Nonpolar substances, definition

When looking for a suitable solvent one should proceed according to basic experience, according to which a definitely nonpolar substance (for example, a hydrocarbon) is best soluble in nonpolar solvents (for... 

Surface-active materials consist of molecules containing both polar and nonpolar portions, i.e., amphiphilic molecules. The proteins are typically amphiphilic, polymeric substances made of amino acid residues combined in definite sequences by peptide bonds (primary structure). In many cases polypeptide chains are present in helical or /3-sheet configuration (secondary structure) which are stabilized by intramolecular (S-S and hydrogen) bonding. The next structural level, the tertiary structure, is determined by the folding of the polypeptide chains to more or less compact globules, maintained by hy-... 

If it is possible to use a solution for recording the spectrum of a substance, there are definite advantages to be had by doing so. It is easiest to interpret a spectrum when the molecule is in the simplest, least complicated, and most reproducible environment. With such conditions established, one can more facilely make useful correlations between vibrational frequencies and molecular structure. The best way to maintain materials in similar and simple surroundings is to dissolve them in dilute solutions in an inert nonpolar solvent. 

Petunia leaves are typically coated with a sticky exudate, and it was of interest to determine if this exudate contained any of the insect-inhibitory steroids. We subjected fresh leaves to an initial five minute soak in water followed by a one minute dip in chloroform with gentle agitation. This chloroform extract contained nonpolar surface lipids and substances tentatively identified as carbohydrate esters (ca 1 % of fresh wt.), but no biologically active materials were shown to be present by HPLC analysis. Further workup of the solvent-washed leaves by grinding with additional chloroform then yielded the usual quantities of active materials, showing that the insect-inhibitory components were definitely neither part of the exudate nor of the leaf surface coating. 

Phospholipids. Lipid is a term applied to those natural substances that are more soluble in nonpolar solvents than in water. In its most general sense, it is a broad definition that includes fats, waxes, hydrocarbons, and so on. In biochemistry, lipids are more narrowly defined as substances that yield fatty acids upon hydrolysis. 

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