Caffeine derivatives, separation

Figure 18-7. Effect of temperature on the separation of caffeine derivatives on a Hypercarb column (1 mm x 100mm). (a) Column at 100°C, mobile phase acetonitrile (b) Colnmn at 180°C, mobile phase water/acetonitrile 70/30. Samples 1, hypoxantine 2, theobromine 3. theophylline 4, caffeine 5, P-hydroxyethyltheophylline. (Reproduced from reference 35, with permission.)...

Separation methods, multichromato-graphic la 56 Serine la 246,356 lb 132 Serotonin la 70,76,239,240,262,355, 380 lb 37-39,231,243,348 Serotonin metabolites lb 327 Serum lipids la 89 Serum proteins la 74 Sesquiterpene derivatives lb 239,446 Sesquiterpene esters lb 239 Sesquiterpene glucosides la 327 Sesquiterpene lactones lb 448 Sevin lb 387-389 Si 50 000, specific surface area la 91 Silica gel, caffeine-impregnated la 85 -, surface modified la 3 Silica gel 60, specific surface area la 91... 

Caffeine (Fig. 11.3), widely used by humans as a stimulatory drug, has so far been detected only in a few plant species. The biological roles of caffeine are believed to be in defense against herbivory or as an allelopathic response to potential competitors.83 Caffeine is derived from the purine alkaloid xanthosine. From xanthosine, three methylations are necessary to produce caffeine. First, xanthosine is methylated on N7 by 7-methylxanthosine synthase (MXS or 7NMT) to produce 7-methylxanthosine, which is enzymatically hydrolyzed to produce 7-methylxanthine and ribose.85,86 The methylations of N1 and N3 of 7-methylxanthine to produce 1,3,7-trimethylxanthine (caffeine) occur in young leaves of tea, and the same enzyme, caffeine synthase, apparently catalyzes both reactions.55 In coffee plants, caffeine is mainly found in the beans but also occurs in the leaves. Caffeine is stored in the vacuoles of coffee leaves as a complex with polyphenols such as chlorogenic acid.87 In contrast to tea, coffee plants appear to have separate enzymes for each step of N-methylation.57... 

Several authors have included one or more naturally occurring xanthine derivatives (caffeine, theobromine and theophylline) in their gas chromatographic separation of alkaloids. Lloyd et al.1 used a packed column with SE-30 on Chromosorb VI, so did Brochmann-Hanssen and... 

The first systematic investigation on the gas chromatographic separation of xanthine de-rivatives was published by Reisch and Walker. The naturally occurring xanthines, caffeine, theobromine and theophylline, as well as a number of derivatives, were gas chromatographed on an 1.5 % packed SE-30 column on Chromosorb W. In Table 20.1 the compounds are given and and in Figure 20.1 typical gas chromatograms. 

Fig. 11.1. Separation of some xanthine derivatives Column pBondapak C18 (300x4 rim ID), mobile phase acetonitrile - 0.01 M sodium acetate buffer (pH 4.0) (7 93), flow rate 2.0 ml/min, detection UV 254 nm. Peaks 1, 1-methyluric acid 2, 3-methyl xanthine 3, 1,3-dimethyl-uric acid 4, theobromine 5, theophylline 6, B-hydroxy-ethyltheophylline 7, phenobarbital 8, caffeine 9, 8--chlorotheophyl1ine. (reproduced with permission from ref. 56, by the courtesy of Clinical Chemistry)...

The first uses of micellar phases by Armstrong were done in GPC and thin layer chromatography (TLC). This was described in Chapter 3. TLCwas a useful tool for the determination of solute partition data in micellar systems. The micellar partition coefficient, Pv, the solute-stationary phase interaction coefficient, P s, and the micellar binding constant, Kd, could be obtained from the solute-Rf parameters with an equation very similar to eq. 13.5 [22]. A number of solutes were separated by micellar TLC such as phenols and dyes [22], indicators, caffeine, biphenyl, naphthol and benzamide [23], PAHs and amino acids [24], vitamins [25] or fluorescein derivatives [26]. The low cost, low toxicity, peculiar selectivity and ease of... 

Some examples of successful commercial selective extractions are the removal of caffeine from coffee or the solubilization of nicotine from tobacco both accomplished on moist matrices to aid in selectively solubilizing the alkaloid component. Selective extraction has been demonstrated for the segregation of essential oil from other lipid components in natural extracts derived from fruits and for the separation of aroma components in cocoa butter from the base oil. Other enrichment SEE schemes that have been reported include the fractionation of carotenoid from leaf protein concentrate [25], the fortification of sterols in seed oils [26], and the isolation of lecithin (phospholipid-containing fraction) from triglycerides [27]. 

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