1. What is pKa?

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution. It quantifies the acidity or basicity of a chemical compound, with lower values indicating stronger acids.

2. How Does the Calculator Work?

The calculator uses QSAR models or structure-based approaches to predict pKa:

Where:

• Molecular descriptors — Quantitative representations of molecular properties
• Structural features — Functional groups and molecular topology

Explanation: The models are trained on experimental pKa data and can predict values based on chemical structure input.

3. Importance of pKa Calculation

Details: pKa values are crucial for understanding drug solubility, permeability, and formulation. They affect absorption, distribution, metabolism, and excretion (ADME) properties.

4. Using the Calculator

Tips: Enter the chemical structure as a SMILES string (simplified molecular-input line-entry system). For best results, ensure the SMILES is valid and represents the correct protonation state.

5. Frequently Asked Questions (FAQ)

Q1: What is the accuracy of pKa predictions?
A: Typical accuracy is ±0.5-1.0 pKa units, depending on the method and chemical class.

Q2: What are typical pKa ranges?
A: Most drugs have pKa values between 2-12. Strong acids have pKa < 0, strong bases have pKa > 14.

Q3: Can this predict multiple pKa values?
A: The current version predicts the most acidic or basic pKa. For polyprotic compounds, advanced methods are needed.

Q4: Are there limitations to these predictions?
A: Predictions may be less accurate for unusual chemical structures, metal complexes, or compounds with strong intramolecular interactions.

Q5: How does this compare to experimental pKa?
A: Experimental measurement is always preferred when high accuracy is needed, but prediction is valuable for screening.