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Dive into the research topics where Glenn R. Ponder is active.

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Featured researches published by Glenn R. Ponder.


Journal of Analytical and Applied Pyrolysis | 1992

Influence of linkage position and orientation in pyrolysis of polysaccharides: A study of several glucans☆

Glenn R. Ponder; Geoffrey N. Richards; Thomas T. Stevenson

Abstract Six naturally occurring and three synthetic glucans have been studied. The natural glucans contain 1,3-, 1,4- and 1,6- linkages with α- and β-orientations, while the synthetic glucans contain all possible linkage positions and orientations and also varying proportions of pyranose and furanose forms. The volatile products of pyrolysis are very dependent on the presence of trace amounts of inorganic-contaminants, which were detected as metal ions in all of the natural glucans. For most glucans these contaminants were effectively removed by washing with dilute acid. This removal of contaminants was, however, incomplete in the cases of amylose and of laminaran. The glucans, after purification in this way, all gave very similar pyrolytic yields of levoglucosan (LG), showing that LG formation is not dependent on polysaccharide linkage position or orientation, and thus confirming a recent hypothesis for mechanism of LG formation. The presence during pyrolysis of inorganic compounds (either indigenous or added), always led to decrease in LG and increase in yield of formic and acetic acids, glycolaldehyde, hydroxyacetone and phenols, thus indicating that the mechanism of formation of such compounds is also not dependent on polysaccharide linkage position or orientation.


Carbohydrate Research | 1991

Thermal synthesis and pyrolysis of a xylan

Glenn R. Ponder; Geoffrey N. Richards

Abstract A xylan has been synthesized in yields up to 64% by thermal polymerization of methyl β- d -xylopyranoside, catalyzed by phosphoric acid. The polymer is highly branched, with d.p. ∼20. The xylose units in the polymer are predominantly pyranose, with some furanose, and 14% of the nonreducing end groups are in the furanose form. The “reducing” end groups are at least partly in the form of methyl xylosides. Vacuum pyrolysis of the pure synthetic xylan gave a high char yield (48%, compare, for example 5% from pure cellulose), 1,4-anhydro-α- d -xylopyranose (5.7%), and 1,5-anhydro-4-deoxypent-1-en-3-ulose (2.4%). The structure of the latter compound was verified by degradation experiments and it was shown to be the compound previously isolated from pyrolysis of natural xylans and incorrectly assigned as 3-hydroxy-2-penteno-1,5-lactone. This glyculose has considerable importance as a marker compound for xylans in pyrolysis of biomass materials.


Carbohydrate Polymers | 1997

Arabinogalactan from Western larch, Part III: alkaline degradation revisited, with novel conclusions on molecular structure

Glenn R. Ponder; G.N. Richards

Abstract Alkaline degradation of larch arabinogalactan (AG) involves rapid peeling of the (1→3)-galactan main chain from the reducing end. The products are the original side chains attached to galactometasaccharinic (GalMS) acids derived from main-chain residues. These products have been separated by GPC and studied by compositional, methylation and NMR analyses. Results confirm that in a typical AG molecule most main-chain residues carry a side chain on C-6. About half of these side chains are β-(1→6)-linked Gal p dimers, and about a quarter are single Gal p residues. The rest contain three or more residues and include most of the Ara (arabinose) found in the polysaccharide. About one-fifth of the original Ara is consumed by the peeling reaction, and Ara groups at the non-reducing end of the main chain are proposed, predominantly as arabinobiosyl groups [β- l -Ara p -(1→3)-L-Ara f -(1→.. In general for the larger side chains abundance decreases with size, while branching and Ara content increase with size. Most terminal Ara f residues occur in three- and four-residue side chains, while most arabinobiosyl groups are found in side chains of more than three residues. The Ara probably occurs only as these monomeric or dimeric groups, and since no Ara is found in side chains smaller than three residues, this implies that there are no Ara branches attached directly to the main chain.


