Complexing agents, caffeine

Where the complexing agent is phenolic, the pH must be such that the phenol is undissociated usually such complexes form at a pH below 6. Free caffeine concentrations are increased above pH 6.14... 

Fig. 9 Phase solubility diagram showing the changes in the apparent aqueous solubility of p-aminobenzoic acid (PABA) brought about by the addition of the complexing agent, caffeine, at 30°C. (The data are adapted from Ref. 51.)...

These results show that losses of PAHs from static solutions to surfaces occur in short periods of time. The use of caffeine as a PAH complexing agent (32) reduces these losses but does not eliminate them (see Table VI). Stirring the solutions causes only small reductions in these losses. The PAH losses shown in Table VI for stirred solutions are less than those reported in Table V for static solutions. 

The presence of complexing agents (pyridine, hexamethylbenzene, durene, caffeine, cytosine, acenaphthene) influences the reaction rate. The effect is relatively small 10%) on account of the very unfavourable experimental conditions (e.g. low solubility). 

Complexation. It has been well established in the literature that complexation is an effective way to solubilize hydrophobic compounds. Nicotinimide is known to complex with aromatic drugs through tt donor-7r acceptor interaction (101). Similar tt-tt interaction also occurs between salts of benzoic acid or salicylic acid and drugs containing aromatic rings such as caffeine (102).Obviously, aromaticity is an important factor in this type of complexation. Unfortunately, from a safety perspective the use of these types of complex-ing agents for products is not really very viable. 

Nicotinamide, or vitamin B3, characterized by a low toxicity, has been proven to solubilize a number of drugs, such as, for example, riboflavin (35) and nifedipine (36). A 36-fold increase of the solubility of riboflavin, which has a multi-aromatic ring system, at nicotinamide concentrations of about 2M, has been observed (35). It has been shown that complexation occurs between the riboflavin and the hydrotropic agents cytosine and caffeine, respectively (35). However, in the case of nicotinamide, no evidence for complexation between riboflavin and nicotinamide. 

Impregnating agents that are able to form charge transfer complexes. An example is the HPTLC precoated plate silica gel 60 impregnated with caffeine, which has been introduced in 1994. 

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