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Chemistry	50%

Selected Abstracts

Conjugated linoleic acid conversion by dairy bacteria cultured in MRS broth and buffalo milk

LETTERS IN APPLIED MICROBIOLOGY, Issue 5 2007
C.P. Van Nieuwenhove
Abstract Aims:, To evaluate strains of Lactobacilli, Bifidobacteria and Streptococci for their ability to produce conjugated linoleic acid (CLA) from free linoleic acid (LA). Methods and Results:, Eight dairy bacteria tolerant to LA were grown in MRS broth containing LA (200 ,g ml,1) and CLA was assessed. Seven bacteria were able to form CLA after 24 h of incubation, varying percentage conversion between 17% and 36%. Lactobacillus casei, Lactobacillus rhamnosus, Bifidobacterium bifidum and Streptococcus thermophilus showed the highest LA conversion and were inoculated into buffalo milk supplemented with different concentration of LA. The production of CLA at 200 ,g ml,1 of LA was two- or threefold in milk than MRS broth. All evaluated strains were able to produce CLA from high LA levels (1000 ,g ml,1). Conclusions:, The most tolerant strain to LA was Lact. casei. Lacttobacillus rhamnosus produced the maximum level of CLA at high LA concentrations (800 ,g ml,1). The selected bacteria may be considered as adjunct cultures to be included on dairy fermented products manufacture. Low concentration of LA must be added to the medium to enhance CLA formation. Significance and Impact of the Study:, The production of CLA by strains using milks from regional farms as medium offer a possible mechanism to enhance this beneficial compound in dairy products and those the possibility to develop functional foods. [source]

Low Thresholds in Polymer Lasers on Conductive Substrates by Distributed Feedback Nanoimprinting: Progress Toward Electrically Pumped Plastic Lasers

ADVANCED MATERIALS, Issue 7 2009
Ebinazar B. Namdas
A light-emitting transistor (LEFET) architecture with a distributed feedback (DFB) resonator structure nanoimprinted into the gain medium offers a route to achieving an electrically pumped plastic laser. A 2D DFB laser provides lower lasing thresholds than a 1D DFB laser under identical conditions. The 2D DFB lasers exhibit excellent characteristics with lasing threshold and slope efficiency of 32,nJ/pulse and 1.2%, respectively. [source]

Sharpless Asymmetric Dihydroxylation of Olefins in WaterSurfactant Media with Recycling of the Catalytic System by Membrane Nanofiltration

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2008

Abstract This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1-hexene in a 1.5,mM sodium cholate aqueous solution, using N -methylmorpholine N -oxide (NMO) as co-oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn-over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields. [source]

Ionic Liquid for in situ Vis/NIR and Raman Spectroelectrochemistry: Doping of Carbon Nanostructures

CHEMPHYSCHEM, Issue 9 2003
Ladislav Kavan Prof. Dr.
Abstract 1-butyl-3-methylimidazolium tetrafluoroborate (an ionic liquid) is an advantageous electrolyte for the study of charge-transfer reactions at single-walled carbon nanotubes (SWCNTs) and fullerene peapods (C60@SWCNT). Compared to traditional electrolyte solutions, this medium offers a broader window of electrochemical potentials to be applied, and favorable optical properties for in situ Vis/NIR and Raman spectroelectrochemistry of nano-carbon species. The electrochemistry of both nanotubes and peapods is dominated by their capacitive double-layer charging. Vis/NIR spectroelectrochemistry confirms the charging-induced bleaching of transitions between Van Hove singularities. At high positive potentials, new optical transitions were activated in partly filled valence band. The bleaching of optical transitions is mirrored by the quenching of resonance Raman scattering in the region of tube-related modes. The Raman frequency of the tangential displacement mode of SWCNT shifts to blue upon both anodic and cathodic charging in the ionic liquid. The Raman modes of intratubular C60 exhibit a considerable intensity increase upon anodic doping of peapods. [source]