PdO self-assembly on zeolite SSZ-13 with rows of O3Al(IV)OH selectively incorporated in PdO(101) facets for moisture-resistant methane oxidation

We describe an efficient way to prepare moisture-tolerant methane (hydrocarbon) combustion catalysts based on PdO nanoparticles supported on siliceous SSZ-13 zeolite. Only zeolites with high Si/Al ratios >15 are hydrophobic enough to exclude the Pd from the micropores while forming well-faceted PdO nanoparticles. Simultaneously, during self-assembly mobile Al hydroxo species get incorporated into the as-formed PdO nanoparticles. For the first time, we reveal selective incorporation of rows of O3Al(IV)-OHbridging aluminum hydroxo-species into the (101) facets of PdO nanoparticles that form during thermal self-assembly in Pd/SSZ-13 using state-of-the-art atomically-resolved HAADF-STEM imaging, solid-state NMR, DFT calculations and reactivity measurements. The Al+3-OH moieties form atom-thin rows in place of tri-coordinate Pd ions Pd+2 in Pd1O3 on (101) facets: these tri-coordinate Pd1+2O3 are responsible for C-H bond dissociation of methane and hydrocarbons during catalytic methane oxidation. However, on unmodified or non-zeolite supported PdO nanoparticles in the presence of water vapor from engine exhaust, water competes with methane by forming a deactivated Pdtetra(OH)(H2O)Pdtetra site with two water molecules on contiguous 3-coordinate Pd, which is not active for C-H bond activation. When Al-OH moieties are present in place of some tri-coordinate Pd1O3 sites, water dissociation becomes kinetically unfavorable due to disruption of Pdtetra(OH)(H2O)Pdtetra species formation. Consequently, our catalytic measurements reveal a significantly more stable performance of such catalysts in methane combustion in the presence of water vapor. Our findings provide an unprecedented atomic-level insight into structure-property relationships for supported PdO materials in catalytic methane oxidation and offer a new strategy to prepare moisture-tolerant Pd-containing methane combustion catalysts for green-house gas mitigation by selectively doping atomically thin rows of non-precious metal into specific facets of PdO.

Sediment-Peridotite Reaction Controls Fore-Arc Metasomatism and Arc Magma Geochemical Signatures

Subduction of oceanic crust buries an average thickness of 300–500 m of sediment that eventually dehydrates or partially melts. Progressive release of fluid/melt metasomatizes the fore-arc mantle, forming serpentinite at low temperatures and phlogopite-bearing pyroxenite where slab surface reaches 700–900 °C. This is sufficiently high to partially melt subducted sediments before they approach the depths where arc magmas are formed. Here, we present experiments on reactions between melts of subducted sediments and peridotite at 2–6 GPa/750–1100 °C, which correspond to the surface of a subducting slab. The reaction of volatile-bearing partial melts derived from sediments with depleted peridotite leads to separation of elements and a layered arrangement of metasomatic phases, with layers consisting of orthopyroxene, mica-pyroxenite, and clinopyroxenite. The selective incorporation of elements in these metasomatic layers closely resembles chemical patterns found in K-rich magmas. Trace elements were imaged using LA-ICP-TOFMS, which is applied here to investigate the distribution of trace elements within the metasomatic layers. Experiments of different duration enabled estimates of the growth of the metasomatic front, which ranges from 1–5 m/ky. These experiments explain the low contents of high-field strength elements in arc magmas as being due to their loss during melting of sedimentary materials in the fore-arc.

Engineering site-selective incorporation of fluorine into natural product analogs

While bioactive compounds are commonly derived both by human design as well as from living organisms, man-made and natural products typically display very different structural characteristics. As such, a longstanding goal in the discovery of new molecular function is to develop approaches to incorporate the advantageous elements of both groups of molecules, thereby expanding the molecular space accessible for this purpose. In this work, we report the engineering a fluorine-selective enzyme that can complement mutated acyltransferase (AT) domains of a modular polyketide synthase, which are the main determinants of the identity and location of substituents on polyketides, to produce different fluorinated regioisomers of the erythromycin precursor in vitro. We further show that by engineering cell uptake of fluorinated building blocks, we can control fluorine selectivity in vivo to produce selectively fluorinated polyketides using engineered E. coli. These results demonstrate that it is possible to introduce fluorine, a key synthetic design element for drug development, selectively into the scaffold of a complex natural product and produce these analogs by microbial fermentation.

Mapp v. Ohio, the Exclusionary Rule, and Constitutional Judicial Review

Mapp v. Ohio is the US Supreme Court opinion that imposed the Fourth Amendment exclusionary rule on the states. Mapp overruled earlier cases by holding that evidence obtained by unreasonable government searches and seizures was not admissible in state or local criminal prosecutions, just as it had long been inadmissible in federal cases. It is hard to overstate the impact of this decision, which changed the rules and procedures both for policing and for litigation in criminal cases throughout the United States. But Mapp’s significance extends beyond its specific holding. It adopted an interpretive method, often labeled “selective incorporation,” employed by the Supreme Court in subsequent decisions, that imposed specific provisions contained in the Bill of Rights, the first eight amendments to the Constitution upon the states. These decisions redefined federalism in the United States by establishing federal authority over government actions previously governed by state law. In the realm of search and seizure law, by requiring states to adhere to the Supreme Court’s search and seizure opinions, Mapp also generated potent political and legal opposition. In subsequent opinions the Supreme Court limited the exclusionary rule’s scope, diluting Mapp’s impact on police practices by reducing the situations in which federal constitutional rules required exclusion of evidence.

