Generalized Einstein relation for the mutual diffusion coefficient of a binary fluid mixture

High-Throughput Screening for Colloidal Stability of Peptide Formulations Using Dynamic and Static Light Scattering

Selection of an appropriate formulation to stabilize therapeutic proteins against aggregation is one of the most challenging tasks in early-stage drug product development. The amount of aggregates is more difficult to quantify in the case of peptides due to their small molecular size. Here, we investigated the suitability of diffusion self-interaction parameters (k_D) and osmotic second virial coefficients (B₂₂) for high-throughput (HT) screening of peptide formulations regarding their aggregation risk. These parameters were compared to the effect of thermal stress on colloidal stability. The formulation matrix comprised six buffering systems at two selected pH values, four tonicity agents, and a common preservative. The results revealed that electrostatic interactions are the main driver to control colloidal stability. Preferred formulations consisted of acetate and succinate buffer at pH 4.5 combined with glycerol or mannitol and optional m-cresol. k_D proved to be a suitable surrogate for B₂₂ as an indicator of high colloidal stability in the case of peptides as was previously described for globular proteins and antibodies. Formulation assessment solely based on k_D obtained by HT methods offers important insights into the optimization of colloidal stability during the early development of peptide-based liquid formulations and can be performed with a limited amount of peptide (∼360 mg).

Mutual Diffusivity of an n-Hexane-2,2-Dimethyl Butane Binary Mixture Confined to Zeolite Y

A molecular dynamic study of a mixture of n-hexane and 2,2-dimethyl butane (22DMB) confined to zeolite NaY has been carried out to understand the distinct diffusivity and mutual diffusivity. Results have been compared with the bulk mixture. For each of these mixtures, eight different runs were employed to compute distinct and mutual diffusivity. From the velocity auto- and cross-correlation functions between n-hexane and n-hexane, n-hexane and 22DMB, 22DMB and 22DMB, the self- and distinct diffusivity of the mixture has been computed. The thermodynamic factor and mutual diffusivity have been calculated. The ratio of D₁₁ to D_s is seen to be 1.11 and 0.75 for the confined mixture, while they are 1.21 and 0.79 for the bulk mixture at 200 and 300 K, respectively.