EBOOK Handbook of Natural Colorants Sổ tay về chất màu tự nhiên (Thomas Bechtold Rita Mussak)

Handbook of Natural ColorantsHandbook of Natural Colorants Edited by Thomas Bechtold and Rita Mussak © 2009 John Wiley & Sons, Ltd... Deswarte Editors Biofuels Wim Soetaert and Erick Van

Handbook of Natural Colorants

Handbook of Natural Colorants Edited by Thomas Bechtold and Rita Mussak

© 2009 John Wiley & Sons, Ltd ISBN: 978-0-470-51199-2

in Renewable Resources

Series Editor

Christian V Stevens, Department of Organic Chemistry, Ghent University, Belgium

Titles in the Series

Wood Modification: Chemical, Thermal and Other Processes

Callum A S Hill

Renewables-Based Technology: Sustainability Assessment

Jo Dewulf and Herman Van Langenhove (Editors)

Introduction to Chemicals from Biomass

James H Clark and Fabien E I Deswarte (Editors)

Biofuels

Wim Soetaert and Erick Vandamme (Editors)

Handbook of Natural Colorants

Thomas Bechtold and Rita Mussak (Editors)

Forthcoming Titles

Starch Biology, Structure and Functionality

Anton Huber and Werner Praznik

Industrial Application of Natural Fibres: Structure, Properties and TechnicalApplications

Jo¨rg Mu¨ssig (Editor)

Surfactants from Renewable Resources

Mikael Kjellin and Ingega¨rd Johansson (Editors)

Thermochemical Processing of Biomass

Robert C Brown (Editor)

Bio-based Polymers

Martin Peter and Telma Franco (Editors)

Handbook of Natural

Colorants

Edited by THOMAS BECHTOLD

and

RITA MUSSAK Leopold-Franzens University, Austria

A John Wiley and Sons, Ltd., Publication

The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

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Library of Congress Cataloging-in-Publication Data

Bechtold, Thomas.

Handbook of natural colorants / Thomas Bechtold, Rita Mussak.

p cm.

Includes bibliographical references and index.

ISBN 978-0-470-51199-2 (cloth : alk paper) 1 Dyes and dyeing 2 Dye plants.

3 Dyes and dyeing—Chemistry I Mussak, Rita II Title.

Set in 10/12pt Times by Integra Software Services Pvt Ltd, Pondicherry, India

Printed and bound in Great Britain by CPI Antony Rowe, Chippenham, Wiltshire

Maria J Melo

2 Colours in Civilizations of the World and Natural Colorants:

Dominique Cardon

Harby Ezzeldeen Ahmed

Andrea Biertu¨mpfel and Gu¨nter Wurl

4.4.3 Red Dyeing Plants 43

Veridiana Vera de Rosso and Adriana Zerlotti Mercadante

Hoang Thi Linh

6.15 Caesalpinia Yellow (Botanical Name Caesalpinia pulcherrima

Philip John and Luciana Gabriella Angelini

Maria J Melo, Fernando Pina and Claude Andary

Thomas Bechtold

Riitta Julkunen-Tiitto and Hely Ha¨ggman

15 Chlorophylls 243Ursula Maria Lanfer Marquez and Daniela Borrmann

M Monica Giusti and Taylor C Wallace

Martin Weigl, Andreas Kandelbauer, Christian Hansmann,

Johannes Po¨ckl, Ulrich Mu¨ller and Michael Grabner

Rita A M Mussak and Thomas Bechtold

19 Natural Colorants in Hair Dyeing 339Thomas Bechtold

21.3 Challenges for the Industrial Use of Natural Colorants 370

(Agricultural Primary Production and Residues from Other

List of Contributors

University, Giza, Egypt Present address: Tomes IV, Biotechnology–Chemical EngineeringSchool, National Technical University of Athens, 9 Iroon Polytechniou, 15780, Zografou,Athens, Greece

Pharmacie, UMR 5175 (CEFE)*, 15, Ave Charles Flahault, FR-34093 MontpellierCedex 5, France

Agroecosistema, University of Pisa, Via S Michele degli Scalzi, 2 I-56127 Pisa, Italy

