Effect of variations in annealing temperature and metallic cations on nanostructured molybdate thin films

Crystalline molybdate thin films were prepared by the complex polymerization method. The AMoO(4) (A = Ca, Sr, Ba) films were deposited onto Si wafers by the spinning technique. The Mo-O bond in the AMoO(4) structure was confirmed by FTIR spectra. X-ray diffraction revealed the presence of crystalline scheelite-type phase. The mass, size, and basicity of A(2+) cations was found to be dependent on the intrinsic characteristics of the materials. The grain size increased in the following order: CaMoO4 < SrMoO4 < BaMoO4. The emission band wavelength was detected at around 576 nm. Our findings suggest that the material's morphology and photoluminescence were both affected by the variations in cations (Ca, Sr, or Ba) and in the thermal treatment.

Basicities of primary arylamines and calculated amine nitrogen electronic charges

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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.

Preparation, characterization and electrochemical studies of dinuclear copper(II) complexes with pseudohalides and bidentate amines on platinum electrode in acetonitrile

The complexes: [Cu(N 3) 2(N,N-diEten)] 2, [Cu(N 3) 2(tmeen)] 2, [Cu(N 3)(NCO)(N,N-diEten)] 2, [Cu(N 3) 2(N,N′-diMeen)] 2 and [Cu(N 3)(NCO)(tmeen)] 2 were prepared, characterized and their electrochemical behavior was investigated by cyclic voltammetry and controlled potential electrolysis. Cyclic voltammograms for all complexes studied are similar and exhibit one pair of current peaks in the range of -0.65 to +0.0 V. The number of electrons obtained from controlled potential electrolysis at ca. -0.55 V for all compounds was 1.8 ≤ n ≤ 2.1, indicating that both copper(II) metallic centres in the molecule were reduced to copper (I). Comparing the peak potential values for these complexes one can observe that the redox process corresponding to copper(II)/copper(I) couple is slightly influenced by the σ-basicity of the ligands. © 1997 Soc. Bras. Química.

Sodium titanate as basic catalyst in transesterification reactions

Sodium titanate was synthesized by the sol-gel method and characterized using X-ray diffraction, thermogravimetry-mass spectrometry, atomic absorption spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis and nitrogen physisorption. The non-calcined material was active as a catalyst in transesterification reactions and showed high stability. An appreciable loss of activity on the fourth reuse was accompanied by the appearance of a new species of oxygen and segregated sodium, identified by X-ray photoelectron spectroscopy (XPS). The XPS spectrum showed that the basic nature of the framework oxygen was inferior to the original basicity, which explained the decline in catalytic activity. (C) 2013 Elsevier Ltd. All rights reserved.

Preparação e propriedades de zeólitas faujasita contendo cátions amônio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Descontaminação do resíduo industrial de couro, uma proposta para o desenvolvimento sustentável nos curtumes

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Degradação química e fotoquímica do organofosforado paraoxona

Pós-graduação em Química - IBILCE

Óxidos derivados de hidromagnesitas e hidrotalcitas modificadas como catalisadores heterogêneos na síntese de biodiesel etílico

Pós-graduação em Química - IBILCE

Gas-phase reactivity of protonated 2-oxazoline derivatives: mass spectrometry and computational studies

RATIONALE: Oxazolines have attracted the attention of researchers worldwide due to their versatility as carboxylic acid protecting groups, chiral auxiliaries, and ligands for asymmetric catalysis. Electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis of five 2-oxazoline derivatives has been conducted, in order to understand the influence of the side chain on the gas-phase dissociation of these protonated compounds under collision-induced dissociation (CID) conditions. METHODS: Mass spectrometric analyses were conducted in a quadrupole time-of-flight (Q-TOF) spectrometer fitted with electrospray ionization source. Protonation sites have been proposed on the basis of the gas-phase basicity, proton affinity, atomic charges, and a molecular electrostatic potential map obtained on the basis of the quantum chemistry calculations at the B3LYP/6-31 + G(d, p) and G2(MP2) levels. RESULTS: Analysis of the atomic charges, gas-phase basicity and proton affinities values indicates that the nitrogen atom is a possible proton acceptor site. On the basis of these results, two main fragmentation processes have been suggested: one taking place via neutral elimination of the oxazoline moiety (99 u) and another occurring by sequential elimination of neutral fragments with 72 u and 27 u. These processes should lead to formation of R+. CONCLUSIONS: The ESI-MS/MS experiments have shown that the side chain could affect the dissociation mechanism of protonated 2-oxazoline derivatives. For the compound that exhibits a hydroxyl at the lateral chain, water loss has been suggested to happen through an E2-type elimination, in an exothermic step. Copyright (C) 2012 John Wiley & Sons, Ltd.

