Abstract
Fluorescence in biological systems is usually associated with the presence of aromatic groups. Here, we show that specific hydrogen bonding networks can significantly affect fluorescence employing a combined experimental and computational approach. In particular, we reveal that the single amino acid L-glutamine, by undergoing a chemical transformation leading to the formation of a short hydrogen bond, displays optical properties that are significantly enhanced compared to L-glutamine itself. Ab initio molecular dynamics simulations highlight that these short hydrogen bonds prevent the appearance of a conical intersection between the excited and the ground states and thereby significantly decrease non-radiative transition probabilities. Our findings open the doors for the design of new photoactive materials with biophotonic applications.
Significance statement Intrinsic fluorescence of non-aromatic amino acids is a puzzling phenomenon with an enormous potential for technological and biomedical applications. The physical origins of this effect, however, remain elusive. Herein, we demonstrate how specific hydrogen bond networks can modulate fluorescence. We highlight the key role played by short hydrogen bonds in the networks on the ensuing fluorescence and we provide a detailed molecular mechanism to explain this unusual non-aromatic optical properties. Our findings should benefit the design of novel optically active biomaterials for applications in biosensing and imaging.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
In the revised manuscript we provide excited state molecular dynamics simulations which directly probe the fluorescence mechanism and further advances this work.
Abbreviations
- SEM
- scanning electron microscopy
- XRD
- X-ray diffraction
- THz-TDS
- terahertz time domain spectroscopy
- DFT
- density functional theory
- TD-DFT
- time dependent DFT
- SHB
- short hydrogen bond
- CT
- charge transfer
- L-glu
- L-glutamine
- L-pyro
- L-pyroglutamine
- L-pyro-amm
- L-pyroglutamine complexed with an ammonium ion.