Functional group profiling of medicinal plants using FTIR spectroscopy

*Corresponding author: Madhura Mukadam Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution Liscense 4.0. Functional group profiling of medicinal plants using FTIR spectroscopy Mayuresh Dev and Madhura Mukadam * Department of Zoology, Gogate Jogalekar College, Ratnagiri-415612, Maharashtra. India. World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 Publication history: Received on 30 November 2024; revised on 08 January 2025; accepted on 10 January 2025 Article DOI: https://doi.org/10.30574/wjbphs.2025.21.1.0039 Abstract The chemical diversity of plants underpins their extensive use in medicine, cosmetics, and industry. This study utilizes Fourier Transform Infrared (FTIR) spectroscopy to identify and characterize the functional groups present in five medicinal plants: Curcuma longa (turmeric), Mentha piperita (peppermint), Aegiceras corniculatum (mangrove), Zingiber officinale (ginger), and Piper nigrum (black pepper). FTIR spectroscopy is a non-destructive, rapid technique that identifies molecular vibrations associated with functional groups such as O-H, C-H, C=O, and N-H, facilitating the characterization of both organic and inorganic compounds. The plants analyzed are known for their therapeutic properties, including antioxidant, antimicrobial, anti-inflammatory, and anticancer effects. The FTIR spectra revealed the presence of various functional groups, including hydroxyl, carbonyl, aliphatic C-H, and aromatic groups. The fingerprint region (600–1500 cm⁻¹) exhibited complex absorption bands specific to each plant, reflecting the molecular structure and chemical composition of their bioactive compounds. Unique spectral features such as metal-ligand vibrations in Aegiceras corniculatum highlight the diverse phytochemical profile of this plants. This study underscores the potential of FTIR spectroscopy in identifying bioactive compounds, facilitating their applications in pharmaceutical and nutraceutical development, and contributing to the growing database of FTIR spectral signatures for medicinal plants. Keywords: FTIR spectroscopy; Functional groups; Medicinal plants; Bioactive compounds 1. Introduction Plants are a rich source of bioactive compounds, which are widely utilized in medicine, cosmetics, and industry. The identification of functional groups in plant extracts provides insight into their bioactive compounds, which play critical roles in therapeutic activities such as antioxidant, antimicrobial, and anti-inflammatory effects (Kumar & Pandey, 2015). Fourier Transform Infrared (FTIR) spectroscopy is a powerful, non-destructive analytical technique that identifies molecular vibrations associated with bonds like O-H, C-H, C=O, and N-H, enabling the characterization of organic and inorganic compounds (Stuart, 2004). FTIR spectroscopy is particularly useful in plant science for detecting secondary metabolites such as alkaloids, flavonoids, terpenes, and phenols, which are responsible for plants' pharmacological properties (Coates, 2000). For instance, phenolic compounds exhibit strong hydroxyl (O-H) stretching bands, while carbonyl (C=O) stretching is characteristic of esters, aldehydes, and ketones (Smith, 2011). By analyzing the FTIR spectra of plants, researchers can obtain a molecular fingerprint of their chemical composition, facilitating the identification of functional groups that contribute to its biological activities (Selvaraju et al., 2021). The plants analyzed in this study—Curcuma longa, Mentha piperita, Aegiceras corniculatum, Zingiber officinale, and Piper nigrum—are known for their medicinal properties. For example, Curcuma longa (turmeric) contains curcuminoids, known for their anti-inflammatory and antioxidant activities (Aggarwal et al., 2007). Mentha piperita (peppermint) is World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 244 rich in essential oils with antimicrobial and carminative properties (McKay & Blumberg, 2006). Aegiceras corniculatum is a mangrove plant with phytochemicals showing anti-inflammatory and antifungal properties (Bandaranayake, 2002). Zingiber officinale (ginger) is widely used in traditional medicine for its anti-nausea, anti-inflammatory, and anticancer properties (Ali et al., 2008). Lastly, Piper nigrum (black pepper) contains piperine, which has antioxidant, antiinflammatory, and bioavailability-enhancing properties (Srinivasan, 2009). This study employs FTIR spectroscopy to systematically analyze the functional groups present in these plants. By correlating FTIR peaks to functional groups, the research highlights their chemical diversity and potential applications in pharmaceuticals and nutraceuticals. 