Sol hydrolysis and condensation reaction time influence the sensitivity of class II xerogel-based sensing materials

Simplicity of preparation, a wide variety of precursors, and numerous processing variables (e.g., pH, time, temperature) are often described as attractive aspects of sol–gel derived materials. In the current work we create a series of O₂-responsive xerogel-based sensor films by simultaneously co-hydrolyzing and co-condensing tetramethylorthosilane and n-octyltriethoxysilane. Tris(4,7′-diphenyl-1,10′-phenanthroline) ruthenium(II) ([Ru(dpp)₃]²⁺) is used as the O₂-responsive luminophore. We determine the effects of [Ru(dpp)₃]²⁺ addition time to the sol and the sol hydrolysis and condensation reaction time (H&C) on the xerogel film O₂ sensitivity. [Ru(dpp)₃]²⁺ addition time has no significant effect on the O₂ sensitivity; H&C effects the O₂ sensitivity. The highest O₂ sensitivity is seen at early H&C (0.5 h). This behavior arises because TMOS and C8-TMOS react at different rates to form sols. At early H&C the co-hydrolysis and co-condensation reactions are not complete and the so formed sols are rich in C8-TMOS in comparison to their composition at longer H&C. At longer H&C, the TMOS and C8-TMOS co-hydrolyze and co-condense more completely. SEM images show that xerogel films formed at early H&C is more porous in comparison to those formed a longer H&C. The results of these experiments: (a) highlight the importance of documenting how sols are processed and xerogels formed and (b) demonstrate the use of a single sol formulation and H&C to create suites of sensor materials with different responses.     

Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: improved catalytic activity through statistical effects and cooperativity in successive generations

Dendrimeric polyphenylsulfides, -selenides, and -tellurides are prepared in high yield using propyloxy spacers to connect the phenylchalcogeno groups to the dendrimeric core. The selenides and tellurides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by cyclohexene in two-phase systems. The corresponding sulfides show no catalytic activity. The increase in the rate of catalysis followed statistical effects for 1, 6, and 12 phenyltelluro groups. However, the increase in the rate of catalysis exceeds statistical contributions for the first few generations with 1, 3, 6, and 12 phenylseleno groups and suggested cooperativity among phenylseleno groups. The increase in catalytic rate was lost upon replacing all but one phenylseleno group with phenoxy groups. On the basis of H2O2 consumed, the dendrimer with 12 phenylseleno groups has a turnover number of >60 000 mol of H2O2 consumed per mole of catalyst.     

Comparing Dimerization Free Energies and Binding Modes of Small Aromatic Molecules with Different Force Fields

Dimerization free energies are fundamental quantities that describe the strength of interaction of different molecules. Obtaining accurate experimental values for small molecules and disentangling the conformations that contribute most to the binding can be extremely difficult, due to the size of the systems and the small energy differences. In many cases, one has to resort to computational methods to calculate such properties. In this work, we used molecular dynamics simulations in conjunction with metadynamics to calculate the free energy of dimerization of small aromatic rings, and compared three models from popular online servers for atomistic force fields, namely G54a7, CHARMM36 and OPLS. We show that, regardless of the force field, the profiles for the dimerization free energy of these compounds are very similar. However, significant care needs to be taken when studying larger molecules, since the deviations from the trends increase with the size of the molecules, resulting in force field dependent preferred stacking modes; for example, in the cases of pyrene and tetracene. Our results provide a useful background study for using topology builders to model systems which rely on stacking of aromatic moieties, and are relevant in areas ranging from drug design to supramolecular assembly.     

Synthesis of naphthalene and indene precursors to naphthoic and indenoic acids

As part of ongoing research to investigate structural requirements for lactate dehydrogenase inhibition by highly substituted naphthoic and indenoic acids, certain naphthalene and indene precursors to those types of compounds are required. Described here are efficient preparations of 1-naphthoic acid precursors 6-benzyl-2,3-dimethoxy-1-propylnaphthalenes, including compounds with substituted benzyl groups and 7-benzyl-2,3-dimethoxy-1-propylnaphthalene. Also described are the syntheses of indenoic acid precursors 2-benzyl-5,6-dimethoxy-7-propyl-1H-indenes, including compounds with substituted benzyl groups. These compounds were made from the key intermediates 6,7-dimethoxy-5-propyl-1-tetralone, 6,7-dimethoxy-8-propyl-1-tetralone, and 5,6-dimethoxy-4-propyl-1-indanone.     

On radiative-transfer problems with reflective boundary conditions and internal emission

An integral-transform technique and theF _N method are used to solve basic radiative-transfer problems. Boundary conditions that account for specular and diffuse reflection as well as external illumination are used, and internal emission is allowed. Emphasis is given to the azimuthally symmetric component of the complete radiation field.

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Zusammenfassung Eine Integral-Transformation und dieF _N -Methode werden zur Lösung von grundlegenden Problemen der Strahlungsübertragung herangezogen. Es werden Randbedingungen mit spekulärer und diffuser Reflexion wie auch mit äußerer Bestrahlung benützt, und innere Emission ist zugelassen. Besonders betrachtet werden die Komponenten des gesamten Strahlungsfeldes, welches azimutale Symmetrie besitzt.

     

Sensitivity to parameters of STIRAP in a Cooper Pair Box

The rapid experimental progress in the field of superconducting nanocircuits gives rise to an increasing quest for advanced quantum-control techniques for these macroscopically coherent systems. Here we demonstrate theoretically that stimulated Raman adiabatic passage (STIRAP), a well-established method in quantum optics, should be possible with the quantronium setup of a Cooper-pair box. We find the parameters which optimize the procedure and show how the scheme appears to be robust against decoherence and should be realizable even with the existing technology.     

Non-Abelian holonomies,charge pumping,and quantum computation with Josephson junctions

Non-Abelian holonomies can be generated and detected in certain superconducting nanocircuits. Here we consider an example where the non-Abelian operations are related to the adiabatic charge dynamics of the Josephson network. We demonstrate that such a device can be applied both for adiabatic charge pumping and as an implementation of a quantum computer.     

The PN method for radiative transfer problems with reflective boundary conditions

The P_N method is used to compute the partial heat fluxes relevant to radiative transfer in an anisotropically scattering, plane-parallel medium with specularly and diffusely reflecting boundaries.     

A note on radiative transfer

The formulation of radiative transfer problems with internal energy sources is discussed.