Displaying publications 21 - 40 of 185 in total

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  1. Fulltext Crystallization and preliminary X-ray analysis of recombinant Glomerella cingulata cutinase
    Nyon MP, Rice DW, Berrisford JM, Huang H, Moir AJ, Craven CJ, et al.
    Acta Crystallogr Sect F Struct Biol Cryst Commun, 2008 Jun 01;64(Pt 6):504-8.
    PMID: 18540061 DOI: 10.1107/S1744309108012086
    Cutinase catalyzes the hydrolysis of water-soluble esters and long-chain triglycerides and belongs to the family of serine hydrolases. The enzyme is thought to represent an evolutionary link between the esterase and lipase families and has potential applications in a wide range of industrial hydrolytic processes, for which an understanding of the molecular basis of its substrate specificity is critical. Glomerella cingulata cutinase has been cloned and the protein has been overexpressed in Escherichia coli, purified and subsequently crystallized in a wide range of different crystal forms in the presence and absence of inhibitors. The best crystals are those of the apo cutinase, which diffract to beyond 1.6 A resolution and belong to space group P4(1)2(1)2 or P4(3)2(1)2. Crystals of cutinase with the inhibitors PETFP or E600 belong to space groups P2(1)2(1)2(1) and P2(1), respectively, and diffract to approximately 2.5 A resolution. All of the crystals are suitable for structural studies, which are currently ongoing.
    Matched MeSH terms: Crystallization
  2. Sintering behaviour of hydroxyapatite bioceramics
    Ramesh S, Tan CY, Aw KL, Yeo WH, Hamdi M, Sopyan I, et al.
    Med J Malaysia, 2008 Jul;63 Suppl A:89-90.
    PMID: 19024998
    The sintering behaviour of a commercial HA and synthesized HA was investigated over the temperature range of 700 degrees C to 1400 degrees C in terms of phase stability, bulk density, Young's modulus and Vickers hardness. In the present research, a wet chemical precipitation reaction was successfully employed to synthesize a submicron, highly crystalline, high purity and single phase stoichiometric HA powder that is highly sinteractive particularly at low temperature regimes below 1100 degrees C. It has been revealed that the sinterability of the synthesized HA was significantly greater than that of the commercial HA. The temperature for the onset of sintering and the temperature required to achieve densities above 98% of theoretical value were approximately 150 degrees C lower for the synthesized HA than the equivalent commercial HA. Nevertheless, decomposition of HA phase upon sintering was not observed in the present work for both powders.
    Matched MeSH terms: Crystallization
  3. Synthesis and characterization of magnesium doped biphasic calcium phosphate
    Toibah AR, Sopyan I, Mel M
    Med J Malaysia, 2008 Jul;63 Suppl A:83-4.
    PMID: 19024995
    The incorporation of magnesium ions into the calcium phosphate structure is of great interest for the development of artificial bone implants. This paper investigates the preparation of magnesium-doped biphasic calcium phosphate (Mg-BCP) via sol gel method at various concentrations of added Mg. The effect of calcinations temperature (ranging from 500 degrees C to 900 degrees C) and concentrations of Mg incorporated into BCP has been studied by the aid of XRD, TGA and infrared spectroscopy (IR) in transmittance mode analysis. The study indicated that the powder was pure BCP and Mg-BCP with 100% purity and high crystallinity. The results also indicated that beta-tricalcium phosphate (beta-TCP) phase can be observed when the powder was calcined at 800 degrees C and above.
    Matched MeSH terms: Crystallization
  4. A novel hydrothermal process to produce hydroxyapatite powders
    Sopyan I, Rosli A, Raihana MF
    Med J Malaysia, 2008 Jul;63 Suppl A:81-2.
    PMID: 19024994
    A novel hydrothermal process has been developed various hydroxyapatite(HA) powder. The HA powder was investigated in different calcination temperatures over the range of 200 degrees C-800 degrees C. TG/DTA and XRD analysis revealed that at temperatures of 700-800 degrees C the decomposition processes and phase changes took place. It is due to the appearance of TCP phase substituting the HA phase. FESEM observation showed that the produced hydroxyapatite powder was extraordinarily fine with nanosize primary particles and almost evenly spherical in shaped. Its high purity proved that the powder fulfills medical requirement.
    Matched MeSH terms: Crystallization
  5. Effect of powder calcination on the sintering of hydroxyapatite
    Tan CY, Ramesh S, Aw KL, Yeo WH, Hamdi M, Sopyan I
    Med J Malaysia, 2008 Jul;63 Suppl A:87-8.
