Monomolecular films of phenolic esters.
Abstract The properties of three phenolic esters, characterized by gradual changes in their molecular constitution, have been evaluated in pure monomolecular films, as well as in mixed films with stearic acid. The pressure-area isotherms for the pure compounds reflect a similar orientation for compounds I (resorcinol monoundecanoate) and II (4-chlororesorcinol 1-undecanoate) at the air-water interface. At pressures corresponding to the limiting area per molecule, the molecules are apparently rather erect and anchored to the aqueous subphase surface by the phenolic-OH function; at lower pressures, the molecules are less erect, with their aliphatic chains randomly intertwined. The isotherm characteristics for III (4-chlorophenyl undecanoate), on the other hand, are compatible with an orientation in which the molecule is anchored to the aqueous subphase surface by its ester function, with both the aliphatic chain and the substituted phenyl ring projecting upwards. Isotherms for 1:1 mixtures of each of the phenolic esters with stearic acid indicate that the properties of the mixed films were controlled, generally, by the esters (at low pressures) and by stearic acid (at high pressures), after the esters had been forced out of area-determining positions in the films. The experimentally derived isotherms for the mixtures were compared with those calculated from the isotherms of the pure components, and observed deviations from additive behavior discussed.
Hexachlorophene esters in pure and mixed monomolecular films
Abstract The properties of pure monomolecular films of hexachlorophene monoundecanoate (I), hexachlorophene monostearate (II), and hexachlorophene diundecanoate (III) have been determined. The pressure-area curves for compounds I and II reflect a similar molecular orientation at the air-water interface for these compounds; films of each of the latter were considerably more stable than those of compound III and reflected the significance of the phenolic-OH function in the interaction with the subphase. Pressure-area isotherms for mixtures of compound I, as well as for those of compound II, with stearyl alcohol, stearic acid, methyl stearate, and stearyl acetate, respectively, showed positive deviations from the additivity rule; negative deviations were observed for mixtures of compound I, or of compound II, with tristearin. The data are indicative of interaction between component molecules in the respective films.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.