|MadSci Network: Biochemistry|
To answer somewhat in reverse order. Caffeine is a methylxanthine, found in coffee, tea, chocolate and some other foods. These also have the related theobromine and a few have theophylline. The latter, usually as a salt, aminophylline, is used as a prescription drug, usually for asthma and sometime other breathing difficulties. Theophylline is the most potent followed by caffeine followed by theobromine. (Potency refers not to how much effect it has but to the concentration required to elicit a given effect, thus it takes less theophylline than caffeine to relieve breathing difficulties in an asthmatic, but caffeine would also do the trick, just take more of it.) 1. Caffeine can be tested for in the urine, though one would generally test for metabolites of it since they would be more common. The tests require instrumentation like gas or liquid chromatographs however. To my knowledge there is no simple colorimetric reaction that would be specific for caffeine or its metabolites, or for the related theobromine found in chocolate and tea. 2. Re precipitation tests, if you mean for Ca2+, then there are colorimetric tests for Ca2+, but the concentration in urine would generally be too small and other, more sophisticated tests would be needed. If you mean precipitation for caffeine, see answer 1. 3. Caffeine cannot itself directly leach Ca2+ from bone in a chemical sense. As a drug, caffeine has a weak action to release stored intracellular Ca2+ into the cytosol of most if not all cells so that some (but not all) Ca2+ might (or might not) be released into the general circulation and thus eventually find its way to the urine. The effect on bone would be extremely minor and probably not measureable in terms of Ca2+ loss. There are far stronger influences on bone Ca2+ than caffeine. Put another way, I wouldn't worry about whether a couple of cups of coffee will give me osteoporosis or brittle bones. 4. Caffeine is a methylxanthine and is metabolized by the liver by demethylation to 1,7-dimethylxanthine (paraxanthine) to 1-methylxanthine and by oxidation to 1-methyluric acid. Acetylation also occurs and it is these latter compounds that are found in the urine rather than caffeine itself. Theophylline is metabolized somewhat similarly.
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