27 research outputs found
Asymmetric ligand transformation reactions promoted by cyclometallated complexes
No full textComplex bis(u-chloro)-bis{(R)-1-(dimethylamino)ethyl] naphtyl-C2,N} palladium (II) was found to successfully undergo insertion reactions at the palladium-carbon with the diphenylarsinoprop-1-yne ligand at room temperature which leads to the formation of a new 7-membered metallacyce in the inserted product. This reaction was also carried out on the platinum (II) metal template containing the naphythylamine moiety. The monoarsine precursor complexes has shown to undergo a C-H bond activation followed by a C-C bond coupling at room temperature. This reaction can only be initiated with the presence of a platinum (II) metal. The chiral organopalladium template was used to promote asymmetric hydroarsination reaction between diphenylarsine and various functionalised alkenyl phosphines with hydroxy, methoxy, dimethylamino, ester and ketone as functional groups. The asymmetric Diels-Alder reaction promoted by chiral platinum (II) metal template between DMPP and phenyldi[(Z)]prop-1-enyl]phosphine oxide showed poor stereoselectivity with two isomers (1:1) being formed. The cycloaddition reaction between DMPP and phenyldi[(Z)]prop-1-enyl]phosphine sulphide similarly showed poor selectivity.DOCTOR OF PHILOSOPHY (SPMS
Chemical Constituents and Biological Activities From Garcinia Maingayi and Garcinia Parvifolia
No full textIn this present study, the stem bark of Garcinia maingayi and Garcinia parvifolia were
investigated and resulted in the isolation of nine compounds. There are no previous
reports on chemical components and biological activities from Garcinia maingayi. The
structures of these compounds were elucidated by using spectroscopic experiments
namely NMR, MS, IR and UV.
Being the first report on Garcinia maingayi, detailed chemical studies have afforded
two triterpenoids, stigmasterol and sitosterol, two xanthones, 1,3,7-trihydroxy-2-(3-
methylbut-2-enyl)-xanthone and 1,3,6,8-tetrahydroxyxanthone, one benzophenone,
isoxanthochymol, and one benzoic acid derivative methyl 3,4-dihydroxybenzoate. The
findings are significant as it contributes to the knowledge of the chemotaxonomy on
Garcinia species and all these compounds are new to the species.
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Meanwhile investigations on Garcinia parvifolia have afforded one triterpenoid, α-
amyrin and two xanthones, cowanin and rubraxanthone. Acetylation reaction was
carried out on rubraxanthone to yield triacetate rubraxanthone.
This is also the first report on cytotoxic and larvicidal activities of Garcinia maingayi,
Garcinia parvifolia and rubraxanthone. Cytotoxic tests were performed using HL-60
and CEM-SS cell lines. The crude hexane and chloroform extracts of Garcinia
maingayi were active against HL-60 cell line with IC50 values of less than 30 μg/ml. The
crude hexane and acetone extracts of Garcinia parvifolia were found to be active
against CEM-SS cell line with IC50 values of less than 30 μg/ml meanwhile, the crude
chloroform extract gave a significant activity with an IC50 value of 6.5 μg/ml.
The antimicrobial assay was carried out against four pathogenic bacteria, Methicillin
resistant Staphylococcus aures, Pseudomonas aeruginosa, Staphylococcus typhimurium
and Bacillus subtilis. Most of the crude extracts tested against these microbes gave only
moderate or weak activity. The antifungal activity testing of the plant extracts were
carried out against the fungi Candida albican, Aspergillus ochraceaus, Sacchoromyces
cerevisiae and Candida lypolytica. No activity was observed for all the crude extracts
The larvicidal test was carried out towards the larvae of Aedes aegypti. All the crude
extracts of Garcinia maingayi were weakly active against the larvae with LC50 values of
more than 150 μg/ml. The crude extracts of Garcinia parvifolia showed moderate
activities against the larvae by giving LC50 values of less than 100 μg/ml. The pure
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rubraxanthone showed a strong activity against the larvae with a LC50 value of 15.49
μg/ml
Secondary metabolites from two garcinia species and their biological activities.