Employing perichromism for probing the properties of carboxymethyl cellulose films: an expedient, accurate method for the determination of the degree of substitution of the biopolymer derivative

The properties of films of carboxymethyl cellulose, CMC, of different degree of substitution, DS, have been examined by the use of perichromic indicators (probes). The film properties that have been determined are: empirical polarity, E-T(33); "acidity", alpha; "basicity", beta; and dipolarity/polarizability, pi*. This has been achieved by employing the following perichromic probes: 4-nitroaniline, 4-nitroanisole, 4-nitro-N,N-dimethylaniline, and 2,6-dichloro-4-(2,4,6-triphenyl-pyridinium-1-yl)phenolate, WB. The correlations between both E-T(33)- or pi* and DS were found to be linear; that between beta and DS is a second order polynomial; no obvious correlation was found between alpha and DS. The polarities of CMC films are in the range of those of butyl alcohols. As models for CMC, we have employed cellulose plus CMC of high DS; oxidized cellulose with degree of oxidation = 0.5; sodium glucuronate. The former model behaved akin to CMC, but the plots of the perichromic properties versus DS showed different slopes/intercepts. FTIR data and molecular dynamics simulations on the solvation of WB have shown that this difference can be traced to more efficient hydrogen bonding between the film of the model and the probe. This affects the intra-molecular charge-transfer energy of the latter, leading to different responses to the variation of DS. Based on the excellent linear correlation between E-T(33) and DS, for CMC from different origins, we suggest that perichromism is a simple, accurate, and expedient alternative for the determination of DS of the biopolymer derivative.

Gas-phase reactivity of 2-hydroxy-1,4-naphthoquinones: a computational and mass spectrometry study of lapachol congeners

In order to understand the influence of alkyl side chains on the gas-phase reactivity of 1,4-naphthoquinone derivatives, some 2-hydroxy-1,4-naphthoquinone derivatives have been prepared and studied by electrospray ionization tandem mass spectrometry in combination with computational quantum chemistry calculations. Protonation and deprotonation sites were suggested on the basis of gas-phase basicity, proton affinity, gas-phase acidity (?Gacid), atomic charges and frontier orbital analyses. The nature of the intramolecular interaction as well as of the hydrogen bond in the systems was investigated by the atoms-in-molecules theory and the natural bond orbital analysis. The results were compared with data published for lapachol (2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone). For the protonated molecules, water elimination was verified to occur at lower proportion when compared with side chain elimination, as evidenced in earlier studies on lapachol. The side chain at position C(3) was found to play important roles in the fragmentation mechanisms of these compounds. Copyright (c) 2012 John Wiley & Sons, Ltd.

Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry

Travelling wave ion mobility mass spectrometry (TWIM-MS) with post-TWIM and pre-TWIM collision-induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM-MS. CID performed after TWIM separation (post-TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N-protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH3, whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co-existing protomers of two isomeric porphyrins were also separated and characterized via post-TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO2 loss, but a CID-resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups. Copyright (C) 2012 John Wiley & Sons, Ltd.

