Vitamin C Its Chemistry & Biochemistry: Its Chemistry and Biochemistry (Royal Society of Chemistry Paperbacks) - Softcover

Davies, M. B.; Partridge, D.A.; Austin, J.A.

Softcover

ISBN 10: 0851863337 ISBN 13: 9780851863337

Verlag: Royal Society of Chemistry, 1991

Inhaltsangabe

Vitamin C is the first book to cover the history, chemistry, biochemistry, and medical importance of vitamin C and is the first to provide an in-depth, interdisciplinary study of this essential and fascinating compound. The book provides a comprehensive and systematic account of the vitamin C story, fully surveying the history of scurvy and how its cure led to the suggestion, discovery, and isolation of the vitamin, later named L-ascorbic acid. It describes in detail the vitamin's structure determination, synthesis and manufacture, and its oxidation products, derivatives and related compounds. Its key biochemical roles are fully categorized and explained, and the medical importance of the vitamin, including the recent use of so-called megadoses, is thoroughly discussed. Vitamin C will be of interest to a very wide readership and will provide useful background information and inspiration for students at various levels. It will also be relevant to the interested chemist or lay person, as well as those carrying out research in this area.

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Vitamin C is the first book to cover the history, chemistry, biochemistry, and medical importance of vitamin C and is the first to provide an in-depth, interdisciplinary study of this essential and fascinating compound. The book provides a comprehensive and systematic account of the vitamin C story, fully surveying the history of scurvy and how its cure led to the suggestion, discovery, and isolation of the vitamin, later named L-ascorbic acid. It describes in detail the vitamin's structure determination, synthesis and manufacture, and its oxidation products, derivatives and related compounds. Its key biochemical roles are fully categorized and explained, and the medical importance of the vitamin, including the recent use of so-called megadoses, is thoroughly discussed. Vitamin C will be of interest to a very wide readership and will provide useful background information and inspiration for students at various levels. It will also be relevant to the interested chemist or lay person, as well as those carrying out research in this area.

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Vitamin C

Its Chemistry and Biochemistry

By Michael B. Davies, John Austin, David A. Partridge

Royal Society of Chemistry

Copyright © 1991 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85186-333-7

Contents

Foreword by Professor M. Stacey CBE, FRS, v, 
Acknowledgements, vii, 
Chapter 1 Introduction, 1, 
Chapter 2 History of Vitamin C and Its Role in the Prevention and Cure of Scurvy, 7, 
Chapter 3 Discovery and Structure of Vitamin C, 26, 
Chapter 4 Synthesis, Manufacture, and Further Chemistry of Vitamin C, 48, 
Chapter 5 Biochemistry of Vitamin C, 74, 
Chapter 6 Medical Aspects of Vitamin C, 97, 
Chapter 7 Inorganic and Analytical Aspects of Vitamin C Chemistry, 115, 
Bibliography, 147, 
Subject Index, 149, 

CHAPTER 1

Introduction

Everyone has heard of vitamin C. There can be few simple organic molecules which have excited such universal interest. At least part of the reason for this has been the general interest in the beneficial effects of all vitamins and other trace substances on human health which has developed in recent years along with concern on the effects of other substances, particularly additives, on those who consume food containing them. We know that vitamins are essential to our well-being and because of this they have excited an interest and curiosity which has resulted in many of them being attributed with disease-healing and health-giving properties which they could not possibly have, Vitamin C has itself been said to have almost magical properties by some writers and it is useful to get a picture of the chemistry and biochemistry of this enigmatic compound.

Vitamin C is different. It is different from the other vitamins and we shall see in the course of this book that its chemistry and biochemistry single it out amongst molecules in many important ways, Vitamin C is ubiquitous. It is found throughout the plant and animal kingdoms, where its roles are often not known or are poorly understood. The synthetic vitamin is very widely used as a food additive and therefore has an E number (E300). However, unlike many other additives, few people would object to its presence in foods. There is no doubt that its anti-oxidant properties confer stability on foods to which it has been added.

