Defective hierarchical porous copper-based metal-organic frameworks synthesised via facile acid etching strategy

Introducing hierarchical pore structure to microporous materials such as metal-organic frameworks (MOFs) can be beneficial for reactions where the rate of reaction is limited by low rates of diffusion or high pressure drop. This advantageous pore structure can be obtained by defect formation, mostly via post-synthetic acid etching, which has been studied extensively on water-stable MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a corresponding manner by using phosphoric acid as a size-selective etching agent and a mixture of dimethyl sulfoxide and methanol as a dilute solvent. Interestingly, we demonstrate that the etching process which is time- and acidity- dependent, can result in formation of defective HKUST-1 with extra interconnected hexagonal macropores without compromising on the bulk crystallinity. These findings suggest an intelligent scalable synthetic method for formation of hierarchical porosity in MOFs that are prone to hydrolysis, for improved molecular accessibility and diffusion for catalysis.Comment: 14 pages, 8 figure

Vaccine protein stabilization in silica

Successful eradication or control of prevailing infectious diseases is linked to vaccine efficacy, stability and distribution. The majority of protein based vaccines are transported at fridge temperatures (‘cold-chain’) to maintain their potency. However, this has been shown to be problematic. Proteins are inherently susceptible to thermal fluctuations, occurring during transportation, causing them to denature. This leads to ineffective vaccines and an increase in vaccine preventable diseases, especially in low-income countries. Our research utilizes silica to preserve and eventually distribute vaccines at room temperature, thereby decreasing the load on ‘cold-chain’ logistics. The methodology is based upon sol-gel chemistry where soluble silica is employed to encapsulate, ensilicate, vaccine proteins1. This yields protein-loaded silica nanoparticles in the form of a dry powder (figure 1). The material is stored at room temperature and stress tested (heating, 80°C, 2 hours). Subsequently, ensilicated protein is released using a fast chemical process. Silica, silicon dioxide, is an inert biocompatible material with certain ceramic properties that is beneficial in this scenario. The proof-of-concept work was done with a common vaccine antigen: tetanus toxin C fragment2. This protein is the immunogenic part of the full tetanus neurotoxin. Analysis of TTCF protein before and after stabilization in silica revealed full retention of protein structure at various levels. Additionally, specific antibody binding indicated retention of immunogenic epitopes (figure 2). These finding suggest that this methodology could reduce or perhaps eliminate vaccine waste. More work will be undertaken to verify protein stabilization and functional retention in vivo. Please click Additional Files below to see the full abstract

Isostaticity, auxetic response, surface modes, and conformal invariance in twisted kagome lattices

Model lattices consisting of balls connected by central-force springs provide much of our understanding of mechanical response and phonon structure of real materials. Their stability depends critically on their coordination number $z$. $d$-dimensional lattices with $z=2d$ are at the threshold of mechanical stability and are isostatic. Lattices with $z<2d$ exhibit zero-frequency "floppy" modes that provide avenues for lattice collapse. The physics of systems as diverse as architectural structures, network glasses, randomly packed spheres, and biopolymer networks is strongly influenced by a nearby isostatic lattice. We explore elasticity and phonons of a special class of two-dimensional isostatic lattices constructed by distorting the kagome lattice. We show that the phonon structure of these lattices, characterized by vanishing bulk moduli and thus negative Poisson ratios and auxetic elasticity, depends sensitively on boundary conditions and on the nature of the kagome distortions. We construct lattices that under free boundary conditions exhibit surface floppy modes only or a combination of both surface and bulk floppy modes; and we show that bulk floppy modes present under free boundary conditions are also present under periodic boundary conditions but that surface modes are not. In the the long-wavelength limit, the elastic theory of all these lattices is a conformally invariant field theory with holographic properties, and the surface waves are Rayleigh waves. We discuss our results in relation to recent work on jammed systems. Our results highlight the importance of network architecture in determining floppy-mode structure.Comment: 12 pages, 7 figure