David J. Clifford

A new rapid technique for the characterization of lignin in vascular plants: thermochemolysis with tetramethylammonium hydroxide (TMAH)

Abstract Flash pyrolysis in the presence of tetramethylammonium hydroxide (TMAH) has been utilized for the characterization of lignin in a gymnosperm (pine), angiosperm (alder), and nonwoody ( Juncus effusus L.) vascular plant tissue. The gymnosperm tissue yielded primarily methylated guaiacyl derivatives resulting from cleavage of lignin β-O-4 bonds and subsequent methylation of acidic hydroxy groups. The angiosperm tissue also yielded guaiacyl-type compounds in addition to an analogous suite of methylated syringyl lignin derivatives. The nonwoody angiosperm yielded methylated cinnamyl lignin derivatives in addition to methylated guaiacyl and syringyl compounds. Analysis of alder wood with this technique at a low temperature of 310°C has demonstrated that the dominant reaction with TMAH is mainly a thermally assisted chemolytic degradation rather than degradation induced by pyrolytic bond cleavage. Accordingly, we now call the technique TMAH thermochemolysis.

The organic geochemistry of coal: from plant materials to coal

Coalification is a process that transforms plant remains under the influence of time, temperature, and possibly pressure to a black, generally lustrous solid organic fossil fuel having a very complex chemistry. Although much has been learned in the past two centuries on coal chemistry, we still have little knowledge of the way plant materials undergo these transformations. The problem has been the existence of adequate characterization tools. The advent of some new tools for structural elucidation of macromolecules has led to some revised thinking on coalification. Originally thought to be a process involving the full degradation of plant remains and subsequent reconstitution of these remains, the general consensus today is that the process involves a selective preservation of certain resistant plant components followed by some minor reorganization of the biopolymers that survive. The major components of plants do degrade, and the resistant ones often constitute only a small fraction of the original mass of the plant materials. This paper examines the most recent literature concerning coalification and focuses on the chemistry associated with coalification of certain recognizable plant remains that have been at the center of research activity for the past two decades. Thus, we examine the recent knowledge of the chemistry of resistant biopolymers in extant and fossil wood, cuticles, resins, spores, and algae, knowledge that has been assembled to establish the reaction pathways towards coal macromolecules.

Flash pyrolysis and in situ methylation of humic acids from soil

Conventional flash pyrolysis-gas chromatography-mass spectrometry has tradiditionally been used for the characterization of complex geological substances such as humic materials, but the technique appears to provide a biased representation of the structural components of very polar materials such as humic substances, probably because the polar compounds have insufficient volatility to be analyzed efficiently by gas chromatography. A new technique of in situ methylation (ISM) with tetramethyl ammonium hydroxide, introduced for oxygenated polymers, is applied to humic substances and shown to yield methylated products believed to be more characteristics of the structural components of these polar macromolecules from soils than are data from conventional pyrolysis without methylation. The discovery of benzenecarboxylic acids and long-chain aliphatic acids as the predominant constituents of three humic acids in ISM pyrolysis indicates that a reevaluation of recent structural models of humic acids which are based on conventional pyrolysis studies is in order.

Tetramethylammonium hydroxide (TMAH) thermochemolysis of the aliphatic biopolymer cutan: insights into the chemical structure

Tetramethylammonium hydroxide (TMAH) thermochemolysis has been applied to the diagenetically resistant aliphatic biopolymer cutan derived from the leaf cuticles of Agave americana. Data obtained from the cutan sample using this new analytical method are vastly different in comparison with conventional flash pyrolysis data of the same sample. Under conventional flash pyrolysis conditions, the dominant products were alkanes, alkenes, and α, ω-alkadienes. Under thermochemolysis conditions, however, the cutan biopolymer yielded fatty acid methyl esters (FAMEs) of varying carbon chain length, along with a large number of benzenecarboxylic acid methyl esters that point to the possibility of a chemical structure containing functionalized benzene rings. This type of structure is absent from the current structural model of cutan.

Off-line thermochemolysis versus flash pyrolysis for the in situ methylation of lignin: Is pyrolysis necessary?

