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991.
The preparation of an 1,3-alternate calix[4]arene tetraphosphane ligand, 25,26,27,28-tetrakis{2-(diphenylphosphino)ethoxy}calix[4]arene (4), is described. Ligand 4 is obtained in four steps in 17% overall yield. Reaction of 4 with AgBF4 produced the encapsulated two silver complex [Ag2{(P,P,P,P)-tetraphencalix[4]arene}](BF4)2. The solid-state structure shows that the encapsulated silver undergoes a substantial pi-interaction by two opposite arene rings. Rhodation of 4 employing [Rh(cot)2]BF4 yielded the encapsulated complex with a bent coordination mode. Two organometallic fragments inclusioned inside a 1,3-alternate calix[4]arene tetraphosphane was also achieved by the reaction of 4 with [PtH(PPh3)2 (thf)]+. Full characterization includes X-ray structural studies of compounds 4-6. 相似文献
992.
993.
Theoretical determination of chromophores in the chromogenic effects of aromatic neurotoxicants 总被引:3,自引:0,他引:3
Zhan CG Dixon DA Sabri MI Kim MS Spencer PS 《Journal of the American Chemical Society》2002,124(11):2744-2752
We report the first computational study of the chromophores responsible for the chromogenic effects of aromatic neurotoxicants containing a 1,2-diacetyl moiety in their oxidation metabolites. A series of ab initio electronic structure calculations was performed on two representative aromatic compounds, 1,2-diacetylbenzene (1,2-DAB) and 1,2-diacetyl tetramethyl tetralin (1,2-DATT), the putative active metabolites of the neurotoxic aromatic hydrocarbon compounds 1,2-diethylbenzene (1,2-DEB) and acetyl ethyl tetramethyl tetralin (AETT), and on the products of their possible reactions with proteins that result in chromogenic effects. The electronic excitation energies determined by three different computational approaches were found to be consistent with each other. The calculated results are consistent with the conclusion/prediction that the chromogenic effects of 1,2-DAB (or 1,2-DEB) and 1,2-DATT (or AETT) could result from ninhydrin-like reactions, rather than the formation of pyrrole-like compounds. Our pK(a) calculations further indicate that the chromophore, i.e., the product of the ninhydrin-like reaction showing the blue color, is deprotonated in neutral aqueous solution. The corresponding protonated structure has a different color as it absorbs in the blue region of the visible spectrum, and its chromogenic contribution would be significant in solution at low pH. 相似文献
994.
Hyungrak Kim 《Journal of solid state chemistry》2005,178(6):1935-1939
The compound Ca14MnP11 crystallizes in the Ca14AlSb11 structure type with the tetragonal space group I41/acd (Z=8) and lattice parameters of , c=20.7565(9) at 90 K. The structure consists of MnP49− tetrahedron, P37− trimer, 4 P3− isolated anions and 14 Ca2+ cations. Similar to other compounds of this structure type containing phosphorous, the P37− trimer has a central P atom that is best modeled in the structure as being equally split between two sites. In addition, there is no additional distortion of the manganese-containing tetrahedron compared with the main group analog, Ca14GaP11, suggesting that the Mn oxidation state is Mn2+. Temperature-dependent magnetic susceptibility shows that the compound is paramagnetic over the entire temperature range measured (2-300 K). The data can be fit with a modified Curie-Weiss law and provide an effective magnetic moment of 5.80 (2) B.M. with a Weiss constant of −2.13(2) K and . This moment is significantly higher than those measured for any of the Mn-containing analogs and is consistent with Mn2+. This result will be discussed in light of the electron counting scheme for Mn compounds of the Ca14AlSb11 structure-type. 相似文献
995.
