Question

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 included: a. pK_a between 6 and 8 b. highly water soluble c. minimally permeable to biological membranes d. minimal effects of salt concentration e. minimal effect of temperature on pK_a (Delta pK_a/degree C < 0.02) f. minimal effect of concentration on pK_a 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: pK_2 at 25 degree C = 7.20 Delta pK_a/degree C = -0.0028 does not cross lipid bilayers precipitate forms with Ca^2+ ions all of the above properties fulfill the Good's buffer criteria Properties of HEPES buffer: pK_a at 25 degree C = 7.48 Delta pK_A/degree C = -0.014 water solubility limit is 2.25 M low absorbance of light in UV region all of the above properties fulfill the Good's buffer criteria

Answer 1

For the phosphate buffers, the property that does not meet the criteria is:

Precipitate forms with Ca²⁺ ions

For the HEPES buffer:

All of the properties fulfil the Good's criteria

Hope this helps !