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Bacteria that perform extracellular electron transfer (EET) are central to redox-driven biotechnologies, including microbial fuel cells, bioremediation, and bioelectrosynthesis. However, engineerable EET strains have been restricted to well-characterized, Gram-negative model species. Light et al. identified a previously unknown but widely conserved EET pathway in the Gram-positive bacterium Listeria monocytogenes.

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.

Spatial concentration gradients of antibiotics are prevalent in the natural environment. Yet, the microbial response in these heterogeneous systems remains poorly understood. We used a microfluidic reactor to create an artificial microscopic ecosystem that generates diffusive gradients of solutes across interconnected microenvironments. With this reactor, we showed that chemotaxis toward a soluble electron acceptor (nitrate) allowed Shewanella oneidensis MR-1 to inhabit and sustain metabolic activity in highly toxic regions of the antibiotic ciprofloxacin (>80× minimum inhibitory concentration, MIC). Acquired antibiotic resistance was not observed for cells extracted from the reactor, so we explored the role of transient adaptive resistance by probing multidrug resistance (MDR) efflux pumps, ancient elements that are important for bacterial physiology and virulence. Accordingly, we constructed an efflux pump deficient mutant (∆mexF) and used resistance-nodulation-division (RND) efflux pump inhibitors (EPIs). While batch results showed the importance of RND efflux pumps for microbial survival, microfluidic studies indicated that these pumps were not necessary for survival in antibiotic gradients. Our work contributes to an emerging body of knowledge deciphering the effects of antibiotic spatial heterogeneity on microorganisms and highlights differences of microbial response in these systems versus well-mixed batch conditions.

Extracellular electron transfer (EET) pathways, such as those in the bacterium Shewanella oneidensis, interface cellular metabolism with a variety of redox-driven applications. However, designer control over EET flux in S. oneidensis has proven challenging because a functional understanding of its EET pathway proteins and their effect on engineering parametrizations (e.g., response curves, dynamic range) is generally lacking. To address this, we systematically altered transcription and translation of single genes encoding parts of the primary EET pathway of S. oneidensis, CymA/MtrCAB, and examined how expression differences affected model-fitted parameters for Fe(III) reduction kinetics. Using a suite of plasmid-based inducible circuits maintained by appropriate S. oneidensis knockout strains, we pinpointed construct/strain pairings that expressed cymA, mtrA, and mtrC with maximal dynamic range of Fe(III) reduction rate. These optimized EET gene constructs were employed to create Buffer and NOT gate architectures that predictably turn on and turn off EET flux, respectively, in response to isopropyl β-D-1-thiogalactopyranoside (IPTG). Furthermore, we found that response functions generated by these logic gates (i.e., EET activity vs inducer concentration) were comparable to those generated by conventional synthetic biology circuits, where fluorescent reporters are the output. Our results provide insight on programming EET activity with transcriptional logic gates and suggest that previously developed transcriptional circuitry can be adapted to predictably control EET flux.

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 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 as for creating polymorph distributions in vitro that better match fibril structures found in vivo. Here, we explore how cross-seeding wild-type (WT) Aβ

Individual cells direct non-equilibrium processes through coordinated signal transduction and gene expression, allowing for dynamic control over multicellular, system-wide behavior. This behavior extends to remodeling the extracellular polymer matrix that encases biofilms and tissues, where constituent cells dictate spatiotemporal network properties including stiffness, pattern formation, and transport properties. The majority of synthetic polymer networks cannot recreate these phenomena due to their lack of autonomous centralized actuators (i.e., cells). In addition, non-living polymer networks that perform computation are generally restricted to a few inputs (e.g., light, pH, enzymes), limiting the logical complexity available to a single network chemistry. Toward synergizing the advantages of living and synthetic systems, engineered living materials leverage genetic and metabolic programming to establish control over material-wide properties. Here we demonstrate that a bacterial metal respiration mechanism, extracellular electron transfer (EET), can control metal-catalyzed radical cross-linking of polymer networks. Linking metabolic electron flux to a synthetic redox catalyst allows dynamic, tunable, and predictable control over material formation and bulk polymer network mechanics using genetic circuits. By programming key EET genes with transcriptional Boolean logic, we rationally design computational networks that sense-and-respond to multiple inputs in biological contexts. Finally, we capitalize on the wide reactivity of EET and redox catalyses to predictably control another class of living synthetic materials using copper(I) alkyne-azide cycloaddition click chemistry. Our results demonstrate the utility of EET as a bridge for controlling abiotic materials and how the design rules of synthetic biology can be applied to emulate physiological behavior in polymer networks.