Enantioseparations of (R)- and (S)-6-O-desmethylnaproxens as O-ethoxycarbonyl/(R)-(+)-1-phenylethylamides and (R)- and (S)-naproxens as (R)-(+)-1-phenylethylamides were achieved by achiral gas chromatography in a single run within 11 min. The characteristic mass spectral patterns facilitated easier peak identification. The method for determinations of (R)-naproxen (1.0 to 50 ng) and (S)-naproxen (100 to 2000 ng) was linear with acceptable repeatability and accuracy. The enantiomeric composition ratios between (R)- and (S)-6-O-desmethylnaproxens and between (R)- and (S)-naproxens in urine sample collected six hours after oral administration of (S)-naproxen tablets were measured to be 2.2 (± 0.2):97.8 (± 0.2) and 2.1 (± 0.1):97.9 (± 0.1), respectively. 相似文献
996.
Kim Henrick Mary McPartlin Glen B. Deacon Roderic J. Phillips 《Journal of organometallic chemistry》1980,204(3):287-294
An X-ray crystallographic study has shown that the complex (C6H5)2TlO2CC6F5(OPPh3) has a dimeric structure with unsymmetrical pentafluorobenzoate bridging (TlO 2.531 and 2.789 Å) but an exact crystallographic centre of symmetry. The pentafluorobenzoate groups are also unsymmetrically chelated to thallium (TlO 2.389 and 2.531 Å.), which overall has irregular six coordination. 相似文献
997.
[reaction: see text] Highly stereodivergent Woodward-Prevost reaction applied to iodoacetates derived from homochiral alpha-amino acids afforded enantiopure 3,4-cis- and 3,4-trans-pyrrolidinediol derivatives, with control over the protecting group, allowing for differential protection. 相似文献
998.
Self-assemblies of rigid angular ligands with 120 degrees molecular angle and metal centers have been investigated with the aim of achieving the rational construction and modification of coordination polymer structures. The reactions of Co(NCS)(2) with 1,3-bis(trans-4-styrylpyridyl)benzene (L(1)()), 2,6-bis(trans-4-styrylpyridyl)pyridine (L(2)()), 1,3-bis(trans-4-styrylpyrimidyl)benzene (L(3)()), and 1,3-bis(trans-4-styrylquinoly)benzene (L(4)()) afford complexes [Co(L(1)())(2)(NCS)(2)]( infinity ) (1), [Co(L(2)())(2)(NCS)(2)]( infinity ) (2), Co(L(3)())(2)(NCS)(2)(CH(3)OH)(2) (3), and [Co(L(4)())(NCS)(2)]( infinity ) (4), respectively. The resulting complexes exhibit open framework, stairlike hydrogen-bonded chain and single-stranded helical coil structures, which are controlled by the variation of the geometry around the coordination site in ligands. Moreover, the coordination of L(1)() and L(2)() to Mn(hfac)(2) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate) yields single-stranded helical coordination polymers of [Mn(L(1)())(hfac)(2)]( infinity ) (5) and [Mn(L(2)())(hfac)(2)]( infinity ) (6), respectively. 相似文献
999.
Ru‐Jong Jeng Geng‐Sheng Lo Chih‐Ping Chen Ying‐Ling Liu Ging‐Ho Hsiue Wen‐Chiung Su 《先进技术聚合物》2003,14(2):147-156
Epoxy resins modified by an organosoluble phosphorus‐containing bismaleimide (3,3′‐bis(maleimidophenyl) phenylphosphine oxide; BMPPPO) were prepared by simultaneously curing epoxy/diaminodiphenylmethane (DDM), and BMPPPO. The resulted epoxy resins were found to exhibit glass transition temperatures as high as 212 °C, thermal stability at temperatures over 350 °C, and excellent flame retardancy with Limited oxygen index (LOI) values around 40. Incorporation of BMPPPO into epoxy resins via the thermosetting blend was demonstrated to be an effective way to enhance the thermal properties and flame retardancy simultaneously. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
1000.
Martínez-Alvarez R Martín N Seoane C Suárez M Pérez R Rodríguez H Kayali N 《Rapid communications in mass spectrometry : RCM》2001,15(10):758-762
The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M - H](-) ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed. 相似文献