Nanoscale Configuration of Clay-Interlayer Chemistry: A Precursor to Enhancing Flame Retardant Properties

Nanomaterials are proving to be pivotal to the evolution of controllable, cost-effective and environmentally safe technologies. An important concern is the impact of low-dimensional compositional materials and their ability to significantly reduce the hazardous nature of flame retardants that are reputably harmful through unchecked inhalation. While eco-friendly and recyclable alternatives are necessary requirements to function as replacements for the ‘Next Generation’ of flame retardants, the underlying ‘Chemistry’ at the nanoscale is unfolding unlocking vital clues enabling the development of more effective retardants. In this direction, the dimensional order of particles in naturally occurring nanoclay materials and their associated properties as composites are gaining increasing attention as important constituents of flame retardants. In this review, we examine closer the compositional importance of intercalated/exfoliated nanoclay networks essential to retardant functionality exploring the chemical significance and discussing underlying mechanisms where possible

Insight into the Assembly Properties and Functional Organisation of the Magnetotactic Bacterial Actin-like Homolog, MamK

Magnetotactic bacteria (MTB) synthesize magnetosomes, which are intracellular vesicles comprising a magnetic particle. A series of magnetosomes arrange themselves in chains to form a magnetic dipole that enables the cell to orient itself along the Earth’s magnetic field. MamK, an actin-like homolog of MreB has been identified as a central component in this organisation. Gene deletion, fluorescence microscopy and in vitro studies have yielded mechanistic differences in the filament assembly of MamK with other bacterial cytoskeletal proteins within the cell. With little or no information on the structural and behavioural characteristics of MamK outside the cell, the mamK gene from Magnetospirillium gryphiswaldense was cloned and expressed to better understand the differences in the cytoskeletal properties with its bacterial homologues MreB and acitin. Despite the low sequence identity shared between MamK and MreB (22%) and actin (18%), the behaviour of MamK monitored by light scattering broadly mirrored that of its bacterial cousin MreB primarily in terms of its pH, salt, divalent metal-ion and temperature dependency. The broad size variability of MamK filaments revealed by light scattering studies was supported by transmission electron microscopy (TEM) imaging. Filament morphology however, indicated that MamK conformed to linearly orientated filaments that appeared to be distinctly dissimilar compared to MreB suggesting functional differences between these homologues. The presence of a nucleotide binding domain common to actin-like proteins was demonstrated by its ability to function both as an ATPase and GTPase. Circular dichroism and structural homology modelling showed that MamK adopts a protein fold that is consistent with the ‘classical’ actin family architecture but with notable structural differences within the smaller domains, the active site region and the overall surface electrostatic potential

Rationalizing Structural Hierarchy in the Design of Fuel Cell Electrode and Electrolyte Materials Derived from Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are arguably a class of highly tuneable polymer-based materials with wide applicability. The arrangement of chemical components and the bonds they form through specific chemical bond associations are critical determining factors in their functionality. In particular, crystalline porous materials continue to inspire their development and advancement towards sustainable and renewable materials for clean energy conversion and storage. An important area of development is the application of MOFs in proton-exchange membrane fuel cells (PEMFCs) and are attractive for efficient low-temperature energy conversion. The practical implementation of fuel cells, however, is faced by performance challenges. To address some of the technical issues, a more critical consideration of key problems is now driving a conceptualised approach to advance the application of PEMFCs. Central to this idea is the emerging field MOF-based systems, which are currently being adopted and proving to be a more efficient and durable means of creating electrodes and electrolytes for proton-exchange membrane fuel cells. This review proposes to discuss some of the key advancements in the modification of PEMs and electrodes, which primarily use functionally important MOFs. Further, we propose to correlate MOF-based PEMFC design and the deeper correlation with performance by comparing proton conductivities and catalytic activities for selected works

Rationalizing Structural Hierarchy in the Design of Fuel Cell Electrode and Electrolyte Materials Derived from Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are arguably a class of highly tuneable polymer-based materials with wide applicability. The arrangement of chemical components and the bonds they form through specific chemical bond associations are critical determining factors in their functionality. In particular, crystalline porous materials continue to inspire their development and advancement towards sustainable and renewable materials for clean energy conversion and storage. An important area of development is the application of MOFs in proton-exchange membrane fuel cells (PEMFCs) and are attractive for efficient low-temperature energy conversion. The practical implementation of fuel cells, however, is faced by performance challenges. To address some of the technical issues, a more critical consideration of key problems is now driving a conceptualised approach to advance the application of PEMFCs. Central to this idea is the emerging field MOF-based systems, which are currently being adopted and proving to be a more efficient and durable means of creating electrodes and electrolytes for proton-exchange membrane fuel cells. This review proposes to discuss some of the key advancements in the modification of PEMs and electrodes, which primarily use functionally important MOFs. Further, we propose to correlate MOF-based PEMFC design and the deeper correlation with performance by comparing proton conductivities and catalytic activities for selected works

Characterization of the amino acids from Neisseria meningitidis methionine sulfoxide reductase B involved in the chemical catalysis and substrate specificity of the reductase step.

