearly 245 nm was increased with the increase in the concentration of NS/PS. The binding constant of NS/PS with double-stranded DNA (dsDNA) was larger than that of NS/PS with single-stranded DNA (ssDNA). From these studies, the binding mode of NS/PS with DNA was evaluated to be groove binding. The results of molecular docking further indicated that NS/PS could enter into the minor groove in the A-T rich region of DNA.

Binding interactions between lysozyme and injectable hydrogels derived from albumin-pH/thermo responsive poly(amino urethane) conjugates in aqueous solution

Injectable hydrogels are alternative materials for drug and protein delivery in biomedical applications, which can potentially eliminate the need of surgical implantation in the treatment procedures. Prior to administration, such hydrogels, in a liquid state, must demonstrate good interactions with the incorporated molecules to maintain the sustain release of active agents and to avoid unappreciative burst release. The injectable hydrogels derived from BSA-pH/temperature responsive poly(amino urethane) conjugates have been reported to demonstrated good sustainability for delivery of lysozyme, both in vitro and in vivo. However, the interactions between such conjugates and the loading lysozyme were not fully understood. In this present work, we reported the binding interactions between the studied complex systems, BSA-pH/temperature responsive poly(amino urethane) conjugates (CONJ1 and CONJ2) and lysozyme. Fluorescence spectroscopy in a combination with thermodynamic analysis exhibited that the binding between the conjugates and lysozyme occurred through static quenching and the binding interactions in the complexes were mainly van der Waals forces and hydrogen bonds. The binding constants (KA) determined at 300, 308 and 318K of CONJ1 to lysozyme were 7.96×10(4), 6.45×10(4) and 3.20×10(4)M(-1), respectively and those of CONJ2 to lysozyme were 2.63×10(4), 2.53×10(4) and 1.19×10(4)M(-1), respectively. FTIR analysis showed that the complexes between the conjugates and lysozyme demonstrated sufficiently small deviation in the conformational structures from the native lysozyme. In addition, the morphology revealed by TEM and AFM imaging portrayed the behavior of complex formation in such a way that the conjugates, before complex formation, displayed the core-shell structures. After the complex formation, a number of lysozyme particles were noticeably entrapped as if they penetrated into the preformed core-shell conjugates.

Fluorescence quenching study of 2,6-bis(5-(4-methylphenyl)-1-H-pyrazol-3-yl)pyridine with metal ions

A novel bispyrazole derivative 2,6-bis(5-(4-methylphenyl)-1-H-pyrazol-3-yl)pyridine was synthesized and its structure was confirmed by (1)H NMR, FTIR, MS techniques and elemental analysis. The binding interactions of BMPP with Cd(2+), Co(2+), Pb(2+) and Cu(2+) ions were investigated in MeOH-H2O solution by fluorescence quenching technique at two temperatures (25 and 35°C). Their quenching constants KSV, binding constants K, binding sites n and thermodynamic parameters (ΔH, ΔG and ΔS) were determined. The results indicated that the metal ions quenched the intrinsic fluorescence of the bispyrazole by forming the bispyrazole-metal complexes and their quenching process was a static quenching mechanism. In addition, the process of interaction was spontaneous and mainly ΔS-driven.

Study of interaction between human serum albumin and three phenanthridine derivatives: fluorescence spectroscopy and computational approach

Over the past decades, phenanthridine derivatives have captured the imagination of many chemists due to their wide applications. In the present work, the interaction between phenanthridine derivatives benzo [4,5]imidazo[1,2-a]thieno[2,3-c]quinoline (BTQ), benzo[4,5]imidazo[1,2-a]furo[2,3-c]quinoline (BFQ), 5,6-dimethylbenzo[4,5]imidazo[1,2-a]furo[2,3-c]quinoline (DFQ) and human serum albumin (HSA) were investigated by molecular modeling techniques and spectroscopic methods. The results of molecular modeling simulations revealed that the phenanthridine derivatives could bind on both site I in HSA. Fluorescence data revealed that the fluorescence quenching of HSA by phenanthridine derivatives were the result of the formation of phenanthridine derivatives-HSA complex, and the binding intensity between three phenanthridine derivatives and HSA was BTQ>BFQ>DFQ. Thermodynamics confirmed that the interaction were entropy driven with predominantly hydrophobic forces. The effects of some biological metal ions and toxic ions on the binding affinity between phenanthridine derivatives and HSA were further examined.

