Circular dichroism of collagen, gelatin, and poly(proline) II in the vacuum ultraviolet

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Abstract
Circular dichroism spectra for acid‐soluble calfskin collagen, gelatin, and poly(proline) II in solution have been extended into the vacuum ultraviolet region. The extended spectrum of gelatin reveals that the circular dichroism of this unordered polymer is more closely related to the spectrum of charged polypeptides than might be evident from near ultraviolet work. A short‐wavelength band is found at about 172 nm, which corresponds in position, magnitude, and sign to a band recorded earlier for poly(L‐glutamic acid) at pH 8.0. This band is observed in a helical structure for the first time in the vacuum ultraviolet circular dichroism and absorption spectra of poly(proline) II. Both circular dichroism and absorption spectra point to the assignement of this band as the nσ*. Neither the nσ* nor the expected positive lobe of the ππ* helix band is observed in the extended circular dichroism spectrum of collagen. We postulate that these two bands cancel here in analogy to the case of α‐helical poly(L‐glutamic acid).