Nondestructive Analysis of Biological Materials by FT-IR-ATR. Method I: Direct Evidence for the Existence of Collagen Helix Structure in Lens Capsule

FT-IR spectra were measured in situ for an albino rabbit lens capsule by use of the ATR method, and the spectrum of water was subtracted. The obtained difference spectra resemble the spectrum of purified Type IV collagen in aqueous solution and show intense bands at 1637 and 1553 cm⁻¹ assignable to the amide I and II modes, respectively. These frequencies are very close to those of the amide I and II bands of a 3₁ helix. This is direct evidence for the existence of the so-called collagen helix (a slightly modified 3₁ helix) in the lens capsule. FT-IR spectra were also measured by the diffuse reflectance method for the dried capsule stripped from a dried lens. IR frequencies of the amide I and II bands of the capsule collagen shift from 1637 and 1553 cm⁻¹ to 1654 and 1540 cm⁻¹, respectively, upon going from the intact capsule to the dried one, showing that the collagen helix is converted to a random coil structure upon drying.