Vibrational spectroscopy of intermediates in benzene-to-pheno conversion by FeO<Superscript>+</Superscript>

Gas-phase FeO⁺ can convert benzene to phenol under thermal conditions. Two key intermediates of this reaction are the [HO-Fe-C₆H₅]⁺ insertion intermediate and Fe⁺(C₆H₅OH) exit channel complex. These intermediates are selectively formed by reaction of laser ablated Fe⁺ with specific organic precursors and are cooled in a supersonic expansion. Vibrational spectra of the sextet and quartet states of the intermediates in the O-H stretching region are measured by infrared multiphoton dissociation (IRMPD). For Fe⁺(C₆H₅OH), the O-H stretch is observed at 3598 cm⁻¹. Photodissociation primarily produces Fe⁺+C₆H₅OH; Fe⁺(C₆H₄)+H₂O is also observed. IRMPD of [HO-Fe-C₆H₅]⁺ mainly produces FeOH⁺+C₆H₅ and the O-H stretch spectrum consists of a peak at ∼3700 cm⁻¹ with a shoulder at ∼3670 cm⁻¹. Analysis of the experimental results is aided by comparison with hybrid density functional theory computed frequencies. Also, an improved potential energy surface for the FeO⁺+C₆H₆ reaction is developed based on CBS-QB3 calculations for the reactants, intermediates, transition states, and products.     

Multivariate Optimization and Validation of a CE method for Simultaneous Analysis of Dorzolamide Hydrochloride and Timolol Maleate in Ophthalmic Solution

A fast, accurate, precise, and sensitive capillary electrophoretic method has been developed for simultaneous analysis of dorzolamide hydrochloride and timolol maleate in eye drops. Response-surface methodology with a central composite design was used for optimization of buffer pH, applied potential, and temperature. Capillary electrophoresis at 25??C with NaH₂PO₄ buffer (pH?6.00, 0.025?M), and an applied potential of 20?kV was found to be suitable, and under these optimum conditions, dorzolamide hydrochloride and timolol maleate were separated in approximately 3?min. This method was validated and successfully applied to a pharmaceutical preparation, ophthalmic solution, and the results were compared with those from a spectrophotometric method described in the literature.     

Nanomorphology and fire behavior of polystyrene/organoclay nanocomposites containing brominated epoxy and antimony oxide

Organoclay nanocomposites were prepared by ultrasound‐assisted solution intercalation technique based on polystyrene containing brominated epoxy and a combination of brominated epoxy and antimony oxide. Aspects of nanomorphology and nanodispersion were investigated by X‐ray diffraction and transmission electron microscopy whereas flammability and reaction to fire were evaluated using limiting oxygen index, UL‐94, and mass loss calorimeter tests. Polystyrene/brominated‐epoxy‐blend‐based nanocomposites showed mixed intercalated–exfoliated nanomorphology where polymer‐intercalated crystallites predominantly exist in polystyrene matrix and exfoliated silicate layers reside on polystyrene/brominated epoxy phase boundaries and within brominated epoxy domains. Organoclay was found to impart a compatibilization effect on polystyrene and dispersed brominated epoxy, which facilitates uniform distribution of a fine flame‐retarding phase within the matrix. With the reduction of the rate at which decomposition products evolve into the gas phase, organoclay nanocomposites showed notable reductions in peak heat release rate and increases in limiting oxygen index. The gas‐phase hot radical entrapment by halogenated flame‐retardant system was coupled with the condensed‐phase physical action of nanodispersed organoclay, which increased the overall fire‐retardant effectiveness. Fire‐retardant mechanisms of nanocomposites based on polystyrene/brominated epoxy blends were attributed to nanoconfinement and tortuous pathway effects of organoclay rather than to carbonaceous char formation proposed earlier for polystyrene/organoclay systems without conventional flame retardants. Copyright © 2011 John Wiley & Sons, Ltd.     

Supports of Weighted Equilibrium Measures: Complete Characterization

In this paper, we prove that a compact set K???? ⁿ is the support of a weighted equilibrium measure if and only it is not pluripolar at each of its points, extending a result of Saff and Totik to higher dimensions. Thus, we characterize the supports of weighted equilibrium measures completely. Our proof is a new proof even in one dimension.     

