Luis E. Diaz

A simple approach for relating molecular and structural information to the dipolar coupling 13C14N in CPMAS NMR

Abstract High-resolution solid-state 13 C NMR spectra of 13 C adjacent to 14 N show a characteristic deformation observed mostly as asymmetric doublets, due to the dipolar coupling between 14 N and 13 C not suppressed by magic-angle spinning. A simple theoretical approach allows one to derive an analytical equation which relates the observed splittings with (a) the 14 N quadrupole coupling tensor, (b) the intenuclear distance, (c) the applied magnetic field, and (d) the orientation of the internuclear vector in the principal axis system of the electric field gradient. The analytical treatment is completely general and the results obtained are in good agreement with solid-state 13 C NMR data taken from the literature.

Removal of dyes from water using chitosan hydrogel/SiO2 and chitin hydrogel/SiO2 hybrid materials obtained by the sol-gel method

This work describes the synthesis of chitosan hydrogel/SiO(2) and chitin hydrogel/SiO(2) hybrid mesoporous materials obtained by the sol-gel method for their use as biosorbents. Their adsorption capabilities against four dyes (Remazol Black B, Erythrosine B, Neutral Red and Gentian Violet) were compared in order to evaluate chitin as a plausible replacement for chitosan considering its efficiency and lower cost. Both chitin and chitosan were used in the form of hydrogels. This allowed full compatibility with the ethanol release from tetraethoxysilane. The hybrid materials were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Nitrogen Adsorption Isotherms and (13)C solid-state Nuclear Magnetic Resonance. Adsorption experimental data were analyzed using Langmuir, Freundlich and Dubinin-Radushkevich isotherm models along with the evaluation of adsorption energy and standard free energy (ΔG(0)). The adsorption was observed to be pH dependent. The main mechanism of dye adsorption was found to be a spontaneous charge associated interaction, except for EB adsorption on chitin/SiO(2) matrix, which showed to involve a lower energy physical adsorption interaction. Aside from highly charged dyes the chitin containing matrix has similar or higher adsorption capacity than the chitosan one.

Immobilized chitosan as biosorbent for the removal of Cd(II), Cr(III) and Cr(VI) from aqueous solutions

The generation of layer-by-layer silicate-chitosan composite biosorbent was studied. The films were evaluated on its stability regarding the polymer leakage and its capability in the removal of Cd(II), Cr(III) and Cr(VI) from an aqueous solution. SEM, EDAX and ATR-IR techniques were applied for material characterization. Silicate-chitosan films with a final layer of silicate demonstrated chitosan retention and had better sorption capacities than those without it. For metal species, such as Cd(II) and Cr(III), the greatest adsorption was obtained when the pH of the solution was 7. When Cr(VI) was evaluated, pH 4 was the optimal for its adsorption. Langmuir and Freundlich isotherms were modeled for the equilibrium data. An 80% of the adsorbed metal was recovered by HNO(3) incubation. This non-covalent immobilization method allowed chitosan surface retention and did not affect its adsorption properties. The use of a coated surface would facilitate sorbent removal from medium after adsorption.

Ethanol tolerance in free and sol-gel immobilised Saccharomyces cerevisiae

The tolerance of sol-gel immobilised and free Saccharomyces cerevisiae to ethanol was studied. The effects of ethanol preincubation time showed that the specific death velocity decreased from 2×105 c.f.u. min−1 for free cells to 2×104 c.f.u. min−1 for immobilised cells thus indicating that immobilised yeast was far less sensitive to the ethanol damage. The specific glucose consumption of immobilised and free cells on a per cell basis was 3×10−12 g cell−1 h−1 and 9×10−12 g cell−1 h−1, respectively.

Adsorption of Cd(II) and Pb(II) onto a one step-synthesized polyampholyte: kinetics and equilibrium studies.

A one step-synthesized polyampholyte, bearing carboxylate and 2-methylimidazole (2MI) groups, was tested as adsorbent for the removal of Pb(II) and Cd(II) from aqueous solutions. This material combines the benefits of synthetic polymers, such as high adsorption capacity and chemical stability, and the advantages of biosorbents in regard of costs and simplicity of the production. The short time needed to achieve the adsorption equilibrium indicated a chemical-reaction controlled process. A network expansion was predicted as a result of repulsive interaction between the fixed positive charges. Langmuir model presented the best fitting to isotherm equilibrium data, with a maximum adsorption capacity of 182 mg g(-1) for Cd(II) and 202 mg g(-1) for Pb(II). The metal removal was strongly dependent on pH, involving carboxylate and 2MI residues. An ion-exchange process for Pb(II) and Cd(II), combined with coordination for the later, were the most probable mechanism of interaction. The adsorption of 1.35 ppm Cd(II) was 72±6% in well-water, and the adsorption of 0.50 ppm Pb(II) was 62±5% in tap-water. The recovery figures for Cd(II) in 1% HNO(3) were optimal.

