An Easy Protocol for the Determination of the Botanical Origin of Natural Resins
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Laboratory of Chemistry AN EASY PROTOCOL FOR THE DETERMINATION OF THE BOTANICAL ORIGIN OF NATURAL RESINS Applied to Art and Archeology FROM BURSERA THAT JOINS THE USE OF FTIR SPECTROSCOPY AND X-RAY DIFFRACTION CNRS 7263-IRD 237 1 2 3 1 1 University of Avignon, France Paola LUCERO , L. BUCIO , I. BELIO , C. MATHE , C. VIEILLESCAZES 1 University of Avignon, France 2 Physics Institute National Autonomous University UNAM 3 Sinaloa University [email protected] Introduction Materials of Investigation Previous studies have shown that when copal is heated (Frondel, 1967) or ground (Amaro, 2007) it loses its crystalline structure, therefore our team hypothesized In this research two types of samples of copal resin were studied: that X-ray diffraction could provide some insights into sample history which would A) Fresh resins represented by certified origin samples from 6 species: B. bipinnata, Natural products are known to be complex mixtures of contribute to determining whether a sample was heated or ground during B. excelsa, B. laxiflora, B. stenophylla, B. grandifloia and B. penicillata and organic molecules. Certain spectroscopic techniques are anthropogenic activities. advantageous when identifying these materials, as they do commercial samples from markets in different geographical locations in Mexico. not require the destruction of the sample. B) Archeological resins from the “Templo Mayor” site and from Chichén Itzá. 56000 30000 B. stenophylla 54000 Bursera species are the source of oleoresins that have 52000 25000 50000 48000 B. penicillata 46000 been used in different fields and cultures. In the Pacific Methodology: FTIR Spectroscopy plus PCA (Principal 20000 44000 e 42000 l e t l i t i T 40000 15000 T s i s 38000 Sample from Chichén Itzá i x slope this botanic genre numbers more than 80 species. In B. excelsa x A Component Analysis) and LDA (linear discriminant Analysis) A 36000 Archeological site Y 10000 B. laxiflora Y 34000 the patrimony field, they were used by pre- Columbian B.simaruba 32000 5000 B. grandifolia 30000 alfa amyrin B. bipinnata 28000 26000 cultures, such as the Aztecs and the Mayas, as adhesives, 0 24000 22000 After the collection of IRTF spectra of certified botanical resins, some spectral band 0 20 40 60 80 100 0 20 40 60 80 100 and by outstanding painters such as Diego Rivera and D. X Axis Title X Axis Title Alfaro. Chemically these resins are highly valuable positions were used chosen owing to its contribution to differentiate IRTF spectra because of their triterpen content of oleanane-, ursane-, from one species to another Fig 4. X-ray Diffraction patterns Fig 5. X-ray Diffraction pattern Band Interpretation position by species for fresh resins For an archeological resin lupane- and hopane-like molecules. It has been found that 500 a 3425 Tension O-H broad band considerable variability in terpenoid composition is 400 B. grandifolia b 2945 Tension C-H from alkans CH3, B. penicillata Application of the methodology to samples ) and alkens CH2 . U genetically determined, therefore terpenoids can be often . 300 A B. laxiflora ( e c 1710-1720 Stretching C=O from carboxylic 1 c n a t B. excelsa acid i 200 act as biochemical markers for chemotaxonomic m 9 2 7 s n ,54 1 a r 3 1638 Tension C=C T 8 0 B. stenophylla d 6 classification. 100 e 1454 Symmetric deformation CH2 B. bipinnata Type of Sample During the 2009 archeological excavations in Templo 0 f 1380 Deformation of deflection CH3 4000 3500 3000 2500 2000 1500 1000 Mayor site, many fragments of resin were found which Wavenumber (cm -1) g 1242 Tension C-O-C h 1037 Tension C-O simetrical from presented differences in color and texture. For alcohol Archeological Sample i 883 Fresh Sample conservation professionals many questions arise, from j 687 both archeological and fresh materials (used in restoration k 584 Fig 2. Comparative of FTIR spectra of the different species treatments), concerning botanical origin and the impact of Crystalline Amorphous Crystalline Amorphous different preservation conditions. This data was then used in chemometric analysis. Sample distribution patterns were X-ray pattern X-ray pattern X-ray pattern X-ray pattern In this context, non-destructive techniques such as XRD investigated with principal component analysis (PCA); this is a well known pattern (X-ray diffraction) and FTIR (Fourier Transformed Infrared) recognition technique which projects the data in a reduced hyperspace, defined by the are invaluable for the professionals that