SolEq logoThe IUPAC Stability Constants Database, SC-Database (no longer available commercially)
and Mini-SCDatabase.

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SC-Database and Mini-SCDatabase

SC-Database is a compilation of literature data, intended to direct the user to the original literature reference. It contains all significant stability constants and associated thermodynamic data published from 1887 to the present day, including all stability constants included in the book volumes published by the Chemical Society, London (now the Royal Society of Chemistry) and by IUPAC. It is maintained and kept up-to-date through regular upgrades.

Ligand structures may be displayed in .mol file format, and the database may be searched on any sub-structure fragment. Media include both aqueous, mixed and non-aqueous solvents, measured under a wide range of conditions and by varying methods.Thermochemical data, solubility products and other useful information are included with the experimental data as comments where appropriate. Since the database directs the user to the appropriate literature references, the most relevant data set can be identified.

Mini-SCDatabase is an edited subset of SC-Database containing selected values for all important metal/proton - ligand pairs. In general, only one set of values is selected, preferably in aqueous solution at 25°C and I = 0.1 M. Where data have been critically evaluated by IUPAC the recommended values have been selected. There are no journal references and the experimental details are reduced. It is provided with SC-Database and as part of the Sol-Eq CD-ROM. This is no longer maintained, but is provided free with SC-Database and as part of Sol-Eq.

SC-Database include facilities for selecting data on a wide range of criteria and for inspecting the data on screen, in printed output or through other applications. Data may be corrected for temperature changes (using the van't Hoff equation) and for ionic strength changes (using the Davies equation). They can also be used to calculate and display species distribution curves.

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Features of SC-Database

SC-Database may be searched using any combination (including name fragments) of:

Criteria for searching are described in Using SC-Database

The databases can be browsed to get an idea of their contents :

Following a search, data may be displayed on screen in full or condensed format, or they may be printed or saved to disk as a text file. Ligand structures may also be saved in .mol file format, or edited using EdChemS (copyright V.Solov'ev), the structure drawing package provided (SC-Database only). They may also be copied to the Windows Clipboard for export to other applications. Data may be sorted in several ways (e.g. in the order of ligand/metal/reference or reference/ligand/metal). DG values may be calculated and ionic strength corrections applied. Species distribution curves may be calculated and displayed graphically, or saved either graphically or as numeric values. Solubility products may even be included in the calculations to predict precipitation.

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Using SC-Database

SC-Database is both easy and intuitive to use.

The database may be browsed in general, like leafing through a book, in either ligand order (by empirical formula) or metal order (alphabetic). However, the more powerful method is to access the databases in detail by preparing a specification (or template). The corresponding list of experiments is extracted by matching this specification into the database.

Searching is always case insensitive (i.e. either upper case or lower case may be used) except in empirical formulae. The profile specification may be based on any combination of :

Ligand details : Empirical formulae may be given either in full or as fragments only. Sub- and super-scripts are ignored; formulae are entered as, e.g. C10H23N4O3S. In practice other orders are accepted (e.g. C10O3H23SN4) or fragments may be used (e.g. C10H23) when all ligands with C10H23.... will be selected.

Name matching is equally flexible. Matching can be either from the start (fastest) or from anywhere (*nnn*) within the name. Each name has two possible starts: the first character or the first letter (capital) of the name. For example, 2-Aminoethanoic acid may be regarded for searching as either 2-Aminoethanoic acid or as Aminoethanoic acid. When matching anywhere, structural fragments may be searched for, e.g. *imidaz* selects all ligands containing the imidazole fragment.

Ligand classes: ligands may be selected on one of a total of 25 classes; e.g. biological amino acids, phenols, N,O-macrocycles.

Ligand structures may be displayed on screen or exported to other applications. Ligands may be searched on a sub-structure which can be drawn using EdChemS (provided with SC-Database) or any major structure drawing package (e.g. Chem Draw or Isis Draw)

Metal ion details : individual metal ions or groups of metal ions may be selected; e.g. Cu selects Cu+, Cu++ and Cu+++. Groups may be specified; e.g. lanthanides, alkali or alkaline earth metals. User-defined selections may also be made (e.g. Cu++, Ni++, Zn++) and stored for future use.

Reference details: Author names may be specified in full (e.g. pettit) or as fragments only, again using either the start of the name (pett*) or any intermediate fragment (*etti*).

Journal details may also be matched from either the start or as an intermediate fragment. For example, if you remembered an important paper started at page 1234 but could not remember the journal or year, this routine would find it!

Experimental details: Experiments may be searched on numeric values for some stability constants, searching on either exact, approximate, maximum or minimum values, temperature, background ionic strength, background medium or method of study.

Once a list has been extracted the data may be inspected on screen, printed or saved to disk. They may also be sorted in various ways. Temperature and ionic strength corrections may be applied and the data may be used to calculate and display species distribution curves.

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Species Distribution Curves (Speciation Curves)

The Speciation Application (Species.exe) calculates and displays species distribution curves (speciation curves) from the total concentrations of reactants and overall stability constants of the complexes considered. A solubility product may also be included to check for precipitation. Input data may be saved to disk and reloaded, and several modes of display are possible, e.g. as a function of pH, of another free species concentration (pL) or of a selected total reactant concentration.

The graphics routines allow the user to manipulate or modify the curves in very many ways and they can also be output to any Windows-configured printer. A colour printer is recommended. Data can be displayed as either a line graph in several formats or as a piechart. Both the input data and calculated values for the equilibrium concentrations may be edited dynamically, as may the labels on axes of the graphs.

AlOH concentration

In addition, the calculated equilibrium concentrations which are used to plot the curves may be displayed numerically on screen or saved to disk as a text file. They can therefore be incorporated in a wide range of Windows graph-drawing packages, e.g. Microsoft Excel.

SPECIES.EXE, can handle up to 12 reactants (including hydrogen), 28 constants and 3 solubility products.

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Temperature and Ionic Strength Corrections

Stability constants can vary dramatically with temperature and ionic strength, particularly when enthalpy changes are large or metal and ligand have high charges. Ideally, stability constants should be measured under the experimental conditions applicable, but a number of correction methods are available.

The databases contain an application which uses the van't Hoff equation to correct for temperaturte changes:

Temp corrections

The Davies equation is used to apply ionic strength corrections over the range of 0 to 1 M for a range of 13 different equilibrium reactions. Values above 0.1 M probably have little quantitative meaning, particularly when the charges are high, but they do demonstrate the likely trend in values.

Ionic St. Corr.

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Who Should Use SC-Database?

SC-Database is an essential tool for all scientists who study, or use quantitatively, metal/proton - ligand equilibria in aqueous, mixed or non-aqueous solution. It identifies stability constants measured under a wide range of experimental conditions and media, and directs the user to the literature references. Hence it will be used by both research workers and applications chemists in branches of analytical, biological, environmental, industrial and medicinal chemistry, in oceanography and in pollution studies.

Mini-SCDatabase is an edited subset of selected constants, generally in aqueous solution at 25°C, and is particularly useful for teachers and for all who want fast and easy access to values for metal-complex and protonation constants. The built-in application for calculating and displaying species distribution curves will be particularly useful in this context. It is included automatically with both SC-Database and Sol-Eq.

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