3.3. Circular Dichroism Spectroscopy

All CD measurements were performed on a Jasco J-710 instrument (JASCO Inc., Easton, MD, USA) either at 25 °C or as a function of the temperature (from 25 to 65 °C, step of 10 °C). Spectra were recorded in 10 mM sodium phosphate buffer at pH 7.4, using 2 mm quartz cells in the wavelength region from 190 to 300 nm. A correction for solvent baseline and polysaccharide contribution was made digitally in each case. Analyses were performed using a peptide concentration of 20 µM and varying the polysaccharide concentrations (referred to the mass of the polysaccharide’s repeating unit) as indicated in figures. Spectra were the result of accumulation of two scans. In all experiments, the polysaccharide-buffered solution was added to the buffered solution of peptide up to the desired concentration.

The percentage of α-helix content was determined as [θ]/[θ]_α, where [θ] is the observed molar ellipticity at 222 nm and [θ]_α the molar ellipticity of a fully structured peptide calculated using the equation [θ]_α = −40,000·(1 − 2.5/n), where n is the number of amino acid residues in the peptide and −40,000 the estimated ellipticity of a fully structured infinitely long helix [23,24].