Protonmotive force: development of electrostatic drivers for synthetic molecular motors

Ferrocene has been investigated as a platform for developing protonmotive electrostatic drivers for molecular motors. When two 3-pyridine groups are substituted to the (rapidly rotating) cyclopentadienyl (Cp) rings of ferrocene, one on each Cp, it is shown that the (Cp) eclipsed, pi-stacked rotameric conformation is preferred both in solution and in the solid state. Upon quaternization of both of the pyridines substituents, either by protonation or by alkylation, it is shown that the preferred rotameric conformation is one where the pyridinium groups are rotated away from the fully pi-stacked conformation. Electrostatic calculations indicate that the rotation is caused by the electrostatic repulsion between the charges. Consistently, when the pi-stacking energy is increased pi-stacked population increases, and conversely when the electrostatic repulsion is increased pi-stacked population is decreased. This work serves to provide an approximate estimate of the amount of torque that the electrostatically driven ferrocene platform can generate when incorporated into a molecular motor. The overall conclusion is that the electrostatic interaction energy between dicationic ferrocene dipyridyl systems is similar to the pi-stacking interaction energy and, consequently, at least tricationic systems are required to fully uncouple the pi-stacked pyridine substituents.     

Determination of coenzyme Q10 in human breast milk by high-performance liquid chromatography

An isocratic HPLC method was developed for the determination of coenzyme Q(10) (CoQ(10)) in human breast milk. After a single-step liquid-liquid extraction, the milk extract was injected directly into the HPLC system. The analytical method is based on pre-column inline treatment of CoQ(10). Chromatographic separation of CoQ(10) and coenzyme Q(9) (CoQ(9)) internal standard was achieved using a reversed-phase Microsorb-MV C(18) analytical column. CoQ(10) and CoQ(9) were monitored by an electrochemical detector (ECD). An excellent linearity (r = 0.999) was observed for CoQ(10) in the concentration range 0.06-2.5 micromol L(-1) in breast milk. The limit of quantitation (LOQ) was 60 nmol L(-1). Coefficients of variations (CVs) for intra-day and inter-day assay precisions were less than 5%. A total of 194 breast milk samples were analyzed for the CoQ(10) concentration; the mean value was 0.32 +/- 0.21 micromol L(-1).     

Spatiotemporal dynamics of networks of excitable nodes

A network of excitable nodes based on the photosensitive Belousov-Zhabotinsky reaction is studied in experiments and simulations. The addressable medium allows both local and nonlocal links between the nodes. The initial spread of excitation across the network as well as the asymptotic oscillatory behavior are described. Synchronization of the spatiotemporal dynamics occurs by entrainment to high-frequency network pacemakers formed by excitation loops. Analysis of the asymptotic behavior reveals that the dynamics of the network is governed by a subnetwork selected during the initial transient period.     

Hole defects in the crystal structure of synthetic lipscombite (Fe 4.7 3+ Fe 2.3 2+ )[PO4]4O2.7(OH)1.3 and genetic crystal chemistry of minerals of the lipscombite-barbosalite series

The crystal structure of a synthetic analog of the mineral lipscombite (Fe _2.3 ²⁺ Fe _4.7 ³⁺ )[PO₄]₄O_2.7(OH)_1.3 obtained under hydrothermal conditions in the LiF-Fe₂O₃-(NH₄)₂HPO₄-H₂O system is resolved (R = 0.040) by X-ray diffraction analysis (Bruker Smart diffractometer with a highly sensitive CCD detector, MoK _α radiation): a = 14.776(3) Å, b = 14.959(3) Å, c = 7.394(1) Å, β = 119.188(4)°, sp. gr. C2/c, Z = 4, ρ_exp = 3.8 g/cm³, ρ_calcd = 3.9 g/cm³. Fe²⁺ and Fe³⁺ cations are statistically distributed in each of four crystallographically independent positions, while occupying the corresponding octahedra with probabilities of 60, 90, 100, and 91%. The ratio Fe²⁺/Fe³⁺ in the composition of the crystals was established by Mössbauer spectroscopy. Lipscombite is interpreted as a mineral of variable composition described by the formula (Fe _x ²⁺ Fe _n?x ³⁺ )[PO₄]₄O_y(OH)_4?y . The field of stability is determined as a function of the iron content and the ratio Fe²⁺/Fe³⁺. It is shown that at n = 6 iron cations are ordered in octahedra and barbosalite structure is formed. An interpretation of genetically and structurally related members of the lipscombite family within a unified polysomatic series is proposed.     

Simply-transitive homothety groups

In this paper the spin-coefficient formalism of Penrose and Rindler is applied to the problem of finding space-times that admit a simply-transitive group of homotheties. The method is illustrated by an application to algebraically special vacuum space-times. Vacuum metrics with a fivedimensional homothety group are also considered.     

Stability of a microwave heated fluid Layer

When a time harmonic electromagnetic wave impinges on a slaba certain portion of the wave creates heat within the slab throughdipolar and ohmic heating. The electrical and thermal propertiesof the material dictate the dynamical nature of the heatingprocess, as well as the steady-state temperature profile. Thematerial considered here is a slab of fluid. We consider thecase where the fluid is bounded by thin rigid layers of transparentmaterial. The steady-state heating profile governs the typesof convective motions that can occur and also affects the stabilitycharacteristics of temperature, pressure and velocity perturbationsintroduced in the slab. The main objective here is to examinesuch stability characteristics, initially in the linear regime.Both rigid-rigid and rigid-free configurations are considered.     

On a characterization question for symmetric random variables

If X₁, X₂ are independent with common density g symmetric about zero, then $\text{P(X}{}_1\text{+ αX}{}_2\text{> 0) =}\text{1}\text{2}$ for all real α. We provide a counter example to show that the converse is false and thus settle a question posed by Burdick (1972).