Question

Norman Good and colleagues developed a series of buffer salts that conform to several criteria that made these agents ideal biological buffering agents. What were these criteria? Why are these important to biochemists? Give an example of a non-Good’s buffer and its limitations with regards to its use in biological studies.

Answer 1

Good's buffers (also Good buffers) are twenty buffering agents for biochemical and biological research.

Many Good's buffers became and remain crucial tools in modern biological laboratories.

Selection criteria

Good sought to identify buffering compounds which met several criteria likely to be of value in biological research.

1. pKa. Because most biological reactions take place near-neutral pH between 6 and 8, ideal buffers would have pKa values in this region to provide maximum buffering capacity there.

2. Solubility. For ease in handling and because biological systems are in aqueous systems, good solubility in water was required. Low solubility in nonpolar solvents (fats, oils, and organic solvents) was also considered beneficial, as this would tend to prevent the buffer compound from accumulating in nonpolar compartments in biological systems: cell membranes and other cell compartments.

3. Membrane impermeability. Ideally, a buffer will not readily pass through cell membranes, this will also reduce the accumulation of buffer compound within cells.

4. Minimal salt effects. Highly ionic buffers may cause problems or complications in some biological systems.

5. Influences on dissociation. There should be a minimum influence of buffer concentration, temperature, and ionic composition of the medium on the dissociation of the buffer.

6. Well-behaved cation interactions. If the buffers form complexes with cationic ligands, the complexes formed should remain soluble. Ideally, at least some of the buffering compounds will not form complexes.

7. Stability. The buffers should be chemically stable, resisting enzymatic and non-enzymatic degradation.

8. Biochemical inertness. The buffers should not influence or participate in any biochemical reactions.

9. Optical absorbance. Buffers should not absorb visible or ultraviolet light at wavelengths longer than 230 nm so as not to interfere with commonly used spectrophotometric assays.

10. Ease of preparation. Buffers should be easily prepared and purified from inexpensive materials.

Buffer pKa 20°C ΔpKa/°C Solubility in water at 0oC

MES 6.15 -0.011 0.65M

Bis-tris methane 6.60 M

ADA 6.62 -0.011 -

ACES 6.76

Bis-tris propane 6.80 -

PIPES 6.82 -0.0085 -

ACES 6.88 -0.020 0.22M

MOPSO 6.95 -0.015 0.75M

Cholamine chloride 7.10 -0.027 4.2M (As HCl)

MOPS 7.15 -0.013 3.0M

BES 7.17 -0.016 3.2M

TES 7.5 -0.020 2.6M

HEPES 7.55 -0.014 2.25M

DIPSO 7.6 -0.015 0.24M

MOBS 7.6

Acetamidoglycine 7.7 - Very large

TAPSO 7.6 -0.018 1.0M

TEA 7.8

POPSO 7.85 -0.013 -

HEPPSO 7.9 -0.01 2.2M

EPS 8.0

HEPPS 8.1 -0.015 Large