Scaling function of critical binary mixtures: Nitrobenzene-n-hexane data revisited

Ultrasonic attenuation spectra of the nitrobenzene-n-hexane mixture of critical composition have been analysed. Data between 50 kHz and 1 GHz from different sources have been included to show that at a given temperature the spectra, in addition to the critical contribution, reveal a non-critical relaxation term. Taking this additional term into account inconsistencies in the scaling function reported in the literature are avoided. In the final analysis the scaling function of the nitrobenzene-n-hexane system follows the predictions of the Bhattacharjee-Ferrell theory with critical amplitude and relaxation rate of concentration fluctuations in nice agreement with determinations from independent methods. The low-frequency attenuation data are briefly discussed with a view to a bulk viscosity approach which yields a slightly different proportionality constant in the linear regime of the scaling function than the Bhattacharjee-Ferrell theory. Evidence in favour of the latter is obtained.     

ChemInform Abstract: A Fully Size-Resolved Perspective on the Crystallization of Water Clusters.

Precisely size-selected (H₂O)_n clusters (n = 85—457) are characterized by IR spectroscopy.     

Undulated Multicompartment Cylinders by the Controlled and Directed Stacking of Polymer Micelles with a Compartmentalized Corona

Like a bamboo rod : Long, bamboo‐like undulated cylinders with distinct branch points and end groups (see picture) were obtained by the stacking of block terpolymer micelles that contain a fluorinated polybutadiene core and a compartmentalized corona of poly(4‐tert‐butoxystyrene) and poly(tert‐butyl methacrylate). Stacking of the polymer micelles, which can be reversed, occurred when the solvent was changed from dioxane to ethanol.

     

Tuning the Rates of Long‐Range Charge Transfer across Phenylene Wires

Walking a tight wire: Phototriggered charge transfer across a tetra‐p‐dimethoxybenzene bridge is three orders of magnitude faster than that across a structurally similar tetra‐p‐xylene spacer, despite equal reaction driving forces in both cases (see picture). This result is interpreted in terms of markedly different donor–bridge energy gaps.

     

Importance of covalence,conformational effects and tunneling-barrier heights for long-range electron transfer: Insights from dyads with oligo-p-phenylene,oligo-p-xylene and oligo-p-dimethoxybenzene bridges

This review reports on our recent studies of phototriggered charge transfer in rigid rod-like donor-bridge-acceptor molecules in liquid solution as well as between randomly dispersed electron donors and acceptors in frozen organic glasses. Investigation of the distance dependence of the rates of these reactions provides detailed insight into the various factors that govern long-range charge transfer efficiencies. The importance of covalence can be probed by a comparison of charge tunneling through a frozen toluene matrix to tunneling across an oligo-p-xylene bridge. The distance decay constants for these two processes are β = 1.26 Å^?1 and β = 0.52 Å^?1, respectively, indicating that charge tunneling across a covalent xylene–xylene contact is ～2 orders of magnitude more efficient than that across a noncovalent toluene–toluene contact. Conformational effects were investigated by comparing hole tunneling across oligo-p-xylene and oligo-p-phenylene bridges. The latter are significantly more π-conjugated and mediate long-range hole tunneling with β = 0.21 Å^?1 between a ruthenium–phenothiazine donor–acceptor couple. Quantitative analysis indicates that in this particular instance, tunneling across a phenylene–phenylene contact is roughly 50 times more efficient than tunneling across a xylene–xylene contact. The use of oligo-p-dimethoxybenzene wires instead of the structurally very similar oligo-p-xylene bridges was found to lead to a strong acceleration of long-range hole transfer rates: The 23.5-Å charge transfer step across four xylene units occurs within 20 μs, but the charge transfer over the same distance across four dimethoxybenzene units takes only 17 ns. This is attributed to a tunneling-barrier effect that is caused by a large difference in oxidation potentials between the two types of bridges.     

Enhanced adsorption affinity of anionic perylene-based surfactants towards smaller-diameter SWCNTs

We present evidence from multiple characterization methods, such as emission spectroscopy, zeta potential, and analytical ultracentrifugation, to shed light on the adsorption behavior of synthesized perylene surfactants on single-walled carbon nanotubes (SWCNTs). On comparing dispersions of smaller-diameter SWCNTs prepared by using cobalt-molybdenum catalysis (CoMoCAT) with the larger-diameter SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco), we find that the CoMoCAT-perylene surfactant dispersions are characterized by more negative zeta potentials, and higher anhydrous specific volumes (the latter determined from the sedimentation coefficients by analytical ultracentrifugation), which indicates an increased packing density of the perylene surfactants on nanotubes of smaller diameter. This conclusion is further supported by the subsequent replacement of the perylene derivatives from the nanotube sidewall by sodium dodecyl benzene sulfonate (SDBS), which first occurs on the larger-diameter nanotubes. The enhanced adsorption affinity of the perylene surfactants towards smaller-diameter SWCNTs can be understood in terms of a change in the supramolecular arrangement of the perylene derivatives on the scaffold of the SWCNTs. These findings represent a significant step forward in understanding the noncovalent interaction of π-surfactants with carbon nanotubes, which will enable the design of novel surfactants with enhanced selectivity for certain nanotube species.     

Structural and mechanistic studies on γ-butyrobetaine hydroxylase

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Highlights? Crystal structure of γ-butyrobetaine hydroxylase in complex with substrate and inhibitor ? N-terminal Zn-binding domain involved in dimerization ? The clinically used inhibitor, THP, is also a substrate for BBOX ? BBOX catalyzed rearrangement reaction     

An Efficient Scheme for Stochastic Finite Element Solutions

The Polynomial Chaos expansion in Stochastic Finite Element Methods increases the size of the resulting linear systems dramatically. In iterative scheme which takes the underlying statistics into account is suggested for the efficient numerical solution. Additionally, an approach for the solution of von Mises stresses from the Polynomial Chaos representation of the displacement field is outlined. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Molecular dynamics simulation of lubricated contact between textured surfaces

In this contribution, the friction at atomical scale has been investigated by using molecular dynamics (MD) simulations. This work surves as a preliminary study on the influence of surface texture on the friction at atomic scale, where simple rectangular grooves are added to the contact surface. Our results suggest definite dependence of the friction on the orientation of the grooves, which decreases as the velocity increases. For a given velocity, an optimal direction of sliding which gives the minimum averaged friction coefficient can be identified. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thorium nanochemistry: the solution structure of the Th(iv)-hydroxo pentamer

Tetravalent thorium exhibits a strong tendency towards hydrolysis and subsequent polymerization. Polymeric species play a crucial role in understanding thorium solution chemistry, since their presence causes apparent solubility several orders of magnitude higher than predicted by thermodynamic data bases. Although electrospray mass spectrometry (ESI MS) identifies Th(iv) dimers and pentamers unequivocally as dominant species close to the solubility limit, the molecular structure of Th(5)(OH)(y) polymers was hitherto unknown. In the present study, X-ray absorption fine structure (XAFS) spectroscopy, high energy X-ray scattering (HEXS) measurements, and quantum chemical calculations are combined to solve the pentamer structure. The most favourable structure is represented by two Th(iv) dimers linked by a central Th(iv) cation through hydroxide bridges.