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 (Table 1, Table 2, Table 3) 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 [4], [5], [6], [7]. 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.

Fig. 1

The weight loss of MWL and AOL with temperature.

Table 1

Signal assignment for 1H NMR spectra of MWL and AOL.

Label	δH (ppm)	Assignment
1	7.42–8.00	Aromatic proton in p-hydroxyphenyl units
2	6.75–7.42	Aromatic proton in guaiacyl units
3	6.15–6.75	Aromatic proton in syringyl units
4	5.69–6.15	Hα in β-O-4′ and β-1′ structure
5	5.22–5.69	Hα in β-5′ and α-O-4′ structure
6	4.48–5.22	Hα in β-β′ structure
7	4.01–4.48	Hγ in β-O-4′ structure
8	3.43–4.01	Proton in methoxyl
9	2.15–2.42	Proton in aromatic acetates
10	1.58–2.15	Proton in aliphatic acetates
11	0.66–1.58	Proton in –CH2– and –CH3

Table 2

Signal assignment for13C NMR spectra of MWL and AOL.

δC (ppm)	Assignment	δC (ppm)	Assignment
166.5	C9 in p-coumarates	128.0	Cα and Cβ in Ar-CH <svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="20.666667pt" height="16.000000pt" viewBox="0 0 20.666667 16.000000" preserveAspectRatio="xMidYMid meet"><metadata> Created by potrace 1.16, written by Peter Selinger 2001-2019 </metadata><g transform="translate(1.000000,15.000000) scale(0.019444,-0.019444)" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 480 0 480 0 0 40 0 40 -480 0 -480 0 0 -40z M0 280 l0 -40 480 0 480 0 0 40 0 40 -480 0 -480 0 0 -40z"/></g></svg> CH–CH2OH
160.0	C4 in p-coumarates	125.9	C5/C5’ in non-etherified 5-5′ units
156.4	C4 in p-hydroxyphenyl units	125.1	C1 in p-coumarates
152.9	C3/C3’ in etherified 5-5 units, Cα in –CHCH–CHO units	123.0	C6 in ferulates
152.5	C3/C5 in etherified syringyl units and guaiacyl ring of 4-O-5′ units	122.6	C1 and C6 in Ar–C (=O)C–C unis
151.3	C4 in etherified guaiacyl units with α-CO	119.4/118.4	C6 in guaiacyl units
149.7	C3 in etherified guaiacyl units	115.1/114.7	C5 in guaiacyl units
148.4	C3 in guaiacyl units	111.1/110.4	C2 in guaiacyl units
146.8	C4 in etherified guaiacyl units	106.8	C2/C6 in syringyl units with α-CO
145.8	C4 in non-etherified guaiacyl units	104.3	C2/C6 in S syringyl units
145.0	C4 in etherified 5-5′ units	86.6	Cα in guaiacyl type β-5′ units
143.3	C4 in non-etherified 5-5′ units	84.6	Cβ in guaiacyl type β-O-4′ units (threo)
138.2	C4 in syringyl etherified units	83.8	Cβ in guaiacyl type β-O-4′ units (erythro)
134.6	C1 in etherified syringyl and guaiacyl units	72.4	Cγ in β-β′ and β-aryl ether
133.4	C1 in non-etherified syringyl and guaiacyl units	71.2	Cα in guaiacyl type β-O-4′ units (threo)
132.4	C5 in etherified 5-5′ units	63.2	Cγ in guaiacyl type β-O-4′ units with α-CO
131.1	C1 in non-etherified 5-5′ units	62.8	Cγ in guaiacyl type β-5′, β-1′ units
130.3	C2/C6 in p-coumarates	60.2	Cγ in guaiacyl type β-O-4′ units
129.3	Cβ in Ar-CHCH–CHO	55.6	C in Ar-OCH3
128.1	C2/C6 in p-hydroxyphenyl units	29.2	CH2 in aliphatic side chain

Table 3

Assignment of the polysaccharide signals in the 2D HSQC NMR spectra of LCCs.

Label	δC/δH (ppm)	Assignment
Est	66–62/4.5–4.0	C–H in γ-ester linkages
X5	62.9/3.41	C5–H5 in β-D-xylopyranoside
X2	72.7/3.05	C2–H2 in β-D-xylopyranoside
X22	73.1/4.50	C2–H2 in 2-O-acetyl-β-D-xylopyranoside
X3	73.7/3.29	C3–H3 in β-D-xylopyranoside
X33	74.9/4.81	C3–H3 in 3-O-acetyl-β-D-xylopyranoside
X4	75.5/3.53	C4–H4 in β-D-xylopyranoside
BE1	81.6/4.63	Cα-Hα in benzyl ether (secondary OH of carbohydrate) linkages
Ara4	86.8/4.32	C4–H4 in arabinan
αX1(R)	92.5/4.89	C1–H1 in (1→4)-α-d-xylopyranoside (R)
βX1(R)	97.6/4.25	C1–H1 in (1→4)-β-d-xylopyranoside (R)
X231	99.5/4.74	C1–H1 in 2,3-O-acetyl-β-d-xylopyranoside
X21	99.8/4.52	C1–H1 in 2-O-acetyl-β-d-xylopyranoside
X31	101.9/4.28	C1–H1 in 3-O-acetyl-β-d-xylopyranoside
PhGlc1	100.3/5.09	C1–H1 in phenyl glycoside linkages
PhGlc3	101.9/4.95	C3–H3 in phenyl glycoside linkages
X1/Glc1	103.2/4.29	C1–H1 in β-d-xylopyranoside/β-d-glucopyranoside

Table 5

The position and assignment of absorption peaks in LCCs.

