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71.
Samuel O. Grim Anthony W. Yankowsky 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):191-195
Abstract The 31P chemical shifts of eleven (4-ZC6H4)3P compounds show a slight correlation with the Hammet [sgrave]para constant of Z. The unusually large upfield chemical shifts of (2-ZC6H4)3P compounds are attributed to an extreme “gamma” effect caused by the restricted conformations due to the steric influence of the ortho substituents. Chemical shifts are given for about thirty triarylphosphines, and group contributions to phosphine chemical shifts are listed for twenty-one aryl groups. 相似文献
72.
Samuel O. Grim Mudlagiri B. Goli 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract 1,1-Bis(diphenylphosphino)ethene, 1a, was originally prepared by Colquhoun and McFarlane1 by the reaction of lithium diphenylphosphide and vinylidene chloride. Subsequently, Schmidbaur et al.,2 reported further novel chemistry of 1a and its derivatives such as 1b and 1c. 相似文献
73.
74.
Brian L. Frey Daniel T. Ladror Samuel B. Sondalle Casey J. Krusemark April L. Jue Joshua J. Coon Lloyd M. Smith 《Journal of the American Society for Mass Spectrometry》2013,24(11):1710-1721
The carboxyl groups of tryptic peptides were derivatized with a tertiary or quaternary amine labeling reagent to generate more highly charged peptide ions that fragment efficiently by electron transfer dissociation (ETD). All peptide carboxyl groups—aspartic and glutamic acid side-chains as well as C-termini—were derivatized with an average reaction efficiency of 99 %. This nearly complete labeling avoids making complex peptide mixtures even more complex because of partially-labeled products, and it allows the use of static modifications during database searching. Alkyl tertiary amines were found to be the optimal labeling reagent among the four types tested. Charge states are substantially higher for derivatized peptides: a modified tryptic digest of bovine serum albumin (BSA) generates ~90% of its precursor ions with z? > ?2, compared with less than 40 % for the unmodified sample. The increased charge density of modified peptide ions yields highly efficient ETD fragmentation, leading to many additional peptide identifications and higher sequence coverage (e.g., 70 % for modified versus only 43 % for unmodified BSA). The utility of this labeling strategy was demonstrated on a tryptic digest of ribosomal proteins isolated from yeast cells. Peptide derivatization of this sample produced an increase in the number of identified proteins, a >50 % increase in the sequence coverage of these proteins, and a doubling of the number of peptide spectral matches. This carboxyl derivatization strategy greatly improves proteome coverage obtained from ETD-MS/MS of tryptic digests, and we anticipate that it will also enhance identification and localization of post-translational modifications. Figure
? 相似文献
75.
Samuel I. Stupp 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11-12):1255-1265
The present work focuses on chirality, functionalization, and molecular shape to establish links between molecular architecture and the spatial organization of polymer chains in organic materials. The approach used was to synthesize chiral and racemic homologous polymers exhibiting a preference for extended chain conformations and having the strongly dipolar cyano group as a substituent of the stereogenic center. The strong dipole moment at the chiral center offered potential to combine strong long-range forces with chiral recognition. Electron and optical microscopies were our selected tools to probe three-dimensional structures, and nonlinear optics was used to measure the properties of the materials obtained. We found that the relative stereochemistry of the repeat unit dipole impacts significantly on global chain symmetry and its packing mode. Enantiomeric enrichment of chains changed hexagonally packed cylindrical molecules to board-like molecules which pack edge-to-edge in an orthorhombic lattice. Interestingly, enantiomeric enrichment of chains enhanced the second-order nonlinear optical susceptibility of films prepared from these macromolecules. 相似文献
76.
Aliphatic Polyester Blends Based upon Poly(Lactic Acid) and Oligomeric Poly(Hexamethylene Succinate)
Abstract In an attempt to gain a degree of control over the mechanical and degradation properties of poly(lactic acid) [PLA], large-scale efforts are underway to alter the phase morphology of PLA through chemical and physical modification. Consistent with this theme, our work aims to adjust the molecular architecture of highly amorphous PLA with an increasing concentration of hydroxy-terminated oligomeric poly(hexamethylene succinate) [PHS]. Gel-permeation chromatography (GPC) verifies the enhanced presence of PHS in the blends with a concomitant reduction in number-average molecular weight as the weight fraction of PHS is raised from 0.10 to 0.40. Differential scanning calorimetry (DSC) indicates amorphous phase compatibility between PHS and PLA at weight compositions of 10/90 and 20/80. However, as the amount of PHS approaches 30 and 40 wt%, the PHS exhibits the ability to crystallize independently from the induced PLA crystalline phase. Dynamic mechanical thermal analysis (DMTA) illustrates variable behavior of the materials under tension as a consequence of structural alterations generated by the oligoester. Finally, preliminary results suggest that these alterations may suppress the hydrolytic degradation of PLA. 相似文献
77.
Gregory B. Kharas Selena M. Russell Kerrianne Trickey Daniel P. Baecher Jeffrey H. Becker Samuel Borgmeyer 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1151-1154
Electrophilic trisubstituted ethylene monomers, alkyl ring‐substituted 2‐phenyl‐1,1‐dicyanoethylenes, RC6H4CH?C(CN)2 (where R is 2‐methyl, 3‐methyl,4‐methyl, 4‐ethyl, 4‐isopropyl, 4‐butyl, and 4‐t‐butyl), were synthesized by piperidine catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and malononitrile, and characterized by CHN elemental analysis, IR, 1H‐ and 13C‐NMR. Novel copolymers of the ethylenes and vinyl acetate were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C‐NMR, GPC, DSC, and TGA. High Tg of the copolymers, in comparison with that of polyvinyl acetate, indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 190–700°C range. 相似文献
78.
79.
Aryl/alkyl cyanides were quickly converted into the corresponding esters in the presence of iron(III) chloride in refluxing alcohols with very good yields. 相似文献
80.
A phenanthrene-fused cyclooctatetraene, namely benzo[a]phenanthro[9,10-e]cyclooctene has been synthesized by employing the “Reich-Paquette” procedure. 相似文献