Correlation between solvation of peptide-resins and solvent properties

The solvation properties of model resin and peptide-resins measured in ca. 30 solvent systems correlated better with the sum of solvent electron acceptor (AN) and electron donor (DN) numbers, in 1:1 proportion, than with other solvent polarity parameters. The high sensitivity of the (AN+DN) term to detect differentiated solvation behaviors of peptide-resins, taken as model of heterogeneous and complex solutes, seems to be in agreement with the previously proposed two-parameter model, where the sum of the Lewis acidity and Lewis basicity characters of solvent are proposed for scaling solvent effect. Besides these physicochemical aspects regarding solute-solvent interactions, important implications of this study for the solid phase peptide synthesis were also observed. Each class of peptide-resin displayed a specific salvation profile that was dependent on the amount and the nature of the resin-bound peptide sequence. Plots of resin swelling versus solvent (AN+DN) values allowed the visualization of a maximum salvation region characteristic for each class of resin. This strategy facilitates the selection of solvent systems for optimal solvation conditions of peptide chains in every step of the entire synthesis cycle. Moreover, only the AN and DN concepts allow the understanding of rules for solvation/shrinking of peptide-resins when in homogeneous or in heterogeneous mixed solvents.

Control of retention and fatigue-free characteristics in CaBi4Ti4O15 thin films prepared by chemical method

Ferroelectric CaBi4Ti4O15 (CBTi144) thin films were deposited on Pt/Ti/SiO2/Si substrates by the polymeric precursor method. The films present a single phase of layered-structured perovskite with polar axis orientation after annealing at 700 degrees C for 2 h in static air and oxygen atmosphere. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. It is noted that the films annealed in static air showed good polarization fatigue characteristics at least up to 10(10) bipolar pulse cycles and excellent retention properties up to 10(4) s. on the other hand, oxygen atmosphere seems to be crucial in the decrease of both, fatigue and retention characteristics of the capacitors. Independently of the applied electric field, the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s. (C) 2006 Elsevier B.V. All rights reserved.

Mechanochemical synthesis of ceramic powders with perovskite structure

The mechanical activation is one of the most effective method for obtaining highly disperse system due to mechanical action stress fields form in solids during milling procedure. This effect results in changes of free energy, leading to release of heat, formation of a new surface, formation of different crystal lattice defects and initiation of solid-state chemical reaction. The accumulated deformation energy determines irreversible changes of crystal structure and consequently microstructure resulting in the change of their properties. Mechanochemical processing route has been developed recently for the production of intermetallic and alloy compounds. The intrinsic advantage of this process is that the solid-state reaction is activated due to mechanical energy instead of the temperature. It was shown that the chemical reactivity of starting materials could be improved significantly after mechanochemical activation and, subsequently, the calcination temperature was reduced. Besides, it was apparent that the mechanochemical treatment could enhance the reactivity of constituent oxides; however, the sintering process could not be avoided to develop the desired ceramics. A novel mechanochemical technique for synthesis of fine-grained perovskite structured powders has shown that it is possible to form perovskite at room temperature. The effect of milling on the formation of perovskite structure of barium titanate (BT), lead titanate (PT), PZT, PZN, magnesium niobate (PMN) and LM ceramic materials was analyzed. The dielectric properties of sintered ceramics are comparable with those prepared by other methods in the literature. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Variable influence of ferric and cupric ions on Saccharomyces cerevisiae strains used in asymmetric organic synthesis.

Fe (III) and Cu (II) each at 50 mu M in four commercial strains of Saccharomyces cerevisiae induced an increase of NAD(P)(+) reduction in one strain (Turkish), but two others (Chilean and Brazilian), the presence of Fe(III) and/or Cu(II) diminished NAD(P)(+) reduction presumably due to free radicals formation inside these living cells. Suprisingly, in the American strain, Fe(III) induced a decrease and Cu (II) an increase of NAD(P)(+) reduction.

Thermogravimetric investigations during the synthesis of silica-based MCM-41

MCM-41 material was synthesized starting from hydrogel containing colloidal fumed silica, sodium silicate, cetyltetramethylammonium bromide (CTMABr) as surfactant, and distilled water as solvent. These reactants were mixed to obtain a gel with the following composition: 4SiO(2):1Na(2)O:1CTMABr:200H(2)O. The hydrogel with pH=14 was hydrothermally treated at 100 degreesC, for 4 days. Each day, the pH was measured, and then adjusted to 9.5-10 by using 30% acetic acid solution. Thermogravimetry was the main technique, which was used to monitor the participation of the surfactant on the MCM-41 nanophase, being possible to determine the temperature ranges relative to water desorption as well as the surfactant decomposition and silanol condensation.

