Long-chain Alkanols Research Articles

Anionic surfactants between double metal hydroxide layers

Surfactant films between double metal hydroxide layers are prepared by exchanging interlayer anions of layered double metal hydroxides {M 1− x IIM x III(OH) 2} x+ xX − · zH 2O. Zinc chromium {Zn 2Cr(OH) 6} +(NO) 3 − · 2H 2O is used as an example of this group of layered materials. The nitrate ions are exchanged by alkyl sulfate ions C n C H 2 n C+1 SO 4 − ( n C = 6, 8, …, 18) and dodecyl glycol ether sulfate ions C 12H 25(OCH 2CH 2) m SO 4 − ( m = 0, 1, 2, 4). In equilibrium with the surfactant solutions, monolayers of surfactant ions are formed between the zinc chromium hydroxide layers. The chain axes are perpendicular to the hyroxide sheets [ V1(90°) structure]. After being washed and dried, the materials contain surfactant monolayers with the chains tilted about 56° to the hydroxide sheet [ V1(56°) structure]. These materials take up long-chain alkanols C n A H 2 n A+1 OH ( n A = 6, 8, …, 18) into the interlayer regions. Bilayers are formed consisting of surfactant ions and alkanol molecules. For most combinations of n C and n A, the distance between the hydroxide sheets is determined by pairs of sulfate ions and alkanol molecules that are perpendicular to the hydroxide sheets and shortened by one, two, or three kinks. At extreme differences between n C and n A the pairs are tilted (56–60°), or other arrangements occur. Small organic molecules (water, some diols, N-methyl formamide, dimethyl sulfoxide) are intercalated with maintenance of the 56° chain orientation. In particular cases and if the alkyl chains are not too long, some guest molecules associate forming larger clusters, causing a considerable change in the monolayer structure.

Interfacial tensions and microemulsion formation in heptane–aqueous NaCl systems containing aerosol OT and sodium dodecyl sulphate

The tension, γc, between alkane and aqueous NaCl in systems containing an anionic surfactant (Aerosol OT or sodium dodecyl sulphate, SDS) at the aggregation point can be made ultralow (ca. 1 µN m–1) by adjustment of the salt concentration or the concentration of an added ‘cosurfactant’(e.g. a long-chain alkanol). For the twin-tailed surfactant (AOT) an ultralow minimum in γc can be obtained in the absence of the cosurfactant, whereas the presence of the latter is required in systems containing SDS, which has only a single alkyl chain. Here we discuss how the tensions γc vary in the heptane–aqueous NaCl system containing mixtures of AOT and SDS (in the absence of cosurfactant), and consider the nature of the microemulsions which are formed in these systems. All the effects can be broadly understood in terms of well established ideas on the different molecular geometry of the two surfactants and the way in which monolayers tend to curve.

Rapid in vitro formation of smooth endoplasmic reticulum aggregates within peptide-producing islet cells.

We report here that heptanol (3.5 mM) induces in vitro a rapid formation of smooth endoplasmic reticulum aggregates (SERA) within isolated islets of Langerhans. SERA appeared after only 15 min of exposure to the alkanol and increased in number during the first 30 min of incubation. At that time, SERA represented 2% and 6% of the volume of B- and non-B-cells, respectively. Removal of heptanol resulted in the rapid disappearance of SERA, whereas reintroduction of the alkanol rapidly induced these structures again. SERA formation was seen in different types of endocrine and nonendocrine islet cells. In the insulin-producing B-cells, SERA formation was not modified by conditions known to alter the secretory activity and the microtubular-microfilament network or to inhibit protein synthesis. By contrast, SERA formation was inhibited by low temperature and by conditions depleting the energy sources of the cells. Similar observations were made in the presence of either octanol (1 mM) or nonanol (1 mM) but not of shorter chain alkanols, alkanes, oxidative derivates of either heptanol or octanol, and of other unrelated lipid-soluble compounds. Incubations in the presence of long-chain alkanols provide, therefore, a unique model to study in vitro the formation and disposal of smooth endoplasmic reticulum, as well as a system in which rapid membrane biogenesis is amenable to direct experimental testing.

Molecular origin of biphasic response of main phase-transition temperature of phospholipid membranes to long-chain alcohols

A statistical mechanical theory is proposed which explains the molecular mechanism of the nonlinear response of the phase-transition temperature of phospholipid vesicle membranes to added 1-alkanols. By assuming that the free energy of transfer of 1-alkanols from the aqueous phase to the membrane and the interaction energy between 1-alkanol molecules are linear functions of alkanol alkyl chain-length, the nonlinear behavior is explained in the Bragg-Williams approximation. For dipalmitoylphosphatidylcholine vesicle membranes, the theory reveals a larger free energy of transfer of 1-alkanols from the aqueous phase to the solid-gel membrane than to the liquid-crystalline membrane when the number of carbon atoms of 1-alkanol exceeds 12. When the intermolecular interaction force between 1-alkanol molecules residing in the gel phase is stronger than the interaction force between those residing in the liquid-crystalline phase, the ligand effect is to tighten the lipid matrix structure, causing the transition temperature to rise. The interaction force is a quadratic function of 1-alkanol concentration; hence, the response of the transition temperature to the 1-alkanol concentration is nonlinear. At low concentrations of the long-chain 1-alkanols that predominantly elevate the transition temperature, this intermolecular interaction force is negligible. In this case, the entropic effect of the incorporated ligand molecules, which loosens the lipid matrix, predominates, and the transition temperature decreases. The biphasic action of long-chain 1-alkanols originates from the balance of these two opposing effects: entropy and intermolecular interaction.

Ultrastructure and chemistry of soluble and polymeric lipids in cell walls from seed coats and fibres of Gossypium species

Electron-microscopic examination in conjunction with extraction procedures and chemical analysis have confirmed that a suberin-like lipid biopolymer is located within the concentric polylamellate layers found in the secondary cell walls of green cotton fibres (Gossypium hirsutum cv. green lint). A polymer of similar ultrastructure and chemical constitution also occurs mainly in the secondary seed-coat walls of the outer epidermis of both green and white varieties of G. hirsutum. The suberins composed of predominantly C22 compounds are, however, markedly different from those present in the periderms of the same plants; these comprise mainly C16 and C18 compounds. Long-chain 1-alkanols (C26-C36) and alkanoic acids (C16-C36) are the principal components of the wax from white fibres but these lipid classes comprise a much smaller proportion of that from green fibres. unidentified highmolecular-weight compounds were the major constituents of the green-fibre was extract which also contains a number of yellow-green pigments, probably flavonoid in nature. These pigments are thought to be associated with the ultrahistochemical reaction with silver proteinate that was observed only in the green-fibre cell walls. A total of 16 wild and cultivated cotton species were examined with the electron microscope for the presence of suberin. The outer seed-coat epidermis of all the examined species but only the fibres of the wild ones were found to be suberized. Among the analysed mutants of fibre colour in G. hirsutum only the gene Lg (green lint) seemed to be associated with suberin.

Effect of lysolecithin on blood vessel reactivity and of some ethers and esters of glycerophosphocholine and phosphocholine, respectively, on aggregation of rat platelets.

Infusion of lysolecithin (LPC; e.g. 88 microgram/ml for 0.5-1.0 min) did not significantly impair the vasopressor action of norepinephrine (NE), prostaglandin F2 alpha (PGF2 alpha) and extract of posterior pituitary (EPP) in the isolated perfused hind legs of rats. In other words, vascular smooth muscle behaves differently from the smooth muscle of the guinea-pig small intestine, since, in the latter, contractions evoked by acetylcholine, prostaglandins etc., are inhibited by LPC. Triton X 100 which, by comparison, was used as a detergent effective on the guinea-pig small intestine, depressed the vasopressor effect of NE, PGF2 alpha and EPP. LPC, at low concentrations (40 mumol/l), potentiated (15% max.) ADP-induced platelet aggregation (PA) in rat PRP but, at high concentrations, inhibited PA (IC50 = 390 mumol/l). 2-Hexadecylglycerophosphocholine and its short-chain 1-alkyl ethers, which are structurally related to platelet-activating factor, as well as some long-chain alkanol phosphocholine esters, were somewhat more active than LPC. Dipalmitoyllecithin (4-700 mumol/l) was without any effect.

Stable Alkanol Dispersion to Reduce Evaporation

The poor results obtained from many field studies of evaporation suppression with long-chain alkanols can be attributed to the difficulty in maintaining a continuous monolayer on exposed water surfaces.