Home About us Contact
|
Home About us Contact | ||
|
|
||
Increasing Chain Length (increasing + chain_length)
Selected AbstractsGlobal phase behavior of imidazolium ionic liquids and compressed 1,1,1,2-tetrafluoroethane (R-134a)AICHE JOURNAL, Issue 2 2009Wei Ren Abstract Novel processes involving ionic liquids with refrigerant gases have recently been developed. Here, the complete global phase behavior has been measured for the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) and 1- n -alkyl-3-methyl-imidazolium ionic liquids with the anions hexafluorophosphate [PF6], tetrafluoroborate [BF4] and bis(trifluoromethylsulfonyl)imide [Tf2N] from ,0°C to 105°C and to 33 MPa. All of the systems studied were Type V from the classification scheme of Scott-van Konynenburg with regions of vapor-liquid equilibrium, miscible/critical regions, vapor-liquid-liquid equilibrium, and upper and lower critical endpoints (UCEP and LCEP). The effect of the alkyl chain length has been investigated, for ethyl-([EMIm]), n -butyl-([BMIm]), and n -hexyl-([HMIm]). With increasing chain length, the temperature of the lower critical end points increases and pressure at the mixture critical points decrease. With a common cation, the temperature of the LCEP increased and the mixture critical point pressures decreased in the order of [BF4], [PF6], and [Tf2N]. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Principles of carbopeptoid folding: a molecular dynamics simulation studyJOURNAL OF PEPTIDE SCIENCE, Issue 2 2005Riccardo Baron Abstract The conformational spaces of five oligomers of tetrahydrofuran-based carbopeptoids in chloroform and dimethyl sulfoxide were investigated through nine molecular dynamics simulations. Prompted by nuclear magnetic resonance experiments that indicated various stable folds for some but not all of these carbopeptoids, their folding behaviour was investigated as a function of stereochemistry, chain length and solvent. The conformational distributions of these molecules were analysed in terms of occurrence of hydrogen bonds, backbone torsional-angle distributions, conformational clustering and solute configurational entropy. While a cis -linkage across the tetrahydrofuran ring favours right-handed helical structures, a trans -linkage results in a larger conformational variability. Intra-solute hydrogen bonding is reduced with increasing chain length and with increasing solvent polarity. Solute configurational entropies confirm the picture obtained: they are smaller for cis - than for trans -linked peptides, for chloroform than for dimethyl sulfoxide as solvent and for shorter peptide chains. The simulations provide an atomic picture of molecular conformational variability that is consistent with the available experimental data. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] [5-(p -alkoxy)phenyl-10, 15, 20-tri-phenyl] porphyrin and their rare earth complex liquid crystallineJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2007Miao Yu Abstract Three series of porphyrin liquid crystalline compounds, [5-(p -alkoxy)phenyl-10, 15, 20-tri-phenyl] porphyrin and their rare earth complexes (Tb (III), Dy (III), Er (III), Yb (III)), with a hexagonal columnar discotic columnar(Colh) phase have been synthesized. These compounds were characterized by elemental analysis, molar conductances, UV-visible spectra, infrared spectra, luminescence spectra, and cyclic voltammetry. These compounds exhibit more than one mesophases, which transition points of temperature change from ,33.6 to 16.0,°C, and transition points of temperature for isotropic liquid also increase from 4.9 to 38.2,°C, with increasing chain length. Their surface photovoltage (SPV) response have also been investigated by the means of surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (EFISPS). It was found that their SPV bands are analogous with the UV-visible absorption spectra and derived from the same transition. Copyright © 2007 John Wiley & Sons, Ltd. [source] Termination in Dilute-Solution Free-Radical Polymerization: A Composite ModelMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2003Gregory B. Smith Abstract Literature data are summarized for the chain-length-dependence of the termination rate coefficient in dilute solution free-radical polymerizations. In essence such experiments have yielded two parameter values: the rate coefficient for termination between monomeric free radicals, k, and a power-law exponent e quantifying how kt values decrease with increasing chain length. All indications are that the value e,,,0.16 in good solvent is accurate, however the values of k which have been deduced are considerably lower than well-established values for small molecule radicals. This seeming impasse is resolved by putting forward a ,composite' model of termination: it is proposed that the value e,,,0.16 holds only for long chains, with e being higher for small chains , the value 0.5 is used in this paper, although it is not held to dogmatically. It is then investigated whether this model is consistent with experimental data. This is a non-trivial task, because although the experiments themselves and the ways in which they are analyzed are elegant and not too complicated, the underlying theory is sophisticated, as is outlined. Simulations of steady-state polymerization experiments are first of all carried out, and it is shown that the composite model of termination both recovers the e values which have been found and beautifully explains why these experiments considerably underestimate the true value of k. Simulations of pulsed-laser polymerizations find the same, although not quite so strikingly. It is therefore concluded that our new termination model, which retains the virtue of simplicity and in which all parameter values are physically reasonable, is consistent with experimental data. Taking a wider view, it seems likely that the situation of the exponent e varying with chain length will not just be the case in dilute solution, but will be the norm for all conditions, which would give our model and our work a general relevance. Normalized chain length distributions from PLP simulations. [source] Spatial representation of odorant structure in the moth antennal lobe: A study of structure,response relationships at low dosesTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 1 2003Jocelijn Meijerink Abstract How odorant structure and concentration are spatially represented within the primary olfactory integration center, the antennal lobe (AL) or olfactory bulb (OB) in invertebrates and vertebrates, respectively, is currently a topic of high interest. Here, we show the spatial representation of odorant structure in the antennal lobe of the moth Spodoptera littoralis by imaging calcium activity evoked by straight chain aliphatic alcohols and aldehydes at low doses. Activity patterns of a given odor were most similar to compounds with the same functional group, differing in chain length by only one carbon atom. A chain length dependency was present as the most activated glomerulus in the lobe shifted from a medial to a lateral position with increasing chain length of the molecule. Statistical analysis revealed that in both classes of chemicals the chain length of the molecule was represented in a similar way. No topographically fixed domains were observed for any of the classes. However, activity patterns evoked by lower chain length molecules were spatially more distinct than patterns evoked by higher chain length molecules. The number of activated glomeruli for both classes of chemicals increased with increasing chain length to reach a maximum at eight or nine C atoms followed by a decrease as the chain length further increased. J. Comp. Neurol. 467:11,21, 2003. © 2003 Wiley-Liss, Inc. [source] | ||||||||||