Vitamin C has been the subject of frequent controversy, even before its nature had been established. Its role (as a constituent of fruits and vegetables) in the cure and prevention of scurvy was widely debated for hundreds of years. Its very existence was doubted by many even as recently as the the beginning of the twentieth century. There were quarrels over who was the first to discover it. Even today there is much controversy about the exact role of the vitamin in human health and there is not even agreement over the amount of the vitamin which needs to be consumed for optimum well being, with various authorities recommending amounts varying from 30 mg to 10 g per day. The role in the relief of cold symptoms, in the improvement of quality of life for cancer patients and in other medical areas are all topics for intense discussion. The biochemistry of L-ascorbic acid in mammals is very poorly understood, so that it is not even clear what the biochemical role of the vitamin is in such systems. Although the chemical structure of L-ascorbic acid has been unequivocally established by single crystal X-ray diffraction, the structure of its very important two-electron oxidation product, dehydroascorbic acid, has not been finally established, since it has not yet proved possible to isolate crystals, or indeed the pure compound, as a solid.

Vitamin C is chemically the simplest of the vitamins and for this reason was among the first to be isolated, characterised, and purified and to have its structure determined. *More vitamin C is produced industrially than any other vitamin, or indeed all the other vitamins put together. It is one of the few pure chemical compounds which is taken routinely by human beings in gram quantities (a possible challenger is sugar). I t appears to have no harmful effects even in these large amounts and it is a medicine which it is a pleasure to take, especially in the form of fruit or vegetables.

It may be thought that the chemistry of this simple molecule would no longer hold any surprises after the vast amount of research that has been carried out over the years. However, conferences on aspects of vitamin C chemistry still attract large numbers of workers in the field and new aspects of the chemistry are always being revealed. The reason for the continued interest in the chemistry of L-ascorbic acid lies in the fact that despite it being such a simple molecule, its ene-diol structure provides it with a highly complex chemistry. Thus it has a very complicated redox chemistry involving comparatively stable radical intermediates which is heavily modified by the acidic properties of the molecule. It has been known for many years that L-ascorbic acid is easily oxidised by dioxygen. Although the first product of this process is dehydroascorbic acid, which still has antiscorbutic properties, the further oxidation by oxygen produces compounds which are not readily converted back to L-ascorbic acid, and the vitamin is effectively destroyed. The mechanisms of the reactions involved are still largely unknown, although they have been widely studied. There has been much recent work on the interactions of vitamin C with metal ions, particularly transition metal ions. This has unearthed a rich vein of chemistry involving L-ascorbic acid as both a redox companion and as a complexing agent; indeed the reaction of L-ascorbic acid with oxygen and other oxidising agents is catalysed by transition metal ions, especially copper(II), so that sometimes solutions are stabilised by the addition of EDTA, which complexes the metal ions and arrests the catalysis. It appears that vitamin C may not always act alone in its biochemical processes, but may act synergistically with other substances, of which vitamin E may be a typical example.

Research into vitamin C chemistry appears to have reached a kind of steady state. In the years 1969, 1979, and 1989, there were about the same number of papers published each year on aspects of the chemistry of L-ascorbic acid. Thus the extent of the work on this compound has been remarkably constant over the past twenty years and there is no sign of a diminution of interest yet.

The development of analytical techniques to detect and determine vitamin C has been crucial in the understanding of the presence and stability of the compounds in nature. At first, biological techniques were used and these gradually became replaced by chemical methods which were more sensitive, more selective, and easier to carry out. Today the analysis is largely centred around the use of high-performance liquid chromatography and there are many successful methods available. However, the technique is still limited by the fact that detection of dehydroascorbic acid in the presence of L-ascorbic acid still has a comparatively low sensitivity by virtually all detection techniques. This makes the determination of amounts of dehydroascorbic acid in plants and animals much more difficult than for L-ascorbic acid. The same applies to further oxidation products and there is a need for further work in the development of detection methods for these compounds and to investigate the extent and kinetics of oxidation of L-ascorbic acid in fruits and vegetables by determining the amounts of all oxidation products and the oxidation...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 1991
• Sprache: Englisch
• ISBN 10: 0851863337
• ISBN 13: 9780851863337
• Einband: Taschenbuch
• Anzahl der Seiten: 176
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: preigu; mail@preigu.de; ; Lengericher Landstr. 19; Osnabrück; 49078; Deutschland