PNA Sequences, Melting Temperatures, and Mass Spectroscopy Characterization.

Ac = acetyl group.aTm represents the melting temperature for the duplex formed between the indicated PNA and antiparallel DNA. Conditions for Tm measurement were as follows: 3.0 µM of PNA∶DNA duplex, 150 mM NaCl, 10 mM sodium phosphate buffer, pH 7.0, 0.1 mM EDTA, UV measured at 260 nm from 95 to 25°C, in 1°C increments. All values are averages from two or more experiments.bAccurate mass Electrospray Ionization (ESI) mass spectra were obtained on a Waters LCT Premier time-of-flight (TOF) mass spectrometer. The instrument was operated in W-mode at a nominal resolution of 10000. The electrospray capillary voltage was 2 KV and the sample cone voltage was 60 volts. The desolvation temperature was 275°C and the desolvation gas was nitrogen with a flow rate of 300 L/hr. Accurate masses were obtained using a standard internal reference. The sample was introduced into the mass spectrometer via a direct loop injection. Both positive and negative ion accurate mass data were achieved simply by reversing the instrument's operating polarity. Deconvolution of multiply charged ions was performed with MaxEnt I.