91 research outputs found
Improved access to polythioesters by heterobimetallic aluminium catalysis
Bimetallic Al(III) catalysis mediates thioanhydride/epoxide copolymerisation at greatly improved rates and monomer tolerance than analogous Cr(III) catalysis. Moving to sulfurated monomers furthermore generally improves rates and selectivites
Ring-opening terpolymerisation of phthalic thioanhydride with carbon dioxide and epoxides
In seeking to expand the portfolio of accessible polymer structures from CO2 waste, we report the ring-opening terpolymerisation (ROTERP) of phthalic thioanhydride with CO2 and epoxides, forming statistical poly(ester-thioester-carbonates) by employing heterobimetallic catalysts. Both metal choice and ligand chemistry modulate the amount of CO2 incorporated into the polymer microstructure. Terpolymerisation occurs when maintaining polymerisation rates of the faster parent ring-opening copolymerisation and this finding led us to develop the formation of CO2-derived terpolymers with butylene oxide at low CO2 pressure under bicomponent catalysis. Tetrapolymerisation with added phthalic anhydride leads to the preferential polymerisation of phthalic anhydride before the polymerisation of sulfur derivatives with CO2 and epoxides. Finally, we show that the presence of sulfur-containing thioester links leads to polymers with degradability benefits compared to those from all-oxygen derivatives
Mechanistic mapping of (CS2/CO2)/epoxide copolymerization catalysis leads to terpolymers with improved degradability
The placement of main-group functionalities within polymers represents a strategy to access a wide catalog of materials but is limited by poor understanding of the catalyst selection criteria and polymerization mechanism when moving down the periodic table. Here, we study a series of new heterobimetallic carbon dioxide and carbon disulfide/epoxide copolymerization catalysts that allow for a comparative mechanistic understanding of two ring-opening copolymerization processes. We reveal that the distinct roles each metal plays are preserved from carbon dioxide to carbon disulfide, maintaining activity and selectivity across copolymerizations. Experimental and computational studies show that carbon disulfide/epoxide copolymerization can be understood as a series of structurally related insertion events that are interlinked by a central oxygen/sulfur scrambling reaction at the propagating chain end. This facilitates the synthesis of new carbon dioxide-/carbon disulfide-/epoxide-derived terpolymers with improved degradability over the parent carbon dioxide/epoxide copolymers at low levels of sulfur incorporation
All Optical Implementation of Multi-Spin Entanglement in a Semiconductor Quantum Well
We use ultrafast optical pulses and coherent techniques to create spin
entangled states of non-interacting electrons bound to donors (at least three)
and at least two Mn2+ ions in a CdTe quantum well. Our method, relying on the
exchange interaction between localized excitons and paramagnetic impurities,
can in principle be applied to entangle a large number of spins.Comment: 17 pages, 3 figure
Quantitative insights into the cyanobacterial cell economy
© Zavřel et al. Phototrophic microorganisms are promising resources for green biotechnology. Compared to heterotrophic microorganisms, however, the cellular economy of phototrophic growth is still insufficiently understood. We provide a quantitative analysis of light-limited, light-saturated, and light-inhibited growth of the cyanobacterium Synechocystis sp. PCC 6803 using a reproducible cultivation setup. We report key physiological parameters, including growth rate, cell size, and photosynthetic activity over a wide range of light intensities. Intracellular proteins were quantified to monitor proteome allocation as a function of growth rate. Among other physiological acclimations, we identify an upregulation of the translational machinery and downregulation of light harvesting components with increasing light intensity and growth rate. The resulting growth laws are discussed in the context of a coarse-grained model of phototrophic growth and available data obtained by a comprehensive literature search. Our insights into quantitative aspects of cyanobacterial acclimations to different growth rates have implications to understand and optimize photosynthetic productivity
Precise cooperative sulfur placement leads to semi-crystallinity and selective depolymerisability in CS2/oxetane copolymers
CS2 promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS2 and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however, the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects as well as to enable chemoselective depolymerisation into cyclic dithiocarbonates which can themselves serve as monomers in ring-opening polymerisation. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties
Precise construction of weather-sensitive poly(ester-alt-thioesters) from phthalic thioanhydride and oxetane
We report the selective ring opening copolymerisation (ROCOP) of oxetane and phthalic thioanhydride by a heterobimetallic Cr(III)K catalyst precisely yielding semi-crystalline alternating poly(ester-alt-thioesters) which show improved degradability due to the thioester links in the polymer backbone
Ultrafast Momentum-resolved Hot Electron Dynamics in the Two-dimensional Topological Insulator Bismuthene
Two-dimensional quantum spin Hall (QSH) insulators are a promising material
class for spintronic applications based on topologically-protected spin
currents in their edges. Yet, they have not lived up to their technological
potential, as experimental realizations are scarce and limited to cryogenic
temperatures. These constraints have also severely restricted characterization
of their dynamical properties. Here, we report on the electron dynamics of the
novel room-temperature QSH candidate bismuthene after photoexcitation using
time- and angle-resolved photoemission spectroscopy. We map the transiently
occupied conduction band and track the full relaxation pathway of hot
photocarriers. Intriguingly, we observe photocarrier lifetimes much shorter
than in \red{conventional} semiconductors. This is ascribed to the presence of
topological in-gap states already established by local probes. Indeed, we find
spectral signatures consistent with these earlier findings. Demonstration of
the large band gap and the view into photoelectron dynamics mark a critical
step toward optical control of QSH functionalities.Comment: 13 pages, 11 figure
An Integrative Omics Approach Reveals Involvement of BRCA1 in Hepatic Metastatic Progression of Colorectal Cancer
(1) Background & Aims: The roles of different cells in the tumor microenvironment (TME) are critical to the metastatic process. The phenotypic transformation of the liver cells is one of the most important stages of the hepatic metastasis progression of colorectal cancer (CRC). Our aim was to identify the major molecules (i.e., genes, miRNAs and proteins) involved in this process. (2) Methods: We isolated and performed whole-genome analysis of gene, miRNA, and protein expression in three types of liver cells (Ito cells, Kupffer cells, and liver sinusoidal endothelial cells) from the TME of a murine model of CRC liver metastasis. We selected the statistically significant differentially expressed molecules using the Student’s t-test with Benjamini-Hochberg correction and performed functional statistically-significant enrichment analysis of differentially expressed molecules with hypergeometric distribution using the curated collection of molecular signatures, MSigDB. To build a gene-miRNA-protein network centered in Brca1, we developed a software package (miRDiana) that collects miRNA targets from the union of the TargetScan, MicroCosm, mirTarBase, and miRWalk databases. This was used to search for miRNAs targeting Brca1. We validated the most relevant miRNAs with real-time quantitative PCR. To investigate BRCA1 protein expression, we built tissue microarrays (TMAs) from hepatic metastases of 34 CRC patients. (3) Results: Using integrated omics analyses, we observed that the Brca1 gene is among the twenty transcripts simultaneously up-regulated in all three types of TME liver cells during metastasis. Further analysis revealed that Brca1 is the last BRCA1-associated genome surveillance complex (BASC) gene activated in the TME. We confirmed this finding in human reanalyzing transcriptomics datasets from 184 patients from non-tumor colorectal tissue, primary colorectal tumor and colorectal liver metastasis of the GEO database. We found that the most probable sequence of cell activation during metastasis is Endothelial→Ito→Kupffer. Immunohistochemical analysis of human liver metastases showed the BRCA1 protein was co-localized in Ito, Kupffer, and endothelial cells in 81.8% of early or synchronous metastases. However, in the greater part of the metachronous liver metastases, this protein was not expressed in any of these TME cells. (4) Conclusions: These results suggest a possible role of the co-expression of BRCA1 in Ito, Kupffer, and sinusoidal endothelial cells in the early occurrence of CRC liver metastases, and point to BRCA1 as a potential TME biomarker.D.G. and M.J.A.-B. have been supported by Grants DFG113/18 from Diputación Foral de Gipuzkoa (DFG), Spain, Ministry of Economy and Competitiveness, Spain, MINECO Grant BFU2016-77987-P and Instituto de Salud Carlos III (AC17/00012) Grant co-funded by the European Union (Eracosysmed/H2020 Grant Agreement No. 643271) and European Union (H2020-FETOPEN, Project 899417). D.G., M.J.A.-B. and I.B. have been supported by Grants Health Department of the Basque Government (Spain), RIS3 call, Exp. No. 2020333039 and 2020333001
- …