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71.
Nishimura T Ohsawa S Maeda K Yashima E 《Chemical communications (Cambridge, England)》2004,(6):646-647
Novel [60]fullerene-based poly(phenylacetylene)s prepared by the copolymerization of achiral phenylacetylenes bearing a C(60) or crown ether pendant form a one-handed helix upon complexation with L- and D-alanine, yielding a helical array of the pendant fullerenes with a predominant screw-sense along the polymer backbone. 相似文献
72.
Kon Y Ogasawara J Sakamoto K Kabuto C Kira M 《Journal of the American Chemical Society》2003,125(31):9310-9311
A silicon-containing fused bicyclic compound with a highly strained bridgehead double bond, 2,3,6,7-tetra-tert-butyl-4-(tert-butyldimethylsilyl)-5-(tert-butyldimethylsiloxy)-5-silabicyclo[3.2.0]hepta-1,3,6-triene (2), was synthesized quantitatively by the reaction of 1,2-bis-tert-butyl-4,4-bis(tert-butyldimethylsilyl)-4-silatriafulvene (3) with di-tert-butylcyclopropenone (4) at 80 degrees C. An X-ray crystallographic analysis for 2 not only confirmed a bicyclic structure having a silacyclopentadiene (silole) ring fused with a silacyclobutene ring but also the remarkable deformation around the double bonds; the sum of the bond angles around the unsaturated bridgehead carbon was 333 degrees . The strain energy of a model 5-silabicyclo[3.2.0]hepta-1,3,6-triene was calculated at the MP2/6-31+G(d,p)//B3LYP/6-31+G(d) level (30.2 kcal/mol) to be comparable to that for parent bicyclo[3.2.0]hepta-1,3,6-triene (30.7 kcal/mol). Despite the high steric strain, 2 was stable enough to be kept intact for several months in the air. The high stability is ascribed to the effective steric protection of the ring system by the bulky substituents. 相似文献
73.
Sakamoto M Ohba A Kuriyama J Maruo K Ueno S Sato K 《Colloids and surfaces. B, Biointerfaces》2004,37(1-2):27-33
We examined the crystallization of palm mid fraction (PMF) in oil-in-water (O/W) emulsion, after adding polyglycerol fatty acid esters (PGFEs). We employed ultrasonic velocity measurements and DSC techniques, with special emphases on the influences of fatty acid moiety and esterification of PGFE. Twelve types of PGFEs were examined as additives. PGFEs have a large hydrophilic moiety composed of 10 glycerol molecules to which palmitic, stearic and behenic acids were esterified as the fatty acid moiety with different degrees of esterification. Crystallization temperature (T(c)) of PMF remarkably increased with increasing concentrations of the PGFEs as the chain length of the fatty acid moiety increased, and the PGFE became more hydrophobic in accordance with increasing degree of esterification. We observed that the heterogeneous nucleation of PMF in the O/W emulsion was activated at the oil-water interface, where the template effect of very hydrophobic long saturated fatty acid chains of the PGFE might play the main role of heterogeneous nucleation. 相似文献
74.
The catalytic oxidation of glucose on Pt electrodes modified by adsorbed metals was studied in 1 M HClO4 by linear sweep voltammetry. The adsorbed metals (denoted as Mad, such as Biad and Pbad) formed on Pt in the potential region more positive than the reversible potential of an M=+/Mo couple, lead to a marked increase in the anodic c?urrent of glucose by about one order of magnitude. The catalytic activity depends on the surface coverage by the Mad. The strongly adsorbed species of lactone type, which are responsible for blocking the successive oxidation, are formed on the electrode surface in the anodic processes of glucose on a bare Pt electrode. The formation of such poisonous species is accelerated in the presence of adsorbed hydrogen on Pt. The effects of Mad were discussed on the basis that Mad plays its major role on the Pt electrode surface in removal of the adsorbed hydrogen which initiates the formation of the poisonous species. 相似文献
75.
Liang X Asanuma H Kashida H Takasu A Sakamoto T Kawai G Komiyama M 《Journal of the American Chemical Society》2003,125(52):16408-16415
Two diastereomers of a photoresponsive oligodeoxyribonucleotide tethering a trans-azobenzene, based on the chirality of the central carbon of a diol linker, were separated by reversed-phase HPLC. On the basis of 2D NMR analysis, absolute configurations of the diastereomers alpha and beta (tentatively designated from differences in their retention time) were determined as R- and S-forms, respectively. For both diastereomers, their NMR-determined duplex structure showed that trans-azobenzene intercalates between base pairs, because distinct NOEs were observed between the protons of azobenzene and those of the adjacent base pairs, such as with the imino protons and methyl protons of thymine. The melting temperatures of both duplexes were higher than that of the corresponding native duplex, which contained no azobenzene residue, due to the intercalated trans-azobenzene stabilizing the duplex by a stacking interaction. Between these two diastereomers, differences in T(m) were also found: the melting temperature of the R-form duplex (alpha-isomer) was higher than that of the S-form (beta-isomer). On the basis of the NMR-determined structure, this difference was attributed to the fact that the S-form (beta isomer) causes more stress forming the duplex than does the R-form (alpha isomer) due to disturbances of the right-hand helix. 相似文献
76.
