Vibrational analysis of d-PCL(530)/siloxane based hybrids doped with two lithium salts

Published online: 22 May 2013The present study has been focused on environmentally friendly sol-gel derived electrolytes based on a di-urethane cross-linked d-PCL(530)/siloxane network (where d represents di, PCL identifies the poly(ε–caprolactone) biopolymer and 530 is the average molecular weight in g.mol-1) doped with a wide range of concentration of lithium perchlorate (LiClO4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Fourier Transform Infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies have been applied to evaluate the extent of ionic association. Characteristic bands of the PCL(530) segments, of the urethane cross-links and of the anions have been examined to gain insight into the cation/biopolymer, cation/anion and cation/cross-link interactions. In both electrolyte systems “free” ions and contact ions have been identified. The addition of salt modifies the hydrogen-bonded array of the host matrix, causing the destruction/formation of the urethane/urethane aggregates.Fundação para a Ciência e a Tecnologia (FCT

Self-structuring of lamellar bridged silsesquioxanes with long side spacers

Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils), an indication that the longer side chains in the former materials adopt gauche conformations. It has also allowed us to demonstrate for the first time that the emission features of the urea-related component of the emission of alkylene-based BSs depend critically on the length of the side spacers

Comparative Developmental Expression Profiling of Two C. elegans Isolates

Gene expression is known to change during development and to vary among genetically diverse strains. Previous studies of temporal patterns of gene expression during C. elegans development were incomplete, and little is known about how these patterns change as a function of genetic background. We used microarrays that comprehensively cover known and predicted worm genes to compare the landscape of genetic variation over developmental time between two isolates of C. elegans. We show that most genes vary in expression during development from egg to young adult, many genes vary in expression between the two isolates, and a subset of these genes exhibit isolate-specific changes during some developmental stages. This subset is strongly enriched for genes with roles in innate immunity. We identify several novel motifs that appear to play a role in regulating gene expression during development, and we propose functional annotations for many previously unannotated genes. These results improve our understanding of gene expression and function during worm development and lay the foundation for linkage studies of the genetic basis of developmental variation in gene expression in this important model organism

Crystal Structure and Morphology of Linear Aliphatic n-Polyurethanes

The crystal structure and morphology of a series of linear aliphatic polyurethanes with generic formula -(CH2)nOCONH- and containing from 5 to 12 methylene units have been investigated by using TEM combined with X-ray and electron diffraction analysis. Lamellar crystals with a thickness ranging between 5 and 10 nm displaying a variety of crystal habits were obtained by isothermal crystallization from diluted solution in different sol-vents. A crystal structure similar to that described for the layered a-form of nylons seems to be commonly adopted by these polyurethanes. It essentially consists of a triclinic lattice made of hydrogen-bonded sheets with chains in fully extended conformation. Chains within the sheets are arranged in the antiparallel mode giving a normal scheme of hydrogen bonds. Sheets are stacked along the b-axis and progressively shifted along both a and c axes. The interchain and intersheet distances in this lattice are of values similar to those found in nylons. Energy calculations were in agreement with the arrangement proposed for chain packing. X-ray diffraction recorded from heated samples at real times showed that none of these polyurethanes undergoes Brill transition although odd members displayed structural changes concomitant with the occurrence of an unfinished ongoing process. The IR analysis at variable temperature revealed that approximately 50% of hydrogen bonds were retained upon heating at temperatures fairly above melting