Xinyu Jiang

Influence of B-Ring Hydroxylation on Interactions of Flavonols with Bovine Serum Albumin

The B-ring substitution pattern of flavonols is a significant structural feature for their function as free radical scavengers and antioxidants. In this paper, four differently substituted B-ring hydroxylation flavonols (galangin, kaempferol, quercetin, and myricetin) and a flavonol glycoside (quercitrin) were studied for their ability to bind BSA by quenching the protein intrinsic fluorescence. From the spectra obtained, the biomolecular quenching constants, the apparent static binding constants, and the binding site values were calculated. The B-ring hydroxylation of flavonols significantly affected the binding/quenching process; in general, the binding affinity increased with the number of hydroxyl groups on the B-ring. The binding constants ( Ka) were determined as myricetin (4.90 x 10(8) L/mol) > quercetin (3.65 x 10(7) L/mol) > kaempferol (2.57 x 10(6) L/mol) > galangin (6.43 x 10(5) L/mol). The glycoside substitute at the C-ring position decreased the binding affinity. The chromatographic retention factor ( K) and logarithms of apparent partition coefficient (log Kow) were linear to the logarithms of apparent binding constants (log Ka) for flavonols with increasing hydroxyl groups on the B-ring. These results showed that the hydrogen bond force play an important role in binding flavonols to BSA. These results are also in agreement with the generally accepted structure-dependent free radical scavenger and antioxidant abilities of flavonols.

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58xa0μgxa0L−1, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000xa0μgxa0L−1. The ranges of intra- and interday precision (nxa0=xa05) at 100xa0μgxa0L−1 of nitrophenols were 5.85–7.76 and 10.2–11.9xa0%, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.

Effects of Temperature and Ions on Binding Dihydromyricetin to Bovine Serum Albumin by Spectroscopic Method

ABSTRACT The interaction of dihydromyricetin (DMY) and bovine serum albumin (BSA) in solution was investigated by fluorescence, synchronous fluorescence, and ultraviolet (UV) spectra. These results revealed that DMY quenches the fluorescence of BSA by forming the DMY–BSA complex. The number of binding sites (n), binding constant (K a ), and thermodynamic parameter (ΔG, ΔH, ΔS) were calculated. The primary binding forces between DMY and BSA were found to be the electrostatic force and hydrophobic interaction. The binding distance (r) between the donor (BSA) and acceptor (DMY) was determined as 3.43 nm based on Försters theory. The effect of metal ions (Ni2+, K+, Cu2+, and Co2+) on the binding constant of DMY–BSA complex was also investigated. The effect of DMY on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy and UV-Vis absorption spectroscopy.