S. Chodankar

Surfactant-induced protein unfolding as studied by small-angle neutron scattering and dynamic light scattering

The structural changes of protein bovine serum albumin (BSA) during its unfolding on the addition of anionic surfactant sodium dodecyl sulfate (SDS) have been studied using small-angle neutron scattering (SANS) and dynamic light scattering (DLS). It is observed that at small surfactant concentrations, individual surfactant molecules bind to the protein, increasing the size of the protein. On the other hand, surfactant molecules at higher concentrations aggregate to form micelle-like clusters along the unfolded polypeptide chains of the protein. SANS data indicates the formation of a fractal structure representing a necklace model of micelle-like clusters randomly distributed along the polypeptide chain. The overall size of the complex increases and the fractal dimension decreases on increasing the surfactant concentration. The size of the micelle-like clusters does not show any change, while the number of such micelle-like clusters in protein–surfactant complexes increases with the surfactant concentration. The conformation of the unfolded protein has been determined directly using contrast variation SANS measurements by contrast matching the surfactant to the medium. It is found that the protein acquires a random coil Gaussian conformation on unfolding, with its radius of gyration increasing with an increase in surfactant concentration. The results of DLS measurements are found to be in good agreement with those obtained using SANS.

Effect of pH and Protein Concentration on Rheological and Structural Behavior of Temperature-induced Bovine Serum Albumin Gels

The rheology of a temperature-induced protein bovine serum albumin gel is shown to strongly depend on the solution pH and protein concentration. Small-angle neutron scattering studies showed the presence of a fractal structure of the gels, resembling the aggregation of protein molecules and causing a three-dimensional network kind of arrangement. The fractal dimensions were observed to be constant and independent of the variation of pH and the protein concentration. The results of rheology and scattering experiments are correlated in terms of pH-dependent flexibility of flocs in the gels and hindrance to flow with concentration, while the structure of such flocs remains similar irrespective of the solution conditions.

Structural Studies of Protein‐Surfactant Complexes

The structure of protein‐surfactant complexes of two proteins bovine serum albumin (BSA) and lysozyme in presence of anionic surfactant sodium dodecyl sulfate (SDS) has been studied using small‐angle neutron scattering (SANS). It is observed that these two proteins form different complex structures with the surfactant. While BSA protein undergoes unfolding on addition of surfactant, lysozyme does not show any unfolding even up to very high surfactant concentrations. The unfolding of BSA protein is caused by micelle‐like aggregation of surfactant molecules in the complex. On the other hand, for lysozyme protein there is only binding of individual surfactant molecules to protein. Lysozyme in presence of higher surfactant concentrations has protein‐surfactant complex structure coexisting with pure surfactant micelles.

Characterization of a Water‐based Surfactant Stabilized Ferrofluid by Different Scattering Techniques

Different scattering techniques dynamic light scattering (DLS), small‐angle X‐ray scattering (SAXS) and small‐angle neutron scattering (SANS) have been used to characterize a water‐based surfactant stabilized ferrofluid having ferrite (Fe3O4) particles coated with oleic acid. DLS gives the overall size of the particle along with the thickness of the surfactant (oleic acid) coating and water of hydration attached to the particle. SAXS only measures the size of the ferrite particle due to poor contrast of surfactant coating for X‐rays. SANS with the possibility to vary the contrast provides both the size of the ferrite particle and the thickness of the surfactant coating on the particle.

SANS and DLS Studies of Protein Unfolding in Presence of Urea and Surfactant

Small‐angle neutron scattering (SANS) and dynamic light scattering (DLS) have been used to study conformational changes in protein bovine serum albumin (BSA) during its unfolding in presence of protein denaturating agents urea and surfactant. On addition of urea, the BSA protein unfolds for urea concentrations greater than 4 M and acquires a random coil configuration with its radius of gyration increasing with urea concentration. The addition of surfactant unfolds the protein by the formation of micelle‐like aggregates of surfactants along the unfolded polypeptide chains of the protein. The fractal dimension of such a protein‐surfactant complex decreases and the overall size of the complex increases on increasing the surfactant concentration. The conformation of the unfolded protein in the complex has been determined directly using contrast variation SANS measurements by contrast matching the surfactant to the medium. Results of DLS measurements are found to be in good agreement with those obtained using ...