Spectroscopic Metabolomics using NMR, FTIR and LIBS to study Medicinal Plants
S. Ghatak1, P. K. Rai1, T. Velpandian2, R. Jayasundar1
Department of 1NMR, All India Institute of Medical Sciences, New Delhi, India.
Department of 1Physics, University of Allahabad, Allahabad, India.
Metabolomics of medicinal plants is gaining importance due to growing interest in natural products and botanical drug development1. This study presents a comprehensive spectroscopic profiling of select medicinal plants with reported therapeutic potential, using NMR, Fourier Transform Infrared (FTIR) and Laser-Induced Breakdown Spectroscopy (LIBS)
2. In addition, antioxidant efficacy of these plants was also evaluated since oxidative stress is to be thought involved in the development of many diseases including cancer and antioxidants are considered potential therapeutic agents. The following plants were studied: Withania somnifera, Cinnamomum tamala, Vitis vinifera, Tribulus terrestris, Commiphora mukul, Punica granatum, Zingiber officinale, Agaricus campestris, Cuminum cyminum
and Desmodium gangeticum.
All the plant samples were studied in aqueous form. A 700 MHz NMR spectrometer (Agilent, USA) was used to acquire 1D and 2D proton NMR data. The following parameters were used for 1D data acquisition: relaxation delay - 14 sec, spectral width - 15ppm, 32 scans and 32 K data points. Peak assignments were carried out using 2D NMR. The spectra were subjected to Principle Component Analysis (PCA) using MestReC, Unscrambler X10.2 and SPSS 15.0 softwares. FTIR 660 (Agilent, USA) was used to scan the sample from 750-10,000 nm range in the Attenuated Total Reflection (ATR) mode. LIBS spectra were acquired using a 4-channel spectrometer (Ocean optics LIBS 2000+) in the wavelength range from 200-1100 nm. The laser energy employed was 175-mJ and the repetition rate was 2 Hz. DPPH (1,1-Diphenyl-2-picrylhydrazyl) assay was carried out to evaluate the antioxidant potential of the medicinal plants and IC50 value was calculated3. In addition to primary metabolites like carbohydrates, pyruvate and amino acids observed in all the plants, secondary metabolites such as gingerol, polyphenols and flavonoids were also present in varying intensities. Many of the functional groups seen in the NMR spectra were also seen in the FTIR spectra. For example, OH (1300-1420 cm-1), keto C=O (1661-1681 cm-1), R-COOR (1773 cm-1), R-NH +
2 (2320-2380 cm-1) and alcohol/phenol (3594-3620 cm-1). Many of these
functional groups such as OH, RNH2, RCOOR and C6H5OH are known to be present in abundance in secondary
metabolites which are responsible for high antioxidant activity. Elements such as Mg and Ca were observed in the LIBS
spectra are also known to play a role in antioxidant potential2, which was found to be maximum in Withania somnifera
minimum in Cinnamomum tamala.
Interestingly, PCA plot of the NMR spectral data of plants showed clustering pattern
based on their antioxidant activity. For instance, Vitis vinifera, Tribulus terrestris, Withania somnifera, Commiphora mukul
and Desmodium gangeticum
with similar antioxidant potential showed association in the plot. With increasing interest in
plant based drug development, phytochemical characterising assumes important. The present study has used 3 different
types of spectroscopic techniques along with the antioxidant assay in order to generate comprehensive phytochemical
information on medicinal plants.
(1) Kim, H.K.; Choi, Y.H.; Verpoorte, R. Nature. 2010
; 5(1), 536-549.
(2) Sabsabi, M.; Cielo, P. Appl. Spect
; 49(2), 499-507.
(3) Kedare, S.B.; Singh, R.P. J. Food Sci. Tech
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