Mechanochemical Synthesis, Accelerated Aging, and Thermodynamic Stability of the Organic Mineral Paceite and Its Cadmium Analogue

We demonstrate the use of ball milling mechanochemistry for rapid, simple, and materials-efficient synthesis of the organic mineral paceite CaCu­(OAc)4·6H2O (where OAc– is the acetate ion), composed of coordination polymer chains containing alternating Ca2+ and Cu2+ ions, as well as its cadmium-based analogue CaCd­(OAc)4·6H2O. While the synthesis of paceite in aqueous solutions requires a high excess of the copper precursor, mechanochemistry permits the use of stoichiometric amounts of reagents, as well as the use of poorly soluble and readily accessible calcium carbonate or hydroxide reactants. As established by thermochemical measurements, enthalpies of formation of both synthetic paceite and its cadmium analogue relevant to the mechanochemical reactions are highly exothermic. Reactions can also be conducted using accelerated aging, a synthetic technique that mimics geological processes of mineral weathering. Accelerated aging reactivity involving copper­(II) acetate monohydrate (hoganite) and calcium carbonate (calcite) provides a potential explanation of how complex organic minerals like paceite could form in a geological environment

Mechanochemical Synthesis of a Mercury(II) Metal-Organic Framework Reveals a Two-Dimensional Polymorph Stabilized by Weak Interactions

Solid-state mechanochemistry revealed a novel polymorph of the mercury(II) imidazolate framework, based on square-grid (sql) topology layers. Reaction monitoring and periodic density functional theory calculations show that the sql-structure is of higher stability than the previously reported three-dimensional structure, with the unexpected stabilization of a lower dimensionality structure explained by contributions of weak interactions, which include short C-H···Hg contacts

Proton Conductivity, Stability and Potential for Polymorphism in Metal-Organic Framework Minerals

We demonstrate that rare metal-organic framework (MOF) minerals stepanovite and zhemchuzhnikovite can exhibit properties comparable to known oxalate MOFs, including high proton conductivity at 25 oC, and retention of the framework structure upon thermal dehydration. They also have high thermodynamic stability, with a pronounced stabilizing effect of substituting aluminium for iron, illustrating a simple design to access stable, highly proton-conductive MOFs without using complex organic ligands. <br /

Real-Time in Situ Monitoring of Particle and Structure Evolution in Mechanochemical Synthesis of UiO-66 Metal-Organic Framework

Manuscript about monitoring the mechanochemical reaction of a metal-organic framework model system by in situ X-ray powder diffraction<br /

Experimental and Theoretical Investigation of Structures, Stoichiometric Diversity, and Bench Stability of Cocrystals with a Volatile Halogen Bond Donor

We present a combined experimental and theoretical study of the structures and bench stability of halogen-bonded cocrystals involving the volatile halogen bond donor octafluoro-1,4-diiodobutane, with phenazine and acridine as acceptors. Cocrystallization experiments using mechanochemistry and solution crystallization revealed three chemically and structurally distinct cocrystals. Whereas only one cocrystal form has been observed with acridine, cocrystallization with phenazine led to two stoichiometrically different cocrystals, in which phenazine employs either one or two nitrogen atoms per molecule as halogen bond acceptor sites. Cocrystal stability was evaluated experimentally by simultaneous thermogravimetric analysis and differential thermal analysis or differential scanning calorimetry, real-time powder X-ray diffraction monitoring of cocrystals upon storage in open air, and theoretically by using dispersion-corrected periodic density functional theory. The use of real-time powder X-ray diffraction enabled the comparison of rates of cocrystal decomposition, and the observed trends in cocrystal stability were reproduced by the ranking of theoretically calculated cocrystal decomposition enthalpies. Whereas all cocrystals eventually lose the volatile halogen bond donor upon storage in open air or by heating, these experimental and theoretical studies show that the cocrystal of acridine is the most stable, in agreement with its more basic properties. The stoichiometric variations of the phenazine cocrystal also exhibit a notable difference in stability, with the cocrystal containing the halogen bond acceptor and donor in a 1:1 stoichiometric ratio being of particularly low stability, decomposing in open air within minutes

Controlling the Polymorphism and Topology Transformation in Porphyrinic Zirconium Metal-Organic Frameworks via Mechanochemistry

The mechanochemical approach has been used here for preparation and polymorph resolution in porphyrinic MOF-525/PCN-223 zirconium metal-organic frameworks system, achieving pure target MOF phases in 30-60 minutes milling. In specific reaction condition, MOF-525 forms rapidly by milling but transforms into PCN-223, confirming it to be the kinetic phase in this polymorphic system. ESR measurements showed a strong effect of internal MOF structure on the spin structure of paramagnetic cations coordinated into porphyrin linkers, which show potential for these polymorphic MOFs in spintronics application

3‑Oxo-hexahydro‑1<i>H</i>‑isoindole-4-carboxylic Acid as a Drug Chiral Bicyclic Scaffold: Structure-Based Design and Preparation of Conformationally Constrained Covalent and Noncovalent Prolyl Oligopeptidase Inhibitors

Bicyclic chiral scaffolds are privileged motifs in medicinal chemistry. Over the years, we have reported covalent bicyclic prolyl oligopeptidase inhibitors that were highly selective for POP over a number of homologous proteins. Herein, we wish to report the structure-based design and synthesis of a novel class of POP inhibitors based on hexahydroisoindoles. A docking study guided the selection of structures for synthesis. The stereochemistry, decoration, and position within the molecule of the bicyclic scaffolds were assessed virtually. Following the synthesis of the best candidates, <i>in vitro</i> assays revealed that one member of this chemical series was more active than any of our previous inhibitors with a <i>K</i>_<i>i</i> of 1.0 nM. Additional assays also showed that the scaffold of this potent inhibitor, in contrast to one of our previously reported chemical series, is highly metabolically stable, despite the foreseen potential sites of metabolism. Interestingly, computer docking calculations accurately predicted the optimal features of the inhibitors

3‑Oxo-hexahydro‑1<i>H</i>‑isoindole-4-carboxylic Acid as a Drug Chiral Bicyclic Scaffold: Structure-Based Design and Preparation of Conformationally Constrained Covalent and Noncovalent Prolyl Oligopeptidase Inhibitors

Bicyclic chiral scaffolds are privileged motifs in medicinal chemistry. Over the years, we have reported covalent bicyclic prolyl oligopeptidase inhibitors that were highly selective for POP over a number of homologous proteins. Herein, we wish to report the structure-based design and synthesis of a novel class of POP inhibitors based on hexahydroisoindoles. A docking study guided the selection of structures for synthesis. The stereochemistry, decoration, and position within the molecule of the bicyclic scaffolds were assessed virtually. Following the synthesis of the best candidates, <i>in vitro</i> assays revealed that one member of this chemical series was more active than any of our previous inhibitors with a <i>K</i>_<i>i</i> of 1.0 nM. Additional assays also showed that the scaffold of this potent inhibitor, in contrast to one of our previously reported chemical series, is highly metabolically stable, despite the foreseen potential sites of metabolism. Interestingly, computer docking calculations accurately predicted the optimal features of the inhibitors