Showing papers by "Vadim G. Kessler published in 2008"

Role of the Ancillary Ligand N,N-Dimethylaminoethanol in the Sensitization of EuIII and TbIII Luminescence in Dimeric β-Diketonates

Abstract: Two types of dimeric complexes [Ln2(hfa)6(i2-O(CH2)2NHMe2)2] and [Ln(thd)2(i2,e2-O(CH2)2NMe2)]2 (Ln ) YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- ) hexafluoroacetylacetonato, thd- ) dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the â-diketonate. In [Tb2(hfa)6(i2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1âââTb2 separation of 3.684(1) A. In [Tb(thd)2(i2,e2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1âââTb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 °C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield QLn L ) 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the â-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both â-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

Chemically Triggered Biodelivery Using Metal–Organic Sol–Gel Synthesis†

Abstract: The application of inorganic materials for drug delivery and bioencapsulation has recently attracted the attention of researchers. Silica-based mesoporous monoliths and sol– gel-derived amorphous silica particles have been actively studied for their slow release of adsorbed pharmaceutical agents, while soft silica gels have been demonstrated to act as highly biocompatible matrices for bacterial encapsulation. Silica matrices have even been tested for biodelivery applications, specifically for medical treatments that exploit the delayed liberation of microorganisms able to attack target diseases. In particular, the liberation of viruses from silica gels has been studied for the development of viral gene therapy. The disadvantages of silica gels for such applications are connected with the combination of high porosity and slow biodegradability, which means that the encapsulated viruses may cause an immune rejection before they are released in efficient amounts. Many metal oxides, in particular titanium dioxide, are known to be highly biocompatible, at least when photochemical oxidation processes are prevented. In addition, aluminum oxide gels, produced from inorganic salt precursors and washed to remove excess electrolyte, were demonstrated to be biocompatible hosts for microorganisms. Titania nanotubes have even been investigated as a possible source in the context of slow drug release. Development of titaniabased sol–gel materials for bioencapsulation and controlled drug release has so far been hindered by the high reactivity of the metal–organic sol–gel precursors, titanium alkoxides, which require anhydrous media for the preparation of colloid solutions. We report herein the preparation of biocompatible aqueous titania sols and gels and their application in the encapsulation of microorganisms and pharmaceuticals with the possibility of controlled and chemically and biologically triggered release. Stabilization of metal alkoxide sols is usually achieved by modifying the precursors with chelating organic ligands. This chelation increases the reactivity of the alkoxides in hydrolysis/polycondensation, resulting in facile formation of self-assembled micellar aggregates. These structures, micelles templated by self-assembly of ligands (MTSALs), are covered by residual heteroligands. Commonly applied ligands such as b-diketonates and carboxylates are hydrophobic, which helps in the stabilization of the colloids in organic solvents. We have applied a hydrophilic ligand, triethanolamine, which is highly basic and easily charged (protonated) by the addition of strong acids. The proposed stabilization mechanism for micelles is displayed in Figure 1. In our experiments, solutions of titanium alkoxides

Sol–gel routes for microporous zirconia and titania membranes

Abstract: Zirconia and titania nanoparticle sols were prepared, using either ligand-based precursor stabilization or acid stabilization routes. These sols were used to prepare microporous coatings on γ-alumina substrates. The acetylacetonate-based particles have very small hydrodynamic diameters (1–2 nm), which lead to sol intrusion into the supports. As a result no appropriate membrane layer was formed. A microemulsion-based zirconia sol leads to a membrane that was selective in pervaporation dehydration of a water/n-butanol mixture. An optimized membrane showed stable separation performance for 120 days with a high selectivity toward water. Permporometry and gas permeation results on a titania membrane based on an acid-stabilized sol not only show microporosity, but also a significant contribution from defect flow.

Heteroleptic metal alkoxide "oxoclusters" as molecular models for the sol-gel synthesis of perovskite nanoparticles for bio-imaging applications.

Abstract: Systematic structural study of the molecules, resulting from microhydrolysis of heterometallic β-diketonate alkoxides of barium and strontium (single-source precursors of perovskite oxide materials), demonstrates that the structures of these products result from a thermodynamically driven self-assembly of metal cations and ligands directed towards the most densely packed cores. The ratio between metal cations, and of the cations to bidentate heteroligands, is easily changed to enable the highest packing density. The key to the application of single-source precursors appears to be the use of stoichiometric or superstoichiometric water amounts together with solvents preventing diffusion of possible homometallic intermediates. Eu-doped BaTiO3nanoparticles have been successfully obtained and characterized.

