Chemistry
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Item 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.Item Highly stable CuO incorporated TiO2 catalyst for photocatalytic hydrogen production from H2O(Journal of Photochemical & Photobiological Sciences, 2005) Bandara, J.; Udawatta, C.P.K.; Rajapakse, C.S.K.A CuO incorporated TiO2 catalyst was found to be an active photocatalyst for the reduction of H2O under sacrificial conditions. The catalytic activity originates from the photogeneration of excited electrons in the conduction bands of both TiO2 and CuO resulting in a build-up of excess electrons in the conduction band of CuO. Consequently, the accumulation of excess electrons in CuO causes a negative shift in the Fermi level of CuO. The efficient interparticle charge transfer leads to a higher catalytic activity and the formation of highly reduced states of TiO2/CuO, which are stable even under oxygen saturated condition. Negative shift in the Fermi level of CuO of the catalyst TiO2/CuO gains the required overvoltage necessary for efficient water reduction reaction. The function of CuO is to help the charge separation and to act as a water reduction site. The amount of CuO and crystalline structure were found to be crucial for the catalytic activity and the optimum CuO loading was ca. 5?10% (w/w).Item Synthesis, Characterization, and in vitro Antimalarial and Antitumor Activity of New Ruthenium(II) Complexes of Chloroquine(Journal of Inorganic Chemistry, 2009) Rajapakse, C.S.K.; Martínez, A.; Naoulou, B.; Jarzecki, A.A.; Suárez, L.; Deregnaucourt, C.; Sinou, V.; Schrével, J.; Musi, E.; Ambrosini, G.; Schwartz, G.K.; Sánchez-Delgado, R.A.The new RuII chloroquine complexes [Ru(?6-arene)(CQ)Cl2] (CQ = chloroquine; arene = p-cymene 1, benzene 2), [Ru(?6-p-cymene)(CQ)(H2O)2][BF4]2 (3), [Ru(?6-p-cymene)(CQ)(en)][PF6]2 (en = ethylenediamine) (4), and [Ru(?6-p-cymene)(?6-CQDP)][BF4]2 (5, CQDP = chloroquine diphosphate) have been synthesized and characterized by use of a combination of NMR and FTIR spectroscopy with DFT calculations. Each complex is formed as a single coordination isomer: In 1?4, chloroquine binds to ruthenium in the ?1-N mode through the quinoline nitrogen atom, whereas in 5 an unprecedented ?6 bonding through the carbocyclic ring is observed. 1, 2, 3, and 5 are active against CQ-resistant (Dd2, K1, and W2) and CQ-sensitive (FcB1, PFB, F32, and 3D7) malaria parasites (Plasmodium falciparum); importantly, the potency of these complexes against resistant parasites is consistently higher than that of the standard drug chloroquine diphosphate. 1 and 5 also inhibit the growth of colon cancer cells, independently of the p53 status and of liposarcoma tumor cell lines with the latter showing increased sensitivity, especially to 1 (IC50 8 ?M); this is significant because this type of tumor does not respond to currently employed chemotherapiesItem The mechanism of antimalarial action of the ruthenium(II)?chloroquine complex [RuCl2(CQ)]2(Journal of Biological Inorganic Chemistry, 2008) Martínez, A.; Rajapakse, C.S.K.; Naoulou, B.; Kopkalli, Y.; Davenport, L.; Sánchez-Delgado, R.A.The mechanism of antimalarial action of the ruthenium?chloroquine complex [RuCl2(CQ)]2 (1), previously shown by us to be active in vitro against CQ-resistant strains of Plasmodium falciparum and in vivo against P. berghei, has been investigated. The complex is rapidly hydrolyzed in aqueous solution to [RuCl(OH2)3(CQ)]2[Cl]2, which is probably the active species. This compound binds to hematin in solution and inhibits aggregation to ?-hematin at pH ? 5 to a slightly lower extent than chloroquine diphosphate; more importantly, the heme aggregation inhibition activity of complex 1 is significantly higher than that of CQ when measured at the interface of n-octanol?aqueous acetate buffer mixtures under acidic conditions modeling the food vacuole of the parasite. Partition coefficient measurements confirmed that complex 1 is considerably more lipophilic than CQ in n-octanol?water mixtures at pH ? 