Thermodynamic study of the complexation reactions for a series of amino acids related to serine with copper(II) and nickel(II)

Abstract

The thermodynamic parameters for the complexation reactions of serine, threonine, homoserine, isoserine, 4-amino-3-hydroxybutyric acid, and /3-aminobutyric acid with copper(II) and nickel(II) in aqueous solution at 25°and µ = 0.16 are reported. Values for the formation constants were obtained from potentiometric titrations and enthalpy values determined calorimetrically. The -amino acids studied, as well as /3-aminobutyric acid, were postulated to form the typical amino-carboxyl chelates with copper(II) and nickel(II). The formation of a sixmembered chelate ring was found to be less favorable thermodynamically than the formation of a five-membered chelate ring for both copper(II) and nickel(II) complexes. The thermodynamic data seem to indicate the formation of a chelate ring involving the amino and hydroxy groups of the isoserine with the copper(II). The isoserine ligand was postulated to be functioning as either a bidentate or tridentate ligand with copper(II).It has been shown that for a number of aliphatic amino acids the formation of copper(II) complexes proceeds in a stepwise manner to form the mono and bis copper(II) species.2 These complexes are formed by the elimination of a proton from the zwitterion form of 1 and 2 moles of amino acid, respectively. Chelation occurs between the carboxyl and amino groups of the amino acid and the copper(II) ion. The formation of nickel(II) complexes with aliphatic amino acids proceeds in the same manner, except that a third mole of amino acid can be chelated to the nickel(II) ion to form the tris nickel(II) species. In the case of amino acids interacting with copper(II) there seems to be some dis-agreement3-5 as to whether or not the amino acid zwitterion can function as a monodentate ligand. Recent studies of the interaction of copper(II) with gly-(1) Based on the dissertation of J. E. Letter submitted to the Graduate

Thermodynamics of proton dissociations from aqueous threonine and isoleucine at temperatures from (278.15 to 393.15)K, molalities from (0.01 to 1.0)mol·kg−1, and at the pressure 0.35MPa: Apparent molar heat capacities and apparent molar volumes of zwitterionic, protonated cationic, and deprotonated anionic forms

“…Reference values used for integration constants in this report for threonine at T * = 298.15 are pQ a = (2.26 ± 0.20) [26][27][28][29][36][37][38][39][40][41]43,44] and D r H m = (3.7 5 ± 2.0) kJ AE mol À1 [25][26][27][28][29] for reaction (5), and pQ a = (9.16 ± 0.36) [26][27][28][29][35][36][37][38][39][40][41][43][44][45] and D r H m = (41.51 ± 0.49) kJ AE mol À1 [25][26][27][28][29][33][34][35] for reaction (6). Reference values used for isoleucine at T * = 298.15 are pQ a = (2.345 ± 0.093) [29][30][31][32]36,37] and D r H m = (0.97 9 ± 0.51) kJ AE mol À1 [24,…”

“…We found no results in the literature for D r C p,m for reaction (5) or (6) for threonine. Figure 8 shows D r H m (T, m) for reactions (5) and (6) together with values from the literature [24][25][26][27][28][29][30][31][32][33][34][35]. The differences between our values of D r H m (T, m) for reaction (5) (4) for apparent molar heat capacities C p,/ (T, m) of {HThr ± (aq)}, {HThr ± (aq) + HCl(aq)}, {HThr ± (aq) + NaO-H(aq)}, {H 2 Thr + Cl À (aq)}, and {Na + Thr À (aq)} and those from the literature are in the range D = (À2.20 [25,29] to 1.94 [27]) kJ AE mol À1 with an average difference D = 0.25 kJ AE mol À1 for aqueous threonine, and those differences are D = (À1.81 [31] to 0.52 [31]) kJ AE mol À1 with FIGURE 2.…”

“…The differences between our D r H m (T, m) for reaction (6) and values from the literature are in the range D = (À0.92 [26] to 0.73 [34]) kJ AE mol À1 with an average difference D = À0.15 kJ AE mol À1 for aqueous threonine, and those differences are D = (À2.03 [31] to 0.69 [29,33]) kJ AE mol À1 with an average difference D = À0.49 kJ AE mol À1 for aqueous isoleucine. Figure 9 shows pQ a (T, m) for reactions (5) and (6) and values from the literature [26][27][28][29][30][31][32][35][36][37][38][39][40][41][42][43][44][45]. Our values of pQ a (T, m) for reaction (5) differ from the literature values by D = (À0.20 [26] to 0.45 [37]) with an average difference D = À0.052 for aqueous threonine, and those differences are D = (À0.17 [30,32] to 0.13 [32]) with an average difference D = À0.013 for aqueous isoleucine.…”

Critical evaluation of the stability constants of metal complexes of amino acids with polar side chains (Technical Report)

“…It is also the case for nickel, although to a lesser extent (70LB,72GM,72GMa). Unfortunately, no such comparison is possible for zinc(II).…”

Theoretical Investigation of Linker Effects on New Designed Bodipy-Ferrocene Based Three Channels Calcium (II) Ion Sensors; as Redox, Colorimetric and Fluorescent Properties

“…The contact of the positive metal ion with the ligand donor atoms results in an effective charge neutralization and a positive entropy of association [14]. ΔS value is negative for formation of 1-Ca, 2-Ca and 3-Ca.…”