89 research outputs found

    Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Comparison

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    Knowledge of the relative stabilities of alane (AlH3) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for thirty-eight alane complexes with NH3-nRn (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH2-nRn (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine, and obtaining upper limits of delta G for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. Based on this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system.Comment: Accepted by the Journal of Physical Chemistry

    TRPA1 Contributes to the Acute Inflammatory Response and Mediates Carrageenan-Induced Paw Edema in the Mouse

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    Transient receptor potential ankyrin 1 (TRPA1) is an ion channel involved in thermosensation and nociception. TRPA1 is activated by exogenous irritants and also by oxidants formed in inflammatory reactions. However, our understanding of its role in inflammation is limited. Here, we tested the hypothesis that TRPA1 is involved in acute inflammatory edema. The TRPA1 agonist allyl isothiocyanate (AITC) induced inflammatory edema when injected intraplantarly to mice, mimicking the classical response to carrageenan. Interestingly, the TRPA1 antagonist HC-030031 and the cyclo-oxygenase (COX) inhibitor ibuprofen inhibited not only AITC but also carrageenan-induced edema. TRPA1-deficient mice displayed attenuated responses to carrageenan and AITC. Furthermore, AITC enhanced COX-2 expression in HEK293 cells transfected with human TRPA1, a response that was reversed by HC-030031. This study demonstrates a hitherto unknown role of TRPA1 in carrageenan-induced inflammatory edema. The results also strongly suggest that TRPA1 contributes, in a COX-dependent manner, to the development of acute inflammation

    Expression of Transient Receptor Potential Ankyrin 1 (TRPA1) and Its Role in Insulin Release from Rat Pancreatic Beta Cells

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    <div><h3>Objective</h3><p>Several transient receptor potential (TRP) channels are expressed in pancreatic beta cells and have been proposed to be involved in insulin secretion. However, the endogenous ligands for these channels are far from clear. Here, we demonstrate the expression of the transient receptor potential ankyrin 1 (TRPA1) ion channel in the pancreatic beta cells and its role in insulin release. TRPA1 is an attractive candidate for inducing insulin release because it is calcium permeable and is activated by molecules that are produced during oxidative glycolysis.</p> <h3>Methods</h3><p>Immunohistochemistry, RT-PCR, and Western blot techniques were used to determine the expression of TRPA1 channel. Ca<sup>2+</sup> fluorescence imaging and electrophysiology (voltage- and current-clamp) techniques were used to study the channel properties. TRPA1-mediated insulin release was determined using ELISA.</p> <h3>Results</h3><p>TRPA1 is abundantly expressed in a rat pancreatic beta cell line and freshly isolated rat pancreatic beta cells, but not in pancreatic alpha cells. Activation of TRPA1 by allyl isothiocyanate (AITC), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), 4-hydroxynonenal (4-HNE), and cyclopentenone prostaglandins (PGJ<sub>2</sub>) and a novel agonist methylglyoxal (MG) induces membrane current, depolarization, and Ca<sup>2+</sup> influx leading to generation of action potentials in a pancreatic beta cell line and primary cultured pancreatic beta cells. Activation of TRPA1 by agonists stimulates insulin release in pancreatic beta cells that can be inhibited by TRPA1 antagonists such as HC030031 or AP-18 and by RNA interference. TRPA1-mediated insulin release is also observed in conditions of voltage-gated Na<sup>+</sup> and Ca<sup>2+</sup> channel blockade as well as ATP sensitive potassium (K<sub>ATP</sub>) channel activation.</p> <h3>Conclusions</h3><p>We propose that endogenous and exogenous ligands of TRPA1 cause Ca<sup>2+</sup> influx and induce basal insulin release and that TRPA1-mediated depolarization acts synergistically with K<sub>ATP</sub> channel blockade to facilitate insulin release.</p> </div

    Cowries in the archaeology of West Africa: the present picture

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    Despite the perceived importance of cowrie shells as indicators of long-distance connections in the West African past, their distribution and consumption patterns in archaeological contexts remain surprisingly underexplored, a gap that is only partly explicable by the sparse distribution of archaeological sites within the sub-continent. General writings on the timeline of importation of cowries into West Africa often fail to take into account the latest archaeological evidence and rely instead on accounts drawn from historical or ethnographic documents. This paper is based on a first-hand assessment of over 4500 shells from 78 sites across West Africa, examining chronology, shell species and processes of modification to assess what distribution patterns can tell us about the history of importation and usage of cowries. These first-hand analyses are paralleled by a consideration of published materials. We re-examine the default assumption that two distinct routes of entry existed — one overland from North Africa before the fifteenth century, another coming into use from the time sea links were established with the East African coast and becoming predominant by the middle of the nineteenth century. We focus on the eastern part of West Africa, where the importance of imported cowries to local communities in relatively recent periods is well known and from where we have a good archaeological sample. The conclusion is that on suitably large assemblages shell size can be an indication of provenance and that, while the present archaeological picture seems largely to confirm historical sources, much of this may be due to the discrepancy in archaeological data available from the Sahara/Sahel zone compared to the more forested regions of the sub-continent. Future archaeological work will clarify this matter

    Antidromic vasodilatation and the migraine mechanism

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    Despite the fact that an unprecedented series of new discoveries in neurochemistry, neuroimaging, genetics and clinical pharmacology accumulated over the last 20 years has significantly increased our current knowledge, the underlying mechanism of the migraine headache remains elusive. The present review article addresses, from early evidence that emerged at the end of the nineteenth century, the role of ‘antidromic vasodilatation’ as part of the more general phenomenon, currently defined as neurogenic inflammation, in the unique type of pain reported by patients suffering from migraine headaches. The present paper describes distinctive orthodromic and antidromic properties of a subset of somatosensory neurons, the vascular- and neurobiology of peptides contained in these neurons, and the clinical–pharmacological data obtained in recent investigations using provocation tests in experimental animals and human beings. Altogether, previous and recent data underscore that antidromic vasodilatation, originating from the activation of peptidergic somatosensory neurons, cannot yet be discarded as a major contributing mechanism of the throbbing head pain and hyperalgesia of migraine

    TRP Channels: Their Function and Potentiality as Drug Targets

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    Oxidation of Alcohols and Activated Alkanes with Lewis Acid-Activated TEMPO

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    The reactivity of MCl3(η(1)-TEMPO) (M = Fe, 1; Al, 2; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) with a variety of alcohols, including 3,4-dimethoxybenzyl alcohol, 1-phenyl-2-phenoxyethanol, and 1,2-diphenyl-2-methoxyethanol, was investigated using NMR spectroscopy and mass spectrometry. Complex 1 was effective in cleanly converting these substrates to the corresponding aldehyde or ketone. Complex 2 was also able to oxidize these substrates; however, in a few instances the products of overoxidation were also observed. Oxidation of activated alkanes, such as xanthene, by 1 or 2 suggests that the reactions proceed via an initial 1-electron concerted proton-electron transfer (CPET) event. Finally, reaction of TEMPO with FeBr3 in Et2O results in the formation of a mixture of FeBr3(η(1)-TEMPOH) (23) and [FeBr2(η(1)-TEMPOH)]2(μ-O) (24), via oxidation of the solvent, Et2O
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