Spectroscopic analyses on interaction of bovine serum albumin with novel spiro[cyclopropane-pyrrolizin]

The interaction between novel spiro[cyclopropane-pyrrolizin] (NSCP) and bovine serum albumin (BSA) was analyzed by fluorescence and ultraviolet-visible (UV-Vis) spectroscopy at 298 K, 304 K and 310 K under simulative physiological conditions. The results showed that NSCP can effectively quench the intrinsic fluorescence of BSA via static quenching. The binding constants, binding sites of NSCP with BSA were calculated. Hydrogen binds and van der Waals force played a major role in stabilizing the complex and the binding reaction were spontaneous. According to the Förster non-radiation energy transfer theory, the average binding distances between NSCP and BSA were obtained. What is more, the synchronous fluorescence spectra indicated that the conformation of BSA has been changed.

Biophysical investigation of thymoquinone binding to ‘N’ and ‘B’ isoforms of human serum albumin: exploring the interaction mechanism and radical scavenging activity

Thymoquinone more strongly interacts with the ‘N’ isoform in comparison to the ‘B’ isoform of HSA and also increases its thermal stability but the antioxidant activity is significantly higher at the ‘B’ isoform of HSA.

Study on the interaction between carbonyl-fused N-confused porphyrin and bovine serum albumin by spectroscopic techniques

The interaction between carbonyl-fused N-confused porphyrin (CF-NCP) and bovine serum albumin (BSA) was investigated by fluorescence and ultraviolet-visible (UV-Vis) spectroscopy. The results indicated that CF-NCP has strong ability to quench the intrinsic fluorescence of BSA by forming complexes. The binding constants (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at three different temperatures. The results revealed that the binding process is spontaneous, and the acting force between CF-NCP and BSA were mainly electrostatic forces. According to Förster non-radiation energy transfer theory, the binding distance between CF-NCP and BSA was calculated to be 4.37nm. What is more, the conformation of BSA was observed from synchronous fluorescence spectroscopy.

Spectroscopic studies on the interaction of Phacolysin and bovine serum albumin

The interaction between Phacolysin (PCL) and bovine serum albumin (BSA) under imitated physiological conditions was investigated by spectroscopic (fluorescence, UV-Vis absorption and Circular dichroism) techniques. The experiments were conducted at different temperatures (294K, 302K, 306K and 310K) and the results showed that the PCL caused the fluorescence quenching of BSA through a static quenching procedure. The binding constant (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at different temperatures. The results revealed that the binding process was spontaneous and the acting force between PCL and BSA were mainly hydrogen bonding and van der Waals forces. According to Förster non-radiation energy transfer theory, the binding distance between PCL and BSA was calculated to be 2.41nm. What is more, both synchronous fluorescence and Circular dichroism spectra confirmed the interaction, which indicated the conformational changes of BSA.

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

The fluorescence and ultraviolet-visible (UV-Vis) spectroscopy were explored to study the interaction between Tropicamide (TA) and bovine serum albumin (BSA) at three different temperatures (292, 301 and 310K) under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between TA and BSA was static quenching procedure. The binding constant (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at different temperatures. The results revealed that the binding process is spontaneous, hydrogen binds and vander Waals were the main force to stabilize the complex. According to Förster non-radiation energy transfer theory, the binding distance between TA and BSA was calculated to be 4.90 nm. Synchronous fluorescence spectroscopy indicated the conformation of BSA changed in the presence of TA. Furthermore, the effect of some common metal ions (Mg(2+), Ca(2+), Cu(2+), and Ni(2+)) on the binding constants between TA and BSA were examined.

Binding interactions of β-conglycinin and glycinin with vitamin B12

Vitamin B12 deficiency is a problem for many elderly people around the world that is caused by food-cobalamin malabsorption syndrome due to gastrointestinal problems. In this study, the molecular interactions of VB12 with two major soy protein fractions, β-conglycinin (7S) and glycinin (11S), were studied using fluorescence and far-UV circular dichroism spectroscopic techniques. The results show that the fluorescence of 7S and 11S was quenched by VB12 through binding-related quenching after correcting for the inner-filter effect. Both 7S and 11S had a good affinity to VB12 as indicated by their high binding constant 1.252 (±0.085) × 10(4) M(-1) for 7S and 0.952 (±0.04) × 10(4) M(-1) for 11S at 292 K, respectively. Such binding induced a more organized protein confirmation with increased β-sheet and β-turn structure components and a more folded tertiary structure. It is deduced that VB12 was bound in the interior of protein three-dimensional network mainly via hydrophobic interactions to form 7S-VB12 and 11S-VB12 complexes. The results suggest that soy protein has potential to be used as carrier of VB12.

