Kinetic and thermodynamic parameters forSchiff-rase formation between 5′-deoxypyridoxal and hexylamine

A CO2-responsive hydrogel film for optical sensing of dissolved CO2

CO₂-monitoring plays an important role in medicine, environmental sciences, and food industries. Here, a new CO₂-responsive hydrogel film was fabricated from branched polyethyleneimine (BPEI) and partially oxidized dextran (PO-Dex) via layer-by-layer (LBL) assembly, based on the in situ Schiff base reaction between the two polymers. The swelling behaviours of the films were studied using Fabry-Perot fringes on their reflection spectra. Like ordinary hydrogels, the BPEI/PO-Dex films swell in water. In addition, they swell to a larger degree when CO₂ is introduced, due to the reaction between CO₂ and the amino groups in BPEI. The CO₂-induced swelling can be reported by the shift of the Fabry-Perot fringes on their reflection spectra; therefore, the BPEI/PO-Dex film can be used as an optical sensor for dissolved CO₂. In the new sensor, the BPEI/PO-Dex film acts as a CO₂-sensing material and Fabry-Perot cavity simultaneously. The introduction of ordered structure is no longer required. The response of the sensor to CO₂ is linear and reversible. Unlike other hydrogel-based sensors that suffer from a slow response, the new sensor can respond to CO₂ quickly, making it applicable for real-time, continuous monitoring of CO₂ levels in solution.

Dynamic layer-by-layer films linked with Schiff base bond for sustained drug release

Reversible Schiff base bonds were used to construct dynamic layer-by-layer films. Sustained and intelligent drug release was achieved.

Unexpected isomeric equilibrium in pyridoxamine Schiff bases

Pyridoxamine is a vitamin B(6) derivative involved in biological reactions such as transamination, and can also act as inhibitor in protein glycation. In both cases, it has been reported that Schiff base formation between pyridoxamine and carbonyl compounds is the main step. Nevertheless, few studies on the Schiff base formation have been reported to date. In this work, we conduct a comparative study of the reaction of pyridoxamine and 4-picolylamin (a pyridoxamine analog) with various carbonyl compounds including propanal, formaldehyde and pyruvic acid. Based on the results, 4-picolylamin forms a Schiff base as end-product of its reactions with propanal and pyruvic acid, but a carbinolamine with formaldehyde. On the other hand, pyridoxamine forms a Schiff base with the three reagents, but the end-product is in equilibrium with its hemiaminal form, which results from the attack of the phenolate ion of the pyridine ring on the imine carbon. This isomeric equilibrium should be considered in studying reactions involving amine derivatives of vitamin B(6).

Claisen-Type Addition of Glycine to a Pyridoxal Iminium Ion in Water

The 5'-deoxypyridoxal stabilized glycine carbanion has been generated in water at neutral and mildly basic pH. At pH < 7, this carbanion reacts mainly with the carbonyl carbon of 1 to form a stable Claisen-type adduct. At pH > or = 8, this carbanion reacts with the iminium carbon of the pyridoxal-glycine iminium ion to form the second Claisen-type adduct 3 as the major reaction product.

Photophysical study of the Schiff bases of 5'-deoxypyridoxal and n-hexylamine in cationic micelles

The absorption and fluorescence spectra of the Schiff bases formed between 5'-deoxypyridoxal and n-hexylamine in aqueous media containing different concentrations of the cationic surfactant hexadecyltrimethylammonium bromide were recorded at 25 degrees C. The quantum yields of fluorescence of the different zwitterionic and enol forms of the chemical species of the Schiff bases occurring in media of pH 4.5-8.5 were determined. Also, the fluorescence quenching resulting from the presence of the surfactant and that of iodide ion were analyzed. From the results obtained it follows that the zwitterionic forms do not interact with the cationic surfactant, whereas the enol forms do interact with it.