University Innsbruck, Hoechsterstrasse 73, A-6850 Dornbirn, Austria

D-07778 Dornburg, Germany

Pharmaceutical Science, University of Sa˜o Paulo, Av Prof Lineu Prestes, 580, Bloco 14,05508-900 Sa˜o Paulo, SP, Brazil

University of Sri Jayewardenepura, Gangodawila, Nugegoda, Sri Lanka

10/46, 1020 Vienna, Austria

Zeiselgraben 4, A-3250 Wieselburg, Austria

M Monica Giusti The Ohio State University, Parker Food Science and Technology,Room 110, 2015 Fyffe Road, Columbus, OH 43210, USA

Vienna, Peter Jordan Str 82, A-1190 Vienna, Austria

Oulu, Finland

Wood Chemistry, St Peter Str 25, A-4021 Linz, Austria c/o BOKU – University ofNatural Resources and Applied Life Sciences Vienna, Peter Jordan Str 82, A-1190Vienna, Austria

Whiteknights, Reading RG6 6AS, UK

FIN-80101 Joensuu, Finland

Sciences Vienna, Peter Jordan Str 82, A-1190 Vienna, Austria c/o Wood CarinthianCompetence Center, Klagenfurter Str 87-89, A-9300 St Veit/Glan, Austria

University of Technology, 1-Dai co Viet, Hanoi, Vietnam

Faculty of Pharmaceutical Science, University of Sa˜o Paulo, Av Prof Lineu Prestes,

580, Bloco 14, 05508-900 Sa˜o Paulo, SP, Brazil

Faculty of Sciences and Technology, New University of Lisbon, Campus Caparica,2829-516 monte da Caparica, Portugal

Engineering, University of Campinas – UNICAMP, CP: 6121, 13083-862, Campinas,Brazil

Chemistry, St Peter Str 25, A-4021 Linz, Austria c/o BOKU – University of NaturalResources and Applied Life Sciences Vienna, Peter Jordan Str 82, A-1190 Vienna,Austria

Innsbruck, Hoechsterstrasse 73, A-6850 Dornbirn, Austria

Fernando Pina REQUIMTE, CQFB, Chemistry Department, Faculty of Sciences andTechnology, New University of Lisbon, 2829-516 Monte da Caparica, Portugal

Chemistry, St Peter Str 25, A-4021 Linz, Austria c/o BOKU – University of NaturalResources and Applied Life Sciences Vienna, Peter Jordan Str 82, A-1190 Vienna, Austria

University of Helsinki, Fin-00014 Helsinki, Finland

Paulo – UNI FESP, 11030-400, Santos, Brazil

Room 110, 2015 Fyffe Road, Columbus, OH 43210, USA

Chemistry, St Peter Str 25, A-4021 Linz, Austria c/o BOKU – University of NaturalResources and Applied Life Sciences Vienna, Peter Jordan Str 82, A-1190 Vienna, Austria

Dornburg, Germany

Series Preface

Renewable resources, their use and modification are involved in a multitude of importantprocesses with a major influence on our everyday lives Applications can be found in theenergy sector, chemistry, pharmacy, the textile industry, paints and coatings, to name but afew

The area interconnects several scientific disciplines (agriculture, biochemistry, istry, technology, environmental sciences, forestry, ), which makes it very difficult tohave an expert view on the complicated interaction Therefore, the idea to create a series ofscientific books, focusing on specific topics concerning renewable resources, has been veryopportune and can help to clarify some of the underlying connections in this area

chem-In a very fast changing world, trends are not only characteristic for fashion and politicalstandpoints but science is also not free from hypes and buzzwords The use of renewableresources is again more important nowadays; however, it is not part of a hype or a fashion

As the lively discussions among scientists continue about how many years we will still beable to use fossil fuels, opinions ranging from 50 years to 500 years, they do agree that thereserve is limited and that it is essential not only to search for new energy carriers but alsofor new material sources

In this respect, renewable resources are a crucial area in the search for alternatives forfossil-based raw materials and energy In the field of the energy supply, biomass andrenewable-based resources will be part of the solution alongside other alternatives such assolar energy, wind energy, hydraulic power, hydrogen technology and nuclear energy

