Calculations of the Diffusion Coefficients of n-Alkanes

Paul, Edward G.; Mazo, Robert M.

doi:10.1063/1.1668818

Cited by 23 publications

(13 citation statements)

References 10 publications

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“…The preceding value for a is the geometric mean of the C-O and C-C bond distances from the parameter set. It is analogous to the value of 0.77 Å (1/2 of the C-C bond length) found appropriate for alkanes (49,50) when calculating diffusion constants using the Kirkwood-Riseman equation (51). It is necessary to explicitly include bound water to the array of beads when modeling diffusion of proteins (52,53), micelles (54,55), and carbohydrates (56,57) in water, so it is expected that some level of bound water is required for solutions of PEO and PEG.…”

Section: Calculation Of the Diffusion Coefficient From Simulationmentioning

confidence: 89%

Molecular Dynamics Studies of Polyethylene Oxide and Polyethylene Glycol: Hydrodynamic Radius and Shape Anisotropy

Lee

Venable

MacKerell

et al. 2008

Biophysical Journal

438

474

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A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length lambda = 3.7 A, in quantitative agreement with experimentally obtained values of 3.7 A for PEO and 3.8 A for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent upsilon relating the radius of gyration and molecular weight (R(g) proportional, variantM(w)(upsilon)) of PEO from the simulations equals 0.515 +/- 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R(h)obtained from diffusion measurements in solution. This explains the correspondence of R(h) and R(p), the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.

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Section: Calculation Of the Diffusion Coefficient From Simulationmentioning

confidence: 89%

Molecular Dynamics Studies of Polyethylene Oxide and Polyethylene Glycol: Hydrodynamic Radius and Shape Anisotropy

Lee

Venable

MacKerell

et al. 2008

Biophysical Journal

438

474

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“…Although we are unaware of measurements of the rate of diffusion of acetyl radicals in cyclohexane, the bulk diffusion coefficient (D) of the propyl radical (which is similar in size and shape and has the same mass as acetyl, 43) is 8.0 ¥ 10 -6 cm 2 s -1 in cyclohexane at 25 • C, whereas that of the octadecyl radical is 2.7 ¥ 10 -6 cm 2 s -1 . 12b, 23 Based on the correlation between the lengths of n-alkanes and their diffusion coefficients in organic liquids, 24 D of an octanoyl radical is estimated to be ca. 4.8 ¥ 10 -6 cm 2 s -1 .…”

Section: Comparison Of Photoreactions Of Acetyl Ester 1c and Octanoyl...mentioning

confidence: 99%

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Chen

Weiss

2009

Photochem Photobiol Sci

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Photo-Fries rearrangements and associated photoreactions of four o-cresyl acylates were investigated in cyclohexane and in unstretched and stretched polyethylene (PE) films with different degrees of crystallinity. The esters differ in the number of phenyl substituents attached to the methyl group of the cresyl part and the length of the acyl chain. The influences of intramolecular structural factors and intermolecular environmental effects on the fates of the excited singlet states and the singlet state aryloxy/acyl radical pairs generated subsequently from them are explored. The results indicate that there are definable limits to the selectivity of the photoreactions of aryl esters that are dependent on their shapes and the ability of their environments to interact with them. Quantum yields for the reactions of the o-cresyl acylates were measured in cyclohexane and their values can be understood on the bases of a combination of conformational and electronic factors. The PE cavities holding the less globularly shaped o-cresyl acylates act as templates for the formation of the photoproducts: the ratios of the 2- and 4-position photo-Fries rearrangement products from o-cresyl acetate and 2-benzylphenyl acetate are higher when irradiated in films that are stretched or have higher film crystallinity; control by the PE cavities over the fates of the radical pairs is diminished for the o-cresyl acylate with two phenyl groups appended to the methyl of the cresyl part. The cavities of the PE films exert an interesting influence on the ability of the excited singlet states to undergo concerted decarboxylation reactions as well.

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“…Others, including Paul and Mazo, 3 have discussed solventdependent size parameters in terms of solute−solvent interactions. Stepto and co-workers interpreted their values of c β in terms of the solutes' interactions with the actual structure of the solvents as opposed to their assumed continuous nature.…”

Section: ■ Comparison Of Modelsmentioning

confidence: 99%

“…Paul and Mazo's values of ϕ(r), calculated with an element radius a = 0.77 Å, gave diffusion constants in agreement with those for n-alkanes with 5−32 carbon atoms in CCl 4 . 3 The fit was not as good for n-alkane solutes in other solvents but could be improved using different values of a that were attributed 3 to solute−solvent interactions.…”

Section: ■ Introductionmentioning

confidence: 97%

“…Kirkwood−Riseman theory 1,2 takes these interactions into account and has been used in analyses of macromolecular transport properties. Paul and Mazo, 3 in an early test of the theory, considered chains with up to 40 spherical elements (beads) and used Monte Carlogenerated conformers to calculate the size parameter ϕ(r) in the Stokes−Einstein relation for the translational diffusion constant, D, with stick boundary conditions 4,5…”

Section: ■ Introductionmentioning

confidence: 99%

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Diffusion of Polymethylene Chain Molecules in Nonpolar Solvents

Kowert

2020

J. Phys. Chem. B

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The translational diffusion constants, D, for solutes with polymethylene chains are compared with the predictions of a hydrodynamic bead model based on Kirkwood−Riseman theory. The solute−solvent combinations include (a) n-alkanes in nalkanes; (b) n-alkanes in benzene, toluene, tetralin, decalin, and CCl 4 ; (c) 1-alkenes in n-alkanes; (d) 1-phenylalkanes in n-alkanes;and (e) 1-phenylalkanes in isocetane (2,2,4,4,6,8,8-heptamethylnonane), pristane (2,6,10,14-tetramethylpentadecane), and squalane (2,6,10,15,19,23-hexamethyltetracosane). The bead model gives good overall agreement with an average difference of less than 3% between 207 experimental and calculated diffusion constants that include published data as well as new D values determined for 1-alkenes and 1-phenylalkanes using capillary flow techniques. The calculated values are obtained using chain element (bead) radii that decrease as the solvent viscosity increases. The bead model's results are comparable to those obtained using cylinder and lollipop diffusion for many of the same solute−solvent systems; the three models are compared and discussed. The results for the 1-alkenes and n-alkanes in the n-alkanes are the first from a Kirkwood−Riseman analysis in a homologous series of solvents.

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Calculations of the Diffusion Coefficients of n-Alkanes

Cited by 23 publications

References 10 publications

Molecular Dynamics Studies of Polyethylene Oxide and Polyethylene Glycol: Hydrodynamic Radius and Shape Anisotropy

Molecular Dynamics Studies of Polyethylene Oxide and Polyethylene Glycol: Hydrodynamic Radius and Shape Anisotropy

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Diffusion of Polymethylene Chain Molecules in Nonpolar Solvents

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