Law of Chemical Forces: Transitions, Reactions, and Self-assemblies

Abstract

Physical and biological components are often in a certain phases or conformations that can undergo physical transitions and chemical reactions. The simplest of the reactions or transitions is

$$ A \leftrightarrow B. $$

(7.1)

It denotes transition between states A and B, where the bidirectional arrow $\leftrightarrow$ indicates either forward or backward direction. One class of the examples is biopolymer conformational transition that we already discussed earlier in numerous situations. ‘A’ and ‘B’ can also represent two phases of matter, such as gas and liquid. Often the biochemical systems consist of many species that can react. One simple but important chemical reaction is

$$ 2{\text{H}}_{2} + {\text{O}}_{2} \leftrightarrow 2{\text{H}}_{2} {\text{O}}. $$

(7.2)

One further example is the process of self-assembly or association, in which monomers aggregate into larger structural units, and its backward process called dissociation:

$$ A_{1} + \cdots + A_{1} \leftrightarrow A_{n} , $$

(7.3)

where $A_{n}$ is the aggregate of n units. Here we describe basic relations and conditions of the reactions and transitions at equilibrium, in particular the relations between the concentrations of the substances involved, called the law of mass action (LMA). LMA can be one of most basic laws for biological transitions involving various conformational states of biopolymers and supramolecular aggregates.