Nicolet iz10

ATR-FTIR is a powerful method to investigate the interactions of enhancers with SC lipids and proteins. The skin was mounted to Franz diffusion cells in a water bath at 32 °C and treated with 180 µL of 1% enhancers (Mo10, Mo12, Mo14, Mo18/1) in 60% aqueous PG. Pure distilled water or 60% aqueous PG were applied as controls. After 24 h exposure, the donor phase was carefully removed, the skin was washed by distilled water and the exposed skin was cut out. IR spectra of the skin surface were recorded by an IR spectrometer (Nicolet iZ10, Thermo Scientific, Waltham, MA, USA), equipped with a single reflection MIRacle ZnSe crystal (PIKE Technologies, Madison, WI, USA) at constant clamping pressure. The spectra were generated by the co-addition of 64 scans, collected at a resolution of 2 cm⁻¹ and evaluated by OMNIC™ software (Thermo Scientific, Waltham, MA, USA). Collected spectra were normalised, to reduce potential variations in the overall intensity of the spectra. Selected regions (amide I, amide II and CH₂ stretching vibration bands) were fitted in Origin Pro (OriginLab, Wellesley Hills, MA, USA). The position, height and area of these selected peaks were compared among the particular spectra and the variances between peak characteristics were statistically evaluated by GraphPad Prism^® software (GraphPad Software, Inc., La Jolla, CA, USA).

FTIR spectra of RLZ-NLCs and their components were obtained by Thermo Scientific Nicolet iZ10 equipment, using a ATS diamond and DTGS detector [67 (link)].

To study the functional groups of GP2a, 2 mg of GP2a was weighed and treated with potassium bromide, i.e., KBr pellet. The treated sample was then scanned using FTIR (Nicolet iZ-10, Thermo Fisher Scientific, Waltham, MA, USA) at a wavelength of 4000–400 cm⁻¹.

In an ice bath, PPDA (21.63 g 0.2 mol) was completely dissolved in 756 g NMP at nitrogen atmosphere. Then, ODPA (62.04 g, 0.2 mol) was added evenly into the solution in 1 h. The reaction mixture was stirred for 24 h at room temperature to prepare polyamic acid. Then, at the boiling point of NMP (b.p. 203 °C), the polyamic acid was dehydrated for 10 h to obtain API powder. After being cooled to room temperature, the final yellow powder was filtered and washed 3 times in methanol, and then dried for 4 h under vacuum at 180 °C. The reaction formula for preparing API is shown in Scheme 1. Fourier Transform Infrared (FTIR, Nicolet iZ10, Thermo Fisher Scientific, Inc., Madison, WI, USA) (KBr, cm⁻¹): 1778 (asymmetrical C=O stretch vibration) and 1720 (symmetrical C=O stretch vibration), 1357 (C–N stretch vibration), 695 (C=O bend vibration). Solid-state ¹³C CP/MAS-TOSS NMR (Bruker Daltonics Inc. Karlsruhe, Germany) (δ, ppm): 164.96 (C=O), 159.62 (C–O–), 138.66 (–O–CH–C–C=O), 131.24 (C–N), 129.77 (CH–C–N), 126.35 (CH–CH–C–C=O), 123.04 (CH–CH–C–C=O), 120.21 (CH–CH–C–O–), 113.88 (C–CH–C–O–). Elemental analysis (C₂₂H₁₂N₂O₅)_n:C: 68.56 ± 0.057% (calculated value: 68.74%); H: 3.06 ± 0.028% (calculated value: 3.15%); N: 7.38 ± 0.071% (calculated value: 7.29%). The data from the FTIR and ¹³C NMR are illustrated in Figures S1 and S2, respectively.

The prepared solid sample was evenly mixed with potassium bromide at a ratio of 1:100 and pressed, and then spectra acquired with a Fourier transform infrared spectrometer (Thermo Scientific Nicolet iZ 10). The air background is subtracted before the sample is tested.