4 research outputs found
Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme
We report on a SANS investigation into the potential for these structural
reorganization of complexes composed of lysozyme and small PSS chains of
opposite charge if the physicochemical conditions of the solutions are changed
after their formation. Mixtures of solutions of lysozyme and PSS with high
matter content and with an introduced charge ratio [-]/[+]intro close to the
electrostatic stoichiometry, lead to suspensions that are macroscopically
stable. They are composed at local scale of dense globular primary complexes of
radius ~ 100 {\AA}; at a higher scale they are organized fractally with a
dimension 2.1. We first show that the dilution of the solution of complexes,
all other physicochemical parameters remaining constant, induces a macroscopic
destabilization of the solutions but does not modify the structure of the
complexes at submicronic scales. This suggests that the colloidal stability of
the complexes can be explained by the interlocking of the fractal aggregates in
a network at high concentration: dilution does not break the local aggregate
structure but it does destroy the network. We show, secondly, that the addition
of salt does not change the almost frozen inner structure of the cores of the
primary complexes, although it does encourage growth of the complexes; these
coalesce into larger complexes as salt has partially screened the electrostatic
repulsions between two primary complexes. These larger primary complexes remain
aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition
of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary
complex with a [-]/[+]intro close to 1, only slightly changes the inner
structure of the primary complexes. Moreover, in contrast to the synthesis
achieved in the one-step mixing procedure where the proteins are unfolded for a
range of [-]/[+]intro, the native conformation of the proteins is preserved
inside the frozen core
Internal structures of agar-gelatin co-hydrogels by light scattering, small-angle neutron scattering and rheology
Internal structures of agar-gelatin co-hydrogels were investigated as a function of their volumetric mixing ratio, \ensuremath r=[\mathrm{AG}]:[\mathrm{Ge}]=0.5 , 1.0 and 2.0 using dynamic light scattering (DLS), small-angle neutron scattering (SANS) and rheology. The degree of non-ergodicity ( \ensuremath X=0.2\pm0.02 , which was extracted as a heterodyne contribution from the measured dynamic structure factor data remained less than that of homogeneous solutions where ergodicity is expected (X = 1 . The static structure factor, I(q) , results obtained from SANS were interpreted in the Guinier regime (low-q , which implied the existence of 250 nm long rod-like structures (double-helix bundles), and the power law (intermediate-q regions yielded \ensuremath I(q)\sim q^{-\alpha} , with = 2.3 , 1.8 and 1.6 for r = 0.5 , 1.0 and 2.0. This is indicative of the presence of Gaussian chains at low r , while at r = 2 there was a propensity of rod-shaped structures. The gel strength and transition temperatures measured from frequency sweep and temperature ramp studies were suggestive of the presence of a stronger association between the two biopolymer networks at higher r . The results indicate that the internal structures of agar-gelatin co-hydrogels were highly dependent on the volumetric mixing ratio