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    The action of ammonia on carbohydrates and related carbonyl compounds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University of Manawatu, Palmerston North, New Zealand
    (Massey University, 1965) Grimmett, Murray Ross
    The chromatography of imidazoles has been studied and a method developed for their quantitative estimation. The following facts have been brought to light:- (i) Formaldehyde does not form imidazoles at room temperature in ammoniacal solution. (ii) From the complex mixture resulting from the interaction of glyoxal with aqueous ammonia imidazole and 2,2'-bis-imidazole have been isolated and identified, while 2-formylimidazole has been tentatively identified. (iii) Glycolaldehyde reacts with aqueous ammonia to form imidazole and 2-hydroxymethylimidazole. (iv) DL-Glyceraldehyde reacts with aqueous ammonia to form a complex mixture of neutral and basic compounds. Dihydroxyacetone, glucose, fructose, mannose, arabinose, lyxose and xylose have been tentatively identified by paper chromatography while ribose was suspected in low concentration. 2-Hydroxymethyl-4(5)-methylimidazole, 4(5)-methylimidazole, 4(5)-(2-hydroxyethyl)imidazole and 4(5)-hydroxymethylimidazole have been isolated and characterised, and their orders and rates of formation studied. (v) Pyruvaldehyde reacts exothermically with concentrated ammonia solution to form four imidazolic compounds. Three of these have been isolated and characterised as 2-acetyl-4(5)-methylimidazole, 2,4(5)-dimethylimidazole and 4(5)-methylimidazole. The latter two compounds were formed in approximately equimolecular proportions. These results fail to confirm Bernhauer's finding that pyruvaldehyde cannot act as a source of formaldehyde in imidazole formation. (vi) Hydroxypyruvaldehyde browns rapidly in aqueous ammonia forming 2-hydroxymethyl-4(5)-methylimidazole, 4(5)-methylimidazole and 4(5)-hydroxymethylimidazole. The yields of the latter two compounds have been found to be higher than from a similar mixture of dihydroxyacetone with ammonia. (vii) Both diacetyl and acetoin react with ammonia to form 2,4,5-trimethylimidazole. (viii) 4(5)-(2-Hydroxyethyl)imidazole has been tentatively identified from the mixture resulting from the interaction of 1,4-dihydroxybutan-2-one with aqueous ammonia. (ix) Arabinose reacts with aqueous ammonia to form a complex mixture of imidazoles from which 4(5)-methylimidazole has been isolated and identified. (x) A chromatographic study has been carried out to determine the orders of formation of imidazoles resulting from the interactions of a number of carbohydrates and their degradation products with aqueous ammonia. Arising from this study have come the following main results:- (a) It appears that, contrary to the findings of Komoto, a number of imidazoles with low Rf values (probably polyhydroxyalkyl-substituted) are formed more rapidly than 4(5)-methylimidazole from hexose sugars with ammonia. (b) Differently linked reducing disaccharides give markedly different patterns of imidazoles under ammoniacal conditions. (xi) As a result of (b) above, a micro-method has been developed for determination of the position of the glycosidic link in reducing hexose disaccharides and homogeneously-linked oligosaccharides.
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    Intra-molecular lysine-arginine derived advanced glycation end-product cross-linking in Type I collagen: A molecular dynamics simulation study.
    (2016-11) Collier TA; Nash A; Birch HL; de Leeuw NH
    Covalently cross-linked advanced glycation end products (AGE) are among the major post-translational modifications to proteins as a result of non-enzymatic glycation. The formation of AGEs has been shown to have adverse effects on the properties of the collagenous tissue; they are even linked to a number of age related disorders. Little is known about the sites at which these AGEs form or why certain sites within the collagen are energetically more favourable than others. In this study we have used a proven fully atomistic molecular dynamics approach to identify six sites where the formation of the intra-molecular 3-deoxyglucosone-derived imidazolium cross-link (DOGDIC) is energetically favourable. We have also conducted a comparison of these positions with those of the more abundant glucosepane cross-link, to determine any site preference. We show that when we consider both lysine and arginine AGEs, they exhibit a prevalence to form within the gap region of the collagen fibril.