Inversion Coordinate Research Articles

An unexpected μ4-oxido-bridged tetranuclear Cu(II) inverse coordination complex of a heptadentate bis(pyrazolyl)methane-based ligand: Synthesis, structure, spectroscopic properties, and catecholase activity

A new tetranuclear copper(II) complex, {But-C6H2(O)[CH = N-CH2-CH(pz)2]2}2Cu4(μ4-O)(OAc)4 (L2Cu4(μ4-O)(OAc)4, pz = pyrazolyl ring) has been prepared from the condensation reaction of 4-tert-butyl-2,6-diformylphenol with two equivalents of bis(pyrazolyl)ethanamine moieties in the presence of two equivalents of copper(II) acetate. The complex has been characterized by X-ray diffraction studies in solid state, as well as by UV–Vis, IR, and ESI spectroscopies. The structure of this inverse coordination complex consists of a central oxygen ion surrounded by four copper(II) cations residing in the corners of a distorted tetrahedron; the remaining coordination sites of the Cu2+ ions are filled by imine donors and acetate counter-ions, leaving the bis(pyrazolyl)methane donor groups uncoordinated to the copper(II) centers. In contrast to the solid-state structure, this compound was found to be dinuclear in solution, LCu2(OAc)2(OH). The complex catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC) and 4-tert-butylcatechol (TBC) to their corresponding quinones. The catalytic mechanism was investigated using DTBC as a substrate, and it was found that the oxidation reaction occurs via two different pathways, one involving molecular oxygen and the other hydrogen peroxide as oxidants.

Vibrational analysis of nitrosamine, a molecule with an almost constant potential along the inversion coordinate

ABSTRACTThe fundamental vibrational transitions of nitrosamine and its doubly deuterated isotopologue have been computed by vibrational configuration interaction theory including up to 6-tuple excitations. The potential energy surface has been represented by an n-mode expansion up to 4-mode couplings terms obtained from explicitly correlated coupled-cluster theory, CCSD(T)-F12a. Very good agreement with experimental data has been been achieved and a number of new assignments is provided.

Synthesis and structural characterization of inverse-coordination clusters from a two-electron superatomic copper nanocluster.

We have synthesized and structurally characterized a series of centred cuboctahedral copper clusters, namely [Cu13{S2CNR2}6{C[triple bond, length as m-dash]CR'}4](PF6), 1a-d (where a: R = n Bu, R' = CO2Me; b: R = n Bu, R' = CO2Et; c: R = iPr, R' = CO2Et; d: R = n Pr, R' = 3,5-(CF3)2C6H3); [Cu12(μ12-S){S2CNR2}6{C[triple bond, length as m-dash]CR'}4], 2a-c; [Cu12(μ12-Cl){S2CNR2}6{C[triple bond, length as m-dash]CR'}4](PF6), 3a-e (where e: R = n Bu, R' = Ph); [Cu12(μ12-Br){S2CN n Bu2}6{C[triple bond, length as m-dash]CPh}4](PF6), 4e; and [Cu12(μ12-Cl)(μ3-Cl){S2CN n Bu2}6{C[triple bond, length as m-dash]CCO2Me}3]+ 5a. Cluster 1a is the first structurally characterized copper cluster having a Cu13 centered cuboctahedral arrangement, a miniature of the bulk copper fcc structure. Furthermore, the partial Cu(0) character in the 2-electron superatoms 1 was confirmed by XANES. Inverse coordination clusters 2-5 are the first examples of copper clusters containing main group elements (Cl, Br, S) with a hyper-coordination number, twelve. A combined theoretical and experimental study was performed, which shows that the central copper (formally Cu1-) in nanoclusters 1 can be replaced by chalcogen/halogen atoms, resulting in the formation of clusters 2-5 which show enhanced luminescence properties and increase in the ionic component of the host-guest interaction as Br ≈ Cl > S > Cu, which is consistent with the Cu-X Wiberg indices. The new compounds have been characterized by ESI-MS, 1H, 13C NMR, IR, UV-visible, emission spectroscopy, and the structures 2a-b, 3d-e, 4e and 5a were established by X-ray diffraction analysis.

Spatial correlations in driven-dissipative photonic lattices

We study the nonequilibrium steady-state of interacting photons in cavity arrays as described by the driven-dissipative Bose–Hubbard and spin-1/2 XY model. For this purpose, we develop a self-consistent expansion in the inverse coordination number of the array () to solve the Lindblad master equation of these systems beyond the mean-field approximation. Our formalism is compared and benchmarked with exact numerical methods for small systems based on an exact diagonalization of the Liouvillian and a recently developed corner-space renormalization technique. We then apply this method to obtain insights beyond mean-field in two particular settings: (i) we show that the gas–liquid transition in the driven-dissipative Bose–Hubbard model is characterized by large density fluctuations and bunched photon statistics. (ii) We study the antibunching–bunching transition of the nearest-neighbor correlator in the driven-dissipative spin-1/2 XY model and provide a simple explanation of this phenomenon.

