Selective Hydrogenation and Hydrodeoxygenation of Aromatic Ketones to Cyclohexane Derivatives Using a Rh@SILP Catalyst

Rhodium nanoparticles immobilized on an acid-free triphenylphosphonium-based supported ionic liquid phase (Rh@SILP(Ph3-P-NTf2)) enabled the selective hydrogenation and hydrodeoxygenation of aromatic ketones. The flexible molecular approach used to assemble the individual catalyst components (SiO2, ionic liquid, nanoparticles) led to outstanding catalytic properties. In particular, intimate contact between the nanoparticles and the phosphonium ionic liquid is required for the deoxygenation reactivity. The Rh@SILP(Ph3-P-NTf2) catalyst was active for the hydrodeoxygenation of benzylic ketones under mild conditions, and the product distribution for non-benzylic ketones was controlled with high selectivity between the hydrogenated (alcohol) and hydrodeoxygenated (alkane) products by adjusting the reaction temperature. The versatile Rh@SILP(Ph3-P-NTf2) catalyst opens the way to the production of a wide range of high-value cyclohexane derivatives by the hydrogenation and/or hydrodeoxygenation of Friedel–Crafts acylation products and lignin-derived aromatic ketones. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Selective hydrogenation of fluorinated arenes using rhodium nanoparticles on molecularly modified silica

The production of fluorinated cyclohexane derivatives is accomplished through the selective hydrogenation of readily available fluorinated arenes using Rh nanoparticles on molecularly modified silica supports (Rh@Si-R) as highly effective and recyclable catalysts. The catalyst preparation comprises grafting non-polar molecular entities on the SiO2 surface generating a hydrophobic environment for controlled deposition of well-defined rhodium particles from a simple organometallic precursor. A broad range of fluorinated cyclohexane derivatives was shown to be accessible with excellent efficacy (0.05-0.5 mol% Rh, 10-55 bar H2, 80-100 °C, 1-2 h), including industrially relevant building blocks. Addition of CaO as scavenger for trace amounts of HF greatly improves the recyclability of the catalytic system and prevents the risks associated to the presence of HF, without compromising the activity and selectivity of the reaction. © The Royal Society of Chemistry

Automated tangential-flow diafiltration device

Tangential flow filtration (TFF) is a chemical unit operation used to purify and concentrate liquid suspensions of colloids, proteins, or cells. The solution flows tangentially across a membrane, such that a selective part of the fluid permeates the membrane while the filtrated matter is retained, increasing its concentration. TFF is a mild mechanical purification method that does not interact chemically with the filtrate. It is applied in sensitive separation tasks in protein chemistry, microbiology, or immunology. It is a fast alternative for dialysis applications, also applicable in the field of colloid purification. However, the costs of automated lab-scale devices (30,000 €) and the consumable membrane modules (100–600 €) make TFF currently hardly accessible for lab-scale polymer researchers. Therefore, we built a low-cost TFF system (2400 €) partly automated by an Arduino microcontroller and optimized for diafiltration buffer exchange and concentration processes in soft matter colloid research. We use medical hemodialysis membrane modules that only cost a share (20–50 €) of alternative TFF modules, and we demonstrate the functionality of the system for an exemplary colloidal microgel purification process

Production of highly concentrated and hyperpolarized metabolites within seconds in high and low magnetic fields

Hyperpolarized metabolites are very attractive contrast agents for in vivo magnetic resonance imaging studies enabling early diagnosis of cancer, for example. Real-time production of concentrated solutions of metabolites is a desired goal that will enable new applications such as the continuous investigation of metabolic changes. To this end, we are introducing two NMR experiments that allow us to deliver high levels of polarization at high concentrations (50 mM) of an acetate precursor (55% 13C polarization) and acetate (17% 13C polarization) utilizing 83% para-state enriched hydrogen within seconds at high magnetic field (7 T). Furthermore, we have translated these experiments to a portable low-field spectrometer with a permanent magnet operating at 1 T. The presented developments pave the way for a rapid and affordable production of hyperpolarized metabolites that can be implemented in e.g. metabolomics labs and for medical diagnosis

