First Observation of the Molten Globule State of a Single Homopolymer Chain.

In a recent laser light-scattering study on the “globule-to-coil” transition (melting) of a single poly(Nisopropylacrylamide) (PNIPAM) linear chain in water (the solution is in the stable one-phase region at all temperatures), we observed that at the initial melting stage the ratio of the hydrodynamic radius to the radius of gyration underwent an unexpected maximum s,1.61d which is even higher than s5y3d1y2 predicted for a rigid and uniform globule, indicating a molten globule. This finding suggests that just as with a protein molecule the melting of a homopolymer globule is not an all-or-none process and the molten state is a general phenomenon for macromolecules in solution. [S0031-9007(96)01345-2]