keywords: Carbonatotetraamine, Nd(III), Sm(III), Gd(III); Antimicrobial studies
Carbonatotetraamine complexes of Sm(III), Nd(III) and Gd(III) were synthesized at room temperature. The complexes were characterized by molar conductivity, colour, solubility test and spectrometrically(IR and UV-Vis). The kinetics of complex formation were studied by determining the amount of complex formed with time at different temperatures. The graph of semi-log of yield in mole against time of the various complexes were plotted to obtain the observed rate constants (kobs) which were used to plot lnkobs versus 1/T to obtained activation energy (Ea). Thermodynamics parameters were obtained from plots of ln(kobs/T) versus 1/T and antimicrobial activities of the ligand and its complexes were tested using Agar-well diffusion techniques for zone of inhibition while Agar-dilution techniques was used for minimum inhibitory concentration and bactericidal or fungicidal concentration. The solubility results showed complexes were slightly soluble in formaline, phenylhydrazine and dichloromethyl while the complexes had molar conductivity of 2.7 – 5.6 µS which implied their non-electrolytic nature. The UV spectra suggested octahedral geometries for the complexes. The complexes formed where of the general formula ML where L is the ligand and M is the respective Ln3+ metal ions and the activation energy (Ea) obtained were 24.743, 8.913 and 29.706 kJ for Nd(III), Sm(III) and Gd(III) Complexes which were positive Ea indicating that, the rate of formation increased with increasing temperature. The kinetic results showed that increase in time and temperature increases the yield of the complexes. The results of thermodynamics parameters showed that; the Gibbs free energy change (ΔGo) of the complexes were -334.370, -293.250 and -344.600 kJmol-1 which proved the formation of the complexes were spontaneous, the enthalpy change (ΔHo) were -21.915,-1.464 and -27.054 kJmol-1 for Nd(III), Sm(III) and Gd(III) respectively showing the enthalpy is the driving force for the formation of the complexes. However the positive result of the entropy change (ΔSo) which were 1.031, 0.963 and 1.048 kJmol-1, respectively suggest that entropy was responsible for the complexation process. All the complexes were found to inhibit the growth of E. coli, S. aureus, S. typhi, A. niger, T. rubrum and Candida albicansin the order of SM>Gd>Nd. The complexes displayed higher inhibition zones on the bacteria strains than the fungi strains. The MIC confirmed that the complexes will be more effective against the studied bacterial infections. The complexes were bactericidal and fungicidal showing that they could serve as raw materials for synthesis of new drugs.