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Unambiguous Characterization (unambiguous + characterization)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

Synthesis and characterization of ether derivatives of brominated poly(isobutylene- co -isoprene)

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006
Sergio A. Guillén-Castellanos
Abstract Variations of the Williamson ether synthesis were employed to prepare a range of new derivatives of brominated poly(isobutylene- co -isoprene) (BIIR). Unambiguous characterization of the polymeric products was accomplished by spectroscopic comparisons to low-molecular-weight analogues derived from brominated 2,2,4,8,8-pentamethyl-4-nonene, which served as a model for the reactive functionality found within BIIR. The substitution of bromide from BIIR occurred at moderate temperatures with stoichiometric amounts of quaternary ammonium phenoxide to yield O-alkylation products in high yields. Simple mixtures of BIIR, KOH, and aliphatic alcohols generated the desired allylic ethers when heated above 110 °C in the absence of quaternary ammonium salts. Knowledge gained from these small-molecule alkylations was used to prepare graft copolymers from BIIR and poly(ethylene oxide) through the exploitation of the apparent ability of polyethers to activate potassium alkoxides in nucleophilic substitutions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 983,992, 2006 [source]

Oval in males and triangular in females?

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2010
A quantitative evaluation of sexual dimorphism in the human obturator foramen
Abstract Among the numerous pelvic traits presenting sex differences, the obturator foramen is classically described as being oval in males and triangular in females. However, no demonstrations or detailed studies seem available in the literature. The purpose of this work was to study quantitatively this trait using Fourier analysis, because this methodological approach is particularly well adapted for discrimination between different simple shapes. Using this approach, an outline can be characterized by a series of harmonics (1 to n), each defined by two Fourier descriptors: amplitude (Cn), describing the relative importance of the harmonic contribution to the original shape, and phase (,n), representing the orientation of the harmonic contribution. The material consisted of 104 three-dimensional CT reconstructions of adult pelves (52 males and 52 females). After size normalization, the outlines of the 104 left obturator foramens were studied. Significant differences were demonstrated with, in total, 84.6% of individuals presenting a correct inferred sex. The most discriminating descriptors were the phase of the second harmonic (C2), related to the oval (or elliptic) aspect and thus the elongation of the shape, and the amplitude of the third harmonic (,3), describing the triangularity of the shape. Because the trend for an outline to be more or less oval or triangular is difficult to visually assess and because there is an infinite number of transitional shapes, only a precise quantitative approach such as Fourier analysis allows for unambiguous characterization and statistical analysis. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source]

Genoarchitectonic profile of developing nuclear groups in the chicken pretectum

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 4 2009
J.L. Ferran
Abstract Earlier results on molecularly coded progenitor domains in the chicken pretectum revealed an anteroposterior subdivision of the pretectum in precommissural (PcP), juxtacommissural (JcP), and commissural (CoP) histogenetic areas, each specified differentially (Ferran et al. [2007] J Comp Neurol 505:379,403). Here we examined the nuclei derived from these areas with regard to characteristic gene expression patterns and gradual histogenesis (eventually, migration patterns). We sought a genoarchitectonic schema of the avian pretectum within the prosomeric model of the vertebrate forebrain (Puelles and Rubenstein [2003] Trends Neurosci 26:469,476; Puelles et al. [2007] San Diego: Academic Press). Transcription-factor gene markers were used to selectively map derivatives of the three pretectal histogenetic domains: Pax7 and Pax6 (CoP); FoxP1 and Six3 (JcP); and FoxP2, Ebf1, and Bhlhb4 (PcP). The combination of this genoarchitectonic information with additional data on Lim1, Tal2, and Nbea mRNA expression and other chemoarchitectonic results allowed unambiguous characterization of some 30 pretectal nuclei. Apart from grouping them as derivatives of the three early anteroposterior domains, we also assigned them to postulated dorsoventral subdomains (Ferran et al. [2007]). Several previously unknown neuronal populations were detected, thus expanding the list of pretectal structures, and we corrected some apparently confused concepts in the earlier literature. The composite gene expression map represents a substantial advance in anatomical and embryological knowledge of the avian pretectum. Many nuclear primordia can be recognized long before the mature differentiated state of the pretectum is achieved. This study provides fundamental notions for ultimate scientific study of the specification and regionalization processes building up this brain area, both in birds and other vertebrates. J. Comp. Neurol. 517:405,451, 2009. © 2009 Wiley-Liss, Inc. [source]

Isolation and structure of I-deoxybaccatin VI from the root of taxus chinensis, rehd. var. mairei

CHINESE JOURNAL OF CHEMISTRY, Issue 7 2004
Hai-Xia Lin
Abstract Deoxybaccatin VI (4,,7,,9,,10,,13,-penta-acetoxy-2a-benzoyloxy-5,,20-epoxytax-11-ene) was isolated from the roots of Taxus chinensis, Rehd. var mairei. The structural assignments of the compound were based on their spectral data, including 2D NMR experiments and chemical correlation. The X-ray crystallographic analysis of 1-deoxybaccatin VI provided unambiguous characterization for the structures. In the structure, the six-membered A ring exhibits boat conformation, the eight-membered B ring adopts boat-chair conformation, and the six-membered C ring exhibits a sofa conformation. [source]