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91.
D. A. Vega M. A. Villar J. L. Alessandrini E. M. Valls 《Journal of Polymer Science.Polymer Physics》1999,37(11):1121-1130
A model to describe the dynamics of networks with linear pendant chains has been formulated based on the properties of ensembles of micronetworks, using the Rouse model. This development indicates that the terminal relaxation time of pendant chains with relatively large molecular weight scales with the square of the molecular weight of those chains. On the other hand, when the molecular weight of pendant and elastically active chains are comparable, a nearly exponential growth of the terminal relaxation time with the molecular weight is predicted. The main predictions of the model are compared with experimental results of model poly(dimethyl siloxane) (PDMS) networks, with controlled amounts of linear pendant chains of known molecular weight. The terminal relaxation time of these networks was estimated from the values of the loss modulus G″(ω) measured experimentally. An exponential dependence on the molecular weight of pendant chains was derived for the terminal relaxation time. This behavior is in good agreement with the predictions of our model for micronetworks, provided that the friction coefficient scales linearly with the number of entanglements. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1121–1130, 1999 相似文献
92.
93.
A. Paul Krapcho Silvia Sparapani Amber Leenstra Joshua D. Seitz 《Tetrahedron letters》2009,50(26):3195-3747
The synthesis and structural assignments of 9-chloro-1,1-phenanthroline-2(1H)-thione and 1,10-dihydro-1,10-phenanthroline-2,9-dithione have been accomplished. The sulfur-bridged bis-1,10-phenanthroline macrocycle was readily prepared by heating the thione or equimolar amounts of the dithione and 2,9-dichloro-1,10-phenanthroline in diphenyl ether. Displacements of 2-chloro- or 2,9-dichloro-1,10-phenanthroline with N,N-dimethylethylenediamine afforded the corresponding amine and diamino analogues. An amino-substituted-2,2′-bis-1,10-phenanthroline has been prepared. 相似文献
94.
Smith GL Alguindigue SS Khan MA Powell DR Taylor RW 《Magnetic resonance in chemistry : MRC》2006,44(9):901-904
Three monocyclic polyether dilactams, 17,18-dihydro-5H, 9H-dibenzo[e,n]1,4,10,7,13trioxadiazacyclopentadecine-6,10(7H,11H)-dione (1); 9,10,20,21-tetrahydro-5H, 12H-dibenzo[e,q]1,4,10,13,7,16tetraoxadiazacyclooctadecine-6, 13(7H,14H)-dione (2); and 6,7,9,10-tetrahydro-16H, 20H-dibenzo[h,q]1,4,7,13, 10,16tetraoxadiazacyclooctadecine-17, 21(18H,22H)-dione (3) were isolated during the synthesis of several benzoannelated cryptands. The complete assignments of the 1H and 13C NMR spectra of 1, 2 and 3 in CDCl3 were made using gCOSY, gHMBC, gHMQC, HMQC, HSQC, and NOESY 1D techniques. The ortho (H2) benzene protons show significant downfield shifts (1.16-1.43 ppm) that are consistent with an exodentate orientation for the amide carbonyl groups. The X-ray crystal structures of 1, 2 and 3 show that the carbonyl groups adopt an exodentate conformation in the solid state. 相似文献
95.
96.
《Journal of Coordination Chemistry》2012,65(1-4):155-172
Abstract Four polyammonium macrocycles were synthesized and characterized: two with 21-membered rings and differing numbers of oxygen and nitrogen heteroatoms, [21]N6O (1) and [21]N5O2 (2), and two with bipyridine incorporated into the ring, [24]N4O2bipy (3) and [27]N3O2bipy (4). Their ability to catalyze the dephosphorylation of adenosine triphosphate was examined. It was found that ring size plays a crucial role in the catalytic ability of the macrocycles, with the 21-membered rings being superior to larger macrocycles. Also, rates of dephosphorylation were found to increase with increasing number of nitrogen atoms in the ring. For two of the macrocycles, crystal structures were determined. Macrocycle 2 crystallizes in the tricliriic space group PI, a = 10.692(1), b = 17.037(2), c = 8.1952(8)Å, a = 92.550(9), β = 100.816(9), γ = 106.77(1)°, V = 1396.1(3) Å3; the structure was solved to R = 0.089 and R w = 0.098. Macrocycle 4 crystallizes in the monoclinic space group P21/n, a = 14.589(1), b = 15.427(1), c = 16.382(1) Å, b = 90.137(6)°, V = 3687.0(9) Å3; the structure was solved to R = 0.056 and R w = 0.085. 相似文献
97.
