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We report a combined experimental and computational study of the structure and fragmentation dynamics of mixed ligand gas-phase ion–molecule complexes. Specifically, we have studied the infrared spectroscopy and vibrationally induced photofragmentation dynamics of mass-selected Au(CO)x(N2O)y+complexes. The structures can be understood on the basis of local CO and N2O chromophores in different solvation shells with CO found preferentially in the core. Rich fragmentation dynamics are observed as a function of complex composition and the vibrational mode excited. The dynamics are characterized in terms of branching ratios for different ligand loss channels in light of calculated internal energy distributions. Intramolecular vibrational redistribution appears to be rapid, and dissociation is observed into all energetically accessible channels with little or no evidence for preferential breaking of the weakest intermolecular interactions.

Night-migratory songbirds are remarkably proficient navigators1. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass2,3. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds4–7. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin–tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds.

OCS binding to and reactivity with isolated gold cluster cations, Aun+(n= 1–10), has been studied by infrared multiple photon dissociation (IR-MPD) spectroscopy in conjunction with quantum chemical calculations. The distribution of complexes AunSx(OCS)m+formed reflects the relative reactivity of different cluster sizes with OCS, under the multiple collision conditions of our ablation source. The IR-MPD spectra of Aun(OCS)+(n= 3–10) clusters are interpreted in terms of either μ1or μ2S binding motifs. Analysis of the fragmentation products following infrared excitation of parent Aun(OCS)+clusters reveals strongly size-selective (odd–even) branching ratios for OCS and CO loss, respectively. CO loss signifies infrared-driven OCS decomposition on the cluster surface and is observed to occur predominantly on even nclusters (i.e., those with odd electron counts). The experimental data, including fragmentation branching ratios, are consistent with calculated potential energy landscapes, in which the initial species trapped are molecularly bound entrance channel complexes, rather than global minimum inserted structures. Attempts to generate Rhn(OCS)+and Ptn(OCS)+equivalents failed; only sulfide reaction products were observed in the mass spectrum, even after cooling the cluster source to −100 °C.

It is a remarkable fact that ∼50 μT magnetic fields can alter the rates and yields of certain free-radical reactions and that such effects might be the basis of the light-dependent ability of migratory birds to sense the direction of the Earth’s magnetic field. The most likely sensory molecule at the heart of this chemical compass is cryptochrome, a flavin-containing protein that undergoes intramolecular, blue-light-induced electron transfer to produce magnetically sensitive radical pairs. To learn more about the factors that control the magnetic sensitivity of cryptochromes, we have used a set of de novodesigned protein maquettes that self-assemble as four-α-helical proteins incorporating a single tryptophan residue as an electron donor placed approximately 0.6, 1.1, or 1.7 nm away from a covalently attached riboflavin as chromophore and electron acceptor. Using a specifically developed form of cavity ring-down spectroscopy, we have characterized the photochemistry of these designed flavoprotein maquettes to determine the identities and kinetics of the transient radicals responsible for the magnetic field effects. Given the gross structural and dynamic differences from the natural proteins, it is remarkable that the maquettes show magnetic field effects that are so similar to those observed for cryptochromes.

In this study, mixed carbonyl and nitrous oxide complexes with Rh+were studied by mass-selective infrared photodissociation spectroscopy in a molecular beam. The infrared spectra, recorded in the region of the CO and N2O N═N stretches, were assigned and interpreted with the aid of simulated spectra of low-energy structural isomers. Clear evidence of an inner coordination shell of four ligands is observed. The observed vibrational structure can be understood on the basis of local mode vibrations in the two ligands. However, there is also evidence of multiple low-lying isomers and cooperative binding effects between the two ligands. In particular, σ donation from directly coordinated nitrous oxide ligands drives more classical carbonyl bonding than has been observed in pure carbonyl complexes. The observed fragmentation branching ratios following resonant infrared absorption are explained by simple statistical and energetic arguments, providing a contrast with those of equivalent Au+complexes.

