Aromatic Amino Acids-Guanidinium Complexes through Cation-π Interactions.

Area of Science:

• Computational chemistry
• Molecular interactions
• Biomolecular studies

Background:

• The guanidinium group is crucial in biological systems.
• Aromatic amino acids play vital roles in protein structure and function.
• Understanding cation-aromatic amino acid interactions is key to molecular recognition.

Purpose of the Study:

• To theoretically investigate complexes formed between the guanidinium cation and aromatic amino acids.
• To characterize the nature and strength of interactions, including hydrogen bonds and cation-π interactions.
• To assess the impact of these interactions on the aromaticity of the amino acids.

Main Methods:

• Density Functional Theory (DFT) methods were employed.
• Polarizable Continuum Model (PCM) with water solvation was used.
• Atoms-in-Molecules (AIM) and Natural Bond Orbital (NBO) methodologies were applied for interaction analysis.
• Nitrogen-15 Chemical Shielding (NICS) values were calculated to evaluate aromaticity.

Main Results:

• Complexation between the guanidinium cation and phenylalanine, histidine, tryptophan, and tyrosine was observed.
• Both hydrogen bonds and cation-π interactions were identified as significant binding forces.
• AIM and NBO analyses confirmed the presence and characteristics of these interactions.
• NICS calculations indicated that the aromatic character of the amino acids was not substantially altered upon complexation.

Conclusions:

• Guanidinium cation forms stable complexes with aromatic amino acids through hydrogen bonds and cation-π interactions.
• These interactions are well-defined at the molecular level.
• The aromaticity of the amino acids remains largely preserved, suggesting functional stability in biological contexts.