IR low-temperature matrix, X-ray and ab initio study on L-isoserine conformations

Area of Science:

• Computational Chemistry
• Spectroscopy
• Crystallography
• Amino Acid Chemistry

Background:

• Understanding the conformational landscape of amino acids is crucial for biochemistry and drug design.
• l-isoserine's structural properties in different environments have not been fully elucidated.
• Matrix isolation spectroscopy and X-ray diffraction offer complementary insights into molecular structure.

Purpose of the Study:

• To characterize the low-temperature matrix infrared spectra of l-isoserine for the first time.
• To predict and identify stable conformers of l-isoserine in both inert matrices and aqueous solutions.
• To determine the solid-state crystal structure of l-isoserine.

Main Methods:

• Infrared (IR) spectroscopy of l-isoserine isolated in Argon (Ar) and Krypton (Kr) matrices.
• Anharmonic density functional theory (DFT) calculations (B3LYP/aug-cc-pVTZ and B3LYP/aug-cc-pVDZ) to interpret spectra and predict conformers.
• X-ray diffraction analysis to solve the crystal structure of l-isoserine.

Main Results:

• The IR spectra of l-isoserine in Ar and Kr matrices were successfully registered and interpreted.
• Fifty-four stable conformers were predicted computationally, with conformer 1 identified as dominant in matrices.
• X-ray diffraction revealed l-isoserine crystallizes in a zwitterionic form (P2(1)2(1)2 space group) with strong intermolecular hydrogen bonds.

Conclusions:

• Conformer 1 is the primary species observed in low-temperature Ar and Kr matrices.
• Computational modeling suggests co-existence of neutral and zwitterionic conformers in aqueous solution.
• The crystal structure highlights the importance of zwitterionic character and hydrogen bonding in solid-state l-isoserine.