Wavenumber (cm−1)	Assignment
1724	Stretching vibration of non-conjugate CO
1641	Stretching vibration of conjugate CO
1505	Stretching vibration of benzene ring
1462	Bending vibration of C–H (CH2, CH3)
1401	Stretching vibration of benzene ring
1263	Stretching vibration of C–O in G-unit
1160	Stretching vibration of phenolic acid ester
1086	Bending vibration of C–H and C–O
840	Out-of plane bending vibration of C–H in benzene ring (S/H)

Fig. 4

FTIR spectra of LCCs.

Fig. 2

Main substructures of lignin in rice straw: (A) β-O-4′ linkages with a free –OH at C; (A′) β-O-4′ linkages with acetylated and/or p-hydroxybenzoated –OH at C; (Aox) β-O-4′ linkages with a free –OH at C and a C = O; (B) phenylcoumaran substructures formed by β-5′ and α-O-4′ linkages; (C) resinol substructures formed by β-β′, α-O-γ′ and γ-O-α′ linkages; (D) dibenzodioxocin substructures formed by β-O-4′ and α-O-4′ linkages; (E) α-O-4′ and β-O-4′ linkages with a free –OH at C; (F) spirodienone substructures formed by β-1′ and α-O-α′ linkages; (FA) ferulate substructures; (I) cinnamyl alcohol end-groups; (PCA) p-coumarate substructures; (G) guaiacyl units; (S) Syringyl units; (H) p-hydroxyphenyl units.

Fig. 3

The main products of alkali nitrobenzene oxidation of lignin.

Table 4

The yield and ratio of nitrobenzene oxidation products of LCCs.

Samples	Yield (mmol/g-lignin)				V/S/Ha
	V	S	H	Total
LCCRS	1.20 ± 0.01	0.41 ± 0.01	0.46 ± 0.00	2.07 ± 0.02	58/20/22
LCCAO	0.22 ± 0.00	0.18 ± 0.03	0.18 ± 0.01	0.58 ± 0.01	38/31/31

V = vanillin + vanillic acid; S = syringaldehyde + syringic acid; H = p-hydroxybenzaldehyde + p-hydroxybenzoic acid.

Fig. 5

The ABTS· scavenging ability of MWL and AOL.

Experimental design, materials, and methods

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−1 and the scan area of 4000−400 cm−1.

NMR characterization

MWL and AOL were acetylated according to the method reported by Lu and Ralph [8] for the determination of 1H and 13C NMR. 20 mg of acetylated lignins was dissolved in 0.5 mL DMSO-d6 for 1H NMR detection. For the quantitative 13C NMR experiment, acetylated lignin (150 mg) was dissolved in DMSO-d6 (0.5 mL). Chromium (III) acetylacetonate (20 μL, 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-d6. The number of collected complex points was 2048 for the 1H-dimension with a recycle delay of 1.5 s. The number of transients was 64, and 256 time increments were recorded in the 13C-dimension. The 1JCH used was 145 Hz. Processing used typical matched Gaussian apodization in the 1H-dimension and squared cosine-bell apodization in the 13C-dimension. Prior to Fourier transformation, the data matrices were zero-filled to 1024 points in the 13C-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-4-hydroxybenzaldehyde (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 = 1 and extracted twice with dichloromethane and once with ethyl ether. The combined organic 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 × 10−5 mol/L. ABTS· was generated by reacting 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (7 mM) with 2.45 mM potassium persulfate (K2S2O8) 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:Scavenging ability (%) = [1-(Awhere Ai is the absorbance of the tested sample; Aj is the absorbance of the blank sample via anhydrous ethanol replacing DPPH· or ultrapure water replacing ABTS· solution; A0 is the absorbance of the blank sample via anhydrous ethanol or ultrapure water replacing lignin solution.

Specifications Table

Subject	Agricultural and Biological Sciences (General)
Specific subject area	Structure-antioxidant activity relationship of lignin
Type of data	TablesFigures
How data were acquired	Thermostability (thermogravimetric analyzer, SDT 650, USA), nitrobenzene oxidation (gel chromatography, Shimadzu Co., Kyoto, Japan) equipped with a flame ionization detector and SH-Rtx-5 column (Shimazu Co., Kyoto, Japan), Fourier transform infrared spectroscopy (VERTEX 80 V FTIR spectrometer, Bruker, Germany), radical scavenging ability (microplate spectrophotometer, Infinite M200, Kunshan, China), nuclear magnetic resonance spectra (NMR; AVANCE III 600 MHz instrument, Bruker, Switzerland).
Data format	Raw data, Analyzed data
Parameters for data collection	Parameters of alkali-oxygen treatment were formulated and fine-tuned according to the manufacturing technique of the pulp mill in Jiangsu.Parameters of nitrobenzene oxidation and NMR refer to the published papers [2], [3].
Description of data collection	The data in this article were recorded and collected from the software of corresponding detecting instruments.
Data source location	Nanjing, Jiangsu, China
Data accessibility	Data is available with this article
Related research article	B. Jiang, Y. Zhang, H. Zhao, T. Guo, W. Wu, Y. Jin, Structure-Antioxidant Activity Relationship of Active Oxygen Catalytic Lignin and Lignin-Carbohydrate Complex. International Journal of Biological Macromolecules

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.