Natural zwitterionic organosulfurs as surface ligands for antifouling and responsive properties.

Natural sulfur-containing zwitterionic compounds, l-cysteine (Cys), l-methionine, and glutathionine (GSH), have been employed as surface ligands to prevent protein nonspecific adsorption on planar substrates. These organosulfur compounds form self-assembled monolayers (SAMs) on gold substrates by gold-sulfur interaction. The chemical elements of SAMs were confirmed using x-ray photoelectron spectroscopy. The surface wetting tests for SAMs show that films prepared from Cys and GSH exhibited super-hydrophilicity (contact angles of θ = ~5°) due to their high coverage and strong hydration via ionic solvation and formation of hydrogen bonding. Quartz crystal microbalance with dissipation sensor was used to quantitatively and qualitatively monitor the adsorption of bovine serum albumin (BSA) from buffer onto these SAMs. It was found that the GSH film enables the resistance of BSA adsorption to the best extent at a physiological pH. Moreover, the surface charges of modified substrates were modulated by varying the pH value to control BSA adsorption. The effect of electrostatic repulsion on the antifouling behavior becomes prominent at a pH where the protein and the surface carry same charges. Consolidating the BSA adsorption measurements at different pH values, the antifouling properties of GSH-modified Au should be attributed to prevention of entropy gain and enthalpy loss, making BSA adsorption energetically unfavorable. It is believed that the surface modification with natural organosulfur ligands holds great potential in improving the biocompatibility of medical devices and in offering intelligent biointerfaces in response to environmental stimuli.

Some observations on the synthesis of fully-dispersible nanocrystalline zeolite ZSM-5.

A facile method for the rapid synthesis of fully-dispersible ZSM-5 (Si/Al = 100) of about 30 nm size in high yield (about 91%) is described. The method comprises three steps, viz., concentration of an initial clear solution, low-temperature (80 degrees C) ageing of concentrated sol, and high-temperature (175 degrees C) hydrothermal treatment or microwave heating (175 degrees C) of aged concentrated sol. A simple vacuum-concentration method was used for the extraction of pure NPs of ZSM-5 in solution. XRD, FT-IR, TGA and ASAP characterizations showed that the NPs were partially crystalline. The concentration step accelerated the aggregation of primary units, which helps in the production of a large number of nucleation centers protected by TPA+ ions against aggregation. During low-temperature ageing, the number of critical sized nuclei increases, growing into zeolite. The high-temperature heating results in the complete growth of unreacted silica, giving high yields. A key factor for generating small non-aggregated zeolite crystals is the amount of water in the synthesis sol. The three-step method presented here produces a target material of small and uniform sized, non-aggregated ZSM-5 of about 30 nm in a short reaction time. The results are significant, as the synthesis method adopted here produces much uniform, non-aggregated nanocrystalline ZSM-5 in a shorter time with high yield.

A simple one-pot route to mesoporous silicas SBA-15 functionalized with exceptionally high loadings of pendant carboxylic acid groups.

Ordered SBA-15 functionalized with a high loading of pendant carboxylate groups has been synthesized via co-condensation of tetraethoxysilane (TEOS) and carboxyethylsilanetriol sodium salt (CES) templated by Pluronic P123 under acidic conditions.

Grafting of cyclopentadienyl ruthenium complexes on aminosilane linker modified mesoporous SBA-15 silicates.

Cyclopentadienyl ruthenium phosphane and carbene complexes are grafted on the surface of mesoporous SBA-15 molecular sieves through an aminosilane linker. The nature of the support after the grafting is examined by powder XRD, TEM and N(2) adsorption/desorption analysis. Elemental analysis, FT-IR, DRIFTS, TG-MS and MAS-NMR studies confirm the successful grafting of the complexes on the surface. The grafted materials are applied for catalytic aldehyde olefination and cyclopropanation.

Facile synthesis of stable cubic mesoporous silica SBA-1 over a broad temperature range with the aid of D-fructose.

A highly ordered cubic mesoporous silica SBA-1 with enhanced stability towards washing with water has been synthesized simply by adding D-fructose as an auxiliary agent during the synthesis.

Rapid synthesis of MFI zeolite nanocrystals.

A rapid synthesis procedure for nonagglomerated silicalite nanocrystals has been developed. This was achieved by concentrating the precursor sol before 10-12 h of aging at 80 degrees C, followed by hydrothermal synthesis at 175 degrees C for 90 min. The high silica concentration in the concentrated sol accelerated the aggregation of primary units that were present early in the system. Thus, little silica nutrients were left for growth when the secondary particles were converted to zeolite during hydrothermal reaction. As a result, fully dispersible nanocrystals were obtained within a day instead of weeks as reported previously. The aggregation of primary units during the 80 degrees C aging process as well as the conversion of these aggregates into zeolite has been followed by DLS, XRD, and FTIR. In light of the new results, the nucleation and growth mechanisms of MFI zeolite that have been under debate in the literature were reexamined.