Verbindungen des Germainums und Zinns. 17. Alkylarylstannylen-Komplexe des Chroms und Molybdäns ohne Donorstabilisierung

Compounds of Germanium and Tin. 17 [1]. Alkylarylstannylene Complexes of Chromium and Molybdenum without Donor Stabilization Reaction of the complexes [(OC)₅M(THF)], M = Cr, Mo, with the alkylarylstannylene RR′Sn: R = 2,4,6-tBu₃C₆H₂, R′ = CH₂C(CH₃)₂-3,5-tBu₂C₆H₂, provides the donor-free stannylene complexes [(OC)₅Cr?SnRR′] ( 6 ) and [(OC)₅Mo?SnRR′] ( 8 ), respectively. The X-ray structure analyses of the isotypic compounds 6 and 8 reveal the three coordinate tin atoms in strictly planar environments and acute CSnC angles of 91.2° ( 6 ) and 91.3° ( 8 ).     

1,3-dipolar cycloaddition reactions of porphyrins with azomethine ylides

[reaction: see text] The behavior of porphyrins as dipolarophiles in 1,3-dipolar cycloadditions with azomethine ylides was studied. Depending on the nature of the substituent groups on the porphyrin macrocycles, the reaction can give monoadducts (chlorins) or bisadducts (isobacteriochlorins and bacteriochlorins). When a large excess of azomethine ylide is used, trisadducts can also be obtained. Mixed isobacteriochlorin derivatives were prepared from the reaction of azomethine ylides with the chlorin monoadducts previously obtained via Diels-Alder reactions.     

Modeling of the hysteresis phenomena in finite-sized slitlike nanopores. Revision of the recent results by rigorous numerical analysis

The systematic investigation of the hysteresis phenomena in finite-sized slitlike nanopores via the Aranovich-Donohue (AD) lattice density functional theory (LDFT) is presented. The new reliable quantitative modeling of the adsorption and desorption branch of the hysteresis loop, through the formation and movement of the curved meniscus, is formulated. As a result, we find that our proposal, which closely mimics the experimental findings, can reproduce a rounded shape of the desorption branch of the hysteresis loop. On the basis of the exhausted commutations, we proved that the hysteresis loop obtained in the considered finite-sized slitlike geometry is of the H1 type of the IUPAC classification. This fundamental result and the other most important results do not confirm the results of the recent studies of Sangwichien et al., whereas they fully agree with the recent lattice studies due to Monson et al. We recognize that the nature of the hysteresis loops (i.e. position, width, shape, and the multiple steps) mainly depends on the value of the energy of both the adsorbate-adsorbate and adsorbate-adsorbent interactions; however, the first one is critical for the appearance of hysteresis. Thus, for relatively small adsorbate-adsorbate interactions, the adsorption-desorption process is fully reversible in the whole region of the bulk density. We show that the strong adsorbate-adsorbent interactions produce (also observed experimentally) multiple steps within hysteresis loops. Contrary to the other studies of the hysteresis phenomena in confined geometry via the LDFT formalism, we constructed both ascending and descending scanning curves, which are known from the experimental observations. Additionally, we consider the problem of the stability of both the obtained adsorption and desorption branches of the computed hysteresis loop in finite-sized slitlike nanopores.     

Preconceptional Resveratrol Supplementation Partially Counteracts Age-Related Reproductive Complications in C57BL/6J Female Mice

Aging is associated with a drastic decline in fertility/fecundity and with an increased risk of pregnancy complications. Resveratrol (RES), a natural polyphenolic compound, has shown anti-oxidant and anti-inflammatory activities in both human and animal models, thus representing a potential therapeutic and prophylactic anti-aging supplement. Here, we investigated whether preconceptional resveratrol supplementation improved reproductive outcomes in mid-aged (8-month-old) and old (12-month-old) C57BL/6J female mice. Female siblings were cohoused and assigned to either RES or vehicle supplementation to drinking water for 10 consecutive weeks. Subsequently, females were mated with non-supplemented males and their pregnancy outcomes were monitored. RES improved mating success in old, but not in mid-aged females, and prevented the occurrence of delivery complications in the latter. These results indicate that preconceptional RES supplementation could partially improve age-related reproductive complications, but it was not sufficient to restore fecundity in female mice at a very advanced age.     

Structure sensitivity of alkynol hydrogenation on shape- and size-controlled palladium nanocrystals: which sites are most active and selective?

The activity and selectivity of structure-sensitive reactions are strongly correlated with the shape and size of the nanocrystals present in a catalyst. This correlation can be exploited for rational catalyst design, especially if each type of surface atom displays a different behavior, to attain the highest activity and selectivity. In this work, uniform Pd nanocrystals with cubic (in two different sizes), octahedral, and cuboctahedral shapes were synthesized through a solution-phase method with poly(vinyl pyrrolidone) (PVP) serving as a stabilizer and then tested in the hydrogenation of 2-methyl-3-butyn-2-ol (MBY). The observed activity and selectivity suggested that two types of active sites were involved in the catalysis--those on the planes and at edges--which differ in their coordination numbers. Specifically, semihydrogenation of MBY to 2-methyl-3-buten-2-ol (MBE) occurred preferentially at the plane sites regardless of their crystallographic orientation, Pd(111) and/or Pd(100), whereas overhydrogenation occurred mainly at the edge sites. The experimental data can be fit with a kinetic modeling based on a two-site Langmuir-Hinshelwood mechanism. By considering surface statistics for nanocrystals with different shapes and sizes, the optimal catalyst in terms of productivity of the target product MBE was predicted to be cubes of roughly 3-5 nm in edge length. This study is an attempt to close the material and pressure gaps between model single-crystal surfaces tested under ultra-high-vacuum conditions and real catalytic systems, providing a powerful tool for rational catalyst design.     

cis-Glyco-fused benzopyran compounds as new amyloid-β peptide ligands

A small library of glyco-fused benzopyran compounds has been synthesised. Their interaction features with Aβ peptides have been characterised by using STD-NMR and trNOESY experiments. The conformational analysis of the compounds has also been carried out through molecular mechanics (MM) and molecular dynamics (MD) simulations.     

Interactions of hydrosiloxane and vinylsiloxane groups with aluminum oxide surfaces

Silicone-based materials often contain vinylsiloxane and hydrosiloxane groups for cross-linking by a radical or addition reaction. Such functional groups can influence the interactions with fillers or with surfaces of substrates when used as adhesives. This work examined how these functional groups interact with aluminum oxide surfaces. For this purpose, aluminum oxide powders with large surface areas of 150 m²/g and different acid-base properties were examined. Siloxanes were applied as thin layers to mainly obtain information from the interphase by vibrational spectroscopy. It was observed that vinyl groups show low interactions with aluminum oxide surfaces even at elevated temperatures. In contrast to this, hydrosiloxanes undergo strong interactions and reactions with aluminum oxides already at room temperature. Activated Si─H species were observed as an intermediate state. On the one hand, interactions and reactions might contribute to adhesion, but on the other hand, the cross-linking reaction can be influenced near the surface, leading to lower mechanical strength.     

Quantifying electron transfer during hyperthermal scattering of C60+ from Au(111) and n-alkylthiol self-assembled monolayers

A tandem time-of-flight mass spectrometer with an intermediate surface was used to quantify electron transfer during glancing incidence scattering of hyperthermal C(60) (+) (E(coll)=250-500 eV, theta(in)=75 degrees ) from (i) self-assembled monolayers of n-alkylthiols on gold (of various chain lengths), (ii) partly fluorinated alkylthiols on gold, as well as (iii) clean gold surfaces. Self-assembled monolayers (SAMs) behave as insulating layers with their thicknesses determining the electron tunneling probability during collision. Correspondingly, a roughly exponential dependence of the neutralization probability on the chain length n was found. A pronounced dependence of the neutral yield on the primary beam kinetic energy indicates that dynamic SAM deformation and associated projectile penetration depth also play a role in determining electron transfer efficiency. Results are consistent with the molecular deformability of SAMs as determined with other experimental methods.     

Free energy surfaces from nonequilibrium processes without work measurement

Recent developments in statistical mechanics have allowed the estimation of equilibrium free energies from the statistics of work measurements during processes that drive the system out of equilibrium. Here a different class of processes is considered, wherein the system is prepared and released from a nonequilibrium state, and no external work is involved during its observation. For such "clamp-and-release" processes, a simple strategy for the estimation of equilibrium free energies is offered. The method is illustrated with numerical simulations and analyzed in the context of tethered single-molecule experiments.     

Oscillation of Functions in the Hölder Class

Potential Analysis - We study the size of the set of points where the α-divided difference of a function in the Hölder class Λα is bounded below by a fixed positive constant....