Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution

Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation

Peptide immobilisation on porous silicon surface for metal ions detection

In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization

Modification of Porous Silicon Surfaces with Activated Ester Monolayers

A series of activated esters of undecylenic acid with activated ester end groups (3-nitrophenyl, N-succinimidyl, S-ethyl, and 2,2,2-trifluoroethyl) have been synthesized and covalently linked to a porous silicon (PSi) surface via a thermal hydrosilylation reaction. Diffuse reflectance infrared Fourier transform (DRIFT) or transmission FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the monolayers and to follow the course of reactions with primary amines in aqueous solution. It was found that the reaction of the 3-nitrophenyl undecylenate with the PSi surface resulted in significant oxidation of the surface. A control reaction with nitrobenzene confirmed that the arylnitro group was responsible for the surface oxidation and grafting of the nitroaromatic on the surface via a Si-O-N linkage. The N-succinimidyl (NHS) and thioethyl activated ester-modified surfaces formed monolayers with no apparent oxidation of the PSi surface. However, we find that the hydrophobic end groups prevent wetting of the porous structure and further reaction is not possible. Reactions of these groups could be achieved by the addition of 25% (v/v) of ethanol to the aqueous solution of amine, electrochemical partial oxidation of the surface, or preparation of mixed monolayers consisting of mixtures of undecylenic acid and the activated undecylenate ester in a ratio of 5:1 or higher. Under these conditions the NHS group was displaced by ethanolamine or n-butylamine. As expected, exposure of primary amines to the activated S-ethyl thioester did not result in any reaction. However, amide bond formation was observed upon reaction of the methyl ester of cysteine illustrating specificity of this activating group toward cysteine-terminated proteins.NRC publication: Ye