Abstract The multiwall carbon nanotubes-polypyrrole (MWCNTs-PPy) composite is a well-known hybrid... more Abstract The multiwall carbon nanotubes-polypyrrole (MWCNTs-PPy) composite is a well-known hybrid material suitable for energy storage applications such as capacitors. Since the electrochemical activity, and long-term stability of carbon-PPy systems are critical for their application, we examined the effect of grafting PPy via a 3-ABA linker with MWCNTs with respect to the preference of the donor–acceptor pairs, and furthermore, the durability. X-ray photoelectron spectroscopy studies of C 1s and O 1s signals reveal the electronic interaction between carbon and polymer (π−π* stacking), as well as a binding energy shift for C 1s and O 1s carbonyl signals due to the chemical bonding via the electron donating linker and grafted polymer. Cyclic voltammetry and galvanostatic charge–discharge studies of the capacitor electrode reveal the effect of the reversal doping of the polymer with chloride, as well as the synergy of double layer capacitance (MWCNTs) and pseudo-capacitance of the poly(pyrrole). Impedance spectroscopy studies confirm the improved electrochemical stability for the composite (stable until 1.2 V) in comparison to the bare polymer (degradation at 0.58 V).
Proceedings of the National Academy of Sciences, 2020
Significance F-ATP synthase is a fundamental enzyme supplying adenosine triphosphate (ATP), sprea... more Significance F-ATP synthase is a fundamental enzyme supplying adenosine triphosphate (ATP), spreading across all kingdoms of life. Despite remarkable conservation of its basic structure and function, biophysical studies have revealed discrete differences in the rotary mechanisms of bacterial and eukaryotic F 1 -ATPases (the catalytic portions of the enzymes). Here, we analyzed the rotational dynamics of Paracoccus denitrificans F 1 (PdF 1 ), a bacterial F 1 -ATPase that exhibits high homology with the core functional subunits of its mitochondrial counterpart. Notably, PdF 1 possesses a simplified chemomechanical scheme different from that of all other F 1 -ATPases. Our results reveal an unexpected diversity in the chemomechanical coupling cycle of the F 1 -ATPase machinery and show that features such as homology or phylogenetic relationship cannot uniquely define the rotary scheme pattern.
Diastereomers are characterised by an intrinsic energy difference, and thermodynamics dictate the... more Diastereomers are characterised by an intrinsic energy difference, and thermodynamics dictate their distribution within a dynamic equilibrium. The characteristic mechanistic reversibility and non‐ideal stereoselectivity of catalysts therefore simultaneously promote both synthesis and epimerization of products during the formation of diastereomers. This feature can even result in the thermodynamic inversion of a chiral centre against the catalyst's stereoselectivity. Here, we provide a comprehensive experimental and theoretical study of factors that govern thermodynamic epimerization in catalysis, using enzymes as example. Our analysis highlights, that the deduction of a catalyst's stereoselectivity based on the absolute configuration of the isolated product constitutes a potential pitfall. The selective formation of either the thermodynamic‐, or the kinetic product is less determined by the catalyst, but rather by the reaction conditions. Next to low temperatures, a high max...
A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a fi... more A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a first molecular level comparative study is presented.
The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP),... more The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP), a key effector of cell death, remains controversial. By combining highly purified, fully active bovine F-ATP synthase with preformed liposomes we show that Ca2+ dissipates the H+ gradient generated by ATP hydrolysis. After incorporation of the same preparation into planar lipid bilayers Ca2+ elicits currents matching those of the MMC/PTP. Currents were fully reversible, were stabilized by benzodiazepine 423, a ligand of the OSCP subunit of F-ATP synthase that activates the MMC/PTP, and were inhibited by Mg2+ and adenine nucleotides, which also inhibit the PTP. Channel activity was insensitive to inhibitors of the adenine nucleotide translocase (ANT) and of the voltage-dependent anion channel (VDAC). Native gel-purified oligomers and dimers, but not monomers, gave rise to channel activity. These findings resolve the long-standing mystery of the MMC/PTP and demonstrate that Ca2+ can trans...
The digestive enzyme papain can drive the formation of crystalline titanium dioxide nanoparticles... more The digestive enzyme papain can drive the formation of crystalline titanium dioxide nanoparticles on surfaces. This dual functionality of thin film formation and mineralization promotion has the potential to enable the construction of hierarchical inorganic/organic structures in the form of continuous amorphous titania/protein films.
The aerobic thermoalkaliphile Caldalkalibacillus thermarum strain TA2.A1 is a member of a separat... more The aerobic thermoalkaliphile Caldalkalibacillus thermarum strain TA2.A1 is a member of a separate order of alkaliphilic bacteria closely related to the Bacillales order. Efforts to relate the genomic information of this evolutionary ancient organism to environmental adaptation have been thwarted by the inability to construct a complete genome. The existing draft genome is highly fragmented due to repetitive regions, and gaps between and over repetitive regions were unbridgeable. To address this, Oxford Nanopore Technology’s MinION allowed us to span these repeats through long reads, with over 6000-fold coverage. This resulted in a single 3.34 Mb circular chromosome. The profile of transporters and central metabolism gives insight into why the organism prefers glutamate over sucrose as carbon source. We propose that the deamination of glutamate allows alkalization of the immediate environment, an excellent example of how an extremophile modulates environmental conditions to suit its...
Abstract The multiwall carbon nanotubes-polypyrrole (MWCNTs-PPy) composite is a well-known hybrid... more Abstract The multiwall carbon nanotubes-polypyrrole (MWCNTs-PPy) composite is a well-known hybrid material suitable for energy storage applications such as capacitors. Since the electrochemical activity, and long-term stability of carbon-PPy systems are critical for their application, we examined the effect of grafting PPy via a 3-ABA linker with MWCNTs with respect to the preference of the donor–acceptor pairs, and furthermore, the durability. X-ray photoelectron spectroscopy studies of C 1s and O 1s signals reveal the electronic interaction between carbon and polymer (π−π* stacking), as well as a binding energy shift for C 1s and O 1s carbonyl signals due to the chemical bonding via the electron donating linker and grafted polymer. Cyclic voltammetry and galvanostatic charge–discharge studies of the capacitor electrode reveal the effect of the reversal doping of the polymer with chloride, as well as the synergy of double layer capacitance (MWCNTs) and pseudo-capacitance of the poly(pyrrole). Impedance spectroscopy studies confirm the improved electrochemical stability for the composite (stable until 1.2 V) in comparison to the bare polymer (degradation at 0.58 V).
Proceedings of the National Academy of Sciences, 2020
Significance F-ATP synthase is a fundamental enzyme supplying adenosine triphosphate (ATP), sprea... more Significance F-ATP synthase is a fundamental enzyme supplying adenosine triphosphate (ATP), spreading across all kingdoms of life. Despite remarkable conservation of its basic structure and function, biophysical studies have revealed discrete differences in the rotary mechanisms of bacterial and eukaryotic F 1 -ATPases (the catalytic portions of the enzymes). Here, we analyzed the rotational dynamics of Paracoccus denitrificans F 1 (PdF 1 ), a bacterial F 1 -ATPase that exhibits high homology with the core functional subunits of its mitochondrial counterpart. Notably, PdF 1 possesses a simplified chemomechanical scheme different from that of all other F 1 -ATPases. Our results reveal an unexpected diversity in the chemomechanical coupling cycle of the F 1 -ATPase machinery and show that features such as homology or phylogenetic relationship cannot uniquely define the rotary scheme pattern.
Diastereomers are characterised by an intrinsic energy difference, and thermodynamics dictate the... more Diastereomers are characterised by an intrinsic energy difference, and thermodynamics dictate their distribution within a dynamic equilibrium. The characteristic mechanistic reversibility and non‐ideal stereoselectivity of catalysts therefore simultaneously promote both synthesis and epimerization of products during the formation of diastereomers. This feature can even result in the thermodynamic inversion of a chiral centre against the catalyst's stereoselectivity. Here, we provide a comprehensive experimental and theoretical study of factors that govern thermodynamic epimerization in catalysis, using enzymes as example. Our analysis highlights, that the deduction of a catalyst's stereoselectivity based on the absolute configuration of the isolated product constitutes a potential pitfall. The selective formation of either the thermodynamic‐, or the kinetic product is less determined by the catalyst, but rather by the reaction conditions. Next to low temperatures, a high max...
A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a fi... more A novel large-scale survey approach for microbial nonulosonic acids (sialic acids) including a first molecular level comparative study is presented.
The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP),... more The molecular identity of the mitochondrial megachannel (MMC)/permeability transition pore (PTP), a key effector of cell death, remains controversial. By combining highly purified, fully active bovine F-ATP synthase with preformed liposomes we show that Ca2+ dissipates the H+ gradient generated by ATP hydrolysis. After incorporation of the same preparation into planar lipid bilayers Ca2+ elicits currents matching those of the MMC/PTP. Currents were fully reversible, were stabilized by benzodiazepine 423, a ligand of the OSCP subunit of F-ATP synthase that activates the MMC/PTP, and were inhibited by Mg2+ and adenine nucleotides, which also inhibit the PTP. Channel activity was insensitive to inhibitors of the adenine nucleotide translocase (ANT) and of the voltage-dependent anion channel (VDAC). Native gel-purified oligomers and dimers, but not monomers, gave rise to channel activity. These findings resolve the long-standing mystery of the MMC/PTP and demonstrate that Ca2+ can trans...
The digestive enzyme papain can drive the formation of crystalline titanium dioxide nanoparticles... more The digestive enzyme papain can drive the formation of crystalline titanium dioxide nanoparticles on surfaces. This dual functionality of thin film formation and mineralization promotion has the potential to enable the construction of hierarchical inorganic/organic structures in the form of continuous amorphous titania/protein films.
The aerobic thermoalkaliphile Caldalkalibacillus thermarum strain TA2.A1 is a member of a separat... more The aerobic thermoalkaliphile Caldalkalibacillus thermarum strain TA2.A1 is a member of a separate order of alkaliphilic bacteria closely related to the Bacillales order. Efforts to relate the genomic information of this evolutionary ancient organism to environmental adaptation have been thwarted by the inability to construct a complete genome. The existing draft genome is highly fragmented due to repetitive regions, and gaps between and over repetitive regions were unbridgeable. To address this, Oxford Nanopore Technology’s MinION allowed us to span these repeats through long reads, with over 6000-fold coverage. This resulted in a single 3.34 Mb circular chromosome. The profile of transporters and central metabolism gives insight into why the organism prefers glutamate over sucrose as carbon source. We propose that the deamination of glutamate allows alkalization of the immediate environment, an excellent example of how an extremophile modulates environmental conditions to suit its...
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Papers by Duncan McMillan