l-Amino Acids as Chiral Selectors for the Enantioseparation of (±)-Bupropion by Ligand Exchange Thin-Layer Chromatography Using Cu(II) Complex via Four Different Approaches

JPC – Journal of Planar Chromatography – Modern TLC - The present paper deals with direct enantioresolution of (±)-bupropion using thin-layer chromatography and different...     

H3Mo12O40P-Catalyzed One-Pot Synthesis of Amidoalkyl Naphthols

Solid H₃Mo₁₂O₄₀P is used for an efficient one-pot synthesis of amidoalkyl naphthols using aromatic aldehydes, β-naphthol, and urea or amides in carbon tetrachloride. The catalyst was efficiently recovered from the reaction mixture and reused with negligible loss of catalyst activity. Ambient conditions, simple workup, and good yield are some of the striking features of the present protocol.     

Simple,Efficient, and Green Method for Synthesis of Trisubstituted Electrophilic Alkenes Using Lipase as a Biocatalyst

A simple and efficient Knoevenagel condensation method for the synthesis of trisubstituted electrophilic alkenes was developed using lipase as a biocatalyst. Knoevenagel condensation was performed using the conventional method and using lipases (Aspergillus oryzae or Rhizopus oryzae) as biocatalysts, and reaction time, reaction temperature, yield, and recyclability were compared. Using a lipase as a biocatalyst eliminated the need for bases such as piperidine and pyridine. A wide range of aromatic aldehydes and ketones readily undergo condensation with active methylene compounds. The workup procedure is also very simple, and yields of the reactions are in the range of 75% to 95%. Both the biocatalysts were effectively recycled four times with no major decrease in the yield of product. The remarkable catalytic activity and reusability of lipase widens its applicability in Knoevenagel condensation with good to excellent yields for synthesis of trisubstituted electrophilic alkenes.     

Mechanical and thermodynamic properties of surfactant aggregates at the solid-liquid interface

Surfactants are widely used to stabilize colloidal systems in a variety of industrial applications through the formation of self-assembled aggregates at the solid-liquid interface. Previous studies have reported that the control of surfactant-mediated slurry stability can be achieved through the manipulation of surfactant chain length and concentration. However, a fundamental understanding of the mechanical and energetic properties of these aggregates, which may aid in the molecular-level design of these systems, is still lacking. In this study, experimentally measured force/distance curves between an atomic force microscope (AFM) tip and self-assembled surfactant aggregates on mica or silica substrates at concentrations higher than the bulk critical micelle concentration (CMC) were used to determine their mechanical and thermodynamic properties. The experimental curves were fitted to a model which describes the interaction between a hard sphere (tip) and a soft substrate (surfactant structures) based on a modified Hertz theory for the case of a thin elastic layer on a rigid substrate. The calculated mechanical properties were found to be in the same order of magnitude as those reported for rubber-like materials (e.g., polydimethylsiloxane (PDMS)). By integrating the force/distance curves, the energy required for breaking the surface aggregates was also calculated. These values are close to those reported for bulk-micelle formation.     

Effect of rubbing load on nanoscale charging characteristics of human hair characterized by AFM based Kelvin probe

The manageability and feel of human hair is significantly affected by its surface charge. Understanding and developing ways to control charge build up is hence highly beneficial. Previous studies have looked at static charging characteristics of hair on a macroscale. In this study, static charging characteristics of hair are studied on the nanoscale with an AFM. Hair is charged by rubbing a control area on its surface with an AFM tip, to which a small voltage bias is applied. The resulting charge distribution is characterized by measuring the surface potential of the control area in situ with AFM based Kelvin probe microscopy. The rubbing load is progressively increased, and the effect of this increase on the charge build up is assessed. Virgin, damaged and conditioner treated hair samples are studied for a better understanding of charge build up and dissipation. Relevant mechanisms are discussed.     

Effect of halides on the TLC resolution of amino acids below their isoelectric points

TLC of a fifteen component mixture of amino acids has been carried out in two ways; firstly, the amino acids were treated with halides below their isoelectric points and chromatographed on plain silica plates, and secondly the amino acids in their cationic forms were chromatographed on silica plates impregnated with halides, keeping the same solvent system. The resolution is considered to be affected by hydrophobic interactions between silica gel and amino acid molecule and by the polarity and the flow of the mobile phase. The method provides resolution of 10–11 amino acids from the fifteen component mixture.     

Reversed‐phase liquid chromatographic determination of enantiomers of atenolol in rat plasma using derivatization with Marfey's reagent

An HPLC method was established for enantioseparation of (R,S)‐atenolol (ATE) and determination of enantiomers in rat plasma. Marfey's reagent (1‐fluoro‐2,4‐dinitrophenyl‐5‐L‐alanine amide, FDNP‐L‐Ala‐NH₂, MR) was used as chiral derivatizing reagent with detection of diastereomers at 340 nm. It was shown that the R‐isomer eluted before the S‐isomer. The method was validated for linearity, repeatability, limits of detection and limit of quantification (LOQ). Recovery of ATE at LOQ was 92.8% for (R)‐ATE and 92.6% for (S)‐ATE. Copyright © 2009 John Wiley & Sons, Ltd.