Investigations into the parallel kinetic resolution of 2-phenylpropanoyl chloride using quasi-enantiomeric oxazolidinones

The resolution of 2-phenylpropanoyl chloride using an equimolar combination of quasi-enantiomeric oxazolidinones is discussed. The levels of diastereoselectivity were found to be dependent upon the structural nature of the metallated oxazolidinone, temperature and metal counter-ion.     

Atomic absorption spectrometry of cadmium after solvent extraction with zinc dibenzyldithiocarbamate

The AAS determination of cadmium extracted as dibenzyldithiocarbamate in methyl isobutyl ketone was investigated. Cadmium was quantitatively removed from the aqueous phase at pH 5 ± 0.5 with a single extraction by shaking for 2 min. The sensitivity of the method was found to be 6 ppm (1% absorption). The precision expressed as coefficient of variation was 1.5% at the 40-ppM level. Interference from foreign cations and anions was examined.     

Selective synthesis of isobutanol by means of the Guerbet reaction: Part 2. Reaction of methanol/ethanol and methanol/ethanol/n-propanol mixtures over copper based/MeONa catalytic systems

The synthesis of isobutanol via the Guerbet condensation between methanol and ethanol was studied by using sodium methoxide (MeONa) as soluble basic component and copper-based catalysts as heterogeneous dehydrogenating/hydrogenating metal species. The effect of the nature of the catalyst and the relative amount of its individual components with respect to the reacting alcohols as well as of temperature on productivity and selectivity of the process was investigated. The collected data indicated that the copper chromite/MeONa was more active than Cu-Raney/MeONa system. The reaction was shown to proceed with the formation only of n-propanol and isobutanol. Ethanol conversion up to 61% with selectivity to isobutanol up to 98.4% was obtained. The same catalytic systems were also employed in the reaction of the methanol/ethanol/n-propanol ternary mixture. Again copper chromite/MeONa resulted more active than the Cu-Raney/MeONa system. Finally, experiments were carried out on methanol/n-propanol mixtures in the presence of the copper chromite/MeONa catalytic system by recycling both the recovered solid copper component and the liquid reaction mixture for evidencing eventual copper leaching by MeONa. On the basis of the obtained results it was concluded that in the Guerbet reaction copper chromite works as heterogeneous catalyst.     

Covalent Structures of Phosphorus: A Comprehensive Theoretical Study

Starting from earlier work by Baudler we introduce a chemical heuristic for the systematic deduction and classification of covalent partial structures of phosphorus in polycyclic phosphanes, phosphorus-rich polycyclic phosphides, and allotropes of phosphorus except the black forms. This approach is used to direct ab initio techniques (which also confirm the rules) in the quest for as yet unknown forms of molecular or macromolecular phosphorus. Based on calculated stabilities of systematically generated structural alternatives we rationalize the stabilities of Hittorf's phosphorus and of molecular P₄, confirm the possible existence of at least one other crystalline allotropic form of phosphorus, and provide insight into the probable structure of amorphous red phosphorus. In total, the combined approach of chemical heuristics and large scale ab initio calculations presented in this work supplies a coherent chemical understanding of covalent polyphosphorus structures.     

Asymmetric alkaloid synthesis from (S)-pyroglutamic acid. I. Synthesis of (S)-5-ethyl-2-pyrrolidinone

From (S)-pyroglutamic acid ( 1 ) the asymmetric synthesis of (S)-5-ethyl-2-pyrrolidinone ( 5 ) in 30% yield is described.     

Selenium speciation in foods: Preliminary results on potatoes

The present paper deals with the speciation of selenium in potatoes (enriched or not in selenium). The study was carried out by using differential pulse cathodic stripping voltammetry (DPCSV) for quantifying selenium. Results obtained provide evidence that the selenium content in the protein fraction is rather independent from the selenium added to the plants during their growth. On the contrary, the amount of Se in the non-protein fraction (water and starch) in Se-enriched sample is significantly higher than in non-enriched one, suggesting that it is the main selenium-storing site. In this fraction the Se(VI)/Se(IV) ratio seems independent from selenium application but it may be related to the redox conditions. The accumulation of selenium in the non-protein fraction is tentatively ascribed to the “Se–starch interaction” that should be able to modulate both the Se absorption into proteins and, possibly, its toxic effect for the plant itself.     

Sample preparation for metalloprotein analysis: A case study using horse chestnuts

In the present work, 11 different procedures for protein and metalloprotein extraction from horse chestnuts (Aescullus hippocastanum L.) in natura were tested. After each extraction, total protein was determined and, after protein separation through sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), those metals belonging to the protein structure were mapped by synchrotron radiation X-ray fluorescence (SRXRF). After mapping the elements (Cr, Fe and Mn) in the protein bands (ca. 33 and 23.7 kDa), their concentrations were determined using atomic absorption spectrometry (ET AAS).

Good results were obtained for protein extraction using a combination of grinding and sonication. However, this strategy was not suitable to preserve metal ions in the protein structure. In fact, there was 42% decrease on Mn concentration using this procedure, compared to that performed with sample agitation in water (taken as reference). On the other hand, when grinding and agitation with an extracting buffer was used, there was a 530% increase of Mn concentration, when compared to the reference procedure.

These results indicate agreement between metal identification and determination in proteins as well as the great influence of the extraction procedure (i.e., the sample preparation step) for preserving metals in the protein structures.     

The reactions of iminosulfur difluorides and chlorine monofluoride

The reactions of perfluoroalkyl- and perfluoroacyl-iminosulfur difluorides with chlorine monofluoride result in the preparation of perfluoroalkyldichloroamines and a new class of compounds N,N-dichloroperfluoroamides, R_fC(O)NCl₂, via the elimination of SF₄. The amides, FC(O)NCl₂ and CF₃C(O)NCl₂, in addition to 1,2-bis-(dichloroamino)tetrafluoroethane, Cl₂NCF₂CF₂NCl₂, are reported and characterized. The reactions of CIF with other sulfur(IV) imines proceed in an analogous manner to form perfluoroalkyl-dichloroamines via the elimination of the corresponding sulfur(IV) fluoride.     

Fast exopolysaccharide secretion of Pseudomonas aeruginosa on polar polymer surfaces

The influence of the surface chemical structure and related physicochemical properties on the adhesion of P. aeruginosa has been studied for moderately hydrophobic polymers and for hydrophilic surfaces obtained by O2-plasma treatments and 50 keV Ar+ beam irradiation of poly(hydroxymethylsiloxane) and poly(ethyleneterephthalate). The surface chemical structure has been obtained by X-ray photoelectron spectroscopy, the roughness was measured by atomic force microscopy, and the surface free energy was evaluated from contact angle measurements for all the polymer substrates before and after the irradiation treatments. It is shown that a massive and unusually fast secretion of exopolysaccharides onto highly polar surfaces, corresponding to the formation of complex three-dimensional multilayers (i.e., biofilm-like structures), occurs already after 2 h of incubation. It is suggested that such highly polar surfaces can operate either by promoting, by means of a still unknown biomolecular mechanism, an early gene expression process or by mimicking the P. aeruginosa cellular walls.