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Necessary Precursor (necessary + precursor)

Distribution by Scientific Domains
Humanities and Social Sciences40%
Chemistry40%

Selected Abstracts

Polyyne synthesis using carbene/carbenoid rearrangements

THE CHEMICAL RECORD, Issue 4 2006
Wesley A. Chalifoux
Abstract Rearrangement of a carbene/carbenoid intermediate to form an acetylene moiety, known as the Fritsch,Buttenberg,Wiechell (FBW) rearrangement, was developed for the formation of polyynes and polyyne frameworks within highly conjugated organic materials. Necessary precursors can be prepared through formation of an alkynyl ketone, followed by dibromoolefination under Corey,Fuchs conditions. The carbenoid rearrangement is brought about by treatment of the dibromoolefin with BuLi under mild conditions. The success of these FBW reactions is quite solvent-dependent, and nonpolar hydrocarbon solvents (e.g., hexanes, toluene, benzene) work quite well, while use of ethereal solvents such as diethyl ether and tetrahydrofuran (THF) does not provide the desired polyyne product. This protocol was successfully applied to the formation of silyl, alkyl, alkenyl, and aryl polyynes, including di-, tri-, and tetrayne products, as well as the construction of two-dimensional carbon-rich molecules. A one-pot variant of this procedure is being developed and is particularly applicable toward the synthesis of polyyne natural products. Formation of a series of triisopropylsilyl end-capped polyynes, from the triyne to decayne, was achieved. Third-order nonlinear optical properties of these polyynes were evaluated. This study shows that the molecular second hyperpolarizabilities for the polyynes as a function of length increase at a rate that is higher than all other nonaromatic organic oligomers. © 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 6: 169,182; 2006: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20081 [source]

The role of organizational capabilities in cleaner technology adoption: an analysis of the response of the pharmaceutical manufacturing sector in Ireland to IPC licensing regulations

ENVIRONMENTAL POLICY AND GOVERNANCE, Issue 6 2006
Rachel M. Hilliard
Abstract In introducing integrated pollution control licensing, regulators hope to achieve economic advantages as well as environmental benefits. The licensing is used as a vehicle for encouraging firms to adopt cleaner technology, potentially allowing firms to achieve economic advantages through process efficiencies and reduced environmental control costs. In Ireland, the regulatory approach has been to require firms to make managerial changes in the belief that this is a necessary precursor to the take-up of new technology. This paper examines how the pharmaceutical manufacturing sector has responded to environmental regulations that require cleaner technology adoption and managerial changes. Quantitative indicators are developed using data reported to the Irish Environmental Protection Agency. Analysis shows that firms were differentially able to implement both cleaner technology and the mandated managerial processes. The implications for policy are that regulatory instruments designed to stimulate cleaner technology may not be sufficient to promote change in firms, given that the influence of these instruments is mediated by the role of firm-specific, experience-based organizational capabilities. Copyright © 2006 John Wiley & Sons, Ltd and ERP Environment. [source]

Archaeology of a Naval Battlefield: H. L. Hunley and USS Housatonic

INTERNATIONAL JOURNAL OF NAUTICAL ARCHAEOLOGY, Issue 1 2006
David L. Conlin
The American Civil War shipwrecks H. L. Hunley and USS Housatonic have been the focus of intensive archaeological investigations since the discovery of Hunley in 1995. H. L. Hunley, the world's first successful combat submarine, sank the Union blockader USS Housatonic in 1864, but sank immediately afterwards. In work done prior to the recovery of Hunley in 2000, site-formation processes for both vessels were a primary research focus,a necessary precursor to identifying battlefield behaviour. This paper presents research on the Hunley/Housatonic Naval Engagement Site, where both wrecks are treated as complementary components of a single battlefield site. © 2006 The Authors [source]