No full textDetail chemical studies on Garcinia maingayi have yielded one xanthone, 1,3,7-trihydroxy-2-(3-methylbut-2-enyl)xanthone, one benzophenone, isoxanthochymol, one benzoic acid derivative 3,4-dihydroxy-methylbenzoate and two triterpenoids, stigmasterol and sitosterol. Meanwhile, investigations on Garcinia parvifolia have afforded one triterpenoid, α-amyrin and two xanthones, cowanin and rubraxanthone. Their structures were derived based on spectroscopic evidence, mainly 1D and 2D NMR spectroscopy. Acetylation reaction was carried out on rubraxanthone to yield triacetate rubraxanthone. It was found that the pure rubraxanthone was strongly active against the larvae of Aedes aegypti with LC50 value of 15.49 μg/mL and HL-60 cell line with an IC50 value of 7.5 μg/mL
Chemical constituents from Garcinia maingayi and Garcinia parvifolia (Guttiferae) and their biological activities
No full textDetail chemical studies on Garcinia maingayi have yielded one xanthone, 1,3,7-trihydroxy- 2-(3-methylbut-2-enyl)-xanthone, one benzophenone, isoxanthochymol, one benzoic acid derivative 3,4-dihydroxy-methylbenzoate and two triterpenoids, stigmasterol and sitosterol. Meanwhile, investigations on Garcinia parvifolia have afforded one triterpenoid, ?-amyrin and two xanthones, cowanin and rubraxanthone. Their structures were derived based on spectroscopic evidence, mainly ID and 2D NMR spectroscopy. Acetylation reaction was carried out on rubraxanthone to yield triacetate rubraxanthone. It was found that the pure rubraxanthone was strongly active against the larvae of Aedes aegypti with LC50 value of 15.49 μg/ ml and HL-60 cells line with an IC50 value of 7.5 μg/ ml
Burkholderia paludis sp. nov., an antibiotic-siderophore producing novel Burkholderia cepacia complex species, isolated from malaysian tropical peat swamp soil
No full textA novel Gram negative rod-shaped bacterium, designated strain MSh1T, was isolated from Southeast Pahang tropical peat swamp forest soil in Malaysia and characterized using a polyphasic taxonomy approach. The predominant cellular fatty acids (> 10.0%) were C16:0 (31.7%), C17:0 cyclo (26.6%), and C19:0 cyclo ω8c (16.1%). The polar lipids detected were phosphatidylglycerol, phosphatidylethanolamine, and diphosphatidylglycerol. The predominant ubiquinone was Q-8. This revealed that strain MSh1T belongs to the genus Burkholderia. The type strain MSh1T can be differentiated from other Burkholderia cepacia complex (Bcc) species by phylogenetic analysis of 16S rRNA gene sequence, multilocus sequence analysis (MLSA), average nucleotide identity (ANI) and biochemical tests. DNA-DNA relatedness values between strain MSh1T and closely related type strains were below the 70% threshold value. Based on this polyphasic study of MSh1T, it can be concluded that this strain represents a novel species within the Bcc, for which the name Burkholderia paludis sp. nov. is proposed. The type strain is MSh1T (= DSM 100703T = MCCC 1K01245T). The dichloromethane extract of MSh1T exhibited antimicrobial activity against four Gram positive bacteria (Enterococcus faecalis ATCC 29212, E. faecalis ATCC 700802, Staphylococcus aureus ATCC 29213, S. aureus ATCC 700699) and a Gram negative bacteria (Escherichia coli ATCC 25922). Further purification work has led to the isolation of Compound 1, pyochelin. Pyochelin demonstrated antimicrobial activity against four S. aureus strains and three E. faecalis strains with MIC-values of 3.13 μg/ml and 6.26 μg/ml, respectively. SEM analysis showed that the cellular morphology of E. faecalis ATCC 700802 was not affected by pyochelin; suggesting that it might target the intracellular components. Pyochelin, a siderophore with antimicrobial activity might be useful in treating bacterial infections caused by S. aureus and E. faecalis, however further work has to be done. © 2016 Ong, Aw, Lee, Yule, Cheow and Lee
The role of reactive oxygen species in the antimicrobial activity of pyochelin
