Ibrahim Karume | Makerere University (original) (raw)

Papers by Ibrahim Karume

European journal of applied sciences, Apr 5, 2024

BMC Chemistry, Nov 21, 2023

Sustainable Chemistry for the Environment, Nov 30, 2023

Journal of Molecular Catalysis B-enzymatic, May 1, 2015

ABSTRACT Controlled racemization of enantiopure alcohols is a key step in dynamic kinetic resolut... more ABSTRACT Controlled racemization of enantiopure alcohols is a key step in dynamic kinetic resolution. We recently reported the racemization of enantiopure phenyl-ring-containing alcohols using W110A Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (W110A TeSADH), which relies on selectivity mistakes. Trp-110 lines the large pocket of the active site of TeSADH, which allows W110A TeSADH mutant to accommodate phenyl-ring-containing substrates in Prelog mode, albeit with selectivity mistakes. Here, we report the racemization of enantiopure phenyl-ring-containing alcohols using several Trp-110 mutants of TeSADH in the presence of the oxidized and reduced forms of nicotinamide-adenine dinucleotide. We observed a noticeable enhancement in racemization efficiency when W110G TeSADH was used compared with W110Q, W110 M, W110L, W110I, and W110 V. This observation was anticipated because the W110G mutation is expected to open the large pocket of the active site to a greater extent compared to other mutants of TeSADH at W110. Both enantiomers of 1-phenyl-2-propanol and 4-phenyl-2-butanol were fully racemized by W110G TeSADH. We also constructed a triple mutant of TeSADH, W110A/I86A/C295A, by site-directed mutagenesis with the aim of opening the two pockets of the active site of TeSADH. The W110A/I86A/C295A mutant was employed to racemize enantiopure phenyl-ring-containing alcohols. The current study demonstrates that W110G and W110A/I86A/C295A TeSADH are more efficient catalysts for the racemization of enantiopure secondary alcohols than the previously reported mutant W110A TeSADH [6].

Scholars International Journal of Chemistry and Material Sciences

Solanaceae is family of plants widely used in food, sauce and herbal medicine because its members... more Solanaceae is family of plants widely used in food, sauce and herbal medicine because its members are rich in carbohydrates, proteins, fats, vitamins, mineral salts and other trace and essential nutrients like phenols and flavonoids that retard degenerative diseases and stress. Knowledge on purposeful use of solanaceae in food and medicine in Uganda is low. Aqueous extracts of dry leaves of three selected solanum genera growing in Kabale were compared for their polyphenol and flavonoid contents and antioxidant properties. Total polyphenol (TPC) and total flavonoid (TFC) contents were determined by the Folin-Ciocalteu and aluminium chloride colorimetric methods respectively. Antioxidant properties and radical scavenging were determined using DPPH, hydrogen peroxide, thiocyanate-iron (III) complex and iron (II)/(III)-linoleic acid systems. The polyphenol content of dry leaves of S. anguivi was 1750 ± 0.70, that for S. macrocarpon was 104 ± 0.45 and S. nigrum was 97.80 ± 0.15 GAE/g yet...

Open Access Journal of Environmental#N#and Soil Sciences, Aug 8, 2019

International Journal of Advances in Chemistry, 2021

Pollution resulting from unsustainable agricultural and urbanization activities in the Ruhezamyen... more Pollution resulting from unsustainable agricultural and urbanization activities in the Ruhezamyenda and Bunyonyi catchments are threatening lake Bunyonyi. These have led to high chemical oxygen demand (COD), electrical conductivity, turbidity, pH, iron (II) concentration and low dissolved oxygen (DO5). In this study we have investigated the how COD, turbidity, pH, concentration of iron, total suspended solids, total nutrients and DO5 of water changed with distance in lake. Water sampled from different distances in the lake filtered using Whatman paper at ambient temperatures was tested for COD, electrical conductivity, turbidity, total nutrients, iron, hardness and DO5. COD was 20.8±.0.03mg/L to 16 ± 0.03mg/L; total hardness was 16.5±0.2 mg/L to 18.6 ± 0.3 mg/L total nitrate was 103.5± 2 mg/L to 88 ± 3 mg/L; total phosphate was 100.8 ±.2.5 to 87± 3 mg/L; high TSS values from 3.4 ± 0.1 mg/L to 2.5 ± 0.1 mg/L showed contamination of water. As pH decreased from 8.3 ± 0.03 to 7.6 ± 0.04...

