A Novel Estimation Method of the Distribution of Carboxyl Groups Within Copolymer Particles Using Isothermal Titration Calorimeter

Summary: A novel quantitative method using isothermal titration calorimeter (ITC) for the estimation of the distribution of carboxyl groups within polymer particles has been proposed. The method has been employed to clarify the difference in the distribution between the particles prepared by batch emulsion copolymerization of styrene and methacrylic acid under inefficient and efficient stirring conditions. At inefficient stirring, monomer was floating as a layer on the aqueous medium, whereas at efficient stirring, the monomer phase was dispersed as droplets. Under inefficient stirring, methacrylic acid (MAA) polymerized faster than styrene (S) due to a slower diffusion rate of S than MAA into the aqueous medium, while under efficient stirring, S and MAA copolymerized at similar rates. ITC measurement showed that under inefficient stirring, the carboxyl groups were distributed mainly in the center of the particles, and their number decreased toward the surface. On the other hand, under efficient stirring, carboxyl groups were distributed homogeneously inside the particle.     

ATP-Responsive Nanoparticles Covered with Biomolecular Machine “Chaperonin GroEL”

Herein, we report an ATP-responsive nanoparticle (^GroELNP) whose surface is fully covered with the biomolecular machine “chaperonin protein GroEL”. ^GroELNP was synthesized by DNA hybridization between a gold NP with DNA strands on its surface and GroEL carrying complementary DNA strands at its apical domains. The unique structure of ^GroELNP was visualized by transmission electron microscopy including under cryogenic conditions. The immobilized GroEL units retain their machine-like function and enable ^GroELNP to capture denatured green fluorescent protein and release it in response to ATP. Interestingly, the ATPase activity of ^GroELNP per GroEL was 4.8 and 4.0 times greater than those of precursor ^cysGroEL and its DNA-functionalized analogue, respectively. Finally, we confirmed that ^GroELNP could be iteratively extended to double-layered NP.