. The Biochemistry of B vitamins. Vitamins; Vitamin B complex. p-AMINOBENZOIC ACID 507 the cell of the organism which has a buffering capacity presumably in the same pH range. The molecular and ionized forms of ^-substituted sulfonamides are also indicated in Figure 8. From the standpoint of geo- metrical considerations, the p-aminobenzenesulfonyl group and the p-aminobenzoate ion are very similar, the bond distances differing only slightly, as indicated in Figure 8. Sulfones likewise are similar to the p-aminobenzoate ion. A. H H H / \ / N 1 N 1 () c |< A-»| y-Aminobenzoate ion Fig
. The Biochemistry of B vitamins. Vitamins; Vitamin B complex. p-AMINOBENZOIC ACID 507 the cell of the organism which has a buffering capacity presumably in the same pH range. The molecular and ionized forms of ^-substituted sulfonamides are also indicated in Figure 8. From the standpoint of geo- metrical considerations, the p-aminobenzenesulfonyl group and the p-aminobenzoate ion are very similar, the bond distances differing only slightly, as indicated in Figure 8. Sulfones likewise are similar to the p-aminobenzoate ion. A. H H H / \ / N 1 N 1 () c |< A-»| y-Aminobenzoate ion Figure 8 N / \l t S / \ o „ o I-*— A-»| Sulfonamide. Sulfonamide ion The Structures of the p-Aminobenzoate Ion and Molecular and Ionic Forms of Sulfonamides. If the substituent group, R, of the ^-substituted sulfonamide func- tions solely in affecting the combining power of the p-aminobenzenesul- fonyl group with the enzyme and the substituent within itself does not possess groups which aid in this combining power, the activity of the sulfonamide will depend upon the effect of the substituent group on the combining power of the reactive groups, presumably the basic amino group and the S02 group. Since only slight variations occur in the ioniza- tion constants for the basic amino group of the ^-substituted sulfon- amides, differences in combining power of these sulfonamides with the inhibited enzyme cannot be attributed to the reactivity of the basic amino group, and no relationship between the bacteriostatic activity and these constants has been noted for these analogues. However, this may become an important consideration for other analogues. The acid dissociation constants of ^-substituted sulfonamides vary over a wide range, indicating that the properties of the sulfonamide group are influenced greatly by the N1 substituent. Since the p-aminobenzoate ion possesses an electronic charge which greatly increases the negative character of the C02" group, Bell and Robli
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