    PMID: 19024997
    The sintering behaviour of synthesized HA powder that was calcined at various temperatures ranging from 700 degrees C to 1000 degrees C was investigated in terms of phase stability, bulk density, Young's modulus and Vickers hardness. The calcination treatment resulted in higher crystallinity of the starting HA powder. Decomposition of HA phase to form secondary phases was not observed in all the calcined powders. The results also indicated that powder calcination (up to 900 degrees C) prior to sintering has negligible effect on the sinterability of the HA compacts. However, powder calcined at 1000 degrees C was found to be detrimental to the properties of sintered hydroxyapatite bioceramics.
    Matched MeSH terms: Crystallization
  6. Influence of manganese doping into HA powders on the properties of its dense bodies
    Natasha AN, Sopyan I, Mel M, Ramesh S
    Med J Malaysia, 2008 Jul;63 Suppl A:85-6.
    PMID: 19024996
    The effect of Manganese (Mn) addition on the Vickers hardness and relative density of nanocrystalline hydroxyapatite (HA) dense bodies were studied. The starting Mn doped HA powders was synthesized via sol-gel method with Mn concentration varies from 2 mol% up to 15 mol% Mn. The Mn doped HA disc samples were prepared by uniaxial pressing at 200MPa and subsequently sintered at 1300 degrees C. Characterization was carried out where appropriate to determine the phases present, bulk density, Vickers hardness of the various content of Mn doped HA dense bodies. The addition of Mn was observed to influence the color appearance of the powders and dense bodies as well. Higher Mn concentration resulted in dark grey powders. It was also found that the hardness and relative density of the material increased as the Mn content increased and influenced by the crystallinity of the prepared Mn doped HA powders.
    Matched MeSH terms: Crystallization
  7. Imidazolium-based ionic liquid salts: 3,3'-dimethyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(tetrafluoroborate) and 3,3'-di-n-butyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(trifluoromethanesulfonate)
    Ganesan K, Alias Y, Ng SW
    Acta Crystallogr C, 2008 Sep;64(Pt 9):o478-80.
    PMID: 18758014 DOI: 10.1107/S0108270108023111
    Crystallization of the ionic liquid 3,3'-dimethyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(tetrafluoroborate), C(16)H(20)N(4)(2+).2BF(4)(-), (I), from its solution in water has permitted the first single-crystal study of an imidazolium-based ionic liquid having a tetrafluoroborate ion as counter-ion. Despite the expectation that the anion would not participate in nonclassical hydrogen bonding, the ionic liquid features C-H...F hydrogen bonds. The dication lies about a center of inversion. The ionic liquid 3,3'-di-n-butyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(trifluoromethanesulfonate), C(22)H(32)N(4)(2+).2CF(3)SO(3)(-), (II), features both C-H...F and C-H...O hydrogen bonds.
    Matched MeSH terms: Crystallization
  8. Factors influencing the release of Mitragyna speciosa crude extracts from biodegradable P(3HB-co-4HB)
    Chee JW, Amirul AA, Majid MI, Mansor SM
    Int J Pharm, 2008 Sep 1;361(1-2):1-6.
    PMID: 18584978 DOI: 10.1016/j.ijpharm.2008.05.007
    Copolyesters of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) were produced by Cupriavidus sp. (USMAA2-4) (DSM 19379) from carbon sources of 1,4-butanediol and gamma-butyrolactone. The composition of copolyesters produced varied from 0 to 45 mol% 4HB, depending on the combination of carbon sources supplied. The P(3HB-co-4HB) films containing Mitragyna speciosa crude extract were prepared with the ratio varying from 10 to 40% (w/w). The in vitro crude extract release of the films was studied in 0.1M phosphate buffer (pH 7.4) at 37 degrees C. Although the release rate was slow, it was maintained at a constant rate. This suggests that the crude extract release was due to the polymer degradation because the amount of crude extract released was consistent. The amount of degradation was based on the films' dry weight loss, decrease in molecular weight and surface morphology changes. The degradation rate increased with the 4HB content. This showed that the polymer degradation is dependant on the molecular weight, crystallinity, thermal properties and water permeability. The different drug loading ratio which led to surface morphology changes also gave an effect on polymer degradation.
    Matched MeSH terms: Crystallization
  9. Controlled release compound based on metanilate-layered double hydroxide nanohybrid
    Hussein MZ, Nasir NM, Yahaya AH
    J Nanosci Nanotechnol, 2008 Nov;8(11):5921-8.