The Interplay between Various σ- and π-Hole Interactions of Trigonal Boron and Trigonal Pyramidal Arsenic Triiodides

Boron and arsenic triiodides (BI3 and AsI3, respectively) are similar molecules that differ mainly in their geometries. BI3 is a planar trigonal molecule with D3h symmetry, while AsI3 exhibits a trigonal pyramidal shape with C3v symmetry. Consequently, the As atom of the AsI3 molecule has three σ-holes, whereas the B atom of the BI3 molecule has two symmetrical π-holes. Additionally, there are σ-holes on the iodine atoms in the molecules studied. In the first step, we have studied σ-hole and π-hole interactions in the known monocrystals of BI3 and AsI3. Quantum mechanical calculations have revealed that the crystal packing of BI3 is dominated by π-hole interactions. In the case of AsI3, the overall contribution of dihalogen bonding is comparable to that of pnictogen bonding. Additionally, we have prepared the [Na(THF)6]+[I(AsI3)6]−(AsI3)2 complex, which can be described as the inverse coordination compound where the iodine anion is the center of the aggregate surrounded by six AsI3 molecules in the close octahedral environment and adjacent two molecules in remote distances. This complex is, besides expected dihalogen and pnictogen bonds, also stabilized by systematically attractive dispersion interactions.

Time-evolution study of photoinduced charge-transfer in tertiary amine-fluorophore systems

Photoinduced charge transfer in a fluorescent sensor of organophosphorus nerve agents is examined by solution of the time dependent Schrödinger equation, under the influence of an external electromagnetic field and employing potential energy curves obtained by density functional theory (DFT) and time dependent DFT (TDDFT) calculations for the ground and the excited states, respectively. The systems of interest here consist of a tertiary amine-pyrene molecule, with different numbers of CH2 spacer units between the t-amine and the pyrene. Quenching of pyrene emission has been observed in these systems, to different extent depending on the number of spacer units, which is due to photoinduced electron transfer from the t-amine to pyrene. Here, we present a new approach based on time-evolution for the explanation of the experimental observation of the quenching of pyrene emission. In this work the inversion coordinate at nitrogen is considered as a generalized coordinate for the charge-transfer process. Vibrational levels, dipole moments and dipole transition moments of the ground, excited, and charge transfer electronic states along the inversion coordinate are computed by DFT and TDDFT calculations. The time evolution of the excitation probability between the vibrational levels of the ground state and the first excited state and the charge transfer state has been calculated for different excitation frequencies. The results are in agreement with experimental observations regarding the photoinduced electron transfer and decreasing probability for charge transfer with increasing number of CH2 spacer units between the t-amine and the pyrene.

Fuzzy Control for Walking Balance of the Biped Robot Using ZMP Criterion

The dynamic walking stability of biped robot is a challenging research topic. In this paper, the fuzzy controller on zero movement point (ZMP) criterion is implemented to maintain the balance of dynamic walking. We designed a force sensitive resistor (FSR) sensor circuits to collect information from the sensors for the ZMP trajectory tracking. The robot walking has an imbalance when the ZMP shows the risk of moving out the footprint. The fuzzy controller is provided to drive the ZMP inside the ZMP reference area, by adjusting a suitable angle for the ankle and hip joint. In order to determine the ZMP reference, we compute the inverse kinematic and Jacobian coordinates from the biped robot model. In this research, we also introduce the biped robot configuration for control dynamic walking. A user interface is designed to conventionally observe the ZMP trajectory generation. The experimental results for stability of dynamic walking are presented to appreciate the proposed method.

Imaging of the umbrella motion and tunneling in ammonia molecules by strong-field ionization

The geometry-dependent ionization behavior of ammonia molecules is investigated. Different theoretical approaches for obtaining the ionization yield are compared, all of them showing a strong dependence of the ionization yield on the inversion coordinate at long wavelengths ($\ensuremath{\ge}800$ nm). It is shown how this effect can be exploited to create and probe nuclear wave packets in neutral ammonia using Lochfra\ss{}. Furthermore, imaging of a wave packet tunneling through the barrier of a double-well potential in real time is discussed.