are responsible for principal components, this allows the construction of a model able to predict the the conservation and the restoration of cultural objects, as property of a sample to a category previously defined. Score graphics, using the first Altered sample Alterated sample: it is generally difficult to identify such substances only by Collect FTIR spectra, proceed to PCA two components, revealed a sample agglomeration with good differentiation in 5 out of maybe grinded physical characteristics and olfactive observations. the 6 species (cf Fig 3). As a validation method, our research used LDA (Linear or hetahed Moreover, processes of deterioration often make the discrimination analysis. This method calculated a 95,2% positive recognition for the interpretation of observations carried out on archaeological Graph Interpretation PCA model. The aim of this work was to establish a spectral databank in order to materials difficult. Such sample analysis is of great interest identify the botanical provenance of unknown resin samples. for scientists working towards the understanding of the PCA for 6 species plus B copallifera sample PCA For 6 species plus commercial sample MEXJ1 PCA for 6 species plus Archeological Samples with IRTF data 550 techniques employed in the fabrication of an object. 520 520 500 500 525 t t t n n PCA for 6 species w ith IRTF data n e In this work we present a time-efficient technique for the e e n n n o o o p p 5 5 0 480 p 480 m m m 500 o o o C botanical identification of these materials by means of FTIR C c d d d n n 460 n o o 460 o c c c e e e S and XRD, aiming to be useful as a first approach to these S S 475 5 2 5 440 440 t techniques for non-chemist n e 450 n 420 420 o 2250 2300 2350 2400 2450 2200 2250 2300 2350 2400 2200 2250 2300 2350 2400 p First Component First Component First component m 5 0 0 o c A d n o Fig 6. PCA for a fresh resin from Fig 7. PCA for a commercial Fig 8. PCA for archeological resins c e S 4 7 5 B.copalifera botanical origin (●) sample (●) possible botanical (●)from Templo Mayor (Aztec) origin: B stenophylla or B. (●)from Chichén Itzá (Maya) bipinnata 4 5 0 2 2 0 0 2 2 5 0 2 3 0 0 2 3 5 0 2 4 0 0 First com ponent Conclusions and Perspectives B Fig 3. Distribution in the hyperspace of the first two components of the species according their botanical This method is a quick and efficient tool, that may help in identifying the origin. Variables are shown with different symbols: ●B. laxiflora, ♦B. excelsa, ■ B. stenophylla, ▲B. bipinnata, botanical origin of unknown samples of Mexican resins. It can also provide ►B. grandifloia, ▼B. penicillata. information regarding sample history. Nevertheless some limitations exist and a better understanding of the degradation process of the resin is needed. In C Methodology: XRD the meantime further separative techniques, such as Gas Chromatography coupled to Mass spectrometry (GC/MS) and High Performance Liquid When crystalline components are present in a significant amount in a sample (10% Chromatography (HPLC) may be used in order to accurately interpret the or more), X-ray diffraction will reveal these molecules and may assist with Fig 1. Mexican copal A) archeological samples, B) certified origin information obtained by these means. identification. samples C) Commercial samples In the authentication field this method can be used to distinguish between X ray diffraction patterns for botanically certified origin resins were obtained and botanical origins for archeological samples from different archaeological sites. About the author: differences arising from chemical structure of the resin were noted. As X-ray can Paola LUCERO is a conservation scientist. She firstly obtained a Masters degree diploma in detect the presence or absence of amorphous matter (correlated to the presence Molecular chemistry at Rennes University (France) and by July 2012 she will hold a Ph.D. diploma from Avignon University (France). The focus of her Ph.D research was the study of of volatile compounds) this data, may be used as a reference to estimate the organic materials used in archeological context as adhesives, molding materials and binders relative age of commercial samples. by Aztec and Maya cultures. Orta A. 2007. Copal: microestructura, composición y algunas propiedades relevantes. ESIQIE-IPN. México We thank CONACYT for funding of this researc,h as well as M. López Lújan and Mrs. María Barajas and Aurora Montúfar from Templo Mayor for providing the archeological samples for our research Frondel, J. X-Ray Diffraction Study of Some Fossil and Modern Resins Science 155 (1967) 1411-1413.