    PMID: 19198327
    Metanilate-layered double hydroxide nanohybrid compound was synthesized for controlled release purposes through co-precipitation method of the metal cations and organic anion. The effect of various divalent metal cations (M2+), namely Zn2+, Mg2+ and Ca2+ on the formation of metanilate-LDH nanohybrids, in which metanilate anion was intercalated into three different layered double hydroxide (LDH) systems; Zn-Al, Mg-Al and Ca-Al were investigated. The syntheses were carried out with M2+ to Al3+ initial molar ratio, R of 4. The pH of the mother liquor was maintained at pH 7.5 and 10 during the synthesis, and the resulting mixture was aged at around 70 degrees C for about 18 h. The intercalation of metanilate anion into the host was found to be strongly influenced by the M2+ that formed the inorganic metal hydroxide layers. Under our experimental condition, the formation of the nanohybrid materials was found to be more feasible for the Zn-Al than for the other two systems, in which the former showed well-ordered layered organic-inorganic nanohybrid structure with good crystallinity. Intercalation is confirmed by the expansion of the interlayer spacing to about 15-17 A when metanilate was introduced into the interlamellae of Zn-Al LDHs. In addition, CHNS and FTIR analyses also support that metanilate anion has been successfully intercalated into the interlamellae of the inorganic LDH. Apart from M2+, this study also shows that the initial pH of the mother liquor plays an important role in determining the physicochemical properties of the resulting nanohybrids, especially the mole fraction of the Zn2+ substituted by the Al3+ ion in the LDH inorganic sheets which in turn controlled the loading percentage of the organic anion, surface properties and the true density. Preliminary study shows that LDH can be used to host beneficial guests, active agent with controlled release capability of the guests. Generally the overall process is governed by pseudo second order kinetic but for the first 180 min, the release process can be slightly better described by parabolic diffusion than the other models.
    Matched MeSH terms: Crystallization/methods*
  10. Effect of annealing temperature on the microstructure and dielectric properties of Ba0.6Sr0.4TiO3 Ttin films prepared by sol-gel process
    Dewi R, Ibrahim N, Talib I, Ibarahim Z
    Sains Malaysiana, 2008;37:233-237.
    Thin films of barium strontium titanate (Ba0.6Sr0.4TiO3) perovskite system are promising candidates for microelectronic devices that can be integrated with semiconductor technology. Ba0.6Sr0.4TiO3 thin films have been prepared onto BST/TiO2/RuO2/SiO2/Si substrate using the spin coating and sol-gel process. Then the samples were subsequently annealed at 600oC, 650oC and 700oC for 60 minutes in air. The microstructure and dielectric properties show that the crystallization improved as the annealing temperature was increased. All of the films have nanometer grain size. The average grain size of the films increased as the temperature was increased. The dielectric constant and ac conductivity of the films also increased as the average grain size increased. These results showed that the microstructure and dielectric properties depend on the annealing temperature.
    Matched MeSH terms: Crystallization
  11. Parameters affecting the photocatalytic degradation of dyes using TiO2-based photocatalysts: a review
    Akpan UG, Hameed BH
    J Hazard Mater, 2009 Oct 30;170(2-3):520-9.
    PMID: 19505759 DOI: 10.1016/j.jhazmat.2009.05.039
    This paper presents the review of the effects of operating parameters on the photocatalytic degradation of textile dyes using TiO2-based photocatalysts. It further examines various methods used in the preparations of the considered photocatalysts. The findings revealed that various parameters, such as the initial pH of the solution to be degraded, oxidizing agents, temperature at which the catalysts must be calcined, dopant(s) content and catalyst loading exert their individual influence on the photocatalytic degradation of any dye in wastewaters. It was also found out that sol-gel method is widely used in the production of TiO2-based photocatalysts because of the advantage derived from its ability to synthesize nanosized crystallized powder of the photocatalysts of high purity at relatively low temperature.
    Matched MeSH terms: Crystallization
  12. Fulltext Polymorph identification studies on cocoa butter from Sabah
    Nur Fadzilah Basri, Fauziah Abdul Aziz, Mohd Omar, A.K., Nik Norulaini, A.R.
    Journal of Nuclear and Related Technologies, 2009;2009(1):159-164.
    MyJurnal
    The main purpose of this study was to analyzed and examined the cocoa butter samples from Sabah. This work presence the crystal phases present in cocoa butter sample thus proved the existence of polymorphs obtained from differential scanning calorimeter (DSC) analysis and confirmed by X-ray diffraction (XRD). The cocoa butter samples were extracted using a conventional method by Soxhlet Extraction method. Crystals were formed under controlled static and tempered conditions. Cocoa butter polymorphism demonstrates that it is the actual crystallization temperature, not the cooling rate that determines the polymorph that crystallizes.
