Effect of molecular size

There are many report in the literature on the effects of chain conformation [19-25]. One example is radical bromination of poly(methyl styrene) [20] with Ai-bromosuccinimide-benzoyl peroxide or Br2-K2C03-light. NMR spectroscopy shows differences in reactivities of the methyl groups in the 3 and 4 positions on the benzene rings between isotactic and atactic polystyrenes [20]. 

The differences in reactivities in poly(vinyl alcohol)s between isotactic meso) and syndiotactic ( i/-diol) portions of the polymers and between cis and trans acetals [26-28] is another example. In extending this to model compounds, reactions of stereo isomers of pentane-2,4-diol and heptane-1,4,6-triol with formaldehyde take place much faster for the meso than for the dl-diol portions [26-28]. Even more important are the steric effects imposed by restricted rotations. For instance, quatemizations of chloromethylated polyether sulfmies exhibit decreasing rates at high degrees of substitution. This can be attributed to restricted rotations of the polymeric chains, because this phenomenon is not observed with more flexible chloromethylated polystyrene under identical conditions [23, 24]. 

There are many reports in the literature on the effects of chain conformation One example is radical bromination of poly(methyl styrene) with A-bromosuccinimide-benzoyl peroxide or 

CHAPTER 8 Differences in reactivities in poly(vinyl alcohol)s between isotactic (jneso) and syndiotactic 

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The behavior of binary hqnid solutions is clearly displayed by plots of M, AM, and In % vs. X at constant T and P. The vohime change of mixing (or excess vohime) is the most easily measured of these quantities and is normally small. However, as illustrated by Fig. 4-1, it is subject to individiiahstic behavior, being sensitive to the effects of molecular size and shape and to differences in the nature and magnitude of intermoleciilar forces. 

Molecular Complexity. A measure of the combined effects of molecular size, element and functional-group content, internal connectedness, stereocenter content, reactivity, and instability that lead to difficulties of synthesis. 

Although many of the aromatic compounds based on benzene have pleasant odors, they are usually toxic, and some are carcinogenic. Volatile aromatic hydrocarbons are highly flammable and burn with a luminous, sooty flame. The effects of molecular size (in simple arenes as well as in substituted aromatics) and of molecular symmetry (e.g., xylene isomers) are noticeable in physical properties [48, p. 212 49, p. 375 50, p. 41]. Since the hybrid bonds of benzene rings are as stable as the single bonds in alkanes, aromatic compounds can participate in chemical reactions without disrupting the ring structure. 

A simple estimate of the diffusion coefficients can be approximated from examining the effects of molecular size on transport through a continuum for which there is an energy cost of displacing solvent. Since the molecular weight dependence of the diffusion coefficients for polymers obeys a power law equation [206], a similar form was chosen for the corneal barriers. That is, the molecular weight (M) dependence of the diffusion coefficients was written as ... 

JBM Van Bree, AG De Boer, M Danhof, L Gisel, DD Breimer. Characterization of an in vitro blood-brain barrier Effects of molecular size and lipophilicity on cerebrovascular endothelial transport rates of drugs. J Pharmacol Exp Ther 247 1233-1239, 1988. 

Again, a parabolic correlation between log BB and V indicated the twofold effects of molecular size on BBB penetration. Increasing molecular volume on one hand decreases the log BB value by decreasing the molecular diffusion through a lipid membrane. On the other hand, bigger molecular volume also increases lipophilicity, which, in turn, facilitates BBB penetration when <2o,n and <2h remain unchanged. 

Moller, K. and Gevert, T. 1994, An FTIR solid-state analysis of the diffusion of hindered phenols in low-density polyethylene (LDPE) the effect of molecular size on the diffusion coefficient. J. Appl. Polym. Sci. 51 895-903. 

Published values of BAFs for HOCs, summarized by Swackhamer and Skoglund (10), range from 18 to 1,000,000. The variety of methods used in these studies prevents direct comparison, so it is unclear what factors are responsible for the large variation in BAFs. Several hypotheses have been proposed to explain these variations in accumulation and their deviations from KoW-based predictions. One hypothesis (II, 12) proposed that a lack of complete reversibility in the partitioning process is responsible for the deviations. A second (13-16) theory attributed the deviations to the presence of a third phase (colloids or dissolved organic matter) and the inability to accurately separate the dissolved and sorbed states. A third (17) proposal is that partitioning is dependent on sorbent concentration. And finally, a fourth (18, 19) hypothesis holds that this deviation is a function of the effects of molecular size and shape on cellular transport. 

