Water-fearing

Hydrophobic (Section 2.13) Water-fearing repelled by water. 

The one and only distinctive feature of lipids is that they are all totally hydrophobic (water fearing), or nearly so. They generally will not chemically interact with water and therefore will not dissolve in water. Chemically, lipids fit into several categories, each of which is structurally unique. Common types of lipids include triacylglycerols, phospholipids, and steroids. 

Triacylglycerols are very hydrophobic, while the liquid in blood (plasma) is mostly water and is therefore very hydrophilic. Hydrophobic molecules literally are water fearing or water hating. 

Several models have been suggested for the estimation of the distribution ratios of nonionic solutes between water and (practically) immiscible organic solvents. One model takes 1-octanol to represent, in general, lipophilic ( fat-liking ) media, which hydrophobic ( water-fearing ) solutes would prefer over water. Such media may be oils, biological lipid membranes, and, somewhat less suitably, hydrocarbon solvents. 

A special group of lipids that possess both hydrophilic and hydrophobic (lipophilic) parts are termed as amphiphiles or amphipathics and are also referred to as surfactants. They adsorb at surfaces or interfaces and change the interfacial free energy associated with the building of an interface. A surfactant molecule consists of two distinct chemical groups (i) the head which is hydrophilic (water-loving) and (ii) the tail which is hydrophobic (water-fearing). 

Hydrogen bonds and ionic, hydrophobic (Greek, water-fearing ), and van der Waals interactions are individually weak, but collectively they have a very significant influence on the three-dimensional structures of proteins, nucleic acids, polysaccharides, and membrane lipids. 

The thermodynamic and structural processes that occur when water molecules are in the vicinity of hydrophobic entities (water fearing, insoluble in water) are referred to collectively as hydrophobic hydration (Tanford, 1973 Privalov and Gill, 1988 Blokzijl andEngberts, 1993 Chau and Mancera, 1999). Hydrophobic hydration is important in gas hydrate formation, which usually starts with hydrophobic gas molecules (e.g., methane) being introduced into liquid water. 

Hydrophobic Compounds that are water fearing. Hydrophobic compounds do not dissolve easily in water and are usually nonpolar. Oils and other long hydrocarbons are hydrophobic. 

Generally, the introduction of apolar molecules (such as hydrocarbons or noble gases), or apolar residues in otherwise polar molecules (such as alkyl side chains in biopolymers) into water leads to a reduction of the degrees of freedom (spatial, orientational, dynamic) of the neighbouring water molecules. This effect is called the hydro-phobic effect or hydrophobic hydration [176], Hydrophobic means water-fearing . It should be noted that the interaction between hydrophobic molecules and water molecules is actually attractive because of the dispersion interactions. However, the water/ water interaction is much more attractive. Water molecules simply love themselves too much to let some other compounds get in the way [26b] Therefore, from the point of view of the water molecules, the term hydrophobic is rather a misnomer it would be better to refer to water as being lipophobic . 

Hydrophobic. "Water fearing". Hydrophobic compounds do not dissolve easily in water, and are usually non-polar. Oils and other long hydrocarbons are hydrophobic.or Preferring not to be in contact with water, as is the case with the hydrocarbon portion of a fatty acid or phospholipid chain. 

The ability to determine fat content in foods is vital. Fortunately, it is also routine. Since fats are insoluble in water (hydrophobic, which literally means water fearing ), they may be separated fairly easily from the other components of a food sample via a simple extraction with a hydrophobic solvent such as ether. The procedure generates very accurate data. A word of caution, however. Ether is highly flammable and volatile and, therefore, must be handled with extreme caution to avoid contact with open flames. For procedural details, refer to Procedure 65, Fat Extraction and Determination in the Manual of Food Analysis. 

Objective 9 Organic compounds are often polar in one part of their structure and nonpolar in another part. The polar section, which is attracted to water, is called hydrophilic (literally, water loving ), and the nonpolar part of the molecule, which is not expected to he attracted to water, is called hydrophobic ( water fearing ). If we need to predict the relative water solubility of two similar molecules, we can expect the one with the proportionally larger polar portion to have higher water solubility. We predia that the molecule with the proportionally larger nonpolar portion will be less soluble in water. 

Hydrophobic ( water fearing ) A nonpolar molecule (or a portion of a molecule or polyatomic ion) that is not expected to mix with water. 

Hydrophilic. Water-liking. (12.8) Hydrophobic. Water-fearing. (12.8) Hypothesis. A tentative explanation for a set of observations. (1.3)... 

The side chains of some amino acids are nonpolar. They prefer contact with one another over contact with water and are said to be hydrophobic ("water-fearing") amino acids. They are generally found buried in the interior of proteins, where they can associate with one another and remain isolated from water. Nine amino acids fall into this category alanine, valine, leucine, isoleucine, proline, glycine, methionine, phenylalanine, and tryptophan. The R group of proline is unique it is actually bonded to the a-amino group, forming a secondary amine. 

Molecules and surfaces are often qualitatively categorized as either hydrophilic (water-loving) or hydrophobic (water-fearing). Surface active agents or surfactants have both characteristics. One end of a simple surfactant is hydrophilic, the polar or ionic head group. The rest of the molecule is the hydrophobic tail, such as an oily hydrocarbon. Having very dissimilar parts in solution attracts the molecule to surfaces, as in detergency. 

The basic structure of all soaps is essentially the same, consisting of a long hydrophobic (water-fearing) hydrocarbon tail and a hydrophific (water-loving) anionic head ... 

Hydrocarbons, which are nonpolar and nonionic and cannot form hydrogen bonds, show only limited solubility in water. However, energy is not the only consideration. When such hydrophobic ("water fearing") molecules do dissolve, they do not form hydration shells as hydrophilic substances do. Instead, the regular water lattice forms icelike clathrate structures, or "cages," about nonpolar molecules (Figure 2.13). 

---