Niacin chemical structure

FIGURE 3.7 Chemical structure of B-vitamins found in cereal grains, (a) Thiamine, (b) Riboflavin, (c) Pyridoxine. (d) Niacin, (e) Folic acid. 

Vitamins are chemicals that are necessary in trace amounts for normal body function. They are not produced in sufficient amounts by the body and must come from externa food sources. Their structures, like their diffuse locations in Biochemistryland, are generally diverse and unrelated, as shown in figures 9.1 and 9.2. Molecules that contain (or are) vitamins are indicated in green rectangles on the Biochem-isiryland map. There are actually many more loci on the map that contain vitamins, but which have not been included, to avoid cluttering the map. In particular, NADH (which contains niacin) has not been drawn in at many steps. 

Most vitamins function either as a hormone/ chemical messenger (cholecalciferol), structural component in some metabolic process (pantothenic acid), or a coenzyme (phytonadi-one, thiamine, riboflavin, niacin, pyridoxine, biotin, folic acid, cyanocobalamin). At least one vitamin has more than one biochemical role. Vitamin A as an aldehyde (retinal) is a structural component of the visual pigment rhodopsin and, in its acid form (retinoic acid), is a regulator of cell differentiation. The precise biochemical functions of ascorbic acid and a-tocopherol still are not well defined. 

Elucidation of the structure of the B vitamins resxilted in the development of analytical chemical methods. Such methods are useful in industries manufacturing vitamins in which measurements of microgram to milligram quantities are routine, but these same methods are often not applicable to biological fiuids that contain as little as picogram quantities. Colorimetric and fluorometric techniques have been developed for niacin and folate, but these techniques require complicated extraction procedures and blank determinations. They also suflFer from lack of specificity, and the results are often altered by interference from biologically inactive materials that occur naturally or are produced during extraction (16,20). 

Figure A6.1 Structures of three of the vitamin-derived cofactors. NAD, like several other cofactors, has a handle consisting of adenine (blue) and ribose phosphate (black), but the actual chemistry of oxidation and reduction is done by the nicotinamide (red), which is derived from the vitamin nicotinic add or niacin. Note the positive charge on the ring nitrogen in the oxidised form, NAD+, which is shown here. Pyridoxal phosphate, derived from vitamin carries out its chemical contribution via the aldehyde group (mauve). Biotin likewise contributes its own characteristic chemistry, with the nitrogen atom, shown in blue, readily able to pick up CO2 as a carboxyl group.

Two compounds, nicotinic acid and nicotinamide, have the biological activity of niacin. When nicotinic acid was discovered to be a curative and preventive factor for pellagra, it was already known as a chemical compound, and was therefore never assigned a number among the B vitamins. The name niacin was coined in the USA when it was decided to enrich maize meal with the vitamin to prevent pellagra - it was considered that the name nicotinic acid was not desirable because of the similarity to nicotine. In USA, the term niacin is commonly used to mean specifically nicotinic acid, and nicotinamide is known as niacinamide elsewhere niacin is used as a generic descriptor for both vitamers. Figure 2.16 shows the structures of nicotinic acid, niacin and the nicotinamide nucleotide coenzymes, NAD and NADE... 

Niacin and niacinamide (also known as nicotinic acid and nicotinamide, respectively) or vitamin B3, chemically 3-pyridinecarboxylic acid and 3-pyridinecarboxamide, are able to form various cadmium complexes with known crystal and molecular structures. In order to rationalize the analysis, hereafter the complexes have been differentiated according to the ligand and, within each case, we have only considered the most relevant structures. 

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