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51.
Li BS Kang SZ Cheuk KK Wan L Ling L Bai C Tang BZ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7598-7603
In the present work, we investigated self-assembling of a poly(phenylacetylene) carrying L-valine pendants (PPA-Val) in a water/methanol solution, upon evaporation of the solution on mica, and on the water surface. With intercalation of a fluorescence probe of Ru(phen)2(dppx)2+ (phen = 1,10-phenanthroline, dppx=7,8-dimethyldipyridophenazine) into the hydrophobic cavities associated by the PPA-Val chains, their helical structures were directly detected in solution with an in situ fluorescence microscope. Helical aggregates were observed with AFM upon evaporation of the solvents, suggesting that the helical structures in the solution are the building blocks of the helical aggregates. Self-assembling structures of PPA-Val on the water surface were, however, very different from that formed upon evaporation of its THF solution on the mica surface. The polymer chains associated into a monolayer of extended fibers on the water surface, whereas superhelical fibers formed on the mica surface. Water molecules play a critical role in inducing the polymer to form diverse morphological structures in its bulk solution and on its surface. In solution, the isotropic hydrophobic effect drove the polymer chains to form superhelical aggregates, while on the water surface, the hydrophobic effect concentrated mainly on the lateral part of the polymer, thus giving a monolayer of extended fibers. 相似文献
52.
Amr Nour Al-Deen Douglas J. Cecchini Roger W. Giese 《Journal of chromatography. A》1992,600(2):229-233
A method has been developed in which the DNA of leukocytes (as the buffy coat from blood) is isolated in the form of its constituent deoxynucleotides. The steps in this method are as follows: (1) lyse the leukocytes with sodium dodecyl sulfate (SDS) and enzymatically digest the proteins and RNA, (2) remove the SDS on a non-polar adsorbent (Bio-Beads SM-4) and then trap the DNA on a quaternary amine silica cartridge, (3) wash the column with 1 M NaCl-buffer, (4) digest the DNA on the column with staphylococcal nuclease and (5) elute the digested DNA with 0.5 M NaCl-buffer and digest it further with bovine spleen phosphodiesterase II to deoxynucleotide-3′-monophosphates. From a 40-μl sample of butty coat was obtained 126 ± 14 μg (two experiments, eight sample total) of deoxynucleotides. Reversed-phase high-performance liquid chromatography, which removed the added enzymes, showed only peaks for deoxynucleotides. For comparison, the amount of deoxynucleotides obtained from the leukocytes by an automated phenol extraction procedure was 101 ± 5.4 μg (one experiment in triplicate). 相似文献
53.
54.
Talukder P Datta A Mitra S Rosair G El Fallah MS Ribas J 《Dalton transactions (Cambridge, England : 2003)》2004,(24):4161-4167
A new tridentate Schiff base ligand HL (L = C14H19N2O), derived from the condensation of benzoylacetone and 2-dimethylaminoethylamine in a 1:1 ratio, reacts with copper(ii) acetate and cyanate, thiocyanate or azide, to give rise to several end-to-end polymeric complexes of formulae [CuL(mu(1,3)-NCO)]n 1, [CuL(mu(1,3)-NCS)]n 2 and the complex 3 has two crystallographically independent units of formula [CuL(N3)] in the asymmetric unit cell. Complex 3 exists in dimeric form rather than as a polymeric chain. Compound 1 is the first report of a singly end-to-end cyanate bridged polymeric chain of Cu(II) with a Schiff base as a co-ligand. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones such as compound 2. We have characterized these complexes by analytical, spectroscopic, structural and variable temperature magnetic susceptibility measurements. The coordination geometry around the Cu(II) centers is distorted square pyramidal for 1 and 2 and square planar for complex 3. The magnetic susceptibility data show slight antiferromagnetic coupling for the polymers having J values -0.19 and -0.57 cm(-1) for complexes 1 and 2 respectively. The low values of J are consistent with the equatorial-axial disposition of the bridges in the polymers. 相似文献
55.
Khalfaoui M Knani S Hachicha MA Lamine AB 《Journal of colloid and interface science》2003,263(2):350-356
New theoretical expressions to model the five adsorption isotherm types have been established. Using the grand canonical ensemble in statistical physics, we give an analytical expression to each of five physical adsorption isotherm types classified by Brunauer, Emett, and Teller, often called BET isotherms. The establishment of these expressions is based on statistical physics and theoretical considerations. This method allowed estimation of all the mathematical parameters in the models. The physicochemical parameters intervening in the adsorption process that the models present could be deduced directly from the experimental adsorption isotherms by numerical simulation. We determine the adequate model for each type of isotherm, which fixes by direct numerical simulation the monolayer, multilayer, or condensation character. New equations are discussed and results obtained are verified for experimental data from the literature. The new theoretical expressions that we have proposed, based on statistical physics treatment, are rather powerful to better understand and interpret the various five physical adsorption type isotherms at a microscopic level. 相似文献
56.