Control Of Phosphoinositide Synthesis And Degradation By The Acyltransferase Lycat

Phosphoinositides (PIPs) are important regulators of various cellular phenomena including intracellular signaling, membrane traffic and cell migration. PIPs are formed as a result of the regulated phosphorylation of the inositol headgroup of phosphatidylinositol (PI) on specific positions by certain lipid kinases and phosphatases. It is well appreciated that the enrichment of specific PIPs, defined by inositol headgroup phosphorylation, within specific membrane compartments plays a critical role in organelle identity and membrane traffic. However, while much attention has been given to understanding of the role of inositol headgroup phosphorylation in PIP function, much less is known about the role of dynamic incorporation of specific acyl groups into these phospholipids. Importantly, PI and PIPs exhibit remarkable and unique selectivity for certain acyl groups. For example, about 45% of PIs (but not other phospholipids) are rich in 1-steroyl 2-arachidonyl. We recently identified that the possible control of the selective incorporation of steric acid at the sn-1 position is by the acyltransferase LYCAT, which controls the levels, acyl profile and function of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) (Bone et al. Mol Biol Cell 2017. 28:161-172). Here we examine how perturbation of LYCAT leads to a reduction in the levels of PI(4,5)P2 and phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3). To measure the rate of PI(4,5)P2 synthesis, we treated cells with ionomycin to first ablate this PIP, followed by washout of the drug and monitoring of rate of reappearance via localization of a fluorescent PI(4,5)P2 probe. To measure the rate of PI(4,5)P2 degradation, we arrested PI(4,5)P2 synthesis by a pharmacological inhibitor, phenylarsine oxide (PAO) and monitored the loss of cellular PI(4,5)P2. Lastly, to examine the production of PI(3,4,5)P3, we treated cells with epidermal growth factor (EGF) and monitored the production of this PIP. Together, this work provides new information about how the dynamic and selective remodeling of specific phospholipids controls their levels, localization and function.

Control Of Phosphoinositide Synthesis And Degradation By The Acyltransferase Lycat

Phosphoinositides (PIPs) are important regulators of various cellular phenomena including intracellular signaling, membrane traffic and cell migration. PIPs are formed as a result of the regulated phosphorylation of the inositol headgroup of phosphatidylinositol (PI) on specific positions by certain lipid kinases and phosphatases. It is well appreciated that the enrichment of specific PIPs, defined by inositol headgroup phosphorylation, within specific membrane compartments plays a critical role in organelle identity and membrane traffic. However, while much attention has been given to understanding of the role of inositol headgroup phosphorylation in PIP function, much less is known about the role of dynamic incorporation of specific acyl groups into these phospholipids. Importantly, PI and PIPs exhibit remarkable and unique selectivity for certain acyl groups. For example, about 45% of PIs (but not other phospholipids) are rich in 1-steroyl 2-arachidonyl. We recently identified that the possible control of the selective incorporation of steric acid at the sn-1 position is by the acyltransferase LYCAT, which controls the levels, acyl profile and function of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) (Bone et al. Mol Biol Cell 2017. 28:161-172). Here we examine how perturbation of LYCAT leads to a reduction in the levels of PI(4,5)P2 and phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3). To measure the rate of PI(4,5)P2 synthesis, we treated cells with ionomycin to first ablate this PIP, followed by washout of the drug and monitoring of rate of reappearance via localization of a fluorescent PI(4,5)P2 probe. To measure the rate of PI(4,5)P2 degradation, we arrested PI(4,5)P2 synthesis by a pharmacological inhibitor, phenylarsine oxide (PAO) and monitored the loss of cellular PI(4,5)P2. Lastly, to examine the production of PI(3,4,5)P3, we treated cells with epidermal growth factor (EGF) and monitored the production of this PIP. Together, this work provides new information about how the dynamic and selective remodeling of specific phospholipids controls their levels, localization and function.

Recent Advances in Sequential Infiltration Synthesis (SIS) of Block Copolymers (BCPs)

In the continuous downscaling of device features, the microelectronics industry is facing the intrinsic limits of conventional lithographic techniques. The development of new synthetic approaches for large-scale nanopatterned materials with enhanced performances is therefore required in the pursuit of the fabrication of next-generation devices. Self-assembled materials as block copolymers (BCPs) provide great control on the definition of nanopatterns, promising to be ideal candidates as templates for the selective incorporation of a variety of inorganic materials when combined with sequential infiltration synthesis (SIS). In this review, we report the latest advances in nanostructured inorganic materials synthesized by infiltration of self-assembled BCPs. We report a comprehensive description of the chemical and physical characterization techniques used for in situ studies of the process mechanism and ex situ measurements of the resulting properties of infiltrated polymers. Finally, emerging optical and electrical properties of such materials are discussed.