Calculator Inputs
Result appears above this form after submission.
Injection Heat Output Table
| Injection | Cum Ligand (µM) | Fraction Bound | Incremental Bound (nmol) | Heat (µJ) | Noisy Heat (µJ) |
|---|---|---|---|---|---|
| No calculation yet. | |||||
Example Data Table
| Parameter | Example Value | Units |
|---|---|---|
| Macromolecule concentration | 20 | µM |
| Ligand syringe concentration | 200 | µM |
| Cell volume | 200 | µL |
| Injection volume | 2 | µL |
| Injections | 20 | count |
| Kd | 5 | µM |
| Binding ΔH | -35 | kJ/mol |
| Temperature | 25 | °C |
Formula Used
Association constant: Ka = 1 / Kd
Wiseman c-value: c = n × Ka × [M]t
Approximate occupancy: θ = (Ka[L]) / (1 + Ka[L])
Incremental heat: qi = Δnbound × ΔH + qdil
Thermodynamics: ΔG = RT ln(Kd), and ΔS = (ΔH − ΔG) / T
This calculator provides a practical single-site approximation for planning, sanity checks, and educational interpretation. Final publication-grade fitting should use instrument software and full dilution corrections.
How to Use This Calculator
- Enter cell and syringe concentrations from your ITC experiment design.
- Add instrument setup values: cell volume, injection volume, and injection count.
- Input estimated Kd, stoichiometry, and binding enthalpy from literature or screening.
- Set temperature and optional dilution heat/background noise estimates.
- Click Calculate to generate summary metrics and injection-by-injection heats.
- Review c-value, thermodynamic outputs, and saturation trend for feasibility.
- Export the generated table as CSV or PDF for lab notes.
ITC Data Quality and Experimental Context
Isothermal titration calorimetry measures binding by recording heats from each injection. Those heats can be translated into practical thermodynamic outputs for planning. Strong experiments require accurate concentrations, stable baselines, and measurable signals. This calculator estimates heats, saturation behavior, and summary metrics before instrument time is used. It supports feasibility checks, method development, and sample conservation during early experimental design. It also clarifies expected saturation windows before committing scarce protein batches today.
Parameter Sensitivity and c-Value Planning
The c-value combines stoichiometry, affinity, and macromolecule concentration into one planning metric. Low c-values can produce shallow transitions with weak fitting leverage. High c-values can compress the useful region into very few injections. By reporting c-value with predicted heats, the calculator helps users adjust concentrations before running samples. That improves curve shape and reduces avoidable reruns in busy chemistry workflows. Users can compare alternative syringe strengths quickly and preserve experimental turnaround time.
Heat Profile Interpretation Across Injections
Injection-level output shows where meaningful signal appears and when saturation develops. Early injections often produce larger heats because more binding sites remain available. Later injections usually approach the dilution baseline as occupancy rises. The table lists cumulative ligand concentration, fractional occupancy, incremental bound amount, and estimated heat values. A noise estimate helps analysts preview realistic scatter and signal-to-noise expectations before experiments. This preview improves injection scheduling and supports cleaner baseline validation plans early.
Thermodynamic Outputs for Decision Support
The summary panel reports Ka, Kd, c-value, ΔG, ΔH, and estimated ΔS. These results support rapid comparisons across compounds, buffers, and temperatures. They are useful for planning and internal discussions before formal fitting is completed. Final reporting should still rely on instrument software, controls, and dilution corrections. Even so, precomputed estimates help prioritize conditions and guide sample preparation choices efficiently. Teams can rank conditions sooner and reduce unnecessary buffer preparation steps overall.
Exporting Results and Lab Documentation
Built-in exports improve record keeping and reproducibility across teams. CSV output supports spreadsheet review, plotting, and batch comparisons during optimization work. PDF output provides a portable summary for notebooks and experiment packets. Using the calculator as a pre-run documentation step records chosen concentrations, injection settings, and expected heat ranges. That documentation speeds troubleshooting, improves handoffs, and strengthens consistent laboratory decision making. Exports also simplify review meetings and standardized handoffs between project members.
FAQs
1) What does the c-value indicate in ITC planning?
The c-value estimates whether your concentration setup will generate a useful binding transition. It helps you choose concentrations that improve fit quality.
2) Can this calculator replace instrument fitting software?
No. It is for planning and educational estimates. Final analysis should use instrument software with controls, baseline correction, and dilution treatment.
3) Why do later injections produce smaller heats?
As binding sites become occupied, each injection forms fewer new complexes. Incremental heat drops and approaches the dilution baseline near saturation.
4) What should I enter for dilution heat?
Use an estimate from buffer controls or prior runs. If uncertain, test a conservative value to preview baseline sensitivity during planning.
5) Why include a noise estimate in the output table?
Noise simulation helps you preview realistic experimental scatter. It shows whether predicted heats remain comfortably above expected measurement variability.
6) Which units are displayed in the results?
Kd is shown in µM, Ka in M⁻¹, ΔG and ΔH in kJ/mol, and ΔS in J/mol·K.