Elsevier

Vibrational Spectroscopy

Volume 110, September 2020, 103111
Vibrational Spectroscopy

Chemical analysis and vibrational spectroscopy study of essential oils from Lippia sidoides and of its major constituent

https://doi.org/10.1016/j.vibspec.2020.103111Get rights and content

Highlights

  • The study of the circadian cycle of the Lippia sidoides (Rosemary pepper) essential oil.

  • The analysis of the yield from the essential oil was by means of the gas chromatography coupled to the mass spectrometry.

  • Fourier transform Raman (FT-Raman) and Attenuated Total Reflection Infrared (ATR-IR) to realize a vibrational spectroscopy study.

  • Density Functional Theory (DFT) calculations were performed in the molecular structure of the thymol

Abstract

The chemical composition, vibrational spectroscopy and DFT studies of the essential oils from Lippia sidoides constituents were performed in this study. The harvesting time periods greatly affect the yields of the essential oil extracted from the leaves of the Lippia sidoides plant material. The chemical composition of the essential oil by gas chromatography coupled to mass spectrometry (GCsingle bondMS) showed thymol as the main constituent of the essential oil. Through Fourier transform Raman (FT-Raman) and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy measurements exhibited a good agreement of the thymol component from the essential oil and the polycrystalline thymol. The Density Functional Theory (DFT) calculations were performed over the molecular structure of the thymol and predicted its Raman and infrared spectra. A good correlation between the experimental spectra of the essential oil and the thymol was observed. Complete assignments of the normal modes were presented for both Raman and infrared spectra of the thymol.

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In this research, we have noticed the need to study the circadian cycle of the Lippia sidoides (Rosemary pepper), thus, evaluating the effect of the cutting time on the yield of the Lippia sidoides essential oil and the variation in the concentration of its main constituents. The analysis of the yield from the essential oil was by means of the gas chromatography coupled to the mass spectrometry. Additionally, we apply the techniques Fourier transform Raman (FT-Raman) and Attenuated Total Reflection Infrared (ATR-IR) to realize a vibrational spectroscopy study of the essential oil from leaves of the Lippia sidoides as well as of its majority component thymol. Furthermore, the Density Functional Theory (DFT) calculations were performed in the molecular structure of the thymol and predicted its Raman and infrared spectra, in order to gain a better knowledge concerning its vibrational properties.

Introduction

The studies of plants with therapeutic effects offer potential access to obtain medical drugs and excipients products [[1], [2], [3], [4]]. The Lippia sidoides Cham., Verbenaceae, commonly known as Rosemary Pepper is a native shrub in the northeastern region of Brazil holding great clinical importance in bio-related applications [5]. Indeed, the stem and aromatic leaves of the plant are widely used in day-to-day life throughout the aforesaid Brazilian region for the treatment of wounds as well as yielding products that span in the gastronomy sector [6]. Recently, much interest is being drawn to the biological applications of Lippia sidoides in larvicidal and healing effects due to its antiseptic and anti-inflammatory properties [4,7]. In this contest, essential oils are complex mixtures of fragrant and odorless substances, which are volatile secondary metabolites obtained from medicinal plant materials [4,7]. Generally, the essential oils are very useful against infections and antibacterial agents [3,[8], [9], [10]]. Also, there has been an increased interest in the antimicrobial properties of the essential oils and its compounds in the medicine field, since many of them have biological activities [[11], [12], [13], [14], [15]]. Other applications of the essential oils include their use as active in ingredients in flavorings, foods, beverages, perfumery, and cosmetics industries [[11], [12], [13], [14], [15]]. Particularly, it has been reported that the essential oils are rich mainly in phenolic monoterpenes, thymol, and carvacrol components [4,16,17].

Abundant in volatile essential oils, Lippia sidoides essential oil contains thymol as a major constituent [18]. Such chemical entity named 2-Isopropyl-5-methylphenol, 2-(1-Methylethyl)-5-methylphenol, p-Cymen-3-ol, or thyme camphor is originated from the thyme oil, which structurally has a hydroxyl group at a distinct position on the phenolic ring [12,19,20]. More generally, the thymol has potent antifungal and bactericidal properties with activity against the dengue mosquito larvae [18,21,22]. Moreover, the findings state its potentially antiseptic role in disorders associated with skin damage, including acne, scabies, white-colored cloths, impinges, and dandruff. Current reports illustrate the use of thymol as an allosteric modulator, and adjuvant in some cancers [19,20,23,24]. Noteworthy, thymol is widely used as the active component in medicines such as the Angino-Rub tablets, which is used for inflammatory and painful processes in the mouth and the throat, as well as the Hirudoid 300 ointment, salonpas plaster, the latter being analgesic and topical anti-inflammatories [7,15,25].

