Estimate peptide charge across any chosen pH range. Compare ionizable groups using editable pKa values. Download plots tables and summaries for reports and study.
Use sequence mode for one-letter peptide strings or manual mode for direct residue counts.
This sample illustrates how a small peptide behaves across selected pH values using default pKa settings.
| Example Sequence | Target pH | Estimated pI | Predicted Net Charge | Comment |
|---|---|---|---|---|
| ACDEHKRY | 3.00 | 7.2140 | +1.8400 | Low pH keeps basic groups strongly protonated. |
| ACDEHKRY | 5.00 | 7.2140 | +0.7920 | Acidic groups begin deprotonating more strongly. |
| ACDEHKRY | 7.00 | 7.2140 | +0.1020 | The peptide approaches electrical neutrality. |
| ACDEHKRY | 9.00 | 7.2140 | -1.1770 | Higher pH favors more deprotonated acidic groups. |
| ACDEHKRY | 11.00 | 7.2140 | -2.1180 | Most acidic groups are deprotonated by this region. |
Basic groups: fraction protonated = 1 / (1 + 10^(pH - pKa))
Basic charge contribution: count × fraction protonated
This models groups such as the N-terminus, lysine, arginine, histidine, and optional extra basic sites.
Acidic groups: fraction deprotonated = 1 / (1 + 10^(pKa - pH))
Acidic charge contribution: -count × fraction deprotonated
This models groups such as the C-terminus, aspartate, glutamate, cysteine, tyrosine, and optional extra acidic sites.
Total net charge: sum of all positive contributions + sum of all negative contributions
Estimated pI: the pH where predicted net charge approaches zero.
The pI in this file is estimated numerically from the selected pKa set.
It estimates peptide net charge across pH, predicts an isoelectric point, and shows how each ionizable group contributes to the full titration curve.
No. It is a model-based estimate using Henderson–Hasselbalch behavior and chosen pKa values. Real peptides can shift because of structure, solvent, salt, or neighboring residues.
Ionization can shift with environment, sequence context, and experimental conditions. Editable pKa inputs let you match literature values, measured values, or a specific buffer system.
Sequence mode counts ionizable residues from a one-letter peptide string. Manual mode lets you enter counts directly, which is useful for averaged compositions or custom formulations.
They are optional placeholders for nonstandard modifications, terminal protections, linker groups, or other ionizable sites not covered by the default amino acid list.
Each ionizable group transitions gradually between protonated and deprotonated states. The full peptide curve is the combined effect of all those overlapping transitions.
The CSV includes the titration data table. The PDF includes a compact summary, the selected settings, and the computed charge table for reporting or study notes.
No. It is a strong planning and teaching tool, but measured data should guide final decisions when precision matters for experiments, formulations, or purification work.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.