Analysis of Lignin Aromatic Structure in Wood Based on the IR Spectrum

Journal of Wood Chemistry and Technology (Impact Factor: 1.18). 10/2012; 32(4):294-303. DOI: 10.1080/02773813.2012.666316

ABSTRACT A total of 17 softwoods and 48 hardwoods were analyzed by IR spectroscopy to examine if syringyl ratio (syringyl/(syringyl+guaiacyl)) calculated from nitrobenzene oxidation products can be precisely expressed by area ratios of characteristic peaks of lignin in IR spectrum. Area ratio of two peaks is referred to as that of two wavenumber domains, represented by “wavenumber 1/ wavenumber 2.” Examined peak area ratios were 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/(855+815). Among these ratios, log(1595/1509) and log(1275/1220) showed significant linear relationship with the syringyl ratios with a correlation coefficient of 0.98 for all 65 woods. These two ratios could also be used to distinguish all the hardwoods from the softwoods.

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    ABSTRACT: Background In order to rapidly and efficiently screen potential biofuel feedstock candidates for quintessential traits, robust high-throughput analytical techniques must be developed and honed. The traditional methods of measuring lignin syringyl/guaiacyl (S/G) ratio can be laborious, involve hazardous reagents, and/or be destructive. Vibrational spectroscopy can furnish high-throughput instrumentation without the limitations of the traditional techniques. Spectral data from mid-infrared, near-infrared, and Raman spectroscopies was combined with S/G ratios, obtained using pyrolysis molecular beam mass spectrometry, from 245 different eucalypt and Acacia trees across 17 species. Iterations of spectral processing allowed the assembly of robust predictive models using partial least squares (PLS). Results The PLS models were rigorously evaluated using three different randomly generated calibration and validation sets for each spectral processing approach. Root mean standard errors of prediction for validation sets were lowest for models comprised of Raman (0.13 to 0.16) and mid-infrared (0.13 to 0.15) spectral data, while near-infrared spectroscopy led to more erroneous predictions (0.18 to 0.21). Correlation coefficients (r) for the validation sets followed a similar pattern: Raman (0.89 to 0.91), mid-infrared (0.87 to 0.91), and near-infrared (0.79 to 0.82). These statistics signify that Raman and mid-infrared spectroscopy led to the most accurate predictions of S/G ratio in a diverse consortium of feedstocks. Conclusion Eucalypts present an attractive option for biofuel and biochemical production. Given the assortment of over 900 different species of Eucalyptus and Corymbia, in addition to various species of Acacia, it is necessary to isolate those possessing ideal biofuel traits. This research has demonstrated the validity of vibrational spectroscopy to efficiently partition different potential biofuel feedstocks according to lignin S/G ratio, significantly reducing experiment and analysis time and expense while providing non-destructive, accurate, global, predictive models encompassing a diverse array of feedstocks.
    Biotechnology for Biofuels 06/2014; 7:93. DOI:10.1186/1754-6834-7-93 · 6.22 Impact Factor
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    ABSTRACT: Lignin, the main natural aromatic polymer was always aroused researchers interest. Currently around 90% of this biomaterial is burned for energy. It has a very complex and complicated structure which depends on the separation method and plant species, what determine difficulties to use as a raw material widely. This research presents a physical method to modify lignin by ultrasonic irradiation in order to obtain nanoparticles. The nanoparticles synthesized were dimensionally and morphologically characterized. At the same time the preoccupations were to determine the structural and compositional changes that occurred after sonication. To achieve this, two types of commercial lignins (wheat straw and Sarkanda grass) were used and the modifications were analyzed by FTIR-spectroscopy, GPC-chromatography, (31)P-NMR-spectroscopy and HSQC0. The results confirm that the compositional and structural changes of nanoparticles obtained are not significantly modified at the intensity applied but depend on the nature of lignin.
    Ultrasonics Sonochemistry 09/2014; 23. DOI:10.1016/j.ultsonch.2014.08.021 · 3.82 Impact Factor
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    ABSTRACT: Lignin is the most abundant aromatic plant polymer on earth. Useful information on its structure and interactions is gained by vibrational spectroscopy and relies on the quality of band assignments. B3LYP predictions were recently shown to support band assignments. Further progress calls for a comprehensive study of the quality of available theoretical methods in relation to the task of predicting lignin vibrational properties. The present study examined more than 50 functionals for prediction of IR vibrations of an appropriate lignin model. Based on a basis set incompleteness study, the pc-2 basis set was used. B98, X3LYP and B97-1 were the overall best-performing functionals, and “fingerprint” band positions were predicted by single-factor scaling of harmonic frequencies to an average error of ±3 cm−1 by optimized scaling factors of 1.017, 1.021 and 1.016, respectively. Their performance using instead explicit anharmonic correction was slightly worse giving an error of ca. ±5 cm−1. The X3LYP and B97-1 functionals offer also good description of hydrogen bonding. Error compensation from, e.g., insufficient treatment of solvation is likely to affect these results, and thus at this stage no single functional stands out. These results provide a needed basis for further theoretical developments in relation to vibrational assignments of Infrared and Raman spectra of lignin.
    Theoretical Chemistry Accounts 03/2015; 134(3). DOI:10.1007/s00214-015-1638-2 · 2.14 Impact Factor