Environ. Sci. Technol. 1988,22,1357-1361
Horvath, A. L. Halogenated Hydrocarbons; Marcel Dekker: New York, 1982. Hansch, C.; Vittoria, A.; Silipo, C.; Jow, P. Y. C. J. Med. Chem. 1975,18, 546. P. C. J. Chem. Inf. Comput. Sci. 1985, Stouch, T. R.; JUTS, 25, 92. Gilbert, S. Linear Algebra and its Applications, 2nd ed.; Academic: New York, 1980. Belsley, D. A,; Kuh, E.; Welsh, R. E. Regression Diaognostics: Identifying Influential Data and Sources of Collinearity; Wiley; New York, 1980.
(22) "Long Range Research Agenda, 1987-1991"; U.S. EPA: Grosse Ile, MI, 1987; EPA 600-9-87-003, p 30. (23) Mackay, D.; Shiu, W. Y.; Bobra, A,; Billington, J.; Chau, E.; Yenn, A.; Ng, C.; Szeto, F. U.S.EPA, Gulf Breeze, FL, 1982; EPA Report 600/3-82-019. (24) Atlas, E.; Foster, R.; Glam, C. S. Environ. Sci. Technol. 1982, 16, 283. Received for review October 20, 1987. Revised manuscript received May 27, 1988. Accepted J u n e 11, 1988.
Ozone Fading of Organic Colorants: Products and Mechanism of the Reaction of Ozone with Curcumin Daniel Grosjean,? Paul M. Whitmore,$C. Pamela De Moor, and Glen R. Cass" Environmental Engineering Science Department and Environmental Quality Laboratory, California Institute of Technology, Pasadena, California 91 125
James R. Druzik The Getty Conservation Institute, 4503B Glencoe Avenue, Marina del Rey, California 90292-6537
rn The organic colorant curcumin [177-bis(4-hydroxy-3methoxyphenyl)-l,6-heptadiene-3,bdione] was exposed to
Table I. Compounds Studied
ozone in purified air in the dark, and the exposed samples were analyzed by mass spectrometry. The major reaction products included vanillin (4-hydroxy-3-methoxybenzaldehyde) and vanillic acid (4-hydroxy-3-methoxybenzoic acid). These products and the corresponding loss of chromophore (i.e., fading of curcumin) are consistent with a reaction mechanism involving electrophilic addition of ozone onto the olefinic bonds of curcumin. Vanillin and vanillic acid did not react with ozone under the conditions of this study.
name
MW
purity, mp, ,,A, % "C nm
curcumin [1,7-bis(4-hydroxy-3368 methoxyphenyl)-l,6-heptadiene3,5-dione] vanillic acid (4-hydroxy-3168 methoxybenzoic acid) vanillin (4-hydroxy-3152 methoxybenzaldehyde) ferulic acid (4-hydroxy-3194 methoxvcinnamic acid)
195 97
210
99
113
99
Introduction Recent studies carried out in this laboratory have shown that a number of organic colorants faded substantially when exposed, in the dark, to purified air containing 0.3-0.4 part per million (ppm) ozone. The colorants tested included contemporary artists' pigments ( I , 2 )as well as traditional natural colorants (3). These observations prompted us to initiate a study of the reaction mechanisms involved in the fading of these ozone-fugitive colorants. Thus, major products have been identified and reaction pathways proposed for the reaction of ozone with several indigos ( 4 ) and with alizarin and related colorants (5). In this article, we describe the methods and results of a similar study focusing on curcumin. Curcumin is a traditional natural colorant (e.g., the coloring agent in turmeric) whose poor ozone-fastness has been initially suggested in a study involving Japanese wood-block prints (I) and subsequently confirmed in a detailed kinetic study of the ozone fading of natural colorants on watercolor paper (3). Indeed, curcumin is the most ozone-fugitive of all the colorants, organic or inorganic, synthetic or natural, we have tested to date ( I , 5).
Table 11. Summary of Exposure Experiments
'Department of Chemical Engineering; also with DGA, Inc., 4526 Telephone Rd., Suite 205, Ventura, CA 93003. *Presentaddress: Center for Conservation and Technical Studies, Harvard University Art Museums, 32 Quincy St., Cambridge, MA 02138.