Synthesis of hybrid silicates containing porphyrins incorporated by a sol-gel process and their properties

Porphyrin was incorporated in a silicate network, via a covalent bond, by grafting a functional group with 3-aminopropyltriethoxysilane, using a sol-gel process. We have carried out the synthesis and measured the absorption spectra, nuclear magnetic resonance spectra, infrared (IR) spectra, luminescence spectra and lifetime of these hybrid silicates, porphyrinosilicas. These samples contained the following free-base porphyrins: meso-tetrakis-p-chlorobenzoylporphyrin, meso-tetrakis-2,6-dichloro-3-chlorosulfonylphenylporphyrin. The obtained porphyrinosilicas have similar absorption and luminescence spectra to the free base porphyrins in solution. IR spectra confirm the formation of monomeric species. Lifetime measurement for porphyrinosilica reveals that 32% +/- 2% of porphyrin is covalently bonded to the silica network. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Synthesis and luminescence properties of water dispersible Eu3+-doped boehmite nanoparticles

Nanocrystallized boehmite gamma-AlOOH center dot nH(2)O had been synthesized by spray-drying (SD) of a solution of aluminium tri-sec-butoxide peptized by nitric acid. The sub-micronic spherical particles obtained had an average diameter of 500 nm and were built of 100 nm or less platelet-like sub-particles. The average crystallite size calculated from XRD was 1.6 nm following the b axis (i.e. one unit cell) and 3-4 nm perpendicular to b. As a result of the nanometric sizes of crystallites, there was a large surface free for water adsorption and it was found to be n = 1.18 +/- 0.24H(2)O per AlOOH. The SD spheres spontaneously dispersed in water at room temperature and formed stable-over months-suspensions with nanometre-size particles (25-85 nm). Luminescent europium-doped nanocrystallized boehmites AlOOH: Eu (Al0.98Eu0.02OOH center dot nH(2)O) were synthesized the same way by SD and demonstrated the same crystallization properties and morphologies as the undoped powders. It is inferred from the Eu3+ luminescence spectroscopy that partly hydrated europium species are immobilized on the boehmite nanocrystals where they are directly bonded to alpha(OH) groups of the AlOOH surface. The europium coordination is schematically written [Eu3+(OH)(alpha)(H2O)(7-alpha/2)]. The europium-doped boehmite from SD spontaneously dispersed in water: the luminescence spectroscopy proves that most of the Eu3+ ions were detached from the NPs during water dispersion. The AlOOH: Eu nanoparticles were modified by the amine acid asparagine (ASN). The modification aimed to render the NPs compatible for further bio-functionalization. After surface modification, the NPs easily dispersed in water; the luminescence spectra after dispersion prove that the Eu3+ ions were held at the boehmite surface.

Use of commercial anion-exchange resins as solid support for peptide synthesis and affinity chromatography

This report demonstrates that due to the presence of residual reactive sites in their matrices, classical diethylaminoethyl-attaching commercial anion-exchanger resins such as DEAE-MacroPrep and DEAE-Sephadex A50 supports can be used for peptide synthesis. Moreover, due to the high stability of the peptide-resin bond in the final cleavage treatments, desired peptidyl-resins free of side-chain protecting groups, which enables them to be further used as solid support for affinity chromatography, can be obtained. To demonstrate this potentiality, a fragment corresponding to the antigenic and immunodominant epitope of sporozoites of the Plasmodium falciparum malaria parasite was synthesized in these traditional resins and antibody molecules generated against the peptide sequence were successfully retained in these peptidyl supports. Due to the maintenance of their original anion-exchange capacities, the present findings open the unique possibility of applying, simultaneously, dual anion-exchange and affinity procedures for purification of a variety of macromolecules. (C) 2003 Elsevier B.V. (USA). All rights reserved.

Wet-chemical synthesis of magnesium niobate nanoparticles powders

Nanosized and highly reactive magnesium mobate (MgNb2O6) powders were successfully synthesized by a new wet-chemical method by means of the dissolution of Nb2O5 center dot 5H(2)O and in a solution of oxalic acid followed by the addition of stoichiometric amounts of magnesium carbonate. The Nb-Mg-oxalic acid solution was evaporated resulting in a dry and amorphous powder that was calcined in the temperature range from 200 to 900 degrees C for 2 h. The crystallization process from the amorphous state to the crystalline MgNb2O6 was followed by thermal analysis. The calcined powders characterized by FT-Raman spectroscopy, X-ray diffraction (XRD) and their morphology examined by high resolution scanning electron microscopy (HR-SEM). Pure MgNb2O6, free from the second phases and obtained at 800 degrees C was confirmed by a combined analysis using XRD and FT-Raman. The average diameter of the particles was calculated from the HR-SEM image as 70 urn approximately. This technique allows a better mixing of the constituent elements and thus a better reactivity of the mixture to obtain pre-reaction products with high purity at lower temperatures and reducing cost. It can offer a great advantage in the PMN-PT formation with respect to the solid-state synthesis. (c) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Study of the effect of the peptide loading and solvent system in SPPS by HRMAS-NMR

