UndA is a nonheme iron enzyme that activates oxygen to catalyze the decarboxylation of dodecanoic acid to undecene and carbon dioxide. We report the first optical and Mossbauer spectroscopic characterization of UndA, revealing that the enzyme harbors a coupled dinuclear iron cluster. Single turnover studies confirm that the reaction of the diferrous enzyme with dioxygen produces stoichiometric product per cluster. UndA is the first characterized example of a diiron decarboxylase, thus expanding the repertoire of reactions catalyzed by dinuclear iron enzymes.
Tuning metal oxidation states in
metal–organic framework
(MOF) nodes by switching between two discrete linker photoisomers
via an external stimulus was probed for the first time. On the examples
of three novel photochromic copper-based frameworks, we demonstrated
the capability of switching between +2 and +1 oxidation states, on
demand. In addition to crystallographic methods used for material
characterization, the role of the photochromic moieties for tuning
the oxidation state was probed via conductivity measurements, cyclic
voltammetry, and electron paramagnetic resonance, X-ray photoelectron,
and diffuse reflectance spectroscopies. We confirmed the reversible
photoswitching activity including photoisomerization rate determination
of spiropyran- and diarylethene-containing linkers in extended frameworks,
resulting in changes in metal oxidation states as a function of alternating
excitation wavelengths. To elucidate the switching process between
two states, the photoisomerization quantum yield of photochromic MOFs
was determined for the first time. Overall, the introduced noninvasive
concept of metal oxidation state modulation on the examples of stimuli-responsive
MOFs foreshadows a new pathway for alternation of material properties
toward targeted applications.
BesC catalyzes the iron- and O2-dependent cleavage of
4-chloro-l-lysine to form 4-chloro-l-allylglycine,
formaldehyde, and ammonia. This process is a critical step for a biosynthetic
pathway that generates a terminal alkyne amino acid which can be leveraged
as a useful bio-orthogonal handle for protein labeling. As a member
of an emerging family of diiron enzymes that are typified by their
heme oxygenase-like fold and a very similar set of coordinating ligands,
recently termed HDOs, BesC performs an unusual type of carbon–carbon
cleavage reaction that is a significant departure from reactions catalyzed
by canonical dinuclear-iron enzymes. Here, we show that BesC activates
O2 in a substrate-gated manner to generate a diferric-peroxo
intermediate. Examination of the reactivity of the peroxo intermediate
with a series of lysine derivatives demonstrates that BesC initiates
this unique reaction trajectory via cleavage of the C4–H bond;
this process represents the rate-limiting step in a single turnover
reaction. The observed reactivity of BesC represents the first example
of a dinuclear-iron enzyme that utilizes a diferric-peroxo intermediate
to capably cleave a C–H bond as part of its native function,
thus circumventing the formation of a high-valent intermediate more
commonly associated with substrate monooxygenations.
Increasing levels of energy consumption, dwindling resources, and environmental considerations have served as compelling motivations to explore renewable alternatives to petroleum-based fuels, including enzymatic routes for hydrocarbon synthesis. Phylogenetically diverse species have long been recognized to produce hydrocarbons, but many of the enzymes responsible have been identified within the past decade. The enzymatic conversion of C chain length fatty aldehydes (or acids) to C hydrocarbons, alkanes or alkenes, involves a C-C scission reaction. Surprisingly, the enzymes involved in hydrocarbon synthesis utilize non-heme mononuclear iron, dinuclear iron, and thiolate-ligated heme cofactors that are most often associated with monooxygenation reactions. In this review, we examine the mechanisms of several enzymes involved in hydrocarbon biosynthesis, with specific emphasis on the structural and electronic changes that enable this functional switch.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.