Closed-shell molecules that ionize more readily than cesium     

Cotton FA  Gruhn NE  Gu J  Huang P  Lichtenberger DL  Murillo CA  Van Dorn LO  Wilkinson CC 《Science (New York, N.Y.)》2002,298(5600):1971-1974

We report a class of molecules with extremely low ionization enthalpies, one member of which has been determined to have a gas-phase ionization energy (onset, 3.51 electron volts) lower than that of the cesium atom (which has the lowest gas-phase ionization energy of the elements) or of any other known closed-shell molecule or neutral transient species reported. The molecules are dimetal complexes with the general formula M2(hpp)4 (where M is Cr, Mo, or W, and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), structurally characterized in the solid state, spectroscopically characterized in the gas phase, and modeled with theoretical computations. The low-energy ionization of each molecule corresponds to the removal of an electron from the delta bonding orbital of the quadruple metal-metal bond, and a strong interaction of this orbital with a filled orbital on the hpp ligands largely accounts for the low ionization energies.  相似文献   

Plant Morphology: Its Control in Proserpinaca by Photoperiod, Temperature, and Gibberellic Acid     

Wallenstein A  Albert LS 《Science (New York, N.Y.)》1963,140(3570):998-1000

Growth forms controlled by the photoperiod are modified by temperature and gibberellic acid. Gibberellic acid changes leaf orientation and prostrate growth habit of the short-day plant to that typical of the long-day plant and modifies leaf shape in both types of plants. Low temperature resembles short days in its effect on leaf shape and stem orientation of long-day plants. Geotropic responses of the stem appear to be modified by photoperiod, temperature, and gibberellic acid.  相似文献   

Chemistry. Multidimensional snapshots of chemical dynamics     

Stolow A  Jonas DM 《Science (New York, N.Y.)》2004,305(5690):1575-1577

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Avian H5N1 influenza in cats     

Kuiken T  Rimmelzwaan G  van Riel D  van Amerongen G  Baars M  Fouchier R  Osterhaus A 《Science (New York, N.Y.)》2004,306(5694):241

During the 2003 to 2004 outbreak of avian influenza A (H5N1) virus in Asia, there were anecdotal reports of fatal infection in domestic cats, although this species is considered resistant to influenza. We experimentally inoculated cats with H5N1 virus intratracheally and by feeding them virus-infected chickens. The cats excreted virus, developed severe diffuse alveolar damage, and transmitted virus to sentinel cats. These results show that domestic cats are at risk of disease or death from H5N1 virus, can be infected by horizontal transmission, and may play a role in the epidemiology of this virus.  相似文献   

Editing of CD1d-bound lipid antigens by endosomal lipid transfer proteins   总被引：3，自引：0，他引：3  

Zhou D  Cantu C  Sagiv Y  Schrantz N  Kulkarni AB  Qi X  Mahuran DJ  Morales CR  Grabowski GA  Benlagha K  Savage P  Bendelac A  Teyton L 《Science (New York, N.Y.)》2004,303(5657):523-527

It is now established that CD1 molecules present lipid antigens to T cells, although it is not clear how the exchange of lipids between membrane compartments and the CD1 binding groove is assisted. We report that mice deficient in prosaposin, the precursor to a family of endosomal lipid transfer proteins (LTP), exhibit specific defects in CD1d-mediated antigen presentation and lack Valpha14 NKT cells. In vitro, saposins extracted monomeric lipids from membranes and from CD1, thereby promoting the loading as well as the editing of lipids on CD1. Transient complexes between CD1, lipid, and LTP suggested a "tug-of-war" model in which lipid exchange between CD1 and LTP is on the basis of their respective affinities for lipids. LTPs constitute a previously unknown link between lipid metabolism and immunity and are likely to exert a profound influence on the repertoire of self, tumor, and microbial lipid antigens.  相似文献   

HIV and Smallpox     

Gruters RA  Osterhaus AD 《Science (New York, N.Y.)》2005,308(5726):1258-9; author reply 1258-9

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Another phocine distemper outbreak in Europe     

Jensen T  van de Bildt M  Dietz HH  Andersen TH  Hammer AS  Kuiken T  Osterhaus A 《Science (New York, N.Y.)》2002,297(5579):209

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Applied physics. Plasmonics applied     

Polman A 《Science (New York, N.Y.)》2008,322(5903):868-869

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Biomedical research publication system     

Wang YL  Burridge K  Dembo M  Gabbiani G  Hanks SK  Hosoya H  Janmey P  Karlsson R  Lindberg U  Mabuchi I  Otey C  Rottner K  Small JV  Wang CL  Zigmond S 《Science (New York, N.Y.)》2004,303(5666):1974-1976

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Purkinje cell degeneration (pcd) phenotypes caused by mutations in the axotomy-induced gene, Nna1     

Fernandez-Gonzalez A  La Spada AR  Treadaway J  Higdon JC  Harris BS  Sidman RL  Morgan JI  Zuo J 《Science (New York, N.Y.)》2002,295(5561):1904-1906

The classical recessive mouse mutant, Purkinje cell degeneration (pcd), exhibits adult-onset degeneration of cerebellar Purkinje neurons, retinal photoreceptors, olfactory bulb mitral neurons, and selected thalamic neurons, and has defective spermatogenesis. Here we identify Nna1 as the gene mutated in the original pcd and two additional pcd alleles (pcd2J and pcd3J). Nna1 encodes a putative nuclear protein containing a zinc carboxypeptidase domain initially identified by its induction in spinal motor neurons during axonal regeneration. The present study suggests an unexpected molecular link between neuronal degeneration and regeneration, and its results have potential implications for neurodegenerative diseases and male infertility.  相似文献