《Journal of Coordination Chemistry》2012,65(1-3):189-196
The syntheses of mixed oxygen-nitrogen donor macrocycles incorporating two or three pendant carboxylic acid groups are described. Potentiometric titrations in water (I = 0.1; KNO3) at 25°C have been used to determine the stability constants for the 1: 1 (metal:ligand) complexes of Co(II). Ni(II), Cu(II), Zn(II), and Cd(II). The constants obtained are compared with the previously determined values for the corresponding complexes of the unsubstituted macrocyclic precursors. The results of these studies indicate that each carboxylate function participates in binding to the central metal. For some metal-ion/ligand systems there is evidence that ring size effects influence the overall stability patterns and that, in such cases, both the ether oxygens as well as the tertiary amines of the macrocyclic rings appear to bind to the metal. 相似文献
98.
《Journal of Coordination Chemistry》2012,65(17-18):1553-1561
Three bicadmium(II) complexes with hydroxyethyl pendants were synthesized by [2?+?2] Schiff-base condensation of 2-[bis(2-aminoethyl)amino]ethanol with sodium 2,6-diformyl-4-R-phenolate (for Complex 1, R?=?F; Complex 2, R?=?Cl; Complex 3, R?=?CH3) in the presence of Cd2+. Crystals of 1 were monoclinic, space group P21/c, with a?=?16.251(9), b?=?21.424(11), c?=?12.994(7)?Å and β?=?106.622(9)°. Both Cd(II) atoms were heptacoordinated with monocapped-octahedral geometry. Complex 3 crystals were isolated as triclinic, space group P?1 with α?=?15.502(4), b?=?16.060(4), c?=?16.642(5)?Å and α?=?68.813(4), β?=?80.836(4), γ?= 86.551(4)°. The coordination number and coordination geometry of the Cd ion in one cationic unit of 3 are similar to that of 1, while in the other cationic unit, one Cd atom is N3O4 heptacoordinated and the other Cd atom has an N3O3 coordination environment and possesses a distorted octahedral geometry. The toxicity of these complexes was evaluated by testing antimicrobial activity against bacterial strands. 相似文献
99.
《Journal of Coordination Chemistry》2012,65(17):2820-2829
Two new polyoxometalate-templated supramolecular compounds, [CuI4(bpmb)4][PMoVI11MoVO40] (1) and [CuI4(bpmb)4SiW12O40] (2) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), have been synthesized under hydrothermal conditions and characterized by routine methods. Structural analysis shows that in 1, there exist crown-like [CuI4(bpmb)4] coordination macrocycles, and the Keggin polyanions [PMo VI11MoVO40]4? (abbr. as PMo12), which direct the crown-like macrocycle to form a 3-D supramolecular framework. In 2, there exist unusual meso-helix chains, and these chains are mutually interlaced in a wave–trough pattern, but without intersection resulting in a multi-cavity layer, in which the [SiW12O40]4? (abbr. as SiW12) clusters as guest molecules occupy the cavities of the layers. The distinct structural features of the two compounds suggest that Keggin polyanions should play a significant role in the process of assembly. Electrocatalytic properties of 1 and 2 were investigated. 相似文献
100.
Recursive Lagrangian dynamic modeling and simulation of multi-link spatial flexible manipulator arms
章定国 《应用数学和力学(英文版)》2009,30(10):1283-1294
The dynamics for multi-link spatial flexible manipulator arms consisting of n links and n rotary joints is investigated. Kinematics of both rotary-joint motion and link deformation is described by 4 - 4 homogenous transformation matrices, and the Lagrangian equations are used to derive the governing equations of motion of the system. In the modeling the recursive strategy for kinematics is adopted to improve the computational efficiency. Both the bending and torsional flexibility of the link are taken into account. Based on the present method a general-purpose software package for dynamic simulation is developed. Dynamic simulation of a spatial flexible manipulator arm is given as an example to validate the algorithm. 相似文献