I am titrating an iron-porphyrin catalyst into a solution of carbon nitride quantum dots (g-C3N4).
Analysis of the binding was done using ITC, where i found an unusual isotherm. I recognise a multi site binding interaction, however I'd apprecaite any adivse as to the fitting.
Since the result is not conventional, (e.g., different phases with fractional stoichiometry), some issues must be addressed before analyzing the experiment.
First, you should repeat it.
Second, you should do other experiments at another temperature, at another pH, with a different buffer.
Third, you should titrate the syringe solution into buffer, to rule out any effect from the ligand dilution.
Fourth, you should assess in an independent manner (another technique) if there could be ligand-induced aggregation of the cell solution that could be reflected in the thermogram.
Maybe other people can provide other suggestions.
Agree with Adrian.
How pure/homogenous are your solutions?
Your titrations ends with a molar ratio around 0.6. Is there a chemical explanation that can fit this fact somewhat remotely?
Double the injection volume in the next experiment. That should tell you a lot.
Thank you for your reply Sujay Subbayya Ithychanda ; Firstly, my carbon nitride quantum dots are extreamly difficult to get an accurate concentration. The molar ratio doesn't acuratly reflext the concentrations used (Catalyst: 400 uM, CNQD: 0.1 g/L). When running my samples i input 0.4 and 0.1 mM into the syringe/cell concentrations. That is the reason behind the low molar ratios.
By doubling the injection volume, it looks like i've lost information, the isotherm looks closer to a traditional single or two site curve. It's only when i have an injection volume of around 1uL i see this strange responce.
My samples are homogenous solutions and well degased before any ITC experiments.
Agree with above suggestions. Optimize your titration setup as such after saturation, molar ratio (X-axis) should reach to 1.5-2.0. Only then you can analyze the data. Double the injection volume or ligand concentration.
How does blank titration look like? Are you subtracting blank titration with the substrate-ligand titration?
Thank you Viveka Nand Malviya . The concentration values input into the software aren't completely accurate due to CNQD's being difficult to work out concentrations post-synth. (see answer to Sujay above :) ). The blank titrations look fine, as expected and the solvation effects have been accounted for in these figures.
What are you injecting? The quatum-dots or the iron catalyst?
In addition, if you do not know well any if the concentrations and you do not know well the stoichiometry, that is a problem. If you know the stoichiometry, you may find out the concentration of the unknown concentration.
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