Stearic acid, molecular structure

The FT-IR technique using reflection-absorption ( RA ) and transmission spectra to quantitatively evaluate the molecular orientation in LB films is outlined. Its application to some LB films are demonstrated. In particular, the temperature dependence of the structure and molecular orientation in alternate LB films consisting of a phenylpyrazine-containing long-chain fatty acid and deuterated stearic acid (and of their barium salts) are described in relation to its pyroelectricity. Pyroelectricity of noncentrosymmetric LB films of phenylpyrazine derivatives itself is represented, too. Raman techniques applicable to structure evaluation of pyroelectric LB films are also described. [Pg.156]

No direct method exists by which monolayer film structures on water can be studied. Therefore, the LB method has been used to study molecular structures in past decades. The most useful method for investigating the detailed LB-deposited film structure is the well-known electron diffraction technique (or the scanning probe microscope [Birdi, 2002a]). The molecular arrangements of deposited mono-and multilayer films of fatty acids and their salts, using this technique, have been reported. The analyses showed that the molecules were almost perpendicular to the solid surface in the first monolayer. It was also reported that Ba-stearate molecules have a more precise normal alignment compared to stearic-acid monolayers. In some investigations, the thermal stability of these films has been found to be remarkably stable up to 90°C. [Pg.94]

Jojoba (Simmondsia chincnsis) This is not actually an oil but a liquid wax. It is good for cosmetic use with moisturizing properties and ideal for dry skin and conditions like eczema and psoriasis. It is similar chemically to sebum and able to dissolve it. The oil keeps well owing to a stable molecular structure and analysis shows both saturated and unsaturated fatty acids, with eicosenoic (71%), oleic (14%), stearic (10%) and palmitic (1.5%). The presence of a compound called myristic acid is thought to confer anti-inflammatory properties. [Pg.219]

Turning to SIMS analysis of the same systems, previous work conducted by Wandass, Schmitt and Gardella (3b) indicated evidence for both "matrix" (i.e. substrate surface chemistry) and "structural" (i.e. short range order in the LB film) dependence of (M+H)+ emission from stearic acid LB layers on Ag, Au, and Ge. In particular, (M+H)+ emission was not observed for a single monolayer on Ag, where the molecular orientation positions the carboxylic acid towards the reactive, oxidized Ag surface. However, (M+H)+ emission from a stearic acid monolayer on both Au and Ge was observed. The results indicated that (M+H)+ emission is influenced by the type of interaction/complexation... [Pg.385]

It is likely that one of the major mechanistic requirements for a good enhancer is the ability to induce some sort of motional freedom in the alkyl-chain region of lipid bilayers. Azone appears to be capable of this. These lipid-chain molecular motions may lead to the easier formation of gauche conformers and thus create a greater number of lipid free volumes. Creation of such free volumes has already been associated with greater skin permeability (Potts et al., 1991), and the positive relationship between molecular size of penetrant and rate of permeation is well established. The action of OA may occur in a similar manner but, because of its longer chain, which impedes adjacent lipid chain motion, to a lesser extent. It is likely that the large kink in the OA molecule created by its cis double bond is an important structural feature in its ability to act in this manner (stearic acid seems to condense DPPC monolayers). [Pg.261]

Figure 1. Generalized amphiphilic molecular structure. The lipophilic portion is the long-chain fatty acid stearic acid.

Modifications of LB films, whether caused by the SPM probe or by some other external force, are easily characterized and can provide insight into film structure and -dynamics. With an AFM tip under high force it is possible to maike holes in an LB film. From the image of the hole the thickness per monolayer and number of monolayers can be determined. Virtanen et al. ) induced defect pores in bllayers of stearic acid and cadmium stearate by the application of electric pulses between an STM tip and film surface. Real-time STM images measuring the rates at which these pores refill , provide a means of determining the viscosity of nanometer-scale regions of deposited molecular films. [Pg.385]

