NMR signal amplification by reversible exchange (SABRE) has been observed for pyridine, methyl nicotinate, N-methylnicotinamide, and nicotinamide in D₂O with the new catalyst [Ir(Cl)(IDEG)(COD)] (IDEG=1,3-bis(3,4,5-tris(diethyleneglycol)benzyl)imidazole-2-ylidene). During the activation and hyperpolarization steps, exclusively D₂O was used, resulting in the first fully biocompatible SABRE system. Hyperpolarized ¹H substrate signals were observed at 42.5 MHz upon pressurizing the solution with parahydrogen at close to the Earth's magnetic field, at concentrations yielding barely detectable thermal signals. Moreover, 42-, 26-, 22-, and 9-fold enhancements were observed for nicotinamide, pyridine, methyl nicotinate, and N-methylnicotinamide, respectively, in conventional 300 MHz studies. This research opens up new opportunities in a field in which SABRE has hitherto primarily been conducted in CD₃OD. This system uses simple hardware, leaves the substrate unaltered, and shows that SABRE is potentially suitable for clinical purposes.

The light-driven reduction of protons for the production of molecular hydrogen in multicomponent systems depends on electron relays such as viologens. We describe here the effect of viologens appended with guest moieties (adamantane or bile acid) on the efficiency of a system composed of a cyclodextrin-appended photosensitizer [Ir(ppy)₂(pytl-βCD)]Cl [ppy = 2-phenylpyridine; pytl = 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine; CD = cyclodextrin], cyclodextrin-modified Pt nanoparticles as the catalyst, and ethylenediaminetetraacetic acid (EDTA) as the sacrificial donor. The system was designed to self-assemble in a supramolecular manner in order to promote electron transfer and produce hydrogen. Cyclic voltammetry (CV) measurements in DMF showed that the electron-donating adamantyl substituent decreases the reduction potential of the viologen. The use of symmetric and asymmetric guest-appended viologens gave rise to unexpected phenomena in the H₂ evolution. The presence of adamantane or bile acid groups on the viologen induced stabilization and aggregation of the radical cations in water, which is disadvantageous for hydrogen formation.

Cationic cyclometalated iridium complexes containing two anionic phenylpyridine (ppy) ligands and the neutral bidentate triazole–pyridine ligand, 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine (pytl), were investigated. The complexes display a rich and reversible electrochemical behavior, upon investigations by cyclic voltammetry in strictly aprotic conditions, that couples with excellent emission quantum yields and long lifetimes of the excited states. Therefore, in organic media, all complexes have generated intense green electrochemiluminescence (ECL) through the so-called annihilation procedure and, importantly, a modulation of the emission energy (to blue) has been easily obtained by simple fluorination of the ppy ligand. Finally, taking advantage of their remarkable solubility in water, intense ECL was also obtained from aqueous buffer solutions using the co-reactant method, thus making all the investigated complexes highly promising for their effective use as ECL labels in bioanalytical applications.

Novel 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine (pytl) ligands have been prepared by “click chemistry” and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)₂(pytl-R)]Cl₂ and [Ir(ppy)₂(pytl-R)]Cl (R=methyl, adamantane (ada), β-cyclodextrin (βCD)). The two diastereoisomers of the Ir complex with the appended β-cyclodextrin, [Ir(ppy)₂(pytl-βCD)]Cl, were separated. The [Ru(bpy)₂(pytl-R)]Cl₂ (R=Me, ada or βCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Φ=0.23, τ=1000 ns) of [Ir(ppy)₂(pytl-ada)]Cl are surprisingly enhanced in [Ir(ppy)₂(pytl-βCD)]Cl (Φ=0.54, τ=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the βCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron-withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)₂(pytl-βCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Δ and Λ isomers of the metal complex.

A giant amphiphile consisting of polystyrene end-capped with permethylated β-cyclodextrin was synthesised and found to form vesicular structures when injected as a solution in THF into water. The ability of the cyclodextrins on the surface of the polymersomes to form inclusion complexes with hydrophobic compounds was tested by carrying out a competition experiment with a fluorescent probe sensitive to the polarity of the surrounding medium. It was found that 1-adamantol can displace the fluorescent probe from the cavities of the cyclodextrin moieties of the polymersomes. The recognition of molecules by cell membranes in nature is often based on interactions with specific membrane receptors. To mimic this behaviour, the enzyme horseradish peroxidase was modified with adamantane groups through a poly(ethylene glycol) spacer and its interaction with the polymersomes was investigated. It was established that the presence of adamantane moieties on each enzyme allowed a host–guest interaction with the multifunctional surface of the polymersomes.