In the field of material sciences, the impact of renewable resources will probably be evenbigger Integral utilization of crops and the use of waste streams in certain industries willgrow in importance, leading to a more sustainable way of producing materials

Although our society was much more (almost exclusively) based on renewable resourcescenturies ago, this disappeared in the Western world in the 19th century Now it is time tofocus again on this field of research However, it should not mean a ‘retour a` la nature’, but

it should be a multidisciplinary effort on a highly technological level to perform researchtowards new opportunities, to develop new crops and products from renewable resources.This will be essential to guarantee a level of comfort for a growing number of people living

on our planet It is ‘the’ challenge for the coming generations of scientists to develop moresustainable ways to create prosperity and to fight poverty and hunger in the world A globalapproach is certainly favoured

This challenge can only be dealt with if scientists are attracted to this area and arerecognized for their efforts in this interdisciplinary field It is therefore also essential thatconsumers recognize the fate of renewable resources in a number of products.

Furthermore, scientists do need to communicate and discuss the relevance of their work.The use and modification of renewable resources may not follow the path of the geneticengineering concept in view of consumer acceptance in Europe Related to this aspect, theseries will certainly help to increase the visibility of the importance of renewable resources.Being convinced of the value of the renewables approach for the industrial world, as well

as for developing countries, I was myself delighted to collaborate on this series of booksfocusing on different aspects of renewable resources I hope that readers become aware ofthe complexity, the interaction and interconnections, and the challenges of this field andthat they will help to communicate on the importance of renewable resources

I certainly want to thank the people of John Wiley & Sons, Ltd from the Chichesteroffice, especially David Hughes, Jenny Cossham and Lyn Roberts, in seeing the need forsuch a series of books on renewable resources, for initiating and supporting it and forhelping to carry the project to the end

Last, but not least, I want to thank my family, especially my wife Hilde and childrenPaulien and Pieter-Jan for their patience and for giving me the time to work on the serieswhen other activities seemed to be more inviting

Christian V StevensFaculty of Bioscience Engineering

Ghent University

BelgiumJune 2005

Looking out of the window on a bright and colourful autumn day we can recognize thatnature provides us with a firework of yellow, red and green colours, inspiring mankind tobring more colour into the products of daily life However, we have known for a long timethat access to the colours of nature is coupled with laborious procedures and a high number

of restrictions

The invention of synthetic organic chemistry and the desire for more bright and stablecolorants can be seen as one of the strong driving forces in the historical development ofnatural sciences In the 20th century synthetic colorants dominated almost every field ofpossible application, such as mass coloration of plastics, textiles, paints, cosmetics and food.For almost 100 years research on natural colorants was continued by only a few groupswho were enthusiastic enough to persist against the straightforward arguments for the use

of synthetic dyes, relying on cost, performance, colour strength and brilliance, which caneasily be achieved using artificial dyes

During the last decade more and more new aspects were integrated into the assessment

of any chemical product used Interestingly, every new argument that had to be consideredalso added to the argument strengthening the position of natural colorants Increasedawareness of product safety and higher attention to the possible adverse impact of achemical product on human health brought changes in the regulations for the use ofcolorants in food and cosmetics

Concentration on renewable resources, sustainability and replacement of oil-basedproducts are driving forces to reassess the potential of natural resources including naturalcolorants, at least for application in very specific fields Growing consumer interest inpurchasing ‘green’ products, which exhibit an improved environmental profile, can be seen

as the breakthrough force for reintroducing natural colorants into the modern markets.During our own scientific work on natural dyes for textiles and hair dyeing we learnedthat knowledge about natural colorants and their possible application, at present, is quitefragmented There are collections of knowledge about natural colorants like Schweppe’sHandbuch der Naturfarbstoffe, that summarizes properties and sources of natural dyesfrom a chemical and more historical aspect However, for the demands of the futuredevelopment of natural colorants into applications of the present, there is no useful source

of information available that could help to give an overview of the state of the research andknowledge in the field of natural colorants

