Method for determining the content of tobacco lignin by two-dimensional nuclear magnetic resonance spectroscopy

Abstract

The application discloses a two-dimensional nuclear magnetic resonance spectrum determination method for tobacco lignin content, which comprises three steps of drawing a standard working curve, quantitative determination of alkali-extracted lignin of a tobacco sample to be measured and quantitative determination of total lignin of the tobacco sample to be measured. The application realizes quantitative determination of lignin macromolecules by using two-dimensional heteronuclear single quantum coherence spectrum nuclear magnetic resonance measurement technology (2D HSQC NMR), and is simple in operation, high in testing efficiency, accurate in quantification and suitable for batch determination of tobacco samples.

Description

Technical Field

[0001] This invention belongs to the field of tobacco analytical chemistry research and relates to a two-dimensional nuclear magnetic resonance spectroscopy method for determining the lignin content in tobacco. Background Technology

[0002] Tobacco lignin is an important biopolymer in tobacco, playing a vital role in improving the lodging resistance and disease resistance of tobacco plants during growth. The chemical composition of tobacco is a crucial factor determining the quality of tobacco leaves. During the curing and aging stages, lignin degrades to produce aromatic small-molecule flavoring components that enhance the smoking quality of tobacco, thus contributing to improved tobacco quality. However, during cigarette combustion, lignin undergoes thermal decomposition, generating harmful substances such as small-molecule phenols and tar, which can endanger consumer health. The lignin content has a significant impact on tobacco quality and safety; therefore, developing a rapid and non-destructive quantitative analytical method to determine lignin content is of great importance to analytical chemists.

[0003] Currently, the tobacco industry primarily uses chemical methods to determine the lignin content in tobacco. This involves first removing soluble substances from the tobacco sample using neutral detergent, acidic detergent, and 72% concentrated sulfuric acid, respectively. After drying and ashing, the contents of neutral detergent fiber, acidic detergent fiber, and acid-washed lignin are determined by gravimetric analysis. The contents of cellulose, hemicellulose, and lignin in the sample are then calculated. Therefore, the chemical method for determining tobacco lignin is cumbersome, time-consuming, requires large amounts of chemical reagents, and is prone to environmental pollution, making it difficult to meet the tobacco industry's practical need for rapid, large-scale determination of tobacco lignin content.

[0004] Two-dimensional heteronuclear single-quantum coherent nuclear magnetic resonance (2D HSQC NMR) is one of the most powerful tools for studying the structure and content of lignin. This method combines... 1 Signal detection sensitivity and H NMR experiments 13CNMR spectrum has the advantages of wide range, high resolution, and can maintain the initial state of natural complex macromolecules, and can reveal different structural units and their connecting bonds in lignin. It is widely used in the structural analysis of lignin in plant samples (Nature protocols, 2012, 7(9): 1579-1589). At the same time, the acquisition of quantitative information has become one of the main requirements of 2D HSQC technology (Journal of the American Chemical Society, 2011, 133(46): 1662-1665). The commonly used quantitative technique is to optimize the 2D HSQC NMR pulse sequence to suppress the change of the target chemical bond coupling constant J, and to reduce the fluctuation of HSQC signal (Journal of the American Chemical Society, 2003, 125(14): 4362-4367) to realize the quantification of target substances. In recent years, 2D NMR spectrum quantitative analysis method has been applied to the content detection of lactose in milk (Journal of Agricultural and Food Chemistry, 2007, 55, 4307-4311) and glucose in tomato extract (Metabolomics, 2015, 11: 1231-1242), but generally the target substances to be measured are small molecule compounds. The 2D HSQC NMR quantitative analysis technology for plant macromolecules is still a hot spot for current technology development (Journal of Pharmaceutical and Biomedical Analysis, 2015, 18, 78-85). At present, the 2D HSQC NMR measurement of tobacco lignin can only be limited to semi-quantitative analysis of its structural units and connecting bond units. SUMMARY

[0005] In order to overcome the defects of the prior art, the purpose of the present application is to provide a 2D HSQC NMR quantitative analysis method for the content of tobacco lignin macromolecule with simple process and good quantitative effect, which meets the practical requirements of rapid, convenient and batch determination of tobacco lignin content in tobacco industry.

