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Teicoplanin has been banned in the veterinary field due to the drug resistance of antibiotics. However, teicoplanin residue from the antibiotic abuse of humans and animals poses a threat to people's health. Therefore, it is necessary to develop an efficient way for the highly accurate and reliable detection of teicoplanin from humans, food, and water. In this study, novel imprinted quantum dots of teicoplanin were prepared based on boronate affinity-based precisely controlled surface imprinting. The imprinting factor (IF) for teicoplanin was evaluated and reached a high value of 6.51. The results showed excellent sensitivity and selectivity towards teicoplanin. The relative fluorescence intensity was inversely proportional to the concentration of teicoplanin, in the range of 1.0–17 μM. And its limit of detection (LOD) was obtained as 0.714 μM. The fluorescence quenching process was mainly controlled by a static quenching mechanism via the non-radiative electron-transfer process between QDs and the five-membered cyclic boronate esters. The recoveries for the spiked urine, milk, and water samples ranged from 95.33 to 104.17%, 91.83 to 97.33, and 94.22 to 106.67%, respectively. [ABSTRACT FROM AUTHOR]

A novel class of imprinted quantum dots as fluorescent nanosensors were prepared based on boronate affinity-based template-immobilization surface imprinting for detection of isoquercitrin (Isq). The obtained molecularly imprinted silica coating was used as the recognition element. The quantum dots were used as signal-transduction materials. Under optimum conditions, according to the fluorescence quenching of imprinted APBA-functionalized CdTe QDs by Isq, the imprinting factor (IF) for Isq was evaluated to be 1.69. This result suggests that boronic acid-functionalized quantum dots coated with molecularly imprinted silica were successfully prepared. The prepared isoquercitrin-imprinted APBA-functionalized CdTe QDs exhibited high sensitivity and selectivity toward isoquercitrin. The isoquercitrin-imprinted CdTe QDs exhibited linear fluorescence quenching toward isoquercitrin within the range of 0.20–30 μM. And the detection limit was found to be 0.09 μM. In addition, this study also provides an efficient fluorescence detection method of other cis-diol-containing flavonoids in samples. This method may find widespread use for monitoring of trace flavonoid drugs owing to its advantages of simple preparation, low cost, high sensitivity, good stability and reproducibility. [ABSTRACT FROM AUTHOR]

The binding of isorhamnetin to bovine liver catalase (BLC) was first investigated at 302, 310 and 318 K at pH 7.4 using spectroscopic methods including fluorescence spectra, circular dichroism (CD) and UV-vis absorption. Spectrophotometric observations are rationalized mainly in terms of a static quenching process. The binding constants and binding sites were evaluated by fluorescence quenching methods. Enzymatic activity of BLC in the absence and presence of isorhamnetin was measured using a UV/vis spectrophotometer. The result revealed that the binding of isorhamnetin to BLC led to a reduction in the activity of BLC. The positive entropy change and enthalpy change indicated that the interaction of isorhamnetin with BLC was mainly driven by hydrophobic forces. The distance r between the donor (BLC) and acceptor (isorhamnetin) was estimated to be 2.99 nm according to fluorescence resonance energy transfer. Fluorescence, synchronous fluorescence, and CD spectra showed no obvious change in the conformation of BLC upon the binding of isorhamnetin. In addition, the influence of pH on the binding of isorhamnetin to BLC was investigated and the binding ability of the drug to BLC deceased under other pH conditions (pH 9.0, 6.5, 5.0, 3.5, or 2.0) as compared with that at pH 7.4. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The study on the binding mode of drug with protein is important to understand the pharmacokinetics and toxicity of the drug as well as the relationship of structure and function of the protein. In the study, the interaction between cepharanthine and lysozyme (Lys) in aqueous solution was first investigated by fluorescence spectroscopic techniques at pH 7.4. The obtained quenching rate constant and binding constant indicated the static quenching mechanism and medium binding force. The effect of cepharanthine on the conformation of Lys was analyzed using synchronous fluorescence and three-dimensional (3D) fluorescence. In addition, the effect of urea on the interaction of cepharanthine with Lys was studied and the binding capacity of cepharanthine to the denatured Lys deceases dramatically, as compared with that of cepharanthine to native Lys. Moreover, influence of pH on the interaction of cepharanthine with Lys was investigated. As compared with that at pH 7.4, the binding abilities of the drug to Lys under other pH conditions (pH 9.0, 5.5, 3.5, and 1.9) deceased. Furthermore, the effect of metal ions on the binding constant of cepharanthine with Lys was investigated. [ABSTRACT FROM AUTHOR]

