Edinburgh lp920 spectrometer

Nanosecond time-resolved transient absorption spectra were measured using a flash photolysis setup Edinburgh LP920 spectrometer (Edinburgh Instruments Ltd) combined with a Nd:YAG laser (Spectra-Physics Lab 170, Newport Corp.). Each measurement was performed in a 1 cm path length quartz cuvette at room temperature. The sample was excited by a 355 nm laser pulse (1 Hz, 20 mJ/pulse/cm², fwhm ≈ 7 ns). The analyzing light was from a 450 W pulsed xenon lamp. A monochromator equipped with a photomultiplier for collecting the spectral range from 300 to 700 nm was used to analyze transient absorption spectra. The signals from the photomultiplier were displayed and recorded as a function of time on a 100 MHz (1.25 Gs/s sampling rate) oscilloscope (Tektronix, TDS 3012C), and the data were transferred to a personal computer. Data were analyzed by the online software of the LP920 spectrophotometer. The fitting quality was judged by weighted residuals and reduced χ² value.

Nanosecond time-resolved transient absorption spectra were measured using a flash photolysis setup Edinburgh LP920 spectrometer (Edinburgh Instruments Ltd.) combined with a Nd:YAG laser (Spectra-Physics Lab 170, Newport Corp.). Each measurement was performed in a 1-cm-pathlength quartz cuvette that was put in the Oxford Instruments OptistatDN cryostat and cooled to a certain temperature. The sample was excited by a 355-nm laser pulse (1 Hz; 10 mJ per pulse; full width at half maximum, ≈7 ns). The analyzing light was from a 450-W pulsed xenon lamp. A monochromator equipped with a photomultiplier for collecting the spectral range from 300 to 700 nm was used to analyze the transient absorption spectra. The signals from the photomultiplier were displayed and recorded as a function of time on a 100-MHz (1.25 Gs/s sampling rate) oscilloscope (TDS 3012C, Tektronix), and the data were transferred to a PC. Data were analyzed with online software of the LP920 spectrophotometer. The fitting quality was judged by weighted residuals and reduced χ² value.
The concentration of radicals generated by a single laser pulse (~6.8 μM), estimated by the SO₄^−• absorbance at 450 nm using an extinction coefficient of 1600 M⁻¹ cm⁻¹, was much lower than that of G in free deoxynucleoside (4 mM) or oligonucleotides (1.2 mM), excluding the occurrence of sequential oxidation events of guanine.