Antibody protein injections are used in various therapies. The conflicting requirements of minimizing the injection volumes and of limited injectable viscosities motivate pharmaceutical research on dense aqueous antibody solutions. The macroscopic phase behavior in protein solutions may depend on minute changes of, for instance, the temperature in a physiologically relevant range. We combine small-angle x-ray and neutron scattering, high-resolution neutron spectroscopy as well as x-ray photon correlation spectroscopy to obtain a dynamic picture on the molecular level of antibody solutions, systematically addressing the phase behavior comprising monomeric solution states, cluster formation, as well as gel- and glass-like arrested states depending on external parameters such as temperature or additives.

The protein and cluster center-of-mass diffusion and the internal relaxations on the molecular level is measured simultaneously. The results are interpreted with models and simulations from colloid physics. We expect to better understand the link between microscopic interactions and phase behavior relevant for pharmaceutical applicability, as well as, more fundamentally, the link between macroscopic viscosity and diffusion on nanosecond time scales; and the biological, pharmacological and medical function and specificity of antibodies.

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