JOURNAL OF ADVANCES IN CHEMISTRY, 2020

Pollution is affecting river Rwabakazi in the Nile basin. Its effects are reflected by high turbi... more Pollution is affecting river Rwabakazi in the Nile basin. Its effects are reflected by high turbidity, pH, total suspended solids, (T.S.S.), electrical conductivity, metal ions concentrations, and low concentration of dissolved oxygen (DO5). In this study, we report the variations in selected physicochemical parameters of waters of the Rwabakazi river. Turbidity, pH, concentrations of selected metal ions, T.S.S., and DO5 of water sampled from three selected sites on the river in Kabale were very high. Mean DO5 fell from 96 ± 2 mg/L to 86± 1.5 mg/L downstream. The mean pH fell from 7.8 ± 0.03 to 7.6 ± 0.04, showing the removal of basic components. The turbidity dropped from370 ± 3 NTU to 305 ± 2 NTU, showing that the haziness of water decreased. The concentration of iron(II) fell from 320 ± 0.3 mg/L to 291 ± 0.2 mgL-1 indicating the fair extent of heavy metal ions downstream. The T.S.S. decreased from 330 ± 5 mg/L to 300± 5 mg/L, and concentrations of calcium and magnesium ions also...

Academic Journal of Chemistry, Nov 10, 2019

In order to establish a research-based experimental platform for students to fully mobilize initi... more In order to establish a research-based experimental platform for students to fully mobilize initiative and learning creativity, it is necessary to establish design and exploratory experiments to highlight independent exploration and innovation. Through experimental device improvement and material screening, the three parts of fluidization curve measurement, fixed bed drying and fluidized bed drying of spherical molecular sieve are integrated into an organic entirety. Especially, the traditional basic experiment is promoted to a design and research experimental project. Results show that students experimental design ability and comprehensive quality have been improved, and it also stimulated their learning interest, cultivated the creative ability.

Asian Journal of Chemistry, 2018

The ongoing demand for greener approaches has revolutionized synthetic chemistry demanding effici... more The ongoing demand for greener approaches has revolutionized synthetic chemistry demanding efficient and environmentally friendly methodologies. The interest in CC crosscoupling reactions was triggered by the high demand for biaryl intermediates in pharmaceuticals. Palladium catalyzed Suzuki cross-coupling of aryl and vinylboronic acids with aryl or vinyl halides [1,2] is being employed. However the reactions need exotic catalysts which are expensive and difficult to handle. Catalyst systems based on palladium ranging from simple salts like palladium acetate in the presence of quaternary ammonium salts [3] or water [4] to palladium nanoparticles (Pd-NPs) stabilized by ionic liquids [5], dendrimers [6], polyvinylpyridine (PVP) [7], fluoro ligands [8], phosphine ligands [9], aqueous solutions [10] as well as solid supports such as diatomite [11] and on polymer supports like poly(N,N-dihexylcarbodiimide) (PDHC) [12] have been employed. Most of the catalyst systems reported require sophisticated reaction setups in addition to homogeneity with the media making isolation of the product tedious. Ligand decomposition at higher temperatures has also been reported which tend to reduce the activity of Pd-catalyst systems employed so far [11,13] making the entire process very expensive. In the search for suitable supports, polyxoxometalates (POMs), which possess excellent properties make POMs suitable supports. The chemical properties of POMs can be largely

