Analytical applications of absorption spectroelectrochemistry at grazing incidence

Analytical applications of spectroelectrochemistry are limited by the short path-length, in the absorbing medium, that can be produced with most light-beam/electrode configurations. This disadvantage is overcome for grazing incidence. A cell fitted with glassy-carbon electrodes and used in a conventional spectrophotometer is described and applied to model systems illustrating the use of (a) homogeneous redox reactions, (b) homogeneous redox reaction followed by chemical reaction and (c) electro-deposition followed by stripping into a reagent solution. This last technique is the spectroelectrochemical analogue of anodic-stripping voltammetry.     

Infrared detection of a phenylboronic acid terminated alkane thiol monolayer on gold surfaces

Polarization modulation infrared reflectance absorption spectroscopy (PM-IRRAS) and infrared reflectance absorption spectroscopy (IRRAS) have been used to characterize the formation of a self-assembled monolayer of N-(3-dihydroxyborylphenyl)-11-mercaptoundecanamide) (abbreviated PBA) on a gold surface and the subsequent binding of various sugars to the PBA adlayer through the phenylboronic acid moiety to form a phenylboronate ester. Vibrationally resonant sum frequency generation (VR-SFG) spectroscopy confirmed the ordering of the substituted phenyl groups of the PBA adlayer on the gold surface. Solution FTIR spectra and density functional theory were used to confirm the identity of the observed vibrational modes on the gold surface of PBA with and without bound sugar. The detection of the binding of glucose on the gold surface was confirmed in part by the presence of a C-O stretching mode of glucose and the observed O-H stretching mode of glucose that is shifted in position relative to the O-H stretching mode of boronic acid. An IR marker mode was also observed at 1734 cm(-1) upon the binding of glucose. Additionally, changes in the peak profile of the B-O stretching band were observed upon binding, confirming formation of a phenylboronate ester on the gold surface. The binding of mannose and lactose were also detected primarily through the IR marker mode at approximately 1736 to 1742 cm(-1) depending on the identity of the bound sugar.     

Extraction of arsenic species from spiked soils and standard reference materials

The abilities of various extractants to recover four arsenic species [As(iii), As(v), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA)] from soils spiked with 20 micro g g(-1) As were investigated. The extractants were water, buffer solutions (citrate and ammonium dihydrogen phosphate), acidic solutions (phosphoric acid and acetic acid), a basic solution (sodium hydroxide) and household chemicals (vinegar and Coca Cola). Gentle shaking at room temperature with each extractant for 24 h gave different recoveries for the different arsenic species. With 0.1 M NaOH solution 46% As(iii), 53% DMA, 100% MMA and 84% As(v) were recovered. A rapid extraction procedure using a sonicator probe has been developed to obtain higher extraction efficiencies. Extracts of arsenic-spiked soil, SRM 2711 Montana soil and SRM 2709 San Joaquin soil were analyzed by HPLC-ICP-MS. In the SRM water extracts, DMA and MMA were identified in addition to inorganic arsenic. The solution detection limits (3s) were 0.1, 0.12, 0.13 and 0.15 ng mL(-1) for As(iii), DMA, MMA and As(v), respectively for HPLC-ICP-MS.     

The electronic spectrum of tantalum hydride and deuteride

The diatomic molecule tantalum hydride (TaH) and its isotopologue tantalum deuteride (TaD) have been detected for the first time by laser excitation spectroscopy. The gas-phase molecules were produced in a hollow cathode discharge. Two red-degraded bands, one arising from TaH at 636 nm and the other from TaD at 635 nm, have been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. A rotational analysis shows that both bands are Ω = 2←2 in character, with well-resolved Ω-doubling in the upper state of TaH. Analysis of the ¹⁸¹Ta magnetic dipole and electric quadrupole hyperfine structure reveals that the lower X³Φ₂ electronic state of the two transitions arises from a σ²πδ electronic configuration, in agreement with previous theoretical calculations. The bond length in the TaH X³Φ₂ (v = 0) level is found to be 1.756960(4) Å.     

A simple lecture demonstration of flow injection analysis

Summary The difficulties of explaining the basic concepts of dispersion in flow injection analysis are discussed with particular reference to comparisons with segmented flow analysis and high performance liquid chromatography. The problems with diagrammatic illustration of the laminar flow processes and subsequent dispersion of an injected sample zone are explained. A simple demonstration based on a flow cell for a slide projector consisting of a peristaltic pump tube sandwiched between two slightly modified slide mounts is described.

---

Einfache Vorlesungsdemonstration der Fließinjektionsanalyse

     

Peptides—XXXII: The use of phenyl esters in peptide synthesis

Phenyl esters of N-terminal amino-protected peptides are valuable intermediates in synthesis of polypeptides. The phenyl ester function is stable during the customary manipulations of chain extension, and it can be removed selectively by treatment with one equivalent of hydrogen peroxide at pH 10.5 in a variety of solvents such as 80% acetone, dimethylfonnamide, hexamethylphosphoramide or trifluoroethanol. The method has always been satisfactory providing that dimethylsulphide is used as a scavenger.     

One-pot synthesis of functionalized piperid-4-ones: a four-component condensation

The one-pot synthesis of highly substituted piperid-4-ones has been achieved. Diketene is added to a tosyl imine in the presence of TiCl(4) and MeOH, followed by 1 equiv of aldehyde to generate 2,6-disubstituted nonsymmetrical piperid-4-ones as a mixture of cis-/trans-diastereomers in good yields. This mixture of diastereomers can be converted to a single 2,6- cis-diastereomer by epimerization with K(2)CO(3).