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| 3. |
- Artero, Vincent, et al.
(författare)
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From Enzyme Maturation to Synthetic Chemistry : The Case of Hydrogenases
- 2015
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Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 48:8, s. 2380-2387
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Forskningsöversikt (refereegranskat)abstract
- CONSPECTUS: Water splitting into oxygen and hydrogen is one of the most attractive strategies for storing solar energy and electricity. Because the processes at work are multielectronic, there is a crucial need for efficient and stable catalysts, which in addition have to be cheap for future industrial developments (electrolyzers, photoelectrochemicals, and fuel cells). Specifically for the water/hydrogen interconversion, Nature is an exquisite source of inspiration since this chemistry contributes to the bioenergetic metabolism of a number of living organisms via the activity of fascinating metalloenzymes, the hydrogenases. In this Account, we first briefly describe the structure of the unique dinuclear organometallic active sites of the two classes of hydrogenases as well as the complex protein machineries involved in their biosynthesis, their so-called maturation processes. This knowledge allows for the development of a fruitful bioinspired chemistry approach, which has already led to a number of interesting and original catalysts mimicking the natural active sites. More specifically, we describe our own attempts to prepare artificial hydrogenases. This can be achieved via the standard bioinspired approach using the combination of a synthetic bioinspired catalyst and a polypeptide scaffold. Such hybrid complexes provide the opportunity to optimize the system by manipulating both the catalyst through chemical synthesis and the protein component through mutagenesis. We also raise the possibility to reach such artificial systems via an original strategy based on mimicking the enzyme maturation pathways. This is illustrated in this Account by two examples developed in our laboratory. First, we show how the preparation of a lysozyme-{Mn-I(CO)(3)} hybrid and its clean reaction with a nickel complex led us to generate a new class of binuclear Ni-Mn H-2-evolving catalysts mimicking the active site of [NiFe]-hydrogenases. Then we describe how we were able to rationally design and prepare a hybrid system, displaying remarkable structural similarities to an [FeFe]-hydrogenase, and we show here for the first time that it is catalytically active for proton reduction. This system is based on the combination of HydF, a protein involved in the maturation of [FeFe]-hydrogenase (HydA), and a close mimic of the active site of this class of enzymes. Moreover, the synthetic [Fe-2(adt)(CO)(4)(CN)(2)](2-) (adt(2-) = aza-propanedithiol) mimic, alone or within a HydF hybrid system, was shown to be able to maturate and activate a form of HydA itself lacking its diiron active site. We discuss the exciting perspectives this "synthetic maturation" opens regarding the "invention" of novel hydrogenases by the chemists.
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| 5. |
- Kumar, Ujjwal, et al.
(författare)
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Local global equivalence for unanimous social choice functions
- 2021
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Ingår i: Games and Economic Behavior. - : Elsevier. - 0899-8256 .- 1090-2473. ; 130, s. 299-308
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Tidskriftsartikel (refereegranskat)abstract
- We identify a condition on preference domains that ensures that every locally strategy-proof and unanimous random social choice function is also strategy-proof. Furthermore every unanimous, locally strategy-proof deterministic social choice function is also group strategy-proof. The condition identified is significantly weaker than the characterization condition for local-global equivalence without unanimity in Kumar et al. (2020). The condition is not necessary for equivalence with unanimous random/deterministic social choice functions. However, we show the weaker condition of connectedness remains necessary.
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| 6. |
- Kumar, Ujjwal, et al.
(författare)
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Local-global equivalence in voting models: A characterization and applications
- 2021
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Ingår i: Theoretical Economics. - 1933-6837 .- 1555-7561. ; 16:4, s. 1195-1220
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Tidskriftsartikel (refereegranskat)abstract
- The paper considers a voting model where each voter's type is her preference. The type graph for a voter is a graph whose vertices are the possible types of the voter. Two vertices are connected by an edge in the graph if the associated types are “neighbors.” A social choice function is locally strategy-proof if no type of a voter can gain by misrepresentation to a type that is a neighbor of her true type. A social choice function is strategy-proof if no type of a voter can gain by misrepresentation to an arbitrary type. Local-global equivalence (LGE) is satisfied if local strategy-proofness implies strategy-proofness. The paper identifies a condition on the graph that characterizes LGE. Our notion of “localness” is perfectly general. We use this feature of our model to identify notions of localness according to which various models of multidimensional voting satisfy LGE. Finally, we show that LGE for deterministic social choice functions does not imply LGE for random social choice functions.
