Calculator Inputs
Enter values and compute LogD. The result appears above this form after submission.
Example Data Table
These examples are illustrative and use the same formulas as the calculator.
| Compound type | pH | logP | pKa1 | pKa2 | Assumption | Estimated logD |
|---|---|---|---|---|---|---|
| Monoprotic acid | 7.4 | 2.0 | 4.5 | — | Ion does not partition | ≈ -0.900 |
| Monoprotic base | 7.4 | 2.0 | 8.5 | — | Ion does not partition | ≈ 0.900 |
| Amphoteric | 7.4 | 2.0 | 4.5 | 8.5 | Ion ratio 0.01 | ≈ 0.001 |
Formula Used
This tool estimates distribution at a chosen pH using a partition coefficient for the neutral form and Henderson–Hasselbalch style ionization fractions.
- P = 10^(logP)
- D = P·fu + Pion·(1−fu) (defaults to Pion = 0)
- Monoprotic acid: fu = 1 / (1 + 10^(pH − pKa))
- Monoprotic base: fu = 1 / (1 + 10^(pKa − pH))
- Amphoteric (simplified): fu = 1 / (1 + 10^(pH − pKa_acid) + 10^(pKa_base − pH))
- logD = log10(D)
These are common screening approximations; real systems can differ due to salts, tautomerism, aggregation, and ion-pairing.
How to Use This Calculator
- Select the compound type that matches ionization behavior.
- Enter logP for the neutral form and your target pH.
- Provide the required pKa values for your chosen mode.
- Optionally enable ion partitioning if you have an estimate.
- Click Calculate LogD and review the output above.
- Use CSV or PDF export to save results and share them.
History
Your latest calculations (stored locally in this session).
| Timestamp (UTC) | Mode | pH | logP | fu | D | logD |
|---|---|---|---|---|---|---|
| No history yet. Run a calculation above. | ||||||
FAQs
1) What is LogD?
LogD is the logarithm of the distribution coefficient at a specified pH. It reflects how much compound partitions into an organic phase when ionization is considered.
2) How is LogD different from LogP?
LogP describes partitioning of only the neutral species. LogD accounts for ionization at a specific pH, so it can be lower or higher than LogP depending on pKa and pH.
3) Why do acids usually have lower LogD at high pH?
At higher pH, acids become more ionized. Ionized species typically partition poorly into nonpolar phases, which reduces the effective distribution coefficient and therefore decreases LogD.
4) Why do bases often have higher LogD at higher pH?
Raising pH shifts bases toward the neutral form. A larger neutral fraction usually increases partitioning into the organic phase, which raises the distribution coefficient and the LogD value.
5) What does the ion partition option do?
It allows the ionized form to contribute slightly to distribution. You can specify a ratio relative to the neutral form or provide logPion. If you leave it off, ionized partitioning is treated as negligible.
6) Can I use two pKa values for amphoteric compounds?
Yes. This tool uses a simplified amphoteric model with one acidic and one basic site. It estimates the neutral fraction as suppressed by either ionization pathway, which is useful for quick screening.
7) Are ionic strength and salts included?
No. The calculator uses common screening approximations. Salt effects, ion pairing, micelles, and multiple tautomers can change measured LogD, so consider experimental context for final decisions.
8) What inputs should I use for physiological conditions?
A common screening pH is 7.4. Use the best available pKa values for the relevant ionizable groups and the neutral logP. Export results to compare sensitivity across pH values.
Disclaimer: This calculator provides estimates for educational and screening use.