Formation of silver nanoclusters in transparent polyimides by Ag-K ion-exchange process

Silver nanoclusters embedded in two transparent fluorinated polyimides, 4,4'-hexafluoroisopropylidene diphthalic anhydride – 2,3,5,6-tetramethyl paraphenylene diamine (6FDA-DAD) and 3,3',4,4' – biphenyltetracarboxylic acid dianhydride – 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (BPDA-3F), have been produced by surface modification with KOH aqueous solution followed by K-assisted Ag doping and thermal reduction in hydrogen atmosphere. The reaction rate of the nucleophilic hydrolysis in KOH, studied by Fourier transform infrared spectroscopy (FT-IR) and Rutherford backscattering spectrometry (RBS), depends on the polyimide chemical structure. After ion-exchange in AgNO₃ solution and subsequent annealing, the polyimide structure recovery was monitored by FT-IR whereas the characteristic surface plasmon absorption band of silver nanoparticles was evidenced by optical absorption measurements. The structure of silver nanoclusters as related to size and size distribution in the different polyimide matrices was thoroughly investigated by Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The collected data evidenced a uniform distribution of Ag clusters of nanometric size after thermal treatment at 300 ^○C in both polyimides. For the same ion-exchange treatment parameters and annealing temperature, XRD analyses evidenced the presence of crystallites with similar sizes.     

Macromolecular polyradicals with cyclic triphosphazene as a core. Spectral and electrochemical properties

Stable cyclotriphosphazenes 5 and 6, with three and four carbon radical centers, have been prepared by condensation of (4-hydroxy-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl radical (4) with tetrachloro-2,2'-dioxybiphenylcyclotriphosphazene (7). EPR studies of both polyradicals in fluid solution suggest an electronic communication through the PN multiple bonds of the cycle. EPR spectral results in frozen solutions and magnetic susceptibility measurements in the solid are consistent with very weak electron-electron dipolar interactions. Reductive cyclic voltammetry shows a single three-electron redox couple for triradical 5 and a single four-electron redox couple for tetraradical 6. Both polyradicals 5 and 6 have been chemically oxidized to a stable trication 5(3+) and a tetracation 6(4+), respectively, by electron-transfer reactions.     

On the CH...Cu agostic interaction: chiral copper(II) compounds with ephedrine and pseudoephedrine derivatives

The ephedrine derivative, (H2ceph), yields [Cu(Hceph)2], showing a CH...Cu(II) agostic interaction; while in the analogous compound [Cu(Hcpse)2], with pseudoephedrine (H2cpse), that interaction is absent, despite the fact that these two diasteromers differ only in the orientation of the methyl and phenyl groups: erythro in H2ceph and threo in H2cpse. The X-ray crystal structure of [Cu(Hceph)2], indicates a Cu...HC length of 2.454 A and the theoretical study reveals the formation of a Cu...HC bond since the associated electronic density shows both a bond critical point and a bond ring critical point.     

Reducing activity of polyphenols with stable radicals of the TTM series. Electron transfer versus H-abstraction reactions in flavan-3-ols

A new method to test the antioxidant activity of polyphenols by electron transfer reactions to a stable organic free radical, tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical (HNTTM), is reported. Therefore, the activity of the natural flavanols, (-)-epicatechin, and two synthetic derivatives, 4beta-(S-cysteinyl)epicatechin and 4beta-(2-aminoethylthio)epicatechin, can be differentiated by their capacity to transfer hydrogen atoms to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and to transfer electrons to HNTTM. [structure: see text]     

Retention of Co(II), Ni(II), and Cu(II) on a purified brown humic acid. Modeling and characterization of the sorption process

