Solution equilibria of complex formation between caffeic acid, dihydrocaffeic acid and divalent metal ions

• Main Authors: Nguyen Thi Dieu Thuy, 阮妙翠
• Other Authors: Yi-Hsu Ju
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/52211824435701487927

碩士 === 國立臺灣科技大學 === 化學工程系 === 103 === The solution equilibria between chelating agents (caffeic acid – CA or dihydrocaffeic acid – DCA) and several divalent metal ions (Cu2+, Zn2+, Ni2+, Co2+ and Mn2+) in binary and ternary systems were investigated in this work. The potentiometric measurement was carried out at 37oC and ionic strength 0.15 mol.dm-3 NaCl in order to determine the protonation and formation constants of complexes. The complexation model and speciation diagram were established by computer programs Hyperquad2008 and HySS, respectively. Moreover, UV – Vis spectrophotometry was performed to explore the reliable protonation constants of these ligands and qualitatively confirm the complex formation. In both binary and ternary systems, the stability constant values of formed metal – chelator complexes decrease in the following order: Cu2+ > Zn2+ > Ni2+ > Co2+ > Mn2+. The complex formation between metal ion and DCA system is more stable than metal ion and CA system. In addition, the tendency of complex in the ternary system was revealed and evaluated by calculating the relative stability constant ( ) and the disproportionate constant (log X). Besides, at physiological pH, the sequestering ability of CA and DCA followed the order pL0.5 (Cu2+) > pL0.5 (Zn2+) > pL0.5 (Ni2+) > pL0.5 (Co2+)> pL0.5 (Mn2+).