Long-lived heteronuclear spin-singlet states

We report observation of long-lived spin-singlet states in a 13C-1H spin pair at zero magnetic field. In 13C-labeled formic acid, we observe spin-singlet lifetimes as long as 37 seconds, about a factor of three longer than the T1 lifetime of dipole polarization in the triplet state. We also observe that the lifetime of the singlet-triplet coherence, T2, is longer than T1. Moreover, we demonstrate that this singlet states formed by spins of a heteronucleus and a 1H nucleus, can exhibit longer lifetimes than the respective triplet states in systems consisting of more than two nuclear spins. Although long-lived homonuclear spin-singlet states have been extensively studied, this is the first experimental observation of analogous spin-singlets consisting of a heteronucleus and a proton.Comment: 5 pages, 4 figure

Solvent effects on catalytic activity and selectivity in amine-catalyzed D-fructose isomerization

Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of D-fructose to a valuable rare monosaccharide, D-allulose, as a function of solvent. The isomerization of D-fructose to D-allulose competes with its isomerization to D-glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards D-fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of D-fructose. Our results suggest that the furanose tautomer of D-fructose is isomerized to D-allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF ≈ DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best D-allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy

Optimierungen von Hyperpolarisationsmethoden basierend auf para-Wasserstoff hinsichtlich ihrer Biokompatibilität für in-vivo-Anwendungen in der Kernspinresonanz

The combination of hyperpolarization methods and imaging enables the detection of heteronuclei and opens up innovative fields of application in medical diagnostics. The fascinating properties, such as almost background-free signaling and large chemical shifting differences, which allow the tracking of chemical changes of low-concentrated biomarkers, can provide detailed insight into biochemical processes at the molecular level. The hyperpolarization methods based on parahydrogen (p-H2) have the potential for a wide application as they are simple, cost-effective and fast. However, the biocompatibility in combination with high polarization efficiency is a major challenge. The aim of the work was to optimize the PHIP methods with regard to these points.In the first part, a basis for a proper characterization of PHIP systems was established. A method based on kinetic studies has been developed that allows the determination of the polarization transfer efficiency (PTE) in PHIP experiments. This method was then applied to study homogeneous catalysts to investigate the influence of the chemical system. It was found that the T1 time as well as the lifetime and the concentration of the intermediates decisively influence the PTE. The PTE is a precise parameter which properly characterizes the chemical PHIP system, thus enabling comparison and optimization of known systems as well as the development of new systems. Furthermore, for the first time, PHIP was demonstrated with the help of a novel, artificial metalloenzyme consisting of a Rhodium triphos catalyst covalently bound to a biomolecular framework. The polarization efficiency is exceptionally high compared to other systems. The metalloenzyme is an innovative immobilization method for PHIP catalysts and is ideally suited for biomedical applications due to the activity in water, the easy separability and the high polarization efficiency.In the next chapter, the water-soluble catalyst precursor [Ir(IDEG)(COD)Cl] was used to demonstrate SABRE in a pure water system for the first time. Here, the polarization could be transferred to both protons and 15N nuclei of biomarker molecules, such as diazirine and nicotinamide. The hyperpolarization in pure water without the use of toxic solvents opens the door to the biomedical application of SABRE.The last chapter deals with the polarization of solvents. For the first time, water could be hyperpolarized by means of p-H2 in the presence of [Ir(IDEG)(COD)Cl] and histidine. The polarization of solvent protons can be transferred to heteronuclei of biomedical relevant molecules that are not polarizable by the typical SABRE mechanism.In summary, the hyperpolarization methods based on p-H2 could be significantly optimized with regard to their biocompatibility and thus great steps towards biomedical application could be achieved