Methionine sulfoxide reductases (Msrs) are antioxidant repair enzymes that catalyze the thioredoxin-dependent reduction of methionine sulfoxide back to methionine. The Msr family is composed of two structurally unrelated classes of enzymes named MsrA and MsrB, which display opposite stereoselectivities toward the S and R isomers of the sulfoxide function, respectively. Both classes of Msr share a similar three-step chemical mechanism involving first a reductase step that leads to the formation of a sulfenic acid intermediate. In this study, the invariant amino acids of Neisseria meningitidis MsrB involved in the reductase step catalysis and in substrate binding have been characterized by the structure-function relationship approach. Altogether the results show the following: 1) formation of the MsrB-substrate complex leads to an activation of the catalytic Cys-117 characterized by a decreased pKapp of approximately 2.7 pH units; 2) the catalytic active MsrB form is the Cys-117-/His-103+ species with a pKapp of 6.6 and 8.3, respectively; 3) His-103 and to a lesser extent His-100, Asn-119, and Thr-26 (via a water molecule) participate in the stabilization of the polarized form of the sulfoxide function and of the transition state; and 4) Trp-65 is essential for the catalytic efficiency of the reductase step by optimizing the position of the substrate in the active site. A scenario for the reductase step is proposed and discussed in comparison with that of MsrA

Functionalized and Biomimicked Carbon-Based Materials and Their Impact for Improving Surface Coatings for Protection and Functionality: Insights and Technological Trends

Interest in carbon materials has soared immensely, not only as a fundamental building block of life, but because its importance has been critical to the advancement of many diverse fields, from medicine to electrochemistry, which has provided much deeper appreciation of carbon functionality in forming unprecedented structures. Since functional group chemistry is intrinsic to the molecular properties, understanding the underlying chemistry of carbon is crucial to broadening its applicability. An area of economic importance associated with carbon materials has been directed towards engineering protective surface coatings that have utility as anticorrosive materials that insulate and provide defense against chemical attack and microbial colonization of surfaces. The chemical organization of nanoscale properties can be tuned to provide reliance of materials in carbon-based coating formulations with tunable features to enhance structural and physical properties. The transition of carbon orbitals across different levels of hybridization characterized by sp(1), sp(2), and sp(3) orientations lead to key properties embodied by high chemical resistance to microbes, gas impermeability, enhanced mechanical properties, and hydrophobicity, among other chemical and physical attributes. The surface chemistry of epoxy, hydroxyl, and carboxyl group functionalities can form networks that aid the dispersibility of coatings, which serves as an important factor to its protective nature. A review of the current state of carbon-based materials as protective coating materials are presented in the face of the main challenges affecting its potential as a future protective coating material. The review aims to explore and discuss the developmental importance to numerous areas that connects their chemical functionality to the broader range of applicationsY

Physico-chemical parameters influencing the polymerisation of MamK.

<p>The dependence of polymerisation activity of MamK on divalent metal ion concentration, salt, pH and temperature was monitored by light scattering intensity using a 90° optics scattering angle at a wavelength of 400 nm over a period of 1000 s. All polymerisation reactions were performed using a final concentration of MamK of 10 µM in the assay at 30°C. (a) Divalent metal dependent reactions of MamK were performed in 10 mM imidazole at pH 8.0 and initiated by adding 200 µM ATP containing either calcium or magnesium chloride in the range 0.125–2 mM (b) Salt dependent reactions were performed in 10 mM imidazole at pH 8.0 and initiated by adding 200 µM ATP with varying concentrations of KCl in the range 0–200 mM (100 mM, 50 mM, 25 mM, 12.5 mM, 6.25 mM, 3.125 mM, 1.56 mM) (c) pH dependence of MamK polymerization was performed in 0.1 mM EGTA, 1 mM MgCl2, 20 mM KCl, 200 µM ATP with 10 mM MES at pH 5.5, 10 mM imidazole pH 6.5, 10 mM imidazole pH 7.0, 10 mM imidazole pH 7.0, 10 mM tris pH 7.5, 10 mM tris pH 8.0, 10 mM tris pH 8.5, 10 mM tris pH 9.0 and 10 mM tris pH 9.5 (d) Temperature dependence of MamK polymerization was performed in 10 mM imidazole, 0.1 mM EGTA, 1 mM MgCl2, 20 mM KCl, 200 µM ATP in the range 30–45°C.</p