Investigation on the interactions of clenbuterol to bovine serum albumin and lysozyme by molecular fluorescence technique

Clenbuterol interacting with bovine serum albumin (BSA) or lysozyme (LYS) in physiological buffer (pH 7.4) was investigated by the fluorescence spectroscopy and UV-vis absorption spectroscopy. The results indicated that clenbuterol quenched the intrinsic fluorescence of BSA and LYS via a static quenching procedure. The binding constants of clenbuterol with BSA and LYS were 1.16×10(3) and 1.49×10(3) L mol(-1) at 291 K. The values of ΔH and ΔS implied that hydrophobic and electrostatic interaction played a major role in stabilizing the complex (clenbuterol-BSA or clenbuterol-LYS). In the presence of Fe2+, Fe3+, Cu2+, Mg2+, Ca2+, or Zn2+, the binding constants of clenbuterol to BSA or LYS had no significant differences. The distances between the donor (BSA or LYS) and acceptor (clenbuterol) were 2.61 and 2.19 nm for clenbuterol-BSA and clenbuterol-LYS respectively. Furthermore, synchronous fluorescence spectrometry was used to analyze the conformational changes of BSA and LYS.

Roles of extracellular polymeric substances (EPS) in the migration and removal of sulfamethazine in activated sludge system

The occurrences, transformation of antibiotics in biological wastewater treatment plants have attracted increasing interests. However, roles of extracellular polymeric substances (EPS) of activated sludge on the fate of antibiotics are not clear. In this study, the roles of EPS in the migration and removal of one typical antibiotic, sulfamethazine (SMZ), in activated sludge process were investigated. The interaction between EPS and SMZ was explored through a combined use of fluorescence spectral analysis, laser light scattering and microcalorimetry techniques. Results show that SMZ interacted with the proteins in EPS mainly with a binding constant of 1.91 × 10(5) L/mol. The binding process proceeded spontaneously, and the driving force was mainly from the hydrophobic interaction. After binding, the structure of EPS was expanded and became loose, which favored the mass transfer and pollution capture. The removal of SMZ was influenced by interaction with EPS. SMZ could be effectively adsorbed on EPS, which accounted for up to 61.8% of total SMZ adsorbed by sludge at the initial adsorption stage and declined to around 35.3% at the subsequent biodegradation stage. The enrichment of SMZ by EPS was beneficial for SMZ removal and acquisition by microbes at the subsequent biodegradation stage.

Interaction of pyrrolizine derivatives with bovine serum albumin by fluorescence and UV-Vis spectroscopy

The interaction between pyrrolizine derivatives (PD) and bovine serum albumin (BSA) under imitated physiological conditions was analyzed by fluorescence and ultraviolet spectra. The experiments were conducted at three different temperatures (302, 306 and 310 K) and the results showed that PD caused the fluorescence quenching of BSA through a combined quenching procedure. The binding constant (K(a)), binding-site number (n) between PD and BSA at different temperatures were obtained. According to Förster non-radiation energy transfer theory, the binding distance (r) between BSA and PD was calculated. The corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were also obtained. The comparison of binding potency of PD and BSA suggested that the substituent on the benzene ring could enhance the binding affinity of PD and BSA. Finally, we investigated the possible sub-domain on BSA where bind PD by displacement experiments.

Study on the interaction between novel spiro pyrrolidine and bovine serum albumin by spectroscopic techniques

Spiro pyrrolidines, which were proved with diverse and potent biological activities and they were discovered widespread in nature. In this paper, using fluorescence and ultraviolet spectroscopy, we investigated the interactions between novel spiro pyrrolidine (NSP) and bovine serum albumin (BSA) under the imitated physiological condition. The results show that the NSP binds to BSA molecules. Static quenching and non-radiation energy transfer are the main reasons for fluorescence quenching. We calculated the binding constant (K(a)) and binding sites (n) at different temperatures and obtained the binding distance between the tryptophan residue in BSA and the NSP based on the Förster theory of non-radiation energy transfer. In addition, using synchronous fluorescence spectra, we demonstrated conformation changes of BSA caused by NSP. The comparison of binding potency of NSP and BSA suggests that the substituent on the benzene ring influences the binding ability of NSP and BSA.