JOURNAL OF ADVANCES IN CHEMISTRY, 2020

Pollution resulting from increased human activities is threatening Lake Victoria, its effects are... more Pollution resulting from increased human activities is threatening Lake Victoria, its effects are characterized by eutrophication, high turbidity, pH, iron(II) concentration and chemical oxygen demand (COD). In this study we have investigated the effect of Fe-montmorillonite clay from Chelel on turbidity, pH, concentration of iron, total suspended soils, total nutrients and COD of water sampled from Murchison bay watershed of Nakivubo channel south of Kampala. Varying amounts of clay powder was vigorously stirred with water samples for 5 minutes, filtered using Whitman paper at ambient temperatures. The optimum concentration of clay of 0.4gl-1 was found to produce 73.5+ 2% fall in COD indicating elimination of microbes and organic waste. The pH of water became 6.3+ 0.2 showing that impurities had been bound to clay. The turbidity of filtrate dropped to 15.7+ 0.3NTUshowing that clarity of water was improved by adsorption of suspended solids to clay minerals. The concentration of iron...

Scientific Review, 2019

Cattle dung, cooked food waste, and chicken droppings mixed with coffee husks have been used sepa... more Cattle dung, cooked food waste, and chicken droppings mixed with coffee husks have been used separately and also as mixtures to form anaerobic digestion slurries in a bid to treat to degrade the organic fractions of these wastes and recycle the bio-fertilizer after recovering biogas. Single and mixed substrate slurries evolved significant quantities of methane within 27days together with reduced mass of soil conditioner. The volume of biogas formed in cogeneration mixtures were higher than for single substrate digestion due to the C/N ratio shifting to near 30:1 as a result of mixing. So degradation of organic pollutants was higher in mixed substrate digestion mixtures. Our study yielded average volumes ranging from 315 to 435+ 5.65.mL/L which was in agreement with what is in literature. Digestion of cattle dung, cooked waste foods, and droppings of chicken and mixed substrate slurries using sludge inoculums was very effective in degrading solid waste from homes, thus detoxifying it...

Science of The Total Environment, 2019

Asian Journal of Applied Chemistry Research, May 7, 2024

Herein, we reviewed the main components of dye-sensitized solar cells (DSSCs) which are an emergi... more Herein, we reviewed the main components of dye-sensitized solar cells (DSSCs) which are an emerging cheap and environmentally benign alternative for solar energy capture and conversion to electricity. The role of individual parts such as the semiconductor electrode, counter electrode, photosensitizer, electrolyte, and substrate and their contribution to the overall efficiency (η) of DSSCs are discussed. In addition, parameters such as short circuit current, open circuit voltage, and fill factor used to quantify the efficiency of DSSCs are addressed. The highest solar-to-electric energy conversion efficiency of 13 % has been achieved using titanium dioxide as a semiconductor electrode, a triiodide system as a redox couple, and platinum counter electrodes. Semiconductors

Letters in Organic Chemistry

: The activity and selectivity of W110G Thermoanaerobacter ethanolicus secondary alcohol dehydrog... more : The activity and selectivity of W110G Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase were altered by cosubstrate and cosolvent at varying temperatures. A sharp drop in the enantiomeric excess (ee) was observed at 60 oC in the first 3 h, suggesting increased selectivity mistakes in the reduction of 4-phenyl-2-butanone to the expected (S)-4-phenyl-2-butanol using 5% v/v of 2-propanol as a cosubstrate. The ee increased exponentially with cosubstrate concentration, reaching ≥94% with 30-70% v/v 2-propanol. However, a decrease in enzyme activity was noticed at ≥30% v/v 2-propanol by a sharp drop in conversion. The lowest ee (<3%) was registered using 5% v/v 2- propanol at 30-40 oC, which prolonged enzyme life that allowed reversible redox reaction with selectivity mistakes to give the R-alcohol compared to ≥18% ee at 50-60 oC, where faster reaction rates promoted selectivity mistake, but enzyme life was shortened by protein denaturation at the elevated temperatures. Water-miscible and immiscible organic cosolvents (25% v/v) increased enzyme selectivity. For methanol, ethanol, ethylene glycol and tert-butanol, the activity/conversion decreased with an increase in pKa and log P while the stereoselectivity/ee increased.

