Alejandro Barron | Simon Fraser University (original) (raw)

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Papers by Alejandro Barron

Talanta, 1998

Liquid-liquid extraction of Co(II) and Zn(II) by methylisobutylcetone (MIBK) has been studied sys... more Liquid-liquid extraction of Co(II) and Zn(II) by methylisobutylcetone (MIBK) has been studied systematically from NH 4 SCN/H 2 SO 4 media. The influence of sulphuric acid concentration on the percentage of extraction of Co(II) and Zn(II) has been discussed. It is shown that sulphuric acid concentration has not the same effect on distribution curves of Co(II) and Zn(II). Thus, it is possible to have a separation of Zn(II) of Co(II) when [NH 4 SCN] is 0.5 mol l − 1 and [H 2 SO 4 ] is about 2 mol l − 1 . Under these conditions the separation factor (S Zn/Co ) is around 580. The results are treated in terms of thermodynamic activities in aqueous phase, to determine the composition of the extracted complexes (M:SCN − ) and to discuss the extraction mechanism. S 0 0 3 9 -9 1 4 0 ( 9 7 ) 0 0 1 7 7 -X

Applied Mathematics Letters, 1999

In regard to the problem of determining minimum L-J configurations for clusters of n atoms, we pr... more In regard to the problem of determining minimum L-J configurations for clusters of n atoms, we present here a genetic algorithm able to reproduce all best-known solutions in the 13 < n <: 147 size range. These include not only the classical structures adhering to the icosahedratgrowth, but also seven icosahedral structures with incomplete core, six more following the Marks decahedron geometry, and the unique (n = 38) face-centered cubic configuration that has been found in this range.

Journal of Bacteriology, 2003

Vi capsular polysaccharide production is encoded by the viaB locus, which has a limited distribut... more Vi capsular polysaccharide production is encoded by the viaB locus, which has a limited distribution in Salmonella enterica serovars. In S. enterica serovar Typhi, viaB is encoded on a 134-kb pathogenicity island known as SPI-7 that is located between partially duplicated tRNA pheU sites. Functional and bioinformatic analysis suggests that SPI-7 has a mosaic structure and may have evolved as a consequence of several independent insertion events. Analysis of viaB-associated DNA in Vi-positive S. enterica serovar Paratyphi C and S. enterica serovar Dublin isolates revealed the presence of similar SPI-7 islands. In S. enterica serovars Paratyphi C and Dublin, the SopE bacteriophage and a 15-kb fragment adjacent to the intact tRNA pheU site were absent. In S. enterica serovar Paratyphi C only, a region encoding a type IV pilus involved in the adherence of S. enterica serovar Typhi to host cells was missing. The remainder of the SPI-7 islands investigated exhibited over 99% DNA sequence identity in the three serovars. Of 30 other Salmonella serovars examined, 24 contained no insertions at the equivalent tRNA pheU site, 2 had a 3.7-kb insertion, and 4 showed sequence variation at the tRNA pheU -phoN junction, which was not analyzed further. Sequence analysis of the SPI-7 region from S. enterica serovar Typhi strain CT18 revealed significant synteny with clusters of genes from a variety of saprophytic bacteria and phytobacteria, including Pseudomonas aeruginosa and Xanthomonas axonopodis pv. citri. This analysis suggested that SPI-7 may be a mobile element, such as a conjugative transposon or an integrated plasmid remnant.

Phytochemistry, 1992

A new germacranolide was isolated from the flowers of Tanacetum annuum, which was chemically tran... more A new germacranolide was isolated from the flowers of Tanacetum annuum, which was chemically transformed into three eudesmanolides and a lactone with a rearranged sesquiterpene skeleton.