Protein alpha helix — FTIR absorption peaks and assignments

Quick answer

Protein alpha helix is usually assigned by looking for a recurring cluster of characteristic peaks rather than one exact textbook number. The table below shows where the literature most often places this group in FTIR, ranked by accumulated evidence.

Characteristic FTIR peaks for Protein alpha helix

Showing the 30 best-supported peaks of 97 total for Protein alpha helix.

Spectrum logic

A functional-group assignment becomes more confident when several expected bands appear together. Use this page to find the strongest-supported peaks, then confirm that the same sample exhibits a coherent pattern rather than a single isolated hit.

Real-world usage

These pages are useful for unknown material analysis, peak explanation in reports, polymer troubleshooting, and verifying whether a candidate material family is chemically plausible.

Common mistakes

• Using one functional-group page as a complete material verdict without checking the rest of the spectrum.
• Assuming the strongest band is always the most diagnostic one.
• Forgetting that processing, additives, aging, and mixtures can shift or broaden expected peaks.

Verification advice

Use DSC, GC-MS, or TGA when several material families share similar bands or when mixture effects make the FTIR assignment uncertain.

Literature behind these assignments

• 1695 cm⁻¹ confidence 1.0

  “The broad bands in the raw spectrum at 1695 ad cm-1 (α-helix β-sheet 1637 were associated with amide I and cm-1 structures of proteins) while the signal at 1520 corre-”

  Baldauf 等 - 2007 - Effect of selective growth media on the differenti DOI: 10.1016/j.mimet.2006.06.012
• 1648 cm⁻¹ confidence 1.0

  “cm-1 The vibration 1648 is assigned to C=O stretching of amide I in proteins (mainly - A helix components of proteins) [24, 31].”

  Fourier transform infrared microspectroscopy detects biochemical changes during C. elegans lifespan DOI: 10.1016/j.vibspec.2019.04.005
• 1645 cm⁻¹ confidence 1.0

  “1538 0.066 1537 0.064 Amide II due to N-H bending of proteins [15,17] Amide I due to C=O stretching of α-helix proteins 1645 0.07 1641 0.071 [17] 2924 0.028 2926 0.02 asymmetric stretching symmetric CH2: lipids [18] 2965 0.027 2962 0.019 as”

  A Preliminary Study of FTIR Spectroscopy as a Potential Non-Invasive Screening Tool for Pediatric Precursor B Lymphoblastic Leukemia DOI: 10.3390/molecules
• 1650 cm⁻¹ confidence 1.0

  “The amide I peak (1650 cm-1) is stronger in normal tissues due to the high amount of protein with an α-helical secondary structure.”

  Ghassemi 等 - 2021 - Diagnosis of normal and malignant human gastric ti DOI: 10.1016/j.molstruc.2020.129493
• 1283 cm⁻¹ confidence 1.0

  “At lower wavenumber, the bands at cm-1 α-helices 1283 is assigned to of the amide III absorption band owing to in-phase combination of CH stretching and NH bending vibrations [42].”

  Gupta 等 - 2022 - In vitro cell composition identification of wood d DOI: 10.1098/rsos.201935
• 1550 cm⁻¹ confidence 1.0

  “1550 due to bending vibration of N-H group (60%) α-helix β-sheet and stretching vibration of C-N group (40%).”

  Gene-Transformation-Induced Changes in Chemical Functional Group Features and Molecular Structure Conformation in Alfalfa Plants Co-Expressing Lc-bHLH and C1-MYB Transcriptive Flavanoid Regulatory Genes: Effects of Single-Gene and Two-Gene Insertion DOI: 10.3390/ijms18030664
• 1424 cm⁻¹ confidence 1.0

  “in combination with a visible alteration in the protein 1049.1 and 1158.1 to 1161.5 In Muchmore, cm-1 (α-helix β-sheet) region turned to following pathogenic the peaks at 1423.5, 1375.9, and 1052.5 were cm-1”

  Synchrotron based phase contrast X-ray imaging combined with FTIR spectroscopy reveals structural and biomolecular differences in spikelets play a significant role in resistance to Fusarium in wheat DOI: 10.1186/s12870-014-0357-5
• 1655 cm⁻¹ confidence 1.0

  “Typically, a shoulder at is assigned to β-sheet cm-1 secondary structures of proteins, while the band at 1655 is assigned to α-helix secondary structure [24], thus amide I band of the SC at the latter frequency reflects the”

  Mansour 等 - 2017 - Elucidation of penetration enhancement mechanism o DOI: 10.1016/j.saa.2017.05.026