We provide proof-of-principle that an ambidextrous catalyst is capable of independent, dial-in control of the absolute stereochemistry of two similar nitrostyrene Michael addition reactions by in situ oxidation and reduction of the catalyst. The catalyst is capable of both static and dynamic catalysis modes; in combination both modes allow access to all four possible stereochemical outcomes for the two nitroalkane products in a single process.

A ligand capable of adopting two pseudo-enantiomeric helically chiral states when bound to copper has been applied as an asymmetric catalyst in the Michael addition of malonate substrates to nitrostyrenes. The absolute configuration of the helically chiral ligand is inverted upon oxidation/reduction of the copper center. In this way, the handedness of the Michael addition product (R/S) can be selected based on the handedness of the catalyst (Λ/Δ). Exciton coupled circular dichroism (ECCD) was used to identify which of the two pseudo-enantiomeric forms the catalyst adopted after reduction/oxidation, with additional support from X-ray crystallographic data. The synthesis of the ligand was achieved in five steps with an overall 61% yield. Enantiomeric excesses of the Michael addition products of up to 72% (S) and 70% (R) were obtained in acetonitrile. The ability to choose the handedness of the product based on the chiral state of the catalyst has been demonstrated with several different solvents, bases, nitrostyrene/malonate substrates, and prochiral malonate substrates. A combination of molecular modelling, crystal structure and kinetic data suggest that one urea moiety of the catalyst ligand likely binds the nitrostyrene substrate while blocking the Re face of the nitrostyrene in the transition state.

Several important neurotransmitter precursors were hyperpolarized via homogeneous hydrogenation with parahydrogen. Polarization enhancement was achieved for 1H and 13C spins by several orders of magnitude compared to thermal spectra. Such large signal enhancements of these molecules could facilitate neurotransmitter studies.

Due to the importance of Mn2+ ions in biological processes, it is of growing interest to develop protocols for analysis of Mn2+ uptake and distribution in cells. A supramolecular metal displacement assay can provide ratiometric fluorescence detection of Mn2+, allowing for quantitative and longitudinal analysis of Mn2+ uptake in living cells.

Pyridoxal-5′-phosphate (PLP) represents an active form of Vitamin B6 that shows relatively fast imine formation with hydrazines under physiological conditions without the need of a catalyst. A convenient phosphate/amine conjugation protocol was developed to covalently link PLP to proteins, affording proteins capable of hydrazone formation with bioorthogonal hydrazinyl functional groups. Thus, the lectin Concanavalin A (Con A) was labeled with PLP. Pretreatment with fluorescein hydrazide gave dye-labeled Con A that labeled cell surfaces efficiently. Alternatively, pretargeting was achieved by labeling cells with Con A-PLP, then treatment in vitro with Alexa Fluor 488 hydrazide.

Efficient metal-based chiroptical switches have been designed that are capable of achieving multiple stable and reversible states. Studies in this field have yielded a variety of complex molecular devices whose conformations are controllable by many triggering mechanisms including pressure, solvent, counter ion, redox state, and photoinduction. Many of the systems are monitored with precision using circular dichroism spectroscopy. This review aims to provide a brief background of the development of these systems and a comprehensive overview of recently developed metal-based chiroptical switches. Potential applications in electronics and sensor technologies are discussed.

Ligand design principles based on acyclic conformational analysis, dynamic stereochemistry, and hard-soft ligand–metal coordination have led to the development of several redox-triggered chiroptical molecular switches. Factors controlling the helicity of copper(I) and copper(II) coordination complexes were explored and exploited to create a series of stereodynamic complexes that exhibit remarkable chiroptical properties. In some systems, strong circular dichroic signal could be modulated between on and off states, while in others, it was possible to invert the ellipticity by one-electron oxidation/reduction. These complexes are of inherent interest for their dynamic stereochemical properties, but may also find use in optical display technology, data storage, telecommunications, or electromechanical devices.

The dynamics of molecular conformational changes for Cu(I) complexes of two tripodal ligands were studied. Variable-temperature NMR and circular dichroism in combination with two-dimensional NMR experiments were employed to determine the structural and energetic details of a dynamic process in which one of three arms dissociates from coordination to Cu(I). Dissociation was triggered by addition of a strongly coordinating anion (SCN−). One-electron oxidation to the Cu(II) complex returned coordination of all three ligand arms. The observed phenomena were dependent upon steric crowding; addition of a single methyl group to one arm resulted in marked differences in behavior. The CuSCN and CuPF6 complexes of tris(2-quinolylmethyl)amine (TQA) and the CuPF6 complex of 1-(quinolin-2-yl)-N,N-bis(quinolin-2-ylmethyl)ethanamine (MeTQA) did not give any evidence for differences in coordination over the temperature range 0–35 °C, while CuI(MeTQA)NCS demonstrated marked differences in NMR but not CD spectra over this temperature range. In the latter complex, two diastereotopic arms displace each other with a transition energy of 14.0 kcal mol−1. The structure of the arm-dissociated complex contains a higher degree of stereochemical complexity than the tetradentate complexes.

Ligand design principles based on acyclic conformational analysis, dynamic stereochemistry, and hard-soft ligand–metal coordination have led to the development of several redox-triggered chiroptical molecular switches. Factors controlling the helicity of copper(I) and copper(II) coordination complexes were explored and exploited to create a series of stereodynamic complexes that exhibit remarkable chiroptical properties. In some systems, strong circular dichroic signal could be modulated between on and off states, while in others, it was possible to invert the ellipticity by one-electron oxidation/reduction. These complexes are of inherent interest for their dynamic stereochemical properties, but may also find use in optical display technology, data storage, telecommunications, or electromechanical devices.

Due to the importance of Mn2+ ions in biological processes, it is of growing interest to develop protocols for analysis of Mn2+ uptake and distribution in cells. A supramolecular metal displacement assay can provide ratiometric fluorescence detection of Mn2+, allowing for quantitative and longitudinal analysis of Mn2+ uptake in living cells.

A ligand capable of adopting two pseudo-enantiomeric helically chiral states when bound to copper has been applied as an asymmetric catalyst in the Michael addition of malonate substrates to nitrostyrenes. The absolute configuration of the helically chiral ligand is inverted upon oxidation/reduction of the copper center. In this way, the handedness of the Michael addition product (R/S) can be selected based on the handedness of the catalyst (Λ/Δ). Exciton coupled circular dichroism (ECCD) was used to identify which of the two pseudo-enantiomeric forms the catalyst adopted after reduction/oxidation, with additional support from X-ray crystallographic data. The synthesis of the ligand was achieved in five steps with an overall 61% yield. Enantiomeric excesses of the Michael addition products of up to 72% (S) and 70% (R) were obtained in acetonitrile. The ability to choose the handedness of the product based on the chiral state of the catalyst has been demonstrated with several different solvents, bases, nitrostyrene/malonate substrates, and prochiral malonate substrates. A combination of molecular modelling, crystal structure and kinetic data suggest that one urea moiety of the catalyst ligand likely binds the nitrostyrene substrate while blocking the Re face of the nitrostyrene in the transition state.

Several important neurotransmitter precursors were hyperpolarized via homogeneous hydrogenation with parahydrogen. Polarization enhancement was achieved for 1H and 13C spins by several orders of magnitude compared to thermal spectra. Such large signal enhancements of these molecules could facilitate neurotransmitter studies.