Diffusion Measurements in Aqueous Solutions of Different Viscosities

Biancheria, A.; Kegeles, Gerson

doi:10.1021/ja01579a021

Cited by 28 publications

(10 citation statements)

References 2 publications

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“…Although the presence of any of the four compounds in solution would increase the macroscopic viscosity of the solution, at the microscopic level their behaviors are quite different. According to theory, polymers such as Ficoll and PEG do not influence the rates of diffusion of small molecules (3,28). On the other hand, small-molecule viscogens such as sucrose and glycerol not only will increase the macroscopic viscosity of the solution but also will slow down the diffusion of molecular particles in solution (18,21).…”

Section: Resultsmentioning

confidence: 99%

Class C β-Lactamases Operate at the Diffusion Limit for Turnover of Their Preferred Cephalosporin Substrates

Bulychev

Mobashery

1999

Antimicrob Agents Chemother

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It has been suggested that class C β-lactamases have evolved to carry out a metabolic reaction other than hydrolysis of β-lactam antibiotics. It is demonstrated in the present study that the class C β-lactamase from Enterobacter cloacae P99 has reached the diffusion limit in its ability to hydrolyze its preferred cephalosporin substrates. The increase in the solution viscosity by addition of a microviscogen (sucrose) caused the decline in the parameterk cat/Km for hydrolysis of cephaloridine and cephalosporin C (approximately 2.5-fold at a relative viscosity of 2.9). A similar increase in viscosity has no effect on the turnover rate of the poorer substrates cefepime and penicillin G. Addition of a macroviscogen (polyethylene glycol) to the reaction mixture did not change the rate of turnover for any of the substrates tested because in this case the viscogen would not interfere with the motion of small molecules, as was expected. Therefore, it would appear that the driving force behind the evolution of this class C β-lactamase and, in principle, other enzymes of this class is indeed the functional reaction of this enzyme as a drug resistance factor.

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Section: Resultsmentioning

confidence: 99%

Class C β-Lactamases Operate at the Diffusion Limit for Turnover of Their Preferred Cephalosporin Substrates

Bulychev

Mobashery

1999

Antimicrob Agents Chemother

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“…Studies of the self-diffusion of small, solvent or solute, molecules have been extensively used to investigate colloidal systems containing polymers [1][2][3][4], polyelectrolytes [5][6][7], proteins [8][9][10], micelles, normal [11,12] or reversed [13]. The method has also been applied to microemulsions [14,15], liquid crystals [16,17] and gels [18], and the self-diffusion is obviously of importance also for the study of porous media [19].…”

Section: Introductionmentioning

confidence: 99%

Self-diffusion of small molecules in colloidal systems

Jönsson¹,

Wennerström²,

Nilsson³

et al. 1986

Colloid & Polymer Sci

280

241

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Abstract:The self-diffusion of small molecules in colloidal systems is calculated using the cell model to describe the effect of varying concentration of colloidal particles. The relevant boundary conditions are found using arguments from the thermodynamics of irreversible processes. From a general description of the self-diffusion in systems with spherically symmetrical particles we derive expressions for the concentration dependence of the effective self-diffusion coefficient De~t for several cases of practical importance. It is shown that when the molecule studied is strongly attracted to the particle a minimum in D ~ff is expected around volume fraction 4~ = 0.35. It is also shown that the often made distinction between free and bound molecules is often problematic and a more general description is proposed. The obstruction effect generated by the excluded volume is discussed both for spherical and spheroidal systems. It is pointed out that the often used formula due to Wang ((1954) J Amer Chem Soc 76:4755) is incorrect for self-diffusion and for the obstruction factor for spheres we obtain (1 + 0.5 ~)-1. This expresion is tested both by experiments on water diffusion in systems containing latex particles and through computer simulations and it is found valid over a wide concentration range. For prolate ellipsoids the obstruction factor is not greatly different from that for spheres, while for oblate aggregates the limking obstruction factor of 2/3 can be obtained at low concentrations. It is demonstrated that this effect can be used to distinguish between different aggregate shapes. It is also shown that the disorder present in a solution of colloidal particles leads to a decrease in the obstruction effect.

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“…Thus, in agreement with expectation from protein diffusion experiments,23 the macroscopic relative viscosity provides a good measure of the retarding effect on the mobility. Cases where this was not observed have been investigated by Biancheria and Kegeles,24 who have summarized the earlier work in this field.…”

Section: Discussionmentioning

confidence: 99%