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181.
An automatic sequence is generated by a finite machine (automaton). These sequences can be periodic or not: in the latter case however, they are not random, but rather quasicrystalline. We consider an Ising chain with variable interaction in a uniform external field, at zero temperature, and prove that, if this interaction is automatic, then the induced magnetic field is also automatic. 相似文献
182.
The asymmetric reduction of phenylalkylketones p-X-C6H4COR (X = H, R = C2H5, 1C3H7, 1C4H9 and R = C2H5, X = CH3, OCH3, Cl, CF3) with chiral aromatic Grignard reagents p-YC6H4-CH(C2H5) CH2MgCl (Y = H, OCH3, CF3) give optically active phenylalkylcarbinols. The absolute configuration and the enantiomeric excess depends on electronic effects of substituents carried by the organomagnesium reagent and/or ketone. 相似文献
183.
Sanjay Kumar Mishra Dhananjai Pandey Pierre Ranson Jean-Paul Pinan-Lucarre 《Journal of solid state chemistry》2005,178(9):2846-2857
Results of powder X-ray diffraction and Raman scattering studies on the phase transitions in Sr1−xCaxTiO3 (SCT) are presented for x=0.04, 0.06 and 0.12 in the temperature range 8-473 K. It is proposed that the space group of SCT in the composition range 0.06?x?0.35 is Imma with a0b-b- tilt system and not I4/mcm with a0a0c- tilt system, as assumed by earlier workers. The lowering of the crystal symmetry from I4/mcm to Imma is supported by the observation of additional Raman lines, in agreement with the factor group analysis for the Imma space group. The structural Eg mode, characteristics of the non-cubic phase, is shown to be present even in the cubic phases of x=0.06 and x=0.12 but not of x=0.04 indicating the change in the local structure of the cubic phase of SCT for x?0.06. The presence of symmetry forbidden TO2 mode in the Raman spectra of the cubic phase of SCT for x<0.06 and its absence for x?0.06 provides yet another characteristic feature distinguishing the I4/mcm and Imma space groups. The implications of the change in the tilt system from a0a0c- to a0b-b- on the development of the polar order is also discussed. 相似文献
184.
Amoureux JP Flambard A Delevoye L Montagne L 《Chemical communications (Cambridge, England)》2005,(27):3472-3474
We show that by combining the intrinsically larger (with respect to MQMAS) efficiency of Double-Quantum Filtered Satellite-Transition MAS (DQF-STMAS), with the large S/N gain of the Soft-Pulse Added Mixing (SPAM) concept, a new very sensitive high-resolution solid-state NMR method can be obtained for semi-integer quadrupolar nuclei. 相似文献
185.
Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct enantioseparation of substituted [1-(imidazo-1-yl)-1-phenylmethyl)]-benzothiazolinone and benzoxazolinone derivatives with one chiral center. Those analogues of fadrozole constitute new potent nonsteroidal inhibitors of aromatase (P450 arom). The separations were made using normal phase methodology with a mobile phase consisting of n-hexane-alcohol (ethanol, 1-propanol, or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes along with the temperature of the column on the discrimination between the enantiomers were examined. Baseline separation (Rs > 1.5) was easily obtained in many cases. 相似文献
186.
187.
Solid-phase synthesis of fullerene-peptides 总被引:1,自引:0,他引:1
Pantarotto D Bianco A Pellarini F Tossi A Giangaspero A Zelezetsky I Briand JP Prato M 《Journal of the American Chemical Society》2002,124(42):12543-12549
The solid-phase synthesis of peptides (SPPS) containing [60]fullerene-functionalized amino acids is reported. A new amino acid, fulleropyrrolidino-glutamic acid (Fgu), is used for the SPPS of a series of analogues of different length based on the natural Leu(5)-Enkephalin and on cationic antimicrobial peptides. These fullero-peptides were prepared on different solid supports to analyze the influence of the resin on the synthesis. Optimized protocols for the coupling and deprotection procedures were determined allowing the synthesis of highly pure peptides in sufficient quantities for evaluation of biological activities. In particular, to avoid side reactions of the fullerene moiety with bases and nucleophiles, the removal of the protecting groups was performed under inert conditions (nitrogen or argon in the dark). We have encountered serious problems with the recovery of the crude compounds, especially when Fgu was inserted in the proximity of the resin core as fullero-peptides tend to remain embedded inside the resin. Eventually, all of the fullero-peptides were easily purified, and the cationic peptides were tested for their antimicrobial activities. They displayed a specific activity against the Gram-positive bacterium S. aureus and also lysed erythrocytes. The availability of a fullero-amino acid easily useable in the SPPS of fullero-peptides may thus open the way to the synthesis of new types of biologically active oligomers. 相似文献
188.