[0006] The technical problem solved by the present application adopts the following technical scheme:

[0007] The present application provides a two-dimensional nuclear magnetic resonance spectrum determination method for the content of tobacco lignin, characterized in that the method comprises the following steps:

[0008] (1) Standard working curve drawing

[0009] A commercially available delignified lignin sample with mass gradient was weighed as a standard sample, which was dissolved in the prepared NMR solvent of DMSO-d6 and HMPA-d 18 A series of spectra were obtained by 2D HSQC NMR in the prepared NMR solvent;

[0010] The central peak of the solvent peak DMSO-d6 in the spectrum was selected as the internal reference peak, and each lignin structural unit was selected as the quantitative target peak, and then the ratio of the sum of the peak volumes (A) of each quantitative target peak in each delignified lignin sample to the integral volume (B) of the central peak of DMSO-d6 was calculated;

[0011] The mass of each delignified lignin was taken as the abscissa, and the ratio of the sum of the peak volumes (A) of each quantitative target peak to the integral volume (B) of the internal reference peak was taken as the ordinate, and a standard working curve was established;

[0012] (2) Quantitative determination of alkali-extracted lignin in the tobacco sample to be tested

[0013] A certain mass of tobacco sample powder to be tested was weighed, pretreated, and alkali-extracted lignin test sample was obtained;

[0014] The alkali-extracted lignin test sample was dissolved in the prepared solvent of DMSO-d6 and HMPA-d 18 The spectrum of the sample alkali-extracted lignin was obtained by 2D HSQCNMR;

[0015] The central peak of DMSO-d6 and each quantitative target peak in the 2D HSQC NMR spectrum were processed using MestReNova 6.1 software to obtain target peak volume data, and then the ratio of the sum of the peak volumes (A1) of the lignin quantitative target peaks in the spectrum of the tobacco sample to the volume (B1) of the internal reference peak of DMSO-d6 was calculated;

[0016] The absolute mass (m) of the alkali-extracted lignin in the tobacco sample to be tested was obtained from the ratio of the sum of the peak volumes (A1) of the lignin quantitative target peaks in the spectrum of the tobacco sample to be tested to the volume (B1) of the internal reference peak according to the standard working curve obtained in step (1);

[0017] (3) Quantitative determination of total lignin in the tobacco sample to be tested

[0018] A sufficient number of samples including tobacco leaves, tobacco stems, and papermaking process tobacco sheet are selected, the absolute mass of alkali-extracted lignin of each sample is determined according to step (2), the total lignin content in each sample is determined by using the tobacco industry standard method (Determination of cellulose, hemicellulose and lignin in tobacco and tobacco products by detergent method), parallel three times of measurement, a relationship curve of alkali-extracted lignin converted into total lignin is established, and a correction coefficient (K) for calculating the total lignin content of the sample is obtained;

[0019] The total lignin content (M Lignin ) in the tobacco sample to be measured is calculated by using the correction coefficient according to the absolute mass of alkali-extracted lignin of the tobacco sample to be measured in step (2).

[0020] Formula 2:

[0021] In the formula, M Lignin is the total lignin content of the tobacco sample to be measured (% by mass fraction), K is the correction coefficient between alkali-extracted lignin and total lignin, m is the absolute mass of alkali-extracted lignin in the sample to be measured (mg), and W is the water content of the sample (% by mass fraction).

[0022] As a preferred embodiment of the present application, the lignin structural units in step (1) include syringyl S 2 / 6 , S' 2 / 6 , guaiacyl G2 and G6, p-hydroxyphenyl H 2 / 6 , and ferulic acid ester structure FA2 and FA6. At this time, the sum of the peak volumes (A) of each quantitative target peak in step (1) is calculated according to Formula 1.

[0023] Formula 1: A = I(S 2 / 6 +S' 2 / 6 )+I(G2+G6)+I(H 2 / 6 )+I(FA2+FA6)

[0024] In the formula, I(S 2 / 6 +S' 2 / 6 ), I(G2+G6), I(H 2 / 6 ), and I(FA2+FA6) represent the volume integral values of S and S', G, H, and FA at positions 2 and 6, respectively.

