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

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

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.

Synthesis and Formation Mechanism of Aminated Mesoporous Silica Nanoparticles

We report the room temperature formation of aminated mesoporous silica nanoparticles (NH₂-MSNs) by means of co-condensation of different molar ratios of tetraethyl orthosilicate (TEOS) and 3-aminopropyl triethoxysilane (APTES) in the synthesis feed. The resulting materials are characterized by a combination of transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and N₂ adsorption/desorption measurements. Analysis reveals that an increase in APTES loading (mol %) leads to structural transitions in the MSNs from hexagonal (0–49 mol %) to cubic <i>Pm</i>3̅<i>n</i> (54–64 mol %) to disordered at very high APTES amounts (69 mol %). Investigation of structural evolution during cubic <i>Pm</i>3̅<i>n</i> particle synthesis reveals early particle formation stages that are surprisingly similar to those discussed in recent literature on nonclassical single crystal growth. These include significant heterogeneities in particle density despite crystallographic orientation across the entire particle as well as particle growth via addition of preformed and prestructured silica clusters. Syntheses at varying pH reveal further details of the structure formation process. The results pose fundamental questions about the relation between formation mechanisms of classical crystalline materials and mesoscopically ordered, locally amorphous materials

One-Pot Synthesis of Aminated Bimodal Mesoporous Silica Nanoparticles as Antibacterial Nanocarrier and CO2 Capture Sorbent

Mesoporous silica nanoparticles have highly versatile structural properties that are suitable for a plethora of applications including catalysis, separation and nanotherapeutics. We report a one-pot synthesis strategy that generates bimodal mesoporous silica nanoparticles via co-assembly of a structure-directing Gemini surfactant (C16-3-16) with tetraethoxysilane/(3-aminopropyl)triethoxysilane-derived sol additive. Synthesis temperature enables control of the nanoparticle shape, structure and mesopore architecture. Variations of the aminosilane/alkylsilane molar ratio further enables programmable adjustments of hollow to dense nanoparticle morphologies, bimodal pore sizes and surface chemistry. The resultant Gemini-directed aminated mesoporous silica nanoparticles have excellent carbon dioxide adsorption capacities and antimicrobial properties against E. coli. Our results provide enhanced understandings in the structure formation of multiscale mesoporous inorganic materials that are desirable for numerous applications such as carbon sequestration, water remediation and biomedical-related applications

One-pot synthesis of aminated bimodal mesoporous silica nanoparticles as silver-embedded antibacterial nanocarriers and CO₂ capture sorbents

Mesoporous silica nanoparticles have highly versatile structural properties that are suitable for a plethora of applications including catalysis, separation, and nanotherapeutics. We report a one-pot synthesis strategy that generates bimodal mesoporous silica nanoparticles via coassembly of a structure-directing Gemini surfactant (C16-3-16) with a tetraethoxysilane/(3-aminopropyl)triethoxysilane-derived sol additive. Synthesis temperature enables control of the nanoparticle shape, structure, and mesopore architecture. Variations of the aminosilane/alkylsilane molar ratio further enable programmable adjustments of hollow to core-shell and dense nanoparticle morphologies, bimodal pore sizes, and surface chemistries. The resulting Gemini-directed aminated mesoporous silica nanoparticles have excellent carbon dioxide adsorption capacities and antimicrobial properties against Escherichia coli. Our results provide an enhanced understanding of the structure formation of multiscale mesoporous inorganic materials that are desirable for numerous applications such as carbon sequestration, water remediation, and biomedical-related applications.Nanyang Technological UniversitySubmitted/Accepted versionThis work was supported by a startup grant from Nanyang Technological University, Singapore

A silica sol-gel design strategy for nanostructured metallic materials

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso-to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals-including noble metals-to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stober process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices