Amino Acid Net Charge Calculator For Gas

Net Charge Equation:

\[ \text{Net Charge} = \sum \left( \frac{1}{1 + 10^{(pH - pKa)}} \right) \text{for acidic groups} - \sum \left( \frac{1}{1 + 10^{(pKa - pH)}} \right) \text{for basic groups} \]

pH Value:

Amino Acid:

Net Charge:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Amino Acid Net Charge?

The net charge of an amino acid is the sum of all positive and negative charges on the molecule at a given pH. In the gas phase, pKa values differ from solution phase, affecting protonation states and resulting charge.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation for each ionizable group:

\[ \text{Charge Contribution} = \frac{1}{1 + 10^{(pH - pKa)}} \text{(for acidic groups)} \] \[ \text{Charge Contribution} = -\frac{1}{1 + 10^{(pKa - pH)}} \text{(for basic groups)} \]

Where:

\( pH \) — The pH value of interest
\( pKa \) — Acid dissociation constant for each ionizable group

Explanation: The calculator sums contributions from N-terminus (basic), C-terminus (acidic), and side chain (if applicable) to determine net charge.

3. Importance of Net Charge Calculation

Details: Knowing the net charge is crucial for understanding mass spectrometry results, predicting gas-phase behavior, and studying protein folding in the absence of solvent.

4. Using the Calculator

Tips: Enter pH value (0-14) and select an amino acid. The calculator will determine the net charge based on gas-phase pKa values.

5. Frequently Asked Questions (FAQ)

Q1: Why are gas-phase pKa values different from solution pKa?
A: In the gas phase, there's no solvent stabilization of ions, so proton affinities dominate, leading to different pKa values.

Q2: How accurate are these calculations?
A: Accuracy depends on the pKa values used. Gas-phase pKa values are less well-established than solution values.

Q3: Can I use this for peptides?
A: This calculator is for single amino acids. Peptides require considering all ionizable groups in the sequence.

Q4: Why is the charge fractional?
A: At pH values near pKa, groups are partially protonated, resulting in non-integer net charges.

Q5: How does temperature affect the results?
A: The calculator assumes standard temperature. pKa values are temperature-dependent, but this is often negligible for gas-phase calculations.