Antibody Binding Heterogeneity of Protein A Resins

Protein A affinity chromatography is a core unit operation in antibody manufacturing. Nevertheless, there is not enough understanding of in‐column antibody adsorption in the Protein A capture step. This work aims to investigate in situ the establishment of an antibody (trastuzumab) layer during Protein A chromatography both in terms of energetic contributions and uptake kinetics. Flow microcalorimetry is employed as a technique with an in situ operating detector, which provides an understanding of the thermodynamics of the adsorption process. In addition, the antibody uptake rate is also investigated in order to establish a correlation between its diffusion on the stationary phase and the associated thermodynamics. Two resins with different particle size, intraparticle porosity, and a Protein A ligand structure are studied: the synthetically engineered B‐domain tetrameric MabSelect SuRe and the synthetically engineered C‐domain hexameric TOYOPEARL AF‐rProtein A HC. The uptake rate follows a pore diffusion model at low equilibrium time, showing a slower diffusivity after a certain time because of the heterogeneous binding nature of these two resins. In addition, the microcalorimetric studies show that adsorption enthalpy is highly favourable at low isotherm concentrations and evolves toward an equilibrium with increasing surface concentration. These data suggest that the relationship between adsorption enthalpy and the establishment of the antibody layer in the Protein A chain is consistent with heterogeneous adsorption.     

On the mechanisms of the effect of imino acids on the physical characteristics of collagens

The effect of imino acids on thermodynamic characteristics of the collagen-type structures in collagens from different sources is analyzed. It is demonstrated that the main mechanism of the entropy increase in the system water-protein with an increase in the imino acid content in a polypeptide chain is a change in the number of cooperative regions, detectable during the melting of a fibrous macromolecule. The variation of physical characteristics of the cooperative units determines, in particular, the variation of the hydrogen bond parameters, which appears as a broadening of the bands of NH valence vibrations and the half-widths of transitions in postdenaturation structures. Thus, the main mechanism of how imino acids act on the thermodynamic characteristics of collagens is connected with a complex nature of the denaturation process, when any substitutions of imino acids for amino acids significantly change the dehydration-hydration of the native and denatured states.     

Prediction on elastic properties of Nb-doped Ni systems

On the basis of first-principles simulation, the structure, formation enthalpy and mechanical properties (elastic constant, bulk and shear modulus and hardness) of five Nb-doped Ni systems are systematically studied. The calculated equilibrium volume increases with the Nb concentration increasing. The computational elastic constants and formation enthalpy indicate that all Nb-doped Ni systems are mechanically and thermodynamically stable in our research. The hardness of these systems was predicted after the bulk modulus and shear modulus had been accurately calculated. The results show that the hardness increases with the Nb concentration increasing when the Nb concentration was below 4.9%, beyond which the hardness will decrease; this is within the scope of our study.