Synthesis of highly sterically hindered niobium and tantalum alkoxides and their microhydrolysis in strongly basic medium

Abstract: We have investigated the interaction of niobium and tantalum alkoxides with pinacol and are reporting here isolation and structural characterization of the products, attractive potential precursors of materials with hierarchical porosity. The general feature in the reactivity of alkoxide complexes with additional ligands is that stabilization of the complexes is achieved due to Bronsted acidity of the ligand and possibility of formation of hydrogen bonds in the structure. Presence of strong organic bases does not influence the complex formation. We were able to isolate, for example, highly moisture-sensitive ortho-pinacolates of Nb and Ta, M(O2C6H12)2(OC6H12OH), in the presence of excess of triethylamine. The earlier attempts to prepare these complexes were unsuccessful because of extremely high solubility and easy hydrolysis of these species. The first step in microhydrolysis of M(O2C6H12)2(OC6H12OH), M = Nb, Ta, independently of basicity of the medium provides M2O(O2C6H12)2(OC6H12OH)4, even those highly moisture-sensitive in solution. The general conclusion of this work is that the Lewis acidity and blocking of the coordination sites by bulky alkoxide ligands does not play any important role. The reactivity of the species is not in any way hindered by the complete blocking of the metal centers.

Sol-gel methods for materials processing : focusing on materials for pollution control, water purification, and soil remediation

Abstract: Design of Functionalized Polysiloxane Adsorbents and Their Environmental Applications Y.L. Zub.- Nuclear Magnetic Resonance as Investigation Tool for Pollutant / Sorbent Interactions N. Baccile and F. Babonneau.- Sol-Gel Approaches in the Synthesis of Membrane Materials for Nanofiltration and Pervaporation B.C. Bonekamp et al.- Sol-Gel Synthesis of Nanostructured TiO2 Films for Water Purification YongjunChen, Dionysios D. Dionysiou.- Application of Gel Systems with Various Biocatalysts Detoxifying Neurotoxic Agents for Pollution Control, Water Purification, and Self-defense E. Efremenko et al.- Design of Inorganic and Inorganic-Organic Hybrid Materials by Sol-Gel Processing - from Nanostructures to Hierarchical Networks N. Husing.- Mesoporous Thin Films: Properties and Applications P. Innocenzi et al.- Active sol-gel materials M. Jasiorski et al.- New Insight into Mechanisms of Sol-Gel Process and New Materials and Opportunities for Bioencapsulation and Biodelivery V.G. Kessler, G.A. Seisenbaeva.- Selected Contemporary Topics in Sol-gel Electrochemistry S. Sladkevich et al.- Synthesis of Sol-Gel and Gel-based Materials and Their Use for Adsorption of Organics Short Title: Hybrid Adsorbents from Polysiloxane Xerogels D.J. Macquarrie, W. Hu.- Characterization of Gels and Networks using New Calorimetric Techniques J.-M. Nedelec and M. Baba.- Organic-inorganic Hybrid Nanomaterials with Optical Properties for Use in Medical Applications S. Parola.- Method of Competing Ions for Sol-gel Processing of Sorbents and Catalysts in Aqueous Solutions of Inorganic Salts V. Strelko.- About Interactions between Sol-gel Derived Silica, Titania and Living Organisms R. Viitala and S. Areva.- Mesoporous Silicas: Morphology Control and Template Synthesis inside Large Pores of Silica Gel I.S. Berezovska et al.- Hybrid Siloxane-polyaminoamides for the Absorption of Heparin from Blood D. Cauzzi et al.- Sol-gel Silica Films Doped with Chromium (III)Acetylacetonate on Aluminium Substrate L. Davydenko et al.- Sorption of Hg2 by Mesoporous Silicas with a Functional =Si(CH2)2NHP(S)(OC2H5)2 Group in the Surface Layer O.A. Dudarko et al.- Sol-Gel Process Preparation of Functional Silica Materials and their Application V.E. Gaishun et al.- Sol-gel Derived Films in Porous Anodic Alumina N.V. Gaponenko.- Sol-Gel Synthesis of Mesoporous TiO2 Films for Visible Light Sensitive TiO2/CdS Heterostructures Y. Gnatyuk et al.- Obtaining of the Hybrid Silica-polymer Sorbents for Liquid Chromatography S.S. Hayrapetyan et al.- Bimetallic Co-Based Catalysts Prepared by Sol-Gel for Methane Reforming by Carbon Dioxide S.S. Itkulova et al.- Effect of Sodium Dodecylsulfate and Cetylpyridinium Chloride Act as Templates at Different pH Values on Sorption and Textural Properties of Mesoporous Silicas T.F. Kouznetsova et al.- Factors Influencing the Adsorption Properties of Silicas Functionalized by Macrocycic Ligands O.V. Kuchma and Y.L. Zub.- Sensors with Biorecognition Elements Entrapped into Silica Based Polymers G. Kuncova.- Sol-gel Template-free and Template-structured Silica Films Functionalisation with Methylene Blue Dye and Ag Nanoparticles T. Levchenko, Y. Pluto.- Synthesis, Structure and Adsorption Properties of Hexagonally Ordered Mesoporous Organosilicas Functionalized with Sulfur-Containing Groups Ordered Mesoporous Organosilicas M. Barczak et al.- Sol-Gel Route to Carbon-Silica Molecular Sieving Adsorbents M.S. Mel'gunoV et al.- Study Of Hg2 Sorption from Water Solutions by Mesoporous Silica with Thiourea Functional Groups I.V. Melnyk et al.- Application of Sol-Gel Method for Synthesis of BiosenSitVe Polysiloxafle Matrix R.P. Pogorilyi et al.- EPR Studies of New Silica Synthesis and Hemoglobin Encapsulation F. Sartori et al.- Molecul Precursors of Mixed Oxide Materials for Sensor Applications and Molecular Imaging G.A. Seisenbaeva et al.-

Electrochemical synthesis, structural characterization, and decomposition of rhenium oxoethoxide, Re4O4(OEt)12. Ligand influence on the structure and bonding in the high-valent tetranuclear planar rhenium alkoxide clusters.

