Determine Peptide Concentrations with NMR

The method is similar to that previously described.²⁰ A Varian Unity INOVA 500 MHz was used to determine the one-dimensional ¹H NMR spectrum at room temperature for Ac-H4(1-20) and the Ac-H4(1-20)K5 modified peptides. D₂O solutions containing 1.8 mM (weight-based) of the Ac-H4(1-20) or a Ac-H4(1-20)K5 modified peptide and 0.2 mM 4,4-dimethyl-4-silapentane-1-sulfonic acid (DSS) were prepared for each NMR sample. The integration ratio was measured for each peptide as previously described,²⁰ note (δ = 6.5–8.0). Ac-H4(1-20) and Ac-H4(1-20)K5 modified peptides were dissolved in deionized water to prepare stock solutions. The NMR spectra are available in the supporting information.