Combined effects of double mutations on catalytic activity and structural stability contribute to clinical manifestations of glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy in humans, affecting ~ 500 million worldwide. A detailed study of the structural stability and catalytic activity of G6PD variants is required to understand how different mutations cause varying degrees of enzyme deficiency, reflecting the response of G6PD variants to oxidative stress. Furthermore, for G6PD double variants, investigating how two mutations jointly cause severe enzyme deficiency is important. Here, we characterized the functional and structural properties of nine G6PD variants: G6PD Gaohe, G6PD Mahidol, G6PD Shoklo, G6PD Canton, G6PD Kaiping, G6PD Gaohe + Kaiping, G6PD Mahidol + Canton, G6PD Mahidol + Kaiping and G6PD Canton + Kaiping. All variants were less catalytically active and structurally stable than the wild type enzyme, with G6PD double mutations having a greater impact than single mutations. G6PD Shoklo and G6PD Canton + Kaiping were the least catalytically active single and double variants, respectively. The combined effects of two mutations were observed, with the Canton mutation reducing structural stability and the Kaiping mutation increasing it in the double mutations. Severe enzyme deficiency in the double mutants was mainly determined by the trade-off between protein stability and catalytic activity. Additionally, it was demonstrated that AG1, a G6PD activator, only marginally increased G6PD enzymatic activity and stability

Composite silica nanoparticle/polyelectrolyte microcapsules with reduced permeability and enhanced ultrasound sensitivity

Many chemical and biomedical systems require delivery and controlled release of small molecules, which cannot be achieved by conventional polyelectrolyte-based layer-by-layer capsules. This work proposes an innovative hybrid microcapsule by incorporating in situ formed silica nanoparticles within or on the shell. The influence of various experimental conditions on the stability, mechanical strength and morphology of capsules was investigated and characterised by SEM, TEM, XRD, EDX and FTIR. The multifunctional capabilities of the formed capsules were examined by encapsulating a small molecule rhodamine B (Rh-B) which could be further released by an ultrasonic trigger. The results show that in situ formed SiO2 nanoparticles through hydrolysis greatly reduced the permeability of the shell yet showed increased mechanical strength and ultrasound response. SiO2 nanoparticles were shown to be distributed on the surface or inside the polyelectrolyte shell, acting as supports for free-standing capsules in both liquid and dry environments. Rapid Rh-B molecule release and the fragmentation of the capsule shells were observed under 50 W ultrasound irradiation for a few seconds. Such innovative capsules with the capability of small molecule encapsulation and high ultrasound sensitivity could be promising for many applications where pulse release of small molecules is required

Synthesis, Characterization And Structure Control Of Ordered Mesoporous Silica Nanoparticles

Ordered mesoporous silica materials are characterized by uniform and tunable pore size, high surface area and large pore volume. In particular, nano-sized ordered mesoporous silica particles have drawn interest from several fields, including biorelated areas, because silica is benign, possesses chemical stability and can be integrated with other materials. Structural aspects, such as pore connectivity, geometry and pore size are known to govern materials performance. Extensive efforts have been devoted to synthesize mesoporous silica particles with different structures, functionalities and sizes. In contrast, only a small number of studies so far have concentrated on the formation mechanism of these particles. This is hence the focus of the present dissertation. The first part reports on the synthesis and characterization of ordered mesoporous silica nanoparticles with and without embedded magnetic nanoparticles. The formation mechanism of silica nanocomposites is investigated by capturing particle formation at different time points during the synthesis. A combination of transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS) is used to characterize the structure evolution of resulting materials. Incorporating organic moieties into the silica matrix provides additional functionalities to ordered mesoporous silica nanoparticles. However, it often leads to disordered pore structure or pore blockage. The second part demonstrates the preparation of aminated and ordered mesoporous silica nanoparticles using a cocondensation method. Increasing the amount of aminosilane in the synthesis feed causes a structural transition of organically modified particles from hexagonal to cubic. Pore size of ordered mesoporous silica and aminated ordered mesoporous silica nanoparticles can be tailored by the addition of a swelling agent during the synthesis. The structural transformation from hexagonal to cubic is also observed in the latter case, albeit at different amino silane concentrations. The final part reports on the internalization of nanoparticles into cells. Fluorescent aminated mesoporous silica nanoparticles are first prepared and then coated with poly(ethylene glycol) to improve particle stability and lower protein adsorption. Dye-labeled aminated mesoporous silica nanoparticles are spontaneously internalized by cells

Plasmonic dye-sensitized solar cells using core-shell metal-insulator nanoparticles

We present an investigation into incorporating core-shell Au-SiO 2 nanoparticles into dye-sensitized solar cells. We demonstrate plasmon-enhanced light absorption, photocurrent, and efficiency for both iodide/triiodide electrolyte based and solid-state dye-sensitized solar cells. Our spectroscopic investigation indicates that plasmon-enhanced photocarrier generation competes well with plasmons oscillation damping with in the first tens of femtoseconds following light absorption. © 2010 American Chemical Society

Ordered mesoporous silica nanoparticles with and without embedded iron oxide nanoparticles: Structure evolution during synthesis

This work reports on the structural evolution during room temperature synthesis of hexagonally ordered mesoporous silica nanoparticles with and without embedded iron oxide particles. Oleic acid-capped iron oxide nanoparticles are synthesized and transferred to an aqueous phase using the cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). MCM-41 type silica and composite nanoparticles are fabricated via sol-gel synthesis. Aliquots are taken from the solution during synthesis to capture the particle formation process. Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS) reveal a transition from a disordered to an ordered structure in both synthesis systems. Along with the evolution of structure, iron oxide nanoparticles acting as seeds at the early stages are relocated from the particle centers to the edges. Nitrogen sorption measurements for iron oxide-embedded mesoporous nanoparticles indicate surface areas as high as for the mesoporous silica nanoparticles without iron oxide.