Total Syntheses of Vancomycin and Eremomycin Aglycons

Controlling the elements of planar and axial chirality are the principal challenges in the synthesis of the aglycon of vancomycin. Vancomycin is the prototypical member of the glycopeptide family of antibiotics which are effective for the treatment of infections by methicillin-resistant Staphylococcus aureus. The first total syntheses of the vancomycin and eremomycin aglycons provide insight into the influence of structure on kinetic and thermodynamic control of atropselective macrocyclizations.     

Incorporating solvation effects into density functional theory: Calculation of absolute acidities

An approach to the calculation of molecular electronic structures, solvation energies, and pK_a values in condensed phases is described. The electronic structure of the solute is described by density functional quantum mechanics, and electrostatic features of environmental effects are modeled through external charge distributions and continuum dielectrics. The reaction potential produced by a mode of the molecular charge distribution is computed via finite-difference solutions to the Poisson-Boltzmann equation and incorporated into the self-consistent field procedure. Here we report results on three sets of organic acids, whose pK_a values range over 16 pH units. The first set provides models for ionizable side chains in proteins; the second set considers the effects of substituting one to three chlorine atoms for hydrogens in acetic acid; and the final set consists of 4-substituted-bicyclo-[2.2.2]-octanecarboxylic acids. Successful prediction of “absolute” pK_a values places stringent requirements on the computation of gas-phase proton affinities and on the response to solvation. In some cases the current model shows substantial errors, but overall the results and trends are in good agreement with experiment. Prospects for extending this approach to more complex systems such as proteins are briefly discussed. © 1997 John Wiley & Sons, Inc.     

ChemInform Abstract: Gas‐Phase Molecular Structures of Third Row Transition‐Metal Hexafluorides WF6, ReF6, OsF6, IrF6, and PtF6. An Electron‐Diffraction and ab initio Study.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Modular Metal-Quinone Networks with Tunable Architecture and Functionality

Nanostructured materials with tunable structures and functionality are of interest in diverse areas. Herein, metal ions are coordinated with quinones through metal-acetylacetone coordination bonds to generate a class of structurally tunable, universally adhesive, hydrophilic, and pH-degradable materials. A library of metal-quinone networks (MQNs) is produced from five model quinone ligands paired with nine metal ions, leading to the assembly of particles, tubes, capsules, and films. Importantly, MQNs show bidirectional pH-responsive disassembly in acidic and alkaline solutions, where the quinone ligands mediate the disassembly kinetics, enabling temporal and spatial control over the release of multiple components using multilayered MQNs. Leveraging this tunable release and the inherent medicinal properties of quinones, MQN prodrugs with a high drug loading (>89 wt %) are engineered using doxorubicin for anti-cancer therapy and shikonin for the inhibition of the main protease in the SARS-CoV-2 virus.     

ChemInform Abstract: Molecular Structure of the Aluminum Halides,Al2Cl6, AlCl3, Al2Br6, AlBr3, and AlI3, Obtained by Gas-Phase Electron Diffraction and ab initio Molecular Orbital Calculations.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Correspondence on “Crystalline Porous Organic Salt for Ultrarapid Adsorption/Desorption-Based Atmospheric Water Harvesting by Dual Hydrogen Bond System”

In a recent Research Article, Ben and co-workers reported a hydrogen-bonded framework prepared from a 4⁺ tetra-amidinium component and a 4⁻ tetra-sulfonate component, termed CPOS-6. They showed that CPOS-6 could reversibly adsorb and desorb water over a narrow humidity window, and that this material offered potential for applications in atmospheric water harvesting. This conclusion was supported by experiments that showed the material was stable over 50 adsorption/desorption cycles and that the kinetics of these cycles were very rapid. In this Correspondence we present additional structural data regarding this framework in both its hydrated and dehydrated states and thus discern the mechanism of water binding. These data do not disagree with Ben and co-workers’ findings: rather they emphasise how remarkable the cyclability and rapid kinetics of adsorption/desorption are, as these processes involve a complete crystal-to-crystal rearrangement of the framework.