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M. FE DE LA TORRE Y COLS. AN. R. ACAD. NAC. FARM.

aPPi means that half of the PPi molecules not forming complexes
with Cu(II) appear as PPi anion, and nearly all the rest as
hydrogenpyrophosphate anion. Regarding the Cu not forming
complexes with PPi, only 0.025% appears as free cation, while 98%
is in the form of dihydroxicuprate.

FIGURE 2. Dependence of the values of a ,Cu(II) aPPi, k1’ and k2’ on the pH of
the Cu(II)/PPi system. The maximum values of k1’ and k2’ never reach the
theoretical values of K1 and K2 respectively due to the parasite reactions of
Cu(II) and PPi.

FIGURE 3. Dependence of the A280 of Cu(II) on the pH and the buffer at 37ºC.
In all cases, the blank was a solution of 0.5 mM CuSO4 and 10 mM Na4P2O7.

All buffers were tested at a concentration of 50 mM and adjusted to the final pH
with HCl or NaOH. The different signs correspond to: !, AMPSO, !, BICINE,

", Tris, #, CHES, ", MOPS, $, borate and %, glycine.

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