EP 125. Inverse bimanual visuomotor coordination is predicted by specific executive functions

Introduction Bimanual visuomotor coordination often seems effortless in many everyday activities (e.g., dressing, eating, driving). Nevertheless, coordinating different but interdependent voluntary movements of each hand to achieve a common goal can be rather difficult, as the interaction of the two movements needs to be integrated with perceptual feedback in a top-down fashion. Aim To examine to what degree this integration is predicted by different facets of motor control and executive functioning. Methods Bimanual visuomotor coordination was assessed in 18 young (mean age: 26.0 yrs.) and 20 older (59.1 yrs.) adults using the Inverse Two-Hand Coordination Test (Schuhfried Test System), a computerized task that requires participants to steer a small virtual ball along an on-screen path. Ball movement is controlled via two joysticks: a left-hand one for horizontal, a right-hand one for vertical motion. Note that in the inverse version used here, ball movement direction is inverted relative to the hand movement (e.g., a joystick movement to the left will move the ball to the right). Further tests assessed simple (i.e. non-inverse) two-hand visuomotor coordination, one-hand visuomotor coordination (Trail Making Test [TMT-A and -B]), one-hand motor control (Motor Performance Series), inhibitory control (Go/Nogo task), divided attention, and cognitive flexibility (difference between TMT-B and -A). To identify potential predictors of inverse bimanual coordination (IBC), we compared performance in all tests between those older participants who were able ( n = 13) and those who were unable ( n = 7) to perform the IBC task. Test scores showing a significant group difference were included in a binary logistic regression analysis to test how well they predict group affiliation (IBC success vs. failure). Linear regression analysis examined how well these scores explain different aspects of IBC performance across all (young and old) successful IBC performers ( n = 31). Results Significantly decreased performance in the IBC failure subgroup was observed for TMT-A and TMT-B, Go/Nogo task (mean reaction time), and simple bimanual coordination (average speed and error duration). In a logistic regression model, these 5 scores predicted group affiliation with 88.9% accuracy. In a linear regression, all 5 scores significantly contributed to predicting IBC performance, jointly explaining 40% of variance in speed, 50% in error duration, and 95% in percentage error duration. Discussion Our results show that specific aspects of executive functioning, rather than motor skills per se, explain IBC performance across age. This indicates that the limitations in older adults to perform the task may arise from cognitive aspects of this complex “motor task” (e.g. intentional movement de-coupling, input–output coordinate transformation, error monitoring). We suggest that these parallel cognitive processing demands lead to mutual interference and eventually, reflecting well-known multitasking deficits in the elderly, may lead to a complete breakdown of complex visuomotor coordination.

Photoelectron Spectroscopy of the Methide Anion: Electron Affinities of (•)CH3 and (•)CD3 and Inversion Splittings of CH3(-) and CD3(-).

We report high-resolution photoelectron spectra of the simplest carbanions, CH₃⁻ and CD₃⁻. The vibrationally resolved spectra are dominated by a long progression in the umbrella mode (ν₂) of ˙CH₃ and ˙CD₃, indicating a transition from a pyramidal C(3v) anion to the planar D(3h) methyl radical. Analysis of the spectra provides electron affinities of ˙CH₃ (0.093(3) eV) and ˙CD₃ (0.082(4) eV). These results enable improved determination of the corresponding gas-phase acidities: Δ(acid)H(0K)°(CH₄) = 414.79(6) kcal/mol and Δ(acid)H(0K)°(CD₄) = 417.58(8) kcal/mol. On the basis of the photoelectron anisotropy distribution, the electron is photodetached from an orbital with predominant p-character, consistent with the sp³-hybridized orbital picture of the pyramidal anion. The double-well potential energy surface along the umbrella inversion coordinate leads to a splitting of the vibrational energy levels of the umbrella mode. The inversion splittings of CH₃⁻ and CD₃⁻ are 21(5) and 6(4) cm⁻¹, respectively, and the corresponding anion umbrella vibrational frequencies are 444(13) and 373(12) cm⁻¹, respectively. Quantum mechanical calculations reported herein show good agreement with the experimental data and provide insight regarding the electronic potential energy surface of CH₃⁻.

Double-inversion mechanisms of the X⁻ + CH₃Y [X,Y = F, Cl, Br, I] SN2 reactions.

