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Abstract Silver is one of the most important heavy metals with a broad range of applications; however, it can have significant negative impacts on both the ambient environment and organisms. For this work, an interesting fluorescence polarization sensor based on SH-DNA functionalized gold nanoparticles (AuNPs) was proposed for the detection of Ag+ in aqueous solutions. Moreover, this sensing strategy is quite simple, sensitive, selective, and cost-effective. Ag+ ions can interact specifically with a cytosine–cytosine (C–C) mismatch in DNA duplexes to form stable metal-mediated cytosine–Ag+–cytosine (C–Ag+–C) base pairs. The creation of these C–Ag+–C complexes results in evident changes in the molecular volume and fluorescence polarization signal. The stable hybridization between the two probes occurs with the formation of the C–Ag+–C complex in the presence of Ag+ ions, which leads to obvious fluorescence quenching in contrast to the system without AuNP. This assay may be employed to identify nanomolar levels of Ag+ within 6 min at room temperature. Furthermore, the sensor was successfully adopted to detect Ag+ ions in environmental water samples, which may facilitate the potential development of a range of environmental monitoring applications. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

We investigate the interaction of trypsin with glutathione-stabilized Au nanoparticles (NPs) using fluorescence, synchronous fluorescence and ultraviolet (UV) absorption spectroscopy. We find that trypsin binds strongly to the Au NPs with a static quenching mechanism, and that the interaction is characteristic of positive cooperative binding. Furthermore, we determine the binding constants and the thermodynamic parameters, which suggest that the main binding forces between the glutathione-stabilized Au NPs and trypsin are electrostatic interactions and hydrogen bonding. Analysis of UV–vis absorption spectra suggests that aggregation of the Au NPs occurs in the trypsin/Au NPs system, which significantly alters the conformation of the protein. [ABSTRACT FROM AUTHOR]

Abstract: One of the dihydropyrimidinone derivative 5-(ethoxycarbonyl)-6-methyl-4-(4-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one (EMMD) was synthesized, and its binding properties with calf-thymus DNA (ctDNA) were investigated using spectroscopic, viscometric, isothermal titration calorimetric (ITC) and molecular modeling techniques. Fluorescence spectra suggested that the fluorescence enhancement of the binding interaction of EMMD to ctDNA was a static process with ground state complex formation. The binding constant determined with spectroscopic titration and ITC was found to be in the same order of 104 M−1. According to the results of the viscosity analysis, fluorescence competitive binding experiment, fluorescence quenching studies, absorption spectral and ITC investigations, it can be concluded that EMMD is intercalative binding to ctDNA. Furthermore, the results of molecular modeling confirmed those obtained from spectroscopic, viscosimetric and ITC investigations. Additionally, ITC studies also indicated that the binding interaction is predominantly enthalpy driven. [Copyright &y& Elsevier]

Abstract: In this paper, binding interaction of 5-(ethoxycarbonyl)-6-methyl-4-(4-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one (EMMD) with human serum albumin (HSA) under physiological conditions was investigated by using spectroscopy, isothermal titration calorimetry (ITC) and molecular modeling techniques. The results of spectroscopic studies suggested that EMMD have a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. ITC investigations indicated that drug–protein complex was stabilized by hydrophobic forces and hydrogen bonds, which was consistent with the results of molecular modeling studies. Competitive experiments indicated the displacement of warfarin by EMMD, which revealed that the binding site of EMMD to HSA was located at subdomain IIA. [Copyright &y& Elsevier]

Abstract: The binding mechanism of molecular interaction between 5-(ethoxycarbonyl)-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (a dihydropyrimidinones derivative, EMPD) and human serum albumin (HSA) was studied using spectroscopic methods and modeling technique. The quenching mechanism was investigated in terms of the binding constants and the basic thermodynamic parameters. The results of spectroscopic measurements suggested that EMPD have a strong ability to quench the intrinsic fluorescence of HSA through static quenching procedure. The drug–protein complex was stabilized by hydrophobic forces and hydrogen bonding as indicated from the thermodynamic parameters and synchronous fluorescence spectra, which was consistent with the results of molecular docking and accessible surface area calculation. Competitive experiments indicated that a displacement of warfarin by EMPD, which revealed that the binding site of EMPD to HSA was located at the subdomains IIA. The distance between the donor and the acceptor was 4.85nm as estimated according to Förster''s theory of non-radiation energy transfer. The effect of metal ions on the binding constants was also investigated. The results indicated that the binding constants between EMPD and HSA increased in the presence of common metal ions. [Copyright &y& Elsevier]

Abstract: The molecular mechanism of the binding of norfloxacin (NRF) to trypsin was investigated by fluorescence, synchronous fluorescence and UV–vis absorbance spectroscopy and molecular modeling at physiological conditions. The quenching mechanism and the binding mode were investigated in terms of the association constants and basic thermodynamic parameters. The results of spectroscopic measurements suggested that NRF have a strong ability to quench the intrinsic fluorescence of trypsin through static quenching procedure. Moreover, fluorescence experiments were also performed at different values of pH to elucidate the effect of pH on the binding. The NRF–trypsin complex was stabilized by hydrophobic forces and hydrogen bonding, via tryptophan residue as indicated from the thermodynamic parameters, which was consistent with the results of molecular docking and accessible surface area calculations. [Copyright &y& Elsevier]