Green Chemistry Letters and Reviews

Trends in green chemistry, Aug 8, 2017

ChemistrySelect, 2018

Here, we achieved a single-enzymatic stereoinversion of R-configured alcohols to their correspond... more Here, we achieved a single-enzymatic stereoinversion of R-configured alcohols to their corresponding S enantiomers in high percent conversion and high enantioselectivity. A single mutant of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH) oxidized R alcohols to their corresponding ketones under conditions that allow selectivity mistakes and then reduced them under stereoselective conditions to generate the corresponding S-configured alcohols. The success of this stereoinversion relies on controlling the stereoselectivity of the oxidation and the reduction reactions by varying the amounts of acetone and 2-propanol, respectively. Furthermore, the deployment of the TeSADH mutants W110A and W110G led to stereoinversion of enantiopure R alcohols to their S enantiomers in medium to high enantiomeric excess (up to >99% ee). The disclosed approach of single enzymatic stereoinversion presents a biocatalytic alternative to Mitsunobu inversion reaction.

European Journal of Organic Chemistry, 2018

Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various si... more Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various single and dual site mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). Further expanding the size of the substrate binding pocket in the mutant W110A/I86A not only allowed substrates of the single mutants W110A and I86A to be accommodated within the expanded active site, but also expanded the enzyme's substrate range to ketones bearing two sterically demanding groups (bulky-bulky ketones), which are not substrates for TeSADH single mutants. We also report the regio-and enantioselective reduction of diketones using W110A/I86A TeSADH and single TeSADH mutants. The double mutant exhibited dual stereopreference generating the Prelog products most of the time and the anti-Prelog products in a few cases.

RSC Advances, 2016

The immobilization of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (TeSADH) usi... more The immobilization of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (TeSADH) using sol–gel method enables its use to racemize enantiopure alcohols in organic media, thus allows for a dual enzymatic dynamic kinetic resolution.

European journal of applied sciences, Apr 5, 2024

BMC Chemistry, Nov 21, 2023

Sustainable Chemistry for the Environment, Nov 30, 2023

Journal of Molecular Catalysis B-enzymatic, May 1, 2015

ABSTRACT Controlled racemization of enantiopure alcohols is a key step in dynamic kinetic resolut... more ABSTRACT Controlled racemization of enantiopure alcohols is a key step in dynamic kinetic resolution. We recently reported the racemization of enantiopure phenyl-ring-containing alcohols using W110A Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (W110A TeSADH), which relies on selectivity mistakes. Trp-110 lines the large pocket of the active site of TeSADH, which allows W110A TeSADH mutant to accommodate phenyl-ring-containing substrates in Prelog mode, albeit with selectivity mistakes. Here, we report the racemization of enantiopure phenyl-ring-containing alcohols using several Trp-110 mutants of TeSADH in the presence of the oxidized and reduced forms of nicotinamide-adenine dinucleotide. We observed a noticeable enhancement in racemization efficiency when W110G TeSADH was used compared with W110Q, W110 M, W110L, W110I, and W110 V. This observation was anticipated because the W110G mutation is expected to open the large pocket of the active site to a greater extent compared to other mutants of TeSADH at W110. Both enantiomers of 1-phenyl-2-propanol and 4-phenyl-2-butanol were fully racemized by W110G TeSADH. We also constructed a triple mutant of TeSADH, W110A/I86A/C295A, by site-directed mutagenesis with the aim of opening the two pockets of the active site of TeSADH. The W110A/I86A/C295A mutant was employed to racemize enantiopure phenyl-ring-containing alcohols. The current study demonstrates that W110G and W110A/I86A/C295A TeSADH are more efficient catalysts for the racemization of enantiopure secondary alcohols than the previously reported mutant W110A TeSADH [6].

Scholars International Journal of Chemistry and Material Sciences

Solanaceae is family of plants widely used in food, sauce and herbal medicine because its members... more Solanaceae is family of plants widely used in food, sauce and herbal medicine because its members are rich in carbohydrates, proteins, fats, vitamins, mineral salts and other trace and essential nutrients like phenols and flavonoids that retard degenerative diseases and stress. Knowledge on purposeful use of solanaceae in food and medicine in Uganda is low. Aqueous extracts of dry leaves of three selected solanum genera growing in Kabale were compared for their polyphenol and flavonoid contents and antioxidant properties. Total polyphenol (TPC) and total flavonoid (TFC) contents were determined by the Folin-Ciocalteu and aluminium chloride colorimetric methods respectively. Antioxidant properties and radical scavenging were determined using DPPH, hydrogen peroxide, thiocyanate-iron (III) complex and iron (II)/(III)-linoleic acid systems. The polyphenol content of dry leaves of S. anguivi was 1750 ± 0.70, that for S. macrocarpon was 104 ± 0.45 and S. nigrum was 97.80 ± 0.15 GAE/g yet...

Open Access Journal of Environmental#N#and Soil Sciences, Aug 8, 2019

International Journal of Advances in Chemistry, 2021

Pollution resulting from unsustainable agricultural and urbanization activities in the Ruhezamyen... more Pollution resulting from unsustainable agricultural and urbanization activities in the Ruhezamyenda and Bunyonyi catchments are threatening lake Bunyonyi. These have led to high chemical oxygen demand (COD), electrical conductivity, turbidity, pH, iron (II) concentration and low dissolved oxygen (DO5). In this study we have investigated the how COD, turbidity, pH, concentration of iron, total suspended solids, total nutrients and DO5 of water changed with distance in lake. Water sampled from different distances in the lake filtered using Whatman paper at ambient temperatures was tested for COD, electrical conductivity, turbidity, total nutrients, iron, hardness and DO5. COD was 20.8±.0.03mg/L to 16 ± 0.03mg/L; total hardness was 16.5±0.2 mg/L to 18.6 ± 0.3 mg/L total nitrate was 103.5± 2 mg/L to 88 ± 3 mg/L; total phosphate was 100.8 ±.2.5 to 87± 3 mg/L; high TSS values from 3.4 ± 0.1 mg/L to 2.5 ± 0.1 mg/L showed contamination of water. As pH decreased from 8.3 ± 0.03 to 7.6 ± 0.04...

JOURNAL OF ADVANCES IN CHEMISTRY, 2020

Pollution is affecting river Rwabakazi in the Nile basin. Its effects are reflected by high turbi... more Pollution is affecting river Rwabakazi in the Nile basin. Its effects are reflected by high turbidity, pH, total suspended solids, (T.S.S.), electrical conductivity, metal ions concentrations, and low concentration of dissolved oxygen (DO5). In this study, we report the variations in selected physicochemical parameters of waters of the Rwabakazi river. Turbidity, pH, concentrations of selected metal ions, T.S.S., and DO5 of water sampled from three selected sites on the river in Kabale were very high. Mean DO5 fell from 96 ± 2 mg/L to 86± 1.5 mg/L downstream. The mean pH fell from 7.8 ± 0.03 to 7.6 ± 0.04, showing the removal of basic components. The turbidity dropped from370 ± 3 NTU to 305 ± 2 NTU, showing that the haziness of water decreased. The concentration of iron(II) fell from 320 ± 0.3 mg/L to 291 ± 0.2 mgL-1 indicating the fair extent of heavy metal ions downstream. The T.S.S. decreased from 330 ± 5 mg/L to 300± 5 mg/L, and concentrations of calcium and magnesium ions also...

Academic Journal of Chemistry, Nov 10, 2019

In order to establish a research-based experimental platform for students to fully mobilize initi... more In order to establish a research-based experimental platform for students to fully mobilize initiative and learning creativity, it is necessary to establish design and exploratory experiments to highlight independent exploration and innovation. Through experimental device improvement and material screening, the three parts of fluidization curve measurement, fixed bed drying and fluidized bed drying of spherical molecular sieve are integrated into an organic entirety. Especially, the traditional basic experiment is promoted to a design and research experimental project. Results show that students experimental design ability and comprehensive quality have been improved, and it also stimulated their learning interest, cultivated the creative ability.

