Browsing by Author "Mgaya, James"

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    Preparation of castor oil porous organosilica composites for immobilization of trypsin enzyme
    (University of Dar es Salaam, 2012) Mgaya, James
    Porous organosilica composites have been prepared by co-condensation of 3- mercaptopropyltriethoxysilane and tetraethylorthosilicate in a 1:4 molar ratio respectively using castor oil and dodecylamine templates. FTIR spectroscopy was done to confirm the presence of tethered functional groups on the surface of mesoporous materials before immobilizing the enzyme. Trypsin enzyme was then covalently immobilized on the thiol modified porous materials by Thiol-disulflde interchange. Nitrogen physisorption studies showed that the prepared porous materials have surface areas ranging from 357 to 605 m /g with pore diameters ranged from 5 to 20 nm as determined by BJH method. The average pore volume of thiol modified micelle templated silica materials was 1.0336 cm /g and decreased to 0.8169 cm3/g upon trypsin immobilization. Both free and immobilized trypsin showed maximum activity on N-a- benzoyl-D, L-arginine-/?-nitroanilide hydrolysis at a temperature range of 35 to 38 °C. Covalently immobilized trypsin were stable up to 55 °C while free trypsin had a sharp decrease on activity at that temperature. The activation energies of N-a- benzoyl-D, L-arginine-p-nitroanilide hydrolysis for free and immobilized trypsin were 47.8 and 41.6 kJ /mol respectively, whereas Arrhenius factors were 33 and 23 U /g protein. The Vmax for free and covalently immobilized trypsin on micelle templated silica prepared by castor oil and dodecylamine were 0.32, 0.182 and 0.011 U, respectively whereas KM values were 3.8 xlO'04, 5.2 xlO’04 and 3.1x10‘04 M, respectively. The immobilized trypsin was capable of being reused up to four cycles with slight decrease on its activity.
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    Synthesis of industrial chemicals from cardanol and anacardic acid components of cashew nut shell liquid
    (University of Dar es Salaam, 2017) Mgaya, James
    Anacardic acid and cardanol, components of Cashew Nut Shell Liquid, have been employed to synthesize various chemicals of industrial importance. Metathesis of cardanol with symmetrical alkenes was employed to synthesize short chain derivatives of cardanol. These derivatives were methoxycarbonylated using a highly efficient and selective 1,2-bis(di-tert-butylphosphinomethyl)benzene (DTBPMB) modified palladium catalyst to produce bifunctional monomers with different chain lengths such as C9-COOMe, C10-COOMe, C11-COOMe, C12-COOMe and C15-COOMe. Polymerization of the synthesized monomers produced oligomers that consist of up to seven monomer units as confirmed by MALDI-TOF-MS. Lactone formation was also observed in some cases under polymerization conditions. Hydrogenation of C15-COOMe monomer in the presence of Triphos, ruthenium and hydrogen produced an aminophenol and hydroxyphenol. Polymerization of the hydroxyphenol and the aminophenol with dimethyl nonadecanedioate produced oligomers with improved flexibility. Ethoxylation of C9-COOMe and C15-COOMe monomers followed by polymerization of the synthesized ethoxylates produced gummy like and plastic like oligomers respectively. Isomerisation of monoene anacardic acid using DTBPMB modified palladium catalyst, followed by decarboxylation and metathesis of the formed isoanacardic acid produced 3-propyl phenol in 18 % yield. Apart from bifunctional monomers synthesized, industrial useful alkenes such as 1-octene, (E)-non-2-ene, (E)-dec-3-ene, (E)-undec-4-ene and (E)-hexadec-2-ene were obtained as side products from metathesis reactions of cardanol and its derivatives reported in this study.