The SPPS methodology has continuously been investigated as a valuable model to monitor the solvation properties of polymeric materials. In this connection, the present work applied HRMAS-NMR spectroscopy to examine the dynamics of an aggregating peptide sequence attached to a resin core with varying peptide loading (up to 80%) and solvent system. Low and high substituted BHAR were used for assembling the VQAAIDYING sequence and some of its minor fragments. The HRMAS-NMR results were in agreement with the swelling of each resin, i.e. there was an improved resolution of resonance peaks in the better solvated conditions. Moreover, the peptide loading and the attached peptide sequence also affected the spectra. Strong peptide chain aggregation was observed mainly in highly peptide loaded resins when solvated in CDCl3. Conversely, due to the better swelling of these highly loaded resins in DMSO, improved NMR spectra were acquired in this polar aprotic solvent, thus enabling the detection of relevant sequence-dependent conformational alterations. The more prominent aggregation was displayed by the VQAAIDYING segment and not by any of its intermediary fragments and these findings were also corroborated by EPR studies of these peptide-resins labelled properly with an amino acid-type spin probe. Copyright (c) 2005 European Peptide Society and John Wiley & Sons, Ltd.

Properties and one-step synthesis of (2-acetylpyridine)tetraammineruthenium(II), [Ru-II(2-acpy)(NH3)(4)](2+) and tetraammine(2-benzoylpyridine)ruthenium(II), [Ru-II(NH3)(4)(2-bzpy)](2+) Redox potentials, UV-Vis and NMR spectra

A more direct and efficient route to the syntheses of [Ru(NH3)(4)(X-Y)](BF4)(2), where X-Y can be 2-acetylpyridine (2-acpy) or 2-benzoylpyridine (2-bzpy), based on the reactions of [RuCl(NH3)(5)]Cl-2 with these ortho-substituted azines is described. The [Ru(2-acpy)(NH3)(4)](BF4)(2) and [Ru(NH3)(5)(2-bzpy)](BF4)(2) complexes have a molar conductance of 328 and 292 Ohm(-1) cm(2) mol(-1), respectively, corresponding to a 1:2 species in solution. These complexes showed two intense absorption bands around 620-650 and 380 nm, the energies of which are solvent dependent, decreasing with the increase of the Gutman's donor number of the solvent, and were assigned as metal-to-ligand charge transfer (MLCT). The complexes have oxidation potentials (Ru-II/III) of +0.380 V vs. Ag/AgCl (2-acpy) and +0.400 V vs. Ag/AgCl (2-bzpy), and reduction potentials (X-Y0/-) of -1.10 V vs. Ag/AgCl (2-acpy) and -0.950 V vs. Ag/AgCl (2-bzpy) on CF3COOH/NaCF3COO at pH=3.0, scan rate 100 mV s(-1), [Ru]=1.0x10(-3) mol l(-1). Both processes show a coupled chemical reaction. Upon oxidation of the metal center, the MLCT absorption bands are bleached and restored upon subsequent reduction. In order to confirm the structure of the complexes a detailed LH NMR investigation was performed in d(6)-acetone. Further confirmation of the structure was obtained by recording the N-15 NMR spectrum of [Ru(NH3)(4)(2-bzpy)](2+) in d(6)-DMSO using the INEPT pulse sequence improving the sensitivity of N-15 by polarization transfer from the protons to the N-15. The Nuclear Overhauser Effect (NOE) experiments were made qualitatively for [Ru(NH3)(4)(2-acpy)](2+), and showed that H-6 of the pyridine is close to a NH3 proton, which should then be in a cis position, and, hence, confirming that acpy is acting as a bidentate ligand. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

Low temperature synthesis and electrical properties of PbTiO3 thin films prepared by the polymeric precursor method

Ferroelectric PbTiO3 thin films were successfully prepared on a Pt(111)Ti/SiO2/Si(100) substrate for the first time by spin coating, using the polymeric precursor method. X-ray diffraction patterns of the films indicate that they are polycrystalline in nature. This method allows low temperature (500 degrees C) synthesis and high electrical properties. The multilayer PbTiO3 thin films were granular in structure with a grain size of approximately 110-120 nm. A 380-nm-thick film was obtained by carrying out four cycles of the spin-coating/heating process. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness (=3.4 nm). At room temperature and at a frequency of 100 kHz, the dielectric constant and the dissipation factor were, respectively, 570 and 0.016. The C-V characteristics of perovskite thin film prepared at low temperature show normal ferrolectric behavior. The remanent polarization and coercive field for the films deposited were 13.62 mu C/cm(2) and 121.43 kV/cm, respectively. The high electrical property values are attributed to the excellent microstrutural quality and chemical homogeneity of thin films obtained by the polymeric precursor method. (C) 2000 Elsevier B.V. S.A. All rights reserved.

