Good's buffers
Good's buffers (also Good buffers) are twenty buffering agents for biochemical and biological research selected and described by Norman Good and colleagues during 1966–1980. Most of the buffers were new zwitterionic compounds prepared and tested by Good and coworkers for the first time, some (MES, ADA, BES, Bicine) were known compounds previously overlooked by biologists. Before Good's work, few hydrogen ion buffers between pH 6 and 8 had been accessible to biologists, and very inappropriate, toxic, reactive and inefficient buffers had often been used. Many Good's buffers became and remain crucial tools in modern biological laboratories.
Good sought to identify buffering compounds which met several criteria likely to be of value in biological research.
The Good's buffers are presented in the table below. The table presents “apparent” pKas measured by Good's group at 20oC and concentrations of about 100mM. The apparent pKa is equal to the buffer's pH when the concentrations of two buffering species are equal, and the buffer solution has the maximum buffering capacity. The apparent pKa, and therefore the pH, of any buffer are temperature and concentration dependent. Consequently, the pH of prepared concentrated buffer solutions will change on dilution and with temperature. The apparent pKa at various concentrations and temperatures may be predicted using online calculators.
Different Good's buffers fulfill the selection criteria to various degrees. No one of the buffers is truly and completely inert in biological systems. In Good's own words, "it may be that the quest for universal biological inertness is futile." Only three of Good's buffers do not form noticeable complexes with any metals: MES, MOPS and PIPES. Piperazine-containing buffers (PIPES, HEPES, POPSO and EPPS) can form radicals and should be avoided in studies of redox processes in biochemistry.
Tricine is photo-oxidised by flavins, and therefore reduces the activity of flavone enzymes at daylight. Free acids of ADA, POPSO and PIPES are poorly soluble in water, but they are very soluble as monosodium salts. ADA absorbs UV light below 260 nm, and ACES absorbs it at 230 nm and below.
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