Bismuth film electrode for anodic stripping voltammetric determination of tin

The bismuth film electrode (BiFE), in combination with anodic stripping voltammetry, offers convenient measurement of low concentrations of tin. The procedure involves simultaneous in situ formation of the bismuth film electrode on a glassy carbon substrate electrode, together with electrochemical deposition of tin, in a non-deaerated model solution containing bismuth ions, catechol as complexing agent and the metal analyte, followed by an anodic stripping scan. The BiFE is characterized by an attractive electroanalytical performance, with two distinct voltammetric stripping signals corresponding to tin, accompanied with low background contributions. Several experimental parameters were optimized, such as concentration of bismuth ions and catechol, deposition potential, deposition time and pH of the model solution. In addition, a critical comparison is given with bare glassy carbon and mercury film electrodes, revealing the superior characteristics of BiFE for measurement of tin. BiFE exhibited highly linear behavior in the examined concentration range from 1 to 100 μg L⁻¹ of tin (R² = 0.997), an LoD of 0.26 μg L⁻¹ tin, and good reproducibility with a calculated R.S.D. of 7.3% for 10 μg L⁻¹ tin (n = 10). As an example, the practical applicability of BiFE was tested with the measurement of tin in a real sample of seawater.     

Switching between novel samarium(II)-mediated cyclizations by a simple change in alcohol cosolvent

Gamma,delta-unsaturated ketones undergo two very different stereoselective cyclization reactions mediated by samarium(II) iodide depending upon the alcohol cosolvent used in the reaction. Switching between an unprecedented aldol spirocyclization and a novel cyclobutanol-forming process can be achieved simply by changing the alcohol cosolvent from methanol to tert-butyl alcohol. [reaction: see text]     

Deprotection of pinacolyl boronate esters by transesterification with polystyrene-boronic acid

Mild deprotection of pinacolyl boronate esters to the corresponding boronic acids was achieved in the presence of excess polystyrene-boronic acid via a transesterification process. The procedure allows for the cleavage of pinacolyl boronate esters in the presence of sensitive functional groups.     

Total synthesis of (-)-reveromycin B

[structure: see text] The total synthesis of the epidermal growth factor inhibitor reveromycin B (2) is described. A novel, convergent, and stereoselective reaction sequence was utilized to construct the 5,6-spiroketal system 10 which was converted into the natural product 2 by a 16-step sequence.     

Gene-protein database of Escherichia coli K-12: edition 3

The first two editions of the E. coli Gene-Protein Index were published to provide identifications of protein spots resolved by two-dimensional gel electrophoresis as the products of known genes. This third edition has been expanded to include information about genes and proteins gained directly from two-dimensional gel analysis--including information about protein spots not yet characterized genetically or biochemically--and is therefore more properly called a cellular protein database. An alpha-numeric designation has been uniquely assigned to each of the 616 polypeptide spots in the current database. To this, information is linked about the polypeptide's identification (protein name, gene name, Enzyme Commission--EC number), location on reference gels (x-y coordinates), genetics (Genbank code, DNA sequence reference), biochemistry (molecular weight, isoelectric point), and physiology (steady state level of the protein as a function of media and temperature, membership in various regulons and stimulons).     

An introduction to bismuth film electrode for use in cathodic electrochemical detection

A new electrode surface design, the bismuth film electrode (BiFE), is presented as a promising alternative to mercury and other solid electrodes for direct cathodic electrochemical detection of organic compounds. The preparation of the BiFE, involving an ex situ electroplating of metallic bismuth onto a glassy carbon (GC) substrate electrode, was optimised. The useful negative potential windows of the BiFE in the pH range 1 (−0.2 to −0.8 V vs Ag/AgCl) to 10 (−0.2 to −1.5 V) were determined. The reproducibility of measuring 2-nitrophenol as a model compound (relative standard deviation, r.s.d., n=10) was found to be 0.5% at the same BiFE, and 1.0% at successive newly prepared BiFEs. No polishing or any other pre-treatment of the substrate GC surface was required prior to re-plating of a new Bi film. The BiFE showed similar or even favourable voltammetric behaviour when compared to mercury and bare GC electrodes, and was successfully tested for amperometric detection under hydrodynamic conditions. The results revealed that BiFE is an attractive new non-mercury metallic electrode particularly suitable for cathodic electrochemical detection in flow analytical systems.     

Assessment of X-ray photoelectron spectroscopy for analysis of particulate pollutants in urban air

XPS was used to determine hourly and seasonal changes in urban airborne airborne particulates collected in London, UK. Particles were collected on a Burkard spore trap and on PTFE filters for hourly and daily readings, respectively, at periods during the summer and winter. Analysis within 24 h of collection was advisable to avoid build-up of surface contamination from the atmosphere. Carbon and oxygen species dominated the particulate surface with traces of Na+, Mg2+, Ca2+, SiO2, Cl-, NH4+, NO3- and SO4(2-) present. Major species could not be identified on particles collected by the Burkard spore trap as the peaks from the particles coincided with peaks from the tape in the O 1s and C 1s regions. In addition, particle loads were insufficient to establish changes in surface chemistry of the remaining trace species on an hourly basis. Carbon species could be identified for particles collected on PTFE filters as the binding energies for particles and PTFE are separated by 8 eV in the C 1s region. Three regions were identified, namely C-H/C-C, C-O/C-N and C=O/COO-. There was evidence of higher levels of soot during the winter due to more anthropogenic activity, which is in agreement with other data. Fe was a major element detected by electron probe microanalysis in the bulk of winter particles but not on the surface, implying an organic coating on the particles sufficiently thick (> 2 nm) to absorb the Fe photoelectrons.