2. Materials and Methods 2.1. Plant Materials Plant materials were collected from Ratnagiri, a coastal city located at 16.9954° N latitude and 73.3120° E longitude in the western part of Maharashtra, India, along the Arabian Sea. The samples included the rhizome of Zingiber officinale, leaves of Curcuma longa, Mentha piperita, and Aegiceras corniculatum, as well as seeds of Piper nigrum. After harvesting, the materials were thoroughly washed with water and stored in dry bags. The collected samples were transported to the Department of Zoology laboratory at Gogate Jogalekar College, Ratnagiri, for further processing. 2.2. Sample Preparation The plant parts were chopped into small pieces and air-dried in the shade within the laboratory premises. Once completely dried, the materials were ground into a fine powder using a grinder. The resulting powder was stored in clean, airtight polythene bags to preserve its quality. For FTIR analysis, 10 mg of the dried powder was mixed with 100 mg of potassium bromide (KBr) to form pellets. 2.3. FTIR Spectroscopy FTIR spectra were recorded in the range of 500-4000 cm⁻¹ using a spectrometer. Transmittance was measured to identify the absorption peaks corresponding to various molecular vibrations. 3. Results and Discussion The FTIR spectra of the plant samples revealed diverse functional groups associated with their chemical composition. Key results included the identification of hydroxyl (-OH), carbonyl (C=O), aliphatic C-H, and aromatic groups, among others. Each plant sample exhibited unique spectral characteristics that correlate with its phytochemical composition and potential bioactive compounds. Figure 1 FTIR Spectrum of Curcuma longa Figure 2 FTIR Spectrum of Mentha piperita World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 245 Figure 3 FTIR Spectrum of Aegiceras corniculatum Figure 4 FTIR Spectrum of Zingiber officinale Figure 5 FTIR Spectrum of Piper nigrum Table 1 FTIR Peaks with Functional Group: Curcuma longa Peak (cm⁻¹) Functional Group Interpretation 3710.07 Strong O-H stretching (hydroxyl groups) Presence of alcohols or water 3356.41 O-H stretching Hydrogen bonding, typical in alcohols or phenols 2919.71 C-H stretching (aliphatic hydrocarbons) Presence of alkanes or fatty acids 2854.42 C-H stretching (methyl and methylene groups) Further supports aliphatic compounds 2205.86, 2115.83 C≡C stretching (alkynes) or C≡N stretching (nitriles) Unsaturated hydrocarbons or nitriles 1945.85 May correspond to C=O stretching in ketones/aldehydes Potential carbonyl compounds 1728.74 Strong C=O stretching (carbonyl group) Esters, ketones, or aldehydes 1620.96 C=C stretching (aromatic compounds) Presence of aromatic rings 1417.28, 1314.92 C-H bending vibrations Aliphatic or aromatic hydrocarbons 1244.15, 1150.24 C-O stretching (alcohols, ethers, esters) Alcohols or esters 1026.99 C-O stretching Further indicates alcohols or ethers 891.84 and below (775.29, 661.95, 606.95, 500) Out-of-plane bending vibrations Varies based on sample context World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 246 Table 2 FTIR Peaks with Functional Group: Mentha piperita Peak (cm⁻¹) Functional Group Interpretation 3852.07 O-H stretching (free hydroxyl groups) Presence of alcohols or phenols 3753.23 O-H stretching (hydrogen-bonded) Hydrogen-bonded hydroxyl groups, typical in alcohols or carboxylic acids 3277.87 N-H stretching Presence of amines or amides 2921.39 C-H stretching (aliphatic) Common in alkanes 2855.93 C-H stretching (aliphatic) Confirms the presence of aliphatic hydrocarbons 2114.70, 2069.21 C≡C stretching (alkyne) Suggests the presence of terminal alkynes 1951.63 C=O stretching (carbonyl) Indicates ketones or aldehydes 1731.50 C=O stretching (ester or carbonyl) Typical for esters or saturated carbonyl compounds 1601.63 C=C stretching (aromatic) Presence of aromatic compounds 1412.64 C-H bending (in-plane) Associated with aliphatic compounds 1250.93 C-O stretching Common in alcohols, ethers, and esters 1018.67 C-O stretching Confirms the presence of alcohols or ethers 885.96, 813.35 Out-of-plane C-H bending Typically associated with aromatic compounds 766.75, 699.17 Out-of-plane C-H bending Further confirms the presence of aromatic structures 603.60, 540.73 Skeletal vibrations or out-of-plane bending modes Related to structural features in complex organic compounds Table 3 FTIR Peaks with Functional Group: Aegiceras corniculatum Peak (cm⁻¹) Functional Group Interpretation 500 Metal-ligand or skeletal vibrations Indicates metal-ligand interactions or structural features in organic compounds 800 - 1000 Out-of-plane C-H bending vibrations Associated with aromatic compounds 1000 - 1300 C-O stretching vibrations Common in alcohols, ethers, and esters 1400 - 1500 C-H bending vibrations Typical in aliphatic compounds 1600 - 1700 C=C stretching or C=O stretching Found in alkenes or carbonyl compounds (ketones, aldehydes) 1700 - 1750 Carbonyl (C=O) stretches Common in ketones and carboxylic acids 2100 C≡C stretching vibrations Indicates alkynes 2800 - 3000 C-H stretching vibrations (sp³, sp², or aromatic) Found in alkanes, alkenes, or aromatic compounds 3200 - 3500 O-H or N-H stretching Found in alcohols, carboxylic acids, amines, or amides World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 247 Table 4 FTIR Peaks with Functional Group: Zingiber officinale Peak (cm⁻¹) Functional Group Interpretation Around 3283 O-H stretching Typical of alcohols or phenols 2924 C-H stretching Found in alkanes 1639 C=C stretching Indicates alkenes or aromatic compounds 3813.75, 3723.50 O-H stretching Suggests the presence of hydroxyl groups in alcohols or phenols 3283.11 N-H stretching May indicate amino groups, suggesting the presence of amines 2104.00 C≡C stretching Indicates the presence of alkynes 1639.03, 1518.05 C=C stretching Suggests double bonds typical of alkenes or aromatic systems 1244.52, 1148.50 C-O stretching Indicates ether or alcohol functionalities 997.92, 858.69, 765.26, 706.55 C-H bending vibrations Confirms the presence of aromatic compounds Table 5 FTIR Peaks with Functional Group: Piper nigrum Peak (cm⁻¹) Functional Group Interpretation 3747.12 O-H Stretch (Alcohols, Phenols) Broad peak indicates the presence of hydroxyl groups 3293.99 N-H Stretch (Amines, Amides) Suggests amine or amide functional groups 2919.13, 2852.64 C-H Stretch (Alkanes) Symmetric and asymmetric stretching of C-H bonds in aliphatic hydrocarbons 2319.78 C≡C Stretch (Alkynes) Indicates terminal alkynes 2112.76 C≡N Stretch (Nitriles) Suggests the presence of nitrile groups 1991.41 C=O Stretch (Carbonyls) Indicates carbonyl compounds like ketones or aldehydes 1729.34 C=O Stretch (Esters, Lactones) Strong peak typical of ester or lactone functional groups 1623.49 C=C Stretch (Alkenes) Suggests double bonds in alkenes 1442.75, 1318.72 CH₂ Bending Indicative of methylene bending vibrations in aliphatic compounds 1248.66, 1096.19 C-O Stretch (Alcohols, Ethers) Suggests the presence of alcohols or ethers 1021.81, 885.95 C-O-C Stretch (Ethers) Characteristic of ether linkages 715.51, 614.86 Out-of-plane C-H Bending Indicates substituted aromatic rings 557.39, 500 Metal-ligand vibrations or complex interactions Less commonly associated with organic functional groups 3.1. Curcuma longa The FTIR analysis of Curcuma longa identified significant peaks at 3710 cm⁻¹ and 1728 cm⁻¹, corresponding to O-H and C=O stretching vibrations, respectively. This is consistent with previous studies, where curcumin, a major bioactive compound in turmeric, was shown to exhibit strong carbonyl and hydroxyl absorption bands (Aggarwal et al., 2007). World Journal of Biology Pharmacy and Health Sciences, 2025, 21(01), 243-249 248 Additionally, peaks at 2854 cm⁻¹ and 2919 cm⁻¹ (C-H stretching) were indicative of aliphatic hydrocarbons, supporting reports of sesquiterpenes in turmeric oil (Jayaprakasha et al., 2005). 