Avance neo 700

Optical rotations were measured on a Krüss polarimeter (A. KRÜSS Optronic GmbH, Hamburg, Germany) equipped with a 0.5 dm cell. UV spectra were recorded on a Lambda 40 UV/Vis spectrophotometer (Perkin Elmer Ltd., Beaconsfield, UK). IR spectra were obtained on a Alpha II FTIR spectrometer (Bruker Optik GmbH, Ettlingen, Germany). High-resolution APCI mass spectra were measured on a LTQ Orbitrap Velos mass spectrometer (Thermo Fisher Scientific, Bremen, Germany). NMR spectra were recorded on Avance NEO 950, Avance NEO 700, Avance III 600, and DRX 400 spectrometers (Bruker BioSpin GmbH, Rheinstetten, Germany). Chemical shifts are given on a δ (ppm) scale using TMS as internal standard. The 2D experiments (HSQC, HMBC, COSY, NOESY) were performed using standard Bruker pulse sequences. Column chromatography separations were performed with Kieselgel 60 (Merck, Darmstadt, Germany). HPLC separations were conducted using a Waters 600 liquid chromatography pump equipped with a Waters 410 differential refractometer (Waters Corporation, Milford, MA, USA), using a 25 cm × 10 mm Econosphere Silica 10 μ column (Grace, Columbia, MD, USA). TLC were performed with Kieselgel 60 F₂₅₄ aluminum plates (Merck, Darmstadt, Germany) and spots were detected after spraying with 20% H₂SO₄ in MeOH reagent and heating at 100 °C for 1 min.

The solution-state NMR spectra of a heterogeneous system of fish feed pellets in KPi/D₂O were recorded using an Avance NEO-700 spectrometer (Bruker, Billerica, MA) equipped with an inverse triple-resonance cryogenic probe with a z-axis gradient for 5-mm diameter samples; this system was operated at 700.15 MHz for ¹H and 176.06 MHz for ¹³C. T₂-SMOOSY spectra were recorded at 298 K. The analysis was performed to evaluate fish feed dissolution. For this, 16 complex F2 (¹H) points, 1024 complex F3 (¹H) points, and six points of gradient strength on F1 were recorded from two scans per F1 and F2 increment. The spectral width obtained for F3 was 16 ppm. The maximum gradient strength for F2 was 1.2 G/cm and the minimum was −1.2 G/cm. The increments were at equal intervals. Six increments in the variable counter list used for F1 were 25, 50, 75, 100, 125, and 150 loop counters. Direct (F3) and indirect (F2) dimensions were zero-filled to 2048 and 128 points, respectively. Details of experimental parameters are shown in Supplementary Tables 5 and 6.

Negative ESI LC–MS was carried out on a high performance Dionex UltiMate 3000 LC system (Thermo Scientific) fitted with a Waters CORTECS T3 column (2.7 μm, 150 × 2.1 mm) and linked to a Bruker HCTultra ETD II system (Bruker Daltonics) MS, using a 30–70% gradient of MeCN (0.1% formic acid) in H₂O (0.1% formic acid) over 12 min.
1D and 2D NMR spectra were recorded on a Bruker Avance Neo 700 MHz spectrometer.

¹H NMR spectra were recorded at 700 MHz (Bruker AVANCENeo700) with the standard qNMR conditions: temperature, 298 K; relaxation delay (D1), 60s; flip angle, 90°; acquisition time, 2.34 s; number of scans (nc), 32; and spectral width, 0‒16 ppm. Prior to Fourier transformation (FT) an exponential weighing factor corresponding to a line broadening of 0.3 Hz was applied. The spectra were phased, corrected and integrated automatically using MestReNova software. Where necessary, accurate integration was performed manually for the peaks of interest. The content of allantoin was calculated using the following equation [5 (link)]
$$\text{P[\%]=}\frac{n_{IC\cdot }In{t}_{A\cdot }M{W}_{A\cdot }{m}_{IC}}{n_{A\cdot }In{t}_{IC\cdot }M{W}_{IC\cdot }{m}_S}.P_{IC}$$
Where IC is the internal calibrant, A is allantoin, s is the sample, n is the number of protons, Int is integral, MW is the molecular weight, m is the mass, and P is the purity (in %).

All manipulations were carried out in air unless specified. All the reagents used in this study were obtained from the commercial sources (Aldrich, TCI-Europe, Strem, ABCR). Commercially available solvents were purified by conventional methods and distilled immediately prior to use. NMR spectra were recorded on a Bruker Avance neo-700; chemical shifts (δ) are given in ppm and coupling constants (J) in Hz. C, H, and N elemental analyses were carried out on a Euro EA 3028HT CHNS/O analyzer. Di(2-pyridyl)diselenide was prepared as reported earlier [39 (link),40 (link)].

Solid-state ¹H and ¹³C MAS NMR spectra were acquired at a Bruker Avance NEO 700 MHz NMR spectrometer (Bruker BioSpin, Rheinstetten, Germany) operating at a resonance frequency of 176.0 MHz for ¹³C and 700.1 MHz for ¹H and equipped with an E-free H/C/N probe with a 3.2 mm spinning module. All measurements were recorded at a MAS of 7000 Hz, temperature of 32°C and a 4 μs π/2 pulse.
For the ¹H NMR spectra, we applied a Hahn echo sequence with a relaxation delay of 5 s. For the ¹³C NMR directly excited NMR spectra, a Hahn pulse echo sequence with a relaxation delay of 5 s and ¹H decoupling was used (ω_H/2π = 62.5 kHz). For the cross polarization (CP) spectra we used an ¹H excitation pulse of 4 μs with a CP contact time of 700 μs and a ¹H CP spin lock field of ∼40 kHz. During acquisition, a ∼62 kHz SPINAL64 decoupling was applied and spectra were recorded with a recycle delay of 2.5 s. All NMR spectra were calibrated relative to tetramethylsilane at 0 ppm.