172 research outputs found
Cyclic Alkyl Amino Carbene (CAAC) Ruthenium Complexes as Remarkably Active Catalysts for Ethenolysis
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
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Genetic Control of Radical Crosslinking in a Semi-Synthetic Hydrogel
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.Center for Dynamics and Control of Material
Thermal photons as a measure for the rapidity dependence of the temperature
The rapidity distribution of thermal photons produced in Pb+Pb collisions at
CERN-SPS energies is calculated within scaling and three-fluid hydrodynamics.
It is shown that these scenarios lead to very different rapidity spectra. A
measurement of the rapidity dependence of photon radiation can give cleaner
insight into the reaction dynamics than pion spectra, especially into the
rapidity dependence of the temperature.Comment: 3 Figure
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Functionalized Mesoporous Silicas Direct Structural Polymorphism of Amyloid-β Fibrils
The aggregation of Amyloid-b (Ab) 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 Ab1-40 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 Ab1-40 exposed to SBA-PEG were structurally similar to control fibrils. In contrast,
Ab1-40 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 Ab1-40 and other
amyloidogenic proteins.This work was supported in part by Welch Foundation Research Grants F-1929 (to BKK), F-1722
(to LJW), and F-1938 (to DWT), National Science Foundation CHE-1807215 (to LJW), Army
Research Office Grant W911NF-15-1-0120 (to DWT), a Robert J. Kleberg, Jr. and Helen C.
Kleberg Foundation Medical Research Award (to DWT). Partial support was provided by the
National Science Foundation through the Center for Dynamics and Control of Materials: an NSF
Materials Research Science and Engineering Center under DMR-1720595. D.W.T is a CPRIT
Scholar supported by the Cancer Prevention and Research Institute of Texas (RR160088) and an
Army Young Investigator supported by the Army Research Office (W911NF-19-1-0021). NMR
spectra were collected on a Bruker Avance III HD 400 funded by the National Science Foundation
(CHE 1626211).Center for Dynamics and Control of Material
Microscopic study of freeze-out in relativistic heavy ion collisions at SPS energies
The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding
systems of heavy nuclei at 160 AGeV/ are analyzed within the microscopic
Quark Gluon String Model (QGSM). We found that even for the most heavy systems
particle emission takes place from the whole space-time domain available for
the system evolution, but not from the thin ''freeze-out hypersurface", adopted
in fluid dynamical models. Pions are continuously emitted from the whole volume
of the reaction and reflect the main trends of the system evolution. Nucleons
in Pb+Pb collisions initially come from the surface region. For both systems
there is a separation of the elastic and inelastic freeze-out. The mesons with
large transverse momenta, , are predominantly produced at the early stages
of the reaction. The low -component is populated by mesons coming mainly
from the decay of resonances. This explains naturally the decreasing source
sizes with increasing , observed in HBT interferometry. Comparison with
S+S and Au+Au systems at 11.6 AGeV/ is also presented.Comment: REVTEX, 26 pages incl. 9 figures and 2 tables, to be published in the
Physical Review
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