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Scientific Highlights

Annual report 2017

HIMS scientists published 268 scientific articles in 2017. An anthology of research highlights per research group is given below.

Homogeneous, Supramolecular and Bio-inspired Catalysis

Small organic molecules provide a promising solution for the requirement to store large amounts of hydrogen in a future hydrogen-based energy system. Together with collaborators from the ETH Zürich we showed that diolefin–ruthenium complexes containing the chemically and redox non-innocent ligand trop2dad catalyse the production of H2 from formaldehyde and water in the presence of a base.

The process involves the catalytic conversion of formaldehyde to carbonate salt using aqueous solutions and is the fastest reported for acceptorless formalin dehydrogenation to date. A mechanism supported by density functional theory calculations postulates protonation of a ruthenium hydride to form a low-valent active species, the reversible uptake of dihydrogen by the ligand and active participation of both the ligand and the metal in substrate activation and dihydrogen bond formation.

Trincado, M.*; Sinha, V.; Rodriguez-Lugo, R.E.; Pribanic, B.; de Bruin, B.*; Grützmacher, H.*: Homogeneously Catalysed Conversion of Aqueous Formaldehyde to H2 and Carbonate. Nature Communications, 2017, 8, 14990. DOI: 10.1038/ncomms14990.

Heterogeneous Catalysis and Sustainable Chemistry

A cyanide decomposition catalyst developed by Dr Paula Oulego, Dr Raveendran Shiju and Prof. Gadi Rothenberg is now being tested on an industrial pilot scale.

Dr Shiju and Prof. Rothenberg next to the first two barrels (500kg) of their industrial catalyst. Photo: UvA.

Treating industrial wastewater continuously at a rate of 1000 liters per hour, the pilot is the last step before large-scale industrial application in areas such as gold mining, processing of precious metals, and steel production. The solid catalyst, based on a simple and cheap copper oxide, was invented in 2015. That it was developed in less than two years to an industrial pilot scale attests to the simplicity and efficiency of the process.

The catalyst enables cyanide decomposition by a fast reaction of cyanide ions with hydrogen peroxide at 40 °C, under ambient pressure. This reaction is so quick that the catalyst can be used with cyanide concentrations ranging from 1 mg/liter all the way up to 10 g/liter. It can thus be used for treating a broad range of industrial wastewater flows. 500 kg of the new catalyst were produced industrially especially for this pilot installation.

Synthetic Organic Chemistry

Since unravelling their fascinating architecture some fifteen years ago, the microorganism-derived lasso peptides attract the synthetic community. Five years ago we started the development of new covalent template-mediated methodology aimed at precise folding of a macrocycle over a molecular thread. This resulted in the first synthesis of a spirocyclic compound with an inverted geometry at the connecting carbon atom coined as a quasi[1]catenane by us.

Also the stereoisomer with regular spiro geometry was prepared and, uniquely, although only one stereocenter is present, both compounds have a diastereomeric relationship. By the introduction of scissile bonds at the central carbon atom this methodology should lead to [2]catenanes and [2]rotaxanes and, in the far future, eventually to the lasso peptide series.

Steemers, L.; Wanner, M.J.; Lutz, M.; Hiemstra, H; Van Maarseveen, J.H. Synthesis of spiro quasi[1]catenanes and quasi[1]rotaxanes via a templated backfolding strategy. Nature Communications, 2017,  8,  15392. DOI: 10.1038/ncomms15392

Biocatalysis

α-Chiral amines are key intermediates for the production of active pharmaceutical ingredients, fine chemicals and agrochemicals. Structurally simpler amines are also of interest for the production of polymers, dyes and other materials.

Following its break-through publication in Science on the asymmetric hydrogen-borrowing bioamination of alcohols, the Biocatalysis group has elucidated further the substrate scope and catalytic properties of amine dehydrogenase enzymes (Green Chem. 2017). Additionally, the group has developed a new orthogonal biocatalytic network that enables the quantitative and stereospecific amination of alcohols (Org. Biomol. Chem. 2017).

The system is based on the combination of two redox-neutral enzymatic modules. The first module, driven by NADP-dependent enzymes, oxidizes racemic alcohols to carbonyl compounds intermediates. The second module, driven by NAD-dependent enzymes, performs the asymmetric amination of the intermediate. As the two modules have a divergent co-enzyme specificity (NAD vs NADP), multiple redox reactions run simultaneously in the same vessel without the need for a physical separation. This property in chemistry is defined as “orthogonality”. Orthogonal chemical reactions are very rare as traditional chemical (redox) reagents are not selective. Moreover, the orthogonal biocatalytic network for the conversion of racemic alcohols into enantiopure amines is very efficient because it consumes only O2 and produces only stoichiometric carbonate as by-product.

Sustainable Materials Characterization

A novel lab-based X-ray spectrometer to allow X-ray absorption and emission spectroscopy in the laboratory, on a 24/7 basis, rather than at the synchrotron, was developed in collaboration with the University of Seattle (G. Seitler, D. Mortensen). The instrument enables studies on 3d and 5d transition metals systems, for their detailed structural and mostly electronic properties.

The first publication including data on the lab spectrometer appeared in JACS. Here, a reactive high-valent dinuclear nickel(IV) oxido bridged complex is reported that can be formed at room temperature by reaction of [(L)2Ni(II)2(μ-X)3]X (X = Cl or Br) with NaOCl in methanol or acetonitrile (where L = 1,4,7- trimethyl-1,4,7-triazacyclononane).

The unusual Ni(IV) oxido species is stabilized within a dinuclear tris-μ-oxido-bridged structure as [(L)2Ni(IV)2(μ-O)3]2+. Its structure and its reactivity with organic substrates are demonstrated through a combination of UV−Vis absorption, resonance Raman, 1H NMR, EPR, and X-ray absorption (near-edge) spectroscopy, ESI mass spectrometry, and DFT methods. The identification of a Ni(IV)-O species opens opportunities to control the reactivity of NaOCl for selective oxidations.

Computational Chemistry

Constructing functional forms and their corresponding force field parameters for the metal–linker interface of metal–organic frameworks is challenging. We propose fitting these parameters on the elastic tensor, computed from ab initio density functional theory calculations (J. Chem. Theory. Comput., 13, 3722-3730 (2017)).

The advantage of this top-down approach is that it becomes evident if functional forms are missing when components of the elastic tensor are off. Another advantage of this approach is that the construction of flexible force fields for functionalized MOFs should be straightforward. If the parent material reproduces the elastic constants well, then one can use functional forms and parameters from generic organic force fields to include the flexible modes of the substituted organic linkers.

As a proof-of-concept, a new flexible force field for MIL-47(V) is derived. Negative thermal expansion is observed and framework flexibility has a negligible effect on adsorption and transport properties for small guest molecules. We believe that this force field parametrization approach can serve as a useful tool for developing accurate flexible force field models that capture the correct mechanical behavior of the full periodic structure.

 

Computational Polymer Chemistry & Science for Arts

 

Molecular Photonics

 

Analytical Chemistry

 

 

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