Submillimeter-wave Fourier transform spectroscopy of biological macromolecules

Abstract

In this article we report experimental results on Fourier-transform infrared spectroscopy of deoxyribonucleic acid ͑DNA͒ macromolecules and related biological materials in the submillimeter range ͑i.e., ϳ10-500 cm Ϫ1 ͒. Film samples made from commercial DNA fibers, polyadenylic acid potassium salt, and cellular agents such as the spore form of Bacillus subtillis have been prepared and measured. A broad series of measurements carried out in the low frequency region ͑10-50 cm Ϫ1 ͒ with a higher resolution of 0.2 cm Ϫ1 revealed fine features-multiple dielectric resonances in the submillimeter-wave spectra obtained from DNA samples. These long-wave absorption features are shown to be intrinsic properties of biological materials determined by phonon modes. The emphasis is on reproducibility of experimental spectra and on receiving reliable results. The effects of differences in sample preparation, including sample geometry, orientation, and aging are studied and separated from the phonon effects that determine the fine structure of transmission spectra. A direct comparison of spectra between different DNA samples reveals a large number of modes and a reasonable level of sequence-specific uniqueness. A theoretical study of two double helical DNA fragments has applied a normal mode analysis to predict spectra in the far infrared. Most of the modes determined by long-distance interactions are at frequencies below 220 cm Ϫ1 , with the density higher than one mode per cm Ϫ1 , which is approximately what was observed experimentally.

T-Ray Sensing and Imaging

“…Despite the low power and poor sensitivity of thermal sources and detectors in the THz band, FTIR is used widely and extensively in material and biological studies. 19 THz FTIR spectroscopy relies on THz radiation generated by a mercury arc lamp, or SiC rod (globar), which is directed into two arms of an optical interferometer. The sample to be studied is placed in one arm of the interferometer, and a characteristic interference pattern, influenced by the THz properties of the sample, is measured by scanning the length of one arm of the interferometer.…”

Plasma mechanisms of pulsed terahertz radiation generation

“…Terahertz spectra taken in a broad frequency range make it possible to reveal characteristic "fingerprints" of different molecules, which opens up possibilities for detection and identification of plaster explosive, hazardous chemicals, drugs, express analysis of the composition of ejected gases, diagnostics of different deseases, quality control of food and agricultural stuff, etc. [6,7]. Images obtained with the help of transmitted or reflected terahertz radiation permit one to control the quality of multilayer pills or plane and multilayer integrated circuits.…”

Terahertz optical measurements of correlated motions with possible allosteric function

“…Unfortunately these reports contained irreproducible and/or conflicting observations which likely resulted in false assignments because they did not address one chief artifact in this frequency range, namely, multiple reflection effects or Fabry-Perot etalon (Crowe et al 2004;Edwards et al 1984;Globus et al 2002Globus et al , 2006Parthasarathy et al 2005;Woolard et al 2002). Fabry-Perot etalon is an interference between copropagating light beams arising from reflections at the sample/ window surfaces.…”