JESS - JOINT EXPERT SPECIATION SYSTEM
by Peter M May, School of Mathematical and Physical Sciences,
Chemistry, Murdoch University, Murdoch, Australia
6150
and Kevin Murray, Insight Modelling Services, P.O. Box 38953,
Garsfontein East, South Africa 0060
JESS is a powerful research tool for modelling chemical speciation
in complex aqueous environments. It is designed to solve problems requiring
expert knowledge of solution chemistry. It currently comprises over
250 programs, 2000 subroutines and 234,000 lines of Fortran code. The
software is highly portable and has been implemented under
Windows-XP and a number of other operating systems.
In most JESS modelling, the speciation is calculated using known thermodynamic
parameters for the relevant reactions in aqueous media. All types of
chemical equilibria can be modelled including protonation, complex formation,
redox, solubility and adsorption interactions. The data are taken from
the JESS databases, transformed into a thermodynamically consistent
set of equations and solved. Automation of
this procedure, achieved by a sequence of JESS programs, is the key
to good equilibrium modelling.
Dealing with the reasons why chemical speciation models from different
workers frequently exhibit substantial discrepancies is a special focus
of the approach adopted by JESS.
Facilities also exist to couple large multi-compartment equilibrium
models with kinetic calculations. However, these have particular implementation
requirements and, hence, are distributed only under special arrangement.
Development of the JESS Thermodynamic database is now well advanced.
The system overcomes many problems associated with existing compilations
of equilibrium constants. It is fully interactive. Reactions can be
expressed in any form. Any number of equilibrium constants, enthalpy,
entropy and Gibbs energy values can be associated with a reaction.
Our data span interactions in solution of over 100 metal ions with
more than 3,000 ligands. A suite of computer programs exists to facilitate
the production of sub-databases and the interchange of data between
databases.
The main features of our thermodynamic database are as follows.
* Data are generally stored as closely as possible to the
way they appear in the literature and are only subsequently manipulated
by our system to achieve thermodynamic consistency. This has the advantage
that the data in the database are not converted to conform to a particular
pre-determined basis set, unlike most other speciation databases. The
JESS Parent Database is by far the largest database that can be used
directly by chemical speciation modelling programs.
* Since reactions are treated in an entirely general way, JESS
handles many types of chemical interaction that other databases cannot.
Gibbs energies and heats for formation reactions of species
from their elements in their standard states therefore appear in addition
to metal-ligand and ligand-proton binding reactions. Host-guest equilibria
(involving anions only, say) can also be included, even though so
far not very many of these constants have been entered.
* Unlike all other major compilations of equilibrium constants, ternary
complex formation is naturally represented by the same conventions
as our binary reactions. The data can thus be located directly by
searching on the metal ion and two ligands involved. The
JESS Parent Database is, overwhelmingly, the largest single source
of ternary equilibrium constants.
* Chemical substances are indexed by name, by molecular formula
and, often, by CAS registry number. In general,
we have many more variants of chemical names than are provided in alternative
sources.
* Every thermodynamic parameter value is individually associated
with (i) the conditions under which it was measured, including e.g.
the identity of the background electrolyte, the temperature and the
ionic strength, (ii) a literature reference and (iii) our current
estimation of its reliability, on a scale of 0 - 9. This
approach enables the database to become both comprehensive and critical.
Advantages of the approach taken in JESS are described in
J. Chem. Eng. Data, 2001, 46, 1035
Three papers describing some initial aspects of JESS have been published
in Talanta (Talanta, 1991, 38, 1409; Talanta, 1991, 38, 1419 ; Talanta,
1993, 40, 819). Other subsequent papers are also available (e.g.
Chem. Commun., 2000, 1265). Reprints can be sent on request.
Our Primer documents provide a full iintroduction to JESS and can be
downloaded.
JESS is made available to researchers
for academic (i.e. non-commercial) purposes.
