Non-innocent ligand reservoirs for reducing or oxidizing equivalents in carbonylrhenium(I) complexes: 1,1′-Bis(diphenylphosphino)ferrocene (dppf) and bis-triazinyl-pyridine (BTP)

Organometallic complexes of Re(I) with ligands having opposite redox properties have been synthesized and structurally characterized. X-ray crystal structures of the complexes show typical fac-Re^I(CO)₃ coordination to the redox active ligands. Complete electrochemical and spectroelectrochemical studies on the ligands and the metal complexes were performed. The IR-spectroelectrochemical responses were monitored using the fac-Re(CO)₃ unit as a probe. The 15-20 cm⁻¹ hypsochromic or bathochromic shift of the ν_CO bands upon reduction or oxidation is attributed to ligand-centered processes.     

Importance of organosulfur utilization for survival of Pseudomonas putida in soil and rhizosphere

The sulfur present in both agricultural and uncultivated soils is largely in the form of sulfonates and sulfate esters and not as free, bioavailable inorganic sulfate. Desulfurization of the former compounds in vitro has previously been studied in Pseudomonas putida, a common rhizosphere inhabitant. Survival of P. putida strains was now investigated in three sulfur-deficient Danish soils which were found to contain 60 to 70% of their sulfur in sulfonate or sulfate ester form, as determined by X-ray near-edge spectroscopy. The soil fitness of P. putida S-313 was compared with that of isogenic strains with mutations in the sftR and asfA genes (required for in vitro desulfurization of sulfate esters and arylsulfonates, respectively) and in the ssu locus (required in vitro for the desulfurization of both sulfonates and sulfate esters). asfA or sftR mutants showed significantly reduced survival compared to the parent strain in bulk soil that had been enriched with carbon and nitrogen to mimic rhizosphere conditions, but this reduced survival was not observed in the absence of these additives. In a tomato rhizosphere grown in compost, survival of sftR and ssu mutants was reduced relative to the parent strain. The results demonstrate that the ability to desulfurize sulfonates and sulfate esters is critical for survival of bacteria in the rhizosphere but less so in bulk soils outside the influence of plant roots, where carbon is the limiting nutrient for growth.     

Importance of data structure in comparing two dimension reduction methods for classification of microarray gene expression data

Background  

With the advance of microarray technology, several methods for gene classification and prognosis have been already designed. However, under various denominations, some of these methods have similar approaches. This study evaluates the influence of gene expression variance structure on the performance of methods that describe the relationship between gene expression levels and a given phenotype through projection of data onto discriminant axes.     

Specific binding of sulphated polymers to ram sperm proacrosin

Sulphated polysaccharides and zona pellucida glycoproteins have been shown to bind non-enzymatically to proacrosin, the protein found within the acrosomal vesicle of mammalian spermatozoa. The mechanism of this interaction has been investigated using ¹²⁵I-fucoidan to probe purified ram sperm proacrosin. Results show that (a) binding of' ¹²⁵I-fucoidan to proacrosin is inhibited only by sulphated polymers and (b) recognition is mediated by poly(sulphate) groups and is largely independent of the composition of the polymer chain. It is suggested that a similar mechanism is responsible for the interaction between proacrosin and zona pellueida glycoproteins during the early stages of fertilization in mammals and this process mediates firm binding of spermatozoa to the egg.