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81.
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
82.
Koide T Yuguchi M Kawakita M Konno H 《Journal of the American Chemical Society》2002,124(32):9388-9389
Collagen model peptides that contain 2,2'-bipyridyl (bpy) ligands were designed and synthesized. The thermal stability of the collagenous triple helix was increased by forming an Fe(II)(bpy-peptide)(3) complex. The chirality of the metal center was shifted to form right-handed Delta-isomers induced by the supercoiling of the peptide moiety. Moreover, the refolding rate of the triple helix was increased in the presence of Fe(II). This metal-coordinating system possesses potential to be used to stabilize the triple-helical conformation as well as to probe the folding status of collagen model peptides. 相似文献
83.
Enantio-uracil dinucleotide 5, which consists of two l-uridylic acids and one pyrophosphate, was synthesized for the first time in our laboratory. Benzolyated l-uridine was prepared by a stereoselective glycosylation of silylated uracil with l-1-O-acetyl-2,3,5-tri-O-benzoylribose (l-ABR 7). After deprotection, l-uridine 9 was converted to P1,P4-di(l-uridine 5′-) tetraphosphate tetrasodium salt (l-UP4U 5) by treatment of l-UMP morpholidate 10c with triethylammonium pyrophosphate (TEA-PPi 11b). Spectral data of synthesized l-UP4U 5 are given in the references. All spectral data were identical with those of UP4U 3 except the specific rotation, which showed a positive value compared to UP4U 3 having a negative value. Furthermore, the separation by chiral column chromatography was investigated. 相似文献
84.
Keisuke Kato Chie Matsuba Hiroyuki Takayama Tomoyuki Mochida Tat'yana A. Peganova Oleg V. Gusev 《Tetrahedron》2006,62(42):9988-9999
The oxidative cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols mediated by Pd(II) with chiral bisoxazoline (box ligand) afforded bicyclic-β-alkoxyacrylates. Based on a ligand screening, 2,2′-isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand has been developed. The products with a chiral quaternary carbon were obtained in 71-100% yields with 85-95% ee. 相似文献
85.
Treatment of 1-chlorovinyl p-tolyl sulfoxides, prepared from ketones and chloromethyl p-tolyl sulfoxide, with N-lithio arylamines resulted in the formation of sulfinylaziridines in good to high yields. The sulfinylaziridines were treated with N-lithio aniline or N-lithio p-chloroaniline to afford α-quaternary α-amino aldehydes in good yields. From α-quaternary α-amino aldehydes, α-quaternary α-amino acid esters and β-quaternary β-amino alcohols were obtained. When optically active chloromethyl p-tolyl sulfoxide was used in this procedure, a method for the synthesis of optically active α-quaternary α-amino aldehydes was realized. The reaction mechanism, including asymmetric induction, for the formation of the sulfinylaziridines is described. 相似文献
86.
Sugimoto H Harihara M Shiro M Sugimoto K Tanaka K Miyake H Tsukube H 《Inorganic chemistry》2005,44(18):6386-6392
The cis-dioxo-molybdenum(VI) complexes, [MoO2(L(H))2]2- (1b), [MoO2(L(S))(2)]2- (2b), and [MoO2(L(O))2]2- (3b) (L(H) = cyclohexene-1,2-dithiolate, L(S) = 2,3-dihydro-2H-thiopyran-4,5-dithiolate, and L(O) = 2,3-dihydro-2H-pyran-4,5-dithiolate), with new aliphatic dithiolene ligands were prepared and investigated by infrared (IR) and UV-vis spectroscopic and electrochemical methods. The mono-oxo-molybdenum(IV) complexes, [MoO(L(H))2]2- (1a), [MoO(L(S))2]2- (2a), and [MoO(L(O))2]2- (3a), were further characterized by X-ray crystal structural determinations. The IR and resonance Raman spectroscopic studies suggested that these cis-dioxo molybdenum(VI) complexes (1b-3b) had weaker Mo=O bonds than the common Mo(VI)O2 complexes. Complexes 1b-3b also exhibited strong absorption bands in the visible regions assigned as charge-transfer bands from the dithiolene ligands to the cis-MoO2 cores. Because the oxygen atoms of the cis-Mo(VI)O2 cores are relatively nucleophilic, these complexes were unstable in protic solvents and protonation might occur to produce Mo(VI)O(OH), as observed with the oxidized state of arsenite oxidase. 相似文献
87.
