Sodium 2 2 dimethyl 2 silapentane 5 sulfonate dss

Samples stored at −80 °C were thawed and 110 µL of serum transferred to a fresh 1.5 mL Eppendorf tube, and 450 µL of 1 x DPBS (Gibco Life Technologies), 50 µL of D₂O (Cambridge Isotope Laboratories, Inc, MA, USA), and 10 µL of sodium 2,2-dimethyl-2-silapentane-5-sulfonate (DSS) (Cambridge Isotope Laboratories, Inc, MA, USA) (3.7 mg in 700 µL MilliQ water) added. Samples were centrifuged at 14,000 rpm for 10 min at 4 °C, and 550 µL transferred to an NMR tube. One-dimensional NMR spectra (128 scans) were recorded at 298 K using a standard CPMG sequence on a Bruker Avance III 600 MHz spectrometer equipped with a cryoprobe using automated data collection via IconNMR software (Bruker). Two-dimensional spectra were recorded on selected samples, including COSY, TOCSY, and ¹H-¹³C-HSQC. Samples were processed randomly. Metabolite assignments were based on the Human Metabolome Database^{57 (link)} and chemical shifts derived from standard samples. For the statistical analysis, spectra were normalized to total intensity.

All chemicals were purchased from Sigma-Aldrich (USA). Methanol and chloroform HPLC grade were purchased from Scharlau (Spain). H₂O was deionized using Ultra Clear UV plus TM water system (SG water, Germany) to the quality of 18.2 MΩ. D₂O 99.9% and sodium 2,2-dimethyl-2-silapentane-5-sulfonate (DSS) were purchased from Cambridge Isotope Laboratories Inc. (USA).

aflatoxins B1 and G1 were purchased from Shanghai Yuanye Bio-Technology Co., Ltd and J&K Scientific (Beijing, China), respectively, and the aflatoxins were dissolved in dimethyl sulfoxide-d₆ (DMSO) as stock solution for further use. Tris (D11, 98%) and sodium 2,2-dimethyl-2-silapentane-5-sulfonate (DSS) were from Cambridge Isotope Laboratories. DNA oligos were synthesized by Sangon Biotechnology Co., Ltd (Shanghai, China). NMR samples were prepared by dissolving the lyophilized DNA powder in either D₂O or 90% H₂O/10% D₂O containing 10 mM Tris (1D ¹H NMR spectra) or Tris-d₁₁ (2D NMR spectra), 50 mM NaCl and 50 mM MgCl₂ (pH 6.5–7.5). For 1D ¹H NMR spectra, low-concentration DNA samples (50–100 μM) were used. For 2D NMR study, DNA samples with higher concentration (1–3 mM) were used, and 1–2 equivalents of AFB1 were added.