5. This suggests that the principal target of complex 1 is the heme aggregation process, which has recently been reported to be fast and spontaneous at or near water?lipid interfaces. The enhanced antimalarial activity of complex 1 is thus probably due to a higher effective concentration of the drug at or near the interface compared with that of CQ, which accumulates strongly in the aqueous regions of the vacuole under those conditions. Furthermore, the activity of complex 1 against CQ-resistant strains of P. falciparum is probably related to its greater lipophilicity, in line with previous reports indicating a lowered ability of the mutated transmembrane transporter PfCRT to promote the efflux of highly lipophilic drugs. The metal complex also interacts with DNA by intercalation, to a comparable extent and in a similar manner to uncomplexed CQ and therefore DNA binding does not appear to be an important part of the mechanism of antimalarial action in this case.Item Arene–Ru(II)–chloroquine complexes interact with DNA, induce apoptosis on human lymphoid cell lines and display low toxicity to normal mammalian cells(Journal of Inorganic Biochemistry, 2010) Martínez, A.; Rajapakse, C.S.K.; Sánchez-Delgado, R.A.; Varela-Ramirez, A.; Lema, C.; Aguilera, R.J.The complexes [Ru(?6-p-cymene)(CQ)Cl2] (1), [Ru(?6-benzene)(CQ)Cl2] (2), [Ru(?6-p-cymene)(CQ)(H2O)2][BF4]2 (3), [Ru(?6-p-cymene)(en)(CQ)][PF6]2 (4), [Ru(?6-p-cymene)(?6-CQDP)][BF4]2 (5) (CQ = chloroquine base; CQDP = chloroquine diphosphate; en = ethylenediamine) interact with DNA to a comparable extent to that of CQ and in analogous intercalative manner with no evidence for any direct contribution of the metal, as shown by spectrophotometric and fluorimetric titrations, thermal denaturation measurements, circular dichroism spectroscopy and electrophoresis mobility shift assays. Complexes 1?5 induced cytotoxicity in Jurkat and SUP-T1 cancer cells primarily via apoptosis. Despite the similarities in the DNA binding behavior of complexes 1?5 with those of CQ the antitumor properties of the metal drugs do not correlate with those of CQ, indicating that DNA is not the principal target in the mechanism of cytotoxicity of these compounds. Importantly, the Ru?CQ complexes are generally less toxic toward normal mouse splenocytes and human foreskin fibroblast cells than the standard antimalarial drug CQDP and therefore this type of compound shows promise for drug development.Item The antimalarial activity of Ru?chloroquine complexes against resistant Plasmodium falciparum is related to lipophilicity, basicity, and heme aggregation inhibition ability near water/n-octanol interfaces(Journal of Biological Inorganic Chemistry, 2009) Martínez, A.; Rajapakse, C.S.K.; Jalloh, D.; Dautriche, C.; Sánchez-Delgado, R.A.We have measured water/n-octanol partition coefficients, pK a values, heme binding constants, and heme aggregation inhibition activity of a series of ruthenium??-arene?chloroquine (CQ) complexes recently reported to be active against CQ-resistant strains of Plasmodium falciparum. Measurements of heme aggregation inhibition activity of the metal complexes near water/n-octanol interfaces qualitatively predict their superior antiplasmodial action against resistant parasites, in relation to CQ; we conclude that this modified method may be a better predictor of antimalarial potency than standard tests in aqueous acidic buffer. Some interesting tendencies emerge from our data, indicating that the antiplasmodial activity is related to a balance of effects associated with the lipophilicity, basicity, and structural details of the compounds studied.