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The 351-nanometer photoelectron spectrum of the planar cyclooctatetraene radical anion (COT·-) shows transitions to two electronic states of cyclooctatetraene (COT). These states correspond to the D4h 1A1g state, which is the transition state for COT ring inversion, and the D8h 3A2u state. The electron binding energy of the 1A1g transition state is 1.099 ± 0.010 electron volts, which is lower by 12.1 ± 0.3 kilocalories per mole than that of the 3A2u state. The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule. Vibrational structure is observed for both features and is readily assigned by use of a simple potential energy surface. 相似文献
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Krantz BA Melnyk RA Zhang S Juris SJ Lacy DB Wu Z Finkelstein A Collier RJ 《Science (New York, N.Y.)》2005,309(5735):777-781
The protective antigen component of anthrax toxin forms a homoheptameric pore in the endosomal membrane, creating a narrow passageway for the enzymatic components of the toxin to enter the cytosol. We found that, during conversion of the heptameric precursor to the pore, the seven phenylalanine-427 residues converged within the lumen, generating a radially symmetric heptad of solvent-exposed aromatic rings. This "phi-clamp" structure was required for protein translocation and comprised the major conductance-blocking site for hydrophobic drugs and model cations. We conclude that the phi clamp serves a chaperone-like function, interacting with hydrophobic sequences presented by the protein substrate as it unfolds during translocation. 相似文献
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Segwagwe Basiamisi Ernest Machete James Ntwaetsile Mpho Mushonga Borden Kandiwa Erick 《Tropical animal health and production》2019,51(5):1277-1277
Tropical Animal Health and Production - The article “No evidence of Trichinella spp. in domestic pig carcasses at a selected abattoir in southern Botswana”, written by Basiamisi Ernest... 相似文献
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Borden CE 《Science (New York, N.Y.)》1979,203(4384):963-979
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Examination of electrophoretic mobility patterns indicates that the strain designations of 44 classical strains of Tetrahymena are confused. It is suggested that new designations be made on the basis of phenotypic similarity. 相似文献