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Extracellular electron transfer (EET) is an anaerobic respiration process that couples carbon oxidation to the reduction of metal species. In the presence of a suitable metal catalyst, EET allows for cellular metabolism to control a variety of synthetic transformations. Here, we report the use of EET from the model electroactive bacterium Shewanella oneidensis for metabolic and genetic control over Cu(I)-catalyzed Alkyne-Azide Cycloaddition (CuAAC). CuAAC conversion under anaerobic and aerobic conditions was dependent on live, actively respiring S. oneidensis cells. In addition, reaction progress and kinetics could be further manipulated by tailoring the central carbon metabolism of S. oneidensis. Similarly, CuAAC activity was dependent on specific EET pathways and could be manipulated using inducible genetic circuits controlling the expression of EET-relevant proteins including MtrC, MtrA, and CymA. EET-driven CuAAC also exhibited modularity and robustness in ligand tolerance and substrate scope. Furthermore, the living nature of this system could be exploited to perform multiple reaction cycles without requiring regeneration, something inaccessible to traditional chemical reductants. Finally, S. oneidensis enabled bioorthogonal CuAAC membrane labelling on live mammalian cells without affecting cell viability, suggesting that S. oneidensis can act as a dynamically tunable biocatalyst in complex environments. In summary, our results demonstrate how EET can expand the reaction scope available to living systems by enabling cellular control of CuAAC.

Genetic engineering of nanoparticle biosynthesis in bacteria could help facilitate the production of nanoparticles with enhanced or desired properties. However, this process remains limited due to the lack of mechanistic knowledge regarding specific enzymes and other key biological factors. Herein, we report on the ability of small noncoding RNAs (sRNAs) to affect silver nanoparticle (AgNP) biosynthesis using the supernatant from the bacterium Deinococcus radiodurans. Deletion strains of 12 sRNAs potentially involved in the oxidative stress response were constructed, and the supernatants from these strains were screened for their effect on AgNP biosynthesis. We identified several sRNA deletions that drastically decreased AgNP yield compared to the wild-type (WT) strain, suggesting the importance of these sRNAs in AgNP biosynthesis. Furthermore, AgNPs biosynthesized using the supernatants from three of these sRNA deletion strains demonstrated significantly enhanced antimicrobial and catalytic activities against environmentally relevant dyes and bacteria relative to AgNPs biosynthesized using the WT strain. Characterization of these AgNPs using electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) revealed that the deletion of these small RNAs led to changes within the supernatant composition that altered AgNP properties such as the surface chemistry, surface potential, and overall composition. Taken together, our results demonstrate that modulating specific sRNA levels can affect the composition of supernatants used to biosynthesize AgNPs, resulting in AgNPs with unique material properties and improved functionality; as such, we introduce sRNAs as a new platform for genetically engineering the biosynthesis of metal nanoparticles using bacteria. Many of the sRNAs examined in this work have potential regulatory roles in oxidative stress responses; further studies into their targets could help provide insight into the specific molecular mechanisms underlying bacterial biosynthesis and metal reduction, enabling the production of nanoparticles with enhanced properties.

Metal-organic framework (MOF) thin films allow the unique properties of MOFs to be incorporated into membranes and micro-electronic devices and also permit studies of catalysis employing powerful u...

Amyloid peptides nucleate from monomers to aggregate into fibrils through primary nucleation; pre-existing fibrils can then act as seeds for additional monomers to fibrillize through secondary nucleation. Both nucleation processes can occur simultaneously, yielding a distribution of fibril polymorphs that can generate a spectrum of neurodegenerative effects. Understanding the mechanisms driving polymorph structural distribution during both nucleation processes is important for uncovering fibril structure-function relationships, as well creating polymorph distributions in vitro that better match distributions found in vivo. Here, we explore how cross-seeding WT Aβ1-40 with Aβ1-40 mutants E22G (Arctic) and E22Δ (Osaka), as well as with WT Aβ1-42 affects the distribution of fibril structural polymorphs, and how changes in structural distribution impact toxicity. Transmission electron microscopy analysis reveals that fibril seeds derived from mutants of Aβ1-40 impart their structure to WT Aβ1-40 monomer during secondary nucleation, but WT Aβ1-40 fibril seeds do not affect the structure of fibrils assembled from mutant Aβ1-40 monomers, despite kinetics data indicating accelerated aggregation when cross-seeding of any combination of mutants. Additionally, WT Aβ1-40 fibrils seeded with mutant fibrils to produce similar structural distributions to the mutant seeds also produced similar cytotoxicity on neuroblastoma cell lines. This indicates that mutant fibril seeds not only impart their structure to growing WT Aβ1-40 aggregates, but they also impart cytotoxic properties. Our findings provide clear evidence that there is a relationship between fibril structure and phenotype on a polymorph population level, and that these properties can be passed on through secondary nucleation of succeeding generations of fibrils.

