Detailed Explanation
The mass of a peptide expressed in daltons (Da) or kilodaltons (kDa). Molecular weight is calculated by summing the masses of all amino acid residues plus water (each residue contributes ~110–130 Da minus 18 Da for the water lost in each peptide bond formation). The average amino acid residue mass is approximately 115 Da.
A dipeptide has an MW of ~200–250 Da, insulin ~5,800 Da, and hemoglobin ~64,500 Da. MW determines pharmacological behavior: molecules under ~500 Da may cross cell membranes (Lipinski's Rule of Five), peptides at 500–5,000 Da typically require injection, and proteins >5 kDa need specialized delivery. MW is confirmed by mass spectrometry on Certificates of Analysis.
Key Facts
- The mass of a peptide expressed in daltons (Da) or kilodaltons (kDa).
- Molecular weight is calculated by summing the masses of all amino acid residues plus water (each residue contributes ~110–130 Da minus 18 Da for the water lost in each peptide bond formation).
- The average amino acid residue mass is approximately 115 Da.
- A dipeptide has an MW of ~200–250 Da, insulin ~5,800 Da, and hemoglobin ~64,500 Da.
- MW determines pharmacological behavior: molecules under ~500 Da may cross cell membranes (Lipinski's Rule of Five), peptides at 500–5,000 Da typically require injection, and proteins >5 kDa need specialized delivery.
- MW is confirmed by mass spectrometry on Certificates of Analysis.
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