Highlights: [•] The fluorescence of native and denatured Lys was quenched by sinomenine at pH 7.4. [•] The effect of metal ions on the binding constant of sinomenine with Lys was studied. [•] The pH 7.4 is the optimal acidity in the binding reaction. [•] Sinomenine was harder to bind to the denatured Lys. [Copyright &y& Elsevier]

Highlights: [•] The fluorescence of native and denatured BSA was quenched by cinchonidine at pH 7.4. [•] Fluorescence spectrum indicated urea-induced unfolding of native BSA. [•] The pH 7.40 is the optimal acidity in the binding reaction. [•] Cinchonidine was harder to bind to the denatured BSA. [ABSTRACT FROM AUTHOR]

Abstract: The binding of sinomenine to human serum albumin (HSA) in aqueous solution in the absence and presence of urea has been studied by fluorescence and the three-dimensional (3D) fluorescence at pH 7.40. Subdomain IIA binding site of human serum albumin (HSA) was characterized by examining the change in HSA fluorescence. The quenching rate constants and binding constants were calculated in the absence and presence of the denaturant. The results point to a static quenching mechanism operating in the complexes. However, the binding ability of sinomenine to denatured HSA is weaker than that of sinomenine to native HSA. Denaturation of HSA in the presence of urea is almost complete at [urea]⩾8.0M. Upon unfolding, two fluorescence peaks were observed. One peak was assigned to the fluorescence of Trp-214 residue in a polar environment, and the other peak was assigned to the fluorescence of tyrosine residues. Compared to the free HSA, the HSA-sinomenine complex is more stable in the presence of urea. [Copyright &y& Elsevier]

Abstract: The binding reaction between vitamin B12 (B12, cyanocobalamin) and lysozyme (Lys) has been investigated by fluorescence, synchronous fluorescence, ultraviolet–vis (UV) absorbance, and three-dimensional fluorescence. The intrinsic fluorescence of Lys was strongly quenched by the addition of B12 in different pH buffer solutions (pH 3.4, 7.4, and 9.0) and the spectroscopic observations are mainly rationalized in terms of a static quenching process at lower concentration of B12 (C B12/C Lys <5) and a combined quenching process at higher concentration of B12 (C B12/C Lys >5). The structural characteristics of B12 and Lys were probed, and their binding affinities were determined under different pH conditions (pH 3.4, 7.4, and 9.0). The effect of B12 on the conformation of Lys was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results indicate that the binding of B12 to Lys causes apparent change in the secondary or tertiary structures of Lys. Furthermore, the effect of Zn2+ on the binding constant of B12 with Lys under various pH conditions (pH 3.4, 7.4, and 9.0) was also studied. [Copyright &y& Elsevier]

Abstract: The interaction mechanism between vitamin B12 (B12, cyanocobalamin) and bovine serum albumin (BSA) has been investigated by fluorescence, synchronous fluorescence, ultraviolet–vis (UV) absorbance, and three-dimensional fluorescence. The intrinsic fluorescence of BSA was strongly quenched by the addition of B12 in different pH buffer solutions (pH 2.5, 3.5, 5.0, 7.4, and 9.0) and spectroscopic observations are mainly rationalized in terms of a static quenching process at lower concentration of B12 (C B12/C BSA <5) and a combined quenching process at higher concentration of B12 (C B12/C BSA >5). The structural characteristics of B12 and BSA were probed, and their binding affinities were determined under different pH conditions. The results indicated that the binding abilities of B12 to BSA in the acidic and basic pH regions (pH 2.5, 3.5, 5.0, and 9.0) were lower than that at simulating physiological condition (pH 7.4). In addition, the efficiency of energy transfer from tryptophan fluorescence to B12 was found to depend on the binding distance r between the donor and acceptor calculated using Förster''s theory. The effect of B12 on the conformation of BSA was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results showed that the binding of B12 to BSA causes apparent change in the secondary and tertiary structures of BSA. [Copyright &y& Elsevier]

