Strategies for Control of Lattice Architecture in Low-Dimensional Molecular Metals: Assembly of Partially Oxidized Face-to-Face Linked Arrays of Metallomacrocycles

This paper discusses an approach to control molecular stacking interactions in low-dimensional mixed valence materials by locking partially oxidized metallomacrocycles together in a face-to-face orientation. Thus, doping of the cofacially linked oligomers [M(Pc)0]_n (M = Si, Ge, Sn; Pc = phthalocyaninato) with halogen (I₂, Br₂) or quinone (e.g., TCNQ, DDQ) electron acceptors produces robust, electrically conductive polymers with a wide range of stoichiometrics and properties. The new materials have been studied by a variety of physical methods including X-ray diffraction, resonance Raman and infrared spectroscopy, ESR, static magnetic susceptibility, and variable-temperature four-probe electrical conductivity. Evidence is presented that some of the polymers have “metal-like” conductivity in the stacking direction and that transport properties within the series can be readily manipulated by rational variation of lattice architecture (e.g., the identity of the metal, M) and acceptor characteristics. Additional information is presented on doping experiments with electron donors and on employing metallohemiporphyrazines as polymer building blocks.     

Synthesis, characterization, and photoactivity of Ta2O5-grafted SiO2 nanoparticles

Herein, we discuss the synthesis as well as material and photochemical characterization of nanometer‐sized Ta₂O₅ decorated, in a controlled fashion, on top of 20 nm diameter SiO₂ particles to yield a composite oxide with a tunable band‐gap width. Particular emphasis is paid to control of particle size, and control of the distribution of the overlying oxide. The nanoscale dimension imparts a high surface area and introduces quantum confinement effects that displace the conduction band more negatively and the valence band more positively on the electrochemical scale of potentials. This band shift results in an increase of the number of possible participants in photocatalytic reactions. The band shift is shown to result in an increase in driving force for thermodynamically feasible reactions. By decorating SiO₂ with smaller‐sized Ta₂O₅, the interplay of the Lewis acidity of SiO₂ and the contact area between Ta₂O₅ and SiO₂ is utilized to develop a photocatalyst with higher photoactivity than pure Ta₂O₅.     

On the Debye temperatures of Metal Hydrides

A universal empirical relationship, connecting the Debye temperatures of a metal, θ_M, and its hydride, θ_H, with the hydride's heat of formation, ΔH_f, is derived from experimental data. This relation may be useful in estimating one of the three parameters, θ_M, θ_H or ΔH_f, if the other two are known.     

MRI evaluation of brain iron in earlier- and later-onset Parkinson's disease and normal subjects

Tissue iron levels in the extrapyramidal system of earlier- and later-onset Parkinson's disease (PD) subjects were evaluated in vivo using a magnetic resonance imaging (MRI) method. The method involves scanning subjects in both high- and low-field MRI instruments, measuring tissue relaxation rate (R2), and calculating the field-dependent R2 increase (FDRI) which is the difference between the R2 measured with the two MRI instruments. In tissue, only ferritin iron is known to increase R2 in a field-dependent manner and the FDRI measure is a specific measure of this tissue iron pool. Two groups of male subjects with PD and two age-matched groups of normal control males were studied. The two groups of six subjects with PD consisted of subjects with earlier- or later-onset (before or after age 60) PD. FDRI was measured in five subcortical structures: the substantia nigra reticulata (SNR), substantia nigra compacta (SNC), globus pallidus, putamen, and caudate nucleus, and in one comparison region; the frontal white matter. Earlier-onset PD subjects had significant (p < 0.05) increases in FDRI in the SNR, SNC, putamen, and globus pallidus, while later-onset PD subjects had significantly decreased FDRI in the SNR when compared to their respective age-matched controls. Controlling for illness duration or structure size did not meaningfully alter the results. Published post-mortem studies on SN iron levels indicate decreased ferritin levels and increased free iron levels in the SN of older PD subjects, consistent with the decreased FDRI observed in our later-onset PD sample, which was closely matched in age to the post-mortem PD samples. The FDRI results suggest that disregulation of iron metabolism occurs in PD and that this disregulation may differ in earlier- versus later-onset PD.     

Bilayer-by-bilayer antiferroelectric ordering in freely suspended films of an achiral polymer-monomer liquid crystal mixture

Thin freely suspended films of a mixture of an achiral side-chain liquid crystal polymer and its monomer have been studied with depolarized reflected light microscopy. We observe that regions with an odd number of bilayers exhibit a net spontaneous polarization in the tilt plane of the molecules, while regions with an even number of bilayers have no net polarization. These odd-even effects are direct evidence that the tilted smectic bilayers are anticlinic at the polymer backbone and synclinic at bilayer interface and confirm that the phase is bilayer-by-bilayer antiferroelectric.     

Progress in PET Imaging of Neuroinflammation Targeting COX-2 Enzyme

Neuroinflammation and cyclooxygenase-2 (COX-2) upregulation are associated with the pathogenesis of degenerative brain diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), epilepsy, and a response to traumatic brain injury (TBI) or stroke. COX-2 is also induced in acute pain, depression, schizophrenia, various cancers, arthritis and in acute allograft rejection. Positron emission tomography (PET) imaging allows for the direct measurement of in vivo COX-2 upregulation and thereby enables disease staging, therapy evaluation and aid quantifying target occupancy of novel nonsteroidal anti-inflammatory drugs or NSAIDs. Thus far, no clinically useful radioligand is established for monitoring COX-2 induction in brain diseases due to the delay in identifying qualified COX-2-selective inhibitors entering the brain. This review examines radiolabeled COX-2 inhibitors reported in the past decade and identifies the most promising radioligands for development as clinically useful PET radioligands. Among the radioligands reported so far, the three tracers that show potential for clinical translation are, [11CTMI], [11C]MC1 and [18F]MTP. These radioligands demonstrated BBB permeablity and in vivo binding to constitutive COX-2 in the brain or induced COX-2 during neuroinflammation.     

Morphology changes due to AC induced electromigration in Gd islands on W(1 1 0)

Gd islands were grown on W(1 1 0) surface by evaporating Gd on the substrate at room temperature and subsequent annealing. STM images reveal in many cases islands which have a deep hole inside them. The appearance of the hole is associated with the application of an AC field. No such holes appear when the sample is heated by a DC current. We show that this can be explained by the combined affect of the AC field and the barrier to diffusion introduced by steps that can create a nucleus for further growth of an island which includes a hole in the middle. This may be generalized to a technique of tailoring the size, shape and distances of islands by, for example, two orthogonal AC fields with a phase delay of 90° between them.