Abstract

No abstract

Chylomicrons, the vehicles for the transport of exogeneous triglycerides and cholesterol in the lymph and the blood, were characterized by their size from dynamic light scattering measurements. To achieve an appropriate resolution, correlation data were collected over several hours. Analysis was performed with an extended version of the regularization method CONTIN, and special attention was given to errors in the experimental baseline and to randomness of the residuals. The solutions selected by means of Fisher's F-test by CONTIN agreed with those obtained with the stability plot of Schnablegger and Glatter, when in the case of data of lower statistical accuracy the solution was taken from the lower part of the confidence interval of the F-test. The intensity-weighted size distributions indicated two classes of particle, their mean diameters being 100-140 nm and 330-350 nm. The ability to resolve two peaks of such a size ratio is demonstrated. The numbers of particles associated with the two peaks were estimated by means of the scattering properties of the particles, which showed that the overwhelming majority were small ones. This estimation also suggested that the mean size of the first peak of the number distribution is significantly smaller than the typical size of chylomicrons. This was consistent with the finding that the sample contained not only apolipoprotein B-48 but also a similar amount of apolipoprotein B-100, which is associated with lipoproteins of smaller size. The larger particles of the second peak are probably dietary triglyceride-rich chylomicrons.

The energetics and dynamics of the growth of nonionic n-alkyl poly(ethylene glycol) ether surfactant micelles in the isotropic L1 phase have been analyzed on the basis of a recently described, concentration dependent thermal transition. 1 This highly cooperative endothermic transition is assigned as a sphereto-rod transition. We analyze the thermodynamic data in terms of aggregation-fusion of complete micelles and also discuss the kinetics in the frame of this "random micelle aggregation" model. The analysis of the calorimetric data leads to a cooperative unit of about 160 detergent molecules undergoing simultaneously the transition from spheroidal to cylindrical structure. We investigate the aggregation kinetics in the microsecond to millisecond range using the temperature-jump (TJ) method with observation of scattered and transmitted light and the stress relaxation dynamics monitoring transient electric birefringence (TEB).As expected from the model, the aggregation dynamics gets faster with increasing temperature, while the stress relaxation dynamics slows down with temperature, leading to apparent negative activation energies. At the transition temperatures, the dynamics of the structural transition for C14E8 is characterized by an association and dissociation rate constant of 4.4 × 10 6 M -1 s -1 and 1.8 × 10 3 s -1 , respectively, compared to the much slower dynamics of C16E8 with the corresponding rate constants 8.5 × 10 4 M -1 s -1 and 29 s -1 , respectively. The rate constants of micelle fusion increase, while those of micelle scission decrease with increasing temperature. The TEB results are discussed using the relations derived in the literature for the competition between rotational motion and chain scission. The fast dynamics of C14E8 compared to the much slower dynamics of C16E8 provides an understanding of the differences in stress compliance and viscosity for these systems. As a major result of the study, we present a consistent mechanism of micellar growth which involves the aggregation-fusion of two micelles in a single, rate-limiting reaction step and not the stepwise incorporation of single surfactant molecules into pre-existing micelles. The speeding up of the TJ kinetics in C16E8 at higher temperatures indicates a further structural transition, possibly network formation.