Structure and Flexibility of Copper‐Modified DNA G‐Quadruplexes Investigated by 19F ENDOR Experiments at 34 GHz

DNA G‐quadruplexes (GQs) are of great interest due to their involvement in crucial biological processes such as telomerase maintenance and gene expression. Furthermore, they are reported as catalytically active DNAzymes and building blocks in bio‐nanotechnology. GQs exhibit remarkable structural diversity and conformational heterogeneity, necessitating precise and reliable tools to unravel their structure‐function relationships. Here, we present insights into the structure and conformational flexibility of a unimolecular GQ with high spatial resolution via electron‐nuclear double resonance (ENDOR) experiments combined with Cu(II) and fluorine labeling. These findings showcase the successful application of the 19F‐ENDOR methodology at 34 GHz, overcoming the limitations posed by the complexity and scarcity of higher‐frequency spectrometers. Importantly, our approach retains both sensitivity and orientational resolution. This integrated study not only enhances our understanding of GQs but also expands the methodological toolbox for studying other macromolecules.