Analytical ultracentrifugation for studying molecular cluster solutions

Analytical ultracentrifugation (AUC) is a powerful and information-rich technique for directly characterizing the molecular weight, size, shape, dispersity, and association behavior of species in their native solution environment, spanning a broad molecular weight range of ~ 100 Da to 100 MDa. Unlike many orthogonal methods, AUC does not require immobilization, labeling, or assumptions regarding sample homogeneity. With recent advances in instrumentation and data analysis software, AUC enables more accurate and reliable characterization of diverse solution systems, including biomacromolecules, colloids, surfactants, and polymers. Owing to their uniform and well-defined molecular weights, sizes, and shapes, molecular clusters are particularly well suited for AUC studies. In this work, we investigate molecular cluster solutions using AUC, highlighting its significant potential in this field. Even relatively simple AUC experiments can provide detailed and quantitative insights into molecular cluster systems, including hydration shell thickness, intermolecular distances in dimers, and adsorption of organic ligands such as amino acids.