Nicolet is10 infrared spectrometer

Attenuated total reflectance/Fourier transform infrared (ATR-FTIR) spectroscopy was performed using a Thermo Fisher Scientific Nicolet is10 infrared spectrometer with a scan range of 600–4000 cm⁻¹ over 16 scans.
¹H nuclear mangnetic resonance (¹H-NMR) was performed using an AVANCE-III-500 MHz spectrometer (Bruker, Switzerland) using deuterated acetone (C₃D₆O) as the solvent and tetramethylsilane (TMS) as the standard.
¹⁹F-NMR was performed using an AVANCE-NEO-400 MHz spectrometer (Bruker, Switzerland), and the standard was monofluorotrichloromethane (CFCl₃).
Solid-state ¹⁹F-NMR was performed using an JEOL JNM ECZ600R spectrometer (Japan), and the specific conditions were frequency of 564 MHz, pulse width of 90 deg and rotating speed of 21 kHz.

Before the FTIR spectral measurements, the dry nucleic acid powder was dissolved with ultra-pure Milli-Q water and incubated at 37 °C for 30 min to obtain stable dsDNA. Then the dsDNA was added to a CaF₂ window piece drop by drop and put into a drying oven keeping the temperature at 37 °C for about 20 min until the water of the DNA solution evaporated on the window piece. Then, 5 μL of different inducing solutions were added on the film formed by the dsDNA, the film was quickly covered with another clean CaF₂ window piece, and the connection of the window piece was sealed with sealing film to reduce the evaporation of water. The final concentrations of NaCl were 50 mM, 1 M, 2 M, 3 M, 4 M, 4.5 M, and 5 M, respectively; the final concentrations of MgCl₂ were 0 M, 0.5 M, 1 M, 1.5 M, 2 M, 2.5 M, and 3 M, respectively; and the volume ratios of ethanol were 0, 0.4, 0.5, 0.55, 0.6, 0.65, and 0.7, respectively. The concentration of the DNA solution was 36.32 μg/μL. The structural changes of the dsDNA were detected by a Thermo Fisher Scientific Nicolet iS10 infrared spectrometer.
The parameters of the infrared spectrometer were set as follows: the spectral range was from 4000 cm⁻¹ to 900 cm⁻¹, the spectral resolution was 4 cm⁻¹, and the number of scans was 30. The software Origin 2021 was used for the spectral analysis. At least three replicates were set for each measurement.

Unless otherwise noted, chemical reagents and solvents were purchased from commercial suppliers (Tokyo Chemical Industry, Tokyo, Japan, and Sigma-Aldrich, St. Louis, MO, USA), and used without further purification. The NMR spectra for ¹H and ¹³C were taken on a Bruker DRX 300, and mass spectroscopy samples were observed using a JEOL (JMS-700, JEOL, Tokyo, Japan) mass spectrometer. A UV-visible spectrophotometer (Evolution 600, Thermo scientific, Waltham, MA, USA) was used to obtain the absorption spectra. IR spectra were observed over the range 500–4000 cm⁻¹ using a Thermo scientific Nicolet iS10 infrared spectrometer. The fluorescence spectra were obtained using a RF-5301PC spectrophotometer (Shimadzu, Kyoto, Japan).

The Fourier transform infrared (FT-IR) spectra (4000–500 cm⁻¹) were obtained on a Nicolet iS10 infrared spectrometer (Thermo, USA). The HPLC system was equipped with two pumps (LC-20AT), a C₁₈ reversed-phase column (4.6 × 250 mm, 5 μm) and a UV detector (SPD-20A, Shimadzu, Japan). Mobile phase A was the mixture of ammonium acetate (0.01 mol/L) and acetonitrile (10:90, v/v). Mobile phase B was the mixture of ammonium acetate (0.01 mol/L) and acetonitrile (90:10, v/v). The injection volume was 20 μL, the flow rate was 0.8 mL/min and the detection wavelength was 254 nm.
Histamine was separated using a Beckman P/ACE MDQ capillary electrophoresis system with a diode array detection (DAD) at 211 nm. Separation steps were carried out on uncoated fused-silica capillaries (Yongnian Optical Conductive Fiber Plant, Hebei, China) of 75 μm i.d.. The capillary was firstly thermostated at 25℃ and then successively flushed with 0.1 mol/L NaOH, DDW and the running buffer for 5 min each. Standard solutions and samples were injected by pressure at 0.5 psi for 5 s and separated under 10 kV with a positive voltage. The data were collected and processed by Beckman P/ACE 32 Karat software Version 8.0.