4 4 dimethyl 4 silapentane 1 sulfonic acid dss

The parent peptide, TK9 and its shorter fragments (Scheme 1) were synthesized on a solid phase peptide synthesizer (Aapptec Endeavor 90) using Fmoc protected amino acids and Rink Amide MBHA resin (substitution 0.69 mmol/g; Novabiochem, San Diego, California) by following a solid phase peptide synthesis protocol described elsewhere.^{17 ,18 (link)} All the crude peptides were further purified by reverse phase HPLC (SHIMADZU, Japan) using a Phenomenix C18 column (dimension 250 × 10 mm, pore size 100 Å, 5-μm particle size) by linear gradient elution technique using Water and Methanol as solvent both containing 0.1% TFA as the ion pairing agent. The purity and molecular weight of the eluted peptides were confirmed by MALDI-TOF (Bruker, Germany). 4,4-dimethyl-4-silapentane-1-sulfonic acid (DSS) and deuterium oxide (D₂O) were purchased from Cambridge Isotope Laboratories, Inc. (Tewksbury, MA). Thioflavin T dye was purchased from Sigma Aldrich (St. Louis, MO). Throughout the experiment HPLC grade water was used for sample preparation. hIAPP was purchased from Genscript (Piscataway, NJ). hIAPP was prepared by dissolving the peptide in hexafluoroisopropanol (Sigma Aldrich) followed by lyophilization. Peptide stock was dissolved in 100 μM HCl (pH 4), sonicated for 1 min, diluted into the appropriate buffer system and kept on ice until use.