The search for scientists working on natural colorants who were able and willing to write

a contribution for this book was the major challenge in editing this book The plinary range of content that should be covered by the different authors made our workparticularly difficult, but is understandingly one of the key aspects of this book Theintroduction of natural colorants into modern products is an interdisciplinary task thathas to consider farming, dyestuff extraction, analysis, properties and application at thesame time Success will only be achieved if integrative concepts are presented that considerall stages of production at the same time

interdisci-The organization of the different chapters follows this order In the first chapters a shortreview about plant sources and applications of natural colorants in historical times is given.Aspects of farming crops and product processing are then summarized for the differentchemical classes of dyes In the more application-oriented chapters the use of naturalcolorants in, for example, food, wood, textile and hair dyeing is presented Sustainabilityand consumer aspects are discussed in the final chapters of the book

We would like to thank all authors for their contributions Their expertise in theirparticular field, covering a whole array of specialized knowledge, makes the book a uniquesource of information, which summarizes the present knowledge about natural colorants indepth

We are aware that every collection of information will be incomplete and further aspectscould have been introduced and considered in more detail However, we are convinced thatthe book as it stands will be a useful instrument to overview the fragmented situation ofnatural colorants and will support a rapid and efficient entry of new researchers into thisemerging field of sustainable chemistry From this point of view we are also convinced thatthe book will strengthen the position of natural colorants in the future, by facilitating access

to information and thereby indirectly helping the revival of natural colorants to gainmomentum

Thomas Bechtold and Rita A M Mussak

Dornbirn/Linz

2008

Tombo (Lisbon) Dark blues were painted with indigo, whereas for the backgound the inorganic and precious pigment lapis-lazuli was used (See Figure 1.1)

Handbook of Natural Colorants Edited by Thomas Bechtold and Rita Mussak

© 2009 John Wiley & Sons, Ltd ISBN: 978-0-470-51199-2

author) (See Figure 3.1)

(See Figure 3.2)

B

Plate 4 Mole fraction distribution of the several species of malvidin 3,5-diglycoside: A-free (pK 0

a ¼ 1.7); B-simulation in the case of co-pigmentation with A for a copigment concentration of 0.1 M and an association constant, K 0

according to increasing blue components (b* gets more negative); from left to right in each row: oak, nut, cherry, ash, beech heartwood, beech, Douglas fir, alder, pine, poplar, maple and birch (See Figure 17.5)

Plate 7 Variation of black alder (Alnus glutinosa Gaertn.) wood color due to six independent convection drying processes (See Figure 17.7)

Plate 6 Wood species that had more or less been successfully dyed with chlorophyll sodium salt Species are arranged according to increasing green components (a* gets lower); from left to right in each row: beech heartwood, beech, alder, birch, maple and poplar (See Figure 17.6)

12, 14, 16, 18 and 30 days (second row) (See Figure 17.8)

Plate 9 Thermally treated black alder (Alnus glutinosa Gaertn.) after 1, 2 and 3 days duration (top down) (See Figure 17.9)

Plate 10 Untreated (left) and ammoniated (right) oak (Quercus sp.) wood from the same individual tree (See Figure 17.10)

Plate 12 Comparison of bleached (first and third rows) and untreated wood (second and fourth rows) Species from left to right: poplar, maple, spruce, beech, beech heartwood, birch, alder, ash, pine, cherry, oak and nut (See Figure 17.13)

Plate 13 Color impression of black alder (Alnus glutinosa Gaertn.) steamed for 0, 1, 2, 3, 4, 8 (first row) and 10,

12, 14, 16, 18 and 30 days (second row) after 24 h UV radiation (See Figure 17.15)

Part I Historical Aspects

Handbook of Natural Colorants Edited by Thomas Bechtold and Rita Mussak

© 2009 John Wiley & Sons, Ltd ISBN: 978-0-470-51199-2

1 History of Natural Dyes in the Ancient Mediterranean World

Maria J Melo

The colours used on textiles and artifacts, their social significance and the scope

of their trade, are part and parcel of a people’s overall history.Jenny Balfour-Paul, in Indigo, British Museum Press, 2000

The build-up of Mare Nostrum probably began much earlier than the 6th–5th millennium

