An experiment on a zinc-containing enzyme requires a buffer that (1) maintains pH 7.0 at 37 °C, (2) does not bind Zn²⁺, and (3) can be used at 0.10 M concentration. Data for four common buffers are listed.
Buffer pKa at 25 °C ΔpKa/°C Metal-ion binding
A. Tris 8.06 −0.028 negligible
B. Phosphate 7.21 −0.002 high
C. HEPES 7.55 −0.014 negligible
D. PIPES 6.80 −0.006 negligible
Which buffer best satisfies the experimental requirements?
a) Tris
b) Phosphate
c) PIPES
d) HEPES