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971.
Hirotsugu Kobayashi Kohtaro Okada Takashi Iwashita Nobuhiro Fusetani 《Tetrahedron》2007,63(29):6748-6754
Three new serinolipid derivatives, shishididemniols C (1), D (2), and E (3), were isolated as antibacterial constituents of a tunicate of the family Didemnidae. Their planar structures were elucidated by interpretation of NMR and MS data, whereas the absolute stereochemistry was determined by chemical conversions. Shishididemniols C (3), D (4), and E (5) exhibited antibacterial activity against the fish pathogenic bacterium Vibrio anguillarum. 相似文献
972.
973.
Elongation factor Tu mutants expand amino acid tolerance of protein biosynthesis system 总被引:1,自引:0,他引:1
Doi Y Ohtsuki T Shimizu Y Ueda T Sisido M 《Journal of the American Chemical Society》2007,129(46):14458-14462
Nonnatural amino acids have been introduced into proteins using expanded protein biosynthesis systems. However, some nonnatural amino acids, especially those containing large aromatic groups, are not efficiently incorporated into proteins. Reduced binding efficiency of aminoacylated tRNAs to elongation factor Tu (EF-Tu) is likely to limit incorporation of large amino acids. Our previous studies suggested that tRNAs carrying large nonnatural amino acids are bound less tightly to EF-Tu than natural amino acids. To expand the availability of nonnatural mutagenesis, EF-Tu from the E. coli translation system was improved to accept such large amino acids. We synthesized EF-Tu mutants, in which the binding pocket of the aminoacyl moiety of aminoacyl-tRNA was enlarged. L-1-Pyrenylalanine, L-2-pyrenylalanine, and DL-2-anthraquinonylalanine, which are hardly or only slightly incorporated with the wild-type EF-Tu, were successfully incorporated into a protein using these EF-Tu mutants. 相似文献
974.
Hanczyc MM Toyota T Ikegami T Packard N Sugawara T 《Journal of the American Chemical Society》2007,129(30):9386-9391
Fatty acids have been investigated as boundary structures to construct artificial cells due to their dynamic properties and phase transitions. Here we have explored the possibility that fatty acid systems also demonstrate movement. An oil phase was loaded with a fatty acid anhydride precursor and introduced to an aqueous fatty acid micelle solution. The oil droplets showed autonomous, sustained movement through the aqueous media. Internal convection created a positive feedback loop, and the movement of the oil droplet was sustained as convection drove fresh precursor to the surface to become hydrolyzed. As the system progressed, more surfactant was produced and some of the oil droplets transformed into supramolecular aggregates resembling multilamellar vesicles. The oil droplets also moved directionally within chemical gradients and exhibited a type of chemotaxis. 相似文献
975.
The analytical method of determining enzyme activity by liquid chromatography-mass spectrometry (LC/MS) was developed and
applied for investigation of the effect of polycyclic aromatic hydrocarbons (PAHs) on the enzyme activity of chitinase. The
measurement of chitinase activity by LC/MS is useful in order to use the nonderivatized substrate, which can show in vivo
chitinase activity. Substrate consumption and product formation were monitored in order to determine chitinase activity. It
was shown that, for the first time, in vitro addition of PAHs inhibited the activity of chitinase in a noncompetitive manner.
The IC50 value of benzo[a]pyrene was 1.4 μM, and PAHs containing four or more aromatic rings showed the same or higher inhibitory effect, whereas PAHs
with a lower number of aromatic rings showed lower inhibition of the chitinase activity than benzo[a]pyrene. 相似文献
976.
Inagaki K Narukawa T Yarita T Takatsu A Okamoto K Chiba K 《Analytical and bioanalytical chemistry》2007,389(3):691-696
A coprecipitation method using sample constituents as carrier precipitants was developed that can remove molybdenum, which
interferes with the determination of cadmium in grain samples via isotope dilution inductively coupled plasma mass spectrometry
(ID-ICPMS). Samples were digested with HNO3, HF, and HClO4, and then purified 6 M sodium hydroxide solution was added to generate colloidal hydrolysis compounds, mainly magnesium hydroxide.
