Abstract:In this study we compared the efficiencies of six crystalline matrices and their mixtures for the MALDI of lignin and studied the effect of sample application technique and matrix to analyte ratio on the quality of the mass spectrum. It was found that the best results can be obtained when α cyano 4 hydroxycin namic and 2,5 dihydroxybenzoic acids, and also 2,4,6 trihydroxyacetophenone are used as matrices, taken in 10 to 100 fold excesses with respect to lignin and sequentially applied onto the target in the or… Show more
“…To study this phenomenon, we selected a number of intense peaks of oligomers in the mass spectra of the DL preparation, containing from two to eight guaiacylpropane structural units and that differed in mass by 196.0736 Da. This value corresponds to a guaiacylglycerol unit, the most common for softwood lignin, with the gross formula of C 10 H 12 O 4 , observed previously in the MALDI‐TOF mass spectra of spruce dioxane lignin . The [C 20 H 19 O 6 ] − ion with m / z 355.1184 which is the base peak in all the mass spectra obtained (excluding the peaks of impurities in ESI spectra) was selected for study.…”
Section: Resultsmentioning
confidence: 99%
“…Methods such as matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry and atmospheric pressure ionization mass spectrometry, including those in combination with preliminary chromatographic separation, have been used in various studies. Despite the undoubted advantages of MALDI, this method is not currently favored in structural studies of lignin for several reasons, the most important of which is a low ionization efficiency of the biopolymer achieved using conventional matrices …”
“…To study this phenomenon, we selected a number of intense peaks of oligomers in the mass spectra of the DL preparation, containing from two to eight guaiacylpropane structural units and that differed in mass by 196.0736 Da. This value corresponds to a guaiacylglycerol unit, the most common for softwood lignin, with the gross formula of C 10 H 12 O 4 , observed previously in the MALDI‐TOF mass spectra of spruce dioxane lignin . The [C 20 H 19 O 6 ] − ion with m / z 355.1184 which is the base peak in all the mass spectra obtained (excluding the peaks of impurities in ESI spectra) was selected for study.…”
Section: Resultsmentioning
confidence: 99%
“…Methods such as matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry and atmospheric pressure ionization mass spectrometry, including those in combination with preliminary chromatographic separation, have been used in various studies. Despite the undoubted advantages of MALDI, this method is not currently favored in structural studies of lignin for several reasons, the most important of which is a low ionization efficiency of the biopolymer achieved using conventional matrices …”
“…37,38 The α-cyclodextrin/α-cyano-4-hydroxycinnamic acid (α-CD/CHCA) matrix was prepared by mixing 2.4 ml of a 10 mM aqueous α-CD solution with 75 mM CHCA in 0.4 ml acetonitrile/H 2 O (7/3 v/v) containing 0.1 vol% trifluoroacetic acid. 37,38 The α-cyclodextrin/α-cyano-4-hydroxycinnamic acid (α-CD/CHCA) matrix was prepared by mixing 2.4 ml of a 10 mM aqueous α-CD solution with 75 mM CHCA in 0.4 ml acetonitrile/H 2 O (7/3 v/v) containing 0.1 vol% trifluoroacetic acid.…”
Mechanistic aspects of deconstruction and hydrodeoxygenation of organosolv lignin using zeolite and SiO 2 supported Ni catalysts are reported. Lignin was deconstructed and converted to substituted alicyclic and aromatic hydrocarbons with 5 to 14 carbon atoms. Full conversion with total yield of 70 ± 5 wt% hydrocarbons was achieved at 593 K and 20 bar H 2 . The organosolv lignin used consists of seven to eight monolignol subunits and has an average molecular weight of ca. 1200 g mol −1 . The monolignols were mainly guaiacyl, syringyl and phenylcoumaran, randomly interconnected through β-O-4, 4-O-5, β-1, 5-5' and β-β ether bonds. In situ IR spectroscopy was used to follow the changes in lignin constituents during reaction. The reductive catalytic deconstruction of organosolv lignin starts with the hydrogenolysis of aryl alkyl ether bonds, followed by hydrogenation of the aromatic rings to cyclic alcohols. Oxygen is removed from the alcohols via dehydration on Brønsted acid sites to cyclic alkenes that are further hydrogenated. † Electronic supplementary information (ESI) available. See
“…Matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry has been used in various lignin structural investigations . Notwithstanding its unquestionable advantages, this method is not widely used for the structural analyses of lignin because of the poor ionization efficiency of the lignin biopolymer using conventional matrices …”
Section: Resultsmentioning
confidence: 99%
“…11 Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been used in various lignin structural investigations. [16][17][18][19] Notwithstanding its unquestionable advantages, this method is not widely used for the structural analyses of lignin because of the poor ionization efficiency of the lignin biopolymer using conventional matrices. [16][17][18][19] We have performed the direct analysis of the mixture of lignin oligomers without any chromatographic pre-separation and the determination of the ion formulae was accomplished with the aid of some basic rules in MS and MS/MS.…”
Rationale
We report for the first time the top‐down lignomic analysis of the virgin released lignin (VRL) oligomers obtained from the Saudi date palm wood (SDPW), using a matrix‐assisted laser desorption/ionization time‐of‐flight/time‐of‐flight (MALDI‐TOF/TOF) instrument. In addition, we are proposing new collision‐induced dissociation tandem mass spectrometry (CID‐MS/MS) fragmentation routes for this series of unreported VRL oligomers.
Methods
We have used direct MALDI‐TOF‐MS analysis of the mixture of lignin oligomers without any chromatographic pre‐separation. High‐energy CID‐MS/MS analyses were used to confirm the precursor ion structures.
Results
Six protonated lignin oligomer molecules were identified: [C19H24O8 + H]+ as H(8‐O‐4')G; [C50H52O19 + H]+ as H(8‐O‐4')H(8‐O‐4'')S(8‐O‐4''')S(8‐O‐4'''')G; [C58H54O18+ H]+ as H(8‐O‐4')H(8‐O‐4'')H(8‐O‐4''')G(8‐O‐4'''')S(8‐O‐4''''')G; [C58H54O19 + H]+ as H(8‐O‐4')H(8‐O‐4'')H(8‐O‐4''')S(8‐O‐4'''')S(8‐O‐4''''')G; [C61H68O25 + H]+ as H(8‐O‐4')G(8‐O‐4'')G(8‐O‐4''')S(8‐O‐4'''')S(8‐O‐4''''')G; and [C61H68O26 + H]+ as C(8‐O‐4')G(8‐O‐4'')G(8‐O‐4''')S(8‐O‐4'''')S(8‐O‐4''''')G units (H = coniferyl, S = sinapyl, and G = p‐coumaryl). Two distonic cations were identified as [C39H43O15 + H]+• and [C40H43O16 + H]+• deriving from two tetrameric lignin oligomers. The high‐energy MS/MS analyses allowed the confirmation of the proposed structures of this series of lignin oligomers.
Conclusions
To our knowledge, this is the first elucidation of the lignin structure of the Saudi seedling date palm wood that was accomplished using a top‐down lignomic strategy that has not previously been published. The complex high‐energy CID‐MS/MS fragmentations presented herein are novel and have never been described before.
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