I. INTRODUCTION
Electronic cigarettes are becoming more and more popular. Compared with conventional cigarettes, electronic cigarettes are relatively less harmful to users and bystanders (Yong et al., Reference Yong, Borland, Balmford, Hitchman, Cummings and Driezen2017). Nicotine salts are important parts of e-liquids and meet the need for more effective and appealing e-cigarette products to provide satisfying alternatives to smoking (Grant et al., Reference Grant, Pritchard, Prue, Thompson, Verron, Graf and Walele2019). To the best of our knowledge, the structure of nicotine 2,6-dihydroxybenzoate has not been reported in the literature. In this study, nicotine 2,6-dihydroxybenzoate was synthesized. The single-crystal X-ray diffraction (XRD) and detailed powder XRD data of nicotine 2,6-dihydroxybenzoate were supplied at room temperature (25 °C).
II. EXPERIMENTAL
A. Sample preparation
Nicotine and 2,6-dihydroxybenzoic acid each were accurately weighed to achieve a 1:1 molar mixture when combined. Nicotine was added dropwise to the aqueous solution of 2,6-dihydroxybenzoic acid under full stirring. The reaction liquid was transferred to a dark container, and ultrasonic reaction was conducted in a 30–40 °C water bath for 4 h. The reaction solution was freeze-dried to obtain gray solid powder. The solid powder (500 mg) was dissolved in 4 ml ethanol and kept in dark for 1 week to obtain transparent bulk crystal of nicotine 2,6-dihydroxybenzoate. FT-IR and 1H-NMR spectra (provided in the Supplementary Material) confirmed that the obtained compound was nicotine 2,6-dihydroxybenzoate. There was almost no water in nicotine 2,6-dihydroxybenzoate by a Karl Fischer coulometer. Finally, a portion of the crystals were dried at room temperature and ground into powder.
B. Powder diffraction data collection and reduction
The powder XRD measurement was performed at room temperature using an X'Pert PRO diffractometer (PANalytical Co., Ltd., Netherlands) with a PIXcel 1D detector and CuKα radiation (generator setting: 40 kV and 40 mA). The diffraction data were collected over the angular range from 4 to 50° 2θ with a step size of 0.02626° 2θ. The scan speed is 0.01340 °/s. The powder XRD pattern is shown in Figure 1.
Figure 1. XRD pattern of nicotine 2,6-dihydroxybenzoate using CuKα radiation (red line) and the simulated pattern of ours (black line).
The Material Studio 8.0 (Accelrys Co., Ltd., CA, California, USA) software package was used to process the data in the Analytical & Testing Center (Sichuan University, Chengdu, China). The powder XRD pattern was pre-treated by subtracting the background, smoothing, and stripping off the Kα 2 component. Automatic indexing results obtained by X-Cell algorithm (Neumann, Reference Neumann2003) were refined using the Pawley method (Pawley, Reference Pawley1981), which involves the assignment of Miller indices (h, k, l) to each observed peak in the experimental powder XRD pattern. The Pawley refinement was performed on the raw data.
C. Single-crystal XRD
The single-crystal XRD data for nicotine 2,6-dihydroxybenzoate were collected on an Xcalibur, Eos diffractometer. The crystal was kept at 293.15 K during data collection. The structure was solved with structure solution program Olex2 (Dolomanov et al., Reference Dolomanov, Bourhis, Gildea, Howard and Puschmann2009) using intrinsic phasing. The structure was refined with the ShelXL (Sheldrick, Reference Sheldrick2008) refinement package using least squares minimization (Sheldrick, Reference Sheldrick2015). The single-crystal structure refinement details are provided in the Supplementary Material.
III. RESULTS
The Pawley refinement results confirmed that the title compound was monoclinic with space group P21 and unit-cell parameters: a = 7.726(8) Å, b = 11.724(3) Å, c = 9.437(1) Å, α = 90°, β = 109.081(3)°, γ = 90°, unit-cell volume V = 802.902 Å3, Z = 2, ρ cal = 1.309 g cm−3. The values of 2θ obs, d obs, I obs, h, k, l, 2θ cal, d cal, Δ2θ are listed in Table I. The results were in good agreement with single crystal data [a = 7.7108(7) Å, b = 11.6910(12) Å, c = 9.4114(12) Å, α = 90°, β = 108.996(12)°, γ = 90°, unit-cell volume V = 802.21(16) Å3, Z = 2, ρ cal = 1.310 g cm−3]. The principal acquisition parameters and structure refinement values for single-crystal nicotine 2,6-dihydroxybenzoate compound are listed in Supplementary Table SI. The structural formula of 2,6-dihydroxybenzoate is shown in Figure 2. Crystallographic data for nicotine 2,6-dihydroxybenzoate were deposited with the Cambridge Crystallographic Data Center (CCDC) with a supplementary publication number of CCDC-2084167. The comparison of the experimental powder XRD pattern with the simulated pattern of ours is shown in Figure 1. The presented powder pattern for the nicotine 2,6-dihydroxybenzoate compound has been carefully measured and confirmed via a good match to the calculated pattern based on the crystal structure.
Figure 2. Structural formula of nicotine 2,6-dihydroxybenzoate.
Table I. Indexed X-ray powder diffraction data for nicotine 2,6-dihydroxybenzoate
The d-values were calculated using CuKα 1 radiation (λ = 1.54056 Å), F 20 = 43.3 (0.0145, 32).
IV. DEPOSITED DATA
CIF and RAW data files were deposited with ICDD. You may request this data from ICDD at info@icdd.com.
SUPPLEMENTARY MATERIAL
The supplementary material for this article can be found at https://doi.org/10.1017/S0885715622000070.
