The stability constants for Al(III)-Gallic acid (GA), Al(III)-acid methyl ester (GAME) and Fe(III)-Maltol have been measured potentiometrically. The β values were obtained by the treatment of potentiometric titration data into the computer program “BEST” Al(III)-GA formed 1:2, Al(III)-GAME formed 1:3 and 1:3 and Fe(III)-Maltol formed 1:3 complexes with high stability constants. The β2 value for Al(III)-GA is 29.52, β3 value for Al(III) –GAME is 39.63 and β3 value for FE(III)-Maltol is 28-.2.
The redox potential values of the for the Fe(III)-Maltol complex were determined by spectrophotometric titration with ascorbate are 0.2295V at pH 3.0,0.1436V, 0.1436V at pH 4.0, 0.1066V at pH 5.0 and 0.0442V at pH7.0
The reduction of Fe(III)-Maltol by ascorbate were performed at pH 3.03,3.5,4.0,4.5,5.0,5.5 and 6.0. The rqt law for this reduction is Rate=kobsd[FeIII(Mal)3]; and kobsd=[kr k1[H4] +k4 /k2[Hmal]+Kr [Asc]][Asc], where kr is the rate constants for the reduction of bis Fe(III)-maltol complex and its values are 8.2x103 M-1S-1 at pH 3.0; 6.9x103 M-1S-1at pH 3.5; 6.6x103 M-1S-1 at pH 4.0; 3.8x103 M-1S-1at pH 4.5; 2.5x102 M-1S-1at pH 5.0; 2.0x102 M-1S-1at pH 5.5 and K4 is the rate constants for the reduction of tris complex and the value are 14.5 M-1S-1 at pH 3.0,; 17.4M-1S-1 at pH 3.5; 17.8 M-1S-1 at pH 4.0; 18.0 M-1S-1at pH 4.5; 18.9 M-1S-1at pH 5.5 and 27.2 M-1S-1. The ΔH” values for the ascorbate reduction of bis complex are 102.14KJmo-1 at pH 4.0, 100.57 KJmol-1 at pH 4.5, 97.90 KJmol-1pH 5.0 and the ΔS” values are 154.22 KJmol-1 deg-1 a pH 3.5, 127.21 KJmol-1deg-1at pH 4.0, 144.90 KJmol-1deg-1at pH 4.5 and 131.44 KJmol-1deg-1 at pH 5.0.
The ΔH” values for the reduction of tris complex are 94.48 KJmol-1 at pH 4.0, 95.29 KJmol-1 at pH 4.5, 96.88 KJmol-1at pH 5.0 and the ΔS” values are 88.99 KJmol-1 at pH 4.0, 92.04 KJmol-1deg-1 at pH 4.5 and 97.94 KJmol-1 deg-1 at pH 5.0.
The reduction kinetics with dithionite were determined at 20oC, 25oC, 30oC and 35oC in the pH of 5.0, 5.4, 5.8 nad 7.4. The results conform to the rate law: Rate=kobsd [FeIII(mal)3], where kobsd=[k2 k1K1/2[S2O4 2-]1/2/k-2 [H4]+k2K1/2 [S2O4 2-]1/2] the k1 values at pH 5.8 are at pH 5.0. The k1 values at pH 5.4 are 1.60,2.13,2.53 and 2.62; the k1 values at pH5.8 are 1.53, 2.08,2.44 and 2.66 and at pH 7.4,1.11,2.17 and 2.8. These values at 20oC 25oC, 30oC and 35oC respectively. The k2/k-1values at pH 5.0 are 5.77, 6.73,7.99 and 13.21 at pH 5.4 the values are 5.29, 4.74,4.48 and 7.56, at pH 5.8 the values 1.15,1.01,1.39 and 1.975 and at pH 7.4 the values are 0.0166,0.011,0.01 and 0.013 at 20oC, 25oC, 30oC and 35oC respectively.
Kinetics of reduction with glutathione were also performed and it was observed that at high concentration of glutathione the rate constants did not increase linearly. The results were fitted to the rate law; Rate=kobsd [FeIII(mal)3], where kobsd=[Kket [GSH]/1+K[GSH]]the relevant K values are 90 M-1, 70 M-1, 60 M-1, 40 M-1, 10 M-1 at pH 3.5,4.0,4.5,5.0 and 5.5 respectively and the ket value for this electron transfer reaction is 0.000 S-1