All peptides were synthesized on solid Rink-amide resin using fluorenylmethoxycarbonyl (Fmoc) chemistry on a model 433A peptide synthesizer (Applied Biosystems) or a Tribute peptide synthesizer (Protein Technologies). Lysines were added to the terminal positions of the peptide sequences to encourage aqueous solubility. The peptide CRGDSGK was synthesized as the others, but with the orthogonal protecting group 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde) on the C-terminal lysine. On resin, the N-terminus was capped with acetic anhydride and Dde was selectively removed with 2% hydrazine allowing labeling with 5(6)-carboxy rhodamine (Anaspec) by HATU coupling or with AlexaFluor 488 terafluorophenyl ester (AlexaFluor 488 5-TFP Invitrogen). Peptides were analyzed by reverse-phase high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionisation (MALDI) mass spectrometry and purified by reverse-phase HPLC.
HRMAS 1H-NMR: HRMAS 1H-NMR spectroscopy was performed on a Varian Inova at 400mHz with a 4-mm GHX-Nano probe. Monomer solutions of 10 wt% in phosphate-buffered D2O and 0.05 wt% I2959 inside 40mL capacity nanotubes were exposed to 365-nm light at 10mW cm−2 and periodic NMR measurements were taken. It should be noted that the curvature of the nanotubes, in which polymerization occurs and spectra are taken, interferes with the light exposure, making this a poor technique to measure kinetics. It is, however, an appropriate means to determine the conversion of alkenes relative to the generation of thioethers, confirming the reaction mechanism.
HRMAS 1H-NMR: HRMAS 1H-NMR spectroscopy was performed on a Varian Inova at 400mHz with a 4-mm GHX-Nano probe. Monomer solutions of 10 wt% in phosphate-buffered D2O and 0.05 wt% I2959 inside 40mL capacity nanotubes were exposed to 365-nm light at 10mW cm−2 and periodic NMR measurements were taken. It should be noted that the curvature of the nanotubes, in which polymerization occurs and spectra are taken, interferes with the light exposure, making this a poor technique to measure kinetics. It is, however, an appropriate means to determine the conversion of alkenes relative to the generation of thioethers, confirming the reaction mechanism.