Abstract Lignin, a major biopolymer in vascular plants, is shown to undergo thermochemolysis reactions when subjected to flash pyrolysis with in situ methylation using tetramethylammonium hydroxide. The product distribution, composed of methylated lignin monomers, implies that the thermochemolysis involves cleavage of the β-O-4 ether bonds in the lignin. Because thermochemolysis occurs with equal effectiveness at sub-pyrolysis temperatures of 300 °C, we conclude that the analytical method does not require use of specialized pyrolysis equipment, and can be implemented in a batch mode in which internal standards can be added and the products quantified.

The nature and fate of natural resins in the geosphere. IX Structure and maturation similarities of soluble and insoluble polylabdanoids isolated from Tertiary Class I resinites.

Abstract Soluble polylabdanoids were isolated from five Tertiary Class I resinites by sequential extraction and were characterized by 13 C and 1 H NMR spectroscopy and Py–GC–MS. The structure and maturation characteristics of soluble extracts were strikingly similar to those observed for polylabdanoids in the native resinite. Soluble and insoluble materials undergo parallel geotransformation processes similar to those observed previously, including (i) exomethylene and total olefinic carbon depletion, (ii) double bond redistribution as indicated by ∑C14/∑C15 pyrolysis product ratios and (iii) A-ring defunctionalization. Resonances at 138 and 127 ppm in 13 C NMR spectra were shown to be those of aromatic and olefinic structures in mature samples, indicating that double bond content had been overestimated in the past. Proton NMR analyses have revealed several structural features previously unobserved. Resonances at 5.3 ppm of mature polymers were assigned to trisubstituted olefins in cyclized/cross-linked polylabdanoids. Further evidence in support of this pathway is derived from 13 C NMR spectra, from which an increase in aliphatic carbon content paralleling the loss of olefinic structures was observed.

2,3,6-/3,4,5-Trimethyl substituted diaryl carotenoid derivatives (Chlorobiaceae) in petroleums of the Belarussian Pripyat River Basin

Degradation products of the 2,3,6-/3,4,5-trimethyl substituted analog of isorenieratene were characterized in Belarussian petroleums. Devonian oils of low maturity were found to contain high concentrations (e.g., 35 mg/g) of C40 diaryl isoprenoids (2,3,6-/3,4,5-trimethyl substitution) along with an abundance of maturation-related compounds. A maturation scheme for diaryl carotenoid (2,3,6-/3,4,5-trimethyl substitution) precursors was proposed. Diaryl isoprenoids and aryl isoprenoid (2,3,6- and 3,4,5-trimethyl substitutions) contents were found to decrease as a function of maturity. Maturity parameters based on (i) the ratio of two specific C15 aryl isoprenoids and (ii) the ratio of C15 (2,3,6) aryl isoprenoids to C40 diaryl isoprenoids (2,3,6-/3,4,5) were proposed.

Structural transformations of polylabdanoid resinites during maturation

Abstract Three polylabdanoid resinites ranging in age from Eocene to Miocene were analyzed by pyrolysis-gas chromatography-mass spectrometry and solid-state nuclear magnetic resonance spectroscopy. The goal of the study was to determine effects on the chemical composition of polylabdanoid resinites following maturation processes. The samples studied included two Victorian Brown Coal resinites from the Yallourn and Morwell coal seams in Victoria, Australia, and a resinite from the Brunner coal measure in Nelson, New Zealand. Results of CPMAS 13 C NMR experiments have determined a progressive decrease in total olefinic carbon content (per diterpenoid) with increasing maturity. Olefin reduction occurs primarily via a diminution in exocyclic methylene carbons of the labdatriene precursors (i.e. communic acid, communol, and/or biformene and their analogs). Analysis of Soxhlet extracted samples by py-GC-MS has shown a transformation from pyrolysis products indicative of communic acid polymers (hydronaphthenic acids) to a pyrolyzate containing a significant proportion of alkyl(hydro)naphthalenes. Condensation of the resinite polymer occurring in conjunction with defunctionalization reactions has been proposed.

The nature and fate of natural resins in the geosphere - VIII - NMR and Py-GC-MS characterization of soluble labdanoid polymers isolated from holocene class I resins.

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state {sup 13}C- and {sup 1}H NMR and {sup 13}C-{sup 1}H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py-GC-MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride-methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py-GC-MS, solid-state {sup 13}C CP/MAS and {sup 13}C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.