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11.
12.
Bonner BE Buchanan JA Clement JM Corcoran MD Krishna NM Kruk JW Miettinen HE Moss RM Mutchler GS Nessi-Tedaldi F Nessi M Phillips GC Roberts JB Stevenson PM Tonse SR Birman A Chung SU Etkin A Fernow RC Kirk H Protopopescu SD Willutzki H Hallman T Madansky L Bar-Yam Z Dowd J Kern W King E Mayes BW Pinsky LS 《Physical review D: Particles and fields》1990,41(1):13-16
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The equilibrium volatilities at near infinite dilution of various solutes absorbed in molten polystyrene have been determined by a gas chromatographic technique. This method is much more rapid, although, with the present apparatus, probably less accurate than conventional static techniques. The primary parameters obtained from measurements of retention volumes are the Henry's law constants, from which are derived the weight and volume fraction activity coefficients, the Flory-Huggins interaction parameters, and the heats of dilution and solution. Of the solutes investigated, 2-butanone (MEK) was the least, and benzene the most compatible (highest and lowest volume fraction activity coefficients, respectively) with molten polystyrene. A small, but definite, variation of the activity coefficients with polystyrene molecular weight was observed. 相似文献
15.
King RB 《Dalton transactions (Cambridge, England : 2003)》2004,(21):3420-3424
Nickel and palladium atoms with their closed-shell d(10) electronic configurations are encapsulated in the icosahedral clusters [Ni@Ni(10)E(2)(CO)(18)](4-)(E = Sb, Bi, Sb[rightward arrow]Ni(CO)(3), CH(3)Sn and n-C(4)H(9)Sn) and the geometrically related pentagonal antiprismatic cluster Pd@Bi(10)(4+) found in Bi(14)PdBr(16). Such endohedral d(10) atoms in pentagonal antiprismatic clusters are donors of zero skeletal electrons and interact only weakly with the atoms in the surrounding polyhedron so that they may be regarded as analogous to endohedral noble gases in fullerenes such as He@C(60). On the other hand, endohedral nickel and palladium atoms in 10- and 11-vertex flattened deltahedral bare metal clusters of group 13 metals without five-fold symmetry, such as Ni@E(10)(10-) found in Na(10)NiE(10)(E = Ga, In) and Pd@Tl(11)(7-) found in A(8)Tl(11)Pd (A = Cs, Rb, K), interact significantly with the cluster atoms, particularly those at the flattened vertices of the deltahedron. The role of endohedral d(10) atoms Ni and Pd in polyhedra with five-fold symmetry as "pseudo-noble-gases" can be related to their positions at the "composite divide" of the "Metallurgists' Periodic Table" proposed by H. E. N. Stone on the basis of alloy systematics as well as the equivalence of the five d orbitals in polyhedra with five-fold symmetry. 相似文献
16.
This paper describes the synthesis of three neutral water soluble poly(amidoamine) (PAMAM) dendrimer derivatives. The ability of the two larger dendrimers to bind small acidic hydrophobic molecules is reported. Spectroscopic data and pH behaviour suggested that the acidic hydrophobes were forming stable ion pairs with the dendrimer's internal, basic tertiary nitrogens. With respect to forming 1:1 and 2:1 substrate/dendrimer complexes, both of the larger dendrimers were equally efficient at binding. All dendrimer/substrate complexes were completely miscible with water in all proportions (i.e. infinitely water soluble). When the bound substrates are drug moieties, then the resulting complexes could be considered as potential drug delivery systems. Flow calorimetry demonstrated that the dendrimers were able to release their hydrophobic guests when in contact with a biological cell. 相似文献
17.
