Investigations of the water clusters of the protected amino acid Ac-Phe-OMe by applying IR/UV double resonance spectroscopy: microsolvation of the backbone

Abstract

In order to investigate the influence of hydration on the backbone of a peptide or protected amino acid, the successive aggregation of water to Ac-Phe-OMe is analysed by means of IR/UV double resonance spectroscopy. To achieve meaningful results the spectra have been recorded in the region of the amide A and OH stretching vibrations as well as the amide I/II modes. Comparison with ab initio and DFT calculations leads to size-selective structural assignments. Two isomers of the mono- and dihydrated clusters and one isomer of the trihydrated cluster are observed in the molecular beam leading to a formation of the first solvation shell of the backbone. In case of the trihydrated cluster the backbone geometry is remarkably changed compared to the structure of the monomer since a network of water molecules can be formed.

Isolated Neutral Peptides

“…This type of experiment on hydrates is, however, difficult to interpret and requires heavy reliance on vibrational spectral data to be successful, at least in terms of an unambiguous assignment. Experimental results beyond a single solvent molecule remain seldom; the interpretation being complicated [55,102,136] by vibrational coupling between solvent molecules.…”

“…Theoretically predicted some time ago [196], experimental illustrations of these effects have been published only quite recently. Several groups have shown that peptides or related flexible molecules undergo a significant structural change upon solvation, as indicated by changes in their H-bonding network [53,55,102,129,136]. One of the most dramatic studies, carried out on a capped amino-acid solvated by one water molecule, documented the effect of microhydration and its dependence on the solvation site occupied by the water molecule for each conformation.…”

“…In this scope, complexation of model peptides [46,53,55,65,73,87,90,100,102,120,124,129,136] shed light on the interface between a protein and its environment.…”

It Is Important to Compute Intramolecular Hydrogen Bonding in Drug Design?

“…Useful information can be obtained from experimental gas-phase hydration/solvation studies augmented with theoretical calculations [108][109][110][111][112][113][114][115][116] or specific theoretical calculations for hydrated amino acid side chains, nucleotid base and sugar models [117][118][119][120][121].…”

Structural Analysis of an Isolated Cyclic Tetrapeptide and its Monohydrate by Combined IR/UV Spectroscopy

“…With the established scaling factor of 0.9613 [17] the A-type structures show NH vibrations around 3330 cm…”