Brown humic acids (BHAs) constitute the most polar and soluble fraction of humic acids. Their colloidal character and their high number of functional surface groups justify their higher reactivity as against metallic cations with respect to other humic fractions (i.e., gray humic acids and humins). The aim of this work is to study the retention mechanisms of Cu(II), Ni(II), and Co(II) on a BHA by means of a proper combination of physical and chemical techniques: sorption isotherms, mathematical modeling of these isotherms, molecular modeling, FTIR, and N2 (77 K) and CO2 (273 K) adsorption. Electrostatic retention for the three cations is an important mechanism at very low concentrations. Its magnitude is higher than that of the specific retention in the initial stages of the retention but it decreases progressively with respect to the former as the initial metal concentration increases. The BHA surface area varies with the amount of retained metal. When the initial amount of added metal is low (n0 < 80 mmol kg(-1)), the cations form 2:1 complexes, which are energetically favored due to the chelate effect. To obtain this coordination, the BHA slightly modifies its conformation by decreasing its area. When the initial amount of added metal is sufficiently high to occupy most of the surface functional groups (n0 > 1280 mmol kg(-1)), the cations are heterogeneously retained over the whole surface, thus preventing the available groups at low n0 from giving place to the 2:1 complexes due to the fact that they are already occupied.     

Nonconventional C–H···Cu Interaction Between Copper Cun Clusters (n = 3–20) and Aromatic Compounds

The present study examines bonding patterns between copper Cu_n clusters (n?=?3–20) and aromatic compounds (benzene, phenol, and benzaldehyde) using a density-functional theory (DFT) approach. Hirshfeld population, natural bond orbital (NBO), molecular orbitals, and quantum theory of atoms in molecules (QTAIM) analyses suggested the formation of two types of interactions Cu–arene and C–H···Cu, in the complexation of copper clusters by an aromatic compound.

     

In vitro AND in vivo UPTAKE OF BENZOPORPHYRIN DERIVATIVE INTO HUMAN AND MINISWINE ATHEROSCLEROTIC PLAQUE

Abstract— Befnzoporphyrin derivative(BPD) has been demonstrated to be fnew potent photosentsitze for photodynamic therapy(PDT). Althought most of wrok on BPD has been focused on its potential applications for cancer tratment, BPD amy have potential clilnical uses in the treatment of artheros clerosis. The purposes of this study was to determine in vitro and vivo uptake of BPD into atherosclerotic plaque. Samples of atherosclerotic human femoral and popliteal arteries were incubated with BPD-monoacid, ring A(BPD-MA) for 1 h in the following concentrations: 1, 5, 10, 20, 30 and 40 μg/mL. fluorescence from all samplesd was determined by chemical etraction with a spectrofluorometer. the tissue concentration for human arteries was 0.37 ± 0.03, 2.78 ± 1.5, 3.6 ± 1.91, 7.15 ± 2.36, 8.06 ± 3.09 and 14.6 ± 4.81 μg/g, respectively. In aeddition, three miniswine were rendered atherosclerotic and given BPD 2.0 mg/ Kg intravenously. The concentration of BPD-MA in miniswine aorta was93–190 ng/g and the plaque/normal ration was 1.7–3.5, for miniswine cartoid artery contained 54 ng/g. this study showed that BPD-MA was taken up in atherosclerotic vesselsd both in vitro and in vivo and mey have potential for PDT of atherosclerosis.     

On the impact of viscous drops onto dry smooth surfaces

An experimental study of the impact of glycerol/water drops onto a dry glass surface at Reynolds and Weber numbers around the splashing/deposition threshold is presented. Some new observed phenomena that may shed further light on the mechanisms underlying air bubble entrainment and splashing for high-viscosity liquids are presented and discussed. The experiments were recorded with a high-speed camera using two complementary lighting setups that enhance the visualization of different features of the air entrainment phenomena: backlighting with a light diffuser and oblique lighting without diffuser. Besides the ring of micro-bubbles surrounding the central entrapped bubble and the cloud of bubbles entrained as a result of the interaction between a levitated thin film and the solid surface, which have been studied by other authors in previous works, a second ring of micro-bubbles that delimits the outer cloud of bubbles has been detected in our investigation. Attention is mainly focused on analyzing the dependency of the behavior of the two rings of micro-bubbles on the drop impact velocity, the ranges of the relevant dimensionless numbers in which the rings are formed and the existence, in certain impact conditions, of an abrupt increase in the size of the second ring, which substantially modifies the impact outcome.