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polar and ionic groups in their total structure and thus the overall interactive character may be largely ionic, dispersive or polar depending on the distribution of the different interactive groups. It follows, that terms are required to describe the overall interactive property of a molecule as opposed to the interactive character of its specific groups. Virtually, by default, the most common terms that have been established to describe molecular interactive character are hydrophobic and hydrophilic. A hydrophobic substance is predominantly dispersive in character and� a hydrophilic substance is predominantly polar in character. Two other terms are less commonly used for the same purpose and they are lyophobic and lyophilic which are synonymous to hydrophobic and hydrophilic. The terms have a rather obscure origin and are not based on physical chemical considerations, but have evolved, somewhat arbitrarily, from the discipline of biology. Nevertheless, they are of great

thus called "lyophobic". It follows that "lyophobic", from a physical chemical point of view, would be the same as "hydrophobic", and interactions between hydrophobic and lyophobic materials are dominantly dispersive. The other product of the soap-making industry was glycerol, which remained in the lye and was consequently termed "lyophilic". Thus, glycerol mixes with water because of its many hydroxyl groups and is very polar and hence is a "hydrophilic" or "lyophilic" substance. Hydrophobic and hydrophilic terms are extensively employed in biotechnology to describe the interactive character of the molecule as a whole. The use of a more general term to describe the interactive property of a biomolecule can be understood if one considers the character of a biopolymer, for example a polypeptide. The peptide will contain a large number of different types of amino acids, each having different interactive

, and n-heptane has a small but finite solubility in water. Although water-water interactions and hydrocarbon-hydrocarbon interactions are much stronger than water-hydrocarbon interactions, the latter does exist and is sufficiently strong to allow mutual solubility. The term "hydrophilic force", literally meaning "love of water" force, appears to merely be the complement to "hydrophobic". It is equivalent to the term polar, and polar solvents are hydrophilic solvents because they interact strongly with water or other polar solvents

The origin of the terms lyophobic (meaning fear of lye) and lyophilic (meaning love of lye) to describe interactive forces is very obscure and, in fact, is a product of the distant past. Essentially, these terms are alternatives for terms hydrophobic and hydrophilic, and, as such, might be considered somewhat irrelevant. These terms stemmed from the early days of the soap industry when soap was prepared by boiling a vegetable oil with an alkaline solution obtained from leaching wood ash with water. The alkaline product from the wood ash was a crude solution of sodium and potassium carbonates called lye. The result of boiling vegetable oil with the lye was the soap (sodium and potassium salts of long-chained fatty acids) which, due to the

of a pair of hydrocarbon molecules gaining sufficient energyto part is equal to the statistical probability of a hydrocarbon molecule colliding with a water molecule and interacting. The probability of an interacting hydrocarbon pair gaining sufficient energy to part is very small, so the saturated concentration of heptane in water (which determines the probability of collision) must also be small. Consequently, the mutual solubility of water and hydrocarbons must be very low. The term hydrophilic, meaning "love of water", is the complement to hydrophobic and is equivalent to the term polar, thus, substances that interact strongly with water (i.e., are relatively soluble) are called hydrophilic substances

nbsp; The arginine also provides potential ionic interactions with the free amine group. The overall character of the heptapeptide is, therefor, polar, and thus the peptide would be described as hydrophilic or lyophilic in nature. As already stated, hydrophilic and hydrophobic are terms� used to describe the overall interactive character of a large molecule as opposed to the individual group interactions. Nevertheless they are basically alternative terms that have been adopted to describe the polar and dispersive interactive character of a molecule respectively. Mixed Phases The interactive mechanism involved in mixed phases has been the subject of much controversy and, to some