Terahertz Time Domain Spectroscopy of Crystalline alpha-Lactose Monohydrate

Abstract

Fundamental biological processes require both small- and large-scale structural changes within molecules, including low frequency collective vibrational motions. Many theoretical calculations have predicted that the collective vibrational motion can be characterized as the large-scale intermolecular motions in the terahertz (THz) frequency range. A new measurement technique based on THz time domain spectroscopy (TDS) can probe directly the collective vibrational motions of biomolecules which involve structural changes and specific biological functions. We report the THz TDS of solid state alpha-lactose monohydrate to characterize the collective vibrational motions. Our measurements show that the THz transmission spectrum of alpha-lactose monohydrate has strong absorption peaks centered at 0.531, 1.195, 1.38, and 1.81 THz, which result from intermolecular interactions.