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.

Enhancing materials with the qualities of living systems, including sensing, computation, and adaptation, is an important challenge in designing next-generation technologies. Living materials address this challenge by incorporating live cells as actuating components that control material function. For abiotic materials, this requires new methods that couple genetic and metabolic processes to material properties. Toward this goal, we demonstrate that extracellular electron transfer (EET) from Shewanella oneidensis can be leveraged to control radical cross-linking of a methacrylate-functionalized hyaluronic acid hydrogel. Cross-linking rates and hydrogel mechanics, specifically storage modulus, were dependent on various chemical and biological factors, including S. oneidensis genotype. Bacteria remained viable and metabolically active in the networks for a least 1 week, while cell tracking revealed that EET genes also encode control over hydrogel microstructure. Moreover, construction of an inducible gene circuit allowed transcriptional control of storage modulus and cross-linking rate via the tailored expression of a key electron transfer protein, MtrC. Finally, we quantitatively modeled hydrogel stiffness as a function of steady-state mtrC expression and generalized this result by demonstrating the strong relationship between relative gene expression and material properties. This general mechanism for radical cross-linking provides a foundation for programming the form and function of synthetic materials through genetic control over extracellular electron transfer.

Gold is a critical resource in the jewelry and electronics industries and is facing increased consumer demand. Accordingly, methods for its extraction from waste effluents and environmental water sources have been sought to supplement existing mining infrastructure. Redox-mediated treatments, such as Fe(II)-based platforms, offer promise for precipitating soluble Au(III). We hypothesized that microbial generation of Fe(II) in the presence of sorbent metal–organic frameworks could capitalize on the advantages of both biological- and chemical-driven extraction approaches. Toward this aim, we tested Au(III) removal by Shewanella oneidensis cultured with Fe(III)-based materials (ferrihydrite, Fe-BTC, MIL-100, or MIL-127). Across all tested materials, S. oneidensis generated the highest levels of redox-active Fe(II) (1.99 ± 0.27 mM) when cultured with MIL-127 as a respiratory substrate in a bicarbonate-buffered medium. This translated into superior Au(III) removal performance in terms of both removal rate and capacity (k = 2.55 ± 0.60 h(−1); Q = 183 mg g(−1)). Unlike other materials tested, MIL-127 also maintained cell viability following repeated Au(III) challenges, enabling the regeneration of Fe(II) in the framework. Together, these effects facilitated the treatment of multiple cycles of Au(III) by S. oneidensis-reduced MIL-127. Overall, this work demonstrates that microbial generation of Fe(II) can facilitate the removal of Au(III), augmenting purely adsorptive platforms. Given the biological and chemical modularity of our system, our results suggest that future optimizations to microbial Fe(II) generation may offer promise for improving Au(III) extraction processes.

Extracellular electron transfer (EET) pathways, such as those in the bacterium Shewanella oneidensis, interface cellular metabolism with a variety of redox-driven applications. However, designer control over EET flux in S. oneidensis has proven challenging because a functional understanding of its EET pathway proteins and their effect on engineering parametrizations (e.g., response curves, dynamic range) is generally lacking. To address this, we systematically altered transcription and translation of single genes encoding parts of the primary EET pathway of S. oneidensis, CymA/MtrCAB, and examined how expression differences affected model-fitted parameters for Fe(III) reduction kinetics. Using a suite of plasmid-based inducible circuits maintained by appropriate S. oneidensis knockout strains, we pinpointed construct/strain pairings that expressed cymA, mtrA, and mtrC with maximal dynamic range of Fe(III) reduction rate. These optimized EET gene constructs were employed to create Buffer and NOT gate architectures that predictably turn on and turn off EET flux, respectively, in response to isopropyl β-D-1-thiogalactopyranoside (IPTG). Furthermore, we found that response functions generated by these logic gates (i.e., EET activity vs inducer concentration) were comparable to those generated by conventional synthetic biology circuits, where fluorescent reporters are the output. Our results provide insight on programming EET activity with transcriptional logic gates and suggest that previously developed transcriptional circuitry can be adapted to predictably control EET flux.