Experimental Methods
0013-936X/88/0922-1357$01.50/0
ozone exposure mode oxone exposure mode long term to low O3 short term to high O3 substrate" silica gel cellulose Teflon filter sample extraction methylene chloride methanol none (direct MS analysis) MS analysisb electron impact (EI) chemical ionization (CI)
curcumin vanillin
+ + + + + + I+ + +
430
vanillic ferulic acid acid
+
+
+
+
+
+
+
+
+
+
+
+
" Curcumin was also exposed to ozone on watercolor paper (see ref 2) and as a colorant on a Japanese wood-block print (see ref 1). Reflectance spectra were recorded on both substrates, but chemical analyses of reaction products were not performed. Includes, for all compounds, the analysis of control (unexposed) samples and of all appropriate solvent and substrate blanks.
Compounds Studied. Curcumin, vanillin, vanillic acid and ferulic acid (Table I and Figure 1)were obtained from Aldrich Chemical Co. and were used without further pu-
0 1988 American Chemical Society
Environ. Sci. Technol., Vol. 22, No. l l , 1988 1357
CURCUMIN
Table 111. Methane Chemical Ionization Mass Spectrum of Curcumin (MW 368)
mlz VAN I LL I N
VANILLIC ACID
FERULIC ACID Figure 1. Structures of compounds studied.
rification. Ferulic acid was selected as a simple structural homologue of curcumin in order to verify the consistency of mass fragmentation patterns. Ozone Exposure Protocols. A list of the experiments performed is given in Table I1 according to compound studied, mode of exposure, and substrate. The protocols employed in this study for exposure of colorants to ozone and for mass spectrometry analysis of the exposed samples have been described in detail in ref 5; only a brief summary of these protocols is given here. Two types of experiments were performed, both involving exposure to ozone in purified air in the absence of light. Long-term exposures to low concentrations of ozone (0.36 f 0.11 ppm for 95 days, T = 25 OC, and 49.5 f 1.9% relative humidity (RH), air flow rate 2.5 L/min) involved 100 mg of curcumin airbrushed on cellulose and on silica gel thin-layer chromatography (TLC) plates. Samples prepared in an identical manner but with a lighter loading on cellulose, on silica gel, and on watercolor paper were also exposed in the same conditions (see below). These conditions are similar to those employed in our earlier studies in which curcumin was exposed to ozone on watercolor paper (3) and as colorant on a wood-block print (1). In addition, short-term exposures to higher levels of ozone (-10 ppm for 4 days, T = 24 “C, RH I 20%, air flow rate 1.0 L/min) were carried out with 10 mg of colorant deposited on a Teflon membrane filter. Control samples, prepared in an identical manner but not exposed to ozone, were included for each type of exposure experiment. Mass Spectrometry Analysis. After exposure to ozone, the cellulose and silica gel TLC plate samples were extracted with either methanol or methylene chloride, and the solvent extracts were concentrated prior to analysis. The Teflon filter samples were analyzed directly without solvent extraction. Mass spectrometry analyses were carried out using a Kratos Scientific Instruments Model MS-25 hexapole, double-focusing magnetic sector instrument. All samples were analyzed by direct-insertion probe with two ionization modes, electron impact (EI) or chemical ionization (CI) with methane as reagent gas. The conditions are identical with those described earlier (5). Our earlier convention was also adopted for structural information on reactants and products to be deemed positive, probable, or tentative ( 5 ) , depending upon the availability of reference compounds for comparison. Reaction products that could go undetected in our conditions include (a) volatile products that were no longer present on the substrate at the com-
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397 383 370 369 351 350 339 285 245 233 232 219 205 193 191 190 177 151 147 137 136 124 123 107 91
% of base peak (BP)
1 1
5.5 25 2 6 5 4 3 4 2
13 4 7 7 9 100 (BP) 12 17 26 3 2 2
7 5
fragment M + 29O M + 15’ MH, 13Cb MH MH - HzO M - HzO MH - HZCO, M - HCO XCH=CHCOCHzCOCH=CH‘ MH - XCH XCH=CHCOCHzCOCH XCH=CHCOCHZCO 233 - CO XCH=CHCOCHZ XCH=CHCOCH XCH=CHCO BP - CH=CH BP - HZCO XCH2 XCH XH X XH -OH, X - 0 C6H,0 (phenoxy)
Reagent gas adducts. 13C isotope contribution of MH. X = guaiacyl group, (4-OH-3-CH30)C6H,.
pletion of the ozone-exposure experiments, (b) products formed in very low yields (
