Browsing by Author "Wickramarachchi, S.R."

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Antibacterial Polyketide from Lasiodiplodia theobromae and Pyrenula bahiana on Mangrove Ecosystems in Puttalam Lagoon, Sri Lanka
(Asian Journal of Chemistry, 2022) Paranagama, P.A.; Santhirasegaram, S.; Wickramarachchi, S.R.; Attanayake, R.N.; Weerakoon, G.; Maduranga, K.
Lasiodiplodia theobromae is one of the frequently isolated fast growing endolichenic fungus. This fungus was isolated from the lichen host, Pyrenula bahiana collected from the mangrove ecosystems in Puttlam lagoon and its identification was confirmed based on rDNA-ITS sequence homology. Secondary metabolites of L. theobromae were extracted into ethyl acetate and subjected to antibacterial assay against Escherichia coli (ATCC25922), Staphylococcus aureus (ATCC25923) and Bacillus subtilis (ATCC6051). Crude extract at a concentration of 6.8 μg/mL showed good antibacterial activity against the bacterial strain S. aureus compared with the activity of the standard azithromycin at a concentration of 5.0 μg/mL. Active crude extract was partitioned to obtain methanol, hexane and chloroform fractions. Chloroform fraction showed the highest activity to S. aureus out of three fractions. This fraction was subjected to bioassay-guided separation on silica gel column chromatography to isolate bioactive pure compounds. The bioactive pure compound was identified as (3R)-de-O-methyllasiodiplodin using LC-MS, 1D and 2D NMR spectroscopy.
Antioxidant activity and chemical constituents of methanolic extract of Durio zibethinus Murr. (durian) peels
(MEDICINAL PLANTS - INTERNATIONAL JOURNAL OF PHYTOMEDICINES AND RELATED INDUSTRIES, 2021) Perera, P.J.; Binuwangi, A.K.D.M.; Silva, A.A.G.; Attanayake, R.N.; Wickramarachchi, S.R.; Rajapakse, C.S.K.
This study aimed to determine the DPPH free radical scavenging activity, total phenolic content (TPC) and total flavonoid content (TFC) of methanolic extract of Durio zibethinus Murr. (durian) peels and its fractions. The chemical constituents of durian peels extracted into methanol by soxhlet extraction were sequentially extracted into hexane, dichloromethane and aqueous methanol. Among the fractions, the dichloromethane fraction showed the highest DPPH free radical scavenging activity (IC50 179.9 ± 6.6 μg/ml) with high TPC and TFC (85.82 ± 12.11 mg gallic acid equivalent/g of dried weight of extract and 12.66 ± 1.94 mg of quercetin equivalent/g of dried weight of extract, respectively). A very strong positive correlation (r = 0.9677) was observed between the DPPH free radical scavenging activity and the TPC of fractions and a strong positive correlation (r = 0.7858) was noticed between the DPPH free radical scavenging activity and TFC of the fractions indicating that phenolic compounds in durian peels may contribute to their strong antioxidant activity. As the dichloromethane fraction had constituents with the highest antioxidant activity, it was analyzed by Gas chromatography-Mass spectrophotometry to identify its volatile constituents. The results revealed that the dichloromethane fraction was rich in [1,2-Benzenedicarboxylic acid, bis (2-ethylhexyl) ester], [2,3-diphenylquinoxaline], [2-coumaranone], [4-((1E)-3-hydroxy-1-propenyl)-2-methoxyphenol], [7,9-di-tert-butyl-1-oxaspiro (4,5) deca-6,9-diene-2,8-dione] and [phenol, 2,4-bis(1,1-dimethylethyl)], which are known to exhibit antioxidant activity.
Chemical profile of Terminalia chebula fruit collected from different regions of Sri Lanka and commercial samples from Sri Lanka and India
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Suraweera, K.P.C.D.; Wickramarachchi, S.R.; Tennakoon, T.M.S.G.