Biomass & Bioenergy | 1994

A review of some recent studies on mechanisms of pyrolysis of polysaccharides

Glenn R. Ponder; Geoffrey N. Richards

In seeking to gain a better understanding of the pyrolysis of polysaccharides, the pyrolytic behavior of a variety of naturally occurring and synthetic polysaccharides has been studied. Among the former were various glucans containing different linkage types, and for the latter, synthetic polymers were produced by thermal polymerization of a glucoside and of a xyloside. The study has focused on the effects which linkage types and inorganic additives have on pyrolytic pathways, with emphasis on the chemical mechanisms involved in the formation of one-, two- and three-carbon products, specifically glycolaldehyde, acetol, acetic acid, and formic acid. These compounds are the major non-aqueous components of the −60° condensate of the vacuum pyrolysate after removal of tar by room temperature condensation.13C labels in synthetic glucans were used to reveal the origins of these compounds. In general, the results show that each compound is formed by more than one mechanism. Specifically, glycolaldehyde derives mostly from C-1 and C-2 of the glucose monomers, with C-5 and C-6 also contributing significantly. Acetol and acetic acid derive mostly from contiguous carbons that include a terminal carbon (C-1 or C-6), most often C-6, appearing as the methyl carbon. About half of the formic acid arises from C-1. Some mechanisms derived from solution chemistry are proposed.


Carbohydrate Research | 1993

Pyrolysis of inulin, glucose and fructose

Glenn R. Ponder; Geoffrey N. Richards

The pyrolytic behavior of inulin, a (2-->1)-linked fructofuranan, is described. Parallel investigations of the pyrolysis of glucose and of fructose were conducted to supplement the inulin results and to aid comparison with previous results from glucans. Effects of neutral and basic additives are emphasized. As with glucans, the addition of such additives (especially basic) increases the yields of the one-, two-, and three-carbon products (as well as of hexosaccharinolactones), while generally decreasing the yields of anhydro sugar and furan derivatives. The former products include glycolaldehyde, acetol, dihydroxy-acetone, acetic acid, formic acid, and lactic acid. Mechanistic speculations are made regarding the origins of these compounds, as well as of furan derivatives and saccharinic acid lactones. Parallels with alkaline degradation are considered.


Carbohydrate Research | 1993

Pyrolysis of some 13C-labeled glucans : a mechanistic study

Glenn R. Ponder; Geoffrey N. Richards

An isotopic labeling study has been conducted to investigate the chemical mechanisms involved in the formation of certain pyrolysis products of glucans, specifically glycolaldehyde (GA), acetol (hydroxypropanone), acetic acid, and formic acid, which are the major non-aqueous components of the distillate fraction (−60°C condensate) of the pyrolyzate. 13C labels at C-1, C-2, and C-6 of the glucose rings in synthetic glucans were used to reveal the origins of these compounds. In general, the results show that each compound is formed by several different mechanisms, but suggest that only a few mechanisms predominate in each case. Glycolaldehyde derives predominantly from the C-1–C-2 segment of the glucose monomers, with C-5–C-6 also contributing significantly. Evidence is presented supporting heterolytic mechanism which require a reducing end-group and base catalysis. Acetol derives mostly from three contiguous carbons that include a terminal carbon (C-1 or C-6), most often C-6 and most often appearing as the methyl carbon in the acetol. Acetic acid also arises most often from terminal carbons, the C-5–C-6 segment being the major source, with the methyl carbon usually deriving from C-1 or C-6. About half of the formic acid produced arises from C-1. Mechanisms derived from the chemistry of alkaline degradation and involving acylformylcarbinol intermediates are proposed.


Journal of Carbohydrate Chemistry | 2003

Alternating Stereoregular Head, Tail–Tail, Head‐Poly(Alkylene d‐Glucaramides) Derived from a Homologous Series of Symmetrical Diamido‐di‐d‐Glucaric Acid Monomers

