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Abstract: In the present study, the interaction of vanillin and human serum albumin (HSA) has been characterised by molecular modelling, fluorescence, Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopic methods. The results of molecular modelling suggested that vanillin was located within the binding pocket of subdomain IIA of HSA mainly by hydrophobic forces. The quenching of HSA fluorescence takes place with a binding constant (K) of 8.8, 7.7, 5.7, 4.2×104 M−1 at four different temperatures (288, 298, 308, 318K), respectively. Meanwhile, the number of binding site (n ≈1) was also obtained from fluorescence titration data. The enthalpy change ΔH 0 and the entropy change ΔS 0 were calculated to be −20kJmol−1 and 5.8Jmol−1 K−1 according to the Van’t Hoff equation. Furthermore, the alterations of protein secondary structure in the presence of vanillin were explored by FT-IR and CD spectra. [Copyright &y& Elsevier]

Abstract: In this study, the interaction of the endocrine disruptor bisphenol A (BPA) and human serum albumin (HSA) was investigated by molecular modelling, fluorescence, ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR) and circular dichroism spectroscopy (CD). The association constants between BPA and HSA were determined using the Scatchard equation. The thermodynamic parameters of the binding reaction (ΔG 0, ΔH 0 and ΔS 0) were measured, and they indicated the presence of hydrophobic forces in the BPA–HSA interaction, which agreed well with the results from molecular modelling. The alterations of protein secondary structure in the presence of BPA were confirmed by UV–vis, FT-IR and CD spectroscopy. Lastly, the average binding distance, r, between BPA and HSA was evaluated and found to be 1.82nm according to Förster’s theory of non-radiation energy transfer. [ABSTRACT FROM AUTHOR]

Abstract: Dissolved organic matter (DOM) is a complex and poorly understood mixture of natural polymeric organic material, and plays an important role in material transport and carbon balance in aquatic ecosystems. Fluorescent dissolved organic matter (FDOM) represents a major portion of the total DOM and has often been used as a tracer to identify the source or track the movement of DOM in aquatic environment. In this work, we have applied Excitation/Emission Matrix spectroscopy (EEMs) to study the distribution and characteristics of FDOM in seawater of Bohai Sea in Northern China. Hierarchical Cluster method has been used to assess the similarities and dissimilarities of the entire EEMs data sets of seawater samples collected from different regions of the Bohai Sea. The distribution of different seawater samples as revealed by multivariate results has been used to track the movement of DOM material in the Bay, and the results from such analysis are in good agreement with those obtained from seawater circulation and dynamics models. [Copyright &y& Elsevier]

A new method for phytochelatins by high-performance liquid chromatography (HPLC) was developed based on a condensation reaction with monobromobimane to produce fluorescent derivatives. Glutathione, H-(γ-glutamic acid-cysteine)2-glycine-OH, H-(γ-glutamic acid-cysteine)3-glycine-OH, H-(γ-glutamic acid-cysteine)4-glycine-OH, H-(γ-glutamic acid-cysteine)5-glycine-OH, and H-(γ-glutamic acid-cysteine)6-glycine-OH were well separated, with retention times between 14.68 and 22.0 min. The HPLC method had good linearity (r < 0.9991) between 0.1 mg L−1and 100 mg L−1. The limits of quantification for the analytes (S/N = 3) were 0.08, 0.3, 0.05, 0.3, 0.5, and 0.8 mg L−1, respectively. The recoveries were between 83.0% and 101.33% with relative standard deviations less than 2%. The reported method is simple, accurate, and suitable for the determination of phytochelatins. [ABSTRACT FROM AUTHOR]

Abstract: Phthalate esters (PAEs) are globally pervasive contaminants that are considered to be endocrine disruptor chemicals and toxic environmental priority pollutants. In this paper, the interactions between PAEs and human serum albumin (HSA) were examined by molecular modelling, steady state and time-resolved fluorescence, ultraviolet–visible spectroscopy (UV–vis) and circular dichroism spectroscopy (CD). The association constants between PAEs and HSA were determined using the Stern–Volmer and Scatchard equations. The binding of dimethyl phthalate (DMP) to HSA has a single class of binding site and its binding constants (K) are 4.08×103, 3.97×103, 3.45×103, and 3.20×103 Lmol−1 at 289, 296, 303, and 310K, respectively. The Stern–Volmer and Scatchard plots both had two regression curves for HSA–butylbenzyl phthalate (BBP) and HSA–di-2-ethylhexyl phthalate (DEHP), which indicated that these bindings were via two types of binding sites: the numbers of binding site for the first type were lower than for the second type. The binding constants of the first type binding site were higher than those of the second type binding site at corresponding temperatures, the results suggesting that the first type of binding site had high affinity and the second binding site involved other sites with lower binding affinity and selectivity. The thermodynamic parameters of the binding reactions (ΔG°, ΔH° and ΔS°) were measured, and they indicated the presences of hydrophobic forces and hydrogen interactions in the PAEs–HSA interactions, which agreed well with the results from molecular modelling. The alterations of protein secondary structure in the presence of PAEs were confirmed by UV–vis and CD spectroscopy. The time-resolved fluorescence study showed that the lifetime of Trp residue of HSA decreased after the addition of PAEs, which implied that the Trp residue of HSA was the main binding site. [Copyright &y& Elsevier]

Optical sensing films for ammonia have been investigated based on a fluorescent indicator aminofluorescein (AF). AF was immobilized in diverse organically modified silicates (ORMOSILSs) obtained by copolymerizing various proportions of methyltrimethoxysilane (Me–TriMOS), phenyltrimethoxysilane (Ph–TriMOS), dimethyldimethoxysilane (DiMe–DiMOS), and diphenyldimethoxysilane (DiPh–DiMOS) with tetramethoxysilane (TMOS). The effective polarities of ormosils were probed by using the solvatochromic dye ET (30) [2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)]phenolate. Compared with the fluorescent responses of fluorescein and fluorescein isothiocyanate, the fluorescent intensity enhancement of AF for ammonia was caused by the reaction between ammonia and the NH2 group on AF. The reaction may cause the reduction of the intermolecular self-quenching of AF to make a fluorescence enhancement of sensing film in NH3 solution. The ammonia sensing range and rate of response were found to highly depend on the type and content of organosilicon precursors employed. Films prepared with a 1:3, 1:1.5, 1:1.2, or 1:1 mole ratio (TMOS:Me–TriMOS, TMOS:Ph–TriMOS, TMOS:DiMe–DiMOS, or TMOS:DiPh–DiMOS) was found to be the best in terms of stability and response. Their detection limits for ammonia in water was 0.01, 0.5, 0.2, and 0.5 μg ml−1, respectively. [Copyright &y& Elsevier]