A Vibrational Circular Dichroism Microsampling Accessory: Mapping Enhanced Vibrational Circular Dichroism in Amyloid Fibril Films

Abstract

We report the first vibrational circular dichroism (VCD) measurement of spatial heterogeneity in a sample using infrared (IR) microsampling. Vibrational circular dichroism spectra are typically measured using a standard IR cell with an IR beam diameter of 10 mm or greater making it impossible to investigate the spatial heterogeneity of a solid film sample. We have constructed a VCD sampling assembly with either 3 mm or 1 mm spatial resolution. An XY-translation stage was used to measure spectra at different spatial locations producing IR and VCD maps of the sample. In addition, a rotating sample stage was employed using a dual photoelastic modulator (PEM) setup to suppress artifacts due to linear birefringence in solid-phase or film samples. Infrared and VCD mapping of an insulin fibril film has been carried out at both 3 and 1 mm spatial resolution, and lysozyme films were mapped at 1 mm resolution. The IR spectra of different spots vary in intensity due primarily to sample thickness. The changes in the VCD intensity across the map largely correlate to corresponding changes in the IR map. Closer inspection of the insulin map revealed changes in the relative intensities of the VCD spectra not present in the parent IR spectra, which indicated differences in the degree of supramolecular chirality of the fibrils in the various spatial regions. For lysozyme films, in addition to different degrees of supramolecular chirality, reversal of the net fibril chirality was observed. The large signal-to-noise ratio observed at 1 mm resolution implies the feasibility of further increasing the spatial resolution by one or two orders of magnitude for protein fibril film samples.

Amplified vibrational circular dichroism as a manifestation of the interaction between a water soluble gold nanocluster and cobalt salt

“…Using this enhancement, the study of larger biomolecules or the formation and development of protein amyloid fibrils are now feasible. [25][26][27] In contrast to biomolecules no such enhancement of VCD signals has been reported yet for nanoclusters. In the following we report for the first time enhancement of VCD signal for a water soluble nanocluster.…”

Multidimensional Vibrational Circular Dichroism Apparatus Equipped with Quantum Cascade Laser and Its Use for Investigating Some Peptide Systems Containing d-Amino Acids

“…A time-resolved VCD based on linearly polarized coherent femtosecond light was developed to follow the ultrafast structural changes of limonene . A new mapping-type VCD spectrometer with a microsampling accessory was constructed to analyze the chiral domains within amyloid fibrils …”

Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

“…Experimentally, this task is difficult because of the weakness of the signal and limitations of the infrared optics. Nevertheless, several studies appeared, such as that of Lu et al . Using two additional fast‐focusing lenses placed before and after the sample on a micro‐XY positioning stage, they converted dual‐PEM VCD instrument into a microsampling device with a spatial resolution of about 1 mm, and used it to assess the heterogeneity of insulin and hen egg‐white lysozyme amyloid fibril films.…”