Crystalline silica particle functionalized by PEG for its collision-enhanced detection at ultramicroelectrode.

Detecting individual particulate matter is highly significant in many areas, such as mine safety, environment, and human health. The analytical method based on single entity electrochemistry (SEE) has shown great potential in detecting, counting, and measuring individual particles, especially conductive metals or carbon particles, based on their unique charge transfer reactions at an ultramicroelectrode (UME). In this study, we report an innovative SEE method for improving the sensitivity of the detection of electrochemical inert crystalline silica particles by functionalizing silica particles with polyethylene glycol (PEG) molecules. The PEG surface functionalization of the silica was characterized by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The morphology of silica particles was characterized by a scanning electron microscope (SEM), and a transmission electron microscope (TEM) was employed to calibrate size distribution and determine the elemental composition of silica particles. The surface charges of silica particles were measured by dynamic light scattering techniques. The collision behaviors of crystalline silica particles with UME were investigated by cyclic voltammetric experiments, which are rarely reported in the literature. The crystalline silica particles were detected based on electrochemically blocking the flux of the redox mediator at the surface of UME, which showed significant signal amplification in the proposed method. Our method was demonstrated for detecting crystalline silica functionalized with or without PEG, acquiring the limit of quantification (LOQ) values of 0.391 µM (23.45 µg/L) and 0.824 µM (49.45 µg/L), respectively, which confirmed that a more than two times improvement in LOQ could be achieved over the PEG functionalized silica particles. We further presented a theoretical model using finite element simulations with COMSOL Multiphysics. We deduced a quantitative relation between the distribution of the current step size and the size distribution of silica particles. Therefore, the reported method here provides a paradigm for SEE-based detection of electrochemically inert crystalline silica particles, which extends the previous report substantially concerning particle detection.

The "Nitrogen Effect": Complexation with Macrocycles Potentiates Fused Heterocycles to Form Halogen Bonds in Competitive Solvents.

Weak intermolecular forces are typically very difficult to observe in highly competitive polar protic solvents as they are overwhelmed by the quantity of competing solvent. This is even more challenging for three-component ternary assemblies of pure organic compounds. In this work, we overcome these complications by leveraging the binding of fused aromatic N-heterocycles in an open resorcinarene cavity to template the formation of a three-component halogen-bonded ternary assembly in a protic polar solvent system.

Naphthalene-functionalized resorcinarene as selective, fluorescent self-quenching sensor for kynurenic acid.

Kynurenic acid is a by-product of tryptophan metabolism in humans, with abnormal levels indicative of disease. There is a need for water-soluble receptors that selectively bind kynurenic acid, allowing for detection and quantification. We report here the high-affinity binding of kynurenic acid in aqueous media to a resorcinarene salt receptor decorated with four flexible naphthalene groups at the upper rim. Experimental results from 1H NMR, isothermal titration calorimetry, and electronic absorption and fluorescence spectroscopies all support high-affinity binding and selectivity for kynurenic acid over tryptophan. The measured binding constant (K = 1.46 ± 0.21 × 105 M-1) is one order of magnitude larger than that observed with other resorcinarene receptors. The present host-guest system can be employed for sensory recognition of kynurenic acid. Computational studies reveal the key role of a series of cooperative attractive intra- and inter-molecular interactions contributing to an optimal binding process in this system.

Recent Advances in Halogen Bonded Assemblies with Resorcin[4]arenes.

Resorcinarenes are cavity-containing compounds when in the crown conformation, from the calixarene family of concave compounds. These easy to synthesize macrocycles can be decorated at the upper rim through the eight hydroxyl groups and/or the 2-position of the aromatic ring. They are good synthons in supramolecular chemistry leading to appealing assemblies such as open-inclusion complexes, capsules and tubes through multiple weak interactions with various guests. Halogen bonding (XB) is a highly directional non-covalent interaction by an electron-deficient halogen atom as a donor that interacts with a Lewis base, the XB acceptor. This tutorial review provides an overview of recent advances in halogen-bonded assemblies based on resorcinarenes and their derivatives, specifically focusing on discrete and capsular assemblies.

Functionalized resorcinarenes effectively disrupt the aggregation of αA66-80 crystallin peptide related to cataracts.

Cataracts, an eye lens clouding disease, are debilitating and while operable, remain without a cure. αA66-80 crystallin peptide abundant in cataracted eye lenses contributes to aggregation of αA-crystallin protein leading to cataracts. Inspired by the versatility of macrocycles and programmable guest selectivity through discrete functionalizations, we report on three water-soluble ionic resorcinarene receptors (A, B, and C) that disrupt the aggregation of αA66-80 crystallin peptide. A and B each possess four anionic sulfonate groups, while C includes four cationic ammonium groups with four flexible extended benzyl groups. Through multiple non-covalent attractions, these receptors successfully disrupt and reverse the aggregation of αA66-80 crystallin peptide, which was studied through spectroscopic, spectrometric, calorimetric, and imaging techniques. The αA66-80·receptor complexes were also explored using molecular dynamics simulation, and binding energies were calculated. Even though each of the three receptors can bind with the peptide, receptor C was characterized by the highest binding energy and affinity for three different domains of the peptide. In effect, the most efficient inhibitor was a cationic receptor C via extended aromatic interactions. These results highlight the potential of versatile and tunable functionalized resorcinarenes as potential therapeutics to reverse the aggregation of α-crystallin dominant in eye cataracts.

Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes.

Cethyl-2-methylresorcinarene (A), pyridine (B), and a set of 10 carboxylic acids (Cn) associate to form A·B·Cn ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between A·B and Cn are dependent on the pKa values of carboxylic acids. The weak interactions between A and C further reinforce the interactions between A and B, demonstrating positive cooperativity. Our results reveal that the two-component system such as that formed by A and B can form the basis for the development of specific sensors for the molecular recognition of carboxylic acids.

Cities and floods: A pragmatic insight into the determinants of households' coping strategies to floods in informal Accra, Ghana.

Floods are common events that confront many cities in the developing world. Ghana, a developing country, is persistently challenged with flood events, especially in its major cities. In informal Accra, for instance, despite the severity of flood effects and its associated threats, poor informal residents continue to stay. As a result, these poor urban dwellers have developed local coping strategies made up of mitigation and reactive measures to manage and adapt to flood hazards through their preceding experiences. In this article, we have embraced the convergent parallel mixed method of case study design to echo and explore (1) the major effects of preceding floods on informal households, (2) the local informal coping strategies adopted by households to mitigate and respond to flooding and its effects in the future and (3) the determinants of the coping strategies of households that underpin their continual stay in spite of flood risks in Alajo, an urbanised suburb in Accra metropolis noted as one of the slum communities that easily flood in Ghana. Our analysis has used a mix of qualitative and quantitative data collected from both secondary and primary sources as well as a conceptualised model known as disaster resilience of place. The key findings (Alajo has low degree of adaptive resilience to major floods which might occur in the future because of the lack of social learning in the coping strategies developed through several years of lessons learnt from perennial floods) and proposals (local coordination in implementing the coping strategies to flooding, state support of the local strategies and adoption of rainwater harvesting) also make contributions to managing urban floods in informal settlements in the developing world.