Removal of chromate from water by a new CTAB-silica gelatin composite

A novel composite able to remove hexavalent chromium Cr(VI) from aqueous solutions was obtained by adding the silica precursor tetraethoxysilane (TEOS) to the hexadecyltrimethylammonium bromide (CTAB) microemulsion-based gel. A physical characterization of the new matrix revealed high stability of the silica gelatin composite in water at high temperatures and at neutral pH. Good efficiency in removing chromate from neutral solutions was also demonstrated by the adsorption kinetics. In particular, the adsorption data of chromate obtained with the CTAB-silica gelatin composite at 25 degrees C and pH 7.5 are described by the Freundlich isotherm model. The specific role of CTAB in the silica gelatin composite was also evaluated by comparing the kinetics of the anionic AOT-silica gelatin composite to the CTAB one. The data collected clearly showed that the positively charged surfactant was necessary to efficiently adsorb Cr(VI) from aqueous solutions. SEM and pulsed gradient spin-echo NMR analysis of the composite demonstrated that the silicon is well assembled in the gelatin network, in which water molecules maintain a high mobility. The diffusion coefficient of water in this system was shown to remain close to the value of pure water. Finally, X-ray analyses of the elemental content in the CTAB-silica gelatin composite indicated no difference in terms of percentage of silica distributions in different areas of the matrix and suggested that chromium adsorption could take place in internal areas.     

On relationships between surfactant type and globular proteins interactions in solution

The binding of sodium perfluorooctanoate (C8FONa), sodium octanoate (C8HONa), lithium perfluorooctanoate (C8FOLi), and sodium dodecanoate (C12HONa) onto myoglobin, ovalbumin, and catalase in water has been characterized using electrophoretic mobility. The tendency of the protein-surfactant complexes to change their charge in the order catalase < ovalbumin < myoglobin was observed which was related to the contents of alpha-helices in the proteins. alpha-Helices are more hydrophobic than beta-sheets. The effect of surfactant on the zeta potentials follows C8HONa < C8FONa < C8FOLi < C12HONa for catalase and ovalbumin; and C8HONa < C8FOLi < C8FONa < C12HONa for myoglobin. The numbers of binding sites on the proteins were determined from the observed increases of the zeta-potential as a function of surfactant concentration in the regions where the binding was a consequence of the hydrophobic effect. The Gibbs energies of binding of the surfactants onto the proteins were evaluated. For all systems, Gibbs energies are negative and large at low concentrations (where binding to the high energy sites takes place) and become less negative at higher ones. This fact suggests a saturation process. Changes in Gibbs energies with the different proteins and surfactants under study have been found to follow same sequence than that found for the charge. The role of hydrophobic interactions in these systems has been demonstrated to be the predominant.     

Nucleophilic additions on acetyldioxanes derived from (−)-(1R)-myrtenal used as chiral auxiliaries: substituent effects on the stereochemical outcome

The synthesis of acetyldioxanes 4 and 9a starting from (?)-(1R)-myrtenal is described. The products were treated with a representative series of nucleophilic reagents (RMgX, RLi, NaBH₄ and LiAlH₄) to assess the effect of the substituent at C-3 on the stereochemical outcome. It was observed that the nucleophiles preferred the re-face of the CO group when the equatorial substituent at C-3 was a methyl group, whereas a phenyl group at the same position induced the addition through the si-face, thus allowing access to either desired stereochemistry of a final product. This behavior suggests that the formation of the expected Cram-chelated coordination complex takes a coplanar orientation with the C-3 equatorial substituent. Moreover, Grignard reagents were the most stereoselective nucleophiles. The stereochemistry of the addition was established by X-ray diffraction and chemical correlation.     

New xenicanes from Xenia viridis

The dichloromethane extract of Xenia viridis afforded two new xenicane diterpenoids (3 and 4) by silica gel chromatography. The oxirane ring of 3 was found to be susceptible to a slow ring opening under acidic conditions to afford 5. Their structures were elucidated by extensive 1D and 2D NMR spectroscopy.     

Functionality of photosynthetic reaction centers in polyelectrolyte multilayers: toward an herbicide biosensor

The bacterial reaction center (RC), a membrane photosynthetic protein, has been adsorbed onto a glass surface by alternating deposition with the cationic polymer poly(dimethyldiallylammonium chloride) (PDDA) obtaining as an end result an ordinate polyelectrolyte multilayer (PEM) where the protein retains its integrity and photoactivity over a period of several months. Such a system has been characterized from the functional point of view by checking the protein photoactivity at different hydration conditions, from extensive drought to full hydration. The kinetic analysis of charge recombination indicates that incorporation of RCs into dehydrated PEM hinders the conformational dynamics gating QA- to QB electron-transfer leaving unchanged the protein relaxation that stabilizes the primary charge separated state P+QA-. The herbicide-induced inhibition of the QB activity was studied in some detail. By dipping the PEM in herbicide solutions for short times, kinetics of herbicide binding and release have been determined; binding isotherms have been studied using PEM immersed in herbicide solution. QB functionality of RC has been restored by rinsing the PEM with water, thus allowing the reuse of the same sample. This last point has been exploited to design a simple optical biosensor for herbicides. A suitable kinetic model has been proposed to describe the interplay between forward and back electron-transfer processes upon continuous illumination, and the use of the PDDA-RC multilayers in herbicide bioassays was successfully tested.     

The influence of sodium perfluorooctanoate on the conformational transitions of human immunoglobulin

In the field of bioscience, the study of the interactions between blood proteins and fluorinated materials is very important from both theoretical and applied points of view. Fluorinated materials have potential use in drug delivery, as blood substitutes, and in biotechnology. Using a combination of ultraviolet-visible (UV-vis) and ultraviolet-circular dichroism (UV-CD) spectroscopies and ion-selective electrodes, the complete interaction of sodium perfluorooctanoate (SPFO) and the most important immunoglobulin (on a quantitative basis) in human serum, immunoglobulin G (IgG), has been evaluated. The study has been focused on bulk solution. By the application of an SPFO selective electrode, it was determined that there were true specific unions between surfactant molecules and IgG structure. The experimental data were presented as Koltz and Scatchard plots and analyzed on the basis of an empirical Hill equation. The conformational changes at the bulk solution were well characterized by UV-vis and UV-CD spectroscopies. As a consequence of these changes, the protein structure was affected.     

Structure of SDS micelles with propylene carbonate as cosolvent: a PGSE-NMR and SAXS study

The effect of propylene carbonate on SDS micelles was investigated by means of pulsed gradient spin-echo (PGSE) NMR, small-angle X-ray scattering (SAXS), conductivity and ion-selective electrode (ISE) measurements. The knowledge of the cosolvent partition between continuous phase and micelles (obtained by means of PGSE-NMR) allowed the identification of relevant dilution paths. Along these paths the system is composed of identical micelles that become more and more diluted. The extrapolation of measured self-diffusion coefficient to infinite dilution (where direct and hydrodynamic interactions are negligible) permits the determination of hydrodynamic size of the micelles. Moreover, the micelle ionization degree (measured by means of ISE) combined with PGSE-NMR and conductivity data furnishes an estimate of the aggregation number without any assumptions on micellar shape. On the other hand, troublesome hydrodynamic interactions are irrelevant to SAXS, and scattering data collected at fixed composition can be analyzed according to a reasonable model by exploiting the insight on the propylene carbonate partition gained through PGSE-NMR. By means of these approaches, we have found that propylene carbonate acts mainly as cosurfactant for the SDS micelles, decreasing their size and aggregation number by increasing the mean headgroup area of SDS.     

An immunochemical strategy based on peptidoglycan synthetic peptide epitopes to diagnose Staphylococcus aureus infections

The characteristic pentaglycyl cross-bridge of the Staphylococcus aureus peptidoglycan (PG) cell wall component is an attractive epitope to raise specific antibodies against this microorganism. Based on this approach, we report here for the first time a competitive ELISA able to detect S. aureus down to 10⁴ CFU mL⁻¹, without pre-enrichment on cell culture. The antibodies were raised against peptide-protein bioconjugates prepared by covalently coupling peptide haptens (PSau6 and PSau8) designed and synthesized taking into consideration the complex tridimensional structure in the PG polymer. Deglycosylation of the PG under acidic conditions has found to increase assay detectability. Assay performance has been evaluated in clinical samples such as bronchoalveolar lavage (BAL) and bronchoalveolar endotracheal aspirates (BAS) showing promising results for further implementation of this immunoassay as a daily routine diagnostic tool. Cross-reactivity studies have demonstrated that the immunoassay is specific for S. aureus.     

2H and 139La NMR Spectroscopy in Aqueous Solutions at Geochemical Pressures

Nuclear spin relaxation rates of ²H and ¹³⁹La in LaCl₃+²H₂O and La(ClO₄)₃+²H₂O solutions were determined as a function of pressure in order to demonstrate a new NMR probe designed for solution spectroscopy at geochemical pressures. The ²H longitudinal relaxation rates (T₁) vary linearly to 1.6 GPa, consistent with previous work at lower pressures. The ¹³⁹La T₁ values vary both with solution chemistry and pressure, but converge with pressure, suggesting that the combined effects of increased viscosity and enhanced rates of ligand exchange control relaxation. This simple NMR probe design allows experiments on aqueous solutions to pressures corresponding roughly to those at the base of the Earth’s continental crust.     

Iodine(III)-catalyzed benzylic oxidation by using the (PhIO)n/Al(NO3)3 system

Abstract

The first iodine(III)-based procedure for the benzylic oxidation of different arenes is described by using the (PhIO)_n/Al(NO₃)₃ system under catalytic conditions leading to the formation of the corresponding carbonyl derivatives. The method proceeds under mild, operationally simple, room temperature, short reaction times, and open flask conditions. In light of the organocatalysis relevance and the novelty of our protocol, we wish to communicate our initial results of this novel oxidation.