Figure 6.

(a) Kinetic diagram of the site binding (SB) model from Reference [20]. The graph shows two chained reactions involving the protonation-deprotonation of one hydroxyl binding site. Each state is characterized by a net signed number of elementary charges, $z$, and a probability of the site to be in that state, $f$. The coefficients on the transitions arrows relate the probabilities of the two adjacent states. ($k_a^f$; $k_a^b$) and ($k_b^f$; $k_b^b$) are the forward and backward reaction constants for the first and second protonation reaction, respectively. (b) Equivalent noise circuit of the SB reactions in (a). The chemical noise is represented by the thermal noise of the resistors, here shown as Norton’s equivalent current generators.