Solvent fractions, structural characterization

The system described in this investigation is polystyrene-14C adsorbed on Graphon carbon black (graphitized Spheron 6) from six solvents comprising a wide spectrum from good to poor solvent power. Well-characterized materials were selected to elucidate the conformation of polymer molecules at the solid/liquid interface. So far two models have been postulated to describe the conformation of the adsorbed polymer molecules at the solid/liquid interface (9, 13, 14, 18, 19, 21, 27). In the first model the polymer assumes a loop or coil structure in which only a fraction of the polymer segments are attached directly at the interface, and in the second model the polymer forms a relatively flat and compressed interfacial layer with many segments attached to the solid substrate. 

Structural Characterization of Solvent Fractions from Five Major Coal Liquids by Proton Nuclear Magnetic Resonance... 

It was shown previously that coal liquids from five major demonstration processes (Synthoil, HRI H-Coal, FMC-COED, PAMCO SRC, and Catalytic Inc. SRC) could be separated reproducibly, in high yields (94-99%) into five fractions by solvent fractionation (1,2). We now wish to report structural characterization parameters obtained for these materials by the use of proton nuclear magnetic resonance ( H NMR). 

Solvent Fractionation. To facilitate later structural analysis, we separated the coal into structural types by solvent fractionation. Some other workers using the phenol depolymerization method to solubilize coal have used gas chroma-tography/mass spectroscopy (GC/MS) techniques to identify individual compounds (11, 13). However, with material containing large amounts of phenol and other polar groups, elaborate preparation and separation schemes have to be used to avoid contamination of the chromatography columns. As the emphasis of the present work was on structural characterization of the whole coal rather than on detailed examination of small parts of it in order to elucidate the chemistry of the phenolation reaction, we used the relatively simple scheme shown in Figure 1. 

As an alternative approach, polycarbosilanes 42 bearing pendant zirconocene moieties have also been prepared by the ROP of the spirocyclic monomer 41 (Equation (14)). In this case, the materials were structurally characterized but the soluble fraction was of low molecular weight M < ca. 3,000) and the high molecular weight fraction was insoluble in organic solvents. In the presence of activators, both fractions functioned as ethylene polymerization catalysts with moderate activity. 

Polymeric materials were found in the toluene-insoluble fraction [127]. The materials have no solubility in common organic solvents or so-called fullerene solvents but are partially soluble in DMSO. Evidence for the polymeric nature of the materials includes results of dynamic scattering based on photon correlation spectroscopy of quasi-elastic light scattering (PCS-QELS) [128,129] and gel permeation chromatography using DMSO as mobile phase [117]. The structural characterization of the polymers remains a challenge. 

Preparation of Cyclic Dextrins with More than Eight Glucose Residues. Four new cyclic dextrins which contain more than eight glucose residues have been isolated from starch-amylase digests using precipitation and solvent fractionation methods (48) These dextrins have been only partially characterized structurally. In the isolation procedure most of the a-,, and y-dextrins in the... 

In polymer science and technology, linear, branched and crosslinked structures are usually distinguished. For crosslinked polymers, insolubility and lack of fusibility are considered as characteristic properties. However, insoluble polymers are not necessarily covalently crosslinked because insolubility and infusibility may be also caused by extremely high molecular masses, strong inter-molecular interaction via secondary valency forces or by the lack of suitable solvents. For a long time, insolubility was the major obstacle for characterization of crosslinked polymers because it excluded analytical methods applicable to linear and branched macromolecules. In particular, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect metho ds only [ 1 ], or was expressed relatively by the fraction of crosslinking monomers used in the synthesis. 

To further characterize the structural changes of goat a-lactalbumin during unfolding, we examined the probability distributions of the following four structural parameters in each of the nine clusters of the structural ensemble of MD trajectories (1) the fractional native contact (Q) of the entire molecule, (2) the RMSD of C atoms between a pair of structures that belong to the same cluster, (3) the solvent-accessible surface area (SASA) of hydrophobic side chains, and (4) the SASA of hydrophilic side chains [25]. 

Oils and asphaltenes, which constitute a partial characterization of coal liquids according to solvent extraction, are generally considered to be key intermediates in coal liquefaction. In this regard, the present results do reveal that the asphaltenes contain higher molecular weight homologs in many specific-Z series and different compound types than do the oils. However, our study unequivocally demonstrates that compound types are observed in both the oils and asphaltenes that are equivalent in molecular formula and, hence, presumably in molecular structure. Furthermore, the overlap in the compositions of the two fractions is quantitatively appreciable. Thus, isolation of oils and asphaltenes must involve, in addition to solubility, other physical/... 

The physicochemical properties of alkylated polysaccharides have received some attention, and details of the structures and conformations of 0-methylcelluloses, and their interaction in micelle junctions, have been included in a thorough discussion of polysaccharide gels and networks. Information on the polydispersity of samples of partially methylated cellulose may be obtained from column fractionation and by fractional precipitation from a solvent-nonsolvent system, but, for a more complete characterization of polydispersity, fractionation with a series of solvent-nonsolvent systems is necessary. The solubility, in water, of polysaccharides that are mainly methylated may be considerably improved by introduction of a few suitable ionizing groups, for example, by reaction with monochloroacetic acid to introduce carboxymethyl ether groups. The general sorption and diflFusion features of hydrocarbons and other... 

One can notice that while a shift is observed only for two mutants, the fractional intensities obtained from the lifetime measiu cments are modified in the wild type and in the three mutants (Table 2.7). Emission peak of Tryptophan 4 is not modified with the state of ligation, however fractional intensities ft and increase while f3 is not modified. Emission of tryptophan 170 is located at 338 nm characterizing an emission from a slightly hydrophobic environment. Modification of the state of ligation, Mg instead of Ca, and in the apo form, a red shift to 341 and 350 nm is observed. This means that conformational changes are observed in the vicinity of Trp 170 that is more exposed to the solvent in presence of Mg than in presence of Ca. In the apo form, important structural modifications occur within the protein. 

Our analytical procedure consists of stepwise acetone extraction followed by cyclohexane. Subsequently, the acetone-soluble fraction is partioned between hexane/aqueous ethanol (12,15), and the soluble components are freed of solvents and determined gravimetrically. For lack of specific nomenclature, the botanochemicals isolated by this technique have been referred to as "whole plant oil," "polyphenol," and "polymeric hydrocarbon." Actually, components from these extracts need to be further characterized. However, petroleum refinery processes may be sufficiently insensitive to allow use of carbon-hydrogen rich compounds represented by a broad spectrum of structures. For example, consider the diverse chemicals ranging from methanol to natural rubber which have been converted to gasoline (16). Thus, chemical species may be important if chemical intermediates are being generated but may be nonconsequential for production of fuels, solvents, carbon black, and other basic chemicals. 

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