Monolayer of myristic acid

When a monolayer of myristic acid spread on 0.01N HC1 was used over the same pressure range (5 dynes/cm), the change in pressure on compression and expansion was independent of the position of the wet-table blade from the moving barrier. 

By way of example. Table 7.1 presents values of qic le t>nd Alc le the LC —> LE transition in monolayers of myristic acid, (CH3 - (CH2)i5 - COOH), at the air/ water interface. The main conclusions from these data are that heat is required to disrupt energetically favorable interactions between the surfactant molecules when releasing th from the condensed state. This is accompanied by an increased entropy of the monolayer. Furthermore, the tanperature dependence of q, at con-... 

Heat and Entropy Changes Involved in the LC -> LE Transition in Monolayers of Myristic Acid at the Air/Water Interface... 

Monolayer phase sequences are temperature dependent. For chain lengths greater than that of pentadecanoic acid, the LE phase will not be observed at room temperature. For chain lengths shorter than myristic acid (C14), condensed phases will not be observed at... 

Fig. 14. Surface area dependences of surface pressure and frequency maximum of the CH2 asymmetric band for (a) crystalline stearic acid monolayer and (b) amorphous myristic acid monolayer.

Figure 1. Mixed monolayers of cholesterol- myristic acid system at 23.5°C. and pH 2...

Hydrocarbon-Hydrocarbon Interaction. Figure 5c shows the general characteristics of mixed monolayers in which hydrocarbon-hydrocarbon interaction occurs—e.g., trimyristin-myristic acid monolayers (16). The average area per molecule shows a deviation, whereas the surface potential per molecule follows the additivity rule. Hydrocarbon-hydrocarbon interaction also increases the cohesive force in the lipid layer and therefore reduces the fluidity of the mixed monolayer. It is evident from Figures 3a and 3c that surface fluidity is the only parameter which distinguishes an intermolecular cavity effect from hydrocarbon-hydrocarbon interaction. 

The AV-A relationships for fatty acid monolayers were first investigated over a wide range of pH by Schulman and Hughes (49), who found that for myristic acid (Ci4) films over substrates of pH 0 to 13, AV decreased with pH HC1 or NaOH was added to vary pH. Similar results were reported for stearic acid films over substrates whose pH was varied from 2 to 10 with HC1 and NH4OH (48), and over substrates ranging from pH 2 to 12, containing 0.01M sodium ions (5, 18, 20, 53). 

A mixed monolayer consisting of stearic acid (9.9%), palmitic acid (36.8%), myristic acid (3.8%), oleic acid (33.1%), linoleic acid (12.5%), and palmitoleic acid (3.6%) produces an expanded area/pressure isotherm on which Azone has no apparent effect in terms of either expansion or compressibility (Schuckler and Lee, 1991). Squeeze-out of Azone from such films was not reported, but the surface pressures measured were not high enough for this to occur. The addition of cholesterol (to produce a 50 50 mixture) to this type of fatty acid monolayer results in a reduction of compressibility. However, the addition of ceramide has a much smaller condensing effect on the combined fatty acids (ratio 55 45), and the combination of all three components (free fatty acids/cholesterol/ceramide, 31 31 38) produces a liquid condensed film of moderate compressibility. The condensed nature of this film therefore results primarily from the presence of the membrane-stiffening cholesterol. In the presence of only small quantities of Azone (X = 0.025), the mixed film becomes liquid expanded in nature, and there is also evidence of Azone squeeze-out at approximately 32 mN m. ... 

The phase behavior of octadecanoic (stearic) acid/ tetradecanoic (myristic) acid/" and PDA has been examined by fluorescence microscopy. The observations are similar the most complete measurements have been carried out on PDA. Figure 10 shows the progression of images when a PDA monolayer doped with a fluorescent probe is studied at 25°C. 

The compression or decompression of bovine serum albumin monolayers spread on an aqueous substrate at a pH near the isoelectric point can effect surface tension. The surface pressure changes depend on the distance between the position of the surface pressure measuring device and the compression barrier. This effect is minimal at a pH above or below the isoelectric point and undetected for small molecules (myristic acid and eicosyl sodium sulfate) even when the substrate contains substituted alkyl amines. A theory is proposed which attributes the above observation to surface drag viscosity or the dragging of a substantial amount of substrate with the BSA monolayer. This assertion has been experimentally confirmed by measuring the amount of water dragged per monolayer using the technique of surface distillation. 

The phase change from condensed to expanded monolayer can occur in a number of ways (e.g., by increasing the temperature, increasing the degree of unsaturation in a molecule, or decreasing its hydrocarbon chain length). The unsaturated linoleic acid (18 2) and the short chain myristic acid (14 0) both depress loaf volume. De Stefanis and Ponte (1976) demonstrated that linoleic acid was the component of nonpolar lipid that contributes to deleterious effects on loaf volume and that palmitic acid had no negative effect. 

The equation of state of a gas shows that under suitable conditions gaseous and condensed states may coexist. When hydrogen gas dissolves in palladium, dilute and condensed phases may exist in equilibrium (67), or when a film of myristic, palmitic, or similar fatty acids is spread upon water, compressed and expanded states can occur together at suitable temperature or pH. of the imderlying liquid (58). It is therefore interesting to inquire whether two phases can occur on stable monolayers on tungsten. 

The transfer of phosphatidylcholine from monolayer to vesicles catalyzed by phosphatidylcholine transfer protein shows remarlcable differences for the positional isomers (23). The PC transfer protein acts as a specific carrier of PC between membrane interfaces. This protein has a recognition site for the phosphorylcholine headgroup and binding sites for the sn-1 and sn-2 fatty acyl chain. Lysophosphatidylcholine is not transferred. It was found that the protein transferred C10 0/C18 l PC twice as fast as C18 l/C10 0 PC. Similar differences in rate were observed for C12 0/C18 l PC and C18 l/C12 0 PC but not for isomers carrying myristic acid (Table I). 

It is, therefore, clearly concluded from Figures 9-11 that in the case of conventional fatty acids such as myristic, palmitic, stearic and so on, the crystalline or amorphous phase of monolayer completely depends on the relative magnitude of Tsp to Tm of the monolayer, being independent of the magnitude of surface pressure. The fatty acid monolayers do not show any pressure-induced crystallization during compression of the monolayer on the water surface. The crystalline and amorphous monolayers are schematically summarized in Figure 12. 

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