Abstract: The interaction mechanism between benzocaine (BZC) and lysozyme (Lys) has been investigated by fluorescence, synchronous fluorescence, ultraviolet–vis (UV) absorption spectra, and three-dimensional fluorescence (3-D) in various pH medium. The observations of fluorescence spectra were mainly rationalized in terms of a static quenching process at lower concentration of BZC (C BZC/C Lys <9) and a combined quenching process at higher concentration of BZC (C BZC/C Lys >9) at pH 7.4 and 8.4. However, the fluorescence quenching was mainly arisen from static quenching by complex formation in all studied drug concentrations at pH 3.5. The structural characteristics of BZC and Lys were probed, and their binding affinities were determined under different pH conditions (pH 3.5, 7.4, and 8.4). The results indicated that the binding abilities of BZC to Lys decreased at the pH below and above the simulative physiological condition (pH 7.4) due to the alterations of the protein secondary and tertiary structures or the structural change of BZC. The effect of BZC on the conformation of Lys was analyzed using UV, synchronous fluorescence and three-dimensional fluorescence under different pH conditions. These results indicate that the binding of BZC to Lys causes apparent change in the secondary and tertiary structures of Lys. The effect of Zn2+ on the binding constant of BZC with Lys under various pH conditions (pH 3.5, 7.4, and 8.4) was also studied. [Copyright &y& Elsevier]

Abstract: The interaction mechanism of baicalein and lysozyme (Lys) has been characterized by fluorescence, synchronous fluorescence, ultraviolet–vis absorbance, and three-dimensional (3D) fluorescence. The structural characteristics of baicalein and Lys were probed, and their binding affinities were determined under different pH conditions (pH 7.4, 4.5, and 2.5). The results showed that the binding abilities of the drug to Lys increased under lower pH conditions (pH 4.5 and 2.5) due to the alterations of the protein secondary and tertiary structures or the structural change of baicalein. The effect of baicalein on the conformation of Lys was analyzed using UV, synchronous fluorescence and three-dimensional (3D) fluorescence under different pH conditions. These results indicate that the binding of baicalein to Lys causes apparent change in the secondary and tertiary structure of Lys. In the presence of Cu2+, the decrease of the binding constant in buffer solution of pH 2.5 may result from the competition of the metal ion and baicalein binding to Lys. In addition, the presence of Cu2+ increased the binding constants of baicalein–Lys complex under higher pH conditions (pH 7.4 and 4.5). The possible site of binding of baicalein to Lys has been proposed to explain these observations. [Copyright &y& Elsevier]

Abstract: The binding of farrerol to bovine serum albumin (BSA) in aqueous solution was investigated by fluorescence quenching spectra, synchronous fluorescence spectra, circular dichroism (CD) and the three-dimensional (3D) fluorescence spectra at pH 7.40. The results of fluorescence titration indicated that farrerol could quench the intrinsic fluorescence of BSA in a static quenching way. The cause of showing upward curvy patterns in Stern–Volmer plots was analyzed. The binding sites number n and binding constant K using fluorescence quenching equation at 310K were calculated. The binding distance and the energy transfer efficiency between farrerol and BSA were also obtained according to the theory of Förster''s non-radiation energy transfer. The effect of some metal ions on the binding constant of farrerol with BSA was also studied. The effect of farrerol on the conformation of BSA was analyzed using CD, synchronous fluorescence spectra and three-dimensional (3D) fluorescence spectra under experimental conditions. Furthermore, the fluorescence displacement experiments indicated that farrerol could bind to the site I of BSA. [Copyright &y& Elsevier]

Abstract: The binding of baicalein to bovine serum albumin (BSA) in the absence and presence of Cu2+ or Fe3+ in aqueous solution has been studied by fluorescence, synchronous fluorescence, ultraviolet–visible (UV–vis) spectra, circular dichroism (CD) and the three-dimensional (3D) fluorescence at pH 7.40. The decrease of the binding constant in the presence of Cu2+ or Fe3+ may result from the competition of the metal ions and baicalein binding to BSA. The effect of baicalein on the conformation of BSA was analyzed using UV, CD, fluorescence and three-dimensional (3D) fluorescence. These results indicate that the binding of baicalein to BSA causes apparent change in the secondary structure of BSA, but does not affect the polarity around the chromophore molecule. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of rutin to bovine serum albumin (BSA) in aqueous solution was investigated by fluorescence spectra and ultraviolet–visible (UV–vis) spectra at pH 7.40. There are also some metal ions present in blood plasma, thus the research about the effect of metal ions on the interaction of drugs with proteins is crucial. Therefore, we have studied the effect of Cu2+ or Fe3+ on the interaction between rutin and BSA by using spectroscopic technique at pH 7.40, for the first time. The results of fluorescence titration indicated that rutin could quench the intrinsic fluorescence of BSA in a static quenching way. The binding sites number (n), the binding constant (K) and the spatial-distance (r) of rutin with BSA without or with Cu2+ or Fe3+ at 310K were calculated. The result showed that the presence of Cu2+ or Fe3+ increased the binding constant and changed the binding distance between the acceptor and the donor, which possibly results from the formation of metal ions–BSA complex. The effect of rutin on the conformation of BSA was also analyzed using UV under experimental conditions. Furthermore, the fluorescence displacement experiments indicated that rutin is situated within subdomain IIA of BSA. [Copyright &y& Elsevier]

