cis-Bis(2-Phenylpyridine)platinum(II) (CBPPP). A simple molecular platinum compound preliminary communication

The deprotonated 2-phenylpyridine forms a 2:1 chelate with platinum(II) in cis-configuration, which exists as a dimer in a molecular solid.     

Cholesterol shows preference for the interior of polyunsaturated lipid membranes

Recent neutron scattering experiments showed a striking manifestation of the aversion between polyunsaturated fatty acid (PUFA)-containing lipids and cholesterol. Selectively deuterated cholesterol/ 1,2-diarachidonylphosphatidylcholine (DAPC) samples revealed that the hydroxyl of the sterol resides at the center of the bilayer. Here we use a recently parametrized coarse grain simulation model to shed light on these puzzling experimental observations. Using a simulation setup in close correspondence to the experimental conditions, we reproduce the experimental neutron scattering profiles to a large extent. The simulations allow us to analyze the behavior of cholesterol in detail; we show that the interaction of cholesterol with the PUFA chains of DAPC leads to a fast flip-flop rate for the sterol and an increased preference of the sterol for the unusual location embedded between the monolayer leaflets.     

Interfacial surface properties of thiol-protected gold nanoparticles: a molecular probe EPR approach

We present a molecular probe technique for accessing interfacial surface electrostatics of ligand-protected gold nanoparticles. A series of ligands with variable length of the hydrocarbon bridge between the anchoring sulfur and the reporting pH-sensitive nitroxide is described. The protonation state of this probe is directly observed by EPR spectroscopy. For tiopronin-protected Au nanoparticles, we observed an increase in pKa of up to ca. 1.1 pH units that was affected by the position of the reporter moiety with respect to the monolayer interface.     

Structural properties of opals grown with vertical controlled drying

We have grown thin opals of self-assembled silica colloids by the well-known vertically controlled drying method. The volume fraction at the start of the growth and the temperature were systematically varied. We have quantitatively characterized the lateral domain sizes by scanning electron microscopy. The sample thickness as a function of position was obtained from Fabry-Pérot fringes measured in optical reflectivity. We observe that the sample thickness strongly increases from top to bottom, independent of temperature, in agreement with a model that we propose. The inhomogeneity in thickness contrasts with earlier reports. The lateral domain shapes of the single-crystal domains are found to vary from irregular near the top to rectangular near the bottom. A surprising observation is that, grosso modo, the lateral domain extents increase linearly with thickness (i.e., thin crystals are small, and thick crystals are large). This behavior agrees qualitatively with results on completely different colloids such as disordered slurries. The consequence of our results for optical applications, including photonic crystals, is that unwanted scattering due to grain boundaries is reduced for large domains that are thick. Conversely, thin crystals will scatter relatively strongly from grain boundaries.     

Zinc-catalyzed synthesis of pyrazolines and pyrazoles via hydrohydrazination

A novel regioselective synthesis of aryl-substituted pyrazolines and pyrazoles has been developed. Substituted phenylhydrazines react with 3-butynol in the presence of a catalytic amount of zinc triflate to give pyrazoline derivatives. The resulting products are easily oxidized in a one-pot procedure to the corresponding pyrazoles.     

Optimal protocols for minimal work processes in underdamped stochastic thermodynamics

For systems in an externally controllable time-dependent potential, the optimal protocol minimizes the mean work spent in a finite-time transition between two given equilibrium states. For overdamped dynamics which ignores inertia effects, the optimal protocol has been found to involve jumps of the control parameter at the beginning and end of the process. Including the inertia term, we show that this feature not only persists but that even delta-peak-like changes of the control parameter at both boundaries make the process optimal. These results are obtained by analyzing two simple paradigmatic cases: First, a Brownian particle dragged by a harmonic optical trap through a viscous fluid and, second, a Brownian particle subject to an optical trap with time-dependent stiffness. These insights could be used to improve free energy calculations via either thermodynamic integration or "fast growth" methods using Jarzynski's equality.     

Local structure and disorder in crystalline Pb9Al8O21

Crystalline Pb₉Al₈O₂₁ is a model compound for the structure of non-linear optical glasses containing lone-pair ions, and its structure has been investigated by neutron powder diffraction and total scattering, and ²⁷Al magic angle spinning NMR. Rietveld analysis (space group (No. 205), a=13.25221(4) Å) shows that some of the Pb and O sites have partial occupancies, due to lead volatilisation during sample preparation, and the non-stoichiometric sample composition is Pb_9−δAl₈O_21−δ with δ=0.54. The NMR measurements show evidence for a correlation between the chemical shift and the variance of the bond angles at the aluminium sites. The neutron total correlation function shows that the true average Al-O bond length is 0.8% longer than the apparent bond length determined by Rietveld refinement. The thermal variation in bond length is much smaller than the thermal variation in longer interatomic distances determined by Rietveld refinement. The total correlation function is consistent with an interpretation in which AlO₃ groups with an Al-O bond length of 1.651 Å occur as a result of the oxygen vacancies in the structure. The width of the tetrahedral Al-O peak in the correlation function for the crystal is very similar to that for lead aluminate glass, indicating that the extent of static disorder is very similar in the two phases.     

On Direct Summands of Homological Functors on Length Categories

We show that direct summands of certain additive functors arising as bifunctors with a fixed argument in an abelian category are again of that form whenever the fixed argument has finite length or, more generally, satisfies the descending chain condition on images of nested endomorphisms. In particular, this provides a positive answer to a conjecture of M. Auslander in the case of categories of finite modules over artin algebras. This implies that the covariant Ext functors are the only injectives in the category of defect-zero finitely presented functors on such categories.     

Synthesis of self-organizing mesogenic materials containing a sulfur-based five-membered heterocyclic core

The majority of low molar mass calamitic mesogenic systems in the literature contain linear cores based on the 1,4-disubstituted phenyl ring. Heterocyclic cores such as thiophene impart unique physical properties as their slightly bent structure leads to features including a reduced packing ability (generally giving rise to lower melting points than their phenyl counterparts), a medium to strong lateral dipole, high anisotropy of the polarizability, low viscosity etc. This critical review describes the most recent synthetic methodology that has been used to prepare thiophene, 1,3-thiazole, and 1,3,4-thiadiazole-based mesogenic materials.