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101.
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A number of nucleophilic ring openings of 3-substituted pyridinium salts have been reinvestigated and summarized. The structure of the resulting stable glutaconaldehyde derivatives was investigated in detail by 1H NMR. It has been concluded that in general nucleophilic pyridinium ring openings are highly regiospecific. In each case investigated to date a single product was isolated, as a result of attack by the nucleophile at only one of the pyridine α-positions. With the OH ion as the only nucleophile, attack occurs at the pyridine C-2, while larger nucleophiles such as amines and carbanions attack at the pyridine C-6. This was found to be the case for a variety of 3-substituted pyridines such as 3-methyl, 3-methoxy-, 3-cyano-, 3 chloro-pyridine. 相似文献
105.
Pierre Sebban Maïté Coppey Bernard Alpert Lars Lindqvist † David M. Jameson‡ 《Photochemistry and photobiology》1980,32(6):727-731
Fluorescence excitation and emission spectra, decays, and quantum yields are reported for the porphyrin-globin of hemoglobin (HbdesFe) in aqueous solution of pH 8, at 4°C. A very weak fluorescence was observed in the UV (maximum at 334 nm), due to tryptophan and tyrosine residues, in addition to the strong porphyrin emission in the visible (maxima at 624 and 692 nm) reported previously. The absorption and fluorescence properties of the porphyrins of HbdesFe were compared to those for free porphyrin in organic solvents and in aqueous solution. The close similarity of the fluorescence decays and quantum yields in HbdesFe and in solution indicate the absence of stronger, specific porphyrin-protein interactions; however, slight spectral shifts point to the existence of water molecules in the HbdesFe porphyrin environment. The fluorescence study also demonstrates the existence of efficient Trp-porphyrin energy transfer of Förster type. The extent of transfer is in satisfactory agreement with the value expected from crystallographic data for hemoglobin. The results are discussed and compared to previous fluorescence studies of hemoglobin and apohemoglobin. An improved method for the preparation of HbdesFe is reported. 相似文献
106.
On Coinage Metal Mercury Chalcogenide Halides. IV Hydrothermal Synthesis and Crystal Structure of CuHgSI and CuHg2S2I The hydrothermal reaction of CuI with α‐HgS in diluted aqueous HI‐solution as solvent at 180 °C yields dark red crystals of CuHgSI. The compound crystallizes orthorhombic in the space group Pna21 with a = 718.3(1) pm, b = 834.3(2) pm and c = 698.9(1) pm and Z = 4. CuHg2S2I was obtained by the hydrothermal reaction of CuI with α‐HgS in diluted HI‐solution at 300 °C as black crystals. The compound crystallizes orthorhombic in the space group Cmc21 with a = 1261.8(3) pm, b = 722.4(1) pm and c = 693.7(1) pm and Z = 4. Both crystal structures could be explained as distorted version of the Wurtzite structure type in which two different types of anion‐lattices are built up. 相似文献
107.
Blitz JP Diebel RE Deakyne CA Christensen JM Gun'ko VM 《The journal of physical chemistry. B》2005,109(12):5667-5677
Reactions of trimethylaluminum, triethylaluminum, and diethylaluminum chloride and ethylaluminum dichloride with silica gel have been studied experimentally by infrared spectroscopy and elemental analysis. The silica gel was subjected to different pretreatments to alter surface functionalities prior to reaction. In all cases the extent of surface modification reaction follows the trend unmodified > 600 degrees C pretreated > hexamethyldisilazane (HMDZ) pretreated > 600 degrees C/HMDZ pretreated. All of the aluminum compounds studied completely react non-hydrogen-bonded silanols, while also reacting with hydrogen-bonded silanols and siloxanes. Primarily monomeric surface species result from the surface modification reaction. Ethylaluminum chlorides preferentially react with silanols through cleavage of the Al-C bond rather than the Al-Cl bond. Singly bonded Si(s)-O-AlCl(2) surface species are readily synthesized by reaction of ethylaluminum dichloride with HMDZ-pretreated silica gel. Bridged bonded (Si(s)-O)(2)-AlCl surface species are readily synthesized by reaction of diethylaluminum chloride with HMDZ-pretreated silica gel. Computational ab initio studies of the cluster Si(4)O(6)(OH)(4) as a model to study the reaction of monomeric and dimeric methylaluminum dichloride with a silica silanol are also described. Comparison of the potential energy surface (PES) of monomer and dimer indicates that the energetics favor monomer reaction, consistent with experimental results. The energy cost in the dimer reaction is primarily from cleavage of a bridged Al-Cl bond upon adsorption. This does not occur when the monomer adsorbs. A comparison of the PES for the two reaction pathways resulting from cleavage of either an Al-Cl or Al-C bond indicates that while the former reaction is slightly kinetically favored (E(a) = 23.1 kJ/mol for Al-Cl bond cleavage versus E(a) = 31.1 kJ/mol for Al-C bond cleavage), the latter is strongly thermodynamically favored with an overall free energy difference between the two reaction pathways of 135 kJ/mol favorable to Al-C bond cleavage. These reactions are thermodynamically controlled. 相似文献
108.
Lars S. von Chrzanowski Martin Lutz Anthony L. Spek 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(7):m283-m288
The crystal structure of the title compound, [Co(C5H7O2)3], has been investigated by a multi‐temperature measurement. In contrast to the isomorphous Al compound, the title compound exists in the studied temperature range as its monoclinic α polymorph (space group P21/c) and does not undergo a phase transition. Rigid‐body TLS analyses have been performed and the anisotropic thermal expansion tensor αij has been determined. The cell axes show a linear expansion behavior with respect to the temperature, but the slope is significantly different. A possible explanation are the different strengths of different intermolecular C—H...O contacts, which run in different crystallographic directions. 相似文献
109.
Reed M. Izatt Robert M. Haws John D. Lamb David V. Dearden Philip R. Brown Don W. McBride Jr. James J. Christensen 《Journal of membrane science》1984,20(3):273-284
Cation fluxes were determined for various three-component, equimolar mixtures of alkali metal, alkaline earth, and Pb2+ cations in a H2O---CHCl3---H2O liquid membrane system incorporating macrocyclic polyethers as carriers. Carrier ligands studied were 18-crown-6, dicyclohexano-18-crown-6, 1,10-diaza-18-crown-6, 21-crown-7, dibenzo-24-crown-8, and cryptand [2.2.2]. Correlations were found between transport and relative cation:polyether cavity radii, the type of substituents present on the polyether ring, and the type and number of donor atoms present. All the ligands studied transported Pb2+ at higher rates than the other Mn+ in the mixtures. Transport behavior in these multi-cation systems can be predicted from Mn+—polyether complex stability constant data in most cases. 相似文献
110.
Traceability is not always evident in proficiency testing programs, although this is a requirement in ISO/IEC Guide 43-1. The assigned, or "true", value in most programs is not traceable to an independent entity. The test materials should generally be similar in nature to those routinely tested by participating laboratories. This is far from always the case and it is important to realize that if the difference is large, there may be no traceability to the testing program. It is also important that results from participation in proficiency tests are cited when papers are published, in order to enhance reliability/credibility of the published data.
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