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The effect of solute ionization on the retention of weak acids, bases, and ampholytes on octadecylsllica was investlgated both theoretically and experimentally. The retention was attributed l o a reversible association of the solutes with the hydrocarbonaceous ligand of the stationary phase. A phenomenological treatment of the Corresponding equilibria was developed for various types of lonogenic substances. The energetics of the assoclatlon process was analyzed In a rlgorous fashion in the light of the solvophobic theory and a semi-empirical extension of the Debye-Huckel theory to hlgh ionic strength. The predlcted effect of solute loniratlon on the capacity factors was substantiated by experimental data. The observed dependence of the capacity factors on the lonlc strength of the eluent and the hydrophoblc surface of the solute molecules showed good agreement with the theory. The advantages of the technique in the separatlon of biological substances are illustrated.The great majority of biological substances contain ionogenic functions such as carboxylic or amino groups. In most instances, ion exchange chromatography has been the method of choice for the separation of such compounds having similar chemical structure (1,2). Recent developments in high performance liquid chromatography, however, have demonstrated that columns packed with a nonpolar stationary phase, such as octadecylsilica, are also eminently suitable for the separation of weak acids and bases ( 3 ) .Most effort has been focused on the use of "reversed phase" chromatography with eluents containing anionic or cationic surfactants in hydroorganic solvent mixtures; the technique is frequently called "ion-pair" (4, 5 ) or "soap" (6) chromatography. Recently it has been demonstrated (7) that octadecylsilica columns with neat aqueous eluents, which do not contain organic solvents, can also be successfully employed for the separation of polar organic compounds.We have shown ( 3 ) that the physicochemical phenomena underlying the chromatographic process with nonpolar stationary phases can be readily interpreted in the light of the "solvophobic theory" (8-15) and the factors determining solute retention are amenable to an exact theoretical treatment. In this study, the theory is extended to account for the effect of solute ionization on chromatographic retention, both phenomenologically and by a rigorous treatment of the interaction between ionic solutes and the eluent. THEORYThe chromatographic process is viewed as a reversible association of the solute, s, with the hydrocarbonaceous ligand, L, such as an octadecyl function covalently bound to the surface of the stationary phase:The equilibrium constant for the association, KaSSOC, is given by It is assumed that the equilibrium constant of the process with both neutral and ionized solutes is solely determined by solvophobic interactions ( 3 ) , that is, no ionic or hydrogen bonding occurs between the solute and the stationary phase.In this section, we first will present a phenomenological treatment of the...

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For more than 50 years the identity of "calorigen," the agent that triggers pronounced heat production in the flowers and inflorescences of some thermogenic plants, remained obscure. Mass spectroscopic analysis of highly purified calorigen extracted from the male flowers of Sauromatum guttatum Schott (voodoo lily) revealed the presence of 2-hydroxybenzoic (salicylic) acid. Application of salicylic acid at 0.13 microgram per gram (fresh weight) to sections of the upper part of the plant's immature spadix, known as the appendix, led to temperature increases of as much as 12 Celsius degrees. These increases duplicated, in both magnitude and timing, the temperature increases produced by the crude calorigen extract. The sensitivity of appendix tissue to salicylic acid increases daily with the approach of anthesis and is controlled by the photoperiod. Thus, at least in some Arum lilies, salicylic acid functions as an endogenous regulator of heat production.

We have recently purified calorigen, the natural trigger for heat production in the inflorescences of Sauromatum guttatum Schott (voodoo lily), a thermogenic plant, and identified it as salicylic acid. Since then an analytical assay was developed that allows the quantitation of salicylic acid in plant tissues. This assay was used to demonstrate that on the day preceding the day of blooming the levels of salicylic acid in the thermogenic organs (appendix and lower spadix) of the voodoo lily increased almost 100-fold, reaching a level of 1 ,ug/g of fresh weight. The level of salicylic acid in the appendix started to rise in the afternoon and reached its maximum in the late evening, whereas the maximum accumulation of salicylic acid in the lower spadix occurred late at night. The increase in salicylic acid level in the appendix was followed the next morning by a spectacular metabolic burst that lasted for about 7 hr and at its peak increased the appendix temperature by over 12°C. The second, 14-hr-long, thermogenic episode in the lower spadix started late at night and ended on the following morning, after maximum temperature increases of more than 100C. The concentration of salicylic acid in both thermogenic tissues promptly returned to basal, preblooming levels at the end of the thermogenic periods. The thermogenic response was under strong photoperiodic and developmental control, with salicylic acid eliciting much stronger thermogenic responses in light than in darkness. Similar surges in salicylic acid occurred in nonthermogenic male and female flowers, while the concentration of salicylic acid in the spathe remained consistently below 20 ng/g of fresh weight. Of 33 analogs of salicylic acid tested, only 2,6-dihydroxybenzoic acid and acetylsalicylic acid (aspirin) were thermogenic. The activity of 2,6-dihydroxybenzoic acid exceeded that of salicylic acid.

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