Distance-Dependence of Photo-CIDNP in Biomimetic Tryptophan–Flavin Diads

Abstract

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are essential tools in natural and life sciences, but their low sensitivity often hampers their applicability. Photochemically induced dynamic nuclear polarization (photo-CIDNP) offers a versatile and mild method to overcome this limitation. Here, we report on structure-photo-CIDNP relationship studies in liquid-state NMR utilizing a holistic approach. We synthesized biomimetic tryptophan–flavin diads with varying linker lengths composed of conformationally rigid oligoproline units. The predominant polyproline II (PPII) helical structure ensures consistent donor–acceptor distances. Photo-CIDNP NMR experiments revealed significant hyperpolarization effects, particularly in diads with six proline units, mimicking the spatial arrangement found in natural photoactive proteins. Our findings highlight the potential of these biomimetic diads to enhance nuclear hyperpolarization in NMR spectroscopy. This work provides valuable insights into the design of diads for efficient photo-CIDNP generation, paving the way for advanced studies in modern NMR and bio-MRI.