Question

what would be the best buffering agent to choose if you want to buffer an enzyme reaction or tissue culture at 7.2    a. hepes (4-(2-hydroxyethyl)-1piperazineethanesulfonic acid) pk =7.5 b. histidine pk 1=1.78; pk2=5.97; pk3=8.97 c. bicarbonate; pk=6.1 d. phosphate; pk1=2.0, pk2=6.8; pk3=12.5   e. tris or tris(hydroxymethyl)aminomethane; pk=8.07

Answer 1

we know that

for buffers

pH = pKa + log [conjugate base / acid ]

now

the buffers have maximum capacity in the range

pKa - 1 < pH < pKa + 1

so for a given pH ,

the ideal pKa should be in the range

pH-1 < pKa < pH + 1

given

pH = 7.2

so

7.2 - 1 < pka < 7.2 + 1

6.2 < pKa < 8.2

so the pK values should be within this range

looking at the options

c) bicarbonate ; b) histidine are out of this range

so

they are not all a good choice

Now all the remaining options are in this range

so

they all can be used as buffering agents

Of them

pK for tris is 8.07 is very near to the boundary value of 8.2

so

it is not very preferable

So

a) Hepes and d) phosphate are the best buffering agents