The lankacidin biosynthetic gene cluster in Streptomyces rochei strain 7434AN4 was found to span 31 kb of the giant linear plasmid pSLA2-L and contain a polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) hybrid gene (lkcA), type I PKS genes, and pyrroloquinoline quinone (PQQ) biosynthetic genes (lkcK-lkcO). Feeding of PQQ to a pqq mutant restored the lankacidin production, suggesting its crucial role in an oxidation process. However, formation of the 17-membered macrocyclic ring was not catalyzed by PQQ-dependent dehydrogenase (Orf23), but was by flavin-dependent amine oxidase (LkcE). Compound LC-KA05 isolated from an lkcE disruptant was an acyclic intermediate lacking the C2-C18 linkage. These results suggested a cyclization mechanism for the synthesis of the lankacidin macrocyclic skeleton. 相似文献
77.
The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO4 were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi3+. This indicates the accelerating effect of Bi3+ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb2+, Hg2+, Tl+, Ag+ and Sb3+, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as Mad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co2+, Zn2+, Fe3+ and Ni2+, exhibit no catalytic effect. These facts suggest that the presence of a Mad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the Mad, for example, Cuad, Cdad, Inad, Snad and Moad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the Mad. The maximal effect of the Mad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the Mad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the 13C NMR spectra for the oxidation products, the adsorbed water on the Mad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid. 相似文献
78.
Shimizu T Kimura T Funahashi T Watanabe K Ho IK Yamamoto I 《Chemical & pharmaceutical bulletin》2005,53(3):313-318
Seventy eight N(3)-substituted derivatives of uridine (1), thymidine (2), 2'-deoxyuridine (3), 6-azauridine (4), 2',3'-O-isopropylideneuridine (5), and arabinofuranosyluracil (6) were synthesized and their antinociceptive effects were evaluated. N(3)-(2',4'-Dimethoxyphenacyl)uridine (1l), N(3)-(2',4'-dimethoxyphenacyl)2'-deoxyuridine (3l), and N(3)-(2',5'-dimethoxyphenacyl)arabinofuranosyluracil (6m) possessed 93, 86, and 82% of the antinociceptive effects tested by hot plate, respectively. The antinociceptive effects of three derivatives were 5.8, 5.4, and 5.1-folds of the effect of N(3)-phenacyluridine (1h) (16%), respectively. The structure-activity relationship of N(3)-substituted pyrimidine nucleosides was also discussed. 相似文献
79.
An S-bridged RhIII2PtII2 tetranuclear complex having two nonbridging thiolato groups, [{Pt(NH3)2}2{Rh(aet)3}2]4+ ([1]4+), in which two fac(S)-[Rh(aet)3] units are linked by two trans-[Pt(NH3)2]2+ moieties, was synthesized by the 1:1 reaction of fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate) with trans-[PtCl2(NH3)2] in water. Complex [1]4+ gave both the meso (DeltaLambda) and racemic (DeltaDelta/LambdaLambda) forms, which were separated by fractional crystallization. Of two possible geometries, syn and anti, which arise from the arrangement of two nonbridging thiolato groups, the meso and racemic forms of [1]4+ selectively afforded the anti and syn geometries, respectively. The DeltaLambda-anti and DeltaDelta/LambdaLambda-syn isomers of [1]4+ reacted with Ag+ using two nonbridging thiolato groups to produce a {RhIII2PtII2AgI}n) polymeric complex, {[Ag{Pt(NH3)2}2{Rh(aet)3}2]5+}n) ([2]5+), and a RhIII2PtII2AgI pentanuclear complex, [Ag{Pt2(mu-H2O)(NH3)2}{Rh(aet)3}2]5+ ([3]5+), respectively, which contain octahedral RhIII, square-planar PtII, and linear AgI centers. In [2]5+, each DeltaLambda-anti-[{Pt(NH3)2}2{Rh(aet)3}2]4+ tetranuclear unit is bound to two AgI atoms to form a one-dimensional zigzag chain, indicating the retention of the parental S-bridged structure in DeltaLambda-anti-[1]4+. In [3]5+, two Delta- or Lambda-fac(S)-[Rh(aet)3] units are linked by a [Pt2(mu-H2O)(NH3)2]4+ dinuclear moiety, together with an AgI atom, indicating that two NH3 molecules in [1]4+ have been replaced by a water molecule that bridges two PtII centers, while the parental DeltaDelta/LambdaLambda-syn configuration is retained. The complexes obtained were characterized on the basis of electronic absorption, CD, and NMR spectra, along with single-crystal X-ray analyses. 相似文献
80.
Choji Kashima Shigeki Hibi Tatsuya Maruyama Kazuo Harada Yoshimori Omote 《Journal of heterocyclic chemistry》1987,24(3):637-639
The relative reaction rate of five-membered heterocycles with ozone was evaluated. These relative rates were correlated to the highest bond order value in the corresponding ring, calculated by the convenient HMO method. From this correlation, the reactivity of heterocycles with ozone was able to be predicted. Also it was concluded that the predominant product in the ozonolysis of five-membered heterocycles containing an oxygen atom was the corresponding carboxylic acid, while nitrogen heterocycles gave the corresponding amide. 相似文献