Simultaneous Determination of the Endogenous Free ��-Lipoic Acid and Dihydrolipoic Acid in Human Plasma and Erythrocytes by RP-HPLC with Electrochemical Detection

A highly sensitive, precise, and accurate reversed-phase high-performance liquid-chromatography/electrochemical detection method for simultaneous determination of the endogenous free ??-lipoic acid and dihydrolipoic acid in biological matrices was developed and validated. The two analytes were extracted from the samples with acetonitrile/10% metaphosphoric acid solution_(aqueous) (50/50 v/v). To determine the total lipoic acid, samples were treated with tris(2-carboxyethyl)phosphine solution in phosphate buffer, pH 2.5 with 85% orthophosphoric acid prior to deproteination. The two analytes were separated on a C₁₈ (150 × 4.6 mm, 5 ??m) analytical column using acetonitrile-50 mM phosphate buffer, pH 2.5 with 85% orthophosphoric acid (35/65 v/v) as the isocratic mobile phase pumped at a flow rate of 2.0 mL min^?1 at the column oven temperature of 35 °C. The column eluents were monitored at a potential of 0.9 V. These analytes were efficiently resolved in <7 min. The present method was sufficiently robust and specific for simultaneous determination of the two analytes and demonstrated acceptable values for linearity (r ² = 0.999 in the range of 0.1?C500 and 0.25?C1,000 ng mL^?1 for ??-lipoic acid and dihydrolipoic acid, respectively), recovery (>97%), precision (RSD% <2), and sensitivity (on column limit of detection, 150 and 375 fg for ??-lipoic acid and dihydrolipoic acid, respectively and limit of quantification: 0.5 and 1.25 pg for ??-lipoic acid and dihydrolipoic acid, respectively), indicating that the proposed method was more sensitive, precise, economical, and versatile, and has higher throughput than the previously reported methods for simultaneous determination of the two analytes.     

Comparative evaluation of amphotericin B binding to the native and modified forms of rice lipid-transfer protein: a possible perspective on improving the drug-binding affinity and specificity

Plant non-specific lipid-transfer proteins (nsLTPs) are small basic proteins which transport phospholipids between different cell membranes. They are classified, based on their molecular weight, into two subfamilies: nsLTP1 (9 kDa) and nsLTP2 (7 kDa). These proteins have received an increasing research interest as efficient drug carriers in drug delivery systems. However, there have been few studies conducted on their drug-binding characteristics. The present study aims to comparatively evaluate binding of amphotericin B (AmB, an antifungal drug) to the native and modified forms of rice nsLTP1 and to assess possible applications in drug delivery methods. The LTP1 was purified and then interaction of AmB with the native and modified forms of protein was investigated with various spectroscopic methods. The results showed that the AmB–LTP binding is associated with quenching of the protein intrinsic fluorescence. Furthermore, as temperature of the medium increased, the stability of the AmB–native LTP complex decreased, whereas the stability of the AmB–modified LTP increased. Analysis of the thermodynamic parameters of the AmB–protein complexes and extrinsic fluorescence data indicated that the lysine modification caused a change in the intermolecular interactions between the protein and AmB as well as in the protein surface hydrophobicity (PSH). Furthermore, Dixon plot showed that AmB inhibits ANS binding especially in the AmB–modified RLTP binding. Findings of the current study highlighted the drug-binding characteristics of the modified form of LTP necessitating further studies to profoundly evaluate the characteristics of its mutant forms.     

Zinc chloride catalyzed three-component Ugi reaction: synthesis of N-cyclohexyl-2-(2-hydroxyphenylamino)acetamide derivatives

The ability of zinc chloride as a catalyst to promote the three-component Ugi reaction of 2-aminophenols, aliphatic or aromatic aldehydes, and cyclohexyl isocyanide in methanol at room temperature is described. The N-cyclohexyl-2-(2-hydroxyphenylamino) amide products are obtained in high yields. When N,N-dimethylformamide dimethyl acetal and triethyl orthoformate, as two new components of the three-component Ugi reaction are used instead of the aldehyde the reaction gives N-cyclohexyl-2-(dimethylamino)-2-(2-hydroxyphenylamino)acetamide and N-cyclohexyl-2-(2-hydroxyphenylamino)-2-ethoxyacetamide derivatives, respectively.     

Low-cost,high-throughput and rapid-prototyped 3D-integrated dielectrophoretic channels for continuous cell enrichment and separation

Microfluidic devices for dielectrophoretic cell separation are typically designed and constructed using microfabrication methods in a clean room, requiring time and expense. In this paper, we describe a novel alternative approach to microfluidic device manufacture, using chips cut from conductor–insulator laminates using a cutter plotter. This allows the manufacture of microchannel devices with micron-scale electrodes along every wall. Fabrication uses a conventional desktop cutter plotter, and requires no chemicals, masks or clean-room access; functional fluidic devices can be designed and constructed within a couple of hours at negligible cost. As an example, we demonstrate the construction of a continuous dielectrophoretic cell separator capable of enriching yeast cells to 80% purity at 10 000 cells/s.