Determination of conditional stability constants for some divalent transition metal ion‐EDTA complexes by electrospray ionization mass spectrometry

Abstract

Conditional stability constants of coordination complexes comprising divalent transition metals, Cu(2+), Ni(2+), Zn(2+), Co(2+), and ethylenediaminetetraacetic acid (EDTA) were determined utilizing electrospray ionization mass spectrometry. The deviation of signal response of a reference complex was monitored at addition of a second metal ion. The conditional stability constant for the competing metal was then determined through solution equilibria equations. The method showed to be applicable to a system where Co(2+) and Zn(2+) competed for EDTA at pH 5. When Cu(2+) and Ni(2+) competed for EDTA, the equilibrium changed over time. This change was shown to be affected in rate and size by the type of organic solvent added. In this work, 30% of either methanol or acetonitrile was used. It was found that if calibration curves are prepared for both metal complexes in solution and the measurements are repeated with sufficient time space, any change in equilibrium of sample solutions will be discovered.

Fe- and Cu-Complex Formation with Artificial Ligands Investigated by Ultra-High Resolution Fourier-Transform ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS): Implications for Natural Metal-Organic Complex Studies

“…K + and Na + were present in low amounts, however, and they do not provoke as strong side reactions for EDTA and SA as other salt ions usually found in seawater samples, such as Mg 2+ or Ca 2+ . In fact, we observed the opposite trend of a decreasing logK' CuEDTA with decreasing ionic strengths of the samples, although it should be noted that they were in line with previous reports: The CLE-ACSV results are in the range of those found by Xue and Traina (1996) based on potentiometric titrations of Cu-EDTA in 50-60% methanol-water mixtures (17.35-17.87), while the FT-ICR-MS results are more similar to those calculated by Boija et al (2014) for Cu-EDTA (15.0 ± 0.1), who used Ni as a competing metal ion and conducted measurements by ESI-MS. Thus, the acquired conditional stability constants may be subject to method-dependent artifacts (potentiometric vs. ESI-MS).…”

Metal ion assisted interface re-engineering of a ferritin nanocage for enhanced biofunctions and cancer therapy

“…37 The stability test of 64 Cu 2+ coordinated ferritin derivatives in mouse serum demonstrated the high affinity of 64 Cu 2+ for mutants A and B over 24 h, whereas native ferritin and mutant control showed dramatic 64 Cu 2+ loss within the same time frame (Figure 2E). Ethylenediaminetetraacetic acid (EDTA) has fairly high stability constant to a number of divalent transition metal ions, 38 including Cu 2+ . In our study, we discovered that the high affinity of 64 Cu 2+ for mutants A and B is able to resist competitive binding from EDTA for at least 6 h, and over 50% 64 Cu 2+ remained complexed after 24 h of co-incubation.…”

Determination of Conditional Stability Constants for Phytic Acid Complexes with Mg2+, Ca2+ and Zn2+ Ions Using Electrospray Ionization Mass Spectrometry

“…[19][20][21][22][23] Moreover, ESI-MS has been used to determine conditional stability constants. [24][25][26] One of the most popular methods for the determination of conditional stability constants involves monitoring of the intensities of the bound and unbound guests during a titration experiment. 27 However, this method cannot be applied to systems that involve the formation of neutral complexes or ions that are not easily observed in the mass spectra.…”