Ddr nmr spectrometer

The ¹H NMR spectra were recorded at 298 K on a 600 MHz Varian DDR NMR spectrometer equipped with a 5 mm inverse-detection probe fitted with a gradient module (IDPF probe). The stoichiometry of the complex was determined using 20 mM acetate buffer pH 4.5, prepared with D₂O. Stock solutions of cathinones, native β-CD, and SBE-β-CD were also prepared at 3 mM, and methanol was added to the solutions as a reference (δ = 3.30 ppm).
Conventional 2D experiments (¹H-¹H gCOSY, ROESYAD and ¹H–¹³C gHSQCAD, and HMBC) for structural elucidation were acquired on 20 mM acetate buffer pH 4.5 solutions containing 1 mM of the cathinone analogs and 2 mM native β-CD, 1 mM Succ-β-CD 1 mM 6-(SB)₇-β-CD or 1 mM SBX (resulting in a 1:2 or 1:1 cathinone–CD molar ratio). ROESY experiments were recorded with a 300 ms mixing time using a 4.2 kHz spin-lock field. For 1D ROESY selective excitation, the selexcit pulse sequence available in the VnmrJ program was used.

All NMR experiments were recorded at 298 K on a 600 MHz Varian DDR NMR spectrometer equipped with a 5 mm inverse-detection gradient (IDPFG) probe.
For the pH-dependent series of ¹H NMR spectra, the solvent mixture was H₂O:D₂O = 9:1 by volume, the constant ionic strength and the buffer capacity were adjusted using 0.05 M NaCl and 0.05 M H₃PO₄. An appropriate amount of the corresponding CD was weighed to obtain a 1 mM solution and finally, methanol was added (0.05 mM) as a chemical shift reference (3.31 ppm). The pH was adjusted by using 1 M NaOH. The water resonance was diminished by the dpfgse pulse sequence [25 (link)]. The pH measurements were performed in 25 mL vessels with proper stirring, before transferring 600 μL solutions into the NMR tubes. The pH meter readings were recorded using a Metrohm pH meter, equipped with a Metrohm 6.0234.110 combined glass electrode.
The pK_a values were calculated using the equation (1) for compounds 2, 3, 4 and equation (2) for compound 5, where ${\delta }_{obs}$ is the observed chemical shift of a given nucleus, appearing at the frequency of the weighted average of ${\delta }_L$ , ${\delta }_{HL}$ and ${\delta }_{H_{2}L}$ , the limiting chemical shifts of the species simultaneously present [26 (link)].
${\delta }_{obs}=\frac{{\delta }_L+{\delta }_{HL}\times K\left[H^{+}\right]}{1+K\left[H^{+}\right]}=\frac{{\delta }_L+{\delta }_{HL }\times {10}^{p{K}_a-pH}}{1+{10}^{p{K}_{a }-pH}}$
${\delta }_{obs}=\frac{{\delta }_L+{\delta }_{HL}\times {10}^{p{K}_{a}1-pH}+{\delta }_{H_{2}L}\times {10}^{p{K}_{a}1-pH}\times {10}^{p{K}_{a}2-pH}}{1+{10}^{p{K}_a-pH}+{10}^{p{K}_{a}1-pH}\times {10}^{p{K}_{a}2-pH}}$

For structural characterizations of CD derivatives in D₂O, a 600 MHz Varian DDR NMR spectrometer equipped with a 5 mm inverse-detection gradient probe or a 400 MHz Varian Mercury Plus spectrometer equipped with a 5mm Varian 400 Automation Triple Resonance Broadband Pulsed Field Gradient probe was used. For NMR-pH titrations, the same instruments were used. The pH-dependent series of ¹H NMR spectra were recorded in a solvent mixture of H₂O:D₂O = 9:1 by volume, where the constant ionic strength and the buffer capacity were adjusted using 0.05 M sodium chloride and 0.05 M acetic acid-d₄. An appropriate amount of CD was weighed to obtain a 1 mM solution and finally one drop of methanol was added as a chemical shift reference (3.310 ppm). The water resonance was diminished by the dpfgse pulse sequence [55 (link)] or presaturation. All the spectra were processed using the MestReNova v9.0.1-13254 (Mestralab Research, S.L., Santiago de Compostela, Spain) software.