Search

Research has been conducted on the cyclic ureas. The results of the oxidative carbonylation of 1,3-propanediamine to the urea carried out under different conditions are presented.

[super 23]Na NMR evidence is provided showing that sodium ions can locate itself inside the actual phospholipid bilayer. A vesicular membrane composed of a conventional phospholipid (1-palmitoyl-2-oleoyl phosphatidylcholine or POPC) admixed with a lesser amount of a 'designer' phospholipid that possesses ester groups along its normally all-hydrocarbon chains is used to show that the ester groups create membrane 'pockets' in which sodium ions reside.

A study on ice formation from saline at concentrations near that of seawater, by cryo-etch high-resolution scanning electron microscopy, is presented. The study reveals some surprising morphologies.

Surface tension measurements show that at low concentrations a surfactant bearing two ester groups in its chain assembles into small aggregates or else rearranges at the air/water interface to occupy less area per molecule. Only at higher surfactant concentrations do bona fide micelles form. The air/water interface, it is argued, saturates abruptly and cooperatively (as does the aggregation into micelles at the higher concentrations) to give a "critical monolayer concentration". Yet saturation does not reduce the surface tension a great deal. The bulk of surface tension reduction is imparted by monomeric surfactant in the solution via a mechanism that is obscure but may be related in part to the mechanical perturbation of the saturated film during measurement.

A series of six surfactants, each with two ether oxygens within otherwise all-hydrocarbon chains, were synthesized and examined for their colloidal properties. Since an ether oxygen is sterically and conformationally similar to the methylene group it has replaced, the ether effect on micellization should stem mainly from solvation of the oxygen and, possibly, disrupted hydrophobicity of its adjacent carbons. It was found that critical aggregation values among the surfactants differ only modestly despite the total length of the ether-separated carbon segments ranging from 12 to 18. Shorter ether surfactants with only 12 or 14 total carbons appear to form small, loose aggregates owing, presumably, to a mild hydrophilicity of the ether groups. A surfactant with 18 chain carbons has a greater tendency to associate hydrophobically, but this is counterbalanced by a relatively water-free environment encountered by the ether groups within a more conventional micelle interior. The result is a leveling effect in which the critical aggregation concentration (cac) loses it sensitivity to chain length. Above their cac's, none of the ether surfactants is a good solubilizer of tetramethysilane or mesitylene. This is not necessarily a predictable finding since it was conceivable that the presence of interior ether groups might actually enhance solubilization (much as ether is a better solvent than hexane). Foamability and solid adsorption studies also indicate that the ethers impair surface activity. In response to the question posed in the paper's title, two ether groups are not sufficiently hydrophilic to prevent aggregation, but they do manage to alter the micelles' morphology and properties considerably.