Circular dichroism studies of low molecular weight hydrogelators: The use of SRCD and addressing practical issues

Circular dichroism (CD) spectroscopy has been used extensively for the investigation of the conformation and configuration of chiral molecules, but its use for evaluating the mode of self-assembly in soft materials has been limited. Herein, we report a protocol for the study of such materials by electronic CD spectroscopy using commercial/benchtop instruments and synchrotron radiation (SR) using the B23 beamline available at Diamond Light Source. The use of the B23 beamtime for SRCD was advantageous because of the unique enhanced spatial resolution achieved because of its highly collimated and small beamlight cross section (ca. 250 μm) and higher photon flux in the far UV region (175-250 nm) enhancing the signal-to-noise ratio relative to benchtop CD instruments. A set of low molecular weight (LMW) hydrogelators, comprising two Fmoc-protected enantiomeric monosaccharides and one Fmoc dipeptide (Fmoc-FF), were studied. The research focused on the optimization of sample preparation and handling, which then enabled the characterization of sample conformational homogeneity and thermal stability. CD spectroscopy, in combination with other spectroscopic techniques and microscopy, will allow a better insight into the self-assembly of chiral building blocks into higher order structural architectures.