# The Role of Weak Interactions in Characterizing Peptide Folding Preferences using a QTAIM Interpretation of the Ramachandran Plot ({\phi}-{\psi})

## TL;DR

This paper introduces a novel interpretation of the Ramachandran plot incorporating weak interactions like hydrogen bonds using QTAIM analysis, providing new insights into peptide folding preferences without large data sets.

## Contribution

It develops a QTAIM-based method to interpret the Ramachandran plot, including weak interactions, revealing non-trivial relationships and aligning with physical intuition.

## Key findings

- QTAIM analysis identifies key regions of the Ramachandran plot.
- A non-linear relationship exists between QTAIM and conventional plots.
- Weak bonds correlate with 'unlikely' conformational regions.

## Abstract

The Ramachandran plot is a potent way to understand structures of biomolecules, however, the original formulation of the Ramachandran plot only considers backbone conformations. We formulate a new interpretation of the original Ramachandran plot ($\phi-\psi$) that can include a description of the weaker interactions including both the hydrogen bonds and H$---$H bonds as a new way to derive insights into the phenomenon of peptide folding. We use QTAIM (quantum theory of atoms in molecules) to interpret the Ramachandran plot. Specifically, we show that QTAIM analysis permits identifying key regions of the Ramachandran plot without the need for massive data sets. A highly non-linear relationship is found between the QTAIM vector-derived interpreted Ramachandran plot and the conventional Ramachandran plot ($\phi-\psi$) demonstrating that this new approach is not a trivial coordinate transformation. An investigation of both the backbone and the weaker bonds within the framework of the QTAIM interpreted Ramachandran plot was found to be in line with physical intuition. The least-preferred directions calculated for the hydrogen bonds and H$---$H bonds were found to coincide with the 'unlikely' regions of the Ramachandran plot.

---
Source: https://tomesphere.com/paper/1706.05658