Chemistry

Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/3748

Browse

Start date: 2000End date: 2009Has files: No

Search Results

Now showing 1 - 10 of 28
  • No Thumbnail Available
    Item
    Bioactivity of leaf volatiles of Azadirachta indica A. Juss. and Murraya koenigii Spreng. against Sitophilus oryzae L.(Coleoptera: Curculionidae)
    (National Science Foundation of Sri Lanka., 2002) Paranagama, P.A.; Abeysekera, K.H.T.; Nugaliyadde, L.; Abeywickrama, K.
    Repellent activity, fumigant and contact toxicities of leaf volatiles of Azadirachta indica A. Juss. and Murraya koengii Spreng. were evaluated against Sitophilus oryzae L. In the dual choice repellency test with A indica leaf volatiles, significantly higher number of insects was repelled at doses above 100 mg, whereas volatiles of At. koenigii attracted insects at 25 mg dose and repelled at 300 mg dose. In the fumigant toxicity test 100% mortality was observed at the concentration of 32.5 mg/ml, 3 days after the treatment with 2 volatiles separately. The L C n values for fumigant toxicities were 13.5 and 22.5 mg/ml for A. indica and At. koenigii volatiles, respectively. In contact toxicity test, 100% mortality was observed immediately after 48 h contact exposure of insects at concentrations of 0375 and 0.125 mg/cm1 of A indica and At. koenigii respectively. The respective L C W values were 0.12 and 0.08 mg/cm1 for A. indica and At. koenigii leaf volatiles.
  • No Thumbnail Available
    Item
    Physicochemical changes of stored cowpea, Vigna unguiculata, treated with selected essential oils to control cowpea bruchid, Callosobruchus maculatus (F.)
    (Journal of Food, Agriculture & Environment., 2006) Rubasinghege, G.R.S.; Paranagama, P.; Abeywickrama, K.
    Cowpea (Vigna unguiculata) seeds were treated with essential oils of C. citratus,C. nardus, C. zeylanicum, M. minutum and a standard pesticide (pirimiphos methyl) as fumigant toxicants. At the end of the four month storage period, physical and chemical properties of cowpea from each storage system were analyzed. Variation of physicochemical properties among treated storage systems was insignificant with one exception; 20±5% of moisture was lost in samples treated with essential oils due to absorption of treated oil. Higher protein, fat and dietary fiber contents were reported from essential oil-treated samples compared to those treated with pirimiphos methyl. With lower toxicity to humans and other mammals and less or no significant variation in physicochemical properties, the selected essential oils can be used as fumigant toxicants against Callosobruchus maculatus (F.).
  • No Thumbnail Available
    Item
    Fungicidal activity of essential oils of Cinnamomum zeylanicum (L.) and Syzygium aromaticum (L.) Merr et LM Perry against crown rot and anthracnose pathogens isolated from banana
    (Blackwell Science Ltd., 2002) Ranasinghe, L.; Jayawardena, B.; Abeywickrama, K.
    Aims: To develop a post-harvest treatment system against post-harvest fungal pathogens of banana using natural products. Methods and Results:Colletotrichum musae was isolated and identified as the causative agent responsible for anthracnose peel blemishes while three fungi, namely Lasiodiplodia theobromae, C. musae and Fusarium proliferatum, were identified as causative agents responsible for crown rot. During the liquid bioassay, cinnamon [Cinnamomum zeylanicum (L.)] leaf, bark and clove [Syzygium aromaticum (L.)] oils were tested against the anthracnose and crown rot pathogens. The test oils were fungistatic and fungicidal against the test pathogens within a range of 0·03−0·11% (v/v). Conclusions: Cinnamon and clove essential oils could be used as antifungal agents to manage post harvest fungal diseases of banana. Significance and Impact of the Study: Cinnamon and clove essential oil could be used as alternative post-harvest treatments on banana. Banana treated with essential oil is chemically safe and acceptable to consumers. Benomyl (Benlate), which is currently used to manage fungal pathogens, can cause adverse health effects and could be replaced with volatile essential oils.
  • No Thumbnail Available
    Item
    Deterrent effects of some Sri Lankan essential oils on oviposition and progeny production of the cowpea bruchid, Callosobruchus maculatus (F.)(Coleoptera; Bruchidae)
