Molecular factors affecting

Theoretical treatments of simple coacervation based on the statistical thermodynamics of polymer solutions have been set out by Scott (1949), Tanford (1961), Zeman and Patterson (1972), and Hsu and Prausnitz (1974). These treatments have shown that the main molecular factors affecting the phenomenon are ... 

In this chapter, molecular factors affecting structural behavior of fat polymorphism are discussed in terms of internal influences of the TAG molecules. In particular, the influences of fatty acid compositions and their positions connected to glycerol carbons on the polymorphism of fat crystals are of primary concern. It has been known that the fats with simple and symmetric fatty acid compositions tend to exhibit typical oc, P, and P forms, whereas those with asymmetric mixed-acid moieties often make the P form more stable (1,9). In the mixed-acid TAG containing unsaturated fatty acid moieties, the number and conformation of the double bond, cis or trans, give rise to remarkable influences on the polymorphic structures (10-12). The TAG containing different saturated fatty acids with different chain-lengths also revealed quite diversified polymorphism (13-15). Therefore, it may be worthwhile now to discuss the molecular aspects of the polymorphism of fats. This consideration may also be a prerequisite for molecular design of structured fats, in combination with nutritional and metabolic properties. 

C. Delfolie, L.C. Dickinson, K.F. Freed, J. Dudowicz, W.J. MacKnight, Molecular factors affecting the miscibility behavior of cycloolefin copolymers. Macromolecules 32(23), 7781-7789 (1999)... 

The above considerations suffice to clearly show that a theoretical study aimed to give some insights on the use of nitroxides as spin probes should allow a clear-cut distinction between intrinsic and environmental effects on the EPR parameters of these compounds. Only a reliable assessment of the intra-molecular factors affecting the values of the hfs of nitroxides [12] (nature of the NO substituents, NO conformation...) makes indeed possible to analyze all the environmental effects which govern the magnetic properties of the nitroxide probe polarity and hydrogen bonding power of the solvent, pH, presence of other free radicals, and so on. 

Adsorption Kinetics. In zeoHte adsorption processes the adsorbates migrate into the zeoHte crystals. First, transport must occur between crystals contained in a compact or peUet, and second, diffusion must occur within the crystals. Diffusion coefficients are measured by various methods, including the measurement of adsorption rates and the deterniination of jump times as derived from nmr results. Factors affecting kinetics and diffusion include channel geometry and dimensions molecular size, shape, and polarity zeoHte cation distribution and charge temperature adsorbate concentration impurity molecules and crystal-surface defects. 

Having thus seen that enviromental factors determine viscosity largely by their effect on free volume let us now consider the influence of molecular factors which affect viscosity largely by entanglement effects. 

One consequence of this is that in a thermoplastic injection moulding the molecular orientations will vary from place to place according to the flow pattern. This may well set up sufficient stresses in the moulding to cause it to distort from its intended shape. Factors affecting the amount of orientation were discussed briefly in the previous chapter and by the author elsewhere. Sometimes the conditions required to minimise distortion may be such that the moulding cycle becomes too long to be economic. In these cases it may be necessary to modify the moulding or at least the position and number of feed... 

Apart from the successful imprinting discussed above, the recognition for many templates is far from that is required for the particular application, even after careful optimization of the other factors affecting the molecular recognition properties. Often, a large excess of MAA in the synthesis step is required for recognition to be observed and then only in solvents of low to medium polarity and hydrogen bond... 

The transfection mechanism of plasmid-chitosan complexes as well as the relationship between transfection activity and cell uptake was analyzed by using fluorescein isothiocyanate-labeled plasmid and Texas-Red-labeled chitosan. Several factors affect transfection activity and cell uptake, for example the molecular mass of chitosan, stoichiometry of complex, seriun concentration and the pH of the transfection medium. The level of transfection with plasmid-chitosan complexes was found to be highest when the molecular mass of chitosan was 40 or 84 kDa, the ratio of chitosan nitrogen to DNA phosphate was 5, and serum at pH 7.0 was 10%. Plasmid-chitosan complexes most likely condense to form large aggregates (5-8 p,m), which absorb to the cell surface. After this, plasmid-chitosan complexes are endocytosed, and accumulate in the nucleus [97]. 

The quantitative role of electrical factors affecting the transport of charged molecules is obtained by comparing permeability coefficients with the permeability coefficient P(Lcdi for molecular size-restricted diffusion independent of the charge on the molecule (i.e., the neutral image). With Eqs. (45) and (46) one obtains... 

Diffusion of small molecular penetrants in polymers often assumes Fickian characteristics at temperatures above Tg of the system. As such, classical diffusion theory is sufficient for describing the mass transport, and a mutual diffusion coefficient can be determined unambiguously by sorption and permeation methods. For a penetrant molecule of a size comparable to that of the monomeric unit of a polymer, diffusion requires cooperative movement of several monomeric units. The mobility of the polymer chains thus controls the rate of diffusion, and factors affecting the chain mobility will also influence the diffusion coefficient. The key factors here are temperature and concentration. Increasing temperature enhances the Brownian motion of the polymer segments the effect is to weaken the interaction between chains and thus increase the interchain distance. A similar effect can be expected upon the addition of a small molecular penetrant. 

Name three factors that affect a polymer s random walk configuration. How does each factor affect molecular volume ... 

The rate and selectivity of absorption by the GI tract are highly dependent on many conditions. The type of chemical, its molecular weight, molecule size and shape, acidity, susceptibility to attack by intestinal flora, rate of movement through the GI tract, and many other factors affect the rate of absorption. 

The factors affecting Rf include the quality of the stationary and mobile phases, the thickness and activity of the layer, and the amount of sample. Although standards may have the same Rf value as the sample, this does not uniquely identify the compound. For archaeological samples, the best identification achievable is only at a general class level (e.g., triacylglycerols, fatty acids, aromatic, or aliphatic) and not to individual molecular components. 

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