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31.
32.
Abe K Abt I Acton PD Agnew G Ash WW Aston D Bacchetta N Baird KG Baltay C Band HR Baranko G Bardon O Battiston R Bazarko AO Bean A Belcinski RJ Ben-David R Benvenuti AC Biasini M Bienz T Bilei GM Bisello D Blaylock G Bogart JR Bolton T Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Busza W Calcaterra A Caldwell DO Calloway D Camanzi B Carpinelli M Carr J Cassell R Castaldi R Castro A Cavalli-Sforza M Chadwick GB Chen L Church E Claus R Cohn HO Coller JA Cook V Cotton R 《Physical review letters》1993,71(16):2528-2532
33.
Arturo ArduiniElisabetta Brindani Giovanna GiorgiAndrea Pochini Andrea Secchi 《Tetrahedron》2003,59(38):7587-7594
The synthesis of new hosts specifically designed for the recognition of neutral guests bearing donor-acceptor hydrogen bonding groups is described. These hosts are characterized by the presence of two distinct binding region in close proximity: the rigid π-donor cavity and the H-bond donor N-methylene-N′-phenylureido group inserted onto the upper rim of the calix[4]arene skeleton. The binding abilities of these receptors were investigated toward a series of neutral ditopic organic molecules in CDCl3 solution by 1H NMR spectroscopy. The results obtained show that rigidity of the calix[4]arene apolar cavity is the control element in determining efficiency. In fact, compared with the more rigid 2, host 10, where the rigidity of the cone structure is maintained by hydrogen bonding of the OH of the lower rim, a decrease of efficiency of almost one order of magnitude was observed. The cooperative effect of the two binding region of host 2 was verified with different classes of ditopic guests. Good efficiency in the recognition of urea derivatives and dimethylsulfoxide was achieved. 相似文献
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Arduini A Brindani E Giorgi G Pochini A Secchi A 《The Journal of organic chemistry》2002,67(17):6188-6194
A novel heteroditopic receptor (5) based on a rigid calix[4]arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications. 相似文献
36.
Jean-Philippe Demaret † Simone Brunie Jean-Pierre Ballini Paul Vigny 《Photochemistry and photobiology》1989,50(1):7-21
The results of molecular mechanical calculations on intercalation complexes of 3-carbethoxypsoralen, 5-methoxypsoralen, 8-methoxypsoralen, 7-methylpyrido[3,4-c]psoralen (MepyPs) and 7-methylpyrido[4,3-c]psoralen (2N-MePyPs) with the double stranded duodecanucleotide d(CGCGATATCGCG)2 are presented. In the energy-minimized structures, the psoralens are intercalated with their plane orthogonal to the helix axis. Stacking interactions between the furan ring of the psoralen and the adjacent bases are maximized in most derivatives studied, whereas the effect of the various substituents of the psoralen ring is to specifically push part of the molecule towards either the minor or the major groove, preventing a symmetrical intercalation (with respect to the two strands of the DNA). The relative position of the psoralen ring and of the adjacent thymine foreshadows the formation of furan-side monoadducts in 3-CPs, MePyPs and 2N-MePyPs, whereas the formation of a pyrone-side monoadduct appears as geometrically more favourable in 5-MOP and both furan- and pyrone-side monoadducts can be geometrically envisaged in 8-MOP. A good correlation therefore exists between the more or less favourable equilibrium geometries and the experimentally observed photoreactions. The present study is the first attempt to characterize the geometrical parameters as part of a complex set of geometrical, dynamical and excited state parameters governing the overall DNA-psoralen photoreaction. 相似文献
37.
E. Alabiso P. Ciambelli V. De Simone C. Porcellu R. Valentino 《Reaction Kinetics and Catalysis Letters》1979,12(4):451-456
The catalytic activity of a chabazite tuff in the partial oxidation of H2S to sulfur has been determined. The effects of temperature, feed concentration and chemical composition of the tuff on H2S conversion and selectivity to sulfur have been investigated. Encouraging results in view of a possible use in H2S removal processes have been obtained.
H2S . , H2S . H2S.相似文献
38.
39.
Synthesis and Crystal Structure of [(n‐Bu)4N][W6Cl18] Single‐crystals of [(n‐Bu)4N][W6Cl18] were obtained as thin needles by adding methanol to a solution of W6Cl18 and [(n‐Bu)4N]Cl in tetrahydrofuran. The structure was determined by single‐crystal X‐ray diffraction at 210 K. [(n‐Bu)4N][W6Cl18] crystallizes in the monoclinic space group C 2/c with Z = 8 and the lattice parameters a = 2175.6(1) pm, b = 1738.0(1) pm, c = 2160.36(9) pm, and β = 91.680(5) °. The crystal structure contains isolated [(W6Cl12i)Cl6a]— clusters and [(n‐Bu)4N]+ ions. 相似文献
40.
We studied the thermal diffusion behavior of poly(N-isopropylacrylamide) (PNiPAM) in ethanol in a temperature range from T = 14.0 degrees C to T = 40.0 degrees C by means of thermal diffusion forced Rayleigh scattering. The obtained Soret coefficient S(T) of PNiPAM was positive for lower temperatures (T < 34 degrees C), while S(T) showed a negative value for higher temperatures (T > 34 degrees C). This means PNiPAM molecules move to the cold side for temperatures T < 34 degrees C, whereas they move to the warm side for T > 34 degrees C. This is the first nonaqueous polymeric system for which a sign change with temperature has been observed. We performed static and dynamic light scattering experiments in the same temperature range. The second virial coefficient determined from dilute solutions by static light scattering (SLS) was positive in the comparable temperature range. The results of SLS for the semidilute solution showed a strong repulsion among PNiPAM chains which was enhanced by increasing temperature. These results imply that the observed thermally induced sign change of S(T) does not depend on the intermolecular interactions among PNiPAM chains. 相似文献