The water gas shift reaction (CO + H2O = CO2+ H2) is catalyzed by aqueous metal carbonyl systems derived from simple mononuclear carbonyls such as Fe(CO)5 and M(CO)6 (M = Cr, Mo, and W) and bases in the 140–200 °C temperature range. The water gas shift reaction in a basic methanol-water solution containing Fe(CO)5 is first order in [Fe(CO)5], zero order in [CO], and essentially independent of base concentration and appears to involve an associative mechanism with a metallocarboxylate intermediate [(CO)4Fe-CO2H]–. The water gas shift reactions using M(CO)6 as catalyst precursors are first order in [M(CO)6], inverse first order in [CO], and first order in [HCO2
–] and appear to involve a dissociative mechanism with formatometallate intermediates [(CO)5M-OCHO]–.The Reppe hydroformylation of ethylene to produce propionaldehyde and 1-propanol in basic solutions containing Fe(CO)5 occurs at 110–140 °C. This reaction is second order in [Fe(CO)5], first order in [C2H4] up to a saturation pressure >1.5 MPa, and inhibited by [CO]. These experimental results suggest a mechanism where the rate-determining step involves a binuclear iron carbonyl intermediate. The substitution of Et3N for NaOH as the base facilitates the reduction of propionaldehyde to 1-propanol but results in a slower rate for the overall reaction.The homogeneous photocatalytic decomposition of the formate ion to H2 and CO2 in the presence of Cr(CO)6 appears to be closely related to the water gas shift reaction. The rate of H2 production from the formate ion exhibits saturation kinetics in the formate ion and is inhibited by added pyridine. The infrared spectra of the catalyst solutions indicate an LCr(CO)5 intermediate. Photolysis of the Cr(CO)6/formate system in aqueous methanol in the presence of an aldehyde RCHO (R =n-heptyl,p-tolyl, andp-anisyl) results in catalytic hydrogenation of the aldehyde to the corresponding alcohol RCH2OH by the formate ion. Detailed kinetic studies onp-tolualdehyde hydrogenation by this method indicates saturation kinetics in formate ion, autoinhibition by thep-tolualdehyde, and a threshold effect for Cr(CO)6 at concentrations >0.004 mol L–1. The presence of an aldehyde can interrupt the water gas shift catalytic cycle by interception of an HCr(CO)5
– intermediate by the aldehyde.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1533–1539, September, 1994. 相似文献
18.
19.
A variety of simple alkyl and aryl isocyanides have been polymerized using 0.5% NiCl2 in ethanol as a catalyst. The resulting poly(iminomethylenes) have been characterized by carbon-13 NMR spectroscopy and their polystyrene-equivalent molecular weights have been determined by gel permeation chromatography. Straight chain aliphatic isocyanides having from three to ten carbon atoms in the chain form readily solyble polymers having molecular weights (Mw) in the general range 10,000 to 30,000. Neopentyl isocyanide unlike tert-butyl isocyanide forms an insoluble polymer. A number of new soluble aryl isocyanide polymers have been obtained. However, aryl isocyanides having a single alkyl substituent (CH3, C2H5, CF3) in the ortho position give only insoluble polymers, whereas aryl isocyanides having alkyl substituents in both ortho positions (e.g., 2,6-(CH3)2C6H3NC and 2,4,6-(CH3)3C6H2NC) fail to polymerize under these conditions. The highest molecular weight soluble aryl isocyanide homopolymer is obtained from 3-CH3OC6H4NC(Mw = 26,000). The trimethylsilyl substituted isocyanide (CH3)3SiCH2CH2NC has been obtained from LiCH2NC and (CH3)SiCH2Cl and gives a brown soluble homopolymer with a molecular weight (Mw) of 19,000. 相似文献
20.
King NC Dickinson C Zhou W Bruce DW 《Dalton transactions (Cambridge, England : 2003)》2005,(6):1027-1032
Mesoporous silicates are prepared by templating on the hexagonal (H1) mesophase of surfactant bipyridine complexes of ruthenium(II) using a true liquid-crystal templating approach. On calcination, the surfactant template is removed except for the central metal ion that is oxidised, forming nanoparticles of RuO2 that deposit within the pores. RuO2 is a known oxidation catalyst and, despite its anhydrous nature in these silicates, is found to be very active in catalyzing the oxidation of water by acidic CeIV. 相似文献