The stability of red radish extract to light, heat, and hydrogen peroxide at different pH values (3, 5, and 7) was examined, in which major anthocyanins were pelargonidin glycosides acylated with a combination of p-coumaric, ferulic, or caffeic acids. The light irradiation (fluorescence light, 5000 lx; at 25 degrees C) indicated that the red radish extract was more stable at lower pH than at higher pH. The HPLC analyses revealed that diacylated anthocyanins in the extract were more stable to light at pH 3 than monoacylated anthocyanins. No significant difference in degradation rates of acylated anthocyanins at pH 5 was observed, whereas anthocyanins acylated with p-coumaric or ferulic acids were more stable at pH 7 than ones with caffeic acids. The stability to heat (at 90-95 degrees C) showed a tendency similar to that for light. The number of intramolecular acyl units contributes to stability to light and heat at lower pH, whereas the characteristics of intramolecular acyl units influence the stability at higher pH. The degradation behavior of red radish extract to H2O2 were almost the same to those of light and heat, depending on the pH. However, HPLC analyses revealed that the stability of individual acylated anthocyanins were independent of the pH. These data suggest that the characteristics, the number, and the binding site of intramolecular acyl units affect the stability of anthocyanin to H2O2. DPPH radical scavenging activity of all acylated anthocyanins was higher than those of pelargonidin and perlargonidin-3-glucoside. The activity of acylated anthocyanins mostly depended on the activity of intramolecular acyl units (caffeic acid > ferulic acid > p-coumaric acid). However, the activity was highly affected by the binding site of intramolecular acyl units even if anthocyanins have common acyl units.
A Cu2+-ion selective resin (resin A) was synthesized by a novel template polymerization technique, using oleic acid as a host monomer, divinylbenzene as a matrix-forming monomer and Cu2+ ion as a target molecule. The metal (Cu2+ and Cat) ion complexation equilibria of resin A together with a reference resin (resin B) studied potentiometrically indicate: l) rapid and reversible complexation reactions, and 2) a highly selective binding of resin A to Cu2+ ions. These properties show that Cu2+-ion selective cavities were formed at the surface of resin A. The concept of molecular recognition has drawn special attention in regarding recent separation analytical chemistry. In order to obtain fine guest-recognizing molecules, a large number of studies have been reported concerning the design and synthesis of supramolecules;1 however, the required multi-step preparation procedures are sometimes tedious and the yields are not always high. Another possible approach for guest-recognizing molecules is a template polymerization technique, the idea of which was proposed by Wulff and Sarhan 20 years ago.2The template polymerization technique is well-known as a method for synthesizing host polymers, and is called "molecular imprinting".3 In this technique a target molecule is incorporated into polymerizable compounds with functional groups (host monomers). Then, the complex is polymerized with a matrix-forming monomer to give a resin (Fig. 1). Upon washing out the target molecules cavities remain in the polymer matrix. The cavities memorize the spacial structures and shapes of the target molecule, so that the polymers selectively bind to the molecule. By template polymerization, Wulff et al. have succeeded in separating racemates on polymers having chiral cavities.2 Nishide et al. have synthesized highly selective metal-ion exchange resins by templating metal ion.4In this work we designed template polymerization at an oil-water interface (Fig. 2). Both a target molecule (water-soluble) and a host monomer (amphiphilic) approach at the vicinity of the interface and arrange orderly. The order of the molecular assemblies is controlled by the complexation of the target molecule with the host monomer. The oil phase comprising a matrixforming monomer is polymerized to give a resin, so that target-selective cavities are formed at the resin surface. This enables a rapid and reversible complexation of the target molecule by the host polymers.In this paper we describe the preparation of metal-ion selective resins using surface template polymerization. Resins have been synthesized using oleic acid as an amphiphilic host monomer, divinylbenzene as an oil (resin-forming monomer), and metal ion (Cu2+) as the target molecule. The characteristics of metal-ion (Cu2+ and Cat) complexation equilibria of the resins have also been examined.
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