Inelastic light-scattering study of polyadenilic acid

Association Behavior of Biotinylated and Non-Biotinylated Poly(ethylene oxide)-b-poly(2-(diethylamino)ethyl methacrylate)

Biotinylated and non-biotinylated copolymers of poly(ethylene oxide) (PEO) and poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) were synthesized by the atom transfer radical polymerization technique. The chemical compositions of the copolymers as determined by NMR are represented by PEO(113)PDEAEMA(70) and biotin-PEO(104)PDEAEMA(93), respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering, static light scattering, and transmission electron microscopy. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (R(h)) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with R(h) values of about 6-7 nm. However, at a physiological salt concentration (c(s)) of about 0.16 M NaCl and a pH of 7-8, the copolymers form large loosely packed Gaussian chains, which were not present at the low c(s) of 0.001 M NaCl. The critical micelle concentrations (cmc's) and the cytotoxicities of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical cmc values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05 mg/g (>83% cell survival at this concentration).

Photon correlation spectroscopy and light scattering of eye lens proteins at high concentrations

The bovine eye lens protein, alpha L crystallin, has been studied with photon correlation spectroscopy and statical light scattering in the concentration range up to 200 g/l in different solvent conditions. At higher concentration (c greater than 70 g/l) the scattering behavior is quite complicated, which results in nonexponential correlation functions. Three methods have been used for the analysis of these correlation functions, namely, cumulant analysis, sum of two exponentials analysis, and exponential sampling method. These methods resulted in very similar results. The highly concentrated solutions contain two scattering entities: the single alpha L crystallin and a rather heterogeneous population of large clusters. The statical light-scattering experiments can be interpreted in the same way and gave consistent results for the dimensions of the large scattering units. The formation of these clusters, which are strong light scatterers, is superimposed on an increasing degree of correlation between the bulk of the alpha L-crystallins, resulting in a net decrease of light scattering as a function of concentration.