Thin films of ultrahigh porous metal–organic frameworks (MOFs) are highly desirable because the unique characteristics of MOFs could then be incorporated into micro-electronic devices, sensors, and membranes. Here we report a new thin film growth method for highly oriented Cu3(BTC)2 (HKUST-1) under vacuum without the use of solvents. Using layer-by-layer (LBL) growth, we sequentially deposited H3BTC from a chemical vapor deposition process and Cu from a physical vapor deposition process. Adopting this methodology, we grew thin films of HKUST-1 by sequentially depositing one monolayer (ML) of Cu after each H3BTC deposition cycle. The transition of Cu0 to Cu2+ by forming paddle-wheel units of HKUST-1 was confirmed by XPS, and is facilitated by background gas molecules, O2 and H2O, with no indication of copper oxide formation. Our HKUST-1 thin films have two distinct planes, the (220) plane detected by glancing angle XRD and the (222) plane identified by in-plane XRD, which indicates that the HKUST-1 thin films are highly oriented. Moreover, the thickness of the HKUST-1 thin films linearly increased with the number of LBL cycles by ∼20 nm for each LBL cycle as measured by AFM. Finally, we measured H2O desorption in a 100 nm HKUST-1 film and observed the existence of strongly bound H2O molecules absorbed within the HKUST-1 film, which predominantly desorb at ∼398 K. Overall, we show how to control the growth of highly oriented HKUST-1 thin films through a bottom-up approach by directly depositing H3BTC and Cu under high vacuum.

The aggregation of Amyloid-β (Aβ) is associated with the onset of Alzheimer’s Disease (AD) and involves a complex kinetic pathway as monomers self-assemble into fibrils. A central feature of amyloid fibrils is the existence of multiple structural polymorphs, which complicates the development of disease-relevant structure-function relationships. Developing these relationships requires new methods to control fibril structure. In this work, we demonstrate that mesoporous silicas (SBA-15) functionalized with hydrophobic (SBA-PFDTS) and hydrophilic groups (SBA-PEG) direct the aggregation kinetics and resulting structure of Aβ1-40 fibrils. The hydrophilic SBA-PEG had little effect on amyloid kinetics while as-synthesized and hydrophobic SBA-PFDTS accelerated aggregation kinetics. Subsequently, we quantified the relative population of fibril structures formed in the presence of each material using electron microscopy. Fibrils formed from Aβ1-40 exposed to SBA-PEG were structurally similar to control fibrils. In contrast, Aβ1-40 incubated with SBA-15 or SBA-PFDTS formed fibrils with shorter cross-over distances that were more structurally representative of fibrils found in AD patient-derived samples. Overall, these results suggest that mesoporous silicas and other exogenous materials are promising scaffolds for the de novo production of specific fibril polymorphs of Aβ1-40 and other amyloidogenic proteins.Significance StatementA major challenge in understanding the progression of Alzheimer’s Disease lies in the various fibril structures, or polymorphs, adopted by Amyloid-β (Aβ). Heterogenous fibril populations may be responsible for different disease phenotypes and growing evidence suggests that Aβ fibrils formed in vitro are structurally distinct from patient-derived fibrils. To help bridge this gap, we used surface-functionalized mesoporous silicas to influence the formation of Aβ1-40 fibrils and evaluated the distribution of resulting fibril polymorphs using electron microscopy (EM). We found that silicas modified with hydrophobic surfaces resulted in fibril populations with shorter cross-over distances that are more representative of Aβ fibrils observed ex vivo. Overall, our results indicate that mesoporous silicas may be leveraged for the production of specific Aβ polymorphs.

We report a noncovalent surface functionalization technique for water-stable metal-organic frameworks using short peptide sequences identified via phage display. Specific frameworks-binding peptides were identified for crystalline Zn(MeIM)2 (MeIM: 2-methylimidazole, ZIF-8), semiamorphous Fe-BTC (BTC: 1,3,5-benzene-tricarboxylate), and Al(OH)(C4H2O4) (MIL-53(Al)-FA, FA: fumaric acid), and their thermodynamic binding affinities and specificities were measured. Electron microscopy, powder X-ray diffraction, and gas adsorption analysis confirmed that the peptide-functionalized frameworks retained similar characteristics compared to their as-synthesized counterparts. Confocal laser-scanning microscopy demonstrated that peptide was localized on the surface of the frameworks, whereas surface area measurements showed no evidence of pore blockage. Finally, we measured the pH-dependent release of fluorescein from peptide-functionalized frameworks and discovered that peptide binding can attenuate fluorescein release by improving framework stability under low pH conditions. Our results demonstrate that phage display can be used as a general method to identify specific peptide sequences with strong binding affinity to water-stable metal-organic frameworks and that these peptides can alter drug release kinetics by affecting framework stability in aqueous environments.

An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3 ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340,000, at a catalyst loading of only 1 ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear α-olefins (LAOs) and other terminal-olefin products.

