Dynamic light scattering (DLS) measures time-dependent fluctuations in the scattering intensity arising from particles undergoing random Brownian motion. Diffusion coefficient and particle size information can be obtained from the analysis of these fluctuations. This paper discusses the factors which will influence the lower size limit of DLS and reports the use of sucrose as a test sample to probe this lower limit of the technique. Hydrodynamic diameter values of less than 1 nm are obtained by the use of 173°backscatter detection that is applied to increase the sensitivity of DLS. The peak means (with standard deviations) obtained for the intensity and volume data from a series of sucrose concentrations, ranging from 5 to 35% w/v, were measured as D I,Mean = 0.82 nm (0.11 nm) and D V,Mean = 0.62 nm (0.05 nm), respectively. These sucrose results suggest that sub nanometer measurements are achievable with a precision of 0.1 nm. Evidence to support these size results for sucrose is discussed.

No abstract

No abstract

No abstract

Interactions between dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylserine (DPPS), combined both as binary lipid bilayer assemblies and separately, under the influence of divalent Mg 2+ , a membrane bilayer fusogenic agent, are reported. Infrared vibrational spectroscopic analyses of the lipid acyl chain methylene symmetric stretching modes indicate that aggregates of the two phospholipid components exist as domains heterogeneously distributed throughout the binary bilayer system. In the presence of Mg 2+ , DPPS maintains an ordered orthorhombic subcell gel phase structure through the phase transition temperature, while the DPPC component is only minimally perturbed with respect to the gel to liquid crystalline phase change. The addition of Mg 2+ induces a reorganization of the lipid domains in which the gel phase acyl chain planes rearrange from an hexagonal configuration toward a triclinic, parallel chain subcell. Examination of the acyl chain methylene deformation modes at low temperatures allows a determination of DPPS microdomain sizes, which decrease in size upon the addition of DPPC-d 62 in the absence of Mg 2+ . On adding Mg 2+ , a uniform DPPS domain size is observed in the binary mixtures. In either the presence or absence of Mg 2+ , DPPC-d 62 aggregates remain in a configuration for which microdomain sizes are not spectroscopically measurable. Analysis of the acyl chain methylene deformation modes for DPPC-d 62 in the binary system suggests that clusters of the deuterated lipids are distributed throughout the DPPS matrix. Light scattering and fluorescence measurements indicate that Mg 2+ induces both the aggregation and the fusion of the lipid assemblies as a function of the ratio of DPPS to DPPC. The structural reorganizations of the lipid microdomains within the DPPS/DPPC bilayer are interpreted in the context of current concepts regarding lipid bilayer fusion.