Hydrophilic-lipophilic balance lipids

Lipids with a suitable hydrophilic-lipophilic balance (HLB) are known to spread on the surface of water to form monolayer films. It is obvious that if the lipid-like molecule is highly soluble in water, it will disappear into the bulk phase (as observed for SDS). Thus, the criteria for a monolayer formation are that it exhibits very low solubility in water. The alkyl part of the lipid points away from the water surface. The polar group is attracted to the water molecules and is inside this phase at the surface. This means that the solid crystal, when placed on the surface of water, is in equilibrium with the him spread on the surface. A detailed analysis of this equilibrium has been given in the literature (Gaines, 1966 Adamson and Gast, 1997 Birdi, 2009). The thermodynamics allows one to obtain extensive physical data on this system. It is thus apparent that, by studying only one monolayer of the substance, the effect of temperature can be very evident. 

Different factors govern the formation of these molecular compounds. Where lipids and related substances are concerned the governing factor is the realization of the best hydrophilic-lipophilic balance producing hydration or dispersion. The case of lecithin and sodium cholate associated in the presence of water may be used to illustrate the conditions of association and formation of different types of structure and of micelles. 

Recently, a new class of inhibitors (nonionic polymer surfactants) was identified as promising agents for drug formulations. These compounds are two- or three-block copolymers arranged in a linear ABA or AB structure. The A block is a hydrophilic polyethylene oxide) chain. The B block can be a hydrophobic lipid (in copolymers BRIJs, MYRJs, Tritons, Tweens, and Chremophor) or a poly(propylene oxide) chain (in copolymers Pluronics [BASF Corp., N.J., USA] and CRL-1606). Pluronic block copolymers with various numbers of hydrophilic EO (,n) and hydrophobic PO (in) units are characterized by distinct hydrophilic-lipophilic balance (HLB). Due to their amphiphilic character these copolymers display surfactant properties including ability to interact with hydrophobic surfaces and biological membranes. In aqueous solutions with concentrations above the CMC, these copolymers self-assemble into micelles. 

Anthocyanins are generally more stable at an acidic pH. Therefore, anthocyanins are commonly extracted under cold conditions using either acidic methanol or ethanol to avoid degradation1 5169 (Table 3.4). In comparison, acetone allows more reproducible extraction and avoids problems with pectins. However, it is limited by the coextraction of proanthocyanins.39 In general, ethanol is preferable as an extraction solvent, although it can require an additional step for the removal of lipid-soluble substances. SPE using Ci8, polyamide, HLB (hydrophilic lipophilic balanced stationary phases), or Amberlite has been employed for the purification of anthocyanidins prior to HPLC analysis.39-51 66 69... 

The hydrophile-lipophile balance is related to the solubility of a surfactant. At high HLB the surfactant is very water soluble while at low HLB the surfactant is very lipid soluble. Because HLB is solubility related, it is in turn related to the partition coefficient (or ratio of the solubility of the surfactant in a lipid phase to its solubility in an aqueous phase). A high HLB value suggests a low oil/water partition coefficient, and conversely a low HLB shows a high partition coefficient. Hence, an optimum surfactant HLB for enhancing biological activity also implies an optimum partition coefficient for activity enhancement. 

HLB stands for hydrophile-lipophile balance. Surfactants with a low HLB are more lipid loving and thus tend to make a water-in-oil emulsion while those with a high HLB are more hydrophilic and tend to make an oil-in-water emulsion. The HLB number of a mixture composed of x% of surfactants of HLB A and y% of surfactants of HLB B is obtained by the following formula... 

C for varying periods of time. Clearly the slope of decomposition is reduced as the pH is raised. The stability of hyper-molar urea solution is considerably increased by absorbing the solution into a polysaccharide particle. This particle can then be suspended in a continuous lipid phase with the correct incorporation of surfactants with a hydrophile/lipophile balance value suitable to maintain an aqueous-in lipid, continuous phase. The result of this is a compartmentalized system where the urea is in a more stabilized state and the polysaccharide has been altered in its hydrophobic/lipophilic properties to become what might be termed an ambiphilic matrix. 

Tissue blood PCs indicate the relative affinity of compounds for the various tissues of the body compared to blood. The values are determined by the relative lipophilic/hydrophilic nature of the compound and relative affinity for the macromolecules found in tissue and blood. Each individual tissue will make up a specific balance of water, neutral lipid, phospholipid, and protein. Partitioning therefore is determined by the relative affinity of the compound for the specific tissue constituents. 

The best lcx al anesthetic action is obtained when the lipophilic and hydrophilic centers arc in balance, if the hydrophilic center is the dominant structure, the anesthetic action uf the drug is weak, since its membrane penetration is poor. Similarly, if the lipophilic center is the dominant structure, local anesthetic action is again poor, in this ca.se. the agent can penetrate the lipid membrane of the axon, but its solubility in both extracellular and intracellular fluids is poor. 

The word surfactant is an acronym for surface-active agents. It stands for molecules that tend to adsorb at interfaces when they are in solution. The molecular structure of surfactants is characterized by a polar group connected to a typically long nonpolar hydrocarbon chain. The polar group, frequently referred to as the head of the molecule, is also known as the hydrophilic group because it is compatible with water (hydro). The nonpolar part, frequently referred to as the tail of the molecule, is also known as the hydrophobic (water hating) or lipophilic group because it is compatible with lipids. The relative size of (balance between) the hydrophilic to the lipophilic (frequently abbreviated and known as HLB) determines whether a surfactant will be predominantly water soluble or oil soluble. 

As mentioned earlier, the balance between the hydrophilic and lipophilic (HLB) portions of a surfactant determines whether it will be predominantly water soluble or predominantly oil (lipid) soluble. As the tail or hydrophobic portion gets larger and/or the hydrophilic portion gets smaller or less polar, the solubility of a surfactant in water decreases while its solubility in oil increases. Conversely, decreasing the chain length and/or increasing the size or polarity of the polar group increases the solubility of a surfactant in water. 

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