Modifications in the Near Infra-Red Absorption Spectra of Protein and of Light and Heavy Water Molecules When Water is Bound to Gelatin

Publisher Website
Google Scholar
Abstract
Comparisons are made between the near infra‐red absorption spectra of protein molecules in oven‐dried gelatin and gelatin saturated with light and heavy water vapor respectively. The intensity of the first overtone valence N – H band at 1.50μ is greatly diminished by the addition of H2O molecules, and this band is almost completely destroyed when D2O molecules are taken on. The combination deformation‐valence N – H bands at 2.05μ and 2.18μ are only partially destroyed in either instance. These facts suggest that the dipole moment oscillation of the N – H group constituting a part of the inter‐molecular hydrogen bridge, C = O≡H – N, is reduced when this bridge is broken and water molecules themselves become bridged to the N – H group; that the transverse dipole moment change is less affected than the parallel change; and that D2O is much more effective than H2O. The 1.72μ and 2.28μ C – H bands do not change appreciably in intensity. However, at least the former shifts toward higher frequencies when water is taken on, indicating that the C – H groups are in a more vapor‐like environment and corroborating the usual assumption that water molecules are attached only to the polar groups of the gelatin molecules. The destruction of some of the usual absorption on the short and the long wave sides of the 1.44μ (νσ+νπ) and 1.93μ (νσ+νδ)H2O bands indicates the nonexistence, or a reduction in number, of unperturbed vapor‐like molecules as well as of the more highly perturbed molecules involving three and four hydrogen bridges. The presence of a sharpened and enhanced 1.79μ (νσ+νδ+νR) band indicates hindered rotation of H2O molecules in a field more homogeneous than that in liquid water but having the same average value. A new weak band appears at 1.35μ and is believed to be (νσ+νπ+νR). Somewhat similar results occur with D2O, requiring for complete interpretation, however, frequency contributions from hindered translation νT.

This publication has 25 references indexed in Scilit: