Determination of binding constants and molecular dynamics of the complex system when different ions are added into the Schiff bases

In this study, T1 and T2 relaxation times of five different Schiff base ligands 1- N,N ? -Bis(salicylic)-1,2-diamino ethane, 2- N,N ? -Bis(salicylic)-1,3-diamino propane, 3- N,N¢-Bis(salicylic)-1,7-diamino heptane, 4- N,N ? -Bis(salicylic)-1,8-diamino oktane and 5- N,N ? -Bis(salicylic)-1,9-diamino nonane were studied in terms of temperature in the range of 20 ? 50oC by a 400 MHz NMR spectrometer. Furthermore, T1 relaxation times of the complexes formed by adding different ions (nickel acetate, cobalt acetate and zinc acetate) on these Schiff base ligands were measured in the range of 25 ? 40 oC so that their binding constants, molecular dynamics and ion-dipole interactions were investigated.The experimental studies were carried out in two stages. In the first stage, T1 and T2 relaxation times of the Schiff bases were measured at various temperatures without adding any ions. Activation energies (Ea) and correlation times (?c) of the ligands were calculated by using these relaxation times. Motion kinds of molecules and interaction types were determined using calculated Ea and ?c values.In the second stage, T1 relaxation times of each complexation formed when different ions were added onto different Schiff bases were measured at various temperatures. Their Ea and ?c values were determined by the help of these relaxation times. Then, binding constants (Kf) and free energy (?G) values of the complexations were calculated. Furthermore, how each ion affects chemical shifts were found, interaction and motion types were determined from ion-dipole interactions.By the help of Ea and ?c values it was guessed that Schiff base ligands do molecular tumbling motion. It was determined that dipole-dipole interaction is the dominant interaction type is in ligands and complexations since relaxation times increase with increase in temperature. In addition, because of the fast exchange, it was found that complex molecules do molecular tumbling motion.