A functional material that combines the Cr(VI) reduction activity of Burkholderia sp. with the adsorbent capacity of sol–gel materials

In the present work, Cr(VI) reduction in aqueous as well as in soil environments has been studied using free and sol–gel immobilized Burkholderia sp. Enhanced reduction rates were achieved by immobilized cells, which are found to be protected from the deleterious effects of high Cr(VI) concentrations. Immobilized bacteria showed enhanced performance in comparison with free cells because of the combination of bacteria biotransformation effect and chromium adsorption on silica matrices. Moreover, bacteria did not lose any activity after four cycles of reutilization. Bacteria immobilized in silica matrices had the ability to completely reduce 100 µg ml−1Cr(VI) after 4 days of incubation in aqueous media and to transform 200 µg ml−1Cr(VI) after 7 days in sterile soil. Immobilized bacteria demonstrated highly efficient Cr(VI) reduction over the Cr(VI) concentration range 50–500 µg g−1 and 200–800 µg g−1 in aqueous and soil environments, respectively. These results highlight the potential of this functional material that combines the biological activity of bacterial cells with the adsorbent capacity of sol–gel materials.

Development of Sol-Gel Hybrid Materials for Whole Cell Immobilization

The development of a good biocompatible matrix for immobilization of cells is very crucial for improving the performance of functional biohybrids. The synthesis of solid inorganic materials from alkoxide, aqueous and polyol-modified silanes routes, as well as the incorporation of organic polymers, are further areas being developed to improve the viability of encapsulated cells. This emerging field of material science has generated considerable and increasing interest during the past decade. Recent advances in the field involving biomaterials, biohybrids, and functional nanomaterials provided novel materials, which have gained the attention of the scientific community, Governments and industrial companies. Overall, this review is intended to give an overview on the current state of the art of the patents associated to the immobilization of whole living cells in sol-gel derived hybrid materials and to describe the major challenges to be addressed in the forthcoming years.

Recent patents on the synthesis and application of silica nanoparticles for drug delivery.

Drug delivery systems are designed to improve therapy efficacy as well as patient compliance. This could be accomplished by specifically targeting a medication intact to its active site, therefore reducing side-effects and enabling high local drug concentrations. Silica nanoparticles have gained ground in the biomedical field for their biocompatibility and biodegradability, being themselves inert and stable, thus enabling a variety of formulation designs for application in the pharmaceutical industry. This paper is a review of the recent patents on the applications of silica nanoparticles for drug delivery and their preparation. The review will focus on the different techniques available to obtain silica nanoparticles with variable morphology and their drug targeting applications, providing an overview of silica particles synthesis described in the literature.

Polyphenol–SiO2 hybrid biosorbent for heavy metal removal. Yerba mate waste (Ilex paraguariensis) as polyphenol source: Kinetics and isotherm studies

A low-cost biosorbent hybrid material ready for application was obtained in this work. Yerba mate (Ilex paraguariensis) milling residual dust was used as a polyphenol source by ethanolic extraction. Polyphenols were immobilized within a SiO(2) matrix to form an interpenetrated polymer after glutaraldehyde cross-linking. Pb(II), Cr(III) and Cr(VI) were chosen as model metals for adsorption. The hybrid materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and Nitrogen Adsorption Isotherms. Adsorption experimental data were analysed using Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Redlich-Peterson, Sips and Toth isotherm models along with the evaluation of adsorption energy and standard free energy (ΔG°). The adsorption was observed to be pH dependent. The main mechanism of metal adsorption was found to be a spontaneous charge associated interaction. Electron Spin Resonance (ESR) spectroscopy confirmed that Cr(VI) adsorption was an adsorption-coupled reaction and the adsorbed specie was Cr(V). The hybrid matrix probed its adsorption capacity of Cr(III) in a non-treated tannery wastewater.

Production of monoclonal antibodies from hybridoma cells immobilized in 3D sol–gel silica matrices

The immobilization of mammalian cells in suitable matrices that can retain their viability and capability to produce certain metabolites has gained attention in recent years. In this work, hybridoma cells were immobilized in sol–gel silica matrices for in vitro production of monoclonal antibodies. For that purpose, different matrices were evaluated in terms of cell viability, antibody diffusion to surrounding media and physicochemical properties of the polymeric material. Tetrakis (2-ethoxyethyl) orthosilicate (THEOS) matrices were found to be the best option for hybridoma immobilization. The concentrations of the silica precursor as well as the number of immobilized cells were also optimized. Three hundred mM of THEOS precursor and 5 × 105 hybridoma cells appear to be the most suitable alternative. Hybridoma cells immobilized in THEOS matrices were able to produce monoclonal antibodies to the same extent as free cells, thus introducing the possibility of using them in the design of bioreactors for large-scale production.