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B5 (N): Simulationen mit multipler Auflösung von Quantenchemie über Kraftfelder zu hybriden “particle-field” Modellen

In dem Projekt soll ein neues „Multi-Resolution“-Simulationsverfahren entwickelt werden, das Auflösungen auf der quantenchemischen Ebene über atomistische Kraftfelder bis hin zu mesoskaligen “hybriden particle field” Modellen kombiniert, bei bei denen nach wie vor eine genaue Behandlung langreichweitiger elektrostatischer Effekte gegeben ist, In der geplanten Implementierung sollen alle Ebenen der Quantenchemie (Hartree-Fock-, Dichtefunktional- und, Coupled-Cluster-Theorie sowie Multirefenzmethoden) einbezogen werden, so dass chemische Reaktionen angemessen behandelt werden können. Um die benötigte Rechenzeit weiter zu reduzieren, sollen dynamisches Umschalten und quantenchemisch validierte stochastische Modelle für Reaktionswahrscheinlichkeiten implementiert werden.

Supramolecular Packing Drives Morphological Transitions of Charged Surfactant Micelles
Ken Schäfer, Hima Bindu Kolli, Mikkel Killingmoe Christensen, Sigbjørn Løland Bore, Gregor Diezemann, Jürgen Gauss, Giuseppe Milano, Reidar Lund, Michele Cascella
Angewandte Chemie International Edition, (2020);

The shape and size of self‐assembled structures upon local organization of their molecular building blocks are hard to predict in the presence of long‐range interactions. Combining small‐angle X‐ray/neutron scattering data, theoretical modelling, and computer simulations, sodium dodecyl sulfate (SDS), over a broad range of concentrations and ionic strengths, was investigated. Computer simulations indicate that micellar shape changes are associated with different binding of the counterions. By employing a toy model based on point charges on a surface, and comparing it to experiments and simulations, it is demonstrated that the observed morphological changes are caused by symmetry breaking of the irreducible building blocks, with the formation of transient surfactant dimers mediated by the counterions that promote the stabilization of cylindrical instead of spherical micelles. The present model is of general applicability and can be extended to all systems controlled by the presence of mobile charges.

The Grignard Reaction – Unraveling a Chemical Puzzle
Raphael Mathias Peltzer, Jürgen Gauss, Odile Eisenstein, Michele Cascella
Journal of the American Chemical Society 142 (6), 2984-2994 (2020);

More than 100 years since its discovery, the mechanism of the Grignard reaction remains unresolved. Ambiguities arise from the concomitant presence of multiple organomagnesium species and the competing mechanisms involving either nucleophilic addition or the formation of radical intermediates. To shed light on this topic, quantum-chemical calculations and ab initio molecular dynamics simulations are used to study the reaction of CH3MgCl in tetrahydrofuran with acetaldehyde and fluorenone as prototypical reagents. All organomagnesium species coexisting in solution due to the Schlenk equilibrium are found to be competent reagents for the nucleophilic pathway. The range of activation energies displayed by all of these compounds is relatively small. The most reactive species are a dinuclear Mg complex in which the substrate and the nucleophile initially bind to different Mg centers and the mononuclear dimethyl magnesium. The radical reaction, which requires the homolytic cleavage of the Mg–CH3 bond, cannot occur unless a substrate with a low-lying π*(CO) orbital coordinates the Mg center. This rationalizes why a radical mechanism is detected only in the presence of substrates with a low reduction potential. This feature, in turn, does not necessarily favor the nucleophilic addition, as shown for the reaction with fluorenone. The solvent needs to be considered as a reactant for both the nucleophilic and the radical reactions, and its dynamics is essential for representing the energy profile. The similar reactivity of several species in fast equilibrium implies that the reaction does not occur via a single process but by an ensemble of parallel reactions.

Hybrid Particle-Field Molecular Dynamics Simulations of Charged Amphiphiles in an Aqueous Environment
Hima Bindu Kolli, Antonio de Nicola, Sigbjørn Løland Bore, Ken Schäfer, Gregor Diezemann, Jürgen Gauss, Toshihiro Kawakatsu, Zhong-Yuan Lu, You-Liang Zhu, Giuseppe Milano, Michele Cascella
Journal of Chemical Theory and Computation 14 (9), 4928-4937 (2018);

A fundamental catalytic difference between zinc and manganese dependent enzymes revealed in a bacterial isatin hydrolase
Theis Sommer, Kaare Bjerregaard-Andersen, Lalita Uribe, Michael Etzerodt, Gregor Diezemann, Jürgen Gauss, Michele Cascella, J. Preben Morth
Scientific Reports 8 (1), (2018);


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