Asian Journal of Chemistry, 2018

The ongoing demand for greener approaches has revolutionized synthetic chemistry demanding effici... more The ongoing demand for greener approaches has revolutionized synthetic chemistry demanding efficient and environmentally friendly methodologies. The interest in CC crosscoupling reactions was triggered by the high demand for biaryl intermediates in pharmaceuticals. Palladium catalyzed Suzuki cross-coupling of aryl and vinylboronic acids with aryl or vinyl halides [1,2] is being employed. However the reactions need exotic catalysts which are expensive and difficult to handle. Catalyst systems based on palladium ranging from simple salts like palladium acetate in the presence of quaternary ammonium salts [3] or water [4] to palladium nanoparticles (Pd-NPs) stabilized by ionic liquids [5], dendrimers [6], polyvinylpyridine (PVP) [7], fluoro ligands [8], phosphine ligands [9], aqueous solutions [10] as well as solid supports such as diatomite [11] and on polymer supports like poly(N,N-dihexylcarbodiimide) (PDHC) [12] have been employed. Most of the catalyst systems reported require sophisticated reaction setups in addition to homogeneity with the media making isolation of the product tedious. Ligand decomposition at higher temperatures has also been reported which tend to reduce the activity of Pd-catalyst systems employed so far [11,13] making the entire process very expensive. In the search for suitable supports, polyxoxometalates (POMs), which possess excellent properties make POMs suitable supports. The chemical properties of POMs can be largely

JOURNAL OF ADVANCES IN CHEMISTRY, 2020

Pollution resulting from increased human activities is threatening Lake Victoria, its effects are... more Pollution resulting from increased human activities is threatening Lake Victoria, its effects are characterized by eutrophication, high turbidity, pH, iron(II) concentration and chemical oxygen demand (COD). In this study we have investigated the effect of Fe-montmorillonite clay from Chelel on turbidity, pH, concentration of iron, total suspended soils, total nutrients and COD of water sampled from Murchison bay watershed of Nakivubo channel south of Kampala. Varying amounts of clay powder was vigorously stirred with water samples for 5 minutes, filtered using Whitman paper at ambient temperatures. The optimum concentration of clay of 0.4gl-1 was found to produce 73.5+ 2% fall in COD indicating elimination of microbes and organic waste. The pH of water became 6.3+ 0.2 showing that impurities had been bound to clay. The turbidity of filtrate dropped to 15.7+ 0.3NTUshowing that clarity of water was improved by adsorption of suspended solids to clay minerals. The concentration of iron...

Scientific Review, 2019

Cattle dung, cooked food waste, and chicken droppings mixed with coffee husks have been used sepa... more Cattle dung, cooked food waste, and chicken droppings mixed with coffee husks have been used separately and also as mixtures to form anaerobic digestion slurries in a bid to treat to degrade the organic fractions of these wastes and recycle the bio-fertilizer after recovering biogas. Single and mixed substrate slurries evolved significant quantities of methane within 27days together with reduced mass of soil conditioner. The volume of biogas formed in cogeneration mixtures were higher than for single substrate digestion due to the C/N ratio shifting to near 30:1 as a result of mixing. So degradation of organic pollutants was higher in mixed substrate digestion mixtures. Our study yielded average volumes ranging from 315 to 435+ 5.65.mL/L which was in agreement with what is in literature. Digestion of cattle dung, cooked waste foods, and droppings of chicken and mixed substrate slurries using sludge inoculums was very effective in degrading solid waste from homes, thus detoxifying it...

