Further characterization of the large subunit of the major embryonic Artemia franciscana cysteine protease.

The encysted embryos of Artemia franciscana contain a potentially unique cysteine protease consisting of a cathepsin L-like protease and a tightly associated protein which has been denoted as the large subunit. Whereas the small subunit has been characterized in this laboratory as a cathepsin L-like cysteine protease, the large subunit has not been studied. The dimeric cysteine protease from Artemia encysted embryos was purified to apparent homogeneity using a multi-step method involving gel filtration, anion exchange and affinity chromatography. Five isoforms were separated by fast protein liquid chromatography. The protease subunits from each isoform were isolated using reverse phase high performance liquid chromatography. Protease Lys C and cyanogen bromide treatments were used to generate fragments for N-terminal amino acid sequencing of the large subunit from the major isoform of Artemia cysteine protease. Chromatography of the Artemia cysteine protease on Mono S at pH 5.0 led to the purification of the subunits in the native state. Based on molecular and biochemical data, several possible roles for the large subunit of Artemia cysteine protease are proposed in this thesis. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1999 .P85. Source: Masters Abstracts International, Volume: 39-02, page: 0453. Adviser: Alden Warner. Thesis (M.Sc.)--University of Windsor (Canada), 2000

How Can a Hydrophobic MOF be Water-Unstable? Insight into the Hydration Mechanism of IRMOFs

International audienceWe report an ab initio Molecular Dynamics study of the hydration process in a model IRMOF material. At low water content (one molecule per unit cell), water physisorption is observed on the zinc cation but the free ⇄ bound equilibrium strongly favors the free state. This is consistent with the hydrophobic nature of the host matrix and its type V isotherm observed in a classical Monte Carlo simulation. At higher loading, a water cluster can be formed at the Zn4O site and this is shown to stabilize the water bound state. This structure very rapidly transforms into a linker-displaced state, where water has fully displaced one arm of a linker and which corresponds to the loss of the material's fully-ordered structure. Thus an overall hydrophobic MOF material can also become water unstable, a feature that was not fully understood until now

Liquid metal–organic frameworks

Metal–organic frameworks are a family of chemically diverse materials, with applications in a wide range of fields covering engineering, physics, chemistry, biology and medicine. Until recently research has focused almost entirely on crystalline structures, yet now a clear trend is emerging shifting the emphasis onto disordered states including “defective by design” crystals, as well as amorphous phases such as glasses and gels. Here we introduce a strongly associated MOF liquid, obtained by melting a zeolitic imidazolate framework (ZIF). We combine in-situ variable temperature X-ray, ex-situ neutron pair distribution function experiments, and first principles molecular dynamics simulations to study the melting phenomenon and the nature of the liquid obtained. We demonstrate from structural, dynamical, and thermodynamical information that the chemical configuration, coordinative bonding, and porosity of the parent crystalline framework survive upon formation of the MOF liquid.This work benefitted from the financial support of ANRT (thèse CIFRE 2015/0268). We acknowledge access to HPC platforms provided by a GENCI grant (A0010807069). TDB would like to thank the Royal Society for a University Research Fellowship

Melting of zeolitic imidazolate frameworks with different topologies: insight from first-principles molecular dynamics

Metal–organic frameworks are chemically versatile materials, and excellent candidates for many applications from carbon capture to drug delivery, through hydrogen storage. While most studies so far focus on the crystalline MOFs, there has been a recent shift to the study of their disordered states, such as defective structures, glasses, gels, and very recently liquid MOFs. Following the publication of the melting mechanism of zeolitic imidazolate framework ZIF-4, we use here molecular simulation in order to investigate the similarities and differences with two other zeolitic imidazolate frameworks, ZIF-8 and ZIF-zni. We perform first principles molecular dynamics simulations to study the melting phenomena and the nature of the liquids obtained, focusing on structural characterization at the molecular scale, dynamics of the species, and thermodynamics of the solid–liquid transition. We show how the retention of chemical configuration, the changes in the coordination network, and the variation of the porous volume in the liquid phase are influenced by the parent crystalline framework.<br /