Cadmium can be effectively separated from molybdenum because the cadmium forms hydroxides and adsorbs onto and/or is occluded
in the colloid, while the molybdenum does not form hydroxides or adsorb onto the hydrolysis colloid. The colloid was separated
by centrifugation and then dissolved with 0.2 M HNO3 solution to recover the cadmium. The recovery of Cd achieved using the coprecipitation was >97%, and the removal efficiency
of Mo was approximately 99.9%. An extremely low procedural blank (below the detection limit of ICPMS) was achieved by purifying
the 6 M sodium hydroxide solution via Mg coprecipitation using Mg(NO3)2 solution. The proposed method was applied to two certified reference materials (NIST SRM 1567a wheat flour and SRM 1568a
rice flour) and CCQM-P64 soybean powder. Good analytical results with small uncertainties were obtained for all samples. This
method is simple and reliable for the determination of Cd in grain samples by ID-ICPMS.
Figure Overview of a coprecipitation method using sample constituents 相似文献
977.
Yoshizawa K Nakayama T Kamachi T Kozlowski PM 《The journal of physical chemistry. A》2007,111(5):852-857
The vibronic (vibrational-electronic) interactions in the pi-anion radicals of the metalloporphyrins (M=Cr, Mn, Fe, Co, Ni, Cu, and Zn), which show delocalized D4h structures in the neutral states, are discussed using B3LYP density-functional-theory calculations. The B1g and B2g modes of vibration can remove the degenerate 2Eg state of the pi-anion radicals in the D4h symmetric structures to lead to rectangular and diamond D2h distortions, respectively. Calculated vibronic coupling constants demonstrate that the B1g modes of vibration better couple with the degenerate electronic state, leading to the rectangular D2h distortion. In particular, the B1g modes of nu10 and nu11, which have dominant contributions from Calpha-Cm and Cbeta-Cbeta stretching, give large vibronic coupling constants in the pi-anion radicals. The vibronic coupling constant can be viewed as the Jahn-Teller distortion force, and therefore these C-C stretching B1g modes will play a central role in the Jahn-Teller effect of the pi-anion radicals of the metalloporphyrins. 相似文献
978.
Sakamoto M Unosawa A Kobaru S Fujita K Mino T Fujita T 《Chemical communications (Cambridge, England)》2007,(34):3586-3588
An asymmetric S(N)Ar reaction was performed by using molecular chirality generated and amplified by the spontaneous crystallization of achiral naphthamides; the chirality was retained in a cold solution, caused by slow racemization, and was transferred to stable axially chiral materials with high enantiomeric excesses. 相似文献
979.
Takahashi K Matsumura T Ishihara J Hatakeyama S 《Chemical communications (Cambridge, England)》2007,(40):4158-4160
A total synthesis of dysiherbaine, a potent agonist of AMPA-KA type glutamate receptors, has been accomplished in completely stereocontrolled manner starting from tri-O-acetyl-D-galactal in 25 steps and in 3% overall yield. 相似文献
980.
Shirahata T Kibune M Yoshino H Imakubo T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(27):7619-7630
The unsymmetrical pi donor dimethyl(ethylenedioxy)tetraselenafulvalene (DMEDO-TSeF) has provided six new organic superconductors with a monovalent square-planar [Au(CN)(4)](-) ion and cyclic ethers as solvent of crystallization. The six new organic superconductors kappa-(DMEDO-TSeF)(2)[Au(CN)(4)](solv.) [solv.=1,3-dioxolane (DOL), 2,5-dihydrofuran (DHF), tetrahydropyran (THP), 1,3-dioxane (1,3-DOX), 3,4-dihydro-2H-pyran (DHP), or 1,4-dioxane (1,4-DOX)] are classified into two subphases kappa(L) and kappa' according to the differences in their space group symmetry. kappa(L)-(DMEDO-TSeF)(2)[Au(CN)(4)](solv.) (solv.=DOL, DHF, THP, 1,3-DOX or DHP) crystallizes in the orthorhombic space group Pnma, and T(c) of the kappa(L) phase varies by 1.7-5.3 K according to the size and shape of the solvent of crystallization. On the other hand, kappa'-(DMEDO-TSeF)(2)[Au(CN)(4)](solv.) (solv.=DOL or 1,4-DOX) crystallizes in the noncentrosymmetric monoclinic space group Cc. The kappa'-phase containing 1,4-DOX shows superconductivity at 4.2 K, but the kappa'-phase containing DOL does not show superconductivity down to 1.4 K. Systematic investigation of the six new organic superconductors, together with the two previously reported superconductors kappa(H)- and kappa(L)-(DMEDO-TSeF)(2)[Au(CN)(4)](THF), revealed that the T(c) of the present system is finely tunable by utilizing the effect of the solvent of crystallization. 相似文献