HEPES, Biological Buffer

HEPES, Biological Buffer is as it's name suggests, a buffering agent. It's a zwitterionic organic chemical that is one of the '20 Good's buffers.' Because it's better at maintaining physiological pH despite changes in carbon dioxide, it is widely used in cell culture. It has a decrease of water dissociation with falling temperature, this is especially relevant when working at low temperatures as it maintains enzyme function and structure. That said, it is important when working with HEPES for that particular purpose to keep the HEPES-containing solution in darkness as much as possible.