Experiments performed with biological systems require a buffer that will not interfere with the stability and activities of the biological components. In 1966, Norman Good and his colleagues began a series of investigations that established criteria for new zwitterionic buffers that would be optimal for experimentation with biological systems. These criteria include:

a. pKa between 6 and 8
b. highly water soluble
c. minimally permeable to biological membranes
d. minimal effects of salt concentration
e. minimla effect of temperature on pKa
f. minimal effect of concentration on pKa
g. minimal interaction with metal ions
h. nontoxic
i. high chemical stability
j. minimal absorbance between 240-700 nm

For each buffer below, choose the property that does NOT meet Good's criteria for biochemical buffers. If all of the buffer's properties satisfy the criteria for a Good's buffer, then select the last choice.

Properties of phosphate buffer:

pK2 at25C= 7.20
Δp Ka/C = -0.0028
Does not cross lipid bilayers
Precipitate forms with Ca2+ ions
All of the above properties fulfill the Good's buffer criteria

Properties of HEPES buffer:
pKa at 25'C =7.48
Δp Ka/C =-0.014
Water solubility limit is 2.25 M
Low absorbance of light in I-JV region
all of the above properties fulfill the Good's buffer criteria