Search results for "Interaction"
showing 10 items of 5710 documents
Brownian dynamics simulation of grafted polymer brushes
1995
We present results of computer simulations by the method of Brownian dynamics of polymeric brushes attached to impenetrable planes. For testing both model and method we have used one polymer brush attached to a repulsive plane and compare some results with Monte Carlo results of Lai and Binder on the bond fluctuation model. We have also studied two polymeric brushes attached to two parallel planes at different distances between planes, and investigate the interplay between the interpenetration of the brushes and the configurational properties of the grafted chains.
Can one detach a fully adsorbed flexible polymer chain by an ultra-small external force?
2013
Full adsorption of flexible chains onto typical solid substrates occurs at a surface interaction energy of (5–10) kBT. The corresponding detachment force is in the range 10–50 pN. In contrast to “bare” solid substrates common to non-living materials, surfaces coated with brush-like polymer layers are very common in biological soft matter. We employ a simple mean-field approach to describe the effects of weak attraction between a floating long macromolecule and the brush. We show that even for a moderately thick brush a very small effective attraction is enough to produce complete binding of the long chain. The detachment force scales as , where W is the brush thickness. Hence the force coul…
Residual order in amorphous dry films of polymer latices: indications of an influence of particle interaction
2002
Abstract We report small angle X-ray scattering and atomic force microscopy measurements on macroscopically thick, dry films of polymer latex particles. While the surface of dried droplets has long range order due to layering effects, the overall bulk structure is amorphous. This holds for both low charge polymethylmetacrylate particles and for highly charged polystyrene particles with additional stabilisation with sodiumdodecylsurfate. In the latter case, however, considerable amounts of residual crystal-like order is observed.
NMR Matrix Technique for Detecting Self Diffusion in Polymers
1979
A technique is discussed where monodisperse small spheres or cylindrical fibers of a polymer are embedded in a matrix of the corresponding fully deuterated polymer. On annealing the sample at a temperature above the glass transition the protonated macromolecules diffuse into the deuterated matrix and vice versa. Since the NMR spectrum depends upon the intermolecular proton proton dipolar coupling, the decrease of this coupling can be used to monitor the diffusion process. For particle diameters d ∼ 10−4 cm and annealing times t ∼ 105 s, extremely small diffusion constants D < d2/t are attainable. The NMR analysis of prospective diffusion experiments with polystyrene is discussed in some det…
B-DNA Structure and Stability as Function of Nucleic Acid Composition. Dispersion-Corrected DFT Study of Dinucleoside-Monophosphate Single and Double…
2013
actions of the sugar-phosphate skeleton with water; (6) hydrophobic interactions of the DNA cylindrical core, made up by the hydrogen-bonded and stacked nitrogen bases, with the water solvent. Recently, there has been increasing effort in developing and applying quantum chemical methods able to reproduce the structure of native B-DNA and to correctly describe the energy involved in the intrastrand and interstrand noncovalent interactions between the nucleotide monomers. This topic has been approached by both wave function methods and density functional theory. [2] Water solvent and sodium counterions also play an important role in the formation and relative stabilization of the double-helic…
Molecular squares of Ni(II) and Cu(II): ferromagnetic exchange interaction mediated by syn-anti carboxylate-bridging.
2009
The synthesis of four discrete tetranuclear complexes {[Ni(II)(L(2))][ClO(4)]}(4).MeCN (1), {[Cu(II)(L(1))(O(3)SCF(3))]}(4).H(2)O (), {[Cu(II)(L(3))(OClO(3))]}(4).MeCN () and {[Cu(II)(L(4))][ClO(4)]}(4).3MeCN.4H(2)O (4), supported by a closely similar group of carboxylate-appended (2-pyridyl)alkylamine ligands [L(1)(-): 3-[N-methyl-{2-(pyridin-2-yl)ethyl}amino]propionate; L(2)(-): 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate; L(3)(-): 3-[N-isopropyl-{2-(pyridin-2-yl)methyl}amino]propionate and L(4)(2-): 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)] is described. Structural characterization reveals that each Ni(II) centre in 1 has square-pyramidal Ni(II)N(3)O(2) …
Mukaiyama–Michael Reactions with trans-2,5-Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions, Not from …
2013
The scope of the enantioselective Mukaiyama-Michael reactions catalyzed by trans-2,5-diphenylpyrrolidine has been expanded to include both α- and β-substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C-C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals…
Ternary Polymer Solutions with Hydrogen Bonds, 1
2007
The Flory Huggins methodology coupled to AET has been extended to ternary polymer systems, in particular to solvent (A)/polymer 1 (B)/polymer 2 (C) systems, with the two polymers displaying H-bonding interactions. Because the H-bonding can perturb the randomness of polymeric conformations, the change in Gibbs free energy of mixing, AG, should arise from changes in combinatorial entropy as well as in interaction energy. The combinatorial part of AG is evaluated through AET as a function of the association constant η between B and C components, the autoassociation constant a between B components, and the independent number m of interaction sites of acceptor C. The enthalpic contribution is ev…
One‐Dimensional Coordination Polymers of Mn II , Cu II , and Zn II Supported by Carboxylate‐Appended (2‐Pyridyl)alkylamine Ligands – Structure and Ma…
2009
Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO– = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO– = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxy…
Synthesis, structure, physicochemical characterization and theoretical evaluation of non-covalent interaction energy of a polymeric copper(II)-hydraz…
2019
Abstract One dimensional polymeric copper-hydrazone complex {[Cu(H0.5L)(µ1,3-SCN)]0.5ClO4·0.5MeOH}n (1) has been synthesized with Cu(ClO4)2·xH2O and N'-(1-(pyridin-2-yl)ethylidene)acetohydrazide (HL) in presence of NaSCN. The ligand and the complex have been characterized by several spectroscopic techniques (IR, UV–Vis and EPR), cyclic voltammetry and the structure of 1 has been determined by single crystal X-ray diffraction. The complex is an infinite one dimensional polymer bridged by thiocyanate. The magneto-structural correlation has been determined and the non-covalent interactions present in the molecule have been energetically evaluated by means of DFT calculations.