Controlling guest-host interactions in self-assembled materials

Aqueous solutions of self-assembling macromolecules can be found in many industrial formulations, as well as in many living organisms. Regardless of the specific system, the self-assembling macromolecules are rarely found in the absence of other solutes or guest species. Such components may include fragrance molecules incorporated into block-copolymer micelles for use in detergents, dyes included in micellar precursor solutions for the synthesis of mesostructured silica-block copolymer composites, or specifically designed additives for controlling protein folding and activity. A detailed understanding of the structures and dynamic molecular interactions among the various species in solution and their influences on macromolecule aggregation and phase behaviors is of paramount importance for designing systems with improved properties and performance.; Unambiguous measurements of the loci of interaction and solubilization of small molecule species (e.g., dyes or surfactants) within self-assembling block-copolymer species or proteins in aqueous solutions have been established. This has been achieved by exploiting powerful correlative multidimensional nuclear magnetic resonance (NMR) spectroscopy techniques, including pulsed-field-gradient diffusion measurements, which provide detailed molecular insights into a variety of heterogeneous self-assembled systems. Furthermore, these insights and measurements enable the solution conditions to be established that permit the control and release of such guest molecules from association with macromolecular carrier species into the surrounding solution. Specifically, the use of temperature to control the distribution of porphyrin guest-species in a block-copolymer host and the light-dependent folding and unfolding of bovine serum albumin through varying interactions with an azo-benzene functionalized surfactant are demonstrated. In the absence of long-range order in these complex systems, advanced NMR spectroscopy methods provide crucial and highly selective means for characterizing component structures, dynamics and interactions at a molecular level. The analytical approach and the resulting insights developed here are general and anticipated to be of broad applicability to systems of interest in medicine, biology, and industry.