To assess the ability of the TC-CCC molecular species, two molecular species of phosphatidylcholine, which were synthesized, were subjected to TC-CCC. Dipalmi-toyl phosphatidylcholine (PC C16 0) and distearoyl phosphatidylcholine (PC C18 0), two of the major molecular species of phosphatidylcholine, were completely separated as shown in Fig. 4. Distearoyl phosphatidylcholine contains 2 mol of esterified stearic acids and dipal-mitoyl phosphatidylcholine contains 2 mol of esterified palmitic acid. The structures of these compounds are shown in Fig. 4. These two compounds were completely separated. This result indicates that the TC-CCC system can separate molecular species in both phospholipids and glycolipids categories. [Pg.936]

Bai and co-workers [163] have investigated hydrogen bonded networks of 5,10,15,20-tetrakis (4-carboxyplienyl)-21H,23H-porphyrin (TCPP) on HOPG with STM. TCPP molecules alone did not lead to an observable molecular substructure, however, when co-adsorbed with stearic acid sub-molecular resolution could be obtained in the domains of the 2-D networks, the structure of which differed from the structure of 3-D bulk crystals of TCPP. [Pg.381]

H hHhHhHhHhHhHhHhH Figure 13.16.2 The molecular structure of stearic acid. [Pg.201]

The lipid membrane is made up of a variety of fat-derived chemicals, the most important of which are the phospholipids (or lecithins) and ceramides. Phosphatidylcholine (13.7) is a typical phospholipid. The molecular structure is based on glycerol, propan-1,2,3-triol. Two of the alcohol functions are esterified with fatty acids, stearic acid in this case, and the third (one of the primary alcohol functions) with phosphoric... [Pg.234]

Another concept that has been used freely and frequently in analyzing the coefficient of friction in lubricated sliding involves the dependence of the shear strength of a monomolecular film of fatty acid on the contact pressure, but no detailed model has ever been advanced to show the relation between shear strength and the molecular structure of the film. Bowers and Zisman [45] wrote the following relation for the "bulk" coefficient of friction of stearic acid ... [Pg.234]

Radioisotopic tracer techniques were applied to study the coadsorption of n-octadecane and stearic acid on a metal surface immersed in a n-octadecane solution of stearic acid. Dual labeling was employed for determining the surface concentrations of both n-octadecane and stearic acid. n-Octadecane was labeled with tritium and stearic acid with carbon-14. The results of half-hour adsorption experiments provide direct proof of coadsorption of polar and nonpolar materials on iron, copper, silver, and platinum surfaces. The films produced on silver and copper by 19-hour adsorption consisted of approximately one molecular layer of stearic acid and two molecular layers of octadecane. A new model is proposed to describe the structure of this thick coadsorbed film. [Pg.268]

From hexadecane solutions, cerotic acid is initially adsorbed in patches or islands, while behenic acid is adsorbed in a network which encloses empty areas or holes stearic acid initially forms molecular groups of about 100-A. diameter which tend to coalesce into filamentlike structures. [Pg.290]

The STM image of stearic acid in Fig. 7.5 indeed shows perfect ordering of alkyl chains over a very large area. More examples of this kind of molecular structures revealed by STM imaging and comparisons with electron structure calculations can be fomid in [2]. [Pg.251]

The interaction between zinc oxide and stearic acid in a medium suitable to simulate a vulcanized system has been investigated [65] experimentally using vibrational spectroscopic technique. Confocal Raman micro spectroscopy revealed that at ambient temperature both components are phase-separated in the form of microcrystals. When the reaction temperature (SO C and above) is reached only zinc oxide is present in the form of particles while the stearic acid melts and gets molecularly dispersed within the rahher matrix. The analysis points to a core-shell structure of the reacting system stearic acid diffuses to the surface of zinc oxide domains causing the shrinkage of the zinc oxide core and the formation of a shell of increasing thickness made of zinc stearate. [Pg.45]

Stearic acid is initially widely used as lubricant in medicine industry [1]. Subsequently, because of its surface activity resulted from amphiphilic molecular structure, stearic acid and its derivatives are also used as solubilizer [2], emulsifier [3], defoamer [4], and the basis of cream [5] or suppository [6]. Its other applications, such as enteric coating material [7], binder agent [8] and some other novel usages [9-11] are also described in this chapter. [Pg.60]

Ye et al. investigated the surface molecular structures of LB films of stearic acid... [Pg.6511]

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