Synthesis, crystal structure, spectroscopic and electrochemical characterization of the dinuclear complex {tetra-mu-[(+/-)-2-(p-methoxyphenoxy)-propionato-O,O']bis(aqua)dicopper(II)}

Structural, electrochemical and spectroscopic data of a new dinuclear copper(II) complex with (+/-)-2-(p- methoxyphenoxy) propionic acid are reported. The complex {tetra-mu-[(+/-)-2-(p-methoxyphenoxy)propionato-O,O']-bis( aqua) dicopper(II)} crystallizes in the monoclinic system, space group P2(1)/n with a = 14.149(1) angstrom, b = 7.495(1) angstrom, c = 19.827(1) angstrom, beta = 90.62(1) and Z = 4. X-ray diffraction data show that the two copper(II) ions are held together through four carboxylate bridges, coordinated as equatorial ligands in square pyramidal geometry. The coordination sphere around each copper ion is completed by two water molecules as axial ligands. Thermogravimetric data are consistent with such results. The ligand has an L' type shape due to the angle formed by the beta-carbon of the propionic chain and the linked p-methoxyphenoxy group. This conformation contributes to the occurrence of a peculiar structure of the complex. The complex retains its dinuclear nature when dissolved in acetonitrile, but it decomposes into the corresponding mononuclear species if dissolved in ethanol, according to the EPR measurements. Further, cyclic voltammograms of the complex in acetonitrile show that the dinuclear species maintains the same structure, in agreement with the EPR data in this solvent. The voltammogram shows two irreversible reduction waves at E-pc = -0.73 and -1.04 V vs. Ag/AgCl assigned to the Cu(II)/ Cu(I) and Cu(I)/Cu degrees redox couples, respectively, and two successive oxidation waves at E-pa = -0.01 and +1.41 V vs. Ag/AgCl, assigned to the Cu degrees/Cu(I) and Cu( I)/Cu( II) redox couples, respectively, in addition to the oxidation waves of the carboxylate ligand.

Highly swollen liquid crystals as new reactors for the synthesis of nanomaterials

Synthesis and self-assembly of nanomaterials can be controlled by the properties of soft matter. on one hand, dedicated nanoreactors such as reverse microemulsions or miniemulsions can be designed. on the other hand, direct shape control can be provided by the topology of liquid crystals that confine the reacting medium within a specific geometry. In the first case, the preparation of micro- or miniemulsions generally requires energetic mechanical stirring. The second approach uses thermodynamically stable systems, but it remains usually limited to binary (water + surfactant) systems. We report the preparation of different families of materials in highly ordered quaternary mediums that exhibit a liquid crystal structure with a high cell parameter. They were prepared with the proper ratios of salted water, nonpolar solvent, surfactant. and cosurfactants that form spontaneously swollen hexagonal phases. These swollen liquid crystals can be prepared from all classes of surfactants (cationic, anionic, and nonionic). They contain a regular network of parallel cylinders, whose diameters can be swollen with a nonpolar solvent, that are regularly spaced in a continuous aqueous salt solution. We demonstrate in the present report that both aqueous and organic phases can be used as nanoreactors for the preparation of materials. This property is illustrated by various examples such as the synthesis of platinum nanorods prepared in the aqueous phase or zirconia needles or the photo- or gamma-ray-induced polymerization of polydiacetylene in the organic phase. In all cases, materials can be easily extracted and their final shapes are directed by the structure-directing effect imposed by the liquid crystal.

Direct electron paramagnetic resonance monitoring of the peptide synthesis coupling reaction in polymeric support

This work demonstrates, for the first time. a time-resolved electron paramagnetic resonance (EPR) monitoring of a chemical reaction occurring in a polymeric structure. The progress of the coupling of a N-alpha-tert-butyloxycarbonyl-2.2.6.6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (Boc-TOAC) spin probe to a model peptide-resin was followed through EPR spectra. Progressive line broadening of EPR peaks was observed, indicative of an increased population of immobilized spin probe molecules attached to the solid support. The time for spectral stabilization of this process coincided with that determined in a previous Coupling study. thereby validating this in situ quantitative monitoring of the reaction. In addition, the influence of polymer swelling degree and solvent viscosity, as well as of the steric hindrance within beads. on the rate of coupling reaction was also addressed. A deeper evaluation of the latter effect was possible by determining unusual polymer parameters such as the average site-site distance and site-concentration within resin beads in each solvent system. (c) 2006 Elsevier Ltd. All rights reserved.