Search results for "CEM"
showing 10 items of 3487 documents
2-(4-Fluorophenyl)-1-(4-pyridyl)cyclopentan-1-ol
2007
The crystal structure of the title compound, C16H16FNO, was determined as part of a study of the biological activity of pyridine-substituted cyclopentene derivatives as p38 mitogen-activated protein kinase (MAPK) inhibitors. The 4-fluorophenyl and 4-pyridyl rings are trans positioned with respect to each other. The compound exists as a racemic mixture. The synthesis was achieved via direct interaction between the reactive complex Grignard reagent PyMgCl·LiCl and the enolizable ketone 4-fluorophenylcyclopentanone with the assistance of the neodymium salt catalyst NdCl3·2LiCl. The crystal packing is characterized by zigzag chains of molecules, which are connected by O—H⋯N hydrogen bon…
The chemistry of death--Adipocere degradation in modern graveyards.
2015
The formation of adipocere slows further decomposition and preserves corpses for decades or even centuries. This resistance to degradation is a serious problem, especially with regard to the reuse of graves after regular resting times. We present results from an exhumation series in modern graveyards where coffins from water-saturated earth graves contained adipocere embedded in black humic material after resting times of about 30 years. Based on the assumption that this humic material resulted from in situ degradation of adipocere, its presence contradicts the commonly held opinion that adipocere decomposition only occurs under aerobic conditions. To test our hypothesis, we collected black…
Stereoselective synthesis and properties of 1,3-bis(dicyanomethylidene)indane-5-carboxylic acid acceptor fragment containing nonlinear optical chromo…
2016
A series of organic push–pull type chromophores using indane-1,3-dione 5-carboxylic acid (IDCA) and novel 1,3-bis(dicyanomethylidene)indane 5-carboxylic acid (CICA) electron acceptor fragments have been synthesized and characterized. NMR and X-ray analysis revealed that condensation reactions with the CICA fragment were stereoselective and yielded benzylidenes and azomethines with E double bond configurations. Due to the non-planar geometry these compounds are chiral and were acquired as a racemic mixture. The subsequent functionalization of the carboxylic acid group with 5,5,5-triphenylpentan-1-ol yielded solution-processable glass forming materials (6, 8, 10, 13) with glass transition tem…
Grafted polymer layers under variable solvent conditions: A Monte Carlo simulation
1993
Polymer chains anchored with one end at a hard wall under variable solvent conditions are investigated by Monte Carlo simulations using the bond- fluctuation model. Detail information on the structural properties are obtained above, at, and below the Θ-point and discussed in terms of the appropriate theories. In particular, the scaling of the brush thickness is formulated and verified by the simulation data. For the dynamics at the Θ-point, both the relaxation time of the chain configuration and the mean-square time displacement are studied. At temperatures distinctly below the Θ-point, we find that the layer develops considerable lateral inhomogeneity in its density, which has not been pre…
Fluidizing efficiency of comb-like superplasticizers: The effect of the anionic function, the side chain length and the grafting degree
2015
Superplasticizers and especially polycarboxylate grafted polyethylene oxide (PCE) demonstrated their efficiency to fluidify concrete. The aim of this work is to investigate the evolution of the fluidity as a function of adsorption in a sulfated solution with a wide variety of comb-like superplasticizers and at incomplete adsorption rate. Polymers with various side chain lengths, grafting ratios and also with modified anionic functions (carboxylate, dicarboxylate and phosphate) were synthesized. Inert calcite suspensions were used to mimic early age cementitious materials avoiding the cement hydration. Models of polymer conformation and yield stress prediction have been tested. But the most …
Crystal structure of the bifunctional soybean Bowman-Birk inhibitor at 0.28-nm resolution. Structural peculiarities in a folded protein conformation.
1996
The Bowman-Birk inhibitor from soybean is a small protein that contains a binary arrangement of trypsin-reactive and chymotrypsin-reactive subdomains. In this report, the crystal structure of this anticarcinogenic protein has been determined to 0.28-nm resolution by molecular replacement from crystals grown at neutral pH. The crystal structure differs from a previously determined NMR structure [Werner, M. H. & Wemmer, D. E. (1992) Biochemistry 31, 999-1010] in the relative orientation of the two enzyme-insertion loops, in some details of the main chain trace, in the presence of favourable contacts in the trypsin-insertion loop, and in the orientation of several amino acid side chains. The p…
Cooperative supramolecular polymerization and amplification of chirality in C3-symmetrical OPE-based trisamides.
2011
Sergeants-and-soldiers experiments demonstrate the amplification of chirality that transforms the racemic mixture of helical columns formed from OPE-based trisamides into enantiomerically enriched helical structures (see scheme).The cooperative supramolecular polymerization of the trisamides is investigated by theoretical calculations and temperature-dependent UV/Vis and CD experiments. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Propargyl-functional aliphatic polycarbonate obtained from carbon dioxide and glycidyl propargyl ether.
2013
The synthesis of propargyl-functional poly(carbonate)s with different content of glycidyl propargyl ether (GPE) units is achieved via the copolymerization of propargyl glycidyl ether and carbon dioxide. A new type of functional poly(carbonate) synthesized directly from CO(2) and the glycidyl ether is obtained. The resulting polymers show moderate polydispersities in the range of 1.6-2.5 and molecular weights in the range of 7000-10 500 g mol(-1). The synthesized copolymers with varying number of alkyne functionalities and benzyl azide are used for the copper-catalyzed Huisgen-1,3-dipolar addition. Moreover, the presence of vicinal alkyne groups opens a general pathway to produce functional …
Anomalous diffusion in polymer melts
2002
Abstract We present a study of the anomalous diffusion regimes in polymer melt dynamics performing a Monte Carlo (MC) simulation of the bond-fluctuation lattice model. Special emphasis is laid on the crossover from a Rouse-like motion to the behavior predicted by reptation theory. For the longest chains of N=400 the high statistical accuracy of the data allows for clear identification of the subdiffusive regimes in the center of mass motion and the monomer displacement. They are well compatible with those predicted by reptation theory. Furthermore a detailed analysis of the different short time anomalous diffusion regimes in the melt dynamics of polymer chains is presented and it is shown t…
Static and dynamic scaling behavior of a polymer melt model with triple-well bending potential
2018
We perform molecular-dynamics simulations for polymer melts of the coarse-grained polyvinyl alcohol model that crystallizes upon slow cooling. To establish the properties of its high temperature liquid state as a reference point, we characterize in detail the structural features of equilibrated polymer melts with chain lengths $5\le N \le 1000$ at a temperature slightly above their crystallization temperature. We find that the conformations of sufficiently long polymers with $N >50$ obey essentially the Flory's ideality hypothesis. The chain length dependence of the end-to-end distance and the gyration radius follow the scaling predictions of ideal chains and the probability distributions o…