In this regard, studies on vibrational spectroscopy techniques of essential oils have been reported owing to their several applications in many fields, including examination of the spectral changes in essential oils [[26], [27], [28], [29], [30]]. For instance, the essential oils obtained from various plant species (genera: Origanum, Satureja, Salvia, Sideritis, Thymus, Calamintha, Lavandula, Ziziphora, and Thymbra) have been reported [31]. Complementary studies on ATR/FT-IR and NIR-FT-Raman spectroscopy techniques were carried out to obtain the quantitative analysis of various citrus oils [32] such as garlic (Allium sativum) oil unsaturated acyclic [26] and mastic gum oil [27]. Additionally, non-destructive analysis of plants [28] and identification of secondary metabolites in medicinal and spice plants [29], as for instance, in eucalyptus essential oil [33], were performed.

These studies have given information about the physicochemical properties of the thymol, since its structure has a notorious complexity. Thus, this paper aims to investigate the chemical and vibrational properties of essential oils containing thymol as a chemical constituent. Moreover, the chemical analysis, FT-Raman, and ATR-IR spectroscopy techniques are applied to the essential oil from leaves of the Lippia sidoides as well as its major component, the thymol. Finally, the DFT calculations were performed for the pure thymol.

Section snippets

Plant material and extraction of the essential oil

The leaves of Lippia sidoides were collected before maturity, from the garden of the Catholic University Center (UNICATOLICA) Brazil. The garden is located at Quixadá city (4°58′27.7″S, 39°.00′49.2″W) in the state of Ceará in the northeastern of Brazil.

Samples of the harvested leaves were collected from the adult plants measuring approximately 2.10 m of height. Moreover, these samples were collected at different times, e.g., 08:00 h am and 2:00 h pm within a 4-month period from March to June of

Quantification and chemical composition of essential oil

The quantification of the humidity of the biomass moisture, oil volume and content are illustrated on Table 1. These analyses are taken based on the samples collected and distinct months and times. For the biomass moisture samples collected at 08:00 h am, the humidity of the leaves has a percentage variation of ca. 0.96 % regarding the months of April and May. Contrary, the humidity of the samples collected at 02:00 h p.m. remained quite stable in May and June while the variation is

Conclusion

The chemical composition of the Lippia sidoides constituents was evaluated through the GC–MS, from which we conclude that the thymol is the main constituent among all the chemical multi-components. Indeed, the relative percentage variation was between 75.17 (on April) and 85.52 (on June). Moreover, we observed that the dry mass increases as the humidity decreases and thereby, we concluded that it influences the yield. On the flip side, other factors can contribute to the reduction of the yield

Author Contributions

A. G. Q. Saraiva, F. F. de Sousa and G. D. Saraiva wrote the manuscript and performed the assignments of the Raman and infrared modes. C.E.S. Nogueira and A.M.R. Teixeira performed and reported the theoretical study of the vibrational properties and predicted the assignments of the Raman and infrared modes using first-principle calculation through lattice dynamical calculations. R. L. Albuquerque, L. B. Lima, A. G. Q. Saraiva and B.G. Cruz performed the experiments: gas chromatography coupled

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

G.D. Saraiva, Ph.D., acknowledges the support from the FUNCAP/Edital N 03/2019 (process DEP-0164-00350.01.00/19), MCTI/CNPQ/Universal 28/2018 (Grants# 426995/2018-0) and the MCTI/CNPQ PQ – 12/2017 (Grants# 309510/2017-1). AM.R. Teixeira, Ph.D., also acknowledges the support from PQ/CNPq (Grant#: 305719/2018-1). We thank CENAPAD-SP for the use of the Gaussian09 software package and for computational facilities made available through the project “proj373”. Financial support from FUNCAP and CNPq

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