On the influence of water on the electronic structure of firefly oxyluciferin anions from absorption spectroscopy of bare and monohydrated ions in vacuo

• A complete understanding of the physics underlying the varied colors of firefly bioluminescence remains elusive because it is difficult to disentangle different enzyme-lumophore interactions. Experiments on isolated ions are useful to establish a proper reference when there are no microenvironmental perturbations. Here, we use action spectroscopy to compare the absorption by the firefly oxyluciferin lumophore isolated in vacuo and complexed with a single water molecule. While the process relevant to bioluminescence within the luciferase cavity is light emission, the absorption data presented here provide a unique insight into how the electronic states of oxyluciferin are altered by microenvironmental perturbations. For the bare ion we observe broad absorption with a maximum at 548 ± 10 nm, and addition of a water molecule is found to blue-shift the absorption by approximately 50 nm (0.23 eV). Test calculations at various levels of theory uniformly predict a blue-shift in absorption caused by a single water molecule, but are only qualitatively in agreement with experiment highlighting limitations in what can be expected from methods commonly used in studies on oxyluciferin. Combined molecular dynamics simulations and time-dependent density functional theory calculations closely reproduce the broad experimental peaks and also indicate that the preferred binding site for the water molecule is the phenolate oxygen of the anion. Predicting the effects of microenvironmental interactions on the electronic structure of the oxyluciferin anion with high accuracy is a nontrivial task for theory, and our experimental results therefore serve as important benchmarks for future calculations.

Subject headings

NATURVETENSKAP  -- Kemi -- Teoretisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)

Keyword

Action spectroscopy

Broad absorptions

Influence of water

Molecular dynamics simulations

Non-trivial tasks

Phenolate oxygen

Time dependent density functional theory

Water molecule

Density functional theory

Electronic structure

Experiments

Molecular dynamics

Molecules

Negative ions

Phosphorescence

Bioluminescence

luciferase

luciferin

oxyluciferin

unclassified drug

water

absorption

absorption spectroscopy

article

binding site

calculation

complex formation

crystal structure

dissociation

microenvironment

qualitative analysis

static electricity

Animals

Anions

Color

Electrochemistry

Enzyme-Linked Immunosorbent Assay

Fireflies

Indoles

Luminescence

Mass Spectrometry

Models

Chemical

Models

Molecular

Molecular Dynamics Simulation

Pyrazines

Spectrometry

Mass

Electrospray Ionization

Stereoisomerism

TECHNOLOGY

Publication and Content Type

ref (subject category)

art (subject category)