[0025] In the formula, the molecular structures of lignin structural units syringyl S, S', guaiacyl G, p-hydroxyphenyl H, and ferulic acid ester structure FA are as follows:

[0026]

[0027] As a preferred embodiment of the present application, the nuclear magnetic resonance solvent in step (1) is prepared by DMSO-d6 and HMPA-d 18 According to the volume ratio of 4:1.

[0028] As a preferred embodiment of the present application, the solvent for dissolving the alkali-extracted lignin sample to be tested in step (2) is prepared by DMSO-d6 and HMPA-d 18 According to the volume ratio of 4:1.

[0029] As a preferred embodiment of the present application, the pretreatment step in step (2) includes degreasing and alkali extraction.

[0030] Compared with the prior art, the present application has the beneficial effects of:

[0031] 1. The present application realizes quantitative determination of lignin macromolecules by using two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance measurement technology (2D HSQC NMR).

[0032] 2. The present application uses two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance technology (2D HSQC NMR) for two-dimensional nuclear magnetic resonance signal acquisition, and compared with one-dimensional nuclear magnetic resonance spectrum signal, the spectrum has a wide range and high resolution; the absolute content of alkali-extracted lignin is detected by using a standard working curve.

[0033] 3. The present application uses deuterated dimethyl sulfoxide / deuterated hexamethylphosphoramide (DMSO-d6 / HMPA-d 18 ) as the nuclear magnetic resonance spectrum analysis solvent, so that the alkali-extracted lignin is well dissolved in the solution;

[0034] 4. The present application uses the center peak (δ C / δ H 39.52 / 2.50 ppm) of DMSO-d6 as an internal standard reference peak, which effectively improves the influence of signal fluctuation of the instrument on the determination results and reduces the measurement error;

[0035] 5. The present application uses a correction coefficient, which can quickly convert the total lignin content.

[0036] 6. The test method established by the present application reduces the waste of manpower and material resources, and is suitable for batch testing of tobacco samples. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 Figure 1 is a 2D HSQC NMR spectrum of the dealkalized lignin dissolved in deuterated dimethyl sulfoxide / deuterated hexamethylphosphoramide (DMSO-d6 / HMPA-d 18 , 4:1 v / v) nuclear magnetic resonance solvent in Example 1. Figure 2 is a 2D HSQC NMR spectrum of the alkali-extracted lignin dissolved in deuterated dimethyl sulfoxide / deuterated hexamethylphosphoramide (DMSO-d6 / HMPA-d C , 4:1 v / v) nuclear magnetic resonance solvent in Example 2.H 39.52 / 2.50ppm).

[0038] Figure 2 Example 1: Dealkalized lignin containing syringyl S 2 / 6 S' 2 / 6 Guaiacyl G2, G6, p-hydroxyphenyl H 2 / 6 2D HSQC NMR aromatic region spectra of the quantitative target peaks of ferulic acid esters FA2 and FA6.

[0039] Figure 3 The 2D HSQC NMR aromatic region spectrum of 20.5 mg / mL commercially available dealkalized lignin in Example 1 is shown.

[0040] Figure 4 The 2D HSQC NMR aromatic region spectrum of 40.2 mg / mL commercially available dealkalized lignin in Example 1 is shown.

[0041] Figure 5 The 2D HSQC NMR aromatic region spectrum of 60.8 mg / mL commercially available dealkalized lignin in Example 1 is shown.

[0042] Figure 6 The 2D HSQC NMR aromatic region spectrum of commercially available dealkalized lignin at a concentration of 79.1 mg / mL in Example 1 is shown.

[0043] Figure 7 The 2D HSQC NMR aromatic region spectrum of 99.0 mg / mL commercially available dealkalized lignin in Example 1 is shown.

[0044] Figure 8 This is the standard operating curve diagram for Example 1.

[0045] Figure 9 The image shows the 2D HSQC NMR spectrum of the tobacco sample (Yunyan 87C2F) to be tested in Example 1.

[0046] Figure 10 The 2D HSQC NMR aromatic region spectrum of the tobacco sample (Yunyan 87C2F) to be tested in Example 1 is shown.

[0047] Figure 11 The graph shows the correction coefficients for the alkali-extracted lignin quality and total lignin content of the sample in Example 1. Detailed Implementation

[0048] The present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings.

