The Mechanism of Chromatographic Retention - Chromatographic Interactions > Ionic Interactions > Page 17

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 dispersive interactions between the fatty acid alkane chains, separated from the lye and, consequently, was calledlyophobic. Itfollows, thatlyophobic, is synonymous to "hydrophobic", and thus lyophobic interactions are dispersive. The other product from soap-making is glycerol, which, being strongly polar, remained in the lye and was consequently termed lyophilic. Glycerol is very polar because of its many hydroxyl groups and is completely miscible with water and, hence, is a hydrophilic or lyophilic substance. These alternative terms appear somewhat impertinent and confusing to the physical chemist and perhaps should be avoided by those not involved in the biological sciences. Nevertheless, they are extensively employed in biotechnology to describe the interactive character of a molecule and so their meaning must be understood. Their use becomes more understandable when the need for a term that describes, not merely a particular molecular interaction, but one that can summarize the overall character of a biopolymer, for example a polypeptide is required. A peptide contains a large number of different amino acids, each having quite different interactive groups. All the carbonyl and amide groups will exhibit polar interactions but each amino acid will also contribute its own unique interactive character to the peptide. The diagrams in Figure 7 endeavor to illustrate the interactive character of a hydrophobic polypeptide.