The interaction of 2-mercaptobenzimidazole with human serum albumin as determined by spectroscopy, atomic force microscopy and molecular modeling.

The interaction of 2-mercaptobenzimidazole (MBI) with human serum albumin (HSA) was studied in vitro by equilibrium dialysis under normal physiological conditions. This study used fluorescence, ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared (FT-IR), circular dichroism (CD) and Raman spectroscopy, atomic force microscopy (AFM) and molecular modeling techniques. Association constants, the number of binding sites and basic thermodynamic parameters were used to investigate the quenching mechanism. Based on the fluorescence resonance energy transfer, the distance between the HSA and MBI was 2.495 nm. The ΔG(0), ΔH(0), and ΔS(0) values across temperature indicated that the hydrophobic interaction was the predominant binding Force. The UV, FT-IR, CD and Raman spectra confirmed that the HSA secondary structure was altered in the presence of MBI. In addition, the molecular modeling showed that the MBI-HSA complex was stabilized by hydrophobic forces, which resulted from amino acid residues. The AFM results revealed that the individual HSA molecule dimensions were larger after interaction with MBI. Overall, this study suggested a method for characterizing the weak intermolecular interaction. In addition, this method is potentially useful for elucidating the toxigenicity of MBI when it is combined with the biomolecular function effect, transmembrane transport, toxicological testing and other experiments.

Trace analysis of three antihistamines in human urine by on-line single drop liquid-liquid-liquid microextraction coupled to sweeping micellar electrokinetic chromatography and its application to pharmacokinetic study.

A rapid and efficient dual preconcentration method of on-line single drop liquid-liquid-liquid microextraction (SD-LLLME) coupled to sweeping micellar electrokinetic chromatography (MEKC) was developed for trace analysis of three antihistamines (mizolastine, chlorpheniramine and pheniramine) in human urine. Three analytes were firstly extracted from donor phase (4 mL urine sample) adjusted to alkaline condition (0.5 M NaOH). The unionized analytes were subsequently extracted into a drop of n-octanol layered over the urine sample, and then into a microdrop of acceptor phase (100 mM H(3)PO(4)) suspended from a capillary inlet. The enriched acceptor phase was on-line injected into capillary with a height difference and then analyzed directly by sweeping MEKC. Good linear relationships were obtained for all analytes in a range of 6.25 × 10(-6) to 2.5 × 10(-4)g/L with correlation coefficients (r) higher than 0.987. The proposed method achieved limits of detections (LOD) varied from 1.2 × 10(-7) to 9.5 × 10(-7)g/L based on a signal-to-noise of 3 (S/N=3) with 751- to 1372-fold increases in detection sensitivity for analytes, and it was successfully applied to the pharmacokinetic study of three antihistamines in human urine after an oral administration. The results demonstrated that this method was a promising combination for the rapid trace analysis of antihistamines in human urine with the advantages of operation simplicity, high enrichment factor and little solvent consumption.

Selective extraction of alkaloids in human urine by on-line single drop microextraction coupled with sweeping micellar electrokinetic chromatography.

A novel method of on-line single drop microextraction (SDME) coupled with sweeping micellar electrokinetic chromatography (MEKC) for the selective extraction and dual preconcentration of alkaloids was developed. In this technique, analytes of three alkaloids were firstly extracted from 4.0 mL basic aqueous sample solution (donor phase, 500 mM NaOH) into a layer of n-octanol at temperature 30 °C with the stirring rate of 1150 rpm, then back-extracted into the acidified aqueous acceptor (acceptor phase, 50 mM H3PO4) suspended at the tip of a capillary at 650 rpm. Then, the aqueous acceptor was introduced into capillary by hydrodynamic injection with a height difference of 15 cm between the inlet and outlet of capillary for 300 s, and analyzed directly by on-line sweeping MEKC. With the selective SDME, we were able to extract three alkaloids without any interfering components in human urine samples. Under the optimum conditions, the proposed method achieved limits of detections (LOD) of between 0.2 ng mL⁻¹ and 1.5 ng mL⁻¹ with 1583-3556-fold increases in detection sensitivity for three analytes, which indicated that it was a promising method for analysis of alkaloids in human urine.

Directly suspended droplet microextraction combined with single drop back-extraction as a new approach for sample preparation compatible with capillary electrophoresis.

A simple and novel method of directly suspended droplet microextraction (DSDME) combined with single drop back-extraction prior to capillary electrophoresis (CE) measurement is developed. In this technique, DSDME was firstly carried out under the maximum stirring rate for a desired time. Then, an aqueous droplet as back-extractive phase suspended at the needle tip was immersed in droplet of organic phase for back-extracted. After extraction, the aqueous droplet was transferred into a suitable vial and injected into CE for analysis. Three alkaloids were selected as model compounds for developing and evaluating the method performance. Under the optimum conditions, the enrichment factors ranged from 231 to 524. The relative standard deviations for five replicates were in the range of 4.8-8.1%. The calibration graph was linear in the range of 20-1000 ng mL(-1) yielding correlation coefficients higher than 0.9983. The limit of detections varied from 8.1 to 14.1 ng mL(-1). Human urine samples were spiked with three alkaloids standard to assess the matrix effects and satisfactory results were obtained. The advantages of this method are simplicity of operation, rapid detection, low cost, high enrichment factor and little solvent consumption.

Application of single drop liquid-liquid-liquid microextraction for the determination of fluoroquinolones in human urine by capillary electrophoresis.

A simple and novel method of single drop liquid-liquid-liquid microextraction (SD-LLLME) coupled with capillary electrophoresis (CE) for the determination of six fluoroquinolones (FQs) was developed. The method was eventually applied to extraction and preconcentration of FQs in human urine samples. Good linear relationships were obtained for all analytes in a range of 40-1000 µg L⁻¹ with the correlation coefficients from 0.9913 to 0.9995. The limit of detections (LODs) varied from 7.4 to 31.5 µg L⁻¹ at a signal-to-noise (S/N) of 3. The recoveries at two spiking levels were 81.8-104.9% with relative standard deviations <8.3%.