Time-Resolved Optical Kerr-Effect Spectroscopy of Low-Frequency Dynamics in Di-l-alanine, Poly-l-alanine, and Lysozyme in Solution

Abstract

The low-frequency spectra of peptides and proteins in solution have been investigated with optical heterodyne-detected Raman-induced Kerr-effect spectroscopy. Spectra were obtained for di-l-alanine ALA(2) and poly-l-alanine (PLA) in dichloroacetic acid solution. The conformational dependence of those spectra at low frequency has been analyzed. ALA(2) displays a band centered at 50 cm-1, whereas the alpha-helical PLA shows two shoulders at 60 and 140 cm-1. The similarity of the spectral features observed in PLA to those in water can be explained by analogous acoustic translational modes in the hydrogen network of the PLA alpha-helix. The mostly alpha-helical protein lysozyme in aqueous solution has also been investigated and showed significantly more structure with modes at 10, 35, 73, 106, and 164 cm-1.

Terahertz underdamped vibrational motion governs protein-ligand binding in solution

“…The OKE signal arises from orientational motions that in proteins include the librational motions of amino-acid side chains. It has been shown previously that OKE is sensitive to protein structural motifs that appear in the terahertz region [31][32][33] .…”

A new ultrafast technique for measuring the terahertz dynamics of chiral molecules: The theory of optical heterodyne-detected Raman-induced Kerr optical activity

“…This is similar to a balanced-detection scheme used previously in OHD-RIKES. 3,11,13,15 In Jones-matrix notation:…”

“…Therefore, it is clear that the first OHD-RIKOA experiments should be performed in pure liquids of chiral molecules. The technique would also have promising applications to the study of intermediate-frequency modes in peptides and proteins [11][12][13] where it may be able to clearly distinguish backbone torsional modes from hydrogen-bond stretching modes. It is impossible to predict at this point whether the various intermediate-frequency modes that are typically identified in a fit to an OHD-RIKES spectrum will have very different or similar tensor invariants.…”

“…One especially sensitive technique is based on the ultrafast Kerr effect and is often referred to as optical heterodyne-detected Raman-induced Kerr-effect spectroscopy ͑OHD-RIKES͒. 1 OHD-RIKES has been applied to a great variety of condensed-phase systems such as polar [2][3][4] and nonpolar liquids, 5,6 liquid crystals, 7,8 liquid mixtures, 9 solutions, 10 protein solutions, [11][12][13] and other inhomogeneous media. 14,15 Typical OHD-RIKES spectra cover the approximate range of 0.3 to Ͼ500 cm −1 corresponding to time scales of about 50 fs to 100 ps.…”

Terahertz dynamics of ionic liquids from a combined dielectric relaxation, terahertz, and optical Kerr effect study: evidence for mesoscopic aggregation

“…The full DR spectrum is reconstructed by patching using the Kramers-Kronig transform. OKE measures the <α xy α xy (t)> correlation function of the anisotropic part of the polarisability tensor directly in the time domain [17,[21][22][23][24]. In our set-up using a laser producing 20-fs pulses, delays from 10 fs to 4 ns can be achieved corresponding to the effective frequency range 250 MHz to ~50 THz.…”