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Positive Identification of the Principal Component of a White Powder as Scopolamine by Quantitative One-Dimensional and Two-Dimensional NMR Techniques

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Abstract:

An unidentified white powder collected as evidence in an intelligence investigation was characterized exclusively by nuclear magnetic resonance (NMR) analysis. A small fraction of the powder dissolved in D2O was subjected to a series of one- and two-dimensional techniques which were used to elucidate the molecular structure of the powder’s major component and positively identify it as the scopolamine biotoxin. Quantitative one-dimensional experiments identified individual proton and carbon atom sites, and conventional 14N spectroscopy detected a single nitrogen atom site. Heteronuclear single quantum coherence data correlated all protons to their directly bonded carbon atom, and together with the quantitative spectra, were used to determine the number of protons directly bonded to each carbon atom. The presence of a methyl, carboxyl, and a benzyl group was also identified from these data. Correlation spectroscopy detected a three proton and a nine proton JH,H network, representing a CH2CH moiety and seven carbon atom ring, respectively. These five elements were assembled into an almost complete molecular structure by using long-range, J-coupled, 1H–13C pairs detected by heteronuclear multiple bond correlation (HMBC) spectroscopy and 1H–1H dipolar-coupled pairs found from nuclear Overhauser effect spectroscopy (NOESY) data. Additional oxygen atom sites were inferred from 1H–13C correlation intensities in the HMBC spectra along with 1H and 13C chemical shift values, or directly from NOESY correlations. Only a single oxygen atom site could not be inferred from NMR data, but its presence was inferred from comparisons to target analyte structures to complete the structure of the scopolamine molecule. To confirm these results, an ethanol/H2O solution of the powder was analyzed by direct infusion into an ion trap mass spectrometer. A prominent base signal was observed at m/z 304.1 amu, corresponding to the protonated molecular ion of scopolamine. Subsequently, the ion was selected and subjected to collision-induced dissociation, producing characteristic major MS/MS fragments at m/z 138.1 and 156.1. Comparisons of 1H and 13C chemical shift values and JH,H values measured from our NMR data were found to agree very favorably with previously reported values for scopolamine in D2O.
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Keywords: biological toxins; forensic sciences; mass spectrometry; molecular structure; nuclear magnetic resonance; tropane alkaloids

Document Type: Research Article

Affiliations: 1: U.S. Army Edgewood Chemical Biological Center, AMSRD-ECB-RT-CF, E5100, 5183 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5424. 2: Science Applications International, Corp., Gunpowder Branch, PO Box 68, Aberdeen Proving Ground, MD 21010-0068. 3: Battelle Eastern Science and Technology Center, Battelle Memorial Institute, 1204 Technology Drive, Aberdeen, MD 21001.

Publication date: January 1, 2008

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