Amino Acid Net Charge Calculator For Water

Amino Acid Charge at Neutral pH:

\[ \text{Net Charge} = \sum (\text{Positive Charges}) - \sum (\text{Negative Charges}) \]

Select Amino Acid:

pH (unitless):

Net Charge at pH 7.0:

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. At neutral pH (7.0), most amino acids have a net charge close to zero, except for those with ionizable side chains.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation to determine the charge state of each ionizable group:

\[ \text{Fraction charged} = \frac{1}{1 + 10^{(pH - pKa)}} \text{ (for bases)} \] \[ \text{Fraction charged} = \frac{1}{1 + 10^{(pKa - pH)}} \text{ (for acids)} \]

Where:

\( pH \) — The pH of the solution
\( pKa \) — The acid dissociation constant for each ionizable group

Explanation: The calculator sums the charges from the amino group (positive), carboxyl group (negative), and any ionizable side chains.

3. Importance of Net Charge Calculation

Details: Knowing the net charge of amino acids is crucial for understanding protein behavior in electrophoresis, predicting protein solubility, and designing purification protocols.

4. Using the Calculator

Tips: Select the amino acid from the dropdown and enter the desired pH (typically 7.0 for physiological conditions). The calculator will show the predicted net charge.

5. Frequently Asked Questions (FAQ)

Q1: Why do amino acids have different charges at different pH values?
A: The charge depends on protonation state of ionizable groups, which changes with pH according to their pKa values.

Q2: What is the isoelectric point (pI)?
A: The pH at which the amino acid has a net charge of zero. It's the average of the two pKa values that bracket the neutral form.

Q3: Which amino acids have charged side chains at neutral pH?
A: Aspartic acid, glutamic acid (negative), lysine, arginine (positive), and histidine (partially positive).

Q4: How accurate are these calculations?
A: They provide good estimates, but actual charges may vary slightly depending on local environment and temperature.

Q5: Can I use this for peptides?
A: This calculator is for single amino acids. Peptide charge calculation requires summing charges from all ionizable groups in the sequence.