BC and there is material evidence pointing to such activity as early as the 12th–11thmillennium BC [1] Mare Nostrum, the Roman name for the Mediterranean Sea, was tobecome the home for a global market that expanded beyond its natural borders in the 1stmillennium BC The Phoenicians, the Etruscans, the Greeks and finally the Romans shapedMare Nostrum, a geographic as well as a cultural domain It was also home for the firstglobal dye, Tyrian purple, which was traded by the ingenious and industrious Phoenicians.The purple of Tyre was famous, as were the textiles dyed and produced by the Phoenicians

It is said that the Greeks named the Phoenicians after Phoinikes, the ancient Greek word for

‘red colour’, probably as a result of their famous purple trade

By the time of the founding of the Mediterranean civilizations, what we would considerthe classical palette for natural dyes had already been established, and the most valuedcolours were indigo for the blues, anthraquinone-based chromophores for the reds and

Handbook of Natural Colorants Edited by Thomas Bechtold and Rita Mussak

© 2009 John Wiley & Sons, Ltd ISBN: 978-0-470-51199-2

regardless of distance to be travelled or the price to be paid The natural sources foryellows were much more diverse, so yellows could generally be obtained locally Fordyeing, with the exception of some browns, all other colours and shades, including greenand orange, could be obtained with these blue, red, purple and yellow dyes This classicalpalette was preserved over centuries, if not millennia The first adjustment resulted fromthe loss of Tyrian purple following the fall of Constantinople and the subsequent collapse

of the Roman social and commercial web This was followed by a new entry, cochinealred, brought by the Spanish from the New World [2] However, even with the introduction

of cochineal the chemical nature of the classical pallete was maintained, as carminic acid

is still a substituted 1,2-dihydroxy anthraquinone This classical palette was only lenged by the audacity of chemists, who created new molecules, and colours never seenbefore, from the mid-19th century on [3]

Natural dyes, discovered through the ingenuity and persistence of our ancestors, can resistbrightly for centuries or millennia and may be found hidden in such diverse places as theroots of a plant, a parasitic insect and the secretions of a sea snail By contrast, the brightcolours that we see in the green of a valley, the red of a poppy, the purple of mauve or theblue of cornflower are less stable Natural dyes were used to colour a fibre or to paint It isuseful to distinguish between dyes and pigments based on their solubility in the media used

to apply the colour; dyes are generally organic compounds that are soluble in a solvent,whereas pigments, used in painting, are usually inorganic compounds or minerals that areinsoluble in the paint medium (oil, water, etc.) and are dispersed in the matrix A lakepigment is a pigment formed by precipitation, namely by complexation with a metal ion,forming a dye on the surface of an inorganic substance

Dyeing, in red, blue, purple or yellow, is a complex task that requires skill and edge [4]; this is true now and has been for several millennia Colour is obtained by applying

knowl-a chemicknowl-al compound cknowl-alled knowl-a chromophore or chromogen, something thknowl-at brings orcreates colour When used as a textile dye, the chromophore must also be captured asstrongly as possible into the fibres; i.e it must be resistant to washing Dyes can bind to thesurface of the fibre or be trapped within them They are often bound to the textile with theaid of metallic ions known as mordants, which can also play an important role in the finalcolour obtained Alum, as a source of the aluminium ion, is an important historical mordantand was widely used in the past Other important mordants used in the past were iron,copper and tin ions [4,5] Dyes, like indigo, which are trapped in the fibres due to anoxidation–reduction reaction, without the aid of a mordant, are known as vat dyes.Natural dyes, as lake pigments, have been widely applied in painting For example,anthraquinones and their hydroxy derivatives have been used as red dyes and pigment lakesfrom prehistoric times, and we can find written accounts of the use of anthraquinone redsand purples as dyes in ancient Egypt [5, 6]; anthraquinone lakes (e.g madder red) were alsovery popular with Impressionist painters, including Vincent van Gogh Lake pigments can

be prepared by precipitating the dye extract with aluminium or other inorganic salts, such

as alum [7] Pure dyes such as indigo were also used as painting materials, e.g in medievalilluminations (Figure 1.1)

These eternal colours will be described in more detail in the following sections, after abrief account of the analytical techniques used to reveal the secrets of these ancientmaterials The natural colorants will be organized according to the colour: first theanthraquinone reds, followed by the blues and purple, where indigo and its bromo deriva-tives play a major role Yellows will close this historic overview.

