. 2017 Oct 16;2(10):6728–6740. doi: 10.1021/acsomega.7b00321

Table 2. UV–Visible Spectral Titration pK_a Values and Enolization Rate Constants^e.

UV–visible spectral titration
[Cu^II(H₂Acdica)_keto]¹⁺ ⇆ {[Cu^II(HAcdica)_enolate]} + H⁺	pK_[Cu(H2A)]	3.88 ± 0.02^a	3.85 ± 0.02^a
[Cu^II(HAcdica)_keto]⁰ ⇆ {[Cu^II(Acdica)_enolate]} + H⁺	pK_[Cu(HA)]	4.78 ± 0.03^b	4.71 ± 0.05^b
[Cu^II(HAcdica)_enol]⁰ ⇆ [Cu^II(Acdica)_enolate]^1– + H⁺	pK_[Cu(A)]	6.23 ± 0.04^c
from Larson and Lister (1968)
[CuA]⁰ ⇆ [CuL]^1– + H⁺	pK_CuA(1968)	3.81^d
Enolization rate constant
Cu^II + H₂Acdica^1– _(keto) → [Cu(H₂Acdica)_enol]¹⁺	k^E₃	0.05–0.07 s^–1
Cu^II + HAcdica^2– _(keto) → [Cu(HAcdica)_enol]⁰	k^E_4(ave)	0.213 ± 0.001 s^–1

Obtained from nonlinear fits to the absorbance at 400 and 757 nm shown in Figure 1c.

Obtained from nonlinear fits to the absorbance at 400 and 757 nm shown in Figure 1d.

Obtained from nonlinear fits to the absorbance at 246 nm shown in Figure 2b.

μ = 0.6 M (NaClO₄), temperature = 25 °C.

Note: pK_[Cu(H2A)] and pK_[Cu(HA)] involve deprotonation at the α-carbon methylene groups, whereas pK_[Cu(A)] involves deprotonation at the β-carbonyl oxygen. “{ }” indicates unstable species.

Table 2. UV–Visible Spectral Titration pKa Values and Enolization Rate Constantse.

Table 2. UV–Visible Spectral Titration pK_a Values and Enolization Rate Constants^e.