Intercalation of alkaloids of Cassia auriculata linn. into hIntercalation of alkaloids of Cassia auriculata linn. into h⁺- and al³⁺- exchanged montmorillonite clays- and al3+- exchanged montmorillonite clays
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Date
2016-11-05
Authors
Abeywansha, A.I.
Bandara, N.C.
Bandara, B.M.R.
Journal Title
Journal ISSN
Volume Title
Publisher
University of Peradeniya, Sri Lanka
Abstract
Montmorillonite [(Na,Ca)₀.₃₃(Al,Mg)₂Si₄O₁₀(OH)₂.nH₂O] is a layered aluminosilicate mineral having an expandable interlayer space of 1-2 nm. The inherent net negative charge on outer surface of the layers is counteracted by the presence of exchangeable cations in the interlayer nanospace. Cation-exchanged H⁺- and Al³⁺-montmorillonite (MMT) clays show Lewis and Bronsted acidities and have the potential to trap alkaloids. In this study, the cation- exchanged clays were used to trap alkaloids present in the Cassia auriculata Linn. leaf extract; C. auriculata is a medicinal plant having anti-diabetic, antioxidant, antimicrobial, anticancer, anthelmintic, anti-inflammatory and analgesic activities. However, it contains hepatotoxic pyrrolizidine alkaloids and their removal may enhance the medicinal value of the plant. Leaf extracts of C. auriculata were obtained by successive extraction of dried leaf powder into hexane and methanol using a Soxhlet apparatus. Alkaloids present in the leaf extracts were analyzed qualitatively by TLC and quantitatively by ion-pair formation (IPF) method coupled with UV-Vis spectroscopy. H⁺- and Al³⁺-MMT clays were prepared by stirring purified Na⁺- MMT in aqueous solutions of HCl and AlCl₃, respectively. Alkaloid intercalated H⁺- and Al³⁺- MMT clay composites were prepared by stirring suspensions of H⁺- and Al³⁺-MMT clays in solutions of C. auriculata leaf methanol extract in 50% MeOH/CH₂Cl₂. The amounts of alkaloids present in the supernatant before and after the intercalation were determined using the coloured ion-pair complexes formed between the protonated alkaloids and methyl orange at an optimum pH of 4.4. UV-Vis measurements of the ion-pair complexes were carried out at 428 nm using brucine as the standard alkaloid. All the clays and their alkaloid composites were characterized using X-ray diffraction (XRD) and Fourier-Transform Infrared (FT-IR) spectroscopy. The intercalation of alkaloids in the MMT clay composites was further confirmed by releasing of the trapped alkaloids in NaOH solution, which was quantified by IPF/UV-Vis method. The results indicated intercalation of 97% and 98% of C. auriculata alkaloids of methanolic leaf extract into H⁺- and Al³⁺-MMT clays, respectively. When the alkaloid-intercalated clay composites were stirred in 0.5 M NaOH, slow releasing of the trapped alkaloids was observed, reaching a maximum of 59% release (after 3 h) from H⁺- MMT and 50% release (after 4 h) from Al³⁺-MMT clay composites. It can be concluded that the alkaloids present in the leaves of Cassia auriculata can be successfully intercalated into cation-exchanged MMT clays and the intercalated alkaloids can be released slowly upon alkali treatment.
Description
Keywords
Montmorillonite , Alkaloids
Citation
Proceedings of the Peradeniya University International Research Sessions (iPURSE) – 2016, University of Peradeniya, P 321