Magnetic fields as weak as the Earth's can change the yields of radical pair reactions even though the energies involved are orders of magnitude smaller than the thermal energy, kBT, at room temperature. Proposed as the source of the light-dependent magnetic compass in migratory birds, the radical pair mechanism is thought to operate in cryptochrome flavoproteins in the retina. Here we demonstrate that the primary magnetic field effect on flavin photoreactions can be amplified chemically by slow radical termination reactions under conditions of continuous photoexcitation. The nature and origin of the amplification are revealed by studies of the intermolecular flavin–tryptophan and flavin–ascorbic acid photocycles and the closely related intramolecular flavin–tryptophan radical pair in cryptochrome. Amplification factors of up to 5.6 were observed for magnetic fields weaker than 1 mT. Substantial chemical amplification could have a significant impact on the viability of a cryptochrome-based magnetic compass sensor.

We present a combined experimental and quantum chemical study of gas-phase group 9 metal nitrosyl complexes, M(NO)n+(M = Co, Rh, Ir). Experimental infrared photodissociation spectra of mass-selected ion-molecule complexes are presented in the region 1600 cm–1to 2000 cm–1which includes the NO stretch. These are interpreted by comparison with the simulated spectra of energetically low-lying structures calculated using density functional theory. A mix of linear and nonlinear ligand binding is observed, often within the same complex, and clear evidence of coordination shell closing is observed at n= 4 for Co(NO)n+and Ir(NO)n+. Calculations of Rh(NO)n+complexes suggest additional low-lying five-coordinate structures. In all cases, once a second coordination shell is occupied, new spectral features appear which are assigned to (NO)2dimer moieties. Further evidence of such motifs comes from differences in the spectra recorded in the dissociation channels corresponding to single and double ligand loss.

The formation of polyaniline (PAni) nanoparticles on silica surfaces has been monitored in situ using evanescent wave cavity ring-down spectroscopy (EW-CRDS). Aniline hydrochloride in aqueous solution at different concentrations was oxidatively polymerized using sodium persulfate. The process was found to involve the nucleation and growth of polymer nanoparticles, whose size and coverages were measured using tapping mode atomic force microscopy (TM-AFM). The formation of PAni was confirmed by replacing the silica surface with indium doped tin oxide (ITO) electrodes and subsequently running cyclic voltammetry experiments on the material deposited, which yielded the characteristic electrochemical response. The number of active groups (monomers) per polymer particle was estimated using the peak current of the cyclic voltammograms, with knowledge of the nanoparticle surface coverage from TM-AFM analysis. The quantity of material in each particle was consistent with TM-AFM height data, assuming hemispherical particle morphology. The polymerization process was found to be governed by surface-controlled kinetics, from a fixed number of particle sites of 35 (±5) μm−2. The reaction was first-order in aniline, with a rate constant for monomer addition of 0.7 (±0.4) × 10−7cm s−1in the limit of large particle size. For smaller nanoparticles, however, at the early stage of polymerization, the polymerization rate constant appeared to be size-dependent and to increase with decreasing nanoparticle radius (assuming a hemispherical geometry). This could also be due to a change in the morphology of the nanoparticles at the very shortest times but may indicate size-dependent polymerization kinetics.

The reactions of niobium cluster cations, Nb+n(n= 2–19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n< 9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n= 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N2loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.

We present an ab initio potential energy surface for the Ã 2Σ+ state of the Ar⋯HS van der Waals molecule. The surface represents a fit to 196 points calculated at the RCCSD(T) level with an aug-cc-pV5Z basis set and encompasses both the Ar⋯SH and Ar⋯HS isomers. We have further calculated vibrational levels on this surface using a discrete variable representation (DVR) approach. The vibrational levels supported within the Ar⋯HS minimum are compared with levels derived from high-resolution laser induced fluorescence spectra. Predictions of vibrational levels for the Ar⋯SH isomer, which have not been observed experimentally, are also presented.

The rate of propagation in the free-radical polymerization of methyl methacrylate in an ionic liquid has been determined and shows unprecedented solvent-induced acceleration, partially explaining the surprising increase in overall rates of polymerization and molecular weights in these solvents.