Characterization of thymoquinone binding to human α₁-acid glycoprotein

Thymoquinone (TQ) is the main bioactive component isolated from Nigella sativa essential oil and seeds and has been used for the treatment of inflammations, liver disorders, arthritis, and is of great importance as a promising therapeutic drug for different diseases including cancer. This paper reports the first experimental evidence on binding of TQ to human α(1)-acid glycoprotein (AGP), an important drug-binding glycoprotein in human plasma, which affects pharmacokinetic properties of various therapeutic agents. The interaction of TQ with AGP has been characterized by Fourier transform infrared (FTIR) and fluorescence spectroscopy, as well as by molecular docking experiments. FTIR spectroscopy showed that the binding of TQ to AGP slightly increases its thermal stability and shifts the existence of a molten globule-like state observed in a previous study to higher temperature. The binding constants K(a); the number of binding sites n; and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy. Fluorescence quenching experiments indicated that TQ binding involves hydrophobic interactions and to a lower extent hydrogen bonds, in agreement with molecular docking experiments. The data on binding ability of TQ to AGP represent basic information for the TQ pharmacokinetics such as drug metabolism and distribution in the body.

Importance of pH and disulfide bridges on the structural and binding properties of human α₁-acid glycoprotein

Human α(1)-acid glycoprotein (AGP) is an acute phase plasma glycoprotein containing two disulfide bridges. As a member of the lipocalin superfamily, it binds and transports several basic and neutral ligands, but a number of other activities have also been described. Thanks to its binding properties, AGP is also a good candidate for the development of biosensors and affinity chromatography media, and in this context detailed structural information is needed. The structural properties of AGP at different p(2)Hs and under reducing conditions were analysed by FT-IR spectroscopy. The obtained data indicate that AGP, when denatured, does not aggregate at neutral or basic p(2)Hs whilst it does at acidic p(2)Hs. Under reducing conditions the protein is remarkably less thermostable than its oxidized counterpart and presents an enhanced tendency to aggregate, even at neutral p(2)H. A heat-induced molten globule-like state (MG) was detected at 55 °C at p(2)H 7.4 and 5.5. At p(2)H 4.5 the MG occurred at 45 °C with an onset of formation at 40 °C. The MG was not observed under reducing conditions. A lower affinity of chlorpromazine and progesterone for the MG formed at p(2)H 4.5 and 40 °C was observed, suggesting that ligand(s) may be released near the negative surfaces of biological membranes. Furthermore, the reduced AGP displays an enhanced affinity for progesterone, indicating the importance of disulfide bonds for the binding capacity of AGP.

Investigation of ketoprofen binding to human serum albumin by spectral methods

The binding of ketoprofen with human serum albumin (HSA) was studied by fluorescence and absorption spectroscopic methods. Quenching of fluorescence of HSA was found to be a static quenching process. At 288.15, 298.15, 308.15 and 318.15 K, the binding constants and binding sites were obtained. The effects of Cu2+, Al3+, Ca2+, Pb2+ and K+ on the binding at 288.15 K were also studied. The thermodynamic parameters, ΔH, ΔG and ΔS were got and the main sort of acting force between ketoprofen and HSA was studied. Based on the Förster's theory of non-radiation energy transfer, the binding average distance, r, between the acceptor (ketoprofen) and the donor (HSA) was calculated.

Thymoquinone, a potential therapeutic agent of Nigella sativa, binds to site I of human serum albumin

Thymoquinone (TQ) is the main constituent of Nigella sativa essential oil which shows promising in vitro and in vivo antineoplastic growth inhibition against various tumor cell lines. Because of the increasing interest to test it in pre-clinical and clinical researches for assessing its health benefits, we here evaluate the interactions between TQ and human serum albumin (HSA), a possible carrier of this drug in vivo. Binding to HSA was studied using different spectroscopic techniques. Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopies suggest that the association between TQ and HSA does not affect the secondary structure of HSA. Using fluorescence spectroscopy, one mole of TQ was found to bind one mole of HSA with a binding constant of 2.39 +/- 0.2 10(4)M(-1). At 25 degrees C (pH 7.4), van't Hoff's enthalpy and entropy that accompany the binding were found to be -10.24 kJ/mol(-1) and 45 J/mol(-1)K(-1) respectively. The thermodynamic analysis of the TQ-HSA complex formation shows that the binding process is enthalpy driven and spontaneous, and that hydrophobic interactions are the predominant intermolecular forces stabilizing the complex. Furthermore, displacement experiments using warfarin and ibuprofen indicate that TQ could bind to site I of HSA, which is also in agreement with the results of the molecular modeling study.