Vitamin C Analysis - Vitamin C Analysis1 Authors B K Kramer...

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Vitamin C Analysis 1 Authors: B. K. Kramer, V. M. Pultz and J. M. McCormick* Last Update: January 13, 2006 Introduction Vitamins are a group of small molecular compounds that are essential nutrients in many multi-cellular organisms, and humans in particular. The name “vitamin” is a contraction of “vital amine”, and came about because many of the first vitamins to be discovered were members of this class of organic compounds. And although many of the subsequently discovered vitamins were not amines, the name was retained. In this exercise you will be studying vitamin C, also known as ascorbic acid. Figure 1. Structure of vitamin C (ascorbic acid). Ascorbic acid (C 6 H 8 O 6 ) is a water-soluble vitamin, whose structure is shown in Fig. 1. Vitamin C is easily oxidized, and the majority of its functions in vivo rely on this property. It plays a key role in the body’s synthesis of collagen and norepinephrine by keeping the enzymes responsible for these processes in their active reduced form. 2 Vitamin C may also play a role in detoxifying by-products of respiration. Occasionally during respiration O 2 is incompletely reduced to superoxide ion (O 2 - ) instead of being reduced completely to its -2 oxidation state (as in H 2 O). Normally an enzyme called superoxide dismutase converts O 2 - to H 2 O 2 and O 2 , but in the presence of Fe 2+ the hydrogen peroxide may be converted into the highly-reactive hydroxyl radical (•OH). The hydroxyl radical can initiate unwanted and deleterious chemistry within a cell when it removes a hydrogen atom (H•) from an organic compound to form H 2 O and a new, potential more reactive free radical. Ascorbic acid can donate a hydrogen atom to a free radical, and thus stop these reactions from occuring. 2 The human body cannot produce ascorbic acid, and so it must be obtained entirely through one’s diet. A vitamin C deficiency in humans results in the disease called scurvy, whose symptoms include hemorrhaging (especially in the gums), joint pain and exhaustion. 2 In its final stages scurvy is characterized by a profound exhaustion, diarrhea, and then pulmonary and kidney failure, which result in death. 3 A very small daily intake of vitamin C (10-15 mg/day for an adult) is required to avoid deficiency and stave off scurvy. 4 However, there has been, and continues to be, vigorous debate on what the optimum daily intake of vitamin C is. Some have argued that 200 mg/day is an
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optimal daily intake for adult humans. Others have suggested 1-2 g/day is best, 3 this despite studies that show that the blood is saturated with vitamin C at 100 mg/day, and any excess is excreted in the urine. In an attempt to balance the competing claims, and ensure the general population’s good health, the Federal Food and Drug Administration has adopted a the recommended dietary allowance (RDA) of 60 mg/day for adults (aged 15 or older), less for children, and more for pregnant and lactating women. 2 Fruits, vegetables, and organ meats (e.g., liver and kidney) are generally the best
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