[0049] Example

[0050] The pretreatment conditions of the tobacco sample in this embodiment of the invention are as follows: (1) The sample is dried at 40℃ for 2h and then mechanically crushed and passed through a 40-mesh sieve. 10g of tobacco biomass is treated by Soxhlet extraction with 80mL toluene and 40mL ethanol for 6h to remove fat, and then dried to obtain residue I. (2) The residue I after degreasing is placed in a 500mL flask, 200mL of 0.5mol / L NaOH solution is added, the flask is placed in a constant temperature water bath and reacted at 100℃ for 4h, centrifuged, filtered, washed with double-distilled water, the filtrate is collected, the pH of the solution is adjusted to the range of 5.5 to 6.0 with 6mol / L HCl, and then concentrated to about 50mL by rotary evaporator. The filtrate is added dropwise to 3 times the volume of 95% ethanol solution for purification, the supernatant is collected by centrifugation, and concentrated again under reduced pressure. The concentrated solution is added dropwise to 10 times the volume of pH2 hydrochloric acid solution to precipitate alkali-extracted lignin, and after freeze-drying, alkali-extracted lignin sample II to be tested by nuclear magnetic resonance is obtained.

[0051] The NMR sample preparation method is as follows: Transfer the sample to be tested, II, into a 5 mm NMR quartz sample tube, and add 0.5 mL of deuterated dimethyl sulfoxide / deuterated hexamethylphosphoric triamine (DMSO-d6 / HMPA-d6). 18 The sample was completely dissolved in the solvent system by vortexing for 10 min and sonicating for 2 h in a 4:1 v / v NMR solvent.

[0052] The instrument conditions for 2D HSQC NMR spectroscopy were as follows: all samples were analyzed on a Bruker 600MHz superconducting nuclear magnetic resonance spectrometer equipped with a 5mm Z-gradient field coil. 1 H / 13 C / 15 The N-type triple-resonance inverse cryogenic probe operates at 298K using the Bruker standard pulse sequence. Specific parameters are as follows: F2 ( 1 The spectral width of the H dimension is 11 ppm, and the sampling point is 1024 (TD1); F1 ( 13 The spectral width in dimension C was 170 ppm, with 256 sampling points (TD2); the number of scans (NS) was 64; and the scan delay (D1) was 1 s. The NMR spectrum of lignin was obtained using DMSO-d6 solvent, with the central peak (δ)... C / δ H Chemical shift calibration was performed using a concentration of 39.52 / 2.50 ppm, and the characteristic peaks in the HSQC spectrum were processed using MestReNova 6.1 software to obtain the target peak volume data.

[0053] Example 1

[0054] First, weigh 20.5 mg of commercially available dealkalized lignin sample and dissolve it in 0.5 mL of deuterated dimethyl sulfoxide / deuterated hexamethylphosphoric triamine (DMSO-d6 / HMPA-d6). 18 2D HSQC NMR spectra were obtained in a 4:1 v / v NMR solvent. A typical 2D HSQC NMR spectrum of commercially available dealkalized lignin is shown below. Figure 1 As shown. The quantitative target peak of lignin is located at... Figure 1 The aromatic regions within. A magnified image of the aromatic regions, such as... Figure 2 As shown.

[0055] right Figure 1 and Figure 2 The central peak of the target peak DMSO-d6, the lignin structural unit syringyl S 2 / 6 S' 2 / 6 Guaiacyl G2, G6, p-hydroxyphenyl H 2 / 6 The positions of the ferulic acid esters FA2 and FA6 are qualitatively assigned in Table 1.

[0056] Table 1. Qualitative assignment of target peaks in lignin 2D HSQC NMR spectra.

[0057]

[0058] Next, accurately weigh 20.5 mg, 40.2 mg, 60.8 mg, 79.1 mg, and 99.0 mg of commercially available dealkalized lignin samples with a lignin content of 95%, respectively, and dissolve them in 0.5 mL of deuterated dimethyl sulfoxide / deuterated hexamethylphosphoric triamine (DMSO-d6 / HMPA-d6). 18 In a 4:1 v / v NMR solvent, a series of spectra were obtained using 2D HSQC NMR. Among them, the magnified spectra of the aromatic region are shown below. Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 As shown.

