Calculator Inputs
Example Data Table
| Sample | Amino Acids Included | Total Count | Mn (g/mol) | Mw (g/mol) | Interpretation |
|---|---|---|---|---|---|
| Peptide Mix A | Gly, Ala, Val, Leu | 40 | 103.12 | 111.48 | Broader mass distribution than a uniform mixture. |
| Peptide Mix B | Ser, Thr, Tyr, Trp | 28 | 148.40 | 161.66 | Heavier aromatic content lifts weight emphasis. |
| Protein Fragment C | Lys, Arg, Glu, Asp | 35 | 150.16 | 154.83 | Charged residues cluster near a narrower spread. |
Formula Used
Number average molecular weight: \( M_n = \frac{\sum N_i M_i}{\sum N_i} \)
Weight average molecular weight: \( M_w = \frac{\sum N_i M_i^2}{\sum N_i M_i} \)
Z average molecular weight: \( M_z = \frac{\sum N_i M_i^3}{\sum N_i M_i^2} \)
Polydispersity index: \( \text{PDI} = \frac{M_w}{M_n} \)
Estimated condensed peptide mass: Total monomer mass minus water loss for each peptide bond.
Here, Ni is the count of each amino acid species and Mi is its molecular weight. Mn treats every molecule equally. Mw gives more influence to heavier components. Mz emphasizes the heaviest tail even more. For peptide estimation, each bond removes one water molecule during condensation.
How to Use This Calculator
- Enter a project or sample name for easier exports.
- Optionally enter sample mass to estimate moles.
- Optionally enter a target peptide mass for residue estimates.
- Provide counts for each amino acid present in your mixture.
- Add custom amino acids if your sample contains modified residues.
- Click the calculate button to show results above the form.
- Review Mn, Mw, Mz, PDI, residue mass, and composition fractions.
- Use the CSV or PDF buttons to save your analysis.
Answers to Requested Questions
Why is weight average molecular weight greater than number average?
Weight average molecular weight gives extra emphasis to heavier molecules because each component is weighted by mass contribution. Number average counts each molecule equally. In any mixture with size variation, larger molecules pull Mw upward more strongly, so Mw is usually equal to or greater than Mn.
Number average molecular weight example
Suppose a mixture contains 2 molecules at 100 g/mol and 3 molecules at 200 g/mol. Mn = [(2×100) + (3×200)] ÷ (2+3) = 800 ÷ 5 = 160 g/mol. This average treats each molecule equally, regardless of whether it is light or heavy.
Sylgard 184 average molecular weight g/mol
Sylgard 184 is a commercial silicone elastomer system, and its exact average molecular weight is not a single fixed public value for all parts and cure states. The effective molecular distribution depends on base polymer composition, crosslinker ratio, and curing. Consult the manufacturer’s technical documents for product-specific details.
Frequently Asked Questions
1. What does this amino acid calculator actually measure?
It estimates molecular weight averages for an amino acid mixture or residue profile. It calculates Mn, Mw, Mz, PDI, composition fractions, total mass contribution, and an estimated condensed peptide mass after water loss.
2. When should I use Mn instead of Mw?
Use Mn when you want the arithmetic average per molecule or residue entry. Use Mw when heavier components matter more, such as in broad mixtures where larger mass fractions influence properties or interpretation.
3. Why can PDI be close to 1.000?
A PDI near 1 means the molecular weight distribution is narrow. In practice, many components have similar masses or counts, so the weight average stays close to the number average.
4. Does this calculator work for peptides and proteins?
Yes, as an estimate. It works best when you know the residue composition or approximate amino acid counts. The condensed chain mass adjusts for water removed during peptide bond formation.
5. Can I include modified or nonstandard amino acids?
Yes. Two custom fields are included for modified residues or nonstandard entries. Add a name, molecular weight, and count to extend the analysis beyond the standard amino acids.
6. What is average residue mass useful for?
Average residue mass helps estimate peptide length from a known target mass. It is also useful for screening composition trends, comparing batches, and building rough sequence or hydrolysate models.
7. Are the values exact for every laboratory situation?
No. Real samples can include salts, hydration, charge states, modifications, and measurement uncertainty. The calculator gives structured theoretical estimates from the composition you enter.
8. Why is water loss included in peptide calculations?
Peptide bonds form by condensation. Each bond removes one water molecule, so the final peptide mass is lower than the simple sum of free amino acid molecular weights.