Protonated glycine supramolecular systems: the need for quantum dynamics

Area of Science:

• Computational Chemistry
• Spectroscopy
• Quantum Dynamics

Background:

• Infrared (IR) spectroscopy is vital for studying molecular vibrations and interactions.
• Experimental IR spectra of protonated glycine supramolecular systems (Gly₂H⁺ and (GlyH + nH₂)) present interpretation challenges.
• Previous theoretical investigations have not definitively resolved spectral assignments or confirmed structural hypotheses for these systems.

Purpose of the Study:

• To address unresolved questions in the experimental IR spectra of protonated glycine dimer (Gly₂H⁺) and (GlyH + nH₂) systems.
• To demonstrate the necessity of including quantum dynamical effects for accurate spectral characterization.
• To provide definitive theoretical confirmation for structural hypotheses.

Main Methods:

• Application of the divide-and-conquer semiclassical initial value representation (SC-IVR) technique.
• Approximation of quantum dynamics in high-dimensional systems with high accuracy.
• Comparison of SC-IVR with scaled-harmonic and classical dynamics approaches.

Main Results:

• The SC-IVR method successfully resolves ambiguities in the IR spectra of protonated glycine systems.
• Quantum dynamical simulations provide accurate characterization, outperforming scaled-harmonic and classical methods.
• Specific insights into the conformer assignment for Gly₂H⁺ and structural features of (GlyH + nH₂) are obtained.

Conclusions:

• Quantum dynamical effects are essential for accurately interpreting IR spectra of complex protonated systems.
• The SC-IVR technique offers a reliable method for studying molecular vibrations in large systems.
• Quantum dynamics should be considered in the analysis of protonated systems, including biological structures.