Calculated Results
These values appear after submission and stay above the form.
Binding Fit Plot
Computed Point Table
| # | Concentration | Observed Signal | Predicted Signal | Residual | Fraction Bound | Bound Complex |
|---|
Calculator Inputs
Enter measured data for fitting, or leave responses empty for a theoretical curve.
Example Data Table
This sample data approximates a one-site saturable binding profile in µM.
| Point | Ligand Concentration (µM) | Observed Signal | Comment |
|---|---|---|---|
| 1 | 0.10 | 0.22 | Near baseline response |
| 2 | 0.30 | 0.39 | Early binding growth |
| 3 | 0.60 | 0.64 | Signal increasing steadily |
| 4 | 1.00 | 0.92 | Mid-rise region |
| 5 | 2.00 | 1.39 | Near useful fit region |
| 6 | 4.00 | 1.86 | Approaching saturation |
| 7 | 8.00 | 2.19 | High occupancy |
| 8 | 15.00 | 2.42 | Late saturation phase |
| 9 | 25.00 | 2.54 | Small incremental gain |
| 10 | 40.00 | 2.61 | Near maximum signal |
Formula Used
One-site Hill binding model:
Predicted Signal = Baseline + Amplitude × (Ln / (Kdn + Ln))
Here, L is ligand concentration, Kd is the dissociation constant, n is the Hill coefficient, and Amplitude is the fitted signal span.
Fraction bound:
θ = Ln / (Kdn + Ln)
Bound complex estimate:
Bound Complex = Receptor Total × θ × Stoichiometry
Standard Gibbs free energy:
ΔG° = -R T ln(Ka) = R T ln(Kd)
Two-temperature van’t Hoff estimate:
ln(Ka₂ / Ka₁) = -(ΔH° / R) × (1/T₂ - 1/T₁)
Entropy estimate:
ΔS° = (ΔH° - ΔG°) / T
How to Use This Calculator
- Choose temperature and concentration units.
- Paste the ligand concentration series.
- Paste observed signals to fit experimental data.
- Leave observed signals blank for a theoretical curve.
- Set whether the Hill coefficient should be fitted.
- Add receptor total and stoichiometry for bound complex estimates.
- Optionally provide a second temperature and constant.
- Click the calculate button.
- Review the summary metrics, plot, and computed table.
- Download the output as CSV or PDF.
Frequently Asked Questions
1) What does this calculator fit?
It fits a one-site binding isotherm with an optional Hill coefficient. The tool estimates Kd, baseline, amplitude, occupancy, and thermodynamic quantities from the supplied conditions and response trend.
2) When should I use Kd instead of Ka?
Use Kd when your assay reports dissociation constants directly. Use Ka when the association constant is available. The calculator converts between them internally using Ka = 1 / Kd.
3) Why is temperature important?
Temperature directly affects Gibbs free energy and van’t Hoff thermodynamic estimates. A change in temperature can shift affinity, so thermodynamic interpretation should always use the correct absolute temperature.
4) What does the Hill coefficient mean here?
The Hill coefficient captures apparent cooperativity or curve steepness. A value near one suggests simple noncooperative behavior, while values above or below one can indicate altered binding response shape.
5) Can I use this for blank theoretical simulations?
Yes. Leave the observed response field empty. The calculator will use the entered constant, baseline, maximum signal, and Hill value to build a predicted curve and summary table.
6) How is ΔH estimated?
If you enter a second temperature and a second constant, the tool uses a two-point van’t Hoff relation. Otherwise, it uses your optional ΔH entry and derives entropy from ΔG and temperature.
7) Why might the fit look poor?
Poor fits can result from noisy data, wrong units, insufficient saturation points, multiple binding sites, or signal drift. Check the concentration range, response scale, and whether a one-site model is appropriate.
8) Does this replace full thermodynamic software?
No. This is a practical screening and interpretation tool. It is useful for rapid checks, teaching, and early analysis, but specialized datasets may require more advanced global fitting workflows.