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991.
Tchebotareva N Yin X Watson MD Samorì P Rabe JP Müllen K 《Journal of the American Chemical Society》2003,125(32):9734-9739
An alkylated hexa-peri-hexabenzocoronene with a covalently tethered pyrene unit serves as a model to study self-assembling discotic pi-system dyads both in the bulk and at a surface. Wide-angle X-ray scattering, polarized light microscopy, and differential scanning calorimetry revealed bulk self-assembly into columnar structures. Relative to a control without a tethered pyrene, the new dyad exhibits a more ordered columnar phase at room temperature but with dramatically lowered isotropization temperature, facilitating homeotropic alignment. These two features are important for processing such materials into molecular electronic devices, e.g., photovoltaic diodes. Scanning tunneling microscopy at a solution-solid interface revealed uniform nanoscale segregation of the large from the small pi-systems, leading to a well-defined two-dimensional crystalline monolayer, the likes of which may be employed in the future to study intramolecular electron transfer processes at surfaces, on the molecular scale. 相似文献
992.
Antiochia R Lavagnini I Pastore P Magno F 《Bioelectrochemistry (Amsterdam, Netherlands)》2004,64(2):157-163
Cyclic voltammetry was successfully applied to study the oxidation of nicotinamide adenine dinucleotide (NADH) both in homogeneous and heterogeneous phase. The first case was realized with a solution containing p-methylamino-phenolsulphate (MAP) as redox mediator and the diaphorase (DI) from Clostridium kluveri as enzyme while the second one by using both a glassy carbon (GC) and a carbon nanotube paste (CNTP) electrode modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde (3,4-DHB). Such systems were successively coupled with glucose dehydrogenase (GDH) reaction to realize the redox chain present in glucose biosensors. A critical comparison of the two systems was also reported. 相似文献
993.
Bersani D Antonioli G Lottici PP Casoli A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(10):2409-2417
Micro-Raman spectroscopy, combined with gas chromatography and ultra-violet fluorescence photography, was used to study some wall paintings in the S. Giovanni Evangelista Abbey in Parma, Italy. The restoration of some painted chapels enabled a comparison between two painters of the 16th century: Parmigianino (Girolamo Francesco Maria Mazzola, 1503-1540) and Michelangelo Anselmi (1492?-1556?). Micro-Raman spectroscopy determined the palette used by the artists, leading to the identification of different white, yellow, red, brown, green, blue and black pigments. Some pigments are evidence of later restorations. Gas chromatography combined with mass spectroscopy revealed the presence of organic binding media and enabled to distinguish between fresco and secco paintings. 相似文献
994.
Gaetano Liso Giuseppe Trapani Vincenza Berardi Paolo Marchini 《Journal of heterocyclic chemistry》1980,17(2):377-379
The title compounds ( 3a-c ) together with the benzothiazolines ( 4b-c ) were obtained by reaction between 2,2′ -dithiodianiline ( 1 ) and acetylenic ketone ( 2a ) or esters ( 2b-c ). A possible pathway involving the formation and subsequent cyclization to 3 of enamine intermediates A and/or B , is suggested. 相似文献
995.
Ottaviani P Giuliano M Velino B Caminati W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(2):538-543
The 1:1 molecular complex between oxetane and water has been investigated by using free-jet millimeter-wave spectroscopy. The rotational spectra of five isotopomers (with H(2)O, D(2)O, DOH, HOD and H(2) (18)O) have been assigned. Partial r(0) and r(s) structures of the complex have been derived. The water moiety lies in the plane of symmetry of oxetane, with the "free" hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the C(beta) carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an O(ring).H distance of about 1.86 A, and the angle between the COC bisector and the O(ring).H bond being congruent with 106 degrees. Additionally, quantum-chemical calculations for the complex were performed and were found to be in agreement with the experimental results. 相似文献
996.
997.
Giuseppe Storti Gianmarco Polotti Paolo Canu Massimo Morbidelli 《Journal of polymer science. Part A, Polymer chemistry》1992,30(5):751-777
A model for evaluating instantaneous degree of polymerization distribution and the chain composition distribution of copolymers produced in emulsion is developed. The approach adopted is based on the mathematics of Markov processes and represents an extension of the one developed for homopolymers in Part I. As in the homopolymer case, the main aspect of the theoretical treatment is the definition of the proper one step transition probability matrix through the so called subprocess-main process procedure. The model accounts for monomolecular and bimolecular termination (both by combination and disproportionation) and, in principle, it can be applied to any number of reacting monomer species as well as to any number of active chains per particle. However, only the 0–1–2 and 0–1–2–3 emulsion copolymerization systems are discussed in detail. In the case of the chain composition distribution, the model allows the calculation of its moments only, through the method of the Generating Function associated with the probability density function. The expression obtained for the instantaneous probability density functions, as well as for the corresponding cumulative distributions, are all in explicit form and involve only algebraic operations among matrices. Efficient numerical procedure for their application are reported in the Appendix. Illustrative calculations are reported for a 0–1–2–3 copolymerization system, simulating the copolymer styrene–methylmethacrylate. The effect of the various termination mechanisms on the distribution of degrees of polymerization and on the first two moments of the chain composition distribution is discussed in detail. Finally, the three dimensional overall distribution function of both chain length and composition is shown under the assumption of Gaussian type chain composition distribution. 相似文献
998.
N-Hydroxy-o-benzenedisulfonimide (now an easily accessible reagent) is a useful selective oxidizing agent; this is contrary to what was previously believed. The oxidation reactions of aldehydes to acids, benzyl alcohols to aldehydes, thiols to disulfides, and sulfides to sulfoxides were investigated (18 examples). 相似文献
999.
Sandro Calogero Paolo Ganis Valerio Peruzzo Giuseppe Tagliavini 《Journal of organometallic chemistry》1980,191(2):381-390
The halogenocarboxylates (cyclo-C6H11)3SnO2CR′, (R′ = CH3, CH2Cl, CHCl2, CCl3 and CF3) have been prepared, and characterized by Mössbauer and IR spectroscopy. The crystal structure of (cyclo-C6H11)3SnO2CCF3 has been determined by X-ray analysis. The crystals are orthorhombic, space group Pcmn, with unit cell parameters a 14.390 ± 0.004, b, 13.427 ± 0.004, c 11.516 ± 0.003 Å. The structure was resolved by Patterson methods and refined to an R value of 0.147. The coordination about the tin atom can be considered distorted trigonal-pyramidal or distorted tetrahedral. Mössbauer data are explained in terms of distortions of bond angles about the tin atom. 相似文献
1000.
Roberto Antonioletti Savina MalanconaFabrizio Cattaruzza Paolo Bovicelli 《Tetrahedron》2003,59(10):1673-1678
The I2-induced cyclisation of 2-alkenyl-1,3-dicarbonyl compounds with the mono- and di-substituted double bond occurred with good diastereoselectivity. A study of stereochemical aspects for different substituents on the allyl side chain was carried out. When the substituents were alkyl groups, the trans isomers formed preferentially, in the case of aromatic substituents the reaction lead instead to cis isomers. 相似文献