Moore-Penrose Inverse in Kreĭn Spaces

We discuss the notion of Moore-Penrose inverse in Kreĭn spaces for both bounded and unbounded operators. Conditions for the existence of a Moore-Penrose inverse are given. We then investigate its relation with adjoint operators, and study the involutive Banach algebra . Finally applications to the Schur complement are given.      

Confinement in nanopores at the oxide/water interface: modification of alumina adsorption properties

There is limited knowledge on the influence of the pore size on surface phenomena (adsorption, dissolution, precipitation, etc.) at the oxide/water interface and a better understanding of the space confinement in nanoscale pores should have practical implications in different areas, such as transport of contaminants in the environment or heterogeneous catalyst preparation, to name a few. To investigate the modifications of the oxide adsorption properties at the oxide/water interface in a confined environment, the surface acidobasic and ion adsorption properties of six different aluminas (5 porous commercial aluminas with pore diameters ranging from 25 to 200 A and 1 non-porous alumina) were determined by means of acid-base titration and Ni(II) adsorption. It is shown that the confinement has a moderate impact on the alumina adsorption capacity because all materials have similar surface charging behaviours and ion saturation coverages. However, a confined geometry has a much larger impact on the ion adsorption constants, which decrease drastically when the average pore diameter decreases below 200 A. These results are discussed in terms of nanoscale pore space confinement.     

Development of a new sequential injection in-line cloud point extraction system for flame atomic absorption spectrometric determination of manganese in food samples

A preconcentration method for manganese determination by sequential injection cloud point extraction with subsequent detection by flame atomic absorption spectrometry (FAAS) has been developed. The enrichment of Mn was performed after a preliminary on-line cloud point extraction and entrapment of manganese-containing surfactant aggregated within a minicolumn packed with cotton. The laboratory-made reagent 4-(5′-bromo-2′-thiazolylazo)orcinol (Br-TAO) and the surfactant Triton X-114 were used for cloud point extraction. The manganese ions were eluted with sulphuric acid solution and directly introduced into the FAAS. Chemical and flow variables affecting the preconcentration were studied. Using a sample volume of 2.80 mL the limit of detection and enrichment factor were calculated to be 0.5 μg L⁻¹ and 14, respectively. The sample frequency is 48 h⁻¹, considering a total run cycle of 75 s. The accuracy of the proposed method has been demonstrated by the analysis of the certified reference biological materials rice flour and tomato leaves. The method has been applied to determination of manganese in food samples.     

Extension of the MST continuum solvation model to the RM1 semiempirical Hamiltonian

The need to simulate large-sized molecules or to deal with large series of compounds is a challenging topic in computational chemistry, which has stimulated the development of accurate semiempirical methods, such as the recently reported Recife Model 1 (RM1; J Comput Chem 2006, 27, 1101). Even though RM1 may prove to be of value simply due to the enhanced quantitative accuracy in gas phase, it is unclear how the new parameters optimized for RM1 affect the suitability of this semiempirical Hamiltonian to study chemical processes in condensed phases. To address this question, we report the parametrization of the MST/RM1 continuum model for neutral solutes in water, octanol, chloroform and carbon tetrachloride, and for ions in water. The results are used to discuss the transferability of the solvation parameters implemented in previous MST/AM1 and MST/PM3 models.     

Absolute rate constants for some intermolecular reactions of alpha-aminoalkylperoxyl radicals. Comparison with alkylperoxyls

Seven alpha-aminoalkylperoxyl radicals have been generated by 355 nm laser flash photolysis (LFP) of oxygen-saturated di-tert-butyl peroxide containing mono-, di-, and trialkylamines and a dialkylarylamine. All these peroxyls possess absorptions in the near-UV (strongest for the trialkylamine-derived peroxyls) which permits direct monitoring of the kinetics of their reactions with many substrates. The measured rate constants for hydrogen atom abstraction from some phenols and oxygen atom transfer to triphenylphosphine demonstrated that all seven alpha-aminoalkylperoxyls have similar reactivities toward each specific substrate. More importantly, a comparison with literature data for alkylperoxyls shows that alpha-aminoalkylperoxyls and these alkylperoxyls have essentially the same reactivities. The combination of LFP and alkylamines provides a quick, reliable method for determining absolute rate constants for alkylperoxyl radical reactions, an otherwise laborious task.     

Structure determination of protein-protein complexes using NMR chemical shifts: case of an endonuclease colicin-immunity protein complex

Nuclear magnetic resonance (NMR) spectroscopy provides a range of powerful techniques for determining the structures and the dynamics of proteins. The high-resolution determination of the structures of protein-protein complexes, however, is still a challenging problem for this approach, since it can normally provide only a limited amount of structural information at protein-protein interfaces. We present here the determination using NMR chemical shifts of the structure (PDB code 2K5X) of the cytotoxic endonuclease domain from bacterial toxin colicin (E9) in complex with its cognate immunity protein (Im9). In order to achieve this result, we introduce the CamDock method, which combines a flexible docking procedure with a refinement that exploits the structural information provided by chemical shifts. The results that we report thus indicate that chemical shifts can be used as structural restraints for the determination of the conformations of protein complexes that are difficult to obtain by more standard NMR approaches.     

New thermosets obtained from DGEBA and Meldrum acid with lanthanum and ytterbium triflates as cationic initiators

Ytterbium and lanthanum triflates were used as cationic initiators to cure mixtures of diglycidylether of bisphenol A (DGEBA) and Meldrum acid (MA) in several proportions of comonomers and initiators. The evolution of epoxy and lactone groups during curing, and of linear ester formed in the final materials were evaluated by Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR).

The global evolution of the curing process was investigated by calorimetric analysis and the activation energy was calculated by isoconversional procedures.

Shrinkage on curing and thermal degradability of the final materials on varying the initiator and the proportion of Meldrum acid in the mixtures were evaluated. The expandable character of MA was confirmed. The materials obtained were more degradable than conventional epoxy resins due to the tertiary ester groups incorporated into the network by copolymerization, especially those obtained with ytterbium triflate. On increasing the proportion of initiator the degradability was also increased.     

Evidence for radical fragmentations from persistent singlet carbenes

Upon warm up, persistent aminohydrazinocarbenes undergo beta-fragmentation reactions. Experimental as well as computational evidences are reported for the involvement of radical processes. This is the first example of a homolytic fragmentation for a persistent singlet carbene.