Table 2 List of the main infrared bands (cm⁻¹) of collagen tannins [25,26,27]

Collagen

~ 3310

Amide A: vN–H

~ 3080

Amide B: vN–H

~ 2960

vC–H

~ 1630

Amide I: vC=O

~ 1545

Amide II: vC–N, δN–H

~ 1450

δCH₂ of proline

~ 1400

δC–O–H, δNH₂

~ 1340

vCH₂ δC–H

~ 1240

Amide III: vC–N, δN–H

~ 1080 and 1030

vC–O, vC–O–C

Common for all tannins

~ 1610

vC=C aromatic ring

~ 1512

vC=C aromatic ring

~ 1450

vC=C aromatic ring

~ 1210

vC–O, δC–OH

~ 1035

βC–H deformation, vC–O

Hydrolysable tannins

~ 1705–1730

vC=O

~ 1320

vC–O and O–H deformation

~ 1085

vC–O–C

~ 871

γOH, γC–H

~ 760

γ aromatic δC–H

Condensed tannins

~ 1285

vC–O pyran ring

~ 1160

vC–O–C

~ 1113

vC–O–C

~ 843

C–H deformation