Relaxation spectra of copper(II)-ATP complexes at low pH

摘要: 1. 1. Acidic solutions (pH 1–5) of copper(II)-adenosine triphosphate yield ultrasonic attenuation spectra consisting three maxima. From the concentration and pH dependence these peaks, by comparison with low ATP, CuCl2 Cu3(PO4)2 solutions, we have assigned spectrum as follows. The overall reaction which fits data best is Cu2+ + H2ATP2− ag CuHATP− H+ The shortest relaxation time (approx. 2 · 10−9 s) ascribed to penetration inner copper(II) hydration shell ligand. next slower process 1 10−8 then due chelate ring closure species formed in faster step. lowest frequency peak (< MHz) has been taken be either a characteristic aqueous ion, already observed other systems (e.g. CuSO4), or formation another (minority) complex such CuH2ATP. In case, presence this does not interfere kinetic analysis processes. 2. 2. On assumption that complexes follows established pattern divalent transition metal ions, obtain at 25 ·C variable ionic strength (0.1–0.8 M), 8.8 108 s−1 for water elimination rate constant, 6.3 107 sterically controlled closure. ion-pair constant consistent 16 M−1. absolute value standard volume change, |ΔVc| estimated 42 ml mole−1 above reaction. 3. Although experimental error associated determination maxima on order 10–20%, values constants, changes are reliable only factor approximately two, uncertainties solution composition approximations made solving equations.