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.