Cooperative binding, whereby an initial binding event facilitates the uptake of additional substrate molecules, is common in biological systems such as haemoglobin. It was recently shown that porous solids that exhibit cooperative binding have substantial energetic benefits over traditional adsorbents, but few guidelines currently exist for the design of such materials. In principle, metal-organic frameworks that contain coordinatively unsaturated metal centres could act as both selective and cooperative adsorbents if guest binding at one site were to trigger an electronic transformation that subsequently altered the binding properties at neighbouring metal sites. Here we illustrate this concept through the selective adsorption of carbon monoxide (CO) in a series of metal-organic frameworks featuring coordinatively unsaturated iron(ii) sites. Functioning via a mechanism by which neighbouring iron(ii) sites undergo a spin-state transition above a threshold CO pressure, these materials exhibit large CO separation capacities with only small changes in temperature. The very low regeneration energies that result may enable more efficient Fischer-Tropsch conversions and extraction of CO from industrial waste feeds, which currently underutilize this versatile carbon synthon. The electronic basis for the cooperative adsorption demonstrated here could provide a general strategy for designing efficient and selective adsorbents suitable for various separations.

Several new C-H activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts were evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g. carboxylates). The use of nitrato-type ligands, in place of carboxylates, afforded a significant improvement in metathesis activity and selectivity. With these catalysts, turnover numbers approaching 1000 were possible for a variety of cross-metathesis reactions, including the synthesis of industrially-relevant products.

The preparation of new phosphonium alkylidene ruthenium metathesis catalysts containing N-heterocyclic carbenes (NHCs) that result in a preference for degenerate metathesis is described. The reaction of the catalysts with ethylene or substrates relevant to ring-closing metathesis (RCM) produced ruthenacyclobutanes that could be characterized by cryogenic NMR spectroscopy. The rate of α/β methylene exchange in ethylene-only ruthenacycles was found to vary widely between ruthenacycles, in some cases being as low as 3.97 s^(–1) at −30 °C, suggesting that the NHC plays an important role in degenerative metathesis reactions. Attempts to generate RCM-relevant ruthenacycles resulted in the low-yielding formation of a previously unobserved species, which we assign to be a β-alkyl-substituted ruthenacycle. Kinetic investigations of the RCM-relevant ruthenacycles in the presence of excess ethylene revealed a large increase in the kinetic barrier of the rate-limiting dissociation of the cyclopentene RCM product compared with previously investigated catalysts. Taken together, these results shed light on the degenerate/productive selectivity differences observed for different metathesis catalysts.

N-aryl, N-alkyl N-heterocyclic carbene (NHC) ruthenium metathesis catalysts are highly selective toward the ethenolysis of methyl oleate, giving selectivity as high as 95% for the kinetic, ethenolysis products over the thermodynamic, self-metathesis products. The examples described herein represent some of the most selective NHC-based ruthenium catalysts for ethenolysis reactions to date. Furthermore, many of these catalysts show unusual preference and stability toward propagating as a methylidene species, and provide good yields and turnover numbers (TONs) at relatively low catalyst loading (

The synthesis and characterization of latent 18-electron ruthenium benzylidene complexes (PCy_3)((^κN,O)-picolinate)_2RuCHPh (5) and (H_2IMes)((^κN,O)-picolinate)_2RuCHPh (6) are described. Both complexes appear as two isomers. The ratio between the isomers is dependent on l-type ligand. The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli. Upon addition of HCl, complexes 5 and 6 become highly active in olefin metathesis reactions. The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation. Trapping experiments suggests that the acid converts the 18-electron complexes into their corresponding highly olefin metathesis active 14-electron benzylidenes.

The first example of ruthenium-mediated ring-opening metathesis polymerization (ROMP) generating highly cis, highly tactic polymers is reported. While the cis content varied from 62 to >95% depending on the monomer structure, many of the polymers synthesized displayed high tacticity (>95%). Polymerization of an enantiomerically pure 2,3-dicarboalkoxynorbornadiene revealed a syndiotactic microstructure.

The mechanism and origins of Z-selectivity in olefin metathesis with chelated Ru catalysts were explored using density functional theory. The olefin approaches from the "side" position of the chelated Ru catalysts, in contrast to reactions with previous unchelated Ru catalysts that favor the bottom-bound pathway. Steric repulsions between the substituents on the olefin and the N-substituent on the N-heterocyclic carbene ligand lead to highly selective formation of the Z product.

Cis-selective ring-opening metathesis polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C–H activated, ruthenium-based metathesis catalyst is reported. The cis content of the isolated polymers depended heavily on the monomer structure and temperature. A cis content as high as 96% could be obtained by lowering the temperature of the polymerization.

The formal cycloaddition between 1,3-diaza-2-azoniaallene salts and alkynes or alkyne equivalents provides an efficient synthesis of 1,3-diaryl-1H-1,2,3-triazolium salts, the direct precursors of 1,2,3-triazol-5-ylidenes. These N,N-diarylated mesoionic carbenes (MICs) exhibit enhanced stability in comparison to their alkylated counterparts. Experimental and computational results confirm that these MICs act as strongly electron-donating ligands. Their increased stability allows for the preparation of ruthenium olefin metathesis catalysts that are efficient in both ring-opening and ring-closing reactions.

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Bronsted acid results in protonolysis of the Ru–MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/MIC catalyst was found to exceed those of current commercial ruthenium catalysts.