Double-stimulus sensitive (temperature and pH) self-assemblable polymers

The rheological properties of block co-polymers in water solution at different pH have been investigated. The block copolymers are based on different architectures containing poly(ethylene glycol), poly(propylene glycol) and different blocks of polymer that change their hydrophobic/hydrophilic behavior as a function of pH. The polymer chains of the starting material were extended at their functional ends with the pH-sensitive units using ATRP; this mechanism of controlled radical polymerization was chosen because of the need to minimize polydispersity and avoid transfer reactions possibly leading to homopolymeric inpurities. The starting material were modified in order to use them as macroinitiator for ATRP. The kinetic of each ATRP reaction has been investigated, in order to be able to synthesize polymers with different degree of polymerization, stopping the reaction when the desired polymers chain length has been reached. We will use polymer chains with different basicity and degree of polymerization to link any possible effect of their presence to the conditions under which they become hydrophobic. It has been shown that the rate of polymerization changes changing the type of macroinitiator and the type of monomer synthesized. The slowest rate of polymerization is the one with the most hindered monomer synthesized using the macroinitiator with the highest molecular weight. The water solubility of the synthesized polymers changes depending on the pH of the solution and on the structure of the polymers. It has been shown using 1H-NMR that some of the synthesized polymers are capable to self-aggregation in water solution. The self-aggregation and the type of aggregation is influenced from the structure of the polymer and from the pH of the solution. Changing the structure of the polymers and the pH it is possible to obtain different type of aggregates in solution. This aggregates differ for the volume occupied from them, and for their hardness. Rheological measurements have been demonstrated that the synthesized polymers are capable to form gel phases. The gelation temperature changes changing the structure of the aggregates in solution and it is possible to correlate the changing in the gelation temperature with the changing in the structure of the polymer.

Reaktionen monovalenter Münzmetalle in flüssigem Ammoniak

Im Rahmen dieser Arbeit konnten erstmals eine Reihe von Ammoniakaten von Münzmetallhalogeniden (M(I)Hal) und Pseudohalogeniden aus flüssigem Ammoniak in einkristalliner Form isoliert und strukturell charakterisiert werden. Mit dem Ammoniakat des Gold(I)-iodids wurden Metathesen in flüssigem Ammoniak durchgeführt, die die Isolierung einiger sehr thermolabiler, teilweise explosiver Alkoholate des Golds ermöglichten. Die Bestimmung der Kristallstruktur eines Gold(I)-phenolates erlaubte erste Einblicke in deren Aufbau.rnIn der Reihe der Ammoniakate der M(I)Hal mit Ausnahme von Silberiodid, werden keine direkten Metall-Halogen-Kontakte ausgebildet. Die Ammoniakate der Chloride und Bromide des Kupfers und Silbers sowie des Kupferiodids besitzen isotype Strukturen. Sie liegen als Trisammoniakate [M(NH3)3]Hal vor. Im Ammoniakat von Silberiodid besitzen die Silberionen durchgängig die Koordinationszahl 4. Neben Ag•••NH3- findet man auch direkte Kationen-rnAnionen-Kontakte und sehr kurze Ag(I)-Ag(I)-Abstände. Das Goldkation im Ammoniakat von Goldiodid besitzt die Koordinationszahl 2 und wird ausschließlich durch Ammoniakmoleküle koordiniert. Die gebildeten H3N-NH3-Hanteln werden über aurophile Wechselwirkungen verknüpft.rn rnDie Ammoniakate der Cyanide von Silber und Gold, enthalten molekulare Baueinheiten des Typs:(H3N)nMCN [(n= 1 für M= Au und n= 2 für M= Ag].rnrnAnders als bei den solvatfreien Homologen wird eine Ausbildung von Polymerketten nicht beobachtet. Das linear aufgebaute Ammoniakat von Goldcyanid ermöglicht die Ausbildung von aurophilen Wechselwirkungen. Metallophile Wechselwirkungen zwischen dem als Dimer vorliegenden Ammoniakat von AgCN scheinen nicht ausgebildet zu werden.rnrnMetatheseversuche von Goldiodid mit einem Amid und diversen Alkanolaten lieferten teilweise explosive Produkte. Es ist davon auszugehen, dass mit zunehmender Basizität der eingesetzten Anionen, die an das Gold(I)-ion koordinierten Ammoniakmoleküle deprotoniert werden und explosives Goldamid gebildet wird. Der als zweites Produkt entstehende Alkohol kann ebenfalls ein Ammoniakat bilden. Im Fall von Li-Fencholat wird ein solches in Form sehr tiefschmelzender Einkristalle erhalten.rnrnDa die Deprotonierung der an Gold koordinierten Ammoniakmoleküle unweigerlich zu explosiven oder sehr instabilen Produkten führt, wurde die geringere Basizität der Phenolate ausgenutzt, um dies zu umgehen. Im Falle der Umsetzung von AuI mit Li-2,6-di-tert.-butylphenolat gelang tatsächlich die Isolierung eines kristallinen Gold(I)-phenolats.rn