189.
Francesca Cardullo Paul Seiler Lyle Isaacs Jean-Franois Nierengarten Richard F. Haldimann Franois Diederich Tiziana Mordasini-Denti Walter Thiel Corinne Boudon Jean-Paul Gisselhrccht Maurice Gross 《Helvetica chimica acta》1997,80(2):343-371
By the tether-directed remote functionalization method, a series of bis- to hexakis-adducts of C60, i.e., 1 – 7 (Fig. 1), had previously been prepared with high regioselectivity. An efficient method for the removal of the tether-reactive-group conjugate was now developed and its utility demonstrated in the regioselective synthesis of bis- to tetrakis(methano)fullerenes ( = di- to tetracyclopropafullerenes-C60-Ih) 9 – 11 starting from 4, 5, and 7, respectively (Schemes 2, 4, and 5). This versatile protocol consists of a 1O2 ene reaction with the two cyclohexene rings in the starting materials, reduction of the formed mixture of isomeric allylic hydroperoxides to the corresponding alcohols, acid-promoted elimination of H2O to cyclohexa-1,3-dienes, Diels-Alder addition of dimethyl acetylenedicarboxylate, retro-Diels-Alder addition, and, ultimately, transesterification. In the series 9 – 11 , all methano moieties are attached along an equatorial belt of the fullerene. Starting from C2v-symmetrical tetrakis-adduct 15 , transesterification with dodecan-1-ol or octan-1-ol yielded the octaesters 16 and 17 , respectively, as noncrystalline fullerene derivatives (Scheme 3). The X-ray crystal structure of a CHCl3 solvate of 11 (Fig. 3) showed that the residual conjugated π-chromophore of the C-sphere is reduced to two tetrabenzopyracylene substructures connected by four biphenyl-type bonds (Fig. 5). In the eight six-membered rings surrounding the two pyracylene (= cyclopent[fg]acenaphthylene) moieties, 6–6 and 6–5 bond-length alteration (0.05 Å) was reduced by ca. 0.01 Å as compared to the free C60 skeleton (0.06 Å) (Fig. 4). The crystal packing (Fig. 6) revealed short contacts between Cl-atoms of the solvent molecule and sp2- and sp3-C-atoms of the C-sphere, as well as short contacts between Cl-atoms and O-atoms of the EtOOC groups attached to the methano moieties of 11 . The physical properties and chemical reactivity of compounds 1 - 11 were comprehensively investigated as a function of degree and pattern of addition and the nature of the addends. Methods applied to this study were UV/VIS (Figs. 7–11), IR, and NMR spectroscopy (Table 2), cyclic (CV) and steady-state (SSV) voltammetry (Table 1), calculations of the energies of the lowest uunoccupied mmolecular orbitals (LUMOs) and electron affinities (Figs. 12 and 13), and evaluation of chemical reactivity in competition experiments. It was found that the properties of the fullerene derivatives were not only affected by the degree and pattern of addition but also, in a remarkable way, by the nature of the addends (methano vs. but-2-ene-1, 4-diyl) anellated to the C-sphere. Attachment of multiple thano moieties along an equatorial belt as in the series 8 – 11 induces only a small perturbation of the original fullerene π-chromophore. In general, with increasing attenuation of the conjugated fullerene π-chromophore, the optical (HOMO-LUMO) gap in the UV/VIS spectrum is shifted to higher energy, the number of reversible one-electron reductions decreases, and the first reduction potential becomes increasingly negative, the computed LUMO energy increases and the electron affinity decreases, and the reactivity of the fullerene towards nucleophiles and carbenes and as dienophile in cycloadditions decreases. 相似文献
190.
Preparation of styryl derivatives of 2-phenyl-imidazo [1, 2-a]pyridine 2-(p-Tolyl)-imidazo [1, 2-a]pyridines and 7-methyl-2-phenyl-imidazo [1,2-a]-pyridines can be converted, in dimethylformamide, on reaction with anils of aromatic aldehydes in the presence of potassium hydroxide or potassium t-butoxide, into the corresponding 2-(stilben-4-yl)- and 2-phenyl-7-styry1-imidazo [1, 2-a]-pyridines (‘Anil-Synthesis’). The 2-(p-tolyl)-imidazo [1,2-a]pyridines react far less readily than the 7-methyl-2-phenyl-imidazo[1,2-a]pyridines. 相似文献