3.2. Mentha piperita The spectrum of Mentha piperita revealed peaks at 3852 cm⁻¹ (free O-H stretching) and 3277 cm⁻¹ (N-H stretching), indicative of hydroxyl and amino groups. Previous studies (McKay & Blumberg, 2006) also reported similar peaks, attributing them to menthol and menthone, key constituents of peppermint essential oil. Peaks at 1731 cm⁻¹ and 1601 cm⁻¹ were attributed to C=O and C=C stretching, corroborating the presence of esters and aromatic compounds, which are characteristic of this plant's bioactive profile. 3.3. Aegiceras corniculatum Distinct features of Aegiceras corniculatum included significant metal-ligand vibrations at lower wavenumbers (5001000 cm⁻¹), suggesting the presence of coordination compounds, as reported earlier (Bandaranayake, 2002). The peak at 1600-1700 cm⁻¹ was indicative of C=C stretching, aligning with findings of polyphenolic compounds in mangrove plants. The clear C-O stretching peaks at 1000-1300 cm⁻¹ suggested the presence of simple alcohols or ethers, consistent with secondary metabolite analysis in mangroves. 3.4. Zingiber officinale The spectrum of Zingiber officinale exhibited a peak at 3283 cm⁻¹ corresponding to O-H stretching, indicative of alcohols and phenols. Peaks at 2924 cm⁻¹ and 1639 cm⁻¹ (C-H and C=C stretching) further pointed to the presence of alkanes and aromatic compounds, in agreement with studies highlighting gingerol and shogaol as major constituents (Ali et al., 2008). Additional peaks at 2104 cm⁻¹ and 1244 cm⁻¹ (C≡C and C-O stretching) indicated alkynes and ethers, which have also been reported in ginger essential oils (Singh, 2008). 3.5. Piper nigrum The FTIR spectrum of Piper nigrum revealed strong O-H and N-H stretching vibrations at 3747 cm⁻¹ and 3293 cm⁻¹, corresponding to hydroxyl and amino groups. These findings align with the presence of piperine, an alkaloid known for its antioxidant and anti-inflammatory properties (Srinivasan, 2007). Peaks at 2919 cm⁻¹ and 1729 cm⁻¹ (C-H and C=O stretching) further supported the presence of aliphatic hydrocarbons and carbonyl groups, consistent with earlier studies (Ravindran et al., 2000). The results demonstrated significant overlap with existing literature, confirming the validity of the FTIR analysis. The presence of hydroxyl group was almost common feature across all samples, highlighting their potential as antioxidants or reactive intermediates in biochemical pathways. The fingerprint region was observed to span the wavenumber range between 600 cm⁻¹ and 1500 cm⁻¹ in all plant samples. This region is distinct for each molecule, providing a unique "fingerprint" that aids in the identification of specific compounds. Unlike the functional group region (above 1500 cm⁻¹), the fingerprint region exhibited a complex array of absorption bands, which arise from various bending, stretching, and vibrational modes of the atoms within the molecule. The peaks in this region are influenced by the overall molecular structure, including the arrangement of atoms and bonds, contributing to the characteristic pattern observed in the FTIR spectrum. 4. Conclusion FTIR spectroscopy demonstrated its effectiveness in identifying diverse functional groups within the analyzed plant samples. Notable differences in spectral features were observed among the samples, such as unique metal-ligand vibrations in Aegiceras corniculatum. The unique "fingerprint" for each molecule was also noted in all plant samples. These findings provide insights into the chemical composition of the plants, which could inform their potential applications in pharmaceuticals and nutraceuticals. Furthermore, these findings contribute to the growing database of FTIR spectral signatures for medicinal plants, aiding in rapid screening and quality control of phytochemicals. Compliance with ethical standards Acknowledgments The authors express their gratitude to the Principal of Gogate Jogalekar College for their support of the research work. 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