Effects of pH on the Interactions and Conformation of Bovine Serum Albumin: Comparison between Chemical Force Microscopy and Small-Angle Neutron Scattering

The conformation of bovine serum albumin (BSA), as well as its interactions with negatively charged mica surfaces in saline solutions of different pH values, have been studied by small-angle neutron scattering (SANS) and chemical force microscopy (CFM), respectively. A new approach to extract the contribution of elementary interactions from the statistically averaged force-extension curves through self-consistent fitting was proposed and used to understand the effects of pH on the interactions and conformation of BSA in saline solutions. When pH increases, the SANS results reveal that the sizes of BSA molecules increase slightly, while the statistical analysis of the CFM results shows that the averaged pull-off force for the elongation monotonously decreases. The decrease of pull-off force with the increase of pH results from the decrease in the strength of hydrogen bonding and the number of interaction pairs, as well as the slight increase of the strength of van der Waals interaction. When pH approaches the isoelectric point (pI) of BSA, results from both SANS and CFM suggest a loss of long-range interactions in BSA molecules. Our results also suggest that the force-extension curve is mainly contributed by the van der Waals interaction. The combination of SANS and CFM provides new insight to understand the interactions and conformation of BSA molecules

Effect of annealing on the deformation mechanism of a styrene/n-butyl acrylate copolymer latex film investigated by synchrotron small-angle X-ray scattering

The deformation mechanism of a styrene/n-butyl acrylate copolymer latex film subjected to uniaxial tensile stress was studied by small-angle X-ray scattering. The influence of annealing at 23, 60, 80, and 100 degrees C for 4 h on microscopic deformation processes was elucidated. It was demonstrated that the microscopic deformation mechanism of the latex films transformed gradually from nonaffine deformation behavior to affine deformation behavior with increasing annealing temperature.