Circular dichroism and Fourier transform infrared spectroscopic studies on self‐assembly of tetrapeptide derivative in solution and solvated film

Abstract

Aggregation of the hydrophobic peptide derivative Boc-Ala-Ile-Ile-Gly-OMe (1) was examined in methanol solution and in solvated film states. Formation of the peptide by self-assembly was evidenced using fluorescence [Mg salt of 8-anilino-naphthalenesulfonic acid (ANS) as an external probe] and circular dichroism (CD) spectroscopic techniques. In solution, peptide 1 formed as a stable aggregate at a concentration around 3 x 10(-4)m. The peptide gelled into a thin film for which we carried out CD and Fourier transform infrared (FTIR) measurements. Our spectroscopic study on peptide films at differing methanol concentrations indicates that the helical content of the peptide decreases with decreasing methanol concentration in solvated films. However, by reducing the methanol concentration we were able to observe a conformational transition from a predominantly helical turn to a beta-sheet structure via a random coil conformation. Our study focused on the aggregation of the alpha-helical turn-forming peptide derivative, which shows conformational transition on changing solvent concentration in the film form.

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“…ANS (an environmentally sensitive probe) is essentially non fluorescent in water, becoming fluorescent in a less polar environment, e.g., when bound to hydrophobic sites in proteins [29,30]. It was shown before that this probe can be used to study peptide assemblies [30].…”

“…ANS (an environmentally sensitive probe) is essentially non fluorescent in water, becoming fluorescent in a less polar environment, e.g., when bound to hydrophobic sites in proteins [29,30]. It was shown before that this probe can be used to study peptide assemblies [30]. Therefore, we used the increase in ANS fluorescence intensity (increased quantum yield) to study the existence of hydrophobic binding between T20 or T-1249 and S peptides because this binding may lead to the formation of hydrophobic grooves where ANS can insert, with a concomitant increase in fluorescence intensity.…”