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.Ac代表乙酰基（acetyl group）。aTm指目标肽核酸（Peptide Nucleic Acid, PNA）与反平行脱氧核糖核酸（Deoxyribonucleic Acid, DNA）形成的双链的解链温度。Tm值测定条件如下：PNA与DNA双链的浓度为3.0 µM，体系含150 mM NaCl、10 mM磷酸钠缓冲液（pH 7.0）及0.1 mM乙二胺四乙酸（Ethylenediaminetetraacetic Acid, EDTA）；采用紫外分光光度法在260 nm波长下监测，温度扫描范围为95℃至25℃，步长为1℃。所有数值均为两次及以上独立实验的平均值。 b 精确质量电喷雾电离（Electrospray Ionization, ESI）质谱数据通过Waters LCT Premier飞行时间（time-of-flight, TOF）质谱仪采集。该仪器以W模式运行，标称分辨率为10000；电喷雾毛细管电压设置为2 kV，样品锥孔电压为60 V；脱溶剂温度为275℃，脱溶剂气为氮气，流速为300 L/hr。精确质量测定采用内标标准品进行校准。样品通过直接环进样方式引入质谱仪。仅需切换仪器的操作极性，即可分别获取正、负离子模式的精确质量数据。多电荷离子的解卷积分析通过MaxEnt I软件完成。