Identifying the dyes and dye sources used in the past has only been possible with thedevelopment, in the past two decades or so, of sensitive new microanalytical techniques[8,9] Chromophores are extracted, then separated chromatographically and characterized

by UV-Vis spectrophotometry or mass spectrometry; whenever possible comparison with

Figure 1.1 Medieval Portuguese illumination, dating from a 12–13th century, Lorva˜o 15, fl 50 kept at Torre

do Tombo (Lisbon) Dark blues were painted with indigo, whereas for the backgound the inorganic and precious pigment lapis-lazuli was used (See Colour Plate 1)

authentic references is performed Currently, the use of HPLC-DAD (high-performanceliquid chromatography with diode array detection) enables dyestuff characterization from

as little as 0.1 mg of thread For unknown components, or those not characterized before,analysis by HPLC-MS (HPLC with mass spectrometric detection) may provide furtherinformation Recently developed mild extraction methods allow more detailed chemicalinformation to be obtained on the historical natural dyes, and as a consequence it issometimes possible to identify the natural sources [10, 11]

Mordant analysis can also provide relevant information about the dyeing method orprocess used The metal ions can be quantified by inductively coupled plasma separationwith atomic emission spectrometric (ICP-AES) or mass spectrometric detection (ICP-MS)

of samples (ca 0.25 mg textile strands) previously digested with nitric acid solutions[12, 13] Before the sample analysis, calibration curves must be constructed usingstandards Concentration linearity in the range of ppb to ppm (or higher) can be achieved

The most stable reds used in antiquity are based on the 1,2-dihydroxy anthraquinonechromophore (Figure 1.2), also known as alizarin Dyes containing anthraquinoneand its derivatives are among the most resistant to light-induced fading [5] These

dyes were obtained from parasitic insects, such as the famous Kermes vermilio, orfrom the roots of plants belonging to the Rubiaceae or madder family, and wereamong the reds that dominated the dye markets of Europe [2, 14] Alizarin andpurpurin are the main chromophores in Rubia tinctorum, the most important species

of the family Rubiaceae In Persia and India, other red dyes – of animal origin –were also used These dyes were imported, or sometimes found locally, and wereconsidered luxury goods Well-known examples are the reds based on the laccaicacids, kermesic acid and carminic acid (Table 1.1), from the parasite insects, lac,kermes and cochineal, respectively [2] The female lac insect secretes a red resin,stick-lac, from which are obtained both the lac dye and the shellac resin Common orIndian lac, Kerria lacca (¼ Laccifer lacca, Carteria lacca, Tachardia lacca andLakshadia lacca) and Kerria chinensis are examples of species that have been widelyexploited [5] In both cochineal (Dactylopius coccus) and kermes (Kermes vermilio)

O

O

OH

OH 1 2

3 4 5

6 7

8 9 10

Figure 1.2 Alizarin; 1,2-dihydroxy anthraquinone

the red dye is obtained from the eggs of the female insect, and therefore there wereharvest seasons that corresponded to the phase where the eggs displayed the highestdye content It was at this stage that the impregnated female insects were croppedbefore depositing their eggs Kermes vermilio is probably the most famous of theEuropean insect parasites and produced a dye ‘brighter than madder and faster thancochineal’ [2, 7a], and was already described in the works of Theophrastusand Pliny The word for worm in many latin languages is based on verme- (or

European languages, namely vermejo, vermelho, vermeil and vermilion in Spanish,Portuguese, French and English, respectively [15]

Other important historical insect sources of red or scarlet dyes derived from species ofPorphyrophora, e.g Polish cochineal (P polonica) and Armenian cochineal (P hamelii) InEurope, most of these sources were replaced in the 16th century by the American cochineal(Dactylopius coccus), which had earlier been carefully domesticated and cultivated by theindigenous peoples of the New World, and was commercialized by the Spanish empire.Although the various species of Porphyrophora also contain carminic acid, dried specimens

of Dactylopius coccus have a much higher content (15–20%) of the dye [2, 5], comparedwith only 0.8% and 0.6% for the Armenian and Polish ones, respectively [5]

Table 1.1 Chemical structures for anthraquinone reds

HO

cochineals

Dactylopius coccus Porphyrophora sp.

