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Updated: Jun 25, 2026

Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy
Published on: December 1, 2023
Spectroscopic identification of gauche and trans conformers in L-phenylalanine Fiber and hydrogel via CH/CD
Ke Lin1, Botao Yao1, Zhiqiang Wang1
1School of Physics, Xidian University, Xi'an 710071, China.
Abstract:
Weak molecular interactions and subtle conformational variations can directly modulate CH bond strength, yet their spectroscopic signatures as a probe of polymorphism remain largely unexplored. Here, chiral phenylalanine in anhydrous Form I, hemihydrated fiber, and hydrogel states were investigated by Raman, IR, and vibrational circular dichroism (VCD) spectroscopy combined with DFT calculations, focusing on the CH stretching region. Isotopic substitution combined with VCD analysis reveals coexistence of gauche (G-) and trans (T) conformers in the fiber and hydrogel. The methine CD stretching vibration of the T conformer exhibits a marked blue shift relative to the G- conformer, indicating strengthening of the CH bond induced by close-range electrostatic repulsion from a neighboring NH₃+ group. Raman analysis of the hydrogel demonstrates preservation of the local G-/T hydrogen-bonded pairing motif and associated π-π interactions despite the absence of long-range crystalline order. These results demonstrate that CH stretching vibrations serve as highly sensitive reporters of weak molecular interactions and local structural organization in condensed phases.
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