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.
Grisan derivatives in pure and mixed monomolecular films.
Abstract Pressure-area isotherms for monolayers of two synthetic grisan derivatives have been determined and correlated with molecular orientations of these entities at the air-water interface. Isotherms for equimolar mixtures of the grisan derivatives with stearic acid, cholesterol, and l -α-lecithin, respectively, are reported. The pressure-area curves show, in general, the predominant influence of the grisan derivatives at low pressures, and ejection of these from the monolayer at intermediate pressure values. At higher pressures the curves reflect largely the properties of the respective lipids. Theoretical curves for the mixtures were calculated assuming additivity, and compared with the corresponding experimentally derived isotherms.
Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil.
Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.