5 research outputs found
Reversible Generation of Metastable Enols in the 1,4-Addition of Thioacetic Acid to α,β-Unsaturated Carbonyl Compounds
Addition of thioacetic acid to reactive α,β-unsaturated
carbonyl compounds like acrolein or crotonaldehyde in acetone-<i>d</i><sub>6</sub> generates metastable (<i>E</i>)-
and (<i>Z</i>)-1-alkenols, which tautomerize slowly at ambient
temperature. The 1,4-addition of thioacetic acid and crotonaldehyde
to (<i>Z</i>)-3-(acetylsulfanyl)-1-propen-1-ol is reversible
with <i>K</i><sub>eq</sub> = 5.5 ± 0.5 L/mol. A concerted,
cyclic 1,4-addition mode is proposed to explain the preferred (<i>Z</i>)-stereoselectivity in lower polarity, nonprotic solvents
Synthesis of Soai Aldehydes for Asymmetric Autocatalysis by Desulfurative Cross-Coupling
Palladium-catalyzed
dehydrosulfurative Liebeskind–Srogl
coupling of terminal alkynes with 2-mercapto-1,3-pyrimidine-5-carbaldehyde
under base-free conditions provides 2-(alkynyl)-1,3-pyrimidine-5-carbaldehydes,
which are substrates for autocatalytic amplification of chirality
according to Soai et al. The mercapto aldehyde acceptor is obtained
by condensation of Arnold’s vinamidinium salt with thiourea
Oxyluciferin Derivatives: A Toolbox of Environment-Sensitive Fluorescence Probes for Molecular and Cellular Applications
In this work, we
used firefly oxyluciferin (<b>OxyLH</b><sub><b>2</b></sub>) and its polarity-dependent fluorescence mechanism
as a sensitive tool to monitor biomolecular interactions. The chromophores, <b>OxyLH</b><sub><b>2</b></sub>, and its two analogues, <b>4-MeOxyLH</b> and <b>4,6′-DMeOxyL</b>, were modified
trough carboxylic functionalization and then coupled to the N-terminus
part of Tat and NCp7 peptides of human immunodeficiency virus type-1
(HIV-1). The photophysical properties of the labeled peptides were
studied in live cells as well as in complex with different oligonucleotides
in solution. By monitoring the emission properties of these derivatives
we were able, for the first time, to study <i>in vitro</i> biomolecular interactions using oxyluciferin as a sensor. As an
additional application, cyclopropyl-oxyluciferin (<b>5,5-Cpr-OxyLH</b>) was site-specifically conjugated to the thiol group (Cys-232) of
the human protein α-1 antytripsin to investigate its interaction
with porcine pancreatic elastase. Our data demonstrate that <b>OxyLH</b><sub><b>2</b></sub> and its derivatives can be
used as fluorescence reporters for monitoring biomolecular interactions
Bioinspired Molecular Lantern: Tuning the Firefly Oxyluciferin Emission with Host–Guest Chemistry
Fireflies
generate flashes of visible light via luciferase-catalyzed
chemiexcitation of the substrate (luciferin) to the first excited
state of the emitter (oxyluciferin). Microenvironment effects are
often invoked to explain the effects of the luciferase active pocket
on the emission; however, the exceedingly complex spectrochemistry
and synthetic burdens have precluded elucidation of the nature of
these interactions. To decipher the effects of microenvironment on
the light emission, here the hydrophobic interior of cucurbit[7]uril
(CB7) is used to mimic the nonpolar active pocket of luciferase. The
hydrophobic interior of CB7 induces shifts of the ground-state p<i>K</i><sub>a</sub>s by 1.9–2.5 units to higher values.
Upon sequestration, the emission maxima of neutral firefly oxyluciferin
and its conjugate monodeprotonated base are blue-shifted by 40 and
39 nm, respectively, resulting in visual color changes of the emitted
light
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