The double-inversion and front-side attack transition states as well as the proton-abstraction channels of the X(-) + CH3Y [X,Y = F, Cl, Br, I] reactions are characterized by the explicitly correlated CCSD(T)-F12b/aug-cc-pVTZ(-PP) level of theory using small-core relativistic effective core potentials and the corresponding aug-cc-pVTZ-PP bases for Br and I. In the X = F case the double-inversion classical(adiabatic) barrier heights are 28.7(25.6), 15.8(13.4), 13.2(11.0), and 8.6(6.6) kcal mol(-1) for Y = F, Cl, Br, and I, respectively, whereas the barrier heights are in the 40-90 kcal mol(-1) range for the other 12 reactions. The abstraction channels are always above the double-inversion saddle points. For X = F, the front-side attack classical(adiabatic) barrier heights, 45.8(44.8), 31.0(30.3), 24.7(24.2), and 19.5(19.3) kcal mol(-1) for Y = F, Cl, Br, and I, respectively, are higher than the corresponding double-inversion ones, whereas for the other systems the front-side attack saddle points are in the 35-70 kcal mol(-1) range. The double-inversion transition states have XH···CH2Y(-) structures with Cs point-group symmetry, and the front-side attack saddle points have either Cs (X = F or X = Y) or C1 symmetry with XCY angles in the 78-88° range. On the basis of the previous reaction dynamics simulations and the minimum energy path computations along the inversion coordinate of selected XH···CH2Y(-) systems, we suggest that the double inversion may be a general mechanism for SN2 reactions.

Contrasting patterns of coupling between the CH stretches and the large-amplitude motions in the molecules, CH3NH2, CH3OH2+ and CH3CH2[rad

In each of the title molecules, torsional and inversion tunneling occurs between six equivalent minima. The coupling between these large-amplitude motions and the CH stretch vibrations stems from the variation of the CH stretching force constants as a function of the torsional and inversion coordinates. First principles 2D maps of the variation of the CH-stretch force constants are reported. Although the torsional barriers differ by more than a factor of 20, the torsion–inversion–vibration coupling is similar for two of the species, CH3NH2 and CH3CH2, but is much weaker and qualitatively different in form for the third species, CH3OH2+.

The role of the umbrella inversion mode in proton diffusion

Here, using ab initio molecular dynamics (AIMD) simulations, we elucidate the role of the umbrella inversion mode of the hydronium in proton transfer (PT) in liquid water. The hydrophobic face of the hydronium oxygen experiences asymmetries in the solvent potential along the inversion coordinate and this has a rather drastic effect on the barrier for proton transfer. This behavior is coupled to the fluctuations of voids or cavities in the vicinity of the hydronium in the water network. The peculiar inversion mode can either trap or release the proton from different parts of the water network.

Low Frequency Resonant Impulsive Raman Modes Reveal Inversion Mechanism for Azobenzene

Azobenzenes are versatile photoswitches that find application in optical memory, light-driven motors, and molecular gating. Despite many studies, the molecular details of their light induced trans to cis isomerization are still debated. To inform this discussion we probed the low frequency skeletal motions in an azobenzene derivative, 4-nitro-4'-dimethylamino-azobenzene (NDAB), with resonant impulsive stimulated Raman spectroscopy (RISRS). Four previously unobserved modes at 14, 47, 150, and 201 cm(-1) were found. Of these, the ∼50 cm(-1) inversion motion and the ∼15 cm(-1) torsional motion had particularly large intensities, suggesting that the excited state potential energy surface is steeply sloped along these coordinates in the Franck-Condon region. These data support a model in which NDAB isomerizes predominantly along a prompt inversion coordinate as well as a slower torsional motion that mitigates the phenyl-phenyl interactions on the pathway to the isomerized product.

Potential energy surface and proton HFI constants of the cyclopentane radical cation

According to the data of UB3LYP/6-31G* and UMP2/cc-pVTZ calculations, the adiabatic potential energy surface of the cyclopentane radical cation is very intricate and combines six types of stationary structures of Cs and C2 symmetry. Ten equivalent Cs structures with the totally symmetric electronic state (Cs (2A′)) correspond to global minima. Conformational transitions between the global minima occur along the inversion and pseudorotation coordinates, for each pair of minima the conformational transition occurring in one stage (through the only transition state). The inversion barrier is ∼2 kcal/mol; pseudorotation barriers are ∼4–8 kcal/mol. The structure of the potential surface provides the interpretation of the EPR data as a result of dynamic averaging over 20 Cs (2A′) and C2 (2A) stationary structures.

A rational approach to the regioselective deacetylation of 2′,3′,5′-tri-O-acetyluridine by Novozym 435 catalysed alcoholysis

To give a rational explanation for the behaviour of 2′,3′,5′-tri-O-acetyluridine (TAU) catalysed alcoholysis using Novozym 435, the commercial biocatalyst with immobilized Candida antarctica lipase B (CALB), a set of experiments analyzing the role of the alcohol/substrate (A/S) molar ratio, alcohol/biocatalyst (A/B) and substrate/biocatalyst (S/B) mass ratios were carried out. At a A/S=120 and a S/B=6.16, 2′,3′-di-O-acetyluridine (DAU) was obtained in 92% at 22h. The observed trend towards the exclusive formation of DAU at very high alcohol amounts can be explained on the basis of the change of substrate orientation from normal to inverse. The simple molecular modelling analysis supports that key O/H atoms from TAU and the resulting intermediates display the adequate distances to generate productive binding only when the inverse coordination of TAU is present through the 5′-moiety of TAU, at high ethanol concentrations. At these conditions a possible allosteric-like effect of ethanol, combined with water in an H-network in the catalytic triad and in its neighbourhood, could explain the high selectivity towards the production of DAU at selected conditions.

Risky shifts: How the timing and course of mothers' depressive symptoms across the perinatal period shape their own and infant's stress response profiles

We investigated the effects of timing and the course of maternal perinatal depressive symptoms on mother-infant hypothalamic-pituitary-adrenal (HPA) response profiles during an attachment stressor, as well as on within-dyad synchrony of stress profiles: coordination of HPA and sympathetic nervous system and infant-mother HPA attunement. Mothers (n = 86) completed the Center for Epidemiological Studies Depression Scale during pregnancy (Time 1 [T1]) and at 5 months (T2) and 18 months (T3) postnatal. At T3 mother-infant dyads completed the Strange Situation, and four saliva samples collected from both mothers and infants were assayed for cortisol and α-amylase. Hierarchical linear modeling was used to predict mother-infant cortisol response trajectories and within-dyad synchronies by main and interactive effects of T1-T3 Center for Epidemiological Studies Depression Scale scores. Main effects of earlier (T1, T2) depressive symptoms predicted mothers' cortisol trajectories and coordination, and interactions of T1 with postnatal (T2 and T3) symptoms predicted infants' cortisol trajectories, coordination, and attunement. Decomposition of interactions revealed more marked effects on infant cortisol trajectories when the mother shifted from higher to lower depressive symptoms (or vice versa) across the perinatal period. Shifts from lower to higher symptoms also predicted inverse coordination of cortisol with salivary α-amylase and greater attunement of infant with mother cortisol. Implications for the development and transmission of stress dysregulation are discussed.

Femtosecond pump-probe photoionization-photofragmentation spectroscopy of azobenzene cation

We report the studies of ultrafast dynamics of azobenzene cations using femtosecond photoionization-photofragmentation spectroscopy. In our experiment, a femtosecond pump pulse first prepares an ensemble of azobenzene cations via photoionization of neutrals. A delayed probe pulse then brings the evolving ionic system to higher states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cations are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place on this time scale.

Anisotropic generalization of Stinchcombe's solution for the conductivity of random resistor networks on a Bethe lattice

Our study is based on the work of Stinchcombe (1974 J. Phys. C: Solid State Phys. 7 179) and is devoted to the calculations of average conductivity of random resistor networks placed on an anisotropic Bethe lattice. The structure of the Bethe lattice is assumed to represent the normal directions of the regular lattice. We calculate the anisotropic conductivity as an expansion in powers of the inverse coordination number of the Bethe lattice. The expansion terms retained deliver an accurate approximation of the conductivity at resistor concentrations above the percolation threshold. We make a comparison of our analytical results with those of Bernasconi (1974 Phys. Rev. B 9 4575) for the regular lattice.

Femtosecond pump-probe photoionization-photofragmentation spectroscopy: Photoionization-induced twisting and coherent vibrational motion of azobenzene cation

We report studies of ultrafast dynamics of azobenzene cation using femtosecond photoionization-photofragmentation spectroscopy. In our experiments, a femtosecond pump pulse first produces an ensemble of azobenzene cations via photoionization of the neutrals. A delayed probe pulse then brings the evolving ionic system to excited states that ultimately undergo ion fragmentation. The dynamics is followed by monitoring either the parent-ion depletion or fragment-ion formation as a function of the pump-probe delay time. The observed transients for azobenzene cation are characterized by a constant ion depletion modulated by a rapidly damped oscillatory signal with a period of about 1 ps. Theoretical calculations suggest that the oscillation arises from a vibration motion along the twisting inversion coordinate involving displacements in CNNC and phenyl-ring torsions. The oscillation is damped rapidly with a time constant of about 1.2 ps, suggesting that energy dissipation from the active mode to bath modes takes place in this time scale.