Novák-Pékli M, el-Hadi Mesbah M, Pethó G
Semmelweis University of Medicine, Department of Pharmaceutical Chemistry, Budapest, Hungary.
J Pharm Biomed Anal. 1996 Jun;14(8-10):1025-9. doi: 10.1016/s0731-7085(96)01734-7.
Protonation and equilibrium constant for oxytetracycline (OTC) and doxycycline (DOX) with Zn2+, Ca2+ and Mg2+ ions have been determined with Calvin-type pH-metric titrations under physiological conditions (37 degrees C, 0.15 M NaCl ionic strength). Even though OTC and DOX are similar in structure, major differences were found in complex composition with regard to the protonation state: OTC generally formed species with less protons compared to those with DOX. Studies of parent complexes were followed by investigations of ternary complexes where ascorbic acid was used as a secondary ligand. Again, OTC showed a tendency to form complexes in which fewer protons are bound than in those with DOX. This equilibrium difference between OTC and DOX might be because DOX has a better pharmacodynamic effect relative to that of OTC.
在生理条件（37摄氏度，0.15M氯化钠离子强度）下，通过卡尔文型pH滴定法测定了土霉素（OTC）和强力霉素（DOX）与锌离子、钙离子和镁离子的质子化作用及平衡常数。尽管OTC和DOX结构相似，但在质子化状态的配合物组成方面发现了主要差异：与DOX相比，OTC通常形成含质子较少的物种。在对母体配合物进行研究之后，又对以抗坏血酸作为第二配体的三元配合物展开了研究。同样，与DOX相比，OTC显示出形成结合较少质子的配合物的倾向。OTC和DOX之间的这种平衡差异可能是因为DOX相对于OTC具有更好的药效学作用。
