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81.
Vallée RA Marsal P Braeken E Habuchi S De Schryver FC Van der Auweraer M Beljonne D Hofkens J 《Journal of the American Chemical Society》2005,127(34):12011-12020
Experimental (Single Molecule Spectroscopy) and theoretical (quantum-chemical calculations and Monte Carlo and molecular dynamics simulations) techniques are combined to investigate the behavior and dynamics of a polymer-dye molecule system. It is shown that the dye molecule of interest (1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-dicarbocyanine) adopts two classes of conformations, namely planar and nonplanar ones, when embedded in a poly(styrene) matrix. From an in-depth analysis of the fluorescence lifetime trajectories, the planar conformers can be further classified according to the way their alkyl side chains interact with the surrounding poly(styrene) chains. 相似文献
82.
The reaction potential map (RPM) method has been extended so that the molecular reactivity towards nucleophiles can be analyzed. An anion consisting of the nucleus with + 1 charge and a pair of electrons was adopted as the model nucleophile. From the interaction energy between a substrate and this model particle, RPM and its component maps were obtained. With respect to practical applications, the reactivities of acrylic acid and acrylonitrile towards nucleophiles were examined. In these molecules, the exchange interaction as well as the charge-transfer interaction were found to be very important in the elucidation of the observed site selectivity. 相似文献
83.
Kiyoshi Hasebe Satoshi Hikima Hitoshi Yoshida 《Fresenius' Journal of Analytical Chemistry》1991,339(4):261-263
Summary The covalent bonding of l-lactate oxidase (no E.C.) to cross-linked copolymers of chitosan (Chitopearl) using the glutaraldehyde method is described and applied to the determination of l-lactate in serums of diseased and normal animals. The bioreactor packing of the immobilized enzyme is stable for at least 4 months and can be continuously used for the rapid and simple determination of l-lactate. The reduction current of pyruvate, corresponding to the product of enzymatic reaction, is determined by differential pulse polarography. The reproducibility (RSD) for 10 mol/l l-lactate is 0.78% (n=6) and the detection limit is 0.62 mol/l (k=2, confidence level 97.72%). 相似文献
84.
Y. -F. Lu M. Takai T. Nakata S. Nagatomo S. Namba 《Applied Physics A: Materials Science & Processing》1991,52(2):129-134
Maskless deposition of nickel lines on single crystalline Mn-Zn ferrite (MnO:ZnO:Fe2O3=31:17:52) has been investigated in a NiSO4 aqueous solution by Ar+ laser irradiation. A high deposition rate of up to 36.4m/s was achieved by a single scan of laser beam. The purity of deposited nickel layers is up to 86%. In particular, well-defined values of laser power and laser irradiation time were necessary for effective deposition. The deposition process was found to be a thermochemical process.On leave from D. S. Scanner Co., Ltd., 5-3-7. Fukushima, Osaka 553, Japan 相似文献
85.
86.
Accurate, practical prediction of 13C NMR chemical shifts has been achieved with a new system, CAST/CNMR, taking account of stereochemistry. The CAST/CNMR system has solved the critical problem of the accurate distinction of differences and similarities in stereochemical structures around a specific carbon, which has not yet been achieved by any other database-oriented system for prediction of 13C NMR chemical shifts. CAST/CNMR uses a three-dimensional structural database together with a 13C NMR spectral database. Absolute/relative configurational and conformational structural information are described by the CAST (CAnonical-representation of STereochemistry) coding method. This paper provides an overview of the CAST/CNMR system, and describes its application to two natural products as examples. 相似文献
87.
