Local Ordering of Lattice Self-Assembled SDS@2β-CD Materials and Adsorbed Water Revealed by Vibrational Sum Frequency Generation Microscope

VSFG (vibrational sum frequency generation) microscopy was used to study the SDS@2β-CD system, a synthetic capsid-like self-assembled material. We found because of strong hydrogen-bond interactions between water and the assemblies, water molecules are template to adopt the local mesoscopic ordering of the self-assemblies, which allows VSFG to probe water on nonflat interfaces. We show that the origin of the VSFG signal from the self-assembly is a combination of individual molecular chirality and highly coordinated ordering of the self-assembly, which gives rise of anisotropic signals, e.g., under SSS polarization. A similar strategy could be applied to other self-assembled materials composed by molecules without inversion symmetry. Using an imaging process, VSFG spectra of different self-assembly sheets were spatially resolved. We found heterogeneity among different domains, which can be attributed to variations in the hydration level of different domains. Since the SDS@2β-CD system is a synthetic lattice self-assembly, such heterogeneity could also exist in other natural lattice assemblies such as a virus and tubulin.