O

OH HO

HO

OH OH

OH OH

1.2.2 Redwoods

Redwoods, also known in antiquity as brasil [4, 16], were used as sources of dyes andpigment lakes [5, 7a] It is said that the country Brasil was named after those redwoods, thispossibly being the only country in the world named after a tree The name the Portuguese had

in mind was Terra da Vera Cruz (Land of the Holy Cross) The reds obtained from the bark ofthe tree are not as stable as the previously described anthraquinone reds, but they were muchmore affordable and were widely used for dyeing and in medieval miniature painting [17, 7a]

as well as in cosmetics In his book [16], Cennino Cennini recommends the use of a goodverzino (brazilwood) to highlight the reddish-blue tone of purified lapis lazuli This goodverzino should be obtained from a young lady, who, using it for lipstick and other cosmetics,would take care that she had obtained a well-prepared product of a nice colour

The main colorant in Caesalpinia brasiliensis, C echinata, C sappan, C violacea andHaematoxylum brasiletto is brazilin In Haematoxylum campechianum the main colorant ishaematoxylum Through oxidation, brazilin and haematoxylum are converted to the darkerred compounds, brazilein and haematein, respectively (Figure 1.3) [18]

Anthocyanins are ubiquitous water-soluble colorants responsible for the impressivered and blue colours of flowers and fruits (Figure 1.4) Natural flavylium reds can beconsidered their aglycone ancestors There are several references to the use of these

O HO

OH

1' 6'

2 3 9 8

HO

OH R'3

R'5

5

7

+ A

B

Figure 1.4 In the basic structure of anthocyanins, a hydroxyl group is present at positions 4’ and 7, and a sugar

at position 3 (monoglycoside) or positions 3 and 5 (diglycoside)

compounds to substitute for unavailable inorganic pigments or to give special lightingeffects in ancient illustrations The use of these materials ranges from the Roman Empire(described by the famous architect Vitruvius) to paintings of the Maya civilization [19].Their use as ‘watercolours’ has been described in several treatises or recipe books onillumination painting, including the Strasbourg manuscript, an ‘Old Portuguese work onmanuscript illumination: the book on how one makes colours of all shades’ and ‘De ArteIlluminandi’ [20] Anthocyanins were used to produce clothlets/watercolours [16], asdescribed by Cennino Cennini in the 15th century, and to dye textiles [5, 21, 22] Withanthocyanins the colour domain ranges from red to blue, but with natural flavylium dyes it

is limited to the yellow-red One of the most famous examples of a natural flavylium redcan be found in dragon’s blood resins

Dragon’s blood is a natural resin, having a deep, rich red colour, which is obtained fromvarious trees, namely from Dracaena draco and Dracaena cinnabari, which belong to theLiliaceae family The resin appears in injured areas of the plant and has been used forcenturies for diverse medical and artistic purposes [23] These resins contain not only thered chromophores but also additional flavonoids and steroids; Dragon’s blood resins havebeen used in traditional Chinese medicine The molecules responsible for the red colour ofthe resin obtained from the palm tree Daemonorops draco (Calamus draco was used in thepast) have been characterized by Brockmann et al and named dracorubin and dracorhodin(Table 1.2) [24] Brockman et al concluded that dracorhodin was a natural flavyliumchromophore belonging to the Anthocyanin family More recently, other natural flavyliumchromophores, such as dracoflavylium, have been identified in Dracaena draco, Dracaenacinnabari and other Dracaenaceae [23] (Table 1.2)

1.2.3.1 Equilibria in Solution

As stated above, dracorhodin and dracofalvylium are natural flavylium reds related to

and a sugar in position 3 (monoglycosides) or 3 and 5 (diglycosides) On the other hand, inanthocyanidins the hydroxyl groups take the positions of the glycosides, leading to unstablestructures in solution In contrast, the so-called deoxyanthocyanidins correspond to

‘anthocyanidins’ lacking the hydroxyl in position 3 (but bearing a hydroxyl in position 5),and are quite stable in solution [19, 25]

Table 1.2 Chemical structures responsible for the red colour in Dragon’s blood resins The structures correspond to the quinoid bases (A)