[0059] The central peak of the solvent peak DMSO-d6 was selected as the internal standard reference peak, based on the lignin structural units in the spectrum, including syringyl S. 2 / 6 S' 2 / 6 Guaiacyl G2, G6, p-hydroxyphenyl H 2 / 6 Based on the ratio of the sum of the peak volumes (A) of ferulic acid ester structures FA2 and FA6 (Formula 1) to the integral volume (B) of the central peak of DMSO-d6, a standard working curve for dealkalized lignin was established: I = 2.1891m + 1.704(r 2 =0.99698), such as Figure 8As shown. The detection limit of dealkalized lignin was calculated to be 0.52 mg / g and the quantitation limit was 1.65 mg / g at the 3-fold and 10-fold signal-to-noise ratio levels.

[0060] Formula 1: A = I(S) 2 / 6 +S′ 2 / 6 )+I(G2+G6)+I(H 2 / 6 )+I(FA2+FA6)

[0061] Among them, I(S) 2 / 6 +S' 2 / 6 ), I(G2+G6), I(H 2 / 6 ), I(FA2+FA6) represent the volume integral values ​​of S and S', G, H, and FA in 2 and 6 places, respectively.

[0062] Third, accurately weigh 10.0g of flue-cured tobacco leaf sample powder (Yunyan 87C2F), and after the above sample processing and data processing, determine the δ-index of the sample based on the spectrum of the sample to be tested. C / δ H 103.55 / 6.60ppm, δ C / δ H 106.83 / 7.22ppm syringinyl S 2 / 6 S' 2 / 6 Target peak, at δ C / δ H 110.21 / 6.87ppm, δ C / δ H The target peaks for guaiac-based G2 and G6 were 118.36 and 6.73 ppm, respectively, at δ C / δ H 127.01 / 7.13ppm H 2 / 6 Target peak, at δ C / δ H 110.37 / 7.38ppm, δ C / δ H The sum of the volumes (A1) of the target peaks of ferulic acid ester structures FA2 and FA6 at 123.57 / 7.13 ppm, and the values ​​at δ C / δ H The central peak integral volumes (B1) of DMSO-d6 at 39.52 / 2.50 ppm are shown in the following figures. Figure 9 , Figure 10 .

[0063] The ratio of the test samples A1 and B1 is I. x It is 87.17, and then Figure 8 The standard working curve is composed of I xThe m was calculated so that the absolute mass m of the alkali-extracted lignin could be obtained as 39.04 mg.

[0064] Finally, 9 different tobacco leaf samples, 9 different tobacco stem samples, 9 different papermaking process tobacco sheet samples, and the like 27 samples were selected, and the above sample treatment and data processing were performed, and the detection results of the alkali-extracted lignin content in the 27 samples were obtained through parallel measurement for three times. The total lignin content in the 27 samples was measured by using the detergent method commonly used in the tobacco industry (Determination of cellulose, hemicellulose and lignin in tobacco and tobacco products - Detergent method), and the results are shown in Table 2. The relationship curve of the alkali-extracted lignin converted into the total lignin was established according to Table 2, as shown in Figure 11 The correction coefficient K was obtained as 8.35.

[0065] The total lignin content of the tobacco sample to be measured was calculated by formula (2) as 3.26%.

[0066] Formula 2:

[0067] wherein M Lignin is the total lignin content of the tobacco sample to be measured (% by mass fraction), K is the correction coefficient between the alkali-extracted lignin and the total lignin, m is the absolute mass of the alkali-extracted lignin in the sample to be measured (mg), and W is the water content of the sample (% by mass fraction).

[0068] Table 2 Detection results of the alkali-extracted lignin mass and the total lignin content of the sample

[0069]

[0070]

[0071] Example 2

[0072] 10 g of tobacco leaves (accurately weighed to 0.0002 g) (Yunyan 87C2F) were weighed in parallel for 5 times (sample numbers 1-5), and the test and data processing of Example 1 were repeated to obtain the average value, standard deviation, and relative standard deviation of the total lignin content of the sample in 5 repeated tests, and the results are shown in Table 3.