No full textThe increase in prevalence of antimicrobial-resistant bacteria (ARB) is currently a serious threat, thus there is a need for new antimicrobial compounds to combat infections caused by these ARB. An antimicrobial-producing bacterium, Burkholderia paludis was recently isolated and was able to produce a type of siderophore with antimicrobial properties, later identified as pyochelin. The chelating ability of pyochelin has been well-characterized but not for its antimicrobial characteristics. It was found that pyochelin had MIC values (MBC values) of 3.13 µg/mL (6.26 µg/mL) and 6.26 µg/mL (25.00 µg/mL) against three Enterococcus strains and four Staphylococcus strains. Pyochelin was able to inhibit E. faecalis ATCC 700802 (a vancomycin-resistant strain) in a time and dose dependent manner via killing kinetics assay. It was demonstrated that pyochelin enhanced the production of intracellular reactive oxygen species (ROS) over time, which subsequently caused a significant increase in malondialdehyde (MDA) production (a marker for lipid peroxidation) and ultimately led to cell death by disrupting the integrity of the bacterial membrane (validated via BacLight assay). This study has revealed the mechanism of action of pyochelin as an antimicrobial agent for the first time and has shown that pyochelin might be able to combat infections caused by E. faecalis in the future
Physical properties, sensory profile and storage stability of compound chocolates made with cocoa butter replacer consisting of mango kernel fat and rice bran oil
No full textThis study analyzed the physical properties of a dark compound chocolate made with a cocoa butter replacer (CBR). The CBR was made up of enzymatically produced mango kernel fat and rice bran oil. The control (dark chocolate) was produced using cocoa butter. For dark compound chocolates, 5 %, 20 %, and 50 % CBR were used, and all the samples were stored at 4 °C, 20 °C, and 33 °C for 12 weeks. Physical, sensory, and storage stability were assessed. The control and 5 % CBR chocolate demonstrated similar melting peaks (at 33 °C), color, and hardness (11–14 N at 20 °C) profiles. However, 20 % and 50 % CBRs compound chocolates had considerably lower melting peaks (about 31 °C), enthalpies (15–20 J/g), and hardness (3–6 N at 20 °C). Bloom formation started after week 6 at 20 °C for control, 5 %, and 20 % CBR chocolates. The earliest bloom formation was observed for all the chocolates stored at 33 °C, followed by chocolates stored at 20 °C. The chocolates were stable at 4 °C throughout the storage period of 12 weeks. Besides some of the physical properties, the overall sensory acceptance, mouthfeel, and taste were similar to the control chocolate with 20 % CBR compound chocolate.</p
Co-cultivation, metal stress and molasses:strategies to improving exopolymeric yield and metal removal efficacy
No full textThis study investigated and compared several improvement strategies to increase the yield and quality of exopolymeric substances (EPS) from Bacillus cereus. This includes co-culturing of B. cereus with Trichoderma asperellum, cultivation in media with metal (Zn) stress and supplementation with molasses. EPS is subsequently extracted from these different cultures and subjected to characterization and metal removal tests in single-metal systems (Cu, Pb, Zn, Cd, Cr). Results indicate that co-cultivation of B. cereus and T. asperellum produced EPS which have attributes differing from single cultivation. These changes were detected via functional group changes using Fourier-Transform Infrared Spectroscopy, as well as the increase in carbohydrate and protein content. However, the interaction of these two microbes were merely additive and did not result in improved EPS yield nor the subsequent metal removal efficacy in comparison to single cultivation (control). By contrast, supplementation of Zn (metal stress with 50 mg L− 1 Zn) improved EPS quality and metal removal, but decreased EPS yield. The application of 1% molasses was the only strategy demonstrating high yield and efficient metal removal. EPS quality and yield (0.45 mg mL− 1) and metal removal efficacy (Cu: 58%, Pb: 98%, Zn: 83%, Cd: 73%, Cr: 96%) were improved significantly. This study showed that among the three improvement strategies (co-cultivation, metal stress, molasses), supplementation with molasses was the most effective as it improved both yield and quality of EPS significantly, suggesting that this approach may be adopted for future production of bulk EPS for up-scaling of wastewater treatment.</p
