Jack H. Schulman

FORMATION OF MICROEMULSIONS BY AMINO ALKYL ALCOHOLS

The use of emulsions in biological systems is becoming technically important for the study of the particulate fat absorption process in the intestine and production of chylmicrons for oil/water systems and for the delayed absorption of proteins, such as allergens, from subcutaneous injections of water/oil emulsions. In each case the emulsion-stabilizing agents must be compatible with the absorbing material and with biological systems involved. I t has recently been shown1f2 that certain amino alkyl alcohols are excellent agents for the production of microemulsions and the study of the mechanism of formation of these emulsions by such compounds has now been undertaken.

The adsorption of CO gas by metals supported on silica

Abstract The adsorption of CO gas by the metals Rh, Ir, Os, Re, Ru and Au supported on silica was studied. From electron micrographs and measurements of the surface area of metal covered silica, the metal particles appear as thin clusters on the silica surface ranging from about 20 A in diameter and probably approaching monolayer thickness. The infrared spectra shows adsorbed CO species of the type M-CO, M2-CO and M-(CO)2. At the higher pressures used with Rh, Ir and Os, a band at 2080 cm−1 is attributed to a weakly held CO in sites already containing one chemisorbed CO. The possible occupancy of corner and edge sites in Re and Ru by more than two CO molecules is discussed. A correlation is presented between the force constant of M-CO species and the number of d holes of the metal indicating a decrease of the bond order of adsorbed CO on account of the formation of metal-carbon bonds. The correlation is additional evidence of the role of d electrons in adsorption.

MECHANISM OF THE SELECTIVE FLUX OF SALTS AND IONS THROUGH NONAQUEOUS LIQUID MEMBRANES

Most living cells possess asymmetric membranes in which the concentration of ions in the interior is quite different from that in the extracellular fluid. The unequal distribution of ions plays a major role in the generation of small electric currents that conduct the nerve impulse. This condition appears associated with an exchange of extracellular sodium with intracellular potassium. J. H. Schulman and H. L. Rosanol have used a liquid membrane model for studying the selective flux of various salts through short chain alkyl alcohols. The apparatus consisted essentially of a thermostated polystyrene box with a partition. An aqueous solution was placed in each compartment over which was floated a nonaqueous liquid membrane (FIGURE 1). The advantage of a liquid membrane is twofold: interfacial orientation; interfacial homogeneity versus pore size with a solid membrane. The use of a physicochemical model makes it possible to investigate an initially simple system in which the complexity of the actual membrane can be achieved by adding different physiological components. Schulman and Rosano have studied the diffusion of different salts through different oil layers under varying conditions. This phenomenon was called diffusion transport. In the presence of an amphoteric phospholipid (carrier) in the oil membrane interface, the transport is markedly increased; this phenomenon was called carrier transport. This carrier transport functions also when the diffusion process has been blocked. With regard to the effect of biological components upon the selective flux of salts and ions through nonaqueous membranes, a review of the diffusion transport will be given.

Surface chemistry of the monoglyceride-bile salt system: Its relationship to the function of bile salts in fat absorption

Abstract Ingested triglyceride is hydrolyzed by pancreatic lipase to yield monoglycerides and fatty acids, which are dispersed by bile salts into aggregates of micellar size. To determine the molecular arrangement of these aggregates, the surface interaction of appropriate fatty acids, glycerides, and their analogs with synthetically prepared, pure bile salts varying in conjugation, number, and position of hydroxyl groups and type of A/B ring juncture has been characterized. Monoolein was readily penetrated by bile salts. The degree of penetration was proportional to the intrinsic surface activity of the bile salt, and this correlated with the number and position of hydroxyl substituents: taurocholate π A and Δ V A indicated that at high areas the bile salt nucleus lies parallel to the interface; as the area was reduced, the nucleus became perpendicular and the ionic head of the bile salt was forced into the aqueous phase. With further compression, dihydroxy and trihydroxy bile salts separated from the monolayer and passed into the bulk phase; monohydroxy bile salts remained associated with the film, reflecting their greater surface activity. Penetration of monoglycerides, monoglyceride analogs, diglycerides, and triglycerides of oleyl and stearyl homologs indicated that the interaction of bile salts with monoglycerides was much stronger than that with higher glycerides, fatty acids, or propylene glycol monoesters. At 25°C, penetration did not occur unless spacing between the polar heads of monoglycerides was present. The mechanism of penetration was considered to be hydrogen bonding between the hydroxyl groups of the bile salt nucleus and those of the glycerol moiety of the monoglyceride. Monoglycerides form a mesomophic phase in water. Bile salts adsorb to the presumably lamellar or cylindrical arrays and round them off into smaller aggregates; a spherical model of the bile salt-monoglyceride-fatty acid aggregate is proposed. In this model, bile salts function as wetting agents, rather than as detergents, since they adsorb to the interface and do not penetrate the hydrocarbon chains. The ability of bile salts to penetrate films of monoglycerides plus the existence of a mesomorphic phase in the water-poor region of the ternary composition phase diagram of the bile salt-water monoglyceride system suggests that a mesomorphic phase of bile salt-water-monoglyceride and fatty acid may occur during pancreatic lipolysis at the oil/water interface. Thus the mechanism proposed by Lawrence for spontaneous detergence may well occur in biological systems.

A study of molecular interactions and mobility at liquid/liquid interfaces by NMR spectroscopy☆

Abstract The titration of a strong solution of decyltrimethylammonium bromide (DTAB) in water with chloroform resulted successively in the formation of an isotropic phase, a viscous birefringent phase, and a second isotropic phase of low viscosity. High-resolution NMR spectra were taken of the various phases at a variety of chloroform concentrations. The CHCl 3 resonance position was found to shift to the low-field side of the position in pure CHCl 3 as its concentration decreased. The maximum shift was found to be −1.04 p.p.m., which is comparable to the shift in such strong electron-donor solvents as triethylamine. It is concluded that the shift reflects a specific interaction of the CHCl 3 with the polar portion of the DTAB cation, leading to a reduction in electron density and/or diamagnetic circulation at the CHCl 3 proton. The complete absence of all the DTAB resonances in the birefringent liquid-crystal phase stands in marked contrast to the narrow DTAB lines noted in the isotropic phases and the narrow H 2 O line observed in all phases. The absence of the DTAB resonances is attributed to extreme broadening, which is the result of a rigidity in the DTAB chains comprising the liquid-crystal interface. NMR spectra of solutions of DTAB in CHCl 3 at a variety of water concentrations gave evidence for a broadening of the H 2 O resonance with decreasing water concentration. The broadening is attributed to an immobilization or bonding of H 2 O molecules to the interface. NMR spectra were also taken of 2-amino-2-methyl-1-propanol and 2-amino-1-butanol oleates in benzene at a variety of water concentrations. The marked broadening of the H 2 O resonance in the aminomethylpropanol system at low H 2 O content stands in contrast to the nearly invariant H 2 O line width in the aminobutanol system and the close similarity of the resonance positions in the two systems. The broadening in the aminomethylpropanol system is considered to result from the participation of H 2 O molecules in a hydrogen-bond network at the interface. The bulk of the ethyl group in aminobutanol prevents the formation of such a hydrogen-bonded interface and accounts for the near-invariant width observed.

Mechanism of ionic exchange with carrier molecules through non-aqueous liquid membranes

Abstract In salt “diffusion” blocked systems, “carrier” transport by ionic amphipathic molecules through nonaqueous liquid membranes is explained by an ionic exchange mechanism. “Carrier” transport versus pH was established for lauric acid, stearic acid, alkyl phosphates, and cetyl trimethyl ammonium bromide (CTAB) as well as for the phospholipids lecithin and cephalin. The ionic exchange depends upon the state of ionization of these long-chain “carrier” molecules and ion+-ion− and intramolecular ion-dipole associations at the oil-water interface. Potentiometric titration and surface tension measurements on single and dual components were performed in the presence and in the absence of 1-pentanol, and similarities between the titration and the transport curves were found. The marked influence of molecular aggregate surfaces and charged oil-water interfaces on the bulk pH is established.

Direction of electron transfer in FeNi alloy surface

Abstract The direction of electron transfer in FeNi alloys was studied by an infrared technique comparing CO interaction with CuNi and CoNi alloy systems. The results were interpreted by the d-hole relationship of the metals and the saturation magnetization of alloy systems. An electron transfer from Fe to Ni in the FeNi alloy system is proposed, whereas no electron transfer between alloying components is believed to occur in the CoNi alloy system. A critical point for the FeCO interaction on the FeNi alloy surface was observed at 75 Fe25 Ni atom percent; a critical point for CuCO interaction on the CaNi alloy surface was previously found at 85 Cu15 Ni atom percent. No similar critical composition was found on the CONi alloy surfaces. Some of Uhligs corrosion theory of surface passivity was applied to the calculation of critical composition. Infrared band shifts on the alloy surfaces are shown. Infrared absorption bands for CO on silica-supported metal alloy surfaces were determined in the region from 2200 cm −1 to 1600 cm −1 .

THE INFLUENCE OF SURFACE FORCES IN MEMBRANE PERMEABILITY

Recent research work in collaboration with M. Rosoff (Columbia) and D. F. Sears (Tulane Univ.) on membrane permeability deals with two possible aspects of a membrane: ( a ) a liquid structure with two liquid/liquid interfaces, also producing interphases, and ( b ) a solid structure, with a solid/liquid interface. This work brings into emphasis the surface energies of the system and not the bulk energies or chemical and electro-chemical potential terms as the driving forces to produce a flux of material through the membrane and flux selectivity. The classical thermodynamics of membrane permeability ignore the significance of the surface energy terms. The most important term at both liquid/liquid interfaces and the solid/liquid interface appears to be surface entropy in its various manifestations. Recently work has been undertaken to determine experimentally this term for various systems and to show how i t enables the selective flux af ions, salts, and water to be understood through liquid/liquid interfaces, where the salt can partition between the two liquids. Where no partitioning is observed, carrier molecules for the salts and water have to be added to the liquid membrane. The selective permeability of molecular aggregates through membranes, true micelles, amorphous aggregates micellar size, and crystalline aggregates micellar size, is directly related to the entropy of the aggregates and the surface of the membrane and the negative interfacial tension at the solid/liquid interface.’ Entropy differences may arise from different configurations of the molecules forming the aggregates e.g. cisand trans-isomers. Only the amorphous aggregates appear to migrate through the intestinal membrane of the duodenum and jejunum. The entropy term in this case can be measured by determining the heat of wetting of the aggregates and solid surfaces. These researches appear to have possibilities in explaining certain biological phenomena of membrane permeability and have practical applications. This approach is quite different from those using classical physical chemistry to explain the selectivity of ion fluxes through membranes.

The Influence of Amphoteric Surface Active Agents on the Diffusion and Carrier Transport of Salts and Ions Through Liquid Non-Aqueous Membranes

Publisher Summary This chapter discusses the influence of amphoteric surface active agents on the diffusion and carrier transport of salts and ions. In the salt diffusion systems, water is essential as the transport is ionic, while with the carrier mechanism, a double oil soluble cephalin or lecithin salt is being transported, and this requires no water. This mechanism is different from solvent extraction processes, where covalent oil-soluble metal organo-complexes are produced and extracted. In a study described in the chapter, the rates of diffusion of salts through alkyl alcohol liquid membranes were found to be dependent not only on the partition coefficients between the aqueous and nonaqueous phases but also on the hydration of the ions and on the stereochemistry of the alkyl alcohols. In the diffusion transport cases, the partition coefficient and the hydration of the ions are the governing factors in the ionic permeability of the oil layer. In the carrier transport process, the partition coefficient of the salts in the oil and the aqueous phases is not important, as the ions are available to the oil phase whether they are together or counter flowing from one aqueous phase to another.