Bayesian analysis of static light scattering data for globular proteins

Static light scattering is a popular physical chemistry technique that enables calculation of physical attributes such as the radius of gyration and the second virial coefficient for a macromolecule (e.g., a polymer or a protein) in solution. The second virial coefficient is a physical quantity that characterizes the magnitude and sign of pairwise interactions between particles, and hence is related to aggregation propensity, a property of considerable scientific and practical interest. Estimating the second virial coefficient from experimental data is challenging due both to the degree of precision required and the complexity of the error structure involved. In contrast to conventional approaches based on heuristic ordinary least squares estimates, Bayesian inference for the second virial coefficient allows explicit modeling of error processes, incorporation of prior information, and the ability to directly test competing physical models. Here, we introduce a fully Bayesian model for static light scattering experiments on small-particle systems, with joint inference for concentration, index of refraction, oligomer size, and the second virial coefficient. We apply our proposed model to study the aggregation behavior of hen egg-white lysozyme and human γS-crystallin using in-house experimental data. Based on these observations, we also perform a simulation study on the primary drivers of uncertainty in this family of experiments, showing in particular the potential for improved monitoring and control of concentration to aid inference.

Study of the solubilisation process of bacterial model membranes induced by DDAO

Solubilisation of two bacterial model membranes induced by N,N-dimethyl-1-dodecanamine-N-oxide (DDAO) was studied. The first model membrane consisted of a mixture of palmitoyloleoylphosphatidylethanolamine (POPE) and palmitoyloleoylphosphatidylglycerol (POPG) in a molar ratio 0.6:0.4 mol/mol, and a second model membrane was enriched with tetraoleoylcardiolipin (TOCL) with a composition POPE-POPG-TOCL = 0.67:0.23:0.1 mol/mol/mol. Solubilisation of these model membranes was studied by static light scattering (nephelometry). Effective ratio Re (the amount of DDAO integrated into the bilayer to the amount of lipid) at different steps of the solubilisation process was determined. The molar partition coefficient of DDAO was calculated – in case of the POPE-POPG membrane, Kp = 5,300 ± 400, for the POPE-POPG-TOCL membrane, Kp = 6,500 ± 500.

Optimasi Proses Hidrolisis Protein Dari Limbah Bulu Ayam

Limbah bulu ayam yang mengandung protein keratin telah direkomendasikan sebagai sumber nutrisi alternatif yang dapat digunakan untuk pakan ternak, industri kosmetik, dan industri pupuk. Tujuan dari penelitian ini adalah untuk mengetahui pengaruh konsentrasi NaOH terhadap kualitas hidrolisat bulu ayam. Penelitian dilakukan dengan optimasi proses hidrolisis limbah bulu ayam dengan metode basa menggunakan NaOH (rasio 1:6) dengan variasi konsentrasi 5%, 7,5% dan 10% selama 4 jam pada suhu 80ºC. Penentuan rendemen hidrolisat bulu ayam paling optimum dilakukan dengan analisis total protein menggunakan metode Kjeldahl, analisis asam amino dengan menggunakan Amino Acid Analyzer (AAA) dan identifikasi profil protein menggunakan metode Static light scattering (SLS). Hasil optimasi proses hidrolisis dapat disimpulkan bahwa hidrolisat bulu ayam dengan konsentrasi pelarut NaOH 5% menunjukkan hasil optimum dengan rendemen sebesar 70,24% , total protein 62,66 %, total asam amino bebas 39.126 % dan masa molekul protein dengan metode SLS menunjukkan hasil 4,31 kDa.

Volume Fraction Measurement of Soft (Dairy) Microgels by Standard Addition and Static Light Scattering

The volume fraction of the dispersed phase in concentrated soft (dairy) microgels, such as fresh cheese, is directly related to structure and rheology. Measurement or modeling of volume fraction for soft and mechanically sensitive microgel dispersions is problematic, since responsiveness and rheological changes upon mechanical input for these systems limits application of typical functional relationships, i.e., using apparent viscosity. In this paper, we propose a method to measure volume fraction for soft (dairy) microgel dispersions by standard addition and volume-weighted particle size distributions obtained by static light scattering. Relative particle volumes are converted to soft particle volume fraction, based on spiked standard particle volumes. Volume fractions for two example microgel dispersions, namely, differently produced fresh cheeses, were evaluated before and after post-treatments of tempering and mechanical processing. By selecting the size of standard particles based on size ratios and the levels of the mixing ratios/relative fractions, the method could be applied robustly within a wide range of particle sizes (1 to 500 μm) and multimodal size distributions (up to quadmodal). Tempering increased the volume fraction for both example microgel dispersions (P < 0.05). Subsequent mechanical treatment reduced the volume fraction back to the starting value before tempering (P < 0.05). Furthermore, it was shown that the increase and successive decrease in apparent viscosity with tempering and mechanical post-treatments is not exclusively due to particle aggregation and breakdown, but to volume changes of each particle. For environmentally responsive soft matter, the proposed method is promising for measurement of volume fraction.