Science of The Total Environment, 2019

Asian Journal of Applied Chemistry Research, May 7, 2024

Herein, we reviewed the main components of dye-sensitized solar cells (DSSCs) which are an emergi... more Herein, we reviewed the main components of dye-sensitized solar cells (DSSCs) which are an emerging cheap and environmentally benign alternative for solar energy capture and conversion to electricity. The role of individual parts such as the semiconductor electrode, counter electrode, photosensitizer, electrolyte, and substrate and their contribution to the overall efficiency (η) of DSSCs are discussed. In addition, parameters such as short circuit current, open circuit voltage, and fill factor used to quantify the efficiency of DSSCs are addressed. The highest solar-to-electric energy conversion efficiency of 13 % has been achieved using titanium dioxide as a semiconductor electrode, a triiodide system as a redox couple, and platinum counter electrodes. Semiconductors

Letters in Organic Chemistry

: The activity and selectivity of W110G Thermoanaerobacter ethanolicus secondary alcohol dehydrog... more : The activity and selectivity of W110G Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase were altered by cosubstrate and cosolvent at varying temperatures. A sharp drop in the enantiomeric excess (ee) was observed at 60 oC in the first 3 h, suggesting increased selectivity mistakes in the reduction of 4-phenyl-2-butanone to the expected (S)-4-phenyl-2-butanol using 5% v/v of 2-propanol as a cosubstrate. The ee increased exponentially with cosubstrate concentration, reaching ≥94% with 30-70% v/v 2-propanol. However, a decrease in enzyme activity was noticed at ≥30% v/v 2-propanol by a sharp drop in conversion. The lowest ee (<3%) was registered using 5% v/v 2- propanol at 30-40 oC, which prolonged enzyme life that allowed reversible redox reaction with selectivity mistakes to give the R-alcohol compared to ≥18% ee at 50-60 oC, where faster reaction rates promoted selectivity mistake, but enzyme life was shortened by protein denaturation at the elevated temperatures. Water-miscible and immiscible organic cosolvents (25% v/v) increased enzyme selectivity. For methanol, ethanol, ethylene glycol and tert-butanol, the activity/conversion decreased with an increase in pKa and log P while the stereoselectivity/ee increased.

Green Chemistry Letters and Reviews

Trends in green chemistry, Aug 8, 2017

ChemistrySelect, 2018

Here, we achieved a single-enzymatic stereoinversion of R-configured alcohols to their correspond... more Here, we achieved a single-enzymatic stereoinversion of R-configured alcohols to their corresponding S enantiomers in high percent conversion and high enantioselectivity. A single mutant of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH) oxidized R alcohols to their corresponding ketones under conditions that allow selectivity mistakes and then reduced them under stereoselective conditions to generate the corresponding S-configured alcohols. The success of this stereoinversion relies on controlling the stereoselectivity of the oxidation and the reduction reactions by varying the amounts of acetone and 2-propanol, respectively. Furthermore, the deployment of the TeSADH mutants W110A and W110G led to stereoinversion of enantiopure R alcohols to their S enantiomers in medium to high enantiomeric excess (up to >99% ee). The disclosed approach of single enzymatic stereoinversion presents a biocatalytic alternative to Mitsunobu inversion reaction.

European Journal of Organic Chemistry, 2018

Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various si... more Here, we report the asymmetric reduction of selected phenyl-ring-containing ketones by various single and dual site mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). Further expanding the size of the substrate binding pocket in the mutant W110A/I86A not only allowed substrates of the single mutants W110A and I86A to be accommodated within the expanded active site, but also expanded the enzyme's substrate range to ketones bearing two sterically demanding groups (bulky-bulky ketones), which are not substrates for TeSADH single mutants. We also report the regio-and enantioselective reduction of diketones using W110A/I86A TeSADH and single TeSADH mutants. The double mutant exhibited dual stereopreference generating the Prelog products most of the time and the anti-Prelog products in a few cases.

RSC Advances, 2016

The immobilization of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (TeSADH) usi... more The immobilization of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase (TeSADH) using sol–gel method enables its use to racemize enantiopure alcohols in organic media, thus allows for a dual enzymatic dynamic kinetic resolution.