The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2 eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance factor. (2) When A is one of the heavier alkaline earth metals (Ca, Sr, Ba) and B a transition metal, stable compounds ABH3 result only when B is from the Fe, Co, or Ni groups. This stability trend is basically determined by effects associated with d band filling of both the transition metal and the hydride. In contrast to group (1) perovskites, the transition metal-containing compounds are metals. The synthesis of CaNiH3 and its structure determination from CaNiD3 is reported. This compound is a type (2) perovskite hydride with a fully occupied hydrogen position (CaNiD3: a=3.551(4) Å, dNi-D=1.776(2) Å). Its stability is discussed with respect to transition metal hydrides with complex anions (e.g., Mg2NiH4, Na2PdH2, Sr2PdH4). 相似文献
88.
Multilayer vesicles and vesicle clusters formed by the fullerene-based surfactant C60(CH3)5K 总被引:3,自引:0,他引:3
Burger C Hao J Ying Q Isobe H Sawamura M Nakamura E Chu B 《Journal of colloid and interface science》2004,275(2):632-641
The self-assembly behavior of a fullerene-based surfactant, C60(CH3)5K, in water was studied using a combination of static and dynamic light scattering, as well as transmission electron microscopy, and compared to that of the compound C60(C6H5)5K. Both fullerene surfactant systems spontaneously assemble into large vesicles consisting of closed spherical shells formed by bilayers, with critical aggregation concentrations (CAC) lower than 10(-6) g ml(-1). At low concentrations, the aggregate sizes of C60(CH3)5K (radius R approximately 26.8 nm) and C60(C6H5)5K (R approximately 17.0 nm) were found to be substantially different from each other, showing that the change of the substituents surrounding the polar cyclopentadienide head group makes it possible to control the size of the resulting aggregates. Furthermore, the C60(CH3)5K vesicles were found to exist in two qualitatively different types of aggregation with a critical reaggregation concentration (CRC) located at 3.30 x 10(-6) g ml(-1). Above the CRC, larger aggregates were observed (R approximately 37.6 nm), showing a more complex form of supramolecular aggregation, e.g., in terms of multi-bilayer vesicles and/or of clusters of bilayer vesicles. 相似文献
89.
Five-coordinate and six-coordinate 2-methyl-2-propanethiolato complexes of zirconium, [Li(DME)(3)][Zr(SCMe(3))(5)] (1) and [(THF)Li](2)Zr(SCMe(3))(6) (2), were obtained from the ZrCl(4)/LiSCMe(3) reaction system. The control of the Zr coordination number, by the ether ligands, THF or DME, bound to Li, is demonstrated by the conversion of 2 into 1 upon dissolution in DME. 1 and 2 were crystallographically characterized. The structures are extensively disordered. Crystal data follow: 1, hexagonal P6(3)/m, a = b = 12.496(3) ?, c = 17.561(9) ?, Z = 2, V = 2375(1) ?(3), R = 5.0%, R(w) = 6.8%; 2, trigonal R32, a = b = 11.813(3) ?, c = 28.37(1) ?, Z = 3, V = 3428(1) ?(3), R = 5.2%, R(w) = 6.4%. 相似文献
90.
Tetsuji Yano Makoto Ebizuka Hiroyuki Yamamoto Shuichi Shibata Masayuki Yamane 《Journal of Sol-Gel Science and Technology》2000,19(1-3):845-849
Na2O-B2O3-SiO2 (NBS) gels containing a large amount of CdS quantum-dots (10 wt%) were densified using the hot press (HP) sintering method. By HP treatment, full-densification temperature could be lowered by about 40°C than that of the normal non-pressing (NP) heat treatment. Exciton absorption of CdS quantum-dots in HP-sample showed a large blue shift compared with that in the NP sample, and the size-distribution of CdS dots remained very sharp, with a mean particle diameter d = 3.66 nm and a standard deviation of = 0.72. HP pressure had a large effect on the reduction of sintering temperature and time, resulting in the suppression of the aggregation and growth of CdS quantum-dots in NBS glasses. 相似文献