Makio Iwahashi

Adsorption of tritiated surfactants at nitrogen/solution interfaces as determined by sheet scintillation counting☆

Abstract By the use of a counting device designed for determining the surface radioactivity of a solution of a tritiated compound, the adsorbed amounts (Γ) were determined for the solutions of (a) sodium dodecyl-2, 3- 3 H-sulfate (TSDS) in the absence of strong electrolyte, (b) TSDS in the presence of an excessive amount of NaCl, and (c) hexaethyleneglycol monododecyl-2, 3- 3 H ether. The Γ values thus obtained were in fairly good agreement with those calculated by the Gibbs adsorption isotherm for expressing the equilibrium surface tension (γ ∞ ) as a function of the surfactant concentration ( C ). Roughly, n in the conventional equation, Γ = − (1/ n R T ) × [ d γ/ d (ln C )], has been found to be 2 for the case (a) and 1 for the cases (b) and (c), as was predicted by many investigators. Discussions have been made to correlate precisely the surface tension data with the radiotracer results which provide direct information about the adsorption at the gas/solution interfaces.

Radiotracer study on oxidation of oleic acid monolayer on aqueous permanganate solution

Abstract Studies have been made of the mechanisms of the oxidative processes of [ 14 C]oleic acid in its insoluble monolayer spread on aqueous permanganate solution by measuring simultaneously the time ( t ) dependences of surface radioactivity ( R ), apparent molecular area ( A ), and surface pressure (π). Infrared spectroscopic examination of the film material obtained by skimming the monolayer on permanganate solution indicates that the rate-determining intermediate involved in the interfacial processes is predominantly cis-epoxyoctadecanoic ( cis -epoxy) acid and none of the other oxyacids such as dihydroxy (diol), ketohydroxy (ketol), and diketo acids, those having been assumed as intermediate compounds by other investigators. A kinetic analysis of the A - R - π - t relationships leads to the conclusion that the major processes involve (a) relatively quick formation of the cis -epoxy acid in the monolayer and (b) the rate-determining desorption of the cis -epoxy acid into the underlying subphase. In parallel with (b), there is an interfacial reaction through which the cis -epoxy acid is fissured to form azelaic and nonanoic acids to be dissolved instantaneously into the subphase. An increase in π causes a retardation of process (a), an enhancement of process (b), and an enhancement of process (c) in the region of π ≦ ca. 15 dyn/cm beyond which it is retarded markedly. When the monolayer is spread on subphase without permanganate ion, an increase in π causes an enhancement of the desorption of oleic acid (much slower than that of the cis -epoxy acid), while the rate of the autoxidation is not affected by the molecular conformation at the air/water interface.

Insoluble monolayer of [14C] chloramphenicol palmitate at the air-water interface

Abstract The nature of the insoluble monolayer of chloramphenicol palmitate (CPP) at the air-water interface has been studied by simultaneous measurements of surface pressure, π, potential, ΔV, and radioactivity, R, of 14C-labeled CPP as functions of apparent molecular area, A, and time, t, elapsed from the delivery of CPP solution at the interface. The observed time dependences of π, ΔV, and R in relation to A have been accounted for only by reorientation of CPP molecules in the monolayer, with elimination of the possibilities of their evaporation, dissolution, and hydrolysis. The reorientation process from A = 93 A 2 /molecule at t = 0 to A = 152 A2/molecule at t = ∞ is explicable solely by the conformational change of cis- → trans-form of the CPP molecules. It has been shown that the change corresponds to the polymorphic transition of CPP-α → CPP-β in three-dimensional crystals, as has been revealed in the hydrolyzability of CPP molecules upon injection of a lipase solution beneath the monolayer.

Enzymatic hydrolysis of chloramphenicol palmitate in insoluble monolayer at air—Water interface as detected by radiotracer method

Abstract Hydrolysis of chloramphenicol palmitate (CPP) in insoluble monolayer in the presence of lipase in aqueous subphase has been studied by simultaneous determination of molecular area A of CPP and surface radioactivity R as a function of time t under a constant surface pressure. Separate use of CP- 14 C-P and CPP- 14 C, i.e., CPP samples isotopically labeled at hydrophilic and hydrophobic positions, respectively, made it possible to analyze the A ∼ R ∼ t relationship, which reflects the enzymatic reaction to be governed solely by the adsorbed amount of lipase and the fraction of CPP in the α conformation.