Soft Matter & Molecular Biophysics Group    

suITCase: Scripted Utility for Isothermal Titration Calorimetry Analysis & Stoichiometric Examination


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Motivation:

The reliability of the thermodynamic parameters obtained from ITC experiments depends critically on: (i) the volume injected in each titration; (ii) the concentration of the solution in the sample cell; (iii) the concentration of the solution in the syringe; (iv) the number of injections; (v) the number of different chemical species that can be formed upon mixing of both solutions; (vi) which solution is introduced into the sample cell and which is in the injection syringe; and (vii) the value of the thermodynamic parameters associated to the studied reaction.

If the injected volume or any of the concentrations are too small, or if the ratio between both concentration values is not appropriate, then the signal-to-noise ratio will be low and the uncertainty of any result will be high. The control of these factors might be limited by the available amount or the corresponding solutes (they can be expensive or difficult to synthethize/purify). If the total number of injections is low then the solute in the sample cell will not be saturated and the quality of the results will be poor. Additionally, in reactions for which multiple chemical species can be formed it is always better to fit simultaneosly several isotherms, each focusing the sampling in a different concentration region that is more sensitive to any of the species. ITC experiments can be optimized by changing some of the parameters listed above.

What is suITCase for?

The purpose of suITCase is threefold: (i) to guide in the design of ITC experiments, helping to suggest values for the parameters of the technique that can be modified by the user; (ii) to aid in the interpretation of the ITC results by providing the distribution of each chemical species as a function of the concentration ratio between both solutes; and (iii) my actual reason to develop this application is that I am trying to design materials based on one specific chemical species and this tool allows me to find the absolute concentration range under which my favorite supramolecular complex dominates the solution.

A few technical details:

suITCase was designed to produce results for the MicroCal VP-ITC family of calorimeters. suITCase includes the concentration and heat corrections due to the displacement of volume from the sample cell after each titration.

The model implemented in the current version of suITCase is a "Sequential Binding Sites" model that considers the free species of both solutes A and B, plus the hybrid complexes with stoichimetries (1:1, 1:2, 2:1, 2:2). Of course, any subset of this model such as that involving only (1:1, 1:2) complexes or only the complexes with stoichiometry (1:1), is also included here. The general equations describing the model can be found here: J. Phys. Chem. B, 2011, 115 (49), pp 14381-14396..

The publicly available version of suITCase does not fit data to the model required by the user. If you require a more complex model or the fitting of experimental data instead of the single modelling of data, please do not hesitate to contact me: Angel.Pineiro at usc.es. Any type of support to maintain, speed-up or/and extend this project will be highly appreciated.


Disclaimer:

suITCase was designed for educational or academic purposes only. If you intend to use it for commercial purposes you should contact the author.

The author does not accept any responsability for the results provided by this application.

The personal data voluntarily provided by the user is for informational purposes only.



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FUNDING: The present project was supported by the grant MAT2011-25501 (MINECO-Spain).