State-resolved THz spectroscopy and dynamics of crystalline peptide–water systems

Abstract

Vibrationally state-resolved THz spectra are obtained at cryogenic temperatures for three crystalline peptide-water systems that represent different structural motifs. The systems include two types of secondary structures and a hydrophobic peptide nanopore structure. Almost all of these systems are shown to undergo exchange with water at room temperature that alters the hydrogen bonding network in ways easily detectable in the THz region at cryogenic temperatures. Stark differences are observed in the spectra of model a-helical and b-sheet structures upon water removal at hydrophilic binding sites. However, within the confined pore of a hydrophobic nanotube, water in the form of helical wires has a subtle but significant impact on the phonon modes of the tube. The THz spectra are shown to easily distinguish between the different hydration states of the system that have been independently characterized by mass change measurements. Spectral comparisons with quantum chemical predictions of fully relaxed crystal structures confirm the hydration states and give detailed information about the free energies associated with dehydration. The vibrational free energies are shown to make significant contributions to the overall energy balance of the dehydration processes.

Molecular dynamics simulations of macromolecular crystals

“…As a result, much of what has been learned about biological molecules in crystals has been restricted to smaller systems, like carbohydrates and peptides, that contain fragments of macromolecules but which can also be stripped of water . In these cases, molecular dynamics simulations of crystals can give a good account of the observed spectra.…”

Adhesion of Alumina Surfaces through Confined Water Layers Containing Various Molecules

“…Many examples justify such study: (i) cements are hydraulic binders which inherently confine water at the nanometric gaps between their hydrating particles, 9 such confined water having an important effect on the mechanical strength of cementitious materials; 10 (ii) interaction between proteins and their hydration waters, as proteins are separated on average by 2-3 water layers, 11 is one of the most complex problems in biophysics, provided small changes in the structure and dynamical behaviour of the water molecules at peptide-water interface can modify protein conformation, which, in turn, determines its function; 12 and (iii) sea cucumbers are example of echinoderms with the ability to rapidly and reversibly alter the stiffness of their connective tissue, whenever they secrete soluble macromolecules triggered by any threatening condition. Man-made materials inspired by the ability of sea cucumbers to increase elastic modulus by an order of magnitude have already been developed, and water acts as a competitive hydrogen bonding agent in order to control their stiffness.…”

Frontiers in spectroscopy

“…59 David Klug described the application of 2D-IR spectroscopy to the study of proteins 60 followed by David Plusquellic's presentation of the THz spectroscopy of the peptide water system. 61 Martina Havenith presented her studies of hydration and hydrophobicity by means of THz spectroscopy of the solvated amino acids. 62 Tim Zwier presented his IR-and UV spectroscopic studies of conformations in gpeptides.…”