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| 7. |
- Mijangos, Edgar, et al.
(författare)
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Evaluation of two- and three-dimensional electrode platforms for the electrochemical characterization of organometallic catalysts incorporated in non-conducting metal-organic frameworks
- 2017
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 46:15, s. 4907-4911
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Tidskriftsartikel (refereegranskat)abstract
- The development of a reliable platform for the electrochemical characterization of a redox-active molecular diiron complex, [FeFe], immobilized in a non-conducting metal organic framework (MOF), UiO-66, based on glassy-carbon electrodes is reported. Voltammetric data with appreciable current responses can be obtained by the use of multiwalled carbon nanotubes (MWCNT) or mesoporous carbon (CB) additives that function as conductive scaffolds to interface the MOF crystals in "three-dimensional" electrodes. In the investigated UiO-66-[FeFe] sample, the low abundance of [FeFe] in the MOF and the intrinsic insulating properties of UiO-66 prevent charge transport through the framework, and consequently, only [FeFe] units that are in direct physical contact with the electrode material are electrochemically addressable.
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| 9. |
- Pullen, Sonja, et al.
(författare)
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[FeFe] Hydrogenase active site model chemistry in a UiO-66metal-organic framework
- 2017
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X. ; 53:37, s. 5227-5230
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity of [Fe-2(dcbdt)(CO)(6)] (1) confined in a UiO-66(Zr) metal-organic framework towards CO ligand substitutions with phosphines of different sizes was investigated. The reaction with smaller phosphines (PX3, X = Me, Et) is more selective compared to analogous reactions in homogenous solution phase, and two CO ligands at up to 80% of all [FeFe] sites in UiO-66-1 are replaced. The produced [Fe-2(dcbdt)(CO)(4)(PX3)(2)] complexes in the UiO-66 matrix behave like typical [FeFe] hydrogenase active site model complexes, are reduced at more cathodic potentials than their hexacarbonyl analogues, and form bridging hydrides under acidic conditions.
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| 11. |
- Roy, Souvik, et al.
(författare)
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A Systematic Comparative Study of Hydrogen-Evolving Molecular Catalysts in Aqueous Solutions
- 2015
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 8:21, s. 3632-3638
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Tidskriftsartikel (refereegranskat)abstract
- We describe here a systematic, reliable, and fast screening method that allows the comparison of H-2-forming catalysts that work under aqueous conditions with two readily prepared chemical reductants and two commonly used photosensitizers. This method uses a Clark-type microsensor for H-2 detection and complements previous methods based on rotating disk electrode measurements. The efficiencies of a series of H-2-producing catalysts based on Co, Ni, Fe, and Pt were investigated in aqueous solutions under thermal conditions with europium(II) reductants and under photochemical conditions in the presence of two different photosensitizers {[Ru(bipy)(3)]Cl-2 (bipy=2,2-bipyridine) and eosin-Y} and sacrificial electron donors (ascorbate and triethanolamine, respectively). The majority of catalysts tested were active only under specific conditions. However, our results also demonstrate the impressive versatility of a group of Co catalysts, which were able to produce H-2 under different reducing conditions and at various pH values. In particular, a cobaloxime, [Co(dmgH)(2)(H2O)(2)] (dmgH(2)=dimethylglyoxime), and a cobalt tetraazamacrocyclic complex, {Co(CR)Cl-2}(+) [CR=2,12-dimethyl-3,7,11,17-tetraazabicylo(11.3.1)heptadeca-1(17),2,11,13,15-pentaene], displayed excellent catalytic rates under the studied conditions, and the best rates were observed under thermal conditions.
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| 12. |
- Roy, Souvik, et al.
(författare)
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Catalyst accessibility to chemical reductants in metal-organic frameworks
- 2017
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 53:22, s. 3257-3260
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Tidskriftsartikel (refereegranskat)abstract
- A molecular H-2-evolving catalyst, [Fe-2(cbdt)(CO)(6)] ([FeFe], cbdt = 3-carboxybenzene-1,2-dithiolate), