Heneicosanoic acid

The monolayer resulting when amphiphilic molecules are introduced to the water—air interface was traditionally called a two-dimensional gas owing to what were the expected large distances between the molecules. However, it has become quite clear that amphiphiles self-organize at the air—water interface even at relatively low surface pressures (7—10). For example, x-ray diffraction data from a monolayer of heneicosanoic acid spread on a 0.5-mM CaCl2 solution at zero pressure (11) showed that once the barrier starts moving and compresses the molecules, the surface pressure, 7T, increases and the area per molecule, M, decreases. The surface pressure, ie, the force per unit length of the barrier (in N/m) is the difference between CJq, the surface tension of pure water, and O, that of the water covered with a monolayer. Where the total number of molecules and the total area that the monolayer occupies is known, the area per molecules can be calculated and a 7T-M isotherm constmcted. This isotherm (Fig. 2), which describes surface pressure as a function of the area per molecule (3,4), is rich in information on stabiUty of the monolayer at the water—air interface, the reorientation of molecules in the two-dimensional system, phase transitions, and conformational transformations. 

FIG. 4 Surface pressure (ll)-temperature (T) phase diagram for heneicosanoic acid. (Reproduced with permission from Ref. 31a. Copyright 1997 American Institute of Physics.)... 

X-ray diffraction has been applied to spread monolayers as reviewed by Dutta [67] and Als-Nielsen et al. [68], The structure of heneicosanoic acid on Cu and Ca containing subphases as a function of pH has been reported [69], as well as a detailed study of the ordered phases of behenic acid [70], along with many other smdies. Langmuir-Blod-gett films have also been studied by x-ray diffraction. Some recent studies include LB film structure just after transfer [71], variations in the structure of cadmium stearate LB films with temperature [72], and characterization of the structure of cadmium arachidate LB films [73], X-ray [74,75] and neutron reflectivity [76,77] data on LB films can be used to model the density profile normal to the interface and to obtain values of layer thickness and roughness. 

Bohanon et al. [86] studied heneicosanoic acid (which contains 21 carbon atoms) and Lin et al. [87] studied this material with particular reference to the effect of pH and the presence of divalent cations in the subphase. The former authors made use of in-plane diffraction (method 2 above) and obtained first order and second order diffraction peaks. They were able to show that, at high pressures ( r=35 mN m-1), at low pH (pH = 2) and at temperatures in the region of 0-5 °C, the material packs into a distorted hexagonal structure with the tilt towards the nearest neighbours. However, in the region 5-10°C the tilt is towards the next nearest neighbours. In the latter study [87] in-plane diffraction was studied as a function of pH and the presence of Ca2+ or Cu2+ in... 

Pentacosene 1-Hexacosene 1-Heptacosene 1-Octacosene 1-Nonacosene 1-Triacontene Dodecanal Tridecanal Tetradecanal Pentadecanal Hexadecanal Heptadecanal 17- Oxooctadecanoic acid 18- Oxononadecanoic acid 2-Oxopentanedioic acid Nonadecanoic acid methylester Eicosanoic acid methylester Heneicosanoic acid methylester... 

Heneicosanoic acid, 60, 13 Heptadecanoic acid, 60, 13 Heptane, 1-bromo- [629-04-9], 61, 59 Heptanoic acid, 60, 13 2-HEPTYL-2-CYCLOHEXENONE, 61, 59... 

M-heneicosanoic acid. CH3(CH2)19COOH. A saturated fatty acid not normally found in natural fats or waxes. 

Heneicosanoic acid, 19-methyl-, heneicosyl ester H3C-CH2-CH(CH3)-(CH2),7-COO-(CH2)20-CH3 Heneicosanoic acid, 3,7,11,15-tetramethyl-2-hexadecenyl ester phytyl heneicosanoate 103 [see 2809] 3218, 3287, 3308, 4249 103 ... 

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