The temperature effect of infrared absorption of protein molecules in living systems

Infrared rays with 1.1 to 3 /spl mu/m and 5 to 7 /spl mu/m of wavelength can be absorbed by protein molecules which can cause vibrations of amide-I in the amino acid residues. The vibrations of amide-I can result in intermolecular excitations (vibrons or excitons). The main peak of 1665 cm/sup -1/ in the infrared absorption corresponds just to the energy of the exciton. However, the vibrations of amide-I can also cause the deformation of the lattice around it. Then the non-linear interaction between the amides and amino acids could result in self-trapping of the amide-I vibrational quanta (vibrons) or solitons. The mechanism is as follows. Through such an intrinsically nonlinear interaction between them, an amide-I vibrational quantum as a source of phonons causes shifts in the average positions of the ground state of the vibrations of the lattice. These shifts (the lattice distortions) in turn react, through this nonlinear interaction, as a potential well to trap the amide-I vibrational quantum and prevent dispersion of the energy of the amide-I vibrational quantum via the dipole-dipole interaction which exists in neighbouring peptides with certain electric moments. The vibron-soliton occurred in such a case. It is a dynamic self-sustaining entity. The main properties of the soliton is that it can move over macroscopic distances retaining the wave shape, energy, momentum, and other quasiparticles with velocity v. The red shift of the main peak, 1665 cm/sup -1/, is caused by the self-trapping of the exciton or the soliton. Using the following vibron model we can give the red shift and exponential function dependence of the infrared absorption intensity on temperature.