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.

Existe un creciente interes en la biosintesis de nanoparticulas utilizando bacterias debido al potencial de aplicaciones en biorremediacion, catalisis o como antimicrobianos. Sin embargo, la biosintesis sigue siendo limitada por la incapacidad de controlar la morfologia y el tamano de las nanoparticulas debido a la falta de conocimiento sobre los mecanismos moleculares explicitos. Debido a su importancia en la biosintesis de nanoparticulas y como antimicrobianos, enfocamos nuestra discusion en las nanoparticulas de plata, oro y cobre. Discutimos los esfuerzos recientes para dilucidar los mecanismos de reduccion que han identificado enzimas genericas y genes de resistencia de metales como candidatos importantes para facilitar la biosintesis de nanoparticulas. Aunque se sabe que estas enzimas y genes desempenan un papel importante en el mantenimiento de la homeostasis bacteriana, hay pocos informes que analicen este tema. Por lo tanto, discutimos ejemplos de como los genes de resistencia de metales se conservan a traves de las bacterias y se ha demostrado que son importantes tanto para la biosintesis de nanoparticulas como para procesos tales como la virulencia o las respuestas al estres oxidativo. En general, esta revision destaca las conexiones biologicas entre la biosintesis de nanoparticulas y las respuestas al estres mediante el analisis sobre papel de las reductasas y los genes de resistencia del metal en ambos procesos. Este conocimiento proporciona un papel mas importante para la biosintesis de nanoparticulas en bacterias y podria permitir un nivel de biologia de sistemas de control sobre la biosintesis de nanoparticulas

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.

Redox interactions between electroactive bacteria and inorganic materials underpin many emerging technologies, but commonly used materials (e.g., metal oxides) suffer from limited tunability and can be challenging to characterize. In contrast, metal-organic frameworks exhibit well-defined structures, large surface areas, and extensive chemical tunability, but their utility as microbial substrates has not been examined. Here, we report that metal-organic frameworks can support the growth of the metal-respiring bacterium Shewanella oneidensis, specifically through the reduction of Fe(III). In a practical application, we show that cultures containing S. oneidensis and reduced metal-organic frameworks can remediate lethal concentrations of Cr(VI) over multiple cycles, and that pollutant removal exceeds the performance of either component in isolation or bio-reduced iron oxides. Our results demonstrate that frameworks can serve as growth substrates and suggest that they may offer an alternative to metal oxides in applications seeking to combine the advantages of bacterial metabolism and synthetic materials., Interactions between electroactive bacteria and metal oxides are used for bioremediation. Here, the authors report on the application of Fe(III)-containing metal organic frameworks as substrates for bacterial growth which allow for remediation of lethal levels of chromium with high efficacy over several cycles.

Enhancing materials with the qualities of living systems, including sensing, computation, and adaptation, is an important challenge in designing next-generation technologies. Living materials seek to address this challenge by incorporating live cells as actuating components that control material function. For abiotic materials, this requires new methods that couple genetic and metabolic processes to material properties. Toward this goal, we demonstrate that extracellular electron transfer (EET) from Shewanella oneidensis can be leveraged to control radical crosslinking of a methacrylate-functionalized hyaluronic acid hydrogel. Crosslinking rates and hydrogel mechanics, specifically storage modulus, were dependent on a variety of chemical and biological factors, including S. oneidensis genotype. Bacteria remained viable and metabolically active in the crosslinked network for a least one week, while cell tracking revealed that EET genes also encode control over hydrogel microstructure. Moreover, construction of an inducible gene circuit allowed transcriptional control of storage modulus and crosslinking rate via the tailored expression of a key electron transfer protein, MtrC. Finally, we quantitatively modeled dependence of hydrogel stiffness on steady-state gene expression, and generalized this result by demonstrating the strong relationship between relative gene expression and material properties. This general mechanism for radical crosslinking provides a foundation for programming the form and function of synthetic materials through genetic control over extracellular electron transfer.Significance StatementNext-generation materials will require coupling the advantages of engineered and natural systems to solve complex challenges in energy, health, and the environment. Living cells, such as bacteria, naturally possess many of the qualities essential to addressing these challenges, including sensing, computation, and actuation, using their genetic and metabolic machinery. In addition, bacteria are attractive for incorporation into materials due to their durability, ease-of-use, and programmability. Here, we develop a platform for controlling hydrogel properties (e.g., stiffness, crosslinking rate) using extracellular electron transfer from the bacterium Shewanella oneidensis. In our system, metabolic electron flux from S. oneidensis to a metal catalyst generates radical species that crosslink an acrylate-based macromer to form the gel. This synthetic reaction is under direct control of bacterial genetics and metabolism, which we demonstrate through inducible circuits and quantitative modeling of gene expression and resultant hydrogel properties. Developing methods that capitalize on the programmability of biological systems to control synthetic material properties will enable hybrid material designs with unprecedented functions.

Performing radical polymerizations under ambient conditions is a major challenge because molecular oxygen is an effective radical quencher. Here we show that the facultative electrogen Shewanella oneidensis can control metal-catalysed living radical polymerizations under apparent aerobic conditions by first consuming dissolved oxygen via aerobic respiration, and then directing extracellular electron flux to a metal catalyst. In both open and closed containers, S. oneidensis enabled living radical polymerizations without requiring the preremoval of oxygen. Polymerization activity was closely tied to S. oneidensis anaerobic metabolism through specific extracellular electron transfer proteins and was effective for a variety of monomers using low (parts per million) concentrations of metal catalysts. Finally, polymerizations survived repeated challenges of oxygen exposure and could be initiated using lyophilized or spent (recycled) cells. Overall, our results demonstrate how the unique ability of S. oneidensis to use both oxygen and metals as respiratory electron acceptors can be leveraged to address salient challenges in polymer synthesis.

Correction for ‘Solvent-free vacuum growth of oriented HKUST-1 thin films’ by Sungmin Han et al., J. Mater. Chem. A, 2019, 7, 19396–19406.

The relative scarcity of well-defined genetic and metabolic linkages to material properties impedes biological production of inorganic materials. The physiology of electroactive bacteria is intimately tied to inorganic transformations, which makes genetically tractable and well-studied electrogens, such as Shewanella oneidensis, attractive hosts for material synthesis. Notably, this species is capable of reducing a variety of transition-metal ions into functional nanoparticles, but exact mechanisms of nanoparticle biosynthesis remain ill-defined. We report two key factors of extracellular electron transfer by S. oneidensis, the outer membrane cytochrome, MtrC, and soluble redox shuttles (flavins), that affect Pd nanoparticle formation. Changes in the expression and availability of these electron transfer components drastically modulated particle synthesis rate and phenotype, including their structure and cellular localization. These relationships may serve as the basis for biologically tailoring Pd nanoparticle catalysts and could potentially be used to direct the biogenesis of other metal nanomaterials.

Aggregation of Aβ plays a key role in the progression of Alzheimer's disease. Unfortunately, the Aβ aggregation mechanism is complex, leading to a structurally diverse population of oligomers and amyloid fibrils. Heterogeneous interfaces have been shown to influence the rate of fibrilization and may be useful tools to bias amyloid formation toward specific structures. In order to better understand how exogenous materials influence Aβ aggregation, Aβ1-40 was exposed to zeolite Y containing different metal cations, including Na+, Mg2+, Fe3+, Zn2+, and Cu2+. NaY, MgY, and FeY, all accelerated the kinetics of fibrilization by increasing the primary nucleation rate, while CuY and ZnY inhibited fibrilization. These kinetic effects were supported through binding affinity measurements, in which ZnY and CuY showed higher association constants than the other zeolites. In addition to influencing the kinetics of fibrilization, the zeolites also affected the intermediate structures along the pathway. Western blots confirmed that Aβ1-40 was arrested at the oligomeric stage in the presence of ZnY and CuY, while continuing to the fibrillary state in the presence of other zeolites. Seeding studies showed that NaY and FeY form on-pathway oligomers, while ZnY formed off-pathway oligomers. Overall, our results show that zeolites can impact the aggregation and speciation of amyloids.