Abstract: Anodic oxidation of rhenium in ethanol in the presence of LiCl as a conductive additive results with high yield in formation of a new oxoethoxide cluster, Re(4)O(4)(OEt)(12). The structure of the planar centrosymmetric metal-oxygen core of this molecule is composed of four edge-sharing Re(V)O(6) octahedra. Eight electrons are available for the formation of metal-metal bonds indicated by five relatively short Re-Re distances within the Re 4-rhombus, a "planar butterfly" type cluster. The theoretical calculations are indicating relatively low contribution of metal-metal bonding in the stability of the core. The stability of the +V-oxidation state, unusual for rhenium alkoxides can be at least partially attributed to the size effects in the packing of ligands. The X-ray powder study indicates that treatment of Re(4)O(4)(OEt)(12). in ambient atmosphere rapidly transforms it into a mixed-valence derivative Re(4)O(6)(OEt)(10) with a structure related to the earlier investigated cluster Re(4)O(6)(O(i)Pr)(10). Thermal decomposition of the latter rhenium oxoethoxide results in reduction to rhenium metal at as low temperatures as 380 degrees C, producing aggregates of metal nanoparticles with the average size of 3 nm.

New insight into mechanisms of sol-gel process and new materials and opportunities for bioencapsula- tion and biodelivery

Abstract: The review considers principal mechanisms in solution transformations, hydrolysis and condensation of alkoxysilanes and metal alkoxide complexes and the pathways of further transformations of the thus formed colloid systems. The versatility of silica sol-gel is provided by the possibility to direct the kinetically controlled process towards either polymeric or micellar colloids. The hydrolysis of metal alkoxides is kinetically unhindered and results in formation of Micelles Templated by Self-Assembly of Ligands (MTSALs) under the local equilibrium conditions. The morphology, reactivity, long term stability and biocompatibility of MTSALs can be efficiently controlled by the choice of metal cations, ligands and the conditions of hydrolysis. Application of the MTSAL concept for the synthesis of hierarchically porous materials and the prospects of their use in bioencapsulation and biodelivery for water and soil remediation processes are discussed.

Biocompatible titania hydrosols and hydrogels as novel bio- and drug delivery systems

Abstract: Application of inorganic materials for drug delivery and bioencapsulation has recently attracted strong attention of researchers. Silica-based mesoporous monoliths (Vallet-Regi 2007) and sol-gel derived amorphous silica particles (Barbe 2004) have been actively studied as materials for slow release of adsorbed pharmaceutical agents, while soft silica gels have been demonstrated to act as highly biocompatible matrices for bacterial encapsulation (Nassif 2002, Avnir 2006) Many metal oxides, in particular titanium dioxide, TiO2, are known to be highly biocompatible, at least, in the absence of photochemical oxidation processes(Crawford 2007). Titanium nanotubes have even been investigated as possible a matrix for slow drug release (Ayon 2006). Development of titaniumbased sol-gel materials for bioencapsulation and controlled drug release has so far been hindered by high reactivity of the metal-organic sol-gel precursors, titanium alkoxides, which required application of anhydrous media for preparation of colloid solutions (Livage 2004).

Molecular Precursors of Mixed Oxide Materials for Sensor Applications and Molecular Imaging

Abstract: Cation-doped perovskite materials based on barium titanate, such as (Ba,Sr)(Ti,Nb)O3, are of interest as transparent ceramic semiconductors with conductivity strongly dependent both on the cation and the oxygen stoichiometry. Development of precursor systems offering proper control over the cation stoichiometry and permitting to efficiently avoid residual carbon impurities is therefore an important problem. In the present communication we report the synthesis and structural characterization of a series of hetero-metallic precursors of these materials with the general formulae M2 IITi2(L)4(OR)8(ROH)2 and M2 IIM2 V(L)2(OR)12(ROH)2, where R = Et, nPr; MII = Ba, Sr; MV = Nb, Ta; L = thd or R’OAcAc (R’ = tBu, iPr). The compounds have been characterized by single crystal and power X-ray and by 1H and 13C NMR, vibration spectroscopy and mass-spectrometry. These species are very stable in solution and display even considerable gas phase stability. Solution microhydrolysis of the molecules in these series leads most often to oxo-aggregates with the cation stoichiometry rather close to 1:1, which additionally simplifies handling of solutions based on these precursors. The obtained precursors have been used for preparation of powders and films (on Si substrates), which were characterized by SEM-EDS and X-ray powder techniques.