Photon-powered charge separation is achieved in a supramolecular architecture based on the dense packing of functional building blocks. Therefore, self-assembled dimers of interpenetrated coordination cages consisting of redoxactive chromophors were synthesized in a single assembly step starting from easily accessible ligands and Pd(II) cations. Two backbones consisting of electron rich phenothiazine (PTZ) and electron deficient anthraquinone (ANQ) were used to assemble either homo-octameric or mixed-ligand double cages. The electrochemical and spectroscopic properties of the pure cages, mixtures of donor and acceptor cages and the mixedligand cages were compared by steady-state UV−vis and transient absorption spectroscopy, supported by cyclic voltammetry and spectroelectrochemistry. Only the mixedligand cages, allowing close intra-assembly communication between the donors and acceptors, showed the evolution of characteristic PTZ radical cation and ANQ radical anion features upon excitation in the transient spectra. In contrast, excitation of the mixtures of the homo-octameric donor and acceptor cages in solution did not lead to any signs of electron transfer. Densely packed photo-and redox-functional self-assemblies promise molecular-level control over the morphology of the charge separation layer in future photovoltaic applications.

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3-Aminotyrosine (NH2Y) has been a useful probe to study the role of redox active tyrosines in enzymes. This report describes properties of NH2Y of key importance for its application in mechanistic studies. By combining the tRNA/NH2Y-RS suppression technology with a model protein tailored for amino acid redox studies (α3X, X = NH2Y), the formal reduction potential of NH2Y32(O•/OH) (E°’ = 395 ± 7 mV at pH 7.08 ± 0.05) could be determined using protein film voltammetry. We find that the ΔE°’ between NH2Y32(O•/OH) and Y32(O•/OH) when measured under reversible conditions is ~300 – 400 mV larger than earlier estimates based on irreversible voltammograms obtained on aqueous NH2Y and Y. We have also generated D6-NH2Y731-α2 of RNR, which when incubated with β2/CDP/ATP generates the D6-NH2Y731•-α2/β2 complex. By multi-frequency EPR (35, 94 and 263 GHz) and 34 GHz 1H ENDOR spectroscopies, we determined the hyperfine coupling (hfc) constants of the amino protons that establishes RNH2• planarity and thus minimal perturbation of the reduction potential by the protein environment. The amount of Y in the isolated NH2Y-RNR incorporated by infidelity of the NH2YRS/tRNA pair was determined by a generally useful LC-MS method. This information is essential to the usefulness of this NH2Y probe to study any protein of interest and is employed to address our previously reported activity associated with NH2Y-substituted RNRs.

Efficient transfer of spin polarisation from electron to nuclear spins is emerging as a common target of several advanced spectroscopic experiments, ranging from sensitivity enhancement in nuclear magnetic resonance (NMR) and methods for the detection of single molecules based on optically detected magnetic resonance (ODMR) to hyperfine spectroscopy. Here, we examine the feasibility of electron-nuclear cross-polarisation at a modified Hartmann-Hahn condition (called eNCP) for applications in ENDOR experiments with spin-1 deuterium nuclei, which are important targets in studies of hydrogen bonds in biological systems and materials. We have investigated a two-spin model system of deuterated malonic acid radicals in a single crystal. Energy matching conditions as well as ENDOR signal intensities were determined for a spin Hamiltonian under the effect of microwave and radiofrequency irradiation. The results were compared with numerical simulations and 94-GHz ENDOR experiments. The compelling agreement between theoretical predictions and experimental results demonstrates that spin density operator formalism in conjunction with suitable approximations in regard to spin relaxation provides a satisfactory description of the polarisation transfer effect. The results establish a basis for future numerical optimizations of polarisation transfer experiments using multiple-pulse sequences or shaped pulses and for moving from model systems to real applications in disordered systems.

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