Terminalia chebula is a valuable medicinal plant used in traditional medicine. The fruit of T. chebula contains a large number of biologically active chemical compounds. Demand for the herbal drugs is increasing every day and maintaining the quality of herbal drugs is very important. Therefore, the objective of this study is qualitative and quantitative comparison of the chemical profiles of T. chebula fruit (without seeds) of commercial samples and authentic samples. Authentic samples of T. chebula were analyzed to see the effect of climatic zone variation on chemical profile and physicochemical parameters. Authentic samples (SLA) were collected from T. chebula plant itself from onsite visit, from Bibila, Buththala, Padhiyathalawa, Gampaha and Colombo and authenticated from the voucher specimen available at Herbarium, Link Natural Products (Pvt) Ltd (LNP). One composite sample was made according to sampling protocol, WHO 1998, from each region for analysis. Commercial samples are a mixture of fruits obtained from several suppliers from different areas. Commercial samples were obtained separately from three different batches of T. chebula commercial stocks from Sri Lanka (SLC) and India (INC) at LNP. Powdered dried fruits were extracted with 70% aqueous methanol and concentrated using rotatory evaporator. Physicochemical parameters were determined according to WHO and European pharmacopoeia methods. Total tannin was determined using Folin-Denis assay. Crude T. chebula fruit extract was separated by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). Gallic acid content and gallic acid/ellagic acid ratio were calculated using the peak area of HPLC chromatograms. TLC and HPLC showed a large number of compounds in the crude extract of T. chebula fruit. Both showed similar profiles with variations in intensity among the samples. Physicochemical parameters (without water soluble extractive values), total tannin, gallic acid content, gallic acid/ellagic acid ratio are statistically different among SLA samples (P < 0.05). Except physicochemical parameters, other parameters are statistically similar among SLC and INC (P<0.05). Total tannin content (% w/w) of SLA samples was; Padiyathalawa: 33.40 ± 0.17, Buththala: 43.39 ± 0.41, Gampaha: 41.13 ± 0.61, Bibila: 42.31 ± 0.23 and Colombo: 34.12 ± 0.01. Gallic acid content (% w/w) of SLA samples was; Padiyathalawa: 0.49 ± 0.01, Buththala: 0.98 ± 0.01, Gampaha: 1.03 ± 0.02, Bibila: 0.83 ± 0.02 and Colombo: 1.86 ± 0.04. Gallic acid/ellagic acid ratio (% w/w) of SLA samples; Padiyathalawa: 0.15 ± 0.0038, Buththala: 0.18 ± 0.0009, Gampaha: 0.16 ± 0.0003, Bibila: 0.16 ± 0.0041 and Colombo: 0.68 ± 0.0040. Total tannin content, gallic acid content and gallic acid/ellagic acid ratio vary in different batches of commercial samples. Mean of total tannin content (% w/w) of SLC was 49.14 ± 6.09 and INC is 42.79 ± 0.76. Mean of gallic acid content (% w/w) of SLC was 1.13 ± 0.28 and INC is 2.25 ± 0.69. Gallic acid/ellagic acid ratio (% w/w) of SLC was 0.30 ± 0.07 and INC is 0.43 ± 0.05. Chemical composition and quality of T. chebula. dried fruit depend on the geographical location, maturity stage, growth condition and raw material processing condition.
Lemongrass Oil Containing Chitosan Microcapsules by Ionotropic Gelation
(Asian Journal of Chemistry, 2022) Paragodaarachchi, Y.L.; Wickramarachchi, S.R.
Ionotropic gelation using sodium tripolyphosphate (STPP) as the crosslinker was successfully used to formulate lemongrass oil containing chitosan microcapsules. Formation of oil in aqueous chitosan polymer solution was followed by crosslinking with STPP. Optimum formulation for the synthesis of microcapsules was found varying the amounts of lemongrass oil (1-3 g), chitosan solution (1-2%) and STPP (0.5-1.0 g). Microcapsules were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and stage microscope. Encapsulation efficiency, oil content, oil load and release rates were determined by UV-visible spectroscopy. The SEM images indicated that the oil loaded capsules are spherical in shape and possess a smooth surface and their size varied between 100-1000 nm. FTIR spectra confirmed successful encapsulation of lemongrass oil within chitosan. At polymer: 1 g, oil: 3 g and crosslinker: 0.5 g gave microcapsules with higher stability and steady controlled release.
Synthesis of Annona glabra Mediated Silver Nanoparticles, their Photocatalysis and Toxicity on Daphnia magna
(Asian Journal of Chemistry, 2023) Wickramarachchi, S.R.; Paragodaarachchi, Y.L.; De silva, C.R.; Perera, A.D.L.C.; Amarasinghe5, I.D.
This work reports the synthesis of silver nanoparticles (AgNPs) using the leaf extract of Annona glabra as a green synthetic route and assessment of its photocatalytic property using methelyne blue as a model dye and toxic effect against an aquatic model, Daphnia magna. Leaf extract prepared at 100 oC, 1% plant extract, 1 mM of AgNO3, 3 h incubation time were optimized for the synthesis of AgNPs. Surface plasmon resonance peak of AgNPs laid around 419 nm. Spherical nanoparticles were in the size ranges 50-80 and 110-195 nm. Biomolecules were present as capping agents on AgNPs. AgNPs have cubic face centered lattice structure and the average particle size as calculated using Debye-Scherrer formula is 55 nm. Green synthesized AgNPs reduced the absorbance of methelyne blue dye by 89% in 3 h showing prominent photocatalytic activity. The EC50 of AgNPs was found to be 1.78 ± 0.20 mg/L against Daphnia magna showing a lower toxicity than silver ions.