叶酸、二氢叶酸和甲氨蝶呤的酸解离常数。
Acidic dissociation constants of folic acid, dihydrofolic acid, and methotrexate.
作者信息
Poe M
出版信息
J Biol Chem. 1977 Jun 10;252(11):3724-8.
The acidic dissociation constants in the range HO--1.5 to pH 7 of folic acid, dihydrofolic acid, methopterin (N(10)methylfolic acid), and methotrexate have been measured by potentiometric and spectrophotometric titrations. Assignment of these dissociations was made by comparison to model compounds, by proton magnetic resonance measurements, and by examination of associated ultraviolet absorbance changes. For folic acid, the dissociation constants are as follows: N(1), pK' 2.35; N(10), pK' 0.20; N(5), pK' greater than -1.5. For dihydrofolic acid: N(5), pK' 3.84; N(1), pK' 1.38; N(10), pK' 0.28. For methotrexate: N(1), pK' 5.71; gamma-carboxyl, pK' 4.70; alpha-carboxyl, pK' 3.36; N(10), pK' 0.50; N(5), boxyl, pK' 4.70; alpha-carboxyl, pK' 3.36; N(10), pK' 0.50; N(5) pK' greater than -1.5. For methopterin: acidic ionization of amide, pK' 7.68; gamma-carboxyl, pK' 4.62; N(1), pK' 2.40; N(10), pK; 0.36; N(5), pK' greater than -1.5. The pK' values were determined directly for the four compounds at 25 degrees near 0.1 ionic strength, or in 0.1 to 4 M HCl for pK ln 0.1 M NaCl.
通过电位滴定法和分光光度滴定法测量了叶酸、二氢叶酸、甲氨蝶呤（N(10)甲基叶酸）和氨甲蝶呤在pH值为1.5至7范围内的酸解离常数。通过与模型化合物比较、质子磁共振测量以及对相关紫外吸收变化的检查来确定这些解离情况。对于叶酸，解离常数如下：N(1)，pK' 2.35；N(10)，pK' 0.20；N(5)，pK'大于 -1.5。对于二氢叶酸：N(5)，pK' 3.84；N(1)，pK' 1.38；N(10)，pK' 0.28。对于氨甲蝶呤：N(1)，pK' 5.71；γ - 羧基，pK' 4.70；α - 羧基，pK' 3.36；N(10)，pK' 0.50；N(5)羧基，pK' 4.70；α - 羧基，pK' 3.36；N(10)，pK' 0.50；N(5)，pK'大于 -1.5。对于甲氨蝶呤：酰胺的酸电离，pK' 7.68；γ - 羧基，pK' 4.62；N(1)，pK' 2.40；N(10)，pK；0.36；N(5)，pK'大于 -1.5。在25摄氏度、离子强度接近0.1的条件下直接测定了这四种化合物的pK'值，对于pK ln 0.1 M NaCl，是在0.1至4 M HCl中测定的。
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