    (2003) Paranagama, P.; Adhikari, C.; Abeywickrama, K.P.; Bandara, P.
    Essential oils extracted from five plant materials were tested on oviposition and progeny production of F1 adult of cowpea bruchid, Callosobruchus maculatus on cowpea seeds. All oils tested showed a significant inhibition of oviposition and F1 adult emergence compared to the control during no-choice tests. Cymbopogon citratus and C. nardus showed higher effect on oviposition and F1 adult emergence than the essential oils of Alpinia calcarata, Cinnamomum zeylanicum and Murraya koinigii. In the choice test, the percentage ovipositions in all oils treated samples (except 10 mg of M. koinigii) were significantly lower than that of the control and ethanol treated samples. The percentage eggs deposited decreased with increasing doses of the oils ranging from 10 to 160 mg. The percentage of eggs laid was zero in samples treated with 40 mg of C. nardus or A. calcarata, 80 mg of C. citratus and 160 mg of C. zeylanicum. The essential oils of M. koinigii showed the lowest effect on oviposition when compared to other four essential oils.
  • No Thumbnail Available
    Item
    Cymbopogon citratus (lemongrass) and citral a+ b spray treatments alone or in combination with sodium bicarbonate in controlling crown rot in Embul banana (Musa acuminata AAB)
    (2004) Abeywickrama, K.P.; Kularathna, L.; Sarananda, K.; Abeygunawardena, D.
    The mounting pressure against synthetic fungicidal dips and sprays, restrict their use in controlling crown rot, a major post-harvest disease in banana. Generally regarded as safe (GRAS) compounds have a great potential to be used as alternatives to fungicides. Identification of chemical constituents of Cymbopogon citratus oil revealed the presence of citral as the main component. Cymbopogon citratus and citral with sodium bicarbonate (SBC) was fungicidal against the 3 banana fungal pathogens at 0.10-0.20 % v/v and 0.07-0.08 % v/v respectively. Embul banana sprayed with C. citratus alone or in combination with SBC after induced ripening, indicated a crown rot severity of 25 - 5 0% whereas, citral treatment resulted in a slightly lower disease severity. The physico-chemical parameters tested were not affected by the treatments. Oil/citral, SBC treated bananas and control were ranked good to excellent with respect to odour, flavour, taste and overall acceptability. The low disease severity of crown rot due to spray treatment of citral and SBC highlights the importance in adapting this simple, alternate treatment strategy for quality maintenance.
  • No Thumbnail Available
    Item
    Aflatoxigenic Aspergillus flavus and aflatoxin formation in selected spices during storage
    (2009) Rajasinghe, M.; Abeywickrama, K.P.; Jayasekera, R.
    Proliferation of aflatoxigenic fungi and accumulation of aflatoxins take place during storage of spices at various environmental conditions. The objective of this research was to identify the aflatoxigenic fungal species and their aflatoxin forming potential in selected spices during storage in the laboratory and refrigerator. Dilution series of spice samples namely chilli (Capsicum annum) powder, curry powder, turmeric (Curcurma longa) powder and pepper (Piper nigrum) powder (purchased from two producers) were prepared separately and the frequency of occurrence of aflatoxigenic and other fungi were assessed after plating each on Potato Dextrose Agar and incubating at ambient temperature. Aflatoxin formation of A. flavus was confirmed by growing a pure culture on a SMKY medium and identifying toxins on thin layer chromatographic plates. The presence of aflatoxins in spice samples stored at 30 ± 20C and 40C was also confirmed. Long storage of spices leads to aflatoxin production irrespective of storage temperature hence, it is advisable to consume spices such as chilli powerder, tumeric etc. within a relatively short period to avoid build up of aflatoxins.
  • No Thumbnail Available
    Item
    Interactions of Rh(III)-Dihydrido-Bis(phosphine) Complexes with Semicarbazones
    (Inorganic Chemistry, 2005) Ezhova, M.B.; Patrick, B.O.; Senevirathne, K.N.; James, B.R.; Waller, F.J.; Ford, M.E.
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    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).
  • No Thumbnail Available
    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 chemotherapies