Dracorhodin Nordracorhodin Dracorubin Dracoflavylium

O

O

OMe

O O

OMe

O O

OMe

O O

OMe

OH

In the 1970s, it was firmly established by Dubois and Brouillard (anthocyanins) [26a]and McClelland (synthetic flavylium salts) [26b] that both families of compounds undergomultiple structural transformations in aqueous solution, following the same basic mechan-isms [22, 27] (Figure 1.5) The flavylium cation (AH+) is the dominant species in veryacidic solutions, but with increasing pH a series of more or less reversible chemicalreactions take place: (1) proton transfer leading to the quinoidal base (A), (2) hydration

of the flavylium cation giving rise to the colourless hemicetal (B), (3) a tautomerizationreaction responsible for ring opening, to give the pale yellow Z-chalcone, form (Cc), and,finally, (4) cis–trans isomerization to form the pale yellow E-chalcone (Ct) Furthermore,

at a higher pH, and depending on the number of hydroxyl groups, further deprotonated

the red quinoid bases of the respective yellow flavylium cations [23]

Indigo blue was one of the earliest and most popular dyestuffs known to man (Figure 1.6)

It is still a universally used colour, as the worldwide use of indigo-dyed blue jeans can

O O

O–

A –

O O

OH

A

O HO

OH +

AH +

O HO

OH HO

B

OH HO

OH O

Cc

OH HO

7

Figure 1.5 Scheme of chemical reactions for dracoflavylium Reprinted with permission from Reference [23], Melo, M J., et al., Chem Eur J., 13, 1417–1422 (2007) Ó 2007, Wiley–VCH

attest Indigo, as the name implies, has its origins in ancient India In the great civilizations

of Egypt, Greece and Rome, it was prized for its quality as a dye even though transportationcosts meant it was very expensive [28] Indigo sources are found all over the world, andseveral plants were most probably used in antiquity Julius Caesar, in his De bello Gallico,describes the warrior skin paintings of his Gaulish adversaries as being obtained from ablue juice; the warriors’ faces were frightening and they believed that dyeing the skinwould protect them, making them invulnerable!

Isatis tintoria was grown in Europe, but it is known that indigo from Indigofera tinctoriawas traded to Europeans, namely from Persia to Muslim Spain, and from there distributed

to other European countries [29] Species of Indigofera produced a high-quality indigo,which was used in medieval illuminations (Figure 1.1) [30]

Indigo is also one of the most light-stable organic dyes, a characteristic that explains notonly its wide use in antiquity and the pre-modern area but also its longevity as a colorant [31].The stability of indigo is also the reason why it was used in medieval illuminations and bysome of the great masters of the 17th and 18th centuries, such as Rubens [32] Usually, withthe exception of some necessary and almost irreplaceable colour lakes, organic compoundswere avoided in oil painting, as it was known that they were far less stable to light than theinorganic available pigments Highly pure indigo was an exception

In 1865 Bayer started his work on indigo, and some years later proposed the chemicalstructure as well as a possible synthesis of indigo At the time, indigo was an importantmolecule due to its commercial value as a dye; synthetic indigo paved the way not only forthe development of ‘big’ German chemical and pharmaceutical industries but also helped

to end the colonial production of indigo, which until then had come from natural sources inBritish, French and Iberian colonies This particularly affected the British Indian colony,which was the major producer at that time Even at the beginning of the 21st century, indigo

is still a surprisingly important dye Inasmuch as indigo can be obtained from naturalsources using microbial fermentation, its production using ‘green’ chemistry is of con-siderable interest [33]

The precursors of indigo (¼ indigotin) can be extracted entirely from plants The extract,

a solution of the water-soluble indoxyl glucoside, indican, is hydrolysed via fermentation

to give indoxyl (Figure 1.7), which will further react with another indoxyl moleculeproducing indigo or with isatin resulting in indirubin, a reddish dye [5, 34] The indigoderivatives are generally known as vat dyes and, in their oxidized forms, are insoluble inwater [5]

A common characteristic of vat dyes is the presence of one or more carbonyl groups,which, when treated with a reducing agent in the presence of an alkali, form a water-solubledye known as the leuco species The process of dyeing a textile with these species involves

H N

O

N H O

Figure 1.6 Indigo (=indigotin)