Absorption Spectrum
Absorption Spectrum — A plot of absorbance versus wavelength for a compound, used to determine optimal detection wavelengths for peptide quantification.
What Is an Absorption Spectrum?
An absorption spectrum is a plot of a compound's absorbance as a function of wavelength, typically measured by UV-Vis spectrophotometry. For peptides, the absorption spectrum provides both qualitative identification and quantitative concentration measurement. The peptide bond absorbs strongly at 190-220 nm, while aromatic amino acids (Trp, Tyr, Phe) produce characteristic absorption bands between 250-290 nm.
Key Wavelengths for Peptide Analysis
- 214 nm: Peptide bond absorption. Used for universal peptide detection in HPLC. Response is proportional to the number of peptide bonds regardless of sequence
- 280 nm: Tryptophan (ε = 5,690 M⁻¹cm⁻¹) and tyrosine (ε = 1,280 M⁻¹cm⁻¹) absorption. Used for concentration determination when these residues are present
- 257 nm: Phenylalanine fine structure. Weaker absorption but diagnostic for Phe-containing peptides
- 301 nm: Dibenzofulvene absorption. Used to monitor Fmoc deprotection efficiency during synthesis
Research Applications
Beer-Lambert law (A = εlc) enables precise concentration determination from absorbance measurements. For peptides lacking aromatic residues, absorbance at 205 nm or the BCA/Bradford protein assay provides alternative quantification. Mass spectrometry is used alongside spectrophotometric methods when absorption-based quantification is insufficient for complex mixtures.
Common Artifacts
Buffer components (DMSO, TFA, imidazole) absorb in the UV range and can interfere with peptide measurements. Scattering from aggregated peptide solutions artificially inflates apparent absorbance. Always blank against the matched solvent/buffer and verify that solutions are optically clear before measurement.
Frequently Asked Questions
What is Absorption Spectrum?
A plot of absorbance versus wavelength for a compound, used to determine optimal detection wavelengths for peptide quantification.
Why is Absorption Spectrum important in peptide research?
Absorption Spectrum is a fundamental concept in analytical as it relates to peptide science. It directly influences experimental design, compound characterization, and the reliability of research outcomes across biochemistry and molecular biology disciplines.
Authority Sources
- Absorption Spectrum on Wikipedia
- Search Absorption Spectrum on PubChem (NIH)
- Research articles on ScienceDirect