    Matched MeSH terms: Crystallization
  13. Fulltext Rietveld quantitative phase analysis of non-stoichiometric cordierite synthesised from mainly talc and kaolin: effect of sintering temperature
    Banjuraizah Johar, Hasmaliza Mohamad, Zainal Arifin Ahmad
    Journal of Nuclear and Related Technologies, 2009;2009(1):103-110.
    MyJurnal
    Indialite or α-cordierite was synthesized by glass crystallization method using mainly talc and kaolin and with small amount of MgO, Al2O3, SiO2 to compensate the chemical formulation of non-stoihiometric compositions of cordierite. (3MgO.1.5Al2O3.5SiO2). B2O3, P2O5 and CaO was also added to decrease the melting and sintering temperature of cordierite. The glasses were pelletized and sintered from 850 o C up to 1050 o C. Phase compositions of both heat treated glass was quantified by X-ray powder diffraction data by the Rietveld method using TOPAS Ver 3 software. Result shows that about 60wt% of α cordierite has successfully crystallized at 850 o C. Beside secondary phases (forsterite) which come from initial raw materials, phases from grinding media were also presents in the sample. The contamination was considered high since it has reacted with existence phases to form a new phase at higher temperature. Without any contamination from grinding it was expected to obtain more than 90wt% α cordierite using the same composition.
    Matched MeSH terms: Crystallization
  14. Fulltext The effect of high-eenergy milling on the crystallite size of alumina
    Masliana Muslimin, Meor Yusoff, M.S.
    Journal of Nuclear and Related Technologies, 2009;2009(1):95-102.
    MyJurnal
    The experiment aims to investigate the effect of high energy milling to the crystallite size of α-alumina. The starting material used is α-alumina powder with starting crystal size of 86nm. This powder was milled at different time ranges from 0 to 60 minutes and milling speed ranges from 400 rpm to 1100 rpm using a wet milling technique in corundum abrasive materials. The wet milling technique involved the use of water with the alumina to water ratio of 1:6.1. Samples prepared were then examined using the X-Ray Diffraction (XRD) to calculate the crystallite size and scanning electron microscope (SEM) was also used to determine changes in the morphology. Results from these analysis showed that the crystallite size will get smaller when milling speed and time of more than 600rpm and 30 minutes respectively were used. Optimum conditions to achieve the smallest crystal size of 79.7nm are 1000 rpm and 60 minutes.
    Matched MeSH terms: Crystallization
  15. Fulltext Boronate derivatives of functionally diverse catechols: stability studies
    Ketuly KA, Hadi AH
    Molecules, 2010 Apr;15(4):2347-56.
    PMID: 20428047 DOI: 10.3390/molecules15042347
    Benzeneboronate of catecholic carboxyl methyl esters, N-acetyldopamine, coumarin and catechol estrogens were prepared as crystalline derivatives in high yield. Related catechol compounds with extra polar functional group(s) (OH, NH2) do not form or only partially form unstable cyclic boronate derivatives.
    Matched MeSH terms: Crystallization
  16. Fulltext Crystallization and preliminary X-ray crystallographic analysis of highly thermostable L2 lipase from the newly isolated Bacillus sp. L2
    Shariff FM, Rahman RN, Ali MS, Chor AL, Basri M, Salleh AB
    Acta Crystallogr Sect F Struct Biol Cryst Commun, 2010 Jun 1;66(Pt 6):715-7.
    PMID: 20516608 DOI: 10.1107/S174430911001482X
    Purified thermostable recombinant L2 lipase from Bacillus sp. L2 was crystallized by the counter-diffusion method using 20% PEG 6000, 50 mM MES pH 6.5 and 50 mM NaCl as precipitant. X-ray diffraction data were collected to 2.7 A resolution using an in-house Bruker X8 PROTEUM single-crystal diffractometer system. The crystal belonged to the primitive orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 87.44, b = 94.90, c = 126.46 A. The asymmetric unit contained one single molecule of protein, with a Matthews coefficient (V(M)) of 2.85 A(3) Da(-1) and a solvent content of 57%.
    Matched MeSH terms: Crystallization
  17. Fulltext Pharmaceutical quality of nine generic orlistat products compared with Xenical(r)
    Taylor PW, Arnet I, Fischer A, Simpson IN
    Obes Facts, 2010 Aug;3(4):231-7.
    PMID: 20823686 DOI: 10.1159/000319450
    OBJECTIVE: To compare the pharmaceutical quality of Xenical (chemically produced orlistat) with nine generic products, each produced by fermentation processes.

