Understanding the Mechanocatalytic Conversion of Biomass: A Low‐Energy One‐Step Reaction Mechanism by Applying Mechanical Force

On the way to establishing biomass as a renewable and environmentally friendly source to cover the ever‐increasing global demand on energy and chemicals, one great challenge is the efficient depolymerization of cellulose. Enhanced conversion rates have been discovered in ball‐milling experiments, thus opening a mechanocatalytic approach. However, an understanding of the impact of mechanical forces on the acid‐catalyzed cleavage of glycosidic bonds at the molecular level is still missing. Herein, we contribute such fundamental insight based on atomistic modeling. Mechanically stressing the macromolecular backbone radically changes the depolymerization pathway from a complex high‐barrier reaction upon thermal activation to a low‐energy single‐step mechanocatalytic process. In addition to revealing a regioselective increase in basicity under a mechanical force, our results provide molecular‐level explanations of the experimental findings and might therefore guide rational ways to improve such mechanocatalytic processes.     

Singlet Fission in Carbene-Derived Diradicaloids

Herein, we present a new class of singlet fission (SF) materials based on diradicaloids of carbene scaffolds, namely cyclic (alkyl)(amino)carbenes (CAACs). Our modular approach allows the tuning of two key SF criteria: the steric factor and the diradical character. In turn, we modified the energy landscapes of excited states in a systematic manner to accommodate the needs for SF. We report the first example of intermolecular SF in solution by dimer self-assembly at cryogenic temperatures.     

Synthesis of Polymers Containing Potassium Acyltrifluoroborates (KATs) and Post-polymerization Ligation and Conjugation

We report the synthesis of monomers for atom-transfer radical polymerization (ATRP) and a reversible addition-fragmentation chain transfer (RAFT) agent bearing trifluoroborate iminiums (TIMs), which are quantitatively converted into potassium acyltrifluoroborates (KATs) after polymerization. The resulting KAT-containing polymers are suitable for rapid amide-forming ligations for both post-polymerization modification and polymer conjugation. The polymer conjugation occurs rapidly, even under dilute (micromolar) aqueous conditions at ambient temperatures, thereby enabling the synthesis of a variety of linear and star-shaped block copolymers. In addition, we applied post-polymerization modification to the covalent linking of a photocaged cyclic antibiotic (gramicidin S) to the side chains of the KAT-containing copolymer. Cellular assays revealed that the polymer–antibiotic conjugate is biocompatible and provides efficient light-controlled release of the antibiotic on demand.     

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This paper presents a framework for incorporating arbitrary implicit multistep schemes into the lattice Boltzmann method. While the temporal discretization of the lattice Boltzmann equation is usually derived using a second-order trapezoidal rule, it appears natural to augment the time discretization by using multistep methods. The effect of incorporating multistep methods into the lattice Boltzmann method is studied in terms of accuracy and stability. Numerical tests for the third-order accurate Adams-Moulton method and the second-order backward differentiation formula show that the temporal order of the method can be increased when the stability properties of multistep methods are considered in accordance with the second Dahlquist barrier.     

A Study of the Time Constant in Unsteady Porous Media Flow Using Direct Numerical Simulation

We consider unsteady flow in porous media and focus on the behavior of the coefficients in the unsteady form of Darcy’s equation. It can be obtained by consistent volume-averaging of the Navier–Stokes equations together with a closure for the interaction term. Two different closures can be found in the literature, a steady-state closure and a virtual mass approach taking unsteady effects into account. We contrast these approaches with an unsteady form of Darcy’s equation derived by volume-averaging the equation for the kinetic energy. A series of direct numerical simulations of transient flow in the pore space of porous media with various complexities are used to assess the applicability of the unsteady form of Darcy’s equation with constant coefficients. The results imply that velocity profile shapes change during flow acceleration. Nevertheless, we demonstrate that the new kinetic energy approach shows perfect agreement for transient flow in porous media. The time scale predicted by this approach represents the ratio between the integrated kinetic energy in the pore space and that of the intrinsic velocity. It can be significantly larger than that obtained by volume-averaging the Navier–Stokes equation using the steady-state closure for the flow resistance term.     

Interaction of antitumoral drug erlotinib with biodegradable triblock copolymers: a molecular modeling study

Combination of molecular dynamics simulations and miscibility calculations was used to investigate erlotinib drug delivery systems based on poly-ε-caprolactone–polyethylene glycol–poly-ε-caprolactone (PCL–PEG–PCL) and poly-ε-caprolactone–polyglycolic acid–poly-ε-caprolactone (PCL–PGA–PCL) biodegradable copolymers. The molecular modeling strategy involving visual observation of models, concentration profile analysis, Flory–Huggins χ parameter, cohesive energy density, and mean square displacement calculations reproduced experimental evidence of erlotinib release from PCL–PEG–PCL matrix successfully. Increasing portion of PCL in PCL–PEG–PCL copolymer led to dissolution of erlotinib aggregates recorded in visual and concentration profile analyses. Higher portion of PCL led to higher cohesive energy density and lower mean square displacement values. Success of this strategy in reproduction of experimental data made an opportunity to utilize the same modeling design in prediction of erlotinib release from similar but not yet experimentally tested PCL–PGA–PCL matrix. In this case, agglomeration of erlotinib molecules and stronger cohesive energy density values were observed.     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.