Thermal and surface analysis of palladium pyrazolates molecular precursors

The reduction of molecular or ionic precursors represents one of the more suitable and effective methods to obtain small and uniform particles. In the present work, various palladium (Pd(II)) molecular precursors (MPs) were characterized before and after thermal reduction process, as an alternative to form Pd nanoparticles. These MPs are classified in two principal groups; those that contain 3,5-dimethylpyrazole and those that contain 3-phenyl or 3,5-diphenyl pyrazole with some chemical variations: Pd(3,5-Ph₂pzH)₂Cl₂ (MP(I)), Pd(3-PhpzH)₂Cl₂ (MP(II)), Pd(3,5-Me₂pzH)₂Cl₂ (MP(III)), Pd(4-Br-3,5-Me₂pzH)₂Cl₂ (MP(IV)), Pd₂(µ-3,5-Ph₂pz)₂(3,5-Ph₂pzH)₂Cl₂·H₂O (MP(V)), Pd₂(µ-3,5-Me₂pz)₂(3,5-Me₂pzH)₂Cl₂ (MP(VI)), and Pd₃(µ-Phpz)₆ (MP(VII)). In order to obtain Pd nanoparticles, these neutral MPs were reduced under hydrogen atmosphere. Thermogravimetric analyses were carried out to establish the thermal stability of these compounds, an important parameter in order to select the appropriate conditions to form metallic Pd nanoparticles. To confirm the reduction of the precursors, Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis were performed on the molecular cluster precursor powders. The present study is a preparatory guide to establish the appropriate conditions in order to promote the formation of Pd nanoparticles. The temperature of 600 °C emerges as an ideal temperature to reach the decomposition of organic groups in the Pd(II) MPs, as well as the formation of metallic Pd particles, as corroborated by FT-IR and XPS analysis. These Pd MPs represent a new alternative for the preparation of metallic Pd nanoparticles.     

Carbonyl–carbonyl interactions and amide π‐stacking as the directing motifs of the supramolecular assembly of ethyl N‐(2‐acetylphenyl)oxalamate in a synperiplanar conformation

The title compound, C₁₂H₁₃NO₄, is one of the few examples that exhibits a syn conformation between the amide and ester carbonyl groups of the oxalyl group. This conformation allows the engagement of the amide H atom in an intramolecular three‐centred hydrogen‐bonding S(6)S(5) motif. The compound is self‐assembled by C=O...C=O and amide–π interactions into stacked columns along the b‐axis direction. The concurrence of both interactions seems to be responsible for stabilizing the observed syn conformation between the carbonyl groups. The second dimension, along the a‐axis direction, is developed by soft C—H...O hydrogen bonding. Density functional theory (DFT) calculations at the B3LYP/6‐31G(d,p) level of theory were performed to support the experimental findings.     

Optimization of Stability Robustness Bounds for Linear Discrete-Time Systems

In this paper, existing stability robustness measures for the perturbation of both continuous-time and discrete-time systems are reviewed. Optimized robustness bounds for discrete-time systems are derived. These optimized bounds are obtained reducing the conservatism of existing bounds by (a) using the structural information on the perturbation and (b) changing the system coordinates via a properly chosen similarity transformation matrix. Numerical examples are used to illustrate the proposed reduced conservatism bounds.     

Substituted thienyl stibines and bismuthines: syntheses,structures and cytotoxicity

New stibine and bismuthine substituted thienyl ring compounds, i.e. tris(3‐methyl‐2‐thienyl)stibine (1), tris(3‐methyl‐2‐thienyl)bismuthine (2), tris(3‐thienyl)stibine (3), tris(3‐thienyl)bismuthine (4) and tris(5‐chloro‐2‐thienyl)stibine (5), have been synthesized and characterized by IR, mass, ¹H, ¹³C, COSY, and HETCOR NMR spectroscopy. The metal centres in all compounds are pyramidal, and molecules in the stibine compound (1) and bismuthine compound (2) associate via Sb···S or Bi···S interactions to form supramolecular chains. The cytotoxicity of compounds 1 and 5 was determined. For compound 5, 85% of carcinogenic cell growth inhibition (U, K and H) was observed. Compound 1 shows a significant selectivity (>80%) for carcinogenic cell growth (K and U) inhibition. Both the compounds are highly toxic for the growth of normal lymphocytes with ～95% lethality. Compound 1 is approximately 20 times more toxic than 5 against Artemia salina. Copyright © 2005 John Wiley & Sons, Ltd.     

Asymptotic of extremal polynomials in the complex plane

We study the zero location and asymptotic zero distribution of sequences of polynomials which satisfy an extremal condition with respect to a norm given on the space of all polynomials.     

On existence and asymptotic behaviour of solutions of a functional integral equation

The paper contains a result on the existence and asymptotic behaviour of solutions of a functional integral equation. That result is proved under rather general hypotheses. The main tools used in our considerations are the concept of a measure of noncompactness and the classical Schauder fixed point principle. The investigations of the paper are placed in the space of continuous and tempered functions on the real half-line. We prove an existence result which generalizes several ones concerning functional integral equations and obtained earlier by other authors. The applicability of our result is illustrated by some examples.