Effect of the acyl group and the dodecylsulfonate chain on the inclusion of pyrene inside the cavity of β-cyclodextrin

The solubilization of pyrene in aqueous solution of β-cyclodextrin (β-CD) or its derivatives such as β-CD-hexanoyl, β-CD-benzoyl and β-CD-dodecylsulfonate was investigated by spectrophotometry. Linear and non-linear regression methods were used to estimate the association constants (K₁). A 1:1 stoichiometric ratio and different effects of the hexanoyl, benzoyl and dodecylsulfonate groups on the association constant were observed for the binary inclusion complex between pyrene and β-CD. The formation constant was shown to decrease when β-CD was modified by a dodecylsulfonate chain. The value of K₁ was 190 ± 10 L mol⁻¹ for the [pyrene/β-CD] complex and 145 L mol⁻¹ for the [pyrene/β-CD-dodecylsulfonate] complex. Partitioning of the pyrene molecules between the dodecylsulfonate chains and cyclodextrin cavities can explain the decrease in the association constant value. In the cases of β-CD-hexanoyl and β-CD-benzoyl derivatives, no association constants were detected. Results suggest that the high hydrophobicity of the hexanoyl and benzoyl groups prevents the inclusion of pyrene molecules inside the cyclodextrin cavity.     

Viscous linear instability of a sheared liquid-gas interface - Effect of a velocity deficit near the interface

The initial state of liquid atomization by a fast gas stream is considered by viscous linear spatial stability analysis for parallel two-fluid flow. The unbounded basic velocity profile is characterized by different asymptotic velocities and a velocity deficit near the interface. We examine the influence of the velocity deficit on the spatial growth rates of two competing modes originating from the Kelvin-Helmholtz and viscosity contrast mechanisms. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature- and solvent-dependent binding of dihydrogen in iridium pincer complexes

Mixtures of deuterium labeled complexes (p-XPOCOP)IrH2-xDx (1-6-d0-2) {POCOP = [C6H2-1,3-[OP(tBu)2]2] X = MeO (1), Me (2), H (3), F (4), C6F5 (5), and ArF = 3,5-(CF3)2-C6H3 (6)} have been generated by reaction of (p-XPOCOP)IrH2 complexes with HD gas in benzene followed by removal of the solvent under high vacuum. Spectroscopic analysis employing 1H and 2D NMR reveals significant temperature and solvent dependent isotopic shifts and HD coupling constants. Complexes 1-6-d1 in toluene and pentane between 296 and 213 K exhibit coupling constants JHD of 3.8-9.0 Hz, suggesting the presence of an elongated H2 ligand, which is confirmed by T1(min) measurements of complexes 1, 3, and 6 in toluene-d8. In contrast, complex 6-d1 exhibits JHD = 0 Hz in CH2Cl2 or CDCl2F whereas isotopic shifts up to -4.05 ppm have been observed by lowering the temperature from 233 to 133 K in CDCl2F. The large and temperature-dependent isotope effects are attributed to nonstatistical occupation of two different hydride environments. The experimental observations are interpreted in terms of a two component model involving rapid equilibration of solvated Ir(III) dihydride and Ir(I) dihydrogen structures.     

Synthesis and characteristics of a nonaggregating tris(tetrathiafulvaleno)dodecadehydro[18]annulene

A new tris(tetrathiafulvaleno)dodecadehydro[18]annulene with six peripheral n-hexyl substituents was prepared by oxidative Glaser-Hay cyclization of a corresponding diethynylated tetrathiafulvalene (TTF) precursor. The electronic properties of the neutral and oxidized species were studied by both UV/Vis absorption spectroscopy and electrochemistry. From these studies, it transpires that the strongly violet-colored macrocycle does not aggregate in solution to any significant degree, which was confirmed by (1)H NMR spectroscopy. This reluctance towards aggregation contrasts that observed for related TTF-annulenes containing other peripheral substitutents. Oxidation of the TTF-annulene occurs in two three-electron steps as inferred from both the peak amplitudes and the spectroelectrochemical study. We find that the tris(TTF)-fused dehydro[18]annulene is more difficult to oxidize (by +0.20 V) than the silyl-protected diethynylated mono-TTF precursor. In contrast, the first vertical ionization energy calculated at the B3 LYP/6-311+G(2d,p) level for the parent tris(TTF)-fused dehydro[18]annulene devoid of peripheral hexyl substituents is in fact lower (by 0.44 eV). Moreover, the surface morphology of 1 d drop-cast on a mica substrate was investigated by atomic force microscopy (AFM). Crystalline domains with slightly different orientations were observed. The thickness of individual layers seen in the crystalline domains and the thickness of a monolayer obtained from a very dilute solution were determined to 1.8-1.9 nm. This thickness corresponds to the diameter of the macrocycle and the layers seen in the film are apparently formed when the molecules stack in the horizontal direction relative to the substrate.     

