Conformational analysis of tannic acid: environment effects in electronic and reactivity properties

TL;DR

This study combines advanced computational methods and machine learning to analyze how environmental factors influence the structure and electronic properties of tannic acid, highlighting the importance of accurate conformational understanding.

Contribution

It introduces an integrated approach using enhanced sampling, DFT calculations, and machine learning to explore tannic acid conformations and environmental effects at an atomic level.

Findings

Vacuum favors compact TA structures due to weak interactions.

Water environment leads to more open TA conformations.

HOMO-LUMO gap increases in water, affecting reactivity.

Abstract

Polyphenols are natural molecules of crucial importance in many applications, of which tannic acid (TA) is one of the most abundant and established. Most high-value applications require precise control of TA interactions with the system of interest. However, the molecular structure of TA is still not comprehended at the atomic level, of which all electronic and reactivity properties depend. Here, we combine an enhanced sampling global optimization method with density functional theory (DFT)-based calculations to explore the conformational space of TA assisted by unsupervised machine learning visualization, and then investigate its lowest energy conformers. We study the external environment's effect on the TA structure and properties. We find that vacuum favors compact structures by stabilizing peripheral atoms' weak interactions, while in water, the molecule adopts more open conformations. The frontier molecular orbitals of the conformers with lowest harmonic vibrational free energy have a HOMO-LUMO energy gap of 2.21 (3.27) eV, increasing to 2.82 (3.88) eV in water, at the DFT generalized gradient approximation (and hybrid) level of theory. Structural differences also change the distribution of potential reactive sites. We establish the fundamental importance of accurate structural consideration in determining TA and related polyphenols interactions in relevant technological applications.