JOINT EXPERT SPECIATION SYSTEM

JESS - JOINT EXPERT SPECIATION SYSTEM

There are two abbreviated methods of entering a JESS reaction. Neither are entirely general but they can be used to specify many reactions in a quick and easy way.

Both abbreviated methods depend on a preliminary identification of the reactants in terms of a metal ion and one or two ligands. One ligand, called the 'primary ligand' must always be specified.

Beta convention

The first abbreviation method applies when the reaction has as its product a single complex and the reactants are the individual, unassociated components of that complex. For example, if the reaction can be written as X + Y = X_Y, then X_Y is said to be the complex and X,Y are its components. The reaction is then specified simply by a B (for beta) followed by a string of digits that give the stoichiometry of the complex.

In a two component system (i.e. with two digits), the order is ligand first, then proton. In a three component system, the digits refer in order to metal, ligand and proton. In a four component system, the metal comes first, then the primary ligand, then the secondary ligand, and the proton last. Proton stoichiometric coefficients can be negative.

For example, by entering (without quotes) 'B110' you specify the reaction 'M + L = M_L'.

Likewise, 'B012' means 'L + H = L_H(2)', 'B12' means 'L + H = L_H(2)', 'B22-2' means '2<M> + 2<L> + 2<H2O> = M(2)_L(2)_OH(2) + 2<H>, ' B1210' means M + 2<L> + X = M_L(2)_X and so on.

The initial letter B serves to distinguish these stoichiometries from a reaction number (which is not allowed).

MLH convention

In the second method, the letters M, L, X, H and the pair OH are used to identify components. The reaction is specified by formulating an expression for its equilibrium constant: species are represented by combinations of these letters with digits (giving the stoichiometry), separated by a period . for multiplication of species concentration or by a slash / for division.

Thus, for example, by entering (without quotes) 'ML/M.L' you specify the reaction 'M + L = M_L', 'LH/L.H' means 'L + H = L_H', 'LH2/L.H2' means 'L + 2 = L_H(2)', 'LH2/LH.H' means ; L_H + H = L_H(2)', 'M2L2(OH)2.H2/M2.L2' means '2<M> + 2<L> + 2<H2O> = M(2)_L(2)_OH(2) + 2<H>', ' ML2X/M.L2.X' means 'M + 2<L> + X = M_L(2)_X' and so on.

Clearly it is easier to use the 'beta formulation' if it is applicable. Note, however, that the main saving, achieved by both methods, is that (i) symbols do not need to be typed at length and (ii) the variety of symbols and spacing used in the full JTH reaction formulation is avoided.

The MLH formulation has an additional advantage. By employing it, it is almost always possible to specify reactions using the conventions of Smith and Martell in their volumes of Critical Stability Constants. These can be entered directly in the form they give. Hence, when considering a reaction from a Smith and Martell volume, simply type the MLH abbreviation without regard to whether digits occur as superscripts or subscripts. There are exceptions, but this rule works in a very large majority of cases.

In addition to these abbreviation methods, there is also a shortened way for entering a formation reaction (in which a species is formed from its elements).