Abstract: The binding of myricetin to lysozyme (Lys) in aqueous solution was investigated by fluorescence spectroscopy, ultraviolet–visible absorption spectroscopy (UV) and circular dichroism (CD) spectra under physiological conditions. There are also many metal ions present in body, thus the research about the effect of metal ions on the interaction of drugs with proteins is crucial. In this study, we have investigated the effect of both familiar metal ions Cu2+ and Fe3+ on the interaction between myricetin and Lys by using spectroscopy technique at pH 7.40, for the first time. Spectrophotometric observations are rationalized in terms of a static quenching process in a static quenching way. The cause of showing upward curvy patterns in Stern–Volmer plots was analyzed. The binding constants and binding sites of myricetin with Lys with or without Cu2+ and Fe3+ at different concentrations of myricetin were calculated. UV/vis measurements on the enzymatic activity of Lys with or without Cu2+ in the absence or presence of myricetin indicated that the interaction between myricetin and Lys led to a reduction in the activity of Lys. Furthermore, the effect of pH on the binding constant of myricetin with Lys was also examined. [Copyright &y& Elsevier]

Abstract: Interaction of 8-Acetyl-7-hydroxycoumarin with human serum albumin (HSA) at pH 7.40 has been investigated at 291, 301 and 310K, respectively, employing the steady fluorescence, circular dichroism (CD) and molecular modeling methods. The quenching mechanism and binding constants were determined by the fluorescence quenching experiments. Thermodynamic data showed that 8-Acetyl-7-hydroxycoumarin was included in the hydrophobic cavity of HSA via hydrophobic interactions. The result of CD indicated that the binding of 8-Acetyl-7-hydroxycoumarin to HSA causes a slight conformational change of the protein. Furthermore, upon binding with HSA, the fluorescence spectra of the 8-Acetyl-7-hydroxycoumarin exhibits appreciable hypsochromic shift associated with an enhancement in the fluorescence intensity. The binding constant (K) and the standard free energy change (ΔG 0) have been also calculated according to the fluorescence data of the ligand, which is in good agreement with the values determined by fluorescence quenching data of HSA. Computational mapping of the possible binding sites of 8-Acetyl-7-hydroxycoumarin revealed that the molecule was bound in the large hydrophobic cavity of subdomain IIA mainly by the hydrophobic interaction and also by the hydrogen bonding interactions between 8-Acetyl-7-hydroxycoumarin and the residues His 242, Arg 222, and Arg 218. [Copyright &y& Elsevier]

Abstract: Binding of nevadensin to bovine serum albumin (BSA) has been studied in detail at 298 and 310K using spectrophotometric technique. The intrinsic fluorescence of BSA was strongly quenched by the addition of nevadensin and spectroscopic observations are mainly rationalized in terms of a static quenching process at lower concentration of nevadensin (C drug/C BSA <1) and a combined quenching process at higher concentration of nevadensin (C drug/C BSA >1). The binding parameters for the reaction at a pH above (7.40) or below (3.40) the isoelectric point have been calculated according to the double logarithm regression curve. The thermodynamic parameters ΔH 0, ΔG 0, ΔS 0 at different temperatures and binding mechanism of nevadensin to BSA at pH 7.40 and 3.40 were evaluated. The binding ability of nevadensin to BSA at pH 7.40 was stronger than that at pH 3.40. Steady fluorescence, synchronous fluorescence and circular dichroism (CD) were applied to investigate protein conformation. A value of 2.15nm for the average distance r between nevadensin (acceptor) and tryptophan residues (Trp) of BSA (donor) was derived from the fluorescence resonance energy transfer. Moreover, influence of pH on the interaction nevadensin with BSA was investigated. [Copyright &y& Elsevier]

