Complexes of Vitamin B<sub>6</sub>. 23. Interaction of Some Tertiary Ligating Amino Acids with the Binary Complexes of Ni(II) or Cu(II) and Pyridoxamine

Speciation diagrams and stability constants for glutamate (Glu) with (Cr 3þ ) and (Cu 2þ ) in aqueous solutions are presented. The current study covers a larger pH-range affording accurate results, and reveal a different set of species for Cu 2þ and species not previously reported for Cr 3þ . For the Cu 2þ : Glu system, the most successful model that refined the potentiometric data contains the simple one-to-one complex, the bis-complex and the mono-hydroxo complex. The overall stability constants for Cu 2þ -Glu complexes have respective values of log 110 ¼ 7.6 AE 0.2, log 11-1 ¼ 1.3 AE 0.7, log 120 ¼ 13.6 AE 0.2. Attempts to refine the stability constant for the mono-protonated metal complex (log 111 ) that was reported in the literature indicated that this mono-protonated species did not form to an appreciable amount to be important for the model presented here. For the Cr 3þ : Glu system, the overall stability constants for the complexes formed have the values of log 110 ¼ 8.34 AE 0.03, log 11-1 ¼ 1.9 AE 0.1 and log 11-2 ¼ À4.6 AE 0.1. These results for Cr 3þ system covers wider pH-range and have more accuracy than those reported previously. The NMR experiments for Glu revealed downfield shifts of all protons as pH values decrease from 11.21 to 2.85.

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“…Others [46] also suggested the presence of the Cu 2þ -hydroxo species shown in equation (8), further confirming our proposed speciation diagrams.…”

supporting

confidence: 87%

Equilibrium models of Cr³⁺ and Cu²⁺ with glutamate

Hamada

Holyfield

Rosli

et al. 2009

Journal of Coordination Chemistry

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“…A detailed literature survey indicated that the proposed binding mode of Asp to Cr 3+ is supported by the literature data [8,33,[35][36][37][38]. The bis-complex has the proposed structure shown in scheme 2 due to the following reasons: (1) The coordination sphere of the chromium ion is satisfied with six-donor atoms (MN 2 O 4 ), which is well documented in the literature [34][35][36], (2) the stability constants for both the simple one-to-one and the bis-complex have such high values indicating neither a mono-nor a bi-dentate nature; it must be tri-dentate [8,25,26], and (3) such structures have been seen with other metal ions, Cu 2+ and Co 3+ .…”

Section: Resultsmentioning

confidence: 66%

“…The bis-complex has the proposed structure shown in scheme 2 due to the following reasons: (1) The coordination sphere of the chromium ion is satisfied with six-donor atoms (MN 2 O 4 ), which is well documented in the literature [34][35][36], (2) the stability constants for both the simple one-to-one and the bis-complex have such high values indicating neither a mono-nor a bi-dentate nature; it must be tri-dentate [8,25,26], and (3) such structures have been seen with other metal ions, Cu 2+ and Co 3+ . Distribution diagrams clearly showed that the biscomplex is the dominant species at the physiological pH value.…”

Section: Resultsmentioning

confidence: 84%

Reactions of Cr³⁺ with aspartic acid within a wide pH range

et al. 2014

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Formation of the metal complexes of aspartic acid (Asp) with the chromium metal ion (Cr 3+ ) in solutions using potentiometric titrations is presented within a wide pH range (∼3.5 to ∼10.5) at 25 • C and I = 0.10 M NaNO 3 . Concentration distribution diagrams revealed that the main complex formed within this pH range is the bis Cr 3+ complex. Literature stability constant values for the Cr-Asp complexes were used to construct concentration distribution diagrams. Complexes taken into consideration were the simple one-to-one complex, the bis-complex, and the bis-mono-protonated complex, namely, Cr-Asp, Cr(Asp) 2 , and Cr(Asp) 2 H. The corresponding Log β values of these complexes were 12.46, 21.86, and 24.30, respectively. UV-Vis spectra demonstrate Cr 3+ -Asp binding. The UV-Vis spectra were collected from a system that reached a high level of equilibrium state (50 days' equilibrium time).

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“…A survey of the literature data revealed that most of the relevant studies provide the stability constants for only two Cu 2+ complexes with aspartic acid: CuAsp and Various protonated species (CuHAsp + , CuH 2 Asp 2+ , and CuH 2 Asp 2 have been detected in [1][2][3][4][5]; their stability constants are cited. Data on the heat effects of complexation in this system are scarce and contradictory.…”

mentioning

confidence: 99%

“…where Δ r H and Δ r H° are the enthalpy changes in reac tions (1) or (2) CuAsp r H Δ CuAsp r H Table 3. The calculated thermodynamic characteris tics of the complexation in the system Cu(II)-L aspartic acid at I = 0, 0.5, 0.75, and 1.0 and Т = 298.15 K are summarized in Table 3; for comparison, the corresponding data for nickel(II) complexes [20] are cited.…”

mentioning

confidence: 99%