Natural intramolecular isotope measurements in physiology: elements of the case for an effort toward high-precision position-specific isotope analysis,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2001
J. T. Brenna
Chemical information available in organisms can be categorized into three major domains, macromolecular, small molecules, and isotope ratios. Information about physiological state is commonly obtained by qualitative and quantitative analysis in the macromolecular and small molecule domains. Genomics and proteomics are emerging approaches to analysis of macromolecules, and both areas yield definitive information on present physiological state. There is relatively little record of past physiological states of the individual available in these domains. Natural isotopic variability, particularly on an intramolecular level, is likely to retain more physiological history. Because of ubiquitous isotopic fractionation, every stereochemically unique position in every molecule has an isotope ratio that reflects the processes of synthesis and degradation. This fact highlights a vast amount of organismal chemical information that is essentially unstudied. Isotope measurements can be classified according to the chemical complexity of the analyte into bulk, compound-specific, and position-specific or intramolecular levels. Recent advances in analysis of isotope ratios are transforming natural science, and particularly answering questions about ecosystems using bulk methods; however, they have had relatively little impact on physiology. This may be because the vast complexities of physiological questions demand very selective information available in position-specific isotope analysis (PSIA). The relatively few high-precision PSIA studies, based on isotope ratio mass spectrometry (IRMS), have revealed intramolecular isotope ratio differences in pivotal physiological compounds including amino acids, glucose, glycerol, acetate, fatty acids, and purines. The majority of these analyses have been accomplished by laborious offline methods; however, recent advances in instrumentation presage rapid PSIA that will be necessary to attack real physiological problems. Gas-phase pyrolysis has been shown to be an effective method to determine 13C/12C at high precision for molecular fragments, and technologies to extend C-based PSIA to N and other organic elements are emerging. Two related efforts are warranted, (a) development of rapid, convenient, and sensitive methods for high-precision PSIA, a necessary precursor to (b) a concerted investigation into the relationship of metabolic state to intramolecular isotope ratio. Inherent in this latter goal is the need to identify long-lived molecules in long-lived cells that retain a record of early isotopic conditions, as has been shown for post-mortem human neuronal DNA. Using known metabolic precursor-product relationships between intramolecular positions, future studies of physiological isotope fractionation should reveal the relationship of diet and environment to observed isotope ratio. This science of isotope physiology, or simply isotopics, should add an important tool for elucidation of early factors that effect later health, probably the most difficult class of biomedical issues. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Opsin gene polymorphism predicts trichromacy in a cathemeral lemur

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2009
Carrie C. Veilleux
Abstract Recent research has identified polymorphic trichromacy in three diurnal strepsirrhines: Coquerel's sifaka (Propithecus coquereli), black and white ruffed lemurs (Varecia variegata), and red ruffed lemurs (V. rubra). Current hypotheses suggest that the transitions to diurnality experienced by Propithecus and Varecia were necessary precursors to their independent acquisitions of trichromacy. Accordingly, cathemeral lemurs are thought to lack the M/L opsin gene polymorphism necessary for trichromacy. In this study, the M/L opsin gene was sequenced in ten cathemeral blue-eyed black lemurs (Eulemur macaco flavifrons). This analysis identified a polymorphism identical to that of other trichromatic strepsirrhines at the critical amino acid position 285 in exon 5 of the M/L opsin gene. Thus, polymorphic trichromacy is likely present in at least one cathemeral Eulemur species, suggesting that strict diurnality is not necessary for trichromacy. The presence of trichromacy in E. m. flavifrons suggests that a re-evaluation of current hypotheses regarding the evolution of strepsirrhine trichromacy may be necessary. Although the M/L opsin polymorphism may have been independently acquired three times in the lemurid,indriid clade, the distribution of opsin alleles in lemurids and indriids may also be consistent with a common origin of trichromacy in the last common ancestor of either the lemurids or the lemurid,indriid clade. Am. J. Primatol. 71:86,90, 2009. © 2008 Wiley-Liss, Inc. [source]