Detailed investigation on the origin of the acidity of the alpha-protons of a set of the carbonyl molecules was carried out on the basis of properties of the localized molecular orbital. An anomalously high acidity of Meldrum's acid, as compared with those of dimedone and dimethyl malonate, is one of the well-known but unresolved issues. The well-localized sigma orbitals of the C-H bonds at the alpha-position of the carbonyl groups can be obtained with the reactive hybrid orbital (RHO) theory. We found that the energy levels of the unoccupied RHOs of the C-H moiety of Meldrum's acid and other carbonyl compounds showed a good linear correlation with the experimental deprotonation energies. This is probably because the deprotonation reaction to form the proposed naked anions in a polar solvent is a highly endothermic process, in which the thermodynamic energy differences between the neutral molecules and the corresponding anions approximately coincide with the activation energies. We also investigated the effect of the conformational change upon deprotonation on the electron-accepting energy level of the relevant C-H bonds of cyclic/acyclic and monocarbonyl/dicarbonyl compounds. A conformational change occurs in the cases of cyclic six-membered compounds, but its influence on the reactivity of the C-H bond is small. The acidity of dicarbonyl compounds, including Meldrum's acid, showed a good correlation with the deviations from the perpendicular position of the dihedral angles of the relevant C-H bond with respect to the adjacent carbonyl C=O bond. This angle parameter can be related to the magnitude of the in-phase orbital interaction between the sigma(CH) and pi(C)(=)(O) orbitals, which facilitate electron acceptance. These results indicated that the acidity of the alpha-proton of carbonyl compounds can be represented in terms of the electron-accepting orbital levels of the unoccupied RHO of the C-H moiety. All the linear relationships found in the present work strongly suggested that the acidity of Meldrum's acid, which is conventionally regarded as an anomaly, is consistent with those of the other carbonyl compounds. 相似文献
88.
Toshimasa Katagiri Yasuyuki Fujiwara Satoshi Takahashi Kenji Uneyama 《Journal of fluorine chemistry》2005,126(8):1134-1139
A structural feature of hydrogen bonding chains found in the crystals of trifluoromethylated amino alcohols is reported. Hydrogen bondings of 3-(N,N-dialkylamino)-1,1,1-trifluoro-2-propanols construct chiral spiral hydrogen bonding chains. Lone pairs on the nitrogen atoms of the amino alcohols participate in two hydrogen bondings. Detailed structural analysis of the hydrogen bonds of the 3-(N,N-dimethylamino)-1,1,1-trifluoro-2-propanol suggested that the chain built up with alternating intermolecular-medium and intramolecular-weak hydrogen bonds. The medium intermolecular hydrogen bond, which transfers a proton from the hydroxy group to the amino nitrogen, would make a tentative zwitterionic form of the molecule. Then, electrostatic attraction between the charges in the zwitterion centers induced a weak intramolecular hydrogen bond. 相似文献
89.
Enami S Yamanaka T Hashimoto S Kawasaki M Tonokura K 《The journal of physical chemistry. A》2005,109(27):6066-6070
The reactions of Cl atoms with RI (R = n-C3H7, n-C4H9, cyclo-C6H11, C6H5, C6F5, and p-CH3C6H4) have been studied using cavity ring-down spectroscopy at a temperature range of 233-313 K and at 100 Torr total pressure of N2 diluent. Visible absorption spectra of the RI-Cl adducts were recorded at 440-520 nm at 263 K. The yields of the adducts were temperature-dependent. There was no discernible reaction of the adducts in the presence of 100 Torr of O2 at 263 K. Theoretical calculations were performed for C4H9I-Cl and C6H5I-Cl for quantitative explanation of the absorption spectra and the strength of the I-Cl bonds in the charge-transfer complexes. Evidence for the adduct formation following the reaction of Cl with C6H5Br was sought but not found at 440 and 520 nm. 相似文献
90.
Shinsuke Takagi Miharu Eguchi Tetsuya Shimada Satoshi Hamatani Haruo Inoue 《Research on Chemical Intermediates》2007,33(1-2):177-189
Photochemical energy transfer of non-aggregated cationic porphyrins on an anionic-type clay (Smecton SA) surface was investigated. The efficiency of energy transfer and excited-state quenching in the absence of energy transfer were evaluated at various loading levels of porphyrin on the clay surface and were found to be significantly affected by the loading level. As the latter increased, both energy transfer efficiency and excited-state quenching increased. Judging from the dependency of energy-transfer efficiency on the porphyrin loading level, a partially clustered structure, but without aggregation, of porphyrins on the clay surface is proposed. 相似文献