[0073] Table 3 Average value, standard deviation, and relative standard deviation of 5 repeated tests

[0074]

[0075] Example 3

[0076] Take 8 tobacco samples (sample No. 1#-8#), each sample is divided into two parts, one part is tested according to the tobacco industry standard "tobacco and tobacco products cellulose, hemicellulose, lignin determination detergent method", the other part is tested according to the method of step 1, the results are shown in table 4.

[0077] Table 4 comparison of determination results of total lignin in tobacco sample by the method and standard method

[0078]

[0079]

[0080] Therefore, the determination method of tobacco lignin content provided by the present application is a simple, rapid and accurate quantitative analysis method, which provides an effective technical method and means for batch determination of tobacco lignin content in tobacco industry.

Claims

1. A two-dimensional nuclear magnetic resonance spectroscopy method for determining the lignin content of tobacco, characterized in that, The method includes the following steps: (1) Draw the standard working curve A series of commercially available dealkalized lignin samples of different masses were weighed as standard samples and dissolved in a solution of DMSO-d6 and HMPA-d6. 18 A series of spectra of dealkalized lignin were obtained by 2D HSQC NMR in the prepared nuclear magnetic resonance solvent. The central peak of the solvent peak DMSO-d6 in the spectrum was selected as the internal standard reference peak, and each lignin structural unit was selected as the quantitative target peak. Then the ratio of the sum of the peak volumes of each quantitative target peak in each dealkalized lignin sample to the integrated volume of the central peak of DMSO-d6 was calculated. A standard working curve was established with the mass of each dealkalized lignin as the abscissa and the ratio of the sum of the peak volumes of each quantitative target peak to the integral volume of the internal standard reference peak as the ordinate. (2) Quantitative determination of lignin extracted from tobacco samples by alkali extraction A certain mass of tobacco sample powder to be tested was weighed and subjected to a pretreatment step to obtain an alkali-extracted lignin test sample. The lignin-extracting test sample was dissolved in a solution of DMSO-d6 and HMPA-d6. 18 In the prepared solvent, the spectra of alkali-extracted lignin in the sample were obtained by 2D HSQC NMR. The central peak of DMSO-d6 and each quantitative target peak in the 2D HSQC NMR spectrum were processed using MestReNova 6.1 software to obtain the target peak volume data. Then, the ratio of the sum of the peak volumes of the quantitative target peaks of lignin in the spectrum of the tobacco sample to the volume of the internal standard reference peak of DMSO-d6 was calculated. The absolute mass of alkali-extracted lignin in the tobacco sample to be tested is obtained from the ratio of the sum of the peak volumes of the quantitative target peaks of lignin in the spectrum of the tobacco sample to be tested to the peak volume of the internal standard reference peak, based on the standard working curve obtained in step (1). (3) Quantitative determination of total lignin in the tobacco sample to be tested Select a sufficient number of samples including tobacco leaves, tobacco stems, and papermaking tobacco sheets. Determine the absolute mass of alkali-extracted lignin in each sample according to step (2). Perform three parallel measurements. Determine the total lignin content in each sample using the tobacco industry standard method. Establish a relationship curve for converting alkali-extracted lignin to total lignin and obtain the correction coefficient for calculating the total lignin content in the sample. The total lignin content in the tobacco sample is calculated by using the absolute mass of alkali-extracted lignin from the tobacco sample in step (2) and a correction coefficient.

2. The method for determining the lignin content of tobacco using two-dimensional nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, The nuclear magnetic resonance solvent in step (1) consists of DMSO-d6 and HMPA-d 18 It is prepared at a volume ratio of 4:

1.

3. The method for determining the lignin content of tobacco using two-dimensional nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, In step (2), the solvent for dissolving the lignin-extracting test sample in the alkali extraction process consists of DMSO-d6 and HMPA-d6. 18 It is prepared at a volume ratio of 4:

1.

4. The method for determining the lignin content of tobacco using two-dimensional nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, The pretreatment steps in step (2) include defatting and alkaline extraction.

5. The method for determining the lignin content of tobacco using two-dimensional nuclear magnetic resonance spectroscopy according to claim 1, characterized in that, Each lignin structural unit in step (1) includes syringyl S 2 / 6 S' 2 / 6 Guaiacyl G2, G6, p-hydroxyphenyl H 2 / 6 The ferulic acid ester structures are FA2 and FA6.

Images