Stability constants of the ternary copper(II) complexes with 2-(benzo(d)oxazol-2-yl)nicotinic acid and some amino acids

Figures & data

Figure 1. (A) Structure of 2,2′-bipyridine. (B) Structure of 2-(benzo[d]oxazol-2-yl) nicotinic acid.

Table 1. Reported stability constants of the hydroxo complexes of Cu(II) at 25 °C and KNO₃ 1 M as ionic medium [23].

Species	logβ
[Cu(OH)]^+	−7.71(4)
[Cu2(OH)2]^2+	10.99(2)
[Cu3(OH)4]^2+	21.6(3)

Table 2. Reported stability constants of the binary complexes formed in the systems Cu(II)–HSer, Cu(II)–HMet, Cu(II)–HPhe and Cu(II)–HThr at 25 °C and KNO₃ 1 M as ionic medium [23].

Species	HSer log β	HMet log β	HThr log β	HPhe log β
[CuL]^+	−0.4(1)	−1.0(3)	−0.8(2)	−1.3(2)
Cu2(OH)L	−6.4(1)	−6.2(2)	−5.6(1)	–
[CuHL2]^+	1.4(4)	2.3(1)	1.8(2)	2.02(5)
CuL2	−2.9(1)	−3.1(1)	−3.0(1)	−2.45(4)

Table 3. Reported stability constants of the binary complexes formed in the systems Cu(II)–H₂Asp, Cu(II)–H₂Glu and Cu(II)–HHis at 25 °C and KNO₃ 1 M as ionic medium [23].

Species	H2Asp log β	H2Glu log β	HHis log β
[CuH2L]^2+	1.5(3)	2.37(5)	–
[CuHL]^+	−0.65(4)	−0.37(2)	–
CuL	−4.56(3)	−4.43(2)	–
[Cu(OH)L]^–	−11.75(6)	−11.18(4)	–
CuH2L2	−2.6(4)	−21.76(7)	–
[CuHL2]^–	−5.80(7)	−6.35(9)	–
[CuL2]^2–	−10.67(5)	−11.30(4)	–
[CuL]^+	–	–	1.10(4)
Cu(OH)L	–	–	−3.74(4)
[Cu(OH)2L]^–	–	–	−11.45(6)
CuL2	–	–	1.18(4)
[Cu(OH)L2]^–	–	–	−5.01(6)

Table 4. Reported stability constants of the binary complexes formed in the system Cu(II)– HOxa at 25 °C and KNO₃ 1 M as ionic medium [20].

Species	H2Asp log β
[CuL]^+	9.0(2)
CuL2	15.33(6)
[CuL3]^–	16.6 max 17.3
Cu(OH)L	2.5(1)
[Cu(OH)2L]^–	−6.66(3)
[Cu2(OH)2L2]^–	7.8(1)

Table 5. Ternary species with corresponding formation constants for the H⁺-Cu(II)-L-Ser, H⁺-Cu(II)-L-Thr, H⁺-Cu(II)-L-Met and H⁺-Cu(II)-L-Phe systems at KNO₃ 1.0 M and 25 °C.

Compound	Log β Ser	Log β Thr	Log β Met	Log β Phe
[Cu(L)(HA)]^+	30.22(6) 25.15*	30.50(6) 24.0*	30.88(6) 25.19*	29.9(1) 25.02*
[Cu(L)(A)]	24.75(4) 19.93*	24.00(6) 19.7*	23.91(4) 20.25*	24.69(5) 21.55*
[Cu(L)(A)(OH)]^–	15.6(1) 11.55*	14.8(7) 13.11*	14.59(4) 12.72*	14.57(6) 12.8*
[Cu(L)2(A)]^–	28.6(3)	28.8(1)	28.1(1)	29.6(1)
[Cu(L)(A)2]^–	28.0(2)	27.1(9)	–	–
Dispersion (σ)	0.075	0.086	0.064	0.077

Note. The values with the superindex * correspond to the formation constants of the compounds reported in the reference [25] at KNO₃ 1.0 M and 25 °C. Values in parentheses represent 3 times the standard deviations [3σ (log₁₀ β)] on the last significant figure. These uncertainties are from the merging of replicate measurements independently fitted.

Table 6. Ternary species with corresponding formation constants for the H⁺-Cu(II)-L-Asp, H⁺-Cu(II)-L-Glu and H⁺-Cu(II)-L-His systems at KNO₃ 1.0 M and 25 °C.

Compound	Log β Asp	Log β Glu	Log β His
[Cu(L)(HA)]	26.6(6) 24.57*	25.4(1) 24.17*	–
[Cu(L)(A)]^–	21.06(5) 19.88*	19.73(6) 19.18*	–
[Cu(L)(A)(OH)]^2–	13.33(6)	10.72(6)	–
[Cu(L)(HA)]^+	–	–	25.79(9) 26.52*
[Cu(L)(A)]	–	–	20.66(4) 20.8*
[Cu(L)(A)(OH)]^–	–	–	14.22(4) 14.2*
[Cu(L)(A)(OH)2]^2–	–	–	6.38(5) 4.6*
Dispersion (σ)	0.077	0.057	0.071

Note. The values with the superindex * correspond to the formation constants of the compounds reported in the reference [25] at KNO₃ 1.0 M and 25 °C. Values in parentheses represent 3 times the standard deviations [3σ (log₁₀ β)] on the last significant figure. These uncertainties are from the merging of replicate measurements independently fitted.

Figure 2. Z_B versus pH data for the system Cu(II)-L-His.

Figure 3. Species distribution diagram for the systems: (A) Cu(II)-L-His, (B) Cu(II)-L-Ser and (C) Cu(II)-L-Glu[Cu(II)] = 3.0 mM, R = 1:1:1.

Table 7. Δlog K and log χ values calculated for the system studied.

System	Δlog K	log χ
Cu(II)-L-Ser	7.29	19.35
Cu(II)-L-Thr	6.99	18.05
Cu(II)-L-Met	7.01	17.69
Cu(II)-L-Phe	7.94	18.4
Cu(II)-L-Asp	3.24	10.7
Cu(II)-L-Glu	1.4	7.91
Cu(II)-L-His	1.5	6.69

Figure 4. UV–vis spectra at different pH values of the systems: (A) Cu(II)-L-His, (B) Cu(II)-L-Ser and (C) Cu(II)-L-Glu.

L. Hernández, E. Del Carpio, W. Madden, G. Lubes, A. Perez, R.E. Rodríguez-Lugo, V.R. Landaeta, M.L. Araujo, J. Daniel Martínez, V. Lubes. Phys. Chem. Liq., 58, 31 (2020).

 Web of Science ®Google Scholar

N. Urdaneta, W. Madden, V.R. Landaeta, R. Rodríguez-Lugo, L. Hernández, V. Lubes. J. Mol. Liq., 227, 218 (2017).

 Web of Science ®Google Scholar

N. Urdaneta, E. Infante, V.R. Landaeta, R. Rodríguez-Lugo, L. Hernández, M.L. Araujo, V. Lubes. Phys. Chem. Liq., 60, 616 (2022).

 Web of Science ®Google Scholar

Availability of data and materials

Not applicable.