The oxidation of some xylenols with iodine in aqueous ethanolic solutions in the presence of silver ions as a catalyst was investigated and used for microdetermination of these reductants. The study of these redox reactions and the microdetermination of these phenols were performed by volumetric and spectrophotometric methods. These methods were compared. The spectrophotometric method was more accurate at very low concentrations (60–488 μg). The volumetric methods used silver ions as catalyst. The potentiometric method is more accurate than the visual method. Possible schemes for the course of these redox reactions were suggested. One electron processes for oxidation of xylenols have been indicated. 相似文献
57.
CoSm(SeO3)2Cl, CuGd(SeO3)2Cl, MnSm(SeO3)2Cl, CuGd2(SeO3)4 and CuSm2(SeO3)4: Transition Metal containing Selenites of Samarium and Gadolinum The reaction of CoCl2, Sm2O3, and SeO2 in evacuated silica ampoules lead to blue single crystals of CoSm(SeO3)2Cl (triclinic, , Z = 4, a = 712.3(1), b = 889.5(2), c = 1216.2(2) pm, α = 72.25(1)°, β = 71.27(1)°, γ = 72.08(1)°, Rall = 0.0586). If MnCl2 is used in the reaction light pink single crystals of MnSm(SeO3)2Cl (triclinic, , Z = 2, a = 700.8(2), b = 724.1(2), c = 803.4(2) pm, α = 86.90(3)°, β = 71.57(3)°, γ = 64.33(3)°, Rall = 0.0875) are obtained. Green single crystals of CuGd2(SeO3)2Cl (triclinic, , Z = 4, a = 704.3(4), b = 909.6(4), c = 1201.0(7) pm, α = 70.84(4)°, β = 73.01(4)°, γ = 70.69(4)°, Rall = 0.0450) form analogously in the reaction of CuCl2 and Gd2O3 with SeO2. CoSm(SeO3)2Cl contains [CoO4Cl2] octahedra, which are connected via one edge and one vertex to infinite chains. The Mn2+ ions in MnSm(SeO3)2Cl are also octahedrally coordinated by four oxygen and two chlorine ligands. The linkage of the polyhedra to chains occurs exclusively via edges. Both, the cobalt and the manganese compound show the Sm3+ ions in eight and ninefold coordination of oxygen atoms and chloride ions. In CuGd(SeO3)2Cl the Cu2+ ions are coordinated by three oxygen atoms and one Cl— ion in a distorted square planar manner. One further Cl— and one further oxygen ligand complete the [CuO3Cl] units yielding significantly elongated octahedra. The latter are again connected to chains via two common edges. For the Gd3+ ions coordination numbers of ?8 + 1”? and nine were found. Single crystals of the deep blue selenites CuM2(SeO3)4 (M = Sm/Gd, monoclinic, P21/c, a = 1050.4(3)/1051.0(2), b = 696.6(2)/693.5(1), c = 822.5(2)/818.5(2) pm, β = 110.48(2)°/110.53(2)°, Rall = 0.0341/0.0531) can be obtained from reactions of the oxides Sm2O3 and Gd2O3, respectively, with CuO and SeO2. The crystal structure contains square planar [CuO4] groups and irregular [MO9] polyhedra. 相似文献
58.
Loferer MJ Webb BM Grant GH Liedl KR 《Journal of the American Chemical Society》2003,125(4):1072-1078
QM/MM methods were used to study the isomerization step from (2R)-methylmalonyl-CoA to succinyl-CoA. A pathway via a "fragmentation-recombination" mechanism is ruled out on energetic grounds. For the other radicalic pathway, involving an addition recombination step, geometries and vibrational contributions have been determined, and a barrier height of 11.70 kcal/mol was found. The effect of adjacent hydrogen-donating groups was found to reduce the energy barrier by 1-2 kcal/mol each and thus to provide a significant catalytic effect for this reaction. By means of molecular dynamics studies, the stereochemistry of the methylmalonyl-CoA mutase catalyzed reaction was examined. It is shown that TYR89 is essential for maintaining stereoselectivity of the abstraction of a hydrogen in the backreaction. The subsequent selective formation of one isomer of methylmalonyl-CoA is probably due to the presence of a bulky side chain. 相似文献
59.
Peña D López F Harutyunyan SR Minnaard AJ Feringa BL 《Chemical communications (Cambridge, England)》2004,(16):1836-1837
Highly enantioselective Cu-catalysed 1,4-addition of diphenylzinc to cyclohexenone has been achieved for the first time using a monodentate phosphoramidite ligand. 相似文献
60.
Ben Salah M Vilminot S Richard-Plouet M André G Mhiri T Kurmoo M 《Chemical communications (Cambridge, England)》2004,(22):2548-2549
The synthetic mineral Co(II)5(OH)6(SO4)2(H2O)4 (1), obtained by hydrothermal reaction of CoSO4.7H2O and NaOH at 165 degrees C and consisting of brucite-like Co4(OH)6O2 layers pillared by OSO3-Co(H2O)4-O3SO, is a ferromagnet (T(Curie)= 12 K, Hc= 580 Oe). 相似文献