Dataset on structure-antioxidant activity relationship of active oxygen catalytic lignin and lignin-carbohydrate complex

The data presented in this article are related to the research article entitled “Structure-antioxidant activity relationship of active oxygen catalytic lignin and lignin-carbohydrate complex” (Jiang et al.). It supplements the article with thermostability of milled wood lignin (MWL) and alkali-oxygen lignin (AOL), main substructures of lignin in rice straw, main products and yield of nitrobenzene oxidation of lignin-carbohydrate complexes (LCCs), Fourier transform infrared spectroscopy of LCCs, radical (ABTS·) scavenging ability of lignins and signal assignment of lignins and LCCs in nuclear magnetic resonance spectra (1H, 13C, 2D HSQC NMR). The dataset is made publicly available and can be useful for extending the structural and bioactive research and critical analyses of lignin and LCC.


Data
In this report, we present data on the structure-antioxidant activity relationship of lignin and LCC to supplement the analysis of our research article [1]. Thermostability is an important property of antioxidants to identify its antioxidant capacity, which was demonstrated by TGA as shown in Fig. 1. Spectroscopic methods (NMR and FTIR) combined with chemical degradation (nitrobenzene oxidation) can give comprehensive structural analysis of lignin and LCC. The signal assignment of NMR (Tables 1e3) and FTIR (Table 5 and Fig. 4) spectra supplements the information of the main substructures ( Fig. 2) of lignin in rice straw, which can be assigned and analyzed according to the published literatures [4e7]. Chemical degradation of nitrobenzene oxidation (Fig. 3) endows this research with monomeric composition and the condensation degree of lignin, and the raw data were listed in Table 4. The assessment of ABTS$ scavenging ability (Fig. 5) is used to prove the data of corresponding DPPH$ assay and to demonstrate that the AOL has higher antioxidant activity.

Thermostability and FTIR
The thermostability was determined by a thermogravimetric analyzer (SDT 650) using a heating rate of 5 C/min in air from room temperature to 1000 C.
FTIR spectra of LCCs were recorded using a FTIR spectrometer (VERTEX 80 V, Bruker, Germany). 1 mg of samples was mixed with 200 mg of KBr. After grinding and tabletting, the FTIR spectra was recorded with the scan resolution of 4 cm À1 and the scan area of 4000À400 cm À1 . Specifications Table   Subject Agricultural and Biological Sciences (General) Specific subject area Structure-antioxidant activity relationship of lignin  Type of data  Tables  Figures  How data were  acquired   Thermostability (thermogravimetric analyzer,  Value of the data Data are convenient to examine the structural characteristics of milled wood lignin and alkali-oxygen lignin from rice straw and are useful to compare similar studies using other lignocelluloses as feedstocks.
The data throw light on the structure-antioxidant relationship and the molecular mechanism of lignin, which will greatly move forward the value-added applications of lignin. Data can guide the usage of lignin from pulp mills on agriculture and polymeric materials.

NMR characterization
MWL and AOL were acetylated according to the method reported by Lu and Ralph [8] for the determination of 1 H and 13 C NMR. 20 mg of acetylated lignins was dissolved in 0.5 mL DMSO-d 6 for 1 H NMR detection. For the quantitative 13 C NMR experiment, acetylated lignin (150 mg) was dissolved in DMSO-d 6 (0.5 mL). Chromium (III) acetylacetonate (20 mL, 0.01 M) was added to provide complete relaxation of all nuclei. The mixture was then transferred to a Shigemi microtube and characterized at 25 C. The acquisition parameters were: 90 pulse width, a relaxation delay of 1.7 s, and an acquisition time of 1.2 s. A total of 20,000 scans were collected.
For 2D HSQC NMR test of LCCs, the LCC samples (50 mg) were dissolved in 0.5 mL of DMSO-d 6 . The number of collected complex points was 2048 for the 1 H-dimension with a recycle delay of 1.5 s. The number of transients was 64, and 256 time increments were recorded in the 13 C-dimension. The 1 J CH used was 145 Hz. Processing used typical matched Gaussian apodization in the 1 H-dimension and squared cosine-bell apodization in the 13 C-dimension. Prior to Fourier transformation, the data matrices were zero-filled to 1024 points in the 13 C-dimension.

Nitrobenzene oxidation
Nitrobenzene oxidation was applied to the LCCs according to the procedure reported by Chen [2]. Briefly, 10 mg of sample was reacted with 0.25 mL nitrobenzene in a stainless steel bomb at 170 C for 2 h under alkali condition (4 mL 2 mol/L sodium hydroxide). Then, the bomb was cooled in cold water immediately and 1 mL 0.1 mol/L sodium hydroxide solution containing 3-ethoxy-4hydroxybenzaldehyde (0.3 g/L) was added as the internal standard. The mixture was extracted three times with dichloromethane in separating funnel. The aqueous phase was acidified with 4 mol/L HCl to pH ¼ 1 and extracted twice with dichloromethane and once with ethyl ether. The combined organic Table 2 Signal assignment for 13 C NMR spectra of MWL and AOL.   phase was extracted with 20 mL deionized water and the organic phase was mixed with anhydrous sodium sulfate overnight. After removing the insoluble inorganic materials by filtration, the solution was evaporated to dryness and silylated using N,O-bis(trimethylsilyl) acetamide at 100 C for 10 min. The silylated samples were analyzed by gas chromatography (Plus 2010) equipped with a flame ionization detector and SH-Rtx-5 column (Shimazu Co., Kyoto, Japan).

Assessment of DPPH·and ABTS·scavenging ability
The DPPH$ and ABTS$ radical scavenging assay of lignins and LCCs was performed using a spectrophotometric method. Samples were dissolved in 90% 1,4-dioxane/water (v/v). The DPPH$ was dissolved in anhydrous ethanol with the concentration of 6 Â 10 À5 mol/L. ABTS$ was generated by reacting 2,2 0 -Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (7 mM) with 2.45 mM potassium persulfate (K 2 S 2 O 8 ) in ultrapure water and then letting the solution stand for 15 h in the dark at room temperature. The radical solution was adjusted to obtain an UV absorbance of 0.70 ± 0.02  at 517 nm and 734 nm for DPPH$ and ABTS$, respectively. The concentration of lignin and LCCs in tested sample is 0.03 mg/mL. The absorbance of tested sample was measured using a microplate spectrophotometer (Infinite M200, Ku nshan, China). The radical scavenging ability was calculated using the following formula: where A i is the absorbance of the tested sample; A j is the absorbance of the blank sample via anhydrous ethanol replacing DPPH$ or ultrapure water replacing ABTS$ solution; A 0 is the absorbance of the blank sample via anhydrous ethanol or ultrapure water replacing lignin solution.   Stretching vibration of benzene ring 1263 Stretching vibration of CeO in G-unit 1160 Stretching vibration of phenolic acid ester 1086 Bending vibration of CeH and CeO 840 Out-of plane bending vibration of CeH in benzene ring (S/H)