33 research outputs found
Transport and Phototransport in ITO Nanocrystals with Short to Long-Wave Infrared Absorption
Nanocrystals are often described as an interesting strategy for the design of
low-cost optoelectronic devices especially in the infrared range. However the
driving materials reaching infrared absorption are generally heavy
metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to
achieve infrared transition is the use of doped semiconductors presenting
intraband or plasmonic transition in the short, mid and long-wave infrared.
This strategy may offer more flexibility regarding the range of possible
candidate materials. In particular, significant progresses have been achieved
for the synthesis of doped oxides and for the control of their doping
magnitude. Among them, tin doped indium oxide (ITO) is the one providing the
broadest spectral tunability. Here we test the potential of such ITO
nanoparticles for photoconduction in the infrared. We demonstrate that In2O3
nanoparticles presents an intraband absorption in the mid infrared range which
is transformed into a plasmonic feature as doping is introduced. We have
determined the cross section associated with the plasmonic transition to be in
the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made
conductive and photoconductive due to a ligand exchange using a short
carboxylic acid, leading to a dark conduction with n-type character. We bring
further evidence that the observed photoresponse in the infrared is the result
of a bolometric effect
Hetero-trans-ÎČ-glucanase, an enzyme unique to Equisetum plants, functionalises cellulose
Cell walls are metabolically active components of plant cells. They contain diverse enzymes, including transglycanases (endotransglycosylases), enzymes that âcut and pasteâ certain structural polysaccharide molecules and thus potentially remodel the wall during growth and development. Known transglycanase activities modify several cellâwall polysaccharides (xyloglucan, mannans, mixedâlinkage ÎČâglucan and xylans); however, no transglycanases were known to act on cellulose, the principal polysaccharide of biomass. We now report the discovery and characterization of heteroâtransâÎČâglucanase (HTG), a transglycanase that targets cellulose, in horsetails (Equisetum spp., an earlyâdiverging genus of monilophytes). HTG is also remarkable in predominantly catalysing heteroâtransglycosylation: its preferred donor substrates (cellulose or mixedâlinkage ÎČâglucan) differ qualitatively from its acceptor substrate (xyloglucan). HTG thus generates stable celluloseâxyloglucan and mixedâlinkage ÎČâglucanâxyloglucan covalent bonds, and may therefore strengthen ageing Equisetum tissues by interâlinking different structural polysaccharides of the cell wall. 3D modelling suggests that only three key amino acid substitutions (Trp â Pro, Gly â Ser and Arg â Leu) are responsible for the evolution of HTG's unique specificity from the betterâknown xyloglucanâacting homoâtransglycanases (xyloglucan endotransglucosylase/hydrolases; XTH). Among land plants, HTG appears to be confined to Equisetum, but its target polysaccharides are widespread, potentially offering opportunities for enhancing crop mechanical properties, such as wind resistance. In addition, by linking cellulose to xyloglucan fragments previously tagged with compounds such as dyes or indicators, HTG may be useful biotechnologically for manufacturing stably functionalized celluloses, thereby potentially offering a commercially valuable âgreenâ technology for industrially manipulating biomass
Dynamic moisture sorption behavior of cotton fibers with natural brown pigments
The moisture sorption behavior of white and naturally colored cotton fibers is studied by dynamic vapor sorption. Dark brown and brown fibers show a higher sorption capacity compared to beige and white fibers. The differences in sorption capacity are found to be related to the maturity and crystallinity index of the fibers. All fibers exhibited sorption hysteresis to varying degrees throughout the full relative humidity range. The variations in hysteresis behavior are mainly attributed to the differences in crystallinity index of the fibers. In addition the monolayer and polylayer moisture content is analyzed using the Hailwood Horrobin model. Monolayer sorption is most closely related to the crystallinity index and, to a lower extent, maturity of the fibers. For beige and white fibers monolayer sorption remains almost constant, whereas for darker fibers it shows a substantial increase with increasing color difference. In contrast, polylayer sorption shows a general increasing trend over the whole studied color spectrum. Also a noticeable relationship was found between the total hysteresis and the monolayer sorption. Yet such relation was less evident for polylayer sorption. This study contributes to the better understanding of the dynamic moisture sorption behavior of white and naturally colored cotton fibers. This improved understanding is important for optimal application of naturally colored cotton fibers in novel materials
AtCSLA7, a Cellulose Synthase-Like Putative Glycosyltransferase, Is Important for Pollen Tube Growth and Embryogenesis in Arabidopsis
The cellulose synthase-like proteins are a large family of proteins in plants thought to be processive polysaccharide ÎČ-glycosyltransferases. We have characterized an Arabidopsis mutant with a transposon insertion in the gene encoding AtCSLA7 of the CSLA subfamily. Analysis of the transmission efficiency of the insertion indicated that AtCSLA7 is important for pollen tube growth. Moreover, the homozygous insertion was embryo lethal. A detailed analysis of seed developmental progression revealed that mutant embryos developed more slowly than wild-type siblings. The mutant embryos also showed abnormal cell patterning and they arrested at a globular stage. The defective embryonic development was associated with reduced proliferation and failed cellularization of the endosperm. AtCSLA7 is widely expressed, and is likely to be required for synthesis of a cell wall polysaccharide found throughout the plant. Our results suggest that this polysaccharide is essential for cell wall structure or for signaling during plant embryo development