دانلود رایگان مقاله غنی سازی مولفه تیونینگ در اسید آمینه عاملدار شده

Abstract

A straightforward procedure to synthesize cysteine functionalized materials with tailored support properties has been developed. It allows tuning the hydrophobicity of the material via the incorporation of aliphatics, aromatics or silica in the framework structure. The aldol condensation of 4-nitrobenzaldehyde and acetone, as a probe reaction for the catalytic activity of the produced materials, exhibited a remarkable interplay between the reactant, solvent, traces of water and support hydrophobicity. A selective enrichment in the catalyst pores of specific bulk phase molecules is believed to be the key to achieve the targeted catalyst performance.

4. Conclusions

A straightforward synthesis procedure for cysteine functionalized (organo)silicas with an aliphatic, aromatic or silica character has been developed. Catalytic testing of the synthesized materials in the aldol condensation of 4-nitrobenzaldehyde and acetone was indicative of a crucial interplay between the reactant, solvent, traces and support properties in achieving the desired catalyst performance. An organosilica with aromatic linkers exhibited a low catalytic activity, which was attributed to a pronounced 4-nitrobenzaldehyde enrichment enhancing the formation of inhibiting species. Of the two other catalysts, i.e., an organosilica with an aliphatic character and a hydrophilic silica material, the former exhibits the highest catalytic activity. This suggests that a hydrophobic support might lead to a better acetone to 4-nitrobenzaldehyde ratio inside its pores and, hence, would be beneficial for the catalytic activity. Additionally, the hydrophilic silica material loses about 40% of its activity in the presence of a small amount of water due to poisoning of the active sites and suppression of the formation of the reactive enamine intermediate. The aromatic organosilica exhibits an activity decrease of 28% in agreement with its hydrophobic character and the suppression of the formation of inhibiting species while the aliphatic organosilica apparently fully repels water from its pores and retains its activity.