Only a few studies have been reported on the effect of molecular size on the adsorption of normal paraffins in zeolites. For both small- and large-pore low silica/alumina zeolites, in liquid phase... 

Peck, K.D., et al. 1996. Quantitative description of the effect of molecular size upon electroosmotic flux enhancement during iontophoresis for a synthetic membrane and human epidermal membrane. J Pharm Sci 85 (7) 781. 

The effect of molecular size, conjugation length, and competition with ex-cimer formation on ESIPT in conjugated polymers, in which the intramolecularly hydrogen-bonded moieties reside in the main domain, has been examined [204], The polymers were poly(5 -(2 -hydroxy)phenylenebenzobisoxazole (56) and poly(4 -(2 -hydroxy)phenylenebenzobisoxazole (57). A large extent of -rr-elec-tron delocalization is found to inhibit the ESIPT process. Excimer formation is found to be competitive with ESIPT in the polymers studied, whereas molecular size does not inhibit ESIPT. 

De Nobili, M., Bragato, G., and Mori, A. (1998). Combined effects of molecular size and electroendosmotic flow on the capillary electrophoretic behaviour of humic substances. Acta Hydrochim. Hydrobiol. 26,186-190. 

Venturoli, D., and B. Rippe. 2005. Ficoll and dextran vs. globular proteins as probes for testing glomerular permselectivity effects of molecular size, shape, charge, and deformability. Am.J. Physiol. Renal Physiol. 288 F605—613. 

B. Bagchi and A. Chandra, Polarization relaxation, dielectric-dispersion, and solvation dynamics in dense dipolar liquid, J. Chem. Phys., 90 (1989) 7338 -5 A. Chandra and B. Bagchi, Effects of molecular size in solvation dynamics, J. Phys. Chem., 94 (1990) 1874—6. 

An example for the pore pathway is discussed using the example of sulfonamides. For this class of compounds it is generally accepted that the degree of ionization determines the antibacterial activity, the ionized form being more potent then the neutral form. Total ionization, however, leads to decreased activity in whole cells because cell wall permeation becomes the rate-limiting step [99-101]. The possible effect of molecular size on cell wall permeation has been studied on a series of substituted 5-sulfanilamido-l-phenylpyrazoles that show only a small variation in pKa values but a large difference in molecular weight [102]. 

Potts, R.O. and Guy, R.H., A predictive algorithm for skin permeability the effects of molecular size and hydrogen bond activity, Pharm. Res., 12, 1628-1633, 1992. 

The effect of molecular size has recently been examined by Dimitrov et al. (2002, 2003), who showed that the maximal cross-sectional diameter of highly hydrophobic molecules had a significant negative effect on bioconcentration. 

Dimitrov, S.D., Dimitrova, N.C., Walker, J.D., Veith, G.D., and Mekenyan, O.G., Predicting bioconcentration factors of highly hydrophobic chemicals. Effect of molecular size, Pure Appl. Chem., 74, 1823-1830, 2002. 

In this chapter, we focus on iSAFT, a computationally simple, thermodynamically consistent DFT that accurately predicts the structure and thermodynamics of inhomogeneous polymeric solutions and blends (Jain et al., 2007, 2008, 2009 Tripathi and Chapman, 2005a, 2005b). Like molecular simulation, the DFT uses explicit models of molecules, but the DFT is not limited computationally in molecule size or number of components. The DFT shows excellent agreement with molecular simulation for local structure, compressibility effects, and the effects of molecular size. 

Solubility data of the dyestuffs are of interest for the optimization of this particular dyeing technique. Therefore an apparatus was developed for the determination of the solubilities in supercritical solvents at temperatures from 250 to 500 K and pressures up to 250 MPa according to the static analytical method [6, 7]. In particular, investigations on the solubility of some selected anthraquinone dyes in supercritical C02 and N20 and more recently of P-carotene in supercritical C02 and CC1F, were performed as a function of temperature and pressure (see section 4.). For the l,4-bis-(n-alkylamino)-9,10-anthraquinones the alkyl chains were systematically varied in the homologous series in order to study the effects of molecular size and polarity on the solubility phenomena [6-10]. 

Fisher, A., Brown, K., Davis, S., Parr, G., and Smith, D. A. (1987),The effect of molecular size on the nasal absorption of water-soluble compounds in the albino rat, J. Pharm. Pharmacol, 39, 357-362. 

Normally in chromatography (except affinity chromatography) effects of molecular shape on retention are of minor importance in comparison to the effects of molecular size and molecular polarity. In the case of planar non-polar PAH isomers, retention was linearly related to a shape descriptor (a degree of elongation of the analyte molecule) [43,541. 

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