Browsing by Author "Gunaratna, M.J."

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Antifungal activity of fresh fruit extract of Garcinia quaesita against Fusarium proliferatum causing crown rot disease in banana
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Lakmali, G.B.T.; Gunaratna, M.J.
Tropical fruits and vegetables are susceptible to several devastating post-harvest diseases. The crown rot disease of bananas is caused by Fusarium proliferatum, which causes a drastic decrease in consumer compliance and becomes a problem related to consumption. Though it can be controlled by approved natural or commercial fungicides, natural antifungal plant extracts are safer options due to their non-toxicity compared to synthetic fungicides. Garcinia quaesita is an endemic plant in Sri Lanka used as a spice and a medicinal plant. The poisoned food technique was used to determine the percentage inhibition of mycelial growth and the minimum inhibitory concentration of the plant extract on the test pathogens. Hence, the main objective of this study was to determine the antifungal activity of hydroethanolic extract (1:1 v/v) of fresh fruit of G. quaesita at different concentrations against F. proliferatum using the standard food poisoning method. The same procedure was carried out with a positive control (50% Captan) and a negative control (dimethyl sulfoxide). A round disk of 6 mm diameter was taken from a 7-day-old culture with grown mycelium and inoculated in the center of the PDA media plate with the treatments. The zone of inhibition (mm) and the percentage of growth inhibition were determined using three different concentrations of G. quaesita fruit extract (5000 ppm, 2000 ppm, 1000 ppm) with three replicates. All three concentrations of the plant extract significantly inhibited mycelial growth compared to the negative control. G. quaesita fruit showed 47.39% growth inhibition of F. proliferatum. The minimum inhibitory concentration for G. quaesita extract was 5000 ppm, which was significantly different as determined by Tukey's mean comparison test (p ≤ 0.05), with a zone of inhibition of 20 mm. The extract of G. quaesita shows promise as an alternative safe, ecofriendly, cheap, and easily degradable fungicide derived from plants. It also has great potential for providing new fungicides that are highly beneficial.
Synthesis and evaluation of 2,3-diphenylquinazolin-4(3H)-one as a corrosion inhibitor for mild steel in acidic media
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Senanayaka, P.M.A.; Madujith, E.A.D.N,; Gunaratna, M.J.; Madhu, H.M.L.U.
Corrosion is an oxidation-reduction process where a metal is oxidized to a more consistent form such as its oxide, hydroxide, or sulfide by atmospheric oxygen. Corrosion is an excessively costly issue that is reported to cause significant economic damage globally each year. Therefore, the discovery of novel corrosion inhibitors is highly desirable. Corrosion inhibitor molecules are first absorbed into the metal surface by electrostatic interactions. Then coordinate covalent bonding occurs by share or transferring electrons from the inhibitor to the metallic surface. The inhibitor adsorption on to the surface of the metal hinders its active sites where oxidation occurs, and results in reduced corrosion. The adsorption process depends on the inhibitor structure, surface morphology, temperature, pressure as well as the pH. Compounds that possess heteroatoms such as nitrogen, oxygen, phosphorous, and sulfur atoms and multiple bonds in their structure have better corrosion properties as they have higher basicity and higher electron density. Quinazolinone derivatives have various biological, chemical, and physical activities, especially we focused on anticorrosive activities. Quinazolinone derivatives are widely employed as excellent corrosion inhibitors as well. They are capable of decreasing the corrosion process and protect steel in acidic environments. In this research, a quinazolinone derivative, 2,3-diphenylquinazolin-4(3H)-one was synthesized using anthranilic acid via intermediate, 2-phenyl-4H-benzo[d][1,3]oxazin-4-one and aniline and confirmed the structure using infrared (IR), 1H-NMR, and 13C-NMR analysis. The corrosion inhibitory activity of the 2,3-diphenylquinazolin-4(3H)-one on a mild steel, JIS 3113SPHE in 0.5 M hydrochloric acid solution was determined by two different corrosion analysis methods namely, the weight-loss method and the polarization method. Mass loss dependence on the content of inhibitor in the corroding medium, temperature of the corroding medium, and the pH of the solution were measured. Corrosion inhibition of 2,3- diphenylquinazolin-4(3H)-one was analyzed using different concentrations (1×10-4 M - 5×10-4 M). The compound exhibited maximum inhibition efficiency of 80-84 % at 5×10-4 M. When increasing the temperature, mass loss and the corrosion rate was increased. Though the corrosion rates increase gradually as temperature rises, even at 333 K, the corrosion rate of 2,3- diphenylquinazolin-4(3H)-one at 5×10-4 M was only 2.3 x 10-3 gcm-2hr-1 . The mass loss was decreased as the pH of the medium was increased. The results of the potentiodynamic polarization method suggest that 2,3-diphenylquinazolin-4(3H)-one act as a mixed type corrosion inhibitor in the acidic medium. According to the experimental results 2,3-diphenylquinazolin-4(3H)-one is an efficient corrosion inhibitor.
Synthesis, In Silico Studies, and Evaluation of Syn and Anti Isomers of N-Substituted Indole-3-carbaldehyde Oxime Derivatives as Urease Inhibitors against Helicobacter pylori
(molecules, 2021, 2021) Kalatuwawege, I.P.; Gunaratna, M.J.; Udukala, D.N.
• Gastrointestinal tract infection caused by Helicobacter pylori is a common virulent disease found worldwide, and the infection rate is much higher in developing countries than in developed ones. In the pathogenesis of H. pylori in the gastrointestinal tract, the secretion of the urease enzyme plays a major role. Therefore, inhibition of urease is a better approach against H. pylori infection. In the present study, a series of syn and anti isomers of N-substituted indole-3-carbaldehyde oxime derivatives was synthesized via Schiff base reaction of appropriate carbaldehyde derivatives with hydroxylamine hydrochloride. The in vitro urease inhibitory activities of those derivatives were evaluated against that of Macrotyloma uniflorum urease using the modified Berthelot reaction. Out of the tested compounds, compound 8 (IC50 = 0.0516 0.0035 mM) and compound 9 (IC50 = 0.0345 0.0008 mM) were identified as the derivatives with potent urease inhibitory activity with compared to thiourea (IC50 = 0.2387 0.0048 mM). Additionally, in silico studies for all oxime compounds were performed to investigate the binding interactions with the active site of the urease enzyme compared to thiourea. Furthermore, the drug-likeness of the synthesized oxime compounds was also predicted.