Characterization of the physicochemical properties of mango (<i>Mangifera indica</i> L., Dragon variety) kernel fat extracted via supercritical carbon dioxide and Soxhlet techniques
No full textMango kernel fat (MKF) that is high in monounsaturated triacylglycerols is a potential cocoa butter alternative. This study aimed to investigate the yield and physicochemical properties of Dragon variety (Mangifera indica L.) MKF is extracted by supercritical carbon dioxide and Soxhlet. The fatty acid constituent, triacylglycerol constituent, melting and crystallization behavior, and solid fat content (SFC) were analyzed using gas chromatography, high-pressure liquid chromatography, and differential scanning calorimetry, respectively. The yield was 6.59%–9.65% depending on temperature, pressure, and time. Physicochemical properties for both techniques were comparable. The MKF contained higher levels of stearic acid (primarily StOSt, 1,3-distearoyl-2-oleoyl-glycerol) with extraction conditions of 72°C, 30 MPa, and 3 h. Melting and crystallization peaks ranged from 9.84 to 39.13°C and 16.69 to −11.23°C, respectively. SFC was zero between 40 and 45°C. The high StOSt content can aid in fractionation and demonstrates potential in making heat-resistant fat for use in confectioneries. Novelty impact statement: The current study investigated the effect of different extraction techniques and conditions on the percentages of fat yield of the Dragon variety mango kernel (Mangifera indica L.), a by-product of the fruit industry, which has not been previously studied. The highest percentage of fat yield was 9.65% ± 1.1 at 60°C, 30 MPa and 4 h where the yield was comparable and yet was achieved at more energy-efficient extraction conditions than in previous studies. The current study provides a better understanding of the physicochemical properties of Dragon variety mango kernel fat for various food applications.</p
Characterization of Cocoa Butter Replacer Developed from Agricultural Waste of Mango Kernel and Rice Bran
No full textThe unique physicochemical properties of cocoa butter (CB) provide the desired physical properties in chocolate. Due to its high demand, increasing price, and limited supply, people are looking for cocoa butter alternatives (CBAs). In this study, CBA was prepared using enzymatic acidolysis on mango kernel fat stearin with rice bran oil blend. Reaction parameters (time (4-8 h), temperature (50-70°C), and enzyme load (6-10%, w/w)) were optimized using response surface methodology to produce similar triacylglycerol (TAG) composition as CB, and the properties of different proportions of CBAs with CB were assessed. Triacylglycerol content, melting behavior, solid fat content, crystal morphology, and polymorphism were investigated by high-performance liquid chromatography, differential scanning calorimetry, pulse nuclear magnetic resonance, polarized light microscopy, and X-ray diffraction, respectively. The optimum reaction condition to produce comparable percentages of monounsaturated TAGs in the final product was 8 h time, 8% enzyme load, and 50°C. After blending of CBA with CB in different proportions, no significant differences in terms of polymorphism, melting profile, and solid fat content were observed up to 20% CBA replacement. However, the TAG profile was similar up to 10% replacement of CB with CBA. In summary, the enzymatically produced CBA can potentially be used as a cocoa butter replacer up to 20% in the confectionery industry.</p
