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The strategy of anchoring molecular catalysts on electrode surfaces combines the high selectivity and activity of molecular systems with the practicality of heterogeneous systems. The stability of molecular catalysts is, however, far less than that of traditional heterogeneous electrocatalysts, and therefore a method to easily replace anchored molecular catalysts that have degraded could make such electrosynthetic systems more attractive. Here, we apply a non-covalent "click" chemistry approach to reversibly bind molecular electrocatalysts to electrode surfaces via host-guest complexation with surface-anchored cyclodextrins. The host-guest interaction is remarkably strong and allows the flow of electrons between the electrode and the guest catalyst. Electrosynthesis in both organic and aqueous media was demonstrated on metal oxide electrodes, with stability on the order of hours. The catalytic surfaces can be recycled by controlled release of the guest from the host cavities and readsorption of fresh guest. This strategy represents a new approach to practical molecular-based catalytic systems. 3Molecular electrocatalysts can exhibit surprisingly high activities and selectivities that are unmatched by most heterogeneous catalysts. 1,2 Therefore, the development of robust immobilization strategies for these molecular species on electrode surfaces is of great interest if these molecular catalytic activities and selectivities are to be transferred to more practical heterogeneous electrosynthetic systems, 3 which have already shown promising results for CO 2 reduction, water reduction and water oxidation in the context of storage of renewable energy. [4][5][6] Over the past decades, many immobilization strategies have been developed, 7 which can be categorized into covalent binding (achieved by adding anchoring groups such as carboxylate to the catalysts), 8 non-covalent binding (pi-stacking on carbon-based electrodes) 9,10 and polymerization-based binding. [11][12][13] Here, we report a new strategy for surface immobilization of molecular electrocatalysts, which relies on a non-covalent "click" chemistry approach to bind molecular species in welldefined sites on electrode surfaces. 14 The binding of electroactive molecular guests into molecular pockets by means of host-guest complex (HGC) formation has previously been studied by several groups, including those of Stoddart and Kaifer, 15 Reinhoudt 16,17 and Huskens. 18 Liu et al. reported the HGC-formation on gold surfaces with the C 60 monoanion as guest, which was found to be electrochemically stable over prolonged durations. 19 Light-induced electron transfer to and from dye molecules bound via the HGC approach was also demonstrated by Freitag and Galoppini. 20,21 The group of Sun demonstrated the use of HGC to improve electron transfer between a molecular catalyst and a dye molecule bound onto TiO 2 . 22 Among the diverse class of host molecules, cyclodextrins, cucurbiturils and calixarenes are the most studied for HGC formation on different surfaces. 23,24 For cy...

Femtosecond X-ray absorption spectroscopy (XAS) is a powerful method to investigate the dynamical behavior of a system after photoabsorption in real time. So far, the application of this technique has remained limited to large-scale facilities, such as femtosliced synchrotrons and free-electron lasers (FEL). In this work, we demonstrate femtosecond time-resolved soft-X-ray absorption spectroscopy of liquid samples by combining a sub-micrometer-thin flat liquid jet with a high-harmonic tabletop source covering the entire water-window range (284–538 eV). Our work represents the first extension of tabletop XAS to the oxygen edge of a chemical sample in the liquid phase. In the time domain, our measurements resolve the gradual appearance of absorption features below the carbon K-edge of ethanol and methanol during strong-field ionization and trace the valence-shell ionization dynamics of the liquid alcohols with a temporal resolution of ∼30 fs. This technique opens unique opportunities to study molecular dynamics of chemical systems in the liquid phase with elemental, orbital, and site sensitivity.

We report the first systematic photoelectron measurements of the three outer-valence bands of liquid water as a function of the ionizing photon energy in the near-threshold region. We use extreme-ultraviolet (XUV) radiation tunable between ∼17.1 and 35.6 eV, obtained through monochromatization of a high-harmonic source. We show that the absolute values of the apparent vertical ionization energies and their respective peak widths show a decreasing trend of their magnitudes with increasing photon energy close to the ionization threshold. We find that the observed effects do not only depend on the electron kinetic energy but are also different for the various outer-valence bands. These observations are consistent with, but not fully explained by, the effects of inelastic electron scattering.

We report integral cross sections (ICSs) for both positron and electron scattering by glycine and alanine amino acids. These molecules differ only by a methyl group. We computed the scattering cross sections using the Schwinger multichannel method for both glycine and alanine in different levels of approximation for both projectiles. The alanine ICSs are greater in magnitude than the glycine ICSs for both positron and electron scattering, probably due to the larger size of the molecule. In electron scattering calculations, we found two resonances for each molecule. Glycine presents one at 1.8 eV, and another centered at around 8.5 eV, in the static-exchange plus polarization (SEP) approximation. The ICS for alanine shows one resonance at 2.5 eV and another at around 9.5 eV, also in SEP approximation. The results are in good agreement with most of the data present in the literature. The comparison of the electron scattering ICSs for both molecules indicates that the methylation of glycine destabilizes the resonances, shifting them to higher energies.