Susan D. Styron; Donald E. Kiely; Glenn R. Ponder

A method for the synthesis and purification of a homologous series of symmetrical diamido‐diacids derived from d‐glucaric acid and six alkylenediamines is described. Treating d‐glucaro‐6,3‐lactone with an equimolar amount of lithium acetate dihydrate yielded lithium d‐glucarate‐6,3‐lactone, which in turn was reacted with six alkylenediamines in dimethyl sulfoxide to give the target diamido‐diacids. Six new alternating stereoregular polyamides, head, tail–tail, head‐poly(alkylene d‐glucaramides), were then synthesized by simple polycondensation reactions between the activated diamido‐diacids [6,6′‐(N,N′‐alkylene)‐bis(d‐glucaramid‐1‐oic acid)s] and the alkylenediamines. Number average molecular weights for the polyamides were estimated by 1H NMR end group analysis. Models for the three‐dimensional shape of these alternating stereoregular polymers were produced from a combination of 1H NMR data, molecular modeling studies performed on d‐glucaramide, and crystal structures of various acyclic d‐glucaric acid derivatives.


Carbohydrate Research | 1990

Polysaccharides from thermal polymerization of glucosides

Glenn R. Ponder; Geoffrey N. Richards

Abstract As a first step towards synthesis of labeled polysaccharides for studies of mechanisms of pyrolysis, the acid-catalyzed thermal polymerizations of methyl α- d - and phenyl β- d -glucopyranosides have been studied and the optimum yields of polymer determined. The phenyl aglycone is a more facile leaving group than methyl and hence the phenyl glucoside yields polymer more rapidly at lower temperature. However, the byproduct phenol is less rapidly removed than methanol during polymerization, and the polysaccharide products from the phenyl glucoside are less pure. The polymer from methyl α- d -glucopyranoside is a mixed glucopyranan of average degree of polymerization (d.p.) 10–13, as determined by three different methods. The end groups are methyl α- d -glycopyranoside units, the predominant in-chain linkage, determined by methylation analysis, is 1→6, and the predominant branch points are 3,6-linked. Both α- and β-glucopyranosidic linkages are present in-chain in the approximate ratio 2:1. The similar, acid-catalyzed thermal polymerization of 1,6-anhydro-β- d -glucopyranose (levoglucosan, LG) has also been studied, and the mechanisms of the polymerizations are discussed.


Journal of Carbohydrate Chemistry | 1997

Arabinogalactan from Western Larch, Part II; A Reversible Order-Disorder Transition

Glenn R. Ponder; Geoffrey N. Richards

Abstract At the molecular level, larch arabinogalactan (AG) fragments into subunits when exposed to mild alkali or heat. This process is accompanied by a large increase in NMR spectral resolution, especially for NMR signals associated with main-chain units, and by the disappearance of 1H NMR signals probably due to persistent hydrogen bonds. Analysis by size-exclusion chromatography (SEC) shows that smaller AG species undergo the transition in preference to larger ones, and the transition can be reversed by drying from or freezing an aqueous solution of the “fragments” These observations indicate that the fragmentation is a dissociation of a molecular assembly accompanied by an order-disorder transition, analogous to the known triple helix → single-chain random coil transition of (1→6)-branched (1→3)-β-glucans. The small amount of uronic acid units in AG and the consequent ionexclusion effect in SEC provide a probe to study this transition, and results provide evidence in support of the concept that the t...


Journal of Carbohydrate Chemistry | 1997

Arabinogalactan from Western Larch, Part I; Effect of Uronic Acid Groups on Size Exclusion Chromatography

Glenn R. Ponder; Geoffrey N. Richards

Abstract Arabinogalactan (AG) from Western larch has sometimes been reported to contain a small proportion of uronic acid units. This concept is supported and extended by the present work, which shows that these units occur in some AG molecules. Molecular assemblies which contain such molecules are consequently partially excluded from the stationary phase of size exclusion chromatography (SEC) columns when low ion strength eluent is used, and the degree of exclusion is a function of the number of acid units per assembly. In this way the ion exclusion effect provides a sensitive means of measuring low levels of uronic acid content in larch AG. Recognition of this effect helps resolve inconsistencies in the earlier AG literature. The dramatic effect which a few uronic acid groups have on the chromatographic behavior of AG implies possible differences in solution properties and biological activities between the charged and uncharged species.

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Susan D. Styron

University of Alabama at Birmingham

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