AbstarctBiological production of inorganic materials is impeded by relatively few organisms possessing genetic and metabolic linkage to material properties. The physiology of electroactive bacteria is intimately tied to inorganic transformations, which makes genetically tractable and well-studied electrogens, such as Shewanella oneidensis, attractive hosts for material synthesis. Notably, this species is capable of reducing a variety of transition-metal ions into functional nanoparticles, but exact mechanisms of nanoparticle biosynthesis remain ill-defined. We report two key factors of extracellular electron transfer by S. oneidensis, the outer membrane cytochrome, MtrC, and soluble redox shuttles (flavins), that affect Pd nanoparticle formation. Changes in the expression and availability of these electron transfer components drastically modulated particle phenotype, including particle synthesis rate, structure, and cellular localization. These relationships may serve as the basis for biologically tailoring Pd nanoparticle catalysts and could potentially be used to direct the biogenesis of other metal nanomaterials.

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.

Metabolic engineering has facilitated the production of pharmaceuticals, fuels, and soft materials but is generally limited to optimizing well-defined metabolic pathways. We hypothesized that the reaction space available to metabolic engineering could be expanded by coupling extracellular electron transfer to the performance of an exogenous redox-active metal catalyst. Here we demonstrate that the electroactive bacterium Shewanella oneidensis can control the activity of a copper catalyst in atom-transfer radical polymerization (ATRP) via extracellular electron transfer. Using S. oneidensis, we achieved precise control over the molecular weight and polydispersity of a bioorthogonal polymer while similar organisms, such as Escherichia coli, showed no significant activity. We found that catalyst performance was a strong function of bacterial metabolism and specific electron transport proteins, both of which offer potential biological targets for future applications. Overall, our results suggest that manipulating extracellular electron transport pathways may be a general strategy for incorporating organometallic catalysis into the repertoire of metabolically controlled transformations.

The biological synthesis of metal nanoparticles has been examined in a wide range of organisms, due to increased interest in green synthesis and environmental remediation applications involving heavy metal ion contamination. Deinococcus radiodurans is particularly attractive for environmental remediation involving metal reduction, due to its high levels of resistance to radiation and other environmental stresses. However, few studies have thoroughly examined the relationships between environmental stresses and the resulting effects on nanoparticle biosynthesis. In this work, we demonstrate cell-free nanoparticle production and study the effects of metal stressor concentrations and identity, temperature, pH, and oxygenation on the production of extracellular silver nanoparticles by D. radiodurans R1. We also report the synthesis of bimetallic silver and gold nanoparticles following the addition of a metal stressor (silver or gold), highlighting how production of these particles is enabled through the application of environmental stresses. Additionally, we found that both the morphology and size of monometallic and bimetallic nanoparticles were dependent on the environmental stresses imposed on the cells. The nanoparticles produced by D. radiodurans exhibited antimicrobial activity comparable to that of pure silver nanoparticles and displayed catalytic activity comparable to that of pure gold nanoparticles. Overall, we demonstrate that biosynthesized nanoparticle properties can be partially controlled through the tuning of applied environmental stresses, and we provide insight into how their application may affect nanoparticle production in D. radiodurans during bioremediation. IMPORTANCE Biosynthetic production of nanoparticles has recently gained prominence as a solution to rising concerns regarding increased bacterial resistance to antibiotics and a desire for environmentally friendly methods of bioremediation and chemical synthesis. To date, a range of organisms have been utilized for nanoparticle formation. The extremophile D. radiodurans , which can withstand significant environmental stresses and therefore is more robust for metal reduction applications, has yet to be exploited for this purpose. Thus, this work improves our understanding of the impact of environmental stresses on biogenic nanoparticle morphology and composition during metal reduction processes in this organism. This work also contributes to enhancing the controlled synthesis of nanoparticles with specific attributes and functions using biological systems.

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.

