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941.
Hao B Zhao G Kang PT Soares JA Ferguson TK Gallucci J Krzycki JA Chan MK 《Chemistry & biology》2004,11(9):1317-1324
L-pyrrolysine, the 22(nd) genetically encoded amino acid, was previously deduced to be (4R, 5R)-4-substituted-pyrroline-5-carboxylate attached to the epsilon-nitrogen of lysine based on the crystal structure of the M. barkeri monomethylamine methyltransferase (MtmB). To confirm L-pyrrolysine's identity, structures of MtmB have been determined following treatment with hydroxylamine, N-methylhydroxylamine, or dithionite. Analysis of these structures has provided additional support for the presence of the pyrroline ring and, together with previous mass spectroscopy data, has led us to assign the C(4)-substituent to a methyl group. Based on this assignment, synthetic L-pyrrolysine was prepared by chemical methods. Detailed study of this chemically synthesized L-pyrrolysine has allowed us to characterize its physical properties, to study its chemical stability, and to elucidate the role of its C(4) substituent. Future applications of this synthetic L-pyrrolysine include its in vivo incorporation into recombinant proteins. 相似文献
942.
Lyotropic liquid crystalline phases formed in an ionic liquid 总被引:1,自引:0,他引:1
Wang L Chen X Chai Y Hao J Sui Z Zhuang W Sun Z 《Chemical communications (Cambridge, England)》2004,(24):2840-2841
Lyotropic liquid crystalline phases of an amphiphilic block copolymer are constructed and characterized in an ionic liquid with comparison of component and temperature effects. 相似文献
943.
A simple, rapid tandem mass spectrometric method for recognition of chiral molecules by proton transfer reactions with chiral sec-butylamines and sec-butanols is reported. 相似文献
944.
The conservation of transgenic materials is very important, paticularly for their potential future use in crop development. In this study, transgenic callus cultures of 'Newhall' navel orange (Citrus sinensis Osbeck) were cryopreserved by a vitrification method. Transgenic calluses survived cryopreservation and recovered under normal culture conditions. The results of PCR (Polymerase Chain Reaction) amplification, Southern blotting and SSCP (Single-Strand Conformation Polymorphism) assay showed that the GUS gene was still maintained in the genome of callus cultures recovered from cryopreservation. X-Gluc staining further indicated GUS gene expression in callus cultures recovered from cryopreservation. 相似文献
945.
Moresco F Gross L Alemani M Rieder KH Tang H Gourdon A Joachim C 《Physical review letters》2003,91(3):036601
A crucial problem in molecular electronics is the control of the electronic contact between a molecule and its electrodes. As a model system, we investigated the contact between the molecular wire group of a C90H98 (Lander) molecule and the edge of a Cu(111) monatomic step. The reproducible contact and decontact of the wire was obtained by manipulating the Lander with a low temperature scanning tunneling microscope. The electronic standing wave patterns on the Cu(111) surface serve to monitor the local electronic perturbation caused by the interaction of the wire end with the step edge, giving information on the quality of the contact. 相似文献
946.
A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals 总被引:3,自引:0,他引:3
L.-W. Yin M.-S. Li Z.-G. Gong Y.-J. Bai F.-Z. Li Z.-Y. Hao 《Applied Physics A: Materials Science & Processing》2003,76(7):1061-1065
One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated
with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond,
through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures
of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond
single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and
the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy
suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown
diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously
in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively
larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles
in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)23C6, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought
not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be
associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical
size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic
theory during quenching from HPHT to room temperature and ambient pressure.
Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002
RID="*"
ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn 相似文献
947.
The influence of polymerization conditions on the morphology of thin films of poly-(N-methylaniline) (PNMA) was studied. The films were prepared by electropolymerization on gold and platinum electrodes and studied by optical and electron microscopy. It was demonstrated that the film morphology does not depend on the polymerization rate or on the electrode metal. However, it is sensitive to the kind of counter ion of PNMA. The polymers containing acetate or chloride do not form stable films. Polymer films containing phosphate or sulfate display inhomogeneous structures. A formation of sprouts and nanotubes was observed for PNMA sulfate. The films formed by PNMA perchlorate are smooth and transparent (glass-like structure). A sublayer of 4-aminothiophenol increases the adhesion of polymers to the gold surface. 相似文献
948.
Xiangjiu HeJiankuan Li Hao GaoFeng Qiu Ke HuXiangmin Cui Xinsheng Yao 《Tetrahedron》2003,59(34):6603-6607
Four new sulfonate metabolites of andrographolide, 14-deoxy-12(R)-sulfo andrographolide (Metabolite 1), 14-deoxy-12(S)-sulfo andrographolide (Metabolite 2), 14-deoxy-12(R)-sulfo-9(S)-andrographolide (Metabolite 3) and 14-sulfo isoandrographolide (Metabolite 4), were isolated from urine and feces in rats. Their structures were elucidated by chemical and spectroscopic analyses. These four metabolites were formed through a rare metabolic reaction and were all new compounds. 相似文献
949.
950.
[structure: see text] A library of 49 illudinoids was prepared via a three-step synthesis using a parallel synthesizer and solid-phase extractive purification. Products could be rapidly prepared for initial biological testing against three cancer cell lines, which revealed library members that inhibit nonsmall cell lung cancer. The activities of the library members are not easily correlated with structure, meaning the empirical approach used here is essential for such nonintuitive discoveries. 相似文献