Abstract: The patterns of Vitamin C (ascorbic acid) binding to lysozyme (LYSO) and bovine liver catalase (BLC) were investigated at 298, 308 and 316K at pH 7.40 using spectrophotometric techniques. The quenching mechanism, binding constant and the number of binding sites were determined by fluorescence experiments. Moreover, the Stern–Volmer fluorescence quenching constant (K SV) of LYSO by Vitamin C was more sensitive to the temperature changes than that of BLC by Vitamin C. The thermodynamic data suggest that hydrogen bonds were the predominant intermolecular forces in the binding reaction. The effect of Vitamin C on the conformation of LYSO or BLC was analyzed using synchronous fluorescence, UV–vis absorption and circular dichroism (CD) spectra. [Copyright &y& Elsevier]

Abstract: The binding of nevadensin to human serum albumin (HSA) in aqueous solution was investigated for the first time by molecular spectroscopy and modeling at pH 7.4. Spectrophotometric observations are rationalized in terms of a static quenching process and binding constant (K a, K b) and the number of binding sites (n ≈1) were evaluated by fluorescence quenching methods. Thermodynamic data showed that nevadensin was included in the hydrophobic cavity of HSA mainly via hydrophobic interactions. The value of 3.09nm for the distance r between the donor (HSA) and acceptor (nevadensin) was derived from the fluorescence resonance energy transfer. Spectrophotometric techniques were also applied to investigate the structural information of HSA molecules on the binding of nevadensin and the results showed that the binding of nevadensin to HSA did not change significantly molecular conformation of HSA in our experimental conditions. Furthermore, the study of molecular modeling also indicated that nevadensin could strongly bind to the site I (subdomain IIA) of HSA mainly by a hydrophobic interaction and there are hydrogen bond interactions between nevadensin and the residues Arg-218, Arg-222, Lys-195, and Asp-451. As compared to the other flavonoids, the flavonoids containing methoxy groups which are in aromatic rings can bind to HSA with higher affinity. [Copyright &y& Elsevier]

Abstract: Binding of farrerol to lysozyme (LYSO) was investigated at 302, 313 and 318K at pH 7.4 using spectrophotometric techniques such as fluorescence emission, circular dichroism (CD) and UV absorption. The data obtained from fluorescence quenching experiments showed that farrerol was bound to LYSO and the affinity was enhanced by the addition of farrerol. When the concentration ratio of farrerol to LYSO was higher than 5.4, both the binding constant and the binding stoichiometry went up. 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. They indicated that both van der Waals forces and hydrogen bonds are the major interactions between farrerol and LYSO. A value of 2.67nm for the average distance r between farrerol (acceptor) and tryptophan residues (Trp) of LYSO (donor) was derived from the fluorescence resonance energy transfer. Besides, the change in the conformation of LYSO was observed, being caused by the interaction with farrerol. [Copyright &y& Elsevier]

Abstract: Interaction between nevadensin and lysozyme (Lys) was studied using spectrophotometric techniques such as steady fluorescence, synchronous fluorescence, circular dichroism (CD) and UV–vis absorption. The fluorescence emission intensity of Lys was strongly quenched by the addition of nevadensin. Spectrophotometric observations are rationalized in terms of a static quenching process at lower concentration of nevadensin (less than 8μM) and a combined quenching process at higher concentration of nevadensin (8–20μM). Binding constants and binding sites for the nevadensin–Lys system were evaluated. The distance of 2.28nm and the energy transfer efficiency of 0.586 between nevadensin and Lys, evaluated from the Förster non-radioactive resonance energy transfer theory, indicated that the energy transfer from Lys to nevadensin occurred with higher possibility. Thermodynamic data showed that nevadensin was included in the hydrophobic cavity of Lys via hydrophobic interactions. UV/vis measurements on the enzymatic activity of Lys in the absence and presence of nevadensin indicated that the interaction between nevadensin and Lys led to a reduction in the activity of Lys. Furthermore, nevadensin binding to Lys had no influence on the molecular conformation of Lys. [Copyright &y& Elsevier]

Abstract: The binding of flavonoids (quercetin and myricetin) to catalase was investigated by fluorescence and circular dichroism (CD) techniques under physiological conditions. The binding parameters and binding mode between flavonoids and catalase were determined, and the results of synchronous fluorescence spectra and CD indicated a conformational change of catalase with addition of flavonoids. The effect of both Cu2+ and vitamin C on the binding constant of flavonoid-catalase was also examined. The experiment data show that the difference of the structure characteristics of quercetin and myricetin has a significant effect on their binding affinity for catalase. [Copyright &y& Elsevier]