A photobase generator was used to induce metal- organic framework (MOF) nucleation upon UV irradiation. This method was further developed into a simple, one-step method for depositing patterned MOF films. Furthermore, the ability of our method to coat a single substrate with MOF films having different chemical compositions is illustrated. The method is an important step towards integrating MOF deposition with existing lithographic techniques and the incorporation of these materials into sensors and other electronic devices. Metal-organic frameworks (MOFs) are a class of three- dimensional permanently porous materials consisting of metal ion nodes bridged by multitopic organic ligands. The ability to tune the pore structure, surface area, metal ion, and the organic linker has positioned these materials at the forefront of research in gas storage, catalysis, and separa- tions. (1-3) The aforementioned attributes have also increased interest in the use of MOFs as sensors or as low-k dielectrics in microelectronic devices. (4, 5) Integration into devices for these applications requires materials to be obtained as patterned thin films, which is challenging to achieve with MOFs since they are generally synthesized as microcrystalline powders or single crystals. Thus, there is significant interest in developing methods for both producing and patterning MOF thin films and coatings. Current strategies for obtaining patterned films of MOFs have been recently reviewed. (6) These methods include patterned deposition of precursors that are subsequently converted to MOFs, (7-12) selective substrate functionalization followed by patterned framework surface growth when exposed to a synthesis mixture, (13-16) and lithographic tech- niques that generate patterns in a subtractive manner from a continuous MOF coating. (17-19) Among the above tech

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 cross-metathesis of terminal olefins using a novel ruthenium catalyst results in excellent selectivity for the Z-olefin homodimer. The reaction was found to tolerate a large number of functional groups, solvents, and temperatures while maintaining excellent Z-selectivity, even at high reaction conversions.

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 Z-selective ethenolysis activity of chelated ruthenium metathesis catalysts was investigated with experiment and theory. A five-membered chelated catalyst that was successfully employed in Z-selective cross metathesis reactions has now been found to be highly active for Z-selective ethenolysis at low ethylene pressures, while tolerating a wide variety of functional groups. This phenomenon also affects its activity in cross metathesis reactions and prohibits crossover reactions of internal olefins via trisubstituted ruthenacyclobutane intermediates. In contrast, a related catalyst containing a six-membered chelated architecture is not active for ethenolysis and seems to react through different pathways more reminiscent of previous generations of ruthenium catalysts. Computational investigations of the effects of substitution on relevant transition states and ruthenacyclobutane intermediates revealed that the differences of activities are attributed to the steric repulsions of the anionic ligand with the chelating groups.

The first report of Z-selective macrocyclizations using a ruthenium-based metathesis catalyst is described. Selectivity for Z-macrocycles is consistently high for a diverse set of substrates with a variety of functional groups and ring sizes. The same catalyst was also employed for the Z-selective ethenolysis of a mixture of E and Z macrocycles, providing the pure E-isomer. Notably, only an atmospheric pressure of ethylene was required. These methodologies were successfully applied to the construction of several olfactory macrocycles, as well as the formal total synthesis of the cytotoxic alkaloid motuporamine C.

The decomposition of a Z-selective ruthenium metathesis catalyst and structurally similar analogues has been investigated utilizing X-ray crystallography and density functional theory. Isolated X-ray crystal structures suggest that recently reported C-H activated catalysts undergo decomposition via insertion of the alkylidene moiety into the chelating ruthenium-carbon bond followed by hydride elimination, which is supported by theoretical calculations. The resulting ruthenium hydride intermediates have been implicated in previously observed olefin migration, and thus lead to unwanted byproducts in cross metathesis reactions. Preventing these decomposition modes will be essential in the design of more active and selective Z-selective catalysts.

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.

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures.

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 relative TONs of productive and nonproductive metathesis reactions of diethyl diallylmalonate are compared for eight different ruthenium-based catalysts. Nonproductive cross metathesis is proposed to involve a chain-carrying ruthenium methylidene. A second more-challenging substrate (dimethyl allylmethylallylmalonate) that forms a trisubstituted olefin product is used to further delineate the effect of catalyst structure on the relative efficiencies of these processes. A steric model is proposed to explain the observed trends.

Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru−C (benzylidene) rotamers at room temperature, and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), cross-metathesis (CM), and asymmetric ring-opening cross-metathesis (AROCM) and showed surprising selectivity in both CM and AROCM.