    METHODS: Xenical 120 mg capsules (Roche, Basel, Switzerland) were used as reference material. Generic products were from India, Malaysia, Argentina, Philippines, Uruguay, and Taiwan. Colour, melting temperature, crystalline form, particle size, capsule fill mass, active pharmaceutical ingredient content, amount of impurities, and dissolution were compared. Standard physical and chemical laboratory tests were those developed by Roche for Xenical.

    RESULTS: All nine generic products failed the Xenical specifications in four or more tests, and two generic products failed in seven tests. A failure common to all generic products was the amount of impurities present, mostly due to different by-products, including side-chain homologues not present in Xenical. Some impurities were unidentified. Two generic products tested failed the dissolution test, one product formed a capsule-shaped agglomerate on storage and resulted in poor (=15%) dissolution. Six generic products were powder formulations.

    CONCLUSIONS: All tested generic orlistat products were pharmaceutically inferior to Xenical. The high levels of impurities in generic orlistat products are a major safety and tolerability concern.

    Matched MeSH terms: Crystallization
  18. Physicochemical, textural and viscoelastic properties of palm diacylglycerol bakery shortening during storage
    Cheong LZ, Tan CP, Long K, Affandi Yusoff MS, Lai OM
    J Sci Food Agric, 2010 Oct;90(13):2310-7.
    PMID: 20661900 DOI: 10.1002/jsfa.4088
    Diacylglycerol (DAG), which has health-enhancing properties, is sometimes added to bakery shortening to produce baked products with enhanced physical functionality. Nevertheless, the quantity present is often too little to exert any positive healthful effects. This research aimed to produce bakery shortenings containing significant amounts of palm diacyglycerol (PDG). Physicochemical, textural and viscoelastic properties of the PDG bakery shortenings during 3 months storage were evaluated and compared with those of commercial bakery shortening (CS).
    Matched MeSH terms: Crystallization
  19. Two new polymorphs of 2,6-diaminopyrimidin-4(3H)-one monohydrate
    Suleiman Gwaram N, Khaledi H, Ali HM, Olmstead MM
    Acta Crystallogr C, 2011 Jan;67(Pt 1):o6-9.
    PMID: 21206084 DOI: 10.1107/S0108270110046317
    The title compound, C(4)H(6)N(4)O·H(2)O, crystallized simultaneously as a triclinic and a monoclinic polymorph from an aqueous solution of 2,4-diaminopyrimidin-6-ol. Previously, an orthorhombic polymorph was isolated under the same experimental conditions. The molecular geometric parameters in the two present polymorphs and the previously reported orthorhombic polymorph are similar, but the structures differ in the details of their crystal packing. In the triclinic system, the diaminopyrimidinone molecules are connected to one another via N-H···O and N-H···N hydrogen bonding to form infinite chains in the [011] direction. The chains are further hydrogen bonded to the water molecules, resulting in a three-dimensional network. In the monoclinic system, the diaminopyrimidinone molecules are hydrogen bonded together into two-dimensional networks parallel to the bc plane. The water molecules link the planes to form a three-dimensional polymeric structure.
    Matched MeSH terms: Crystallization
  20. Morphology and magnetic characterisation of aluminium substituted yttrium-iron garnet nanoparticles prepared using sol gel technique
    Yahya N, Al Habashi RM, Koziol K, Borkowski RD, Akhtar MN, Kashif M, et al.
    J Nanosci Nanotechnol, 2011 Mar;11(3):2652-6.
    PMID: 21449447
    Aluminum substituted yttrium iron garnet nano particles with compositional variation of Y(3.0-x) A1(x)Fe5O12, where x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 were prepared using sol gel technique. The X-ray diffraction results showed that the best garnet phase appeared when the sintering temperature was 800 degrees C. Nano-crystalline particles with high purity and sizes ranging from 20 to 100 nm were obtained. It was found that the aluminum substitution had resulted in a sharp fall of the d-spacing when x = 2, which we speculated is due to the preference of the aluminum atoms to the smaller tetrahedron and octahedron sites instead of the much larger dodecahedron site. High resolution transmission electron microscope (HRTEM) and electron diffraction (ED) patterns showed single crystal nanoparticles were obtained from this method. The magnetic measurement gave moderate values of initial permeability; the highest value of 5.3 was shown by sample Y3Fe5O12 at more than 100 MHz which was attributed to the morphology of the microstructure which appeared to be homogeneous. This had resulted in an easy movement of domain walls. The substitution of aluminum for yttrium is speculated to cause a cubic to rhombodedral structural change and had weakened the super-exchange interactions thus a fall of real permeability was observed. This might have created a strain in the sub-lattices and had subsequently caused a shift of resonance frequencies to more than 1.8 GHz when x > 0.5.
    Matched MeSH terms: Crystallization/methods
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