Studies presented in this Thesis fall into four distinct groups: 1. Analytical characterizations have been made of the gum exudates from: (a) Eight species of the Series Gummiferae and Vulgares and three highly proteinaceous species of the Series Juliflorae of the genus <i>Acacia</i>; (b) Six species from the genus <i>Leucaena</i> which are chemically very close to gum arabic; (c) Nine specimens of gum obtained from <i>Combretum nigricans</i> growing in different locations; (d) Six <i>A.senegal</i> gum samples from Uganda and a further six 'gum arabic' samples from different regions; (e) Seventeen species of gum exudates from 15 different genera such as <i>Cassia grandis, Cercidium praecox, Parkia nitida, Prosopis chilensis, Sesbania sesban, Atalaya hemiglauca, Sclerocarya birrea, Pseudocedrela kotschyi, Senna nicaraguensis</i>, etc. 2. A study of some of the structural features of <i>Combretum nigricans</i> gum by Smith-degradation showed that uronic acid and rhamnose groups occur in internal locations within the overall structure, and not as end-groups as is the case in gum arabic (<i>A.senegal</i>). 3. Amino acid data and <SUP>13</SUP>C NMR spectra are presented for various fractions of <i>A.senegal</i> gum and for some highly proteinaceous <i>Acacia</i> gums (e.g. <i>A.difficilis, A.eriopoda, A.tumida</i>). The effect of enzymes on these gums is reported. 4. <SUP>13</SUP>C NMR spectra for thirty different gum exudates are presented to show the characteristic 'fingerprint' patterns given by their polysaccharide structures. Information concerning their component monosaccharides, anomeric configurations, and linkages between the various sugar residues is given by spectrum analysis. This provides a most sensitive way to identify botanical species based on the total structure of exuded gums. The arabinose form (pyranose or furanose) and the various linkage configurations (α or β) in the gum structures are important and directly affect the physico-chemical behaviour of gum exudates. <i>Acacia</i> gums in which rhamnose is absent (or nearly absent) generally have a large proportion of β-L-arabinopyranose (<i>A.seyal, A.sieberana, A.arabica</i> gums etc.).

No description available.

Bacterial biofilms are formed when bacteria in a liquid environment adhere to a surface, multiply to form microcolonies and synthesis a protective glycocalyx composed mainly of hydrated exopolysaccharide (EPS). Bacterial biofilms form in natural, medical and industrial environments and are usually highly heterogeneous. Biofilms can be single or multi-species and their characteristics are dictated by the environment in which they develop. The biofilm bacteria analysed were isolated from a factory environment and all were members of the Enterobacteriaceae. The composition of their extracellular polysaccharides was examined using standard biochemical assays, HPLC and paper chromatography. Most were anionic due to uronic acids, except for the EPS of two strains, 53b and Ent (both <I>Enterobacter agglomerans</I>), which contained only neutral sugars and were highly insoluble. Periodate oxidation revealed a high degree of 1→3 linkages. Bacteriophages which possessed polysaccharide depolymerase enzymes specific for the EPS of strains 53b and Ent were isolated from sewage from a number of sources. The glycanase of one phage (SF153b) was highly specific, had optima over a wide range of temperature and pH, and activity was increased by Ca<SUP>2+</SUP> ions. Degradation of 53b and Ent EPS by the depolymerase produced oligosaccharide repeat units. HPLC and size exclusion chromatography gave an estimation of DP for 53b and Ent repeat units of 8-9 and 7-8 respectively. Polysaccharide samples derived from 53b biofilm and planktonic cells were both degraded by the same phage glycanase suggesting that biofilm formation does not stimulate production of a biofilm specific EPS.

No description available.

No description available.

Oligosaccharides were isolated directly from tomato fruit tissue; a series of homo-oligogalacturonides with a DP of 2-6 was identified in red-ripe and over-ripe fruit. Two glucose disaccharides, identified as gentiobiose and nigerose, were isolated from both mature green (MG) and red-ripe fruit. Gentiobiose was able to accelerate the initiation of ripening when vacuum infiltrated into MG tomato fruit, particularly when co-infiltrated with nigerose. The possible origin of these disaccharides is discussed. The potential role of organic acids (ascorbate, citrate and oxalate) in fruit softening was evaluated <i>in vitro</i> on MG tomato fruit alcohol-insoluble residue (AIR). The hydroxyl radical (^•OH), produced via a Fenton reaction in which ascorbate acts as a pro-oxidant, released pectin into solution in the presence of oxygen. ^•OH production <i>in vivo</i> may be localised in the PCW by the positioning of metal ions such as Cu²⁺ on pectins or glycoproteins. Probes used to detect ^·OH in the tomato fruit apoplast produced inconclusive results but suggested that this active oxygen species is present during ripening. The incubation of tomato fruit AIR with naturally occurring chelators such as citrate and oxalate also led to solubilisation of uronate-containing material. The alteration of the PCW during ripening is likely to be the result of a number of processes. These processes may occur throughout the PCW or may occur in specific areas but their contribution to the softening process should not be over-looked in favour of processes only involving hydrolytic enzymes, as this could lead to an over-simplified view fruit ripening.

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1,3-Nucleophilic addition reactions of thiols and amines with pyranosylnitrile oxides have been employed in the synthesis of <i>C</i>-glycosides. The nitrile oxides were generated by base-induced dehydrochlorination of the corresponding hydroximoyl chlorides 106 and 107. D-Glucose derived hydroximoyl chloride 107 was prepared in four steps from D-glucose and employed in collaborative work toward the synthesis of glucosinolate analogue. Reaction of alkyl and aryl thiols with D-xylose nitrile oxide 151 afforded a series of desulfoisoglucosinolates in 55-76% yields. Reactions of allyl and aryl amines with the D-xylose and D-glucose derived nitrile oxides 151 and 115 under basic conditions afforded the corresponding Z-amidoximes. For example, (<i>Z</i>)-<i>N</i>-benzyl-(2,3,4,6-tetra-<i>O</i>-acetyl-β-D-glucopyranosyl)formamide oxime (137) was prepared from 107 and benzylamine in 88% yield. The addition of amino acid derived nucleophiles was also investigated Reaction of the D-xylose and D-glucose nitrile oxides 115 with L-cysteine derivatives 147 under basic conditions afforded thiohydroximates 148 and 150 in high yield. Reaction of the D-xylose nitrile oxide 151 with glycine, L-leucine and L-phenylalanine esters initially afforded amidoximes 152, 155 and 161. Cyclisation of 152, 155 and 161 to form 1,2,4-oxadiazin-6-ones occurred on exposure to silica or prolonged standing. Employing L-proline benzyl ester as the nucleophile led to the formation of predominantly oxadiazinone 163. Attempts to synthesis pyranosyl-1,2,4-oxathiazin-6-ones were not successful 6-Amino-6-deoxy-1,2,3,4-di<i>-O-</i>isopropylidene-α-D-galactopyranose hydrochloride was prepared from D-galactose in 4 steps, and reaction with D-xylose and D-glucose derived nitrile oxides 151 and 115 afforded (1→6) amidoxime linked pseudo-disaccharides 178 (81%) and 181 (75%) D-Xylose and D-glucose amines 182 and 183 were prepared from the parent aldoses in 5 steps. Reaction of these amines with D-xylose and D-glucose nitrile oxides 151 and 115 yielded a series of (1→1) amidoxime linked pseudo-disaccharides (41-49% yields).

No description available.

The composition of gellan gum elaborated by wild type <I>Sphingomonas paucimobilis </I>was studied. Gas chromatographic methods of analysis were compared. Analysis of neutral sugars was carried out by Saemen hydrolysis and Stones method. Stones method was preferred due to its simplicity and the production of comparable results to those obtained following Saemen hydrolysis. The neutral sugars of gellan gum were analysed by GC/MS following preparation of per-methylated alditol acetates (PMAAs). Two methods were used for making alditol acetates, the Hakamori and sodium hydroxide (NaOH) methods. Although the NaOH method was simpler and faster to carry out, the results were not representative of the true composition of gellan gum. The Hakamori method revealed the presence of 33%, 1,4 rha, 30% 1,3 glc and 31% 1,4 glc in agreement with the sugar compositions of O'Neill <I>et al.</I> (1983) and Jansson <I>et al. </I>(1983) who elucidated the structure of gellan gum simultaneously. To determine the glucuronic acid content of gellan gum, samples were carboxy-reduced prior to analysis. Two methods were compared, the lithium aluminium deuteride and tetrahydrofuran (THF) methods. The THF method revealed the presence of 24%, 1, 4 rha, 24% 1,3 glc 26% 1,4 glc and 25% 1,4, 6 glc (corresponding to glcA). Physiological studies were carried out with twenty mutant strains of <I>S. paucimobilis </I>in batch culture. The chemical composition, viscosity, gelation and rheological properties of EPS produced from many of these strains were further investigated. Some of the strains elaborated polysaccharide, named fine precipitate, which differed chemically from gellan gum. Rheological measurements were carried out on several EPS samples using a mechanical rheometer. Large differences in gel strength were detected.