Terahertz Time-domain Spectroscopy Of Nucleosides And Other Biomolecules

Terahertz time-domain spectroscopy (THz-TDS) is a new far-infrared spectrometer based on femto-second laser technology. Spectra in THz range contain abundant physical and chemical information such as low-frequency vibrational and rotational characters of condensed matters and biomolecules. Investigations on THz spectroscopy will help to understand structural characters of biological molecules from a fresh point of view and provide helpful evidences about the relationship between structure and function.Different structural biomolecules including nucleobases, nucleosides and their derivatives, xanthine and the derivatives, reduced and oxidized L-glutathione, saccharides have been investigated by THz-TDS technology for exploring the relation between THz spectroscopy and molecular conformation and component. Observed characteristic power absorption coefficient and refractive index demonstrate high sensitivity of THz spectroscopy to tiny structural difference or change. THz-TDS can be utilized as an excellent analytical tool for chemical and biological analysis. Configuration, constitution, hydrogen bonding and crystalline form always affect THz absoption signal. The results of cytosine and isocytosine illustrate the ability of TDS to identify isomer. Studies on spectral responses of xanthine and the derivative prove substituent effect can induce peak shift or vibrational mode in THz region. Minor structural differences can lead to big changes of THz spectra such asα-D-lactose andβ-D-lactose.Quantum calculation program Gaussian 03 was used to calculate the low frequency vibration of theophylline and inosine and help to understand their THz spectra obtained from measurement. The calculation results suggest that the characteristic low frequencies modes in THz range mainly come from the collective vibrational modes or the intermolecular interaction such as hydrogen bond network.Integrated THz absorption spectrum in the whole measuring range was taken as fingerprint of compound. The analyzing results show that the method of component analysis of mixtures is simple and effective to get the compounds components and their relative percentage of mixtures (such asα-D-lactose andβ-D-lactose, cytosine and isocytosine, hypoxanthine and inosine et al.).In this paper, the terahertz spectra of many biomolecules fill in the blank-band spectrum in the far-infrared. THz-TDS technique is sensitive to molecular structure and conformation, it provides fingerprint spectra of different molecules, so it can be used to identify structurally similar compounds and isomers. THz-TDS provides a new research tool for qualitative and quantitative analysis of compounds and drug testing and quality control.