Synthesis, Characterization, and Reactivity of a Highly Oxidative Mononuclear Manganese(IV)–Bis(Fluoro) Complex

Recently, transition-metal terminal nonoxo complexes have shown a remarkable ability to activate and functionalize C–H bonds via proton-coupled electron transfer (PCET). Here we report the first example of a mononuclear manganese(IV) bis(fluoro) complex bearing a tetradentate pyridinophane ligand, [MnIV(TBDAP)(F)2]2+ (3), with an X-ray single crystal structure and physicochemical characterization. The manganese(IV) bis(fluoro) complex has a very high reduction potential of 1.61 V vs SCE, thereby enabling the four-electron oxidation of mesitylene to 3,5-dimethylbenzaldehyde. Kinetic studies, including the kinetic isotope effect and employment of other toluene derivatives, reveal the electron transfer (ET)-driven PCET in the C–H bond activation of mesitylene by 3. This novel metal halide intermediate would be prominently valuable for expanding transition-metal halide chemistry

Colour and behavioural data, Activity level survey data, and predation experiments data file

Colour and behavioural data, Activity level survey data, and predation experiments data fil

Keratinolytic activity of AWCE.

<p>Time course of decomposition of native chicken feathers by CEAW-1 at 80°C (A) and the release of free amino acids from feather hydrolysates (B) in the presence and absence of 10 mM DTT.</p

Bioinformatic analysis of putative proteases from <i>F</i>. <i>islandiucm</i> AW-1 by MEROPS.

<p>Bioinformatic analysis of putative proteases from <i>F</i>. <i>islandiucm</i> AW-1 by MEROPS.</p

Comparison of the proteolytic activity of AWCE and other proteases towards casein and recombinant keratin substrates.

<p>Enzyme assays for each protease were performed under the standard assay conditions (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172712#sec002" target="_blank">Materials and Methods</a>).</p

The degree of keratin degradation by AWCE.

<p>(A) Purification of fluorescein-5-maleimide (FM)-conjugated Chr27_FK12 β-keratin by Superdex 200 10/300 GL column chromatography. (B) Relative degradation of FM-conjugated Chr27_FK12 by AWCE and proteinase K.</p

Expression and purification of soluble <i>G</i>. <i>gallus</i> β-keratins.

<p>(A) Construction of expression vectors for recombinant Chr2_FK4, Chr25_FK25, and Chr27_FK12 β-keratins. (B) SDS-PAGE analysis of recombinant keratins expressed in <i>E</i>. <i>coli</i>, and purification of soluble Chr2_FK4 and Chr27_FK12 β-keratins. Lane M, molecular weight markers; lane 1, <i>E</i>. <i>coli</i> BL21 (DE3); lane 2, <i>E</i>. <i>coli</i> BL21 (DE3) (pET-28a_Chr2); lane 3, <i>E</i>. <i>coli</i> BL21 (DE3) (pET-28a_Chr25); lane 4, <i>E</i>. <i>coli</i> BL21 (DE3) (pET-28a_Chr27); S, supernatant; P, pellet. (C) Transmission electron microscope images of recombinant β-keratins. (D) Quantification of soluble Chr2_FK4 and Chr27_FK12 β-keratins using Kunitz and ninhydrin assays. Linear correlation between the absorbance at 280 nm and the concentration of purified β-keratins.</p

Physicochemical properties of crude extracts from <i>Fervidobacterium islandicum</i> AW-1 (AWCE).

<p>Effect of temperature (A) and pH (B) on the proteolytic activity of AWCE. (C) Time course of irreversible thermal inactivation of AWCE and papain at various temperatures. (D) Effect of 0.2% (w/v) SDS on the enzyme activity of AWCE and papain at various temperatures. After various periods of incubation at various temperatures, aliquots were withdrawn and their residual activities were measured under the standard assay conditions.</p

Keratin peptide mapping.

<p>(A) <i>In silico</i> digestion of soluble keratins by proteases and AWCE using the program PeptideCutter. (B) LC-MS/MS analysis of keratin hydrolysates generated by AWCE. Keratinolytic peptides matched with soluble Chr2_FK4 and Chr27_FK12 β-keratins are depicted in bold and colored red.</p

Bacterial and fungal keratinolytic enzymes.

<p>Bacterial and fungal keratinolytic enzymes.</p