Electronic and vibrational spectroscopy and vibrationally mediated photodissociation of V+(OCO)

Electronic spectra of gas-phase V+(OCO) are measured in the near-infrared from 6050 to 7420 cm(-1) and in the visible from 15,500 to 16,560 cm(-1), using photofragment spectroscopy. The near-IR band is complex, with a 107 cm(-1) progression in the metal-ligand stretch. The visible band shows clearly resolved vibrational progressions in the metal-ligand stretch and rock, and in the OCO bend, as observed by Brucat and co-workers. A vibrational hot band gives the metal-ligand stretch frequency in the ground electronic state nu3' = 210 cm(-1). The OCO antisymmetric stretch frequency in the ground electronic state (nu1') is measured by using vibrationally mediated photodissociation. An IR laser vibrationally excites ions to nu1' = 1. Vibrationally excited ions selectively dissociate following absorption of a second, visible photon at the nu1' = 1 <-- nu1' = 1 transition. Rotational structure in the resulting vibrational action spectrum confirms that V+(OCO) is linear and gives nu1' = 2392.0 cm(-1). The OCO antisymmetric stretch frequency in the excited electronic state is nu1' = 2368 cm(-1). Both show a blue shift from the value in free CO2, due to interaction with the metal. Larger blue shifts observed for complexes with fewer ligands agree with trends seen for larger V+(OCO)n clusters.     

The critical speed of a moving time-harmonic load acting on a system consisting a pre-stressed orthotropic covering layer and a pre-stressed half-plane

The dynamic response of a system consisting of an initially stressed covering layer and an initially stressed half-plane to a moving time-harmonic load is investigated within the scope of the piecewise-homogeneous body model utilizing three-dimensional linearized wave propagation theory in the initially stressed body. It is assumed that the material of the layer and half-plane is orthotropic. It is also assumed that the velocity of the line-located time harmonic moving load which acts on the covering layer is constant. The investigations were carried out were for the plane-strain state under subsonic velocity of the moving load for two types of contact conditions, namely: complete and incomplete. An algorithm is developed for the determination of the values of the moving load’s critical velocity. For various values of the problem parameters the numerical results were presented and discussed.     

Hierarchical models and chaotic spin glasses

Renormalization-group studies in position space have led to the discovery of hierarchical models which are exactly solvable, exhibiting nonclassical critical behavior at finite temperature. Position-space renormalization-group approximations that had been widely and successfully used are in fact alternatively applicable as exact solutions of hierarchical models, this realizability guaranteeing important physical requirements. For example, a hierarchized version of the Sierpiriski gasket is presented, corresponding to a renormalization-group approximation which has quantitatively yielded the multicritical phase diagrams of submonolayers on graphite. Hierarchical models are now being studied directly as a testing ground for new concepts. For example, with the introduction of frustration, chaotic renormalization-group trajectories were obtained for the first time. Thus, strong and weak correlations are randomly intermingled at successive length scales, and a new microscopic picture and mechanism for a spin glass emerges. An upper critical dimension occurs via a boundary crisis mechanism in cluster-hierarchical variants developed to have well-behaved susceptibilities.     

On a Notion of Linear Replicator Equations

We show that replicator equations follow naturally from the exponential affine structure of the simplex known from information geometry. It is then natural to call replicator equations linear if their fitness function is affine. For such linear replicator equations an explicit solution can be found. The approach is also demonstrated for the example of Eigen’s hypercycle, where some new analytic results are obtained using the explicit solution.     

Chaoticity analysis of the current through pure, hydrogenated and hydrophobically modified PEG-Si thin films under varying relative humidity

Polyethylene Glycol has an irregular current characteristic under constant voltage and slowly varying relative humidity. The current through a thin film of Gamma-isocyanatopropyltriethoxysilane added Polyethylene glycol (PEG-Si), its hydrogenated and hydrophobically modified forms, as a function of increasing relative humidity at equal time steps is analyzed for chaoticity. We suggest that the irregular behavior of current through PEG-Si thin films as a function of increasing relative humidity could best be analyzed for chaoticity using both time series analysis and detrended uctuation analysis; the relative humidity is kept as a slowly varying parameter. The presence of more then one regime is suggested by the calculation of the maximal Lyapunov exponents. Furthermore, the maximal Lyapunov exponent in each of the regimes was positive, thus confirming the presence of low dimensional chaos. DFA also confirms the presence of at least two different regimes, in agreement with the behavior of the maximal Lyapunov exponent in the time series analysis. We also suggest that the irregular behavior of the current through PEG-Si can be reduced by hydrogenating and hydrophobically modifying PEG-Si and the improvement in stability can be confirmed by our study.      

Dynamic transition in tRNA is solvent induced

Dynamics of tRNA was studied using neutron scattering spectroscopy. Despite vast differences in the architecture and backbone structure of proteins and RNA, hydrated tRNA undergoes the dynamic transition at the same temperature as hydrated lysozyme. The similarity of the dynamic transition in RNA and proteins supports the idea that it is solvent induced. Because tRNA essentially has no methyl groups, the results also suggest that methyl groups are not the main contributor of the dynamic transition in biological macromolecules. However, they may explain strong differences in the dynamics of tRNA and lysozyme observed at low temperatures.