Effect of additional metal ions on the ratio between the rates of the transformation of the intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed the Cu2+ ion (Communication 2: Mathematical modeling of the kinetics of the hydrolysis in the presence of additional Mg2+ ions)

It was previously shown that the hydrolysis of the (CuATP^2? · OH₂)₂ dimeric complex to CuADP^? and an inorganic phosphate occurs in a sequence of two rapid and irreversible steps. Along with the hydrolysis through a common intermediate product, (CuATP^2?)₂OH^?-(DOH^?), the OH^? nucleophile at the Cu²⁺ ion is replaced by OH^? at the positively charged phosphorus atom to form an IntK pentacovalent intermediate (step 1). A mathematical modeling of the kinetics of the hydrolysis catalyzed by the Cu²⁺ base metal ion in the presence of additional Mg²⁺ ions at two pH values, 6.48 and 6.71 (at the ascending branch of the dependence of the initial rate of the hydrolysis on the pH value) is performed. Additional ions affect only the pathway of coupling of the conformational conversion of DOH^?. The rate constant for the forward reaction (IntK→ DOH^?), k ₁, increases from 2 · 10⁷ L mol^?1 min^?1 in the absence of Mg²⁺ to 2.9 · 10⁷ L mol^?1 min^?1 upon introduction of Mg²⁺ ions; rate constant of the reverse reaction IntK → DOH→, k ^?1, decreases from 1 · 10⁵ L mol^?1 min^?1 in the absence of Mg²⁺ to 3 · 10⁴ L mol^?1 min^?1 in the presence of Mg²⁺. The relative concentrations of the intermediate products are demonstrated to change during the irreversible hydrolysis. In the presence of Mg²⁺, IntK emerges at much earlier stages of the hydrolysis, the fraction of formed IntK in the balance of NuP₀ is substantially higher, and the growth of its relative concentration with time in the earlier stages of hydrolysis is much more dramatic.     

Influence of additional metal ions on the ratio of the rates of intermediate product transformations in the hydrolysis of adenizine-5′-triphosphoric acid catalyzed by divalent Cu ions

It was shown earlier that the hydrolysis of the (CuATP²⁻)₂ dimeric complex to CuADP⁻ and inorganic phosphate P _i was an irreversible reaction. The main intermediate hydrolysis product, the formation of which should be taken into account at comparatively early hydrolysis stages, was the IntK pentacovalent intermediate. It was formed in parallel with hydrolysis to CuADP⁻ and P _i through the common intermediate product (CuATP²⁻)₂OH⁻ — DOH⁻. We studied the influence of the addition of various concentrations of Mg²⁺ ions to the reaction mixture at pH 7.1–7.2, a range for which the kinetics of hydrolysis is sensitive to the rate constants of deactivation of DOH⁻ active centers (conjugated with CuADP⁻ formation and occurring via the formation of IntK). The conversion of ATP above which stationary hydrolysis regime was observed decreased as the concentration of Mg²⁺ grew. The DOH⁻ $ \underset{{OH^ - }}{\overset{{OH^ - }}{\longleftrightarrow}}$ \underset{{OH^ - }}{\overset{{OH^ - }}{\longleftrightarrow}} IntK equilibrium according to the conversion of ATP was established more rapidly, and it was to a greater extent shifted toward IntK. It was assumed that hydrated Mg²⁺ linked as a second metal ion with ATP β and γ phosphate groups hydrated IntK much stronger than DOH⁻. The Cu · OH₂ · AMP complex played the role of a common acid catalyst and hydrated DOH⁻ better than Mg²⁺ · OH₂. The selective hydration of DOH⁻ by the CuOH₂ · AMP complex at early hydrolysis stages directed the process toward the formation of IntK, which caused the appearance of an induction period in the formation of CuADP⁻.     

The influence of Zn2+ ion on the 1.5 μm laser properties of LiNbO3 crystal heavily doped with Er3+ ion

The spectral characteristics of 1.54 μm emission in a series of Zn/Er:LiNbO₃ crystals with heavy Er content and variable Zn content were reported. The inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration of Er³⁺ ion in the crystal. The absorption and emission spectra of Zn/Er:LiNbO₃ crystals were measured. Based on Judd–Ofelt theory, the spectral parameters such as intensity parameters Ω_t (t=2, 4 and 6), transition strengths, radiative transition probabilities, radiative lifetime and fluorescence branching ratio have been obtained in Zn/Er:LiNbO₃ system. The emission cross section corresponding to ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ion was obtained according to Füchtbauer–Ladenburg theory. The gain cross section of Er:LiNbO₃ crystal codoped with 6 mol% Zn²⁺ ions were also discussed in this work.