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Lesson 21 Isolation of an Alkaloid: Caffeine Tea and coffee are popular beverages [] 饮料 known from antiquity [] 古代. Both are rich in caffeine [],a central nervous system (CNS), respiratory [ i] 呼吸的, and cardiac [] 强心剂; 心脏的 stimulant [] 刺激物. Caffeine is also a diuretic [] 利尿剂; 利尿的 agent (tending to increase urine []尿 production) and can produce nervousness 神经过敏, insomnia [] 失眠, and racing heartbeat (tachycardia [] 心 动过速). Heavy consumption [] 消费 can lead toa caffeine dependence such that headache and even nausea [] 恶心 can be experienced without it. Caffeine is one of the alkaloids [] 生物碱, which are basic nitrogen-pounds found in certain plant materials. Structurally, it is 1,3,7-trimethylxanthine []. It is also a derivative of purine [] and is therefore related to the purine bases in nucleic [] 核的 acids and to uric [] acid. Two closely pounds are the dimethylxanthines, theophylline [] 茶碱, which occurs along with caffeine in tea, and theobromine [] 可可碱, which occurs instead of caffeine in cocoa [] 可可豆. HNNH N HN NN N HN O O HNNH NH HN O O O Xanthine Purine Uric acid [] 黄嘌呤[] 嘌呤, 咖啡碱[] 尿酸 The caffeine content [] 含量 of coffee beans is about 1% ~ 2% by weight and in tea leaves is about 2%-4%. Because of differences in methods of brewing [] 酿造 brew up[俗] 泡茶, however, an average cup of coffee contains about twice as much caffeine asa cup of tea (100 mg versus 50 mg). C ola nuts [] 可乐果