Incoherent Neutron Scattering and Terahertz Time-Domain Spectroscopy on Protein and Hydration Water.

Area of Science:

• Molecular dynamics
• Spectroscopy
• Biophysics

Background:

• Incoherent inelastic and quasi-elastic neutron scattering (INS) and terahertz time-domain spectroscopy (THz-TDS) probe molecular dynamics using different mechanisms.
• Neutrons interact with nuclei, while THz-TDS detects dipole moment correlations, leading to distinct information and sample condition requirements.
• Both methods overlap in measurable energy regions, offering complementary perspectives on molecular motion.

Purpose of the Study:

• To compare the quantum beam properties, advantages, and disadvantages of INS and THz-TDS for molecular spectroscopy.
• To highlight the complementary nature of these techniques in studying molecular dynamics.
• To emphasize the utility of combining INS and THz-TDS for biomolecular and hydration water dynamics analysis.

Main Methods:

• Incoherent inelastic and quasi-elastic neutron scattering (INS) utilizes neutron scattering, sensitive to atomic position auto-correlation functions and hydrogen atom interactions.
• Terahertz time-domain spectroscopy (THz-TDS) employs light as a probe, measuring dipole moment cross-correlation functions.
• INS requires large facilities (reactors/accelerators), while THz-TDS is laboratory-based.

Main Results:

• INS is sensitive to translational diffusion, especially for hydrogenous materials.
• THz-TDS excels at observing rotational motion and is affected by water absorption in biomolecular samples.
• INS can selectively observe molecules using isotopic differences in scattering cross-sections.

Conclusions:

• INS and THz-TDS are complementary techniques for molecular dynamics studies.
• INS primarily captures translational motion, whereas THz-TDS focuses on rotational motion.
• Combining INS and THz-TDS provides a powerful approach for analyzing complex biomolecular and hydration water dynamics.