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

Abstract

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.

Nanoscale Probing of the Supramolecular Assembly in a Two‐Component Gel by Near‐Field Infrared Spectroscopy

“…[6][7][8][9][10][11] To date, the secondary and higher-order architectures of the gelator molecules are mainly probed by ultraviolet-visible (UV-vis), circular dichroism (CD) and far-field FTIR spectroscopy techniques. [12][13][14][15][16][17][18][19] However, these techniques solely probe the intermolecular interactions of the gelator molecules and higher-order molecular assemblies within the gel network at the macroscale (i. e. in bulk systems). Indeed, the farfield ATR-FTIR spectra of supramolecular gels contain the average of the vibrational bands of the gel system.…”

Chirality in peptide‐based materials: From chirality effects to potential applications

“…27,28 For these soft materials, the Mueller matrix polarimetry or ellipsometry could be used to probe their chiral parameters. 29,30 Nuclear magnetic resonance (NMR) is also a powerful tool for the identification of chemical structure of chiral polypeptides, especially for probing the narrow conformational space like α-helices and 3 10 -helices, 31,32 or left-handed polyproline type II helices. 33,34 Furthermore, Fourier transform infrared spectrum (FT-IR), 35,36 Raman spectrum, 37,38 and isothermal titration calorimetry (ITC) [39][40][41] have been successfully used to investigate the roles of delicate groups in chiral recognition and assembly behaviors.…”

“…Since the function and activity of peptides are closely related to their foldings, the characterization of chiroptical properties of the films is essential for the uniform reproduction 27,28 . For these soft materials, the Mueller matrix polarimetry or ellipsometry could be used to probe their chiral parameters 29,30 . Nuclear magnetic resonance (NMR) is also a powerful tool for the identification of chemical structure of chiral polypeptides, especially for probing the narrow conformational space like α‐helices and 3 10 ‐helices, 31,32 or left‐handed polyproline type II helices 33,34 .…”

CD Imaging at High Spatial Resolution at Diamond B23 Beamline: Evolution and Applications

“…The self-assembly of three different peptide-based compounds, GalNHFmoc (1 in Figure 1M), GlcNHFmoc (2 in Figure 1M), and Fmoc-FF (3 in Figure 1M) from sol to gel state was for the first time investigated using the B23 vertical chamber developed for high throughput CD (HTCD) (Hussain et al, 2016) to probe the homogeneity and uniformity of the supramolecular structure of the three hydrogel materials (Sitsanidis et al, 2018) of different adjacent spots of about 100 μm size. This was achieved by using a 10 × objective lens that focused the beamlight to about 100 μm in diameter on the sample without creating spectral distortions.…”

“…All samples were gelled in the cuvette cells at a concentration of 2.0 mg ml −1 . For each specimen, three different positions were measured as illustrated in the insert [redrawn from Sitsanidis et al (2018)]. supramolecular structure of the polymer.…”