Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy of Aryl Cobinamides in the Gas Phase: How Good Are the Calculations for Vitamin B-12 Derivatives?

Aryl corrins represent a novel class of designed B12 derivatives with biological properties of antivitamins B12. In our previous study, we experimentally determined bond strength in a series of aryl-corrins by the threshold collision-induced dissociation experiments (T-CID) and compared the measured bond dissociation energies (BDEs) with those calculated with density functional theory (DFT). We found that the BDEs are modulated by the side chains around the periphery of the corrin unit. Given that aryl cobinamides have many side chains that increase their conformational space and that the question of a specific structure, measured in the gas phase, was important for further evaluation of our T-CID experiment, we proceeded to analyze structural properties of aryl cobinamides using cryogenic ion vibrational predissociation (CIVP) spectroscopy, static DFT, and Born-Oppenheimer molecular dynamic (BOMD) simulations. We found that none of the examined DFT models could reproduce the CIVP spectra convincingly; both static DFT calculations and dynamic BOMD simulations provide a surprisingly poor representation of the vibrational spectra, specifically of the number, position, and intensity of bands assigned to hydrogen-bonded versus non-hydrogen-bonded NH and OH moieties. We conclude that, for a flexible molecule with ca. 150 atoms, more accurate approaches are needed before definitive conclusions about computed properties, specifically the structure of the ground-state conformer, may be made.

Automated summary

We studied the structure and properties of aryl corrins derivatives and found that their bond dissociation energies (BDEs) are modulated by the side chains. To evaluate our experimental results, we analyzed the structural properties of aryl cobinamides using CIVP spectroscopy, static DFT, and dynamic BOMD simulations. The results showed that neither static DFT calculations nor dynamic BOMD simulations could accurately reproduce the CIVP spectra for these flexible molecules, indicating the need for more accurate approaches for characterizing their properties and conformations.