The Angular Momentum Dilemma and Born–Jordan Quantization

The rigorous equivalence of the Schrödinger and Heisenberg pictures requires that one uses Born–Jordan quantization in place of Weyl quantization. We confirm this by showing that the much discussed “ angular momentum dilemma” disappears if one uses Born–Jordan quantization. We argue that the latter is the only physically correct quantization procedure. We also briefly discuss a possible redefinition of phase space quantum mechanics, where the usual Wigner distribution has to be replaced with a new quasi-distribution associated with Born–Jordan quantization, and which has proven to be successful in time-frequency analysis.     

On the Accuracy of Elastic Strain Field Measurements by Laue Microdiffraction and High-Resolution EBSD: a Cross-Validation Experiment

Determining the accuracy of elastic strain measurements in plastically deformed alloys is an experimental challenge. To develop a novel cross-validation procedure, a controlled elasto-plastic strain gradient was created in a stainless steel single crystal by four point bending deformation. The corresponding elastic strain field was probed, with an intragranular spatial resolution, in-situ by Laue microdiffraction and ex-situ by High Resolution EBSD. Good agreement is found for the two independent measurements and the predictions of a mechanical model, at plastic strains below 0.5 %. The accuracy of the measurements is estimated at 3.2 × 10^{? 4}.     

Radical 4-exo cyclizations via template catalysis

The mechanism of catalytic 4-exo cyclizations without gem-dialkyl substitution was investigated by a comparison of cyclic voltammetry, EPR, and computational studies with previously published synthetic results. The most active catalyst is a super-unsaturated 13-electron titanocene(III) complex that is formed by supramolecular activation through hydrogen bonding. The template catalyst binds radicals via a two-point binding that is mandatory for the success of the 4-exo cyclization. The computational investigations revealed that formation of the observed trans-cyclobutane product is not possible from the most stable substrate radical. Instead, the most stable product is formed with the lowest energy of activation from a disfavored substrate in a Curtin-Hammett related scenario.     

Deoxygenation of coordinated oxaphosphiranes: a new route to pc double-bond systems

Phosphaalkenes: Deoxygenation of oxaphosphirane complexes 1 and 2 by using Ti(III) complexes gave mixtures of E/Z phosphaalkene complexes 3?a,?b and 4?a,?b. Theoretical calculations of deoxygenation pathways of 1 revealed that the final products are obtained via intermediate 5 providing the final products by reaction with a second [TiCpCl(2) ] unit and C?O bond cleavage.     

Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines

The cationic Ir(III) acetone complex (POCOP)Ir(H)(2)(acetone)(+) (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH(3)(SiEt(2)H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et(2)SiH(2) under H(2). Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH(3)(SiEt(2)H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et(2)SiH(2). Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10,000.     

Structural and algorithmic properties for parametric minimum cuts

We consider the minimum s, t-cut problem in a network with parametrized arc capacities. Following the seminal work of Gallo et?al. (SIAM J. Comput. 18(1):30–55, 1989), classes of this parametric problem have been shown to enjoy the nice Structural Property that minimum cuts are nested, and the nice Algorithmic Property that all minimum cuts can be computed in the same asymptotic time as a single minimum cut by using a clever Flow Update step to move from one value of the parameter to the next. We present a general framework for parametric minimum cuts that extends and unifies such results. We define two conditions on parametrized arc capacities that are necessary and sufficient for (strictly) decreasing differences of the parametric cut function. Known results in parametric submodular optimization then imply the Structural Property. We show how to construct appropriate Flow Updates in linear time under the above conditions, implying that the Algorithmic Property also holds under these conditions. We then consider other classes of parametric minimum cut problems, without decreasing differences, for which we establish the Structural and/or the Algorithmic Property, as well as other cases where nested minimum cuts arise.