Spectroscopic and morphological characterization of inflow cannulas of left ventricular assist devices.

Despite the consistent clinical data on the positive effects of left ventricular assist devices (LVADs) in the treatment of refractory heart failure, unfortunately these devices yet show some limitations such as the risk of stroke, infection, and device malfunction. The complex interplay between blood and the foreign material has a major role in the occurrence of these complications and biocompatibility of the inflow cannula would be pivotal in these terms. In this study, we carried out an in-depth physicochemical characterization of two commercially available LVADs by means of field emission gun scanning electron microscopy, energy dispersive X-ray, and X-ray photoelectron spectra. Our results show that, despite both pumps share the same physicochemical concepts, major differences can be identified in the surface nature, morphology, and chemical composition of their inflow cannulas.

Fascinating role of the number of f electrons in dipolar and octupolar contributions to quadratic hyperpolarizability of trinuclear lanthanides-biscopper Schiff base complexes.

The trinuclear [Ln(NO3)3(CuL)2] complexes (Ln = La, Ce, Sm, Eu and Er, L = N,N'-1,3-propylen-bis(salicylideniminato) have been investigated by a combination of HLS and EFISH techniques to evaluate both the dipolar and octupolar contributions to their significant quadratic hyperpolarizability and to confirm that f electrons may tune their second-order NLO response. In the complexes investigated, the major contribution to the total quadratic hyperpolarizability is largely controlled by the octupolar contribution, but the values of both ßEFISH and [parallel]ß(J=1)[parallel], that is the dipolar part, are significantly influenced by the number of f electrons, confirming that the unexpected polarizable character of f electrons may be the origin of such fascinating evidence.

Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites.

Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state (13)C-cross-polarization magic angle spinning nuclear magnetic resonance ((13)C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η(5)-C(5)H(5))(2)ZrR(2) (R = H, CH(3)) and [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(3) adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ~100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The (13)C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(2)(+)· · · AlS(-) interaction with greatly elongated Zr · · · O(AlS) distances of ~2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H(2) delivery to surface [η(5)-C(5)(CH(3))(5)]ZrH(2)(benzene)(+)· · · AlS(-) species, observable by solid-state NMR and XAS.

Insight into Group 4 Metallocenium-Mediated Olefin Polymerization Reaction Coordinates Using a Metadynamics Approach.

We report here the first application of the computationally efficient metadynamics approach for analyzing single-site olefin polymerization mechanisms. The mechanism of group 4 metallocenium catalysis for ethylene homopolymerization is investigated by modeling the ethylene insertion step at the cationic (η(5)-C5H5)Zr(CH3)2(+) center using molecular dynamics simulations within the Density Functional Theory (DFT) framework. In particular, the metadynamics formalism is adopted to enable theoretical characterization of covalent bond forming/breaking processes using molecular dynamics ab initio tools. Analysis of the ethylene insertion step free energy surface indicates a slightly exoergic process (-3.2 kcal/mol) with a barrier of 8.6 kcal/mol, in good agreement with conventional ab initio static calculations. Analysis of the structural and dynamic aspects of the simulated reaction coordinate reveals a preferred olefin configuration which aligns parallel to the Zr-CH3 vector in concert with insertion and a slightly bent conformation of the product n-propyl chain to avoid nonbonded repulsion between methylene groups. It is found that the unsaturated/electrophilic CpZr(CH3)2(+) center drives the insertion step, thus promoting the formation of the Zr-alkyl bond. The metadynamics analysis uniquely encompasses all energetically possible reaction coordinates, thus providing a more detailed mechanistic picture. These results demonstrate the potential of metadynamics in the conformational and geometrical analysis of transition metal-centered homogeneous catalytic processes.

Fluorinated beta-diketonate diglyme lanthanide complexes as new second-order nonlinear optical chromophores: the role of f electrons in the dipolar and octupolar contribution to quadratic hyperpolarizability.

The second-order nonlinear optical (NLO) properties of [Ln(hfac)(3)(diglyme)] (hfac = hexafluoroacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of f electrons in tuning the second-order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, beta(EFISH), initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the beta(EFISH) value of the Lu complex being only 1.2 times that of the Gd complex. The increase of beta(HLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good beta(HLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

Molecular recognition on a cavitand-functionalized silicon surface.

A Si(100) surface featuring molecular recognition properties was obtained by covalent functionalization with a tetraphosphonate cavitand (Tiiii), able to complex positively charged species. Tiiii cavitand was grafted onto the Si by photochemical hydrosilylation together with 1-octene as a spatial spectator. The recognition properties of the Si-Tiiii surface were demonstrated through two independent analytical techniques, namely XPS and fluorescence spectroscopy, during the course of reversible complexation-guest exchange-decomplexation cycles with specifically designed ammonium and pyridinium salts. Control experiments employing a Si(100) surface functionalized with a structurally similar, but complexation inactive, tetrathiophosphonate cavitand (TSiiii) demonstrated no recognition events. This provides evidence for the complexation properties of the Si-Tiiii surface, ruling out the possibility of nonspecific interactions between the substrate and the guests. The residual Si-O(-) terminations on the surface replace the guests' original counterions, thus stabilizing the complex ion pairs. These results represent a further step toward the control of self-assembly of complex supramolecular architectures on surfaces.

Proximity and cooperativity effects in binuclear d(0) olefin polymerization catalysis. theoretical analysis of structure and reaction mechanism.

This contribution focuses on the distinctive center-to-center cooperative catalytic properties exhibited by bimetallic "constrained geometry catalysts" (CGCs), and analyzes metal-metal proximity effects on ethylene polymerization processes mediated by (mu-CH(2)-3,3'){(eta(5)-indenyl)[1-H(2)Si((t)BuN)](ZrMe(2))}(2) (Zr(2))-derived catalysts using density functional theory. Precatalyst geometries are first discussed, and then ion-pair formation/heterolytic dissociation processes involving the binuclear bis(borane) cocatalyst 1,4-(C(6)F(5))(2)BC(6)F(4)B(C(6)F(5))(2) (BN(2)), are analyzed and compared with those in the parent mononuclear analogue. It is found that, on proceeding from the mononuclear to binuclear catalyst system, ion-pair dissociation energies increase due to the stronger catalyst center-counterdianion interactions. Moreover, in the binuclear case, the interaction energies are markedly sensitive to geometrical matching between the binuclear bis(borane) and the precatalyst Zr-methyl positions. Binuclear catalytic effects between the metal centers are then explored, with the specific contribution from the proximity of the second metal center. Possible agostic interactions of alpha-alkenes pi-coordinated to one Zr center with the second Zr center of the binuclear catalyst are scrutinized for the case of 1-octene. It is argued that these agostic interactions are at least partly responsible for the unusual enchainment properties of the bimetallic catalysts. In particular, the greater polyethylene product branch densities found experimentally for the bimetallic catalysts can be correlated with an intramolecular reinsertion process, assisted by agostic interactions. Moreover, these same agostic interactions involving a chain growing at one metal site with the second metal site of the binuclear catalyst modify the environment to increase propagation/termination rate ratios, in turn favoring increased product molecular weight (M(n)). These effects are observed experimentally at closer Zr...Zr proximities in olefin polymerizations mediated by binuclear CGC catalysts.

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass.

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Stereochemical control mechanisms in propylene polymerization mediated by C1-symmetric CGC titanium catalyst centers.

This work analyzes stereochemical aspects of olefin polymerization processes mediated by the C1-symmetric constrained geometry catalyst H2Si(ind)(tBuN)TiCH3+ (ind = indenyl), including the role of the cocatalyst/counteranion. The energetics of catalyst activation are first analyzed and shown to compare favorably with experiment. The energetics of heterolytic ion pair separation are next scrutinized, and the effects of solvation environment are assessed. Computed thermodynamic profiles for ethylene insertion at H2Si(ind)(tBuN)TiCH3+ indicate that the kinetics of insertion processes at the H2Si(ind)(tBuN)TiR+ cation can be analyzed in terms of SCF potential energies. We next compare the energetic profile for ethylene insertion at the naked H2Si(ind)(tBuN)TiCH3+ cation with that at the related H2Si(ind)(tBuN)TiCH3+H3CB(C6F5)3- ion pair to understand counterion effects. It is seen that the counterion, although affecting overall catalytic activity, does not significantly influence enchainment stereochemistry or polymer microtacticity. Next, the second ethylene insertion at H2Si(ind)(tBuN)Ti(nC3H7)+H3CB(C6F5)3- is analyzed to evaluate counteranion influence on the propagation barrier. It is found that the ethylene uptake transition state is energetically comparable to the first insertion transition state and that solvation has negligible effects on the energetic profile. These findings justify analysis of the propylene insertion process within the less computationally demanding "naked cation" model. Thus, monomer enchainment at H2Si(ind)(tBuN)TiR+ is analyzed for H2Si(ind)(tBuN)TiCH3+ + propylene (first insertion) and for H2Si(ind)(tBuN)Ti(iC4H6)+ + propylene (second insertion). Data describing the first insertion highlight the sterically dominated regioselection properties of the system with activation energies indicating that olefin insertion regiochemistry is predominantly 1,2 (primary), while the second insertion similarly reflects the catalyst stereoinduction properties, with steric effects introduced by the growing chain (mimicked by an isobutyl group) preferentially favoring insertion pathways that afford isotactic enrichment, in agreement with experiment.

Self-assembly of nanosize coordination cages on si(100) surfaces.

Bottom-up fabrication of 3D organic nanostructures on Si(100) surfaces has been achieved by a two-step procedure. Tetradentate cavitand 1 was grafted on the Si surface together with 1-octene (Oct) as a spatial spectator by photochemical hydrosilylation. Ligand exchange between grafted cavitand 1 and self-assembled homocage 2, derived from cavitand 5 bearing a fluorescence marker, led to the formation of coordination cages on Si(100). Formation, quantification, and distribution of the nanoscale molecular containers on a silicon surface was assessed by using three complementary analytical techniques (AFM, XPS, and fluorescence) and validated by control experiments on cavitand-free silicon surfaces. Interestingly, the fluorescence of pyrene at approximately 4 nm above the Si(100) surface can be clearly observed.

Template-free and seedless growth of Pt nanocolumns: imaging and probing their nanoelectrical properties.

The electrical conductivity of platinum nanocolumns has been imaged and measured by conductive atomic force microscopy. The successful syntheses of well-aligned 100-oriented Pt nanocolumns on both random and oriented substrates have been carried out via a simple and seedless metal-organic chemical vapor deposition process. Control of the crystalline quality has been achieved by carefully selecting operational conditions. The growth mechanism, depending on deposition parameters (including deposition temperature, oxygen partial pressures, deposition time, and substrate nature), has been examined in detail.

Grafting cavitands on the Si(100) surface.

Cavitand molecules having double bond terminated alkyl chains and different bridging groups at the upper rim have been grafted on H-terminated Si(100) surface via photochemical hydrosilylation of the double bonds. Pure and mixed monolayers have been obtained from mesitylene solutions of either pure cavitand or cavitand/1-octene mixtures. Angle resolved high-resolution X-ray photoelectron spectroscopy has been used as the main tool for the monolayer characterization. The cavitand decorated surface consists of Si-C bonded layers with the upper rim at the top of the layer. Grafting of pure cavitands leads to not-well-packed layers, which are not able to efficiently passivate the Si(100) surface. By contrast, monolayers obtained from cavitand/1-octene mixtures consist of well-packed layers since they prevent silicon oxidation after aging. AFM measurements showed that these monolayers have a structured topography, with objects protruding from the Si(100) surface with average heights compatible with the expected ones for cavitand molecules.

Cathodoluminescence investigation of residual stress in Er3+:YAlO3 thin films grown on (110) SrTiO3 substrate by metal-organic chemical vapor deposition.

YAlO3 thin films doped with different amounts of Er3+ have been grown directly onto (110) SrTiO3 substrate using the metal-organic chemical vapor deposition method (MOCVD). X-ray diffraction patterns and the rocking curve of the (002) reflection point to the growth of <001>-oriented YAlO3 phase. Piezo-spectroscopic (PS) biaxial calibration was performed on two luminescence bands, related to transitions from the (4)S3/2 excited state, using a specially designed ball-on-ring loading jig. Such a PS calibration allowed us to retrieve the rate of wavelength shift with stress without separating the grown film from the substrate. The outcome of the PS calibration has been applied to build up in the field emission scanning electron microscope (FEG-SEM) high-resolution maps of the residual stress field developed in the film. Results indicate that the residual stress in Er3+:YAlO3 films were compressive in nature and increased with increasing Er3+ dopant concentration.

Calcium copper-titanate thin film growth: tailoring of the operational conditions through nanocharacterization and substrate nature effects.

A novel approach based on a molten multicomponent precursor source has been applied for the MOCVD fabrication of high-quality CaCu(3)Ti(4)O(12) (CCTO) thin films on various substrates. The adopted in situ strategy involves a molten mixture consisting of Ca(hfa)(2).tetraglyme, Ti(tmhd)(2)(O-iPr)(2), and Cu(tmhd)(2) [Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme = 2,5,8,11,14-pentaoxapentadecane; Htmhd = 2,2,6,6-tetramethyl-3,5-heptandione; O-iPr = isopropoxide] precursors. Film structural and morphological characterizations have been carried out by several techniques [X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM)], and in particular the energy filtered TEM mapping and X-ray energy dispersive (EDX) analysis in TEM mode provided a suitable correlation between nanostructural properties of CCTO films and deposition conditions and/or the substrate nature. Correlation between the nanostructure and optical/dielectric properties has been investigated exploiting spectroscopic ellipsometry.

Density control of dodecamanganese clusters anchored on silicon(100).

A synthetic strategy to control the density of Mn12 clusters anchored on silicon(100) was investigated. Diluted monolayers suitable for Mn12 anchoring were prepared by Si-grafting mixtures of the methyl 10-undecylenoate precursor ligand with 1-decene spectator spacers. Different ratios of these mixtures were tested. The grafted surfaces were hydrolyzed to reveal the carboxylic groups available for the subsequent exchange with the [Mn12O12(OAc)16(H2O)4]4 H2O2 AcOH cluster. Modified surfaces were analyzed by attenuated total reflection (ATR)-FTIR spectroscopy, X-ray photoemission spectroscopy (XPS), and AFM imaging. Results of XPS and ATR-FTIR spectroscopy show that the surface mole ratio between grafted ester and decene is higher than in the source solution. The surface density of the Mn12 cluster is, in turn, strictly proportional to the ester mole fraction. Well-resolved and isolated clusters were observed by AFM, using a diluted ester/decene 1:1 solution.

Synthesis, characterization and application of Ni(tta)2.tmeda to MOCVD of nickel oxide thin films.

A novel nickel beta-diketonate adduct, Ni(tta)2.tmeda, has been synthesized using 2-thenoyltrifluoroacetone as the beta-diketonate and N,N,N,'N'-tetramethylethylendiamine as the Lewis base. It has been characterized by elemental analyses, IR, 1H NMR, 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Physical and thermal properties of Ni(tta)2.tmeda precursor have been also extensively investigated. Its efficacy as a metal-organic chemical vapour deposition (MOCVD) precursor for the growth of nickel oxide films has been fully tested by applying it to the deposition of NiO films on quartz substrate. NiO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy and UV spectroscopy.

A novel diamine adduct of zinc bis(2-thenoyl-trifluoroacetonate) as a promising precursor for MOCVD of zinc oxide films.

A novel diamine (N,N,N',N'-tetramethyletilendiamine) adduct of zinc bis(2-thenoyl-trifluoroacetonate) has been synthesized in a single-step reaction. Single-crystal X-ray diffraction studies of Zn(tta)(2).tmeda provide evidence of a mononuclear structure with a six-coordinated zinc ion. The thermal behavior of this adduct points to mass-transport properties suitable for its application to MOCVD processes. This novel compound has been successfully applied as a precursor for the deposition of ZnO films on (100) Si and quartz substrates. The good quality of the deposited films indicates that the adduct is a very attractive precursor for MOCVD applications.

Multifunctional cadmium single source precursor for the selective deposition of CdO or CdS by a solution route.

We report on the interesting properties of a novel single precursor, Cd(tta)2 x tmeda (Htta = 2-thenoyl-trifluoroacetone, tmeda = N,N,N',N'-tetramethylethylenediamine), ideally suited for the selective and reproducible fabrication of pure quality films of CdS or CdO through a simple solution process.

Recent advances in characterization of CaCu3Ti4O12 thin films by spectroscopic ellipsometric metrology.

CaCu3Ti4O12 (CCTO) thin films were successfully grown on LaAlO3(100) and Pt/TiO2/SiO2/Si(100) substrates by a novel MOCVD approach. Epitaxial CCTO(001) thin films have been obtained on LaAlO3(100) substrates, while polycrystalline CCTO films have been grown on Pt/TiO2/SiO2/Si(100) substrates. Surface morphology and grain size of the different nanostructured deposited films were examined by AFM, and spectroscopic ellipsometry has been used to investigate the electronic part of the dielectric constant (epsilon2). Looking at the epsilon2 curves, it can be seen that by increasing the film structural order, a greater dielectric response has been obtained. The measured dielectric properties accounted for the ratio between grain volumes and grain boundary areas, which is very different in the different structured films.