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Structural elucidation and thermal behavior of l-tyrosine hydroiodide: Hirshfeld surface analysis, halogen-dependent

Carlos A A S Santos¹, Alejandro P Ayala², Bruno S Araujo²

¹Imperatriz Science Center, Federal University of Maranhão, Imperatriz, MA 65900-410, Brazil; Engineering, Pharmacy and Biomedicine Center, UniFacimp Wyden University Center, Imperatriz, MA 65914-335, Brazil; Center for Exact, Natural, and Technological Sciences, State University of the Tocantina Region of Maranhão, Imperatriz, MA 65901-050, Brazil.

Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy

|March 22, 2026

Abstract:

This investigation elucidates the crystal structure, thermal behavior, and vibrational dynamics of L-tyrosine hydroiodide (LTHI), comparing it with its chloride (LTHCl) and bromide (LTHBr) analogue. Single-crystal X-ray diffraction analysis confirmed the monoclinic (P2₁) symmetry of LTHI, featuring asymmetric units interconnected via OH⋯O hydrogen bonds and NH⋯I contact. Differential scanning calorimetry (DSC) demonstrated enhanced thermal stability for LTHI (decomposition at 591 K), attributed to the large ionic radius of I^-, which elongates NH⋯I bonds (3.54 Å) and facilitates stabilizing CH⋯π contacts. Raman spectroscopy data revealed systematic low-frequency shifts (102 cm^-1 for LTHI) with increasing halide size, indicating reduced lattice rigidity due to iodide's polarizability. Hirshfeld surface analysis enabled quantification of the intermolecular interactions, highlighting the key contributions from H⋯I/H⋯I (26.3%) and H⋯C/C⋯H (13.6%) contacts. Electronic structure calculations correlated iodide's polarizability with reduced chemical hardness (η = 2.83 eV) and reversible vibrational responses during heating cycles. These insights highlight halogen-dependent stability mechanisms in amino acid salts for biomaterial design.

Keywords:

Crystal structure Halogen bonding Hirshfeld surface L-tyrosine hydroiodide Raman spectroscopy Thermal stability

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