Palladium hydrogenation catalysts modified with aluminum-and phosphorus-containing compounds and with alcohols: Effect of modifiers

The catalytic properties of nanosize catalysts derived from Pd(acac)₂ and triethylaluminum in hydrogenation of organic substrates were studied, and the optimal conditions for the catalyst preparation were found. The maximum observed on the plot of the catalyst specific activity vs. Al/Pd ratio was explained by experiments.     

On the nature op continuum emission production op photons,emitted by the products op repractory metal sputtering

Bombardment of a clean Ta target by 4 keV Cs⁺ ions under ultra high vacuum (UHV) has been experimentally shown to give rise to photon continuum emission by sputtered products.     

Mesoscale and clusters of synchrony in networks of bursting neurons

We study the role of network architecture in the formation of synchronous clusters in synaptically coupled networks of bursting neurons. We give a simple combinatorial algorithm that finds the largest synchronous clusters from the network topology. We demonstrate that networks with a certain degree of internal symmetries are likely to have cluster decompositions with relatively large clusters, leading potentially to cluster synchronization at the mesoscale network level. We also address the asymptotic stability of cluster synchronization in excitatory networks of Hindmarsh-Rose bursting neurons and derive explicit thresholds for the coupling strength that guarantees stable cluster synchronization.     

Homoclinic bifurcations leading to the emergence of bursting oscillations in cell models

We present a qualitative analysis of a generic model structure that can simulate the bursting and spiking dynamics of many biological cells. Four different scenarios for the emergence of bursting are described. In this connection a number of theorems are stated concerning the relation between the phase portraits of the fast subsystem and the global behavior of the full model. It is emphasized that the onset of bursting involves the formation of a homoclinic orbit that travels along the route of the bursting oscillations and, hence, cannot be explained in terms of bifurcations in the fast subsystem. In one of the scenarios, the bursting oscillations arise in a homoclinic bifurcation in which the one-dimensional (1D) stable manifold of a saddle point becomes attracting to its whole 2D unstable manifold. This type of homoclinic bifurcation, and the complex behavior that it can produce, have not previously been examined in detail. We derive a 2D flow-defined map for this situation and show how the map transforms a disk-shaped cross-section of the flow into an annulus. Preliminary investigations of the stable dynamics of this map show that it produces an interesting cascade of alternating pitchfork and boundary collision bifurcations. Received 24 June 1999 and Received in final form 17 February 2000     

C–O,C–S,C–N,and C–C Bond Formation at the Periphery of the Macrocycle during Chemical Modification of Phytochlorins: Key Methods and Synthetic Applications

Russian Journal of General Chemistry - The main methods of C-O, C-S, C-N, and C-C bond formation at the periphery of the macocrocycle during chemical modification of phytochlorins in the synthesis...     

Synthesis,properties, and activity of nanosized palladium catalysts modified with elemental phosphorus for hydrogenation

The applicability of elemental phosphorus as a modifier of palladium catalysts for hydrogenation was demonstrated, and the conditions for the synthesis of nanoparticles that are highly efficient in hydrogenation catalysis were optimized. The modifying effect of elemental phosphorus depends on the P/Pd ratio; it is associated with changes in the catalyst dispersity and the nature of the formed nanoparticles containing various palladium phosphides (PdP₂, Pd5P₂, and Pd₆P) and Pd(0) clusters. The main stages of the formation of palladium catalysts for hydrogenation were determined, and a model of an active catalyst, in which the Pd₆P phosphide is the core of a nanoparticle and Pd(0) clusters form a shell, was proposed.     

Ziegler-type nickel-based hydrogenation catalysts: The effect of the water content of the nickel precursor on the size and nature of the resulting particles

The size and nature of the nanoparticles forming in systems based on Ni(acac)₂ · nH₂O (n = 0, 0.5, 3.0) and AlEt₃ have been determined by high-resolution electron microscopy and X-ray microanalysis. The nickel cluster size depends on the water content of the precursor. The average particle diameter increases from 1.2 nm (Ni(acac)₂ · 0.5H₂O precursor) to 2.4 nm (Ni(acac)₂ · 3H₂O precursor). A homogeneous solution forms in the Ni(acac)₂–5AlEt₃ system, as was demonstrated by examining the system under an electron microscope whose resolving power allows particles larger than 0.7 nm to be detected.     

Design,synthesis and evaluation of the antioxidant and neuroprotective properties of alkyl- and terpenylphenolchlorin conjugates

The new amide conjugates were synthesized from methyl pheophorbide a and its carboxyl derivatives by reactions with aminomethyl derivatives of 2,4-dimethylphenol, 2-isocamphyl-4- methylphenol, 2-bornyl-4-methylphenol, and 2-isobornyl-4-methylphenol. The antioxidant activity of some conjugates was established by investigation of their ability to inhibit the accumulation of secondary products of lipid peroxidation in a brain of laboratory mice in vitro. The neuroprotective properties of porphyrin and terpenylphenol conjugates have been studied on the model of H₂O₂-induced oxidative stress in SH-SY5Y cells (neuroblastoma).

     

Formation of Nanosized Catalysts Based on Palladium Phosphine Complexes and the Nature of Their Activity

Findings on the formation and features of nanosized particles based on palladium complexes, which are active in hydrogenation catalysis, are summarized. Depending on the nature of a reducing agent, nanosized particles formed by the reduction of palladium(II) phosphine complexes are either metallic nuclei stabilized by organophosphorus ligands or associates of polynuclear phosphido or phosphinideno palladium complexes whose surface contains immobilized Pd(0) clusters. The ensembles of the Pd(0) atoms are active in hydrogenation.