The Application of Gas-Phase Methods to the Analysis of Naturally Occurring Compounds

Reid, William James (1975) The Application of Gas-Phase Methods to the Analysis of Naturally Occurring Compounds. PhD thesis, University of Glasgow.

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In the last few years, increasing interest has been shown in the related techniques of gas liquid chromatography (GLC), and combined gas chromatography and mass spectrometry (GC-MS), and in particular in the application of these techniques to the analysis of small amounts of material, such as those which may be found in natural systems. This thesis investigates the use of these techniques in two distinct fields; the first is the examination of boronic acids as reagents for the formation of derivatives of sugars suitable for GC and. GC-MS analysis, and the second is the application of the techniques to the investigation of extracts from plant tissue for the purpose of locating and identifying any compounds of a particular type which may be present in the plant. In 1968, Brooks and Watson introduced the concept of boronate esters as suitable derivatives, for GLC and GC-MS, of compounds possessing a cis bifunctionality, such as cis diols. They suggested the applicability of the derivative to carbohydrate analysis, and also showed that pregnanetriol boronate could easily be trimethylsilyated. without disturbing the cyclic ester group. Brooks and Harvey also showed, in a later paper, that triple derivatives of a compound could be made, for example, the methyl oxime of a cyclic boronate trimethylsilyl ether. In this same paper the authors demonstrated that acyclic boronates formed from isolated hydroxyl groups could be displaced by trimethylsilyation without affecting a cyclic boronate also present in the molecule. This last observation was extremely important, as it showed that excess boronic acid could be used to form a derivative of a compound and any acyclic boronates formed could be removed in this way. This was ideal for the study of compounds like sugars, where there are a number of hydroxyl groups present. Excess boronic acid could be used to form the cyclic boronates, and the compound would then be trimethylsilylated to eliminate any undesired acyclic boronates formed. The trimethylsilylation would also result in a less polar, more volatile compound which would have better GLC properties. Shortly after the inception of the present research, there appeared the first of a number of papers on this topic; these demonstrated that it was possible to use the boronates in such a way, and that where the reaction resulted in one or more hydroxyls remaining under-ivatised, it was possible to convert them to the trimethylsilyl ethers, without destroying the boronate already present, producing a mixed derivative that was suitable for GLC and GC-MS. To investigate these derivatives further, a comparison has been made of the GLC properties of the methyl-, n-butyl; and phenylboronates and boronate TMSi ethers of a number of sugars, each of which was known to be, initially, in a cyclic form, and hence to have a preferred conformation which would influence the course of the boronation reaction in which the boronic acids react only with cis-bifunctional systems. The GC-MS properties of the methyl- and phenyl- derivatives have also been studied, the difference of 62 mass units between the methyl and phenyl groups being an aid to the identification of boron-containing peaks. From the gas chromatographic data and mass spectra, and in some instances the nuclear magnetic resonance data, an attempt has been made to determine the structure of the boronates and boronate TMSi ethers formed by each sugar. The boronates, and. the boronate TMSi ethers, have been found to be good derivatives for GLC, giving sharp, non-tailing peaks on both 1% SE-30 and 1% QF-1, and though the tendency of the sugars to form multiple derivatives would make this method difficult for the routine analysis of a large number of compounds, it does simplify the identification of individual sugars by increasing the number of useful parameters characteristic of each sugar. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Physical chemistry
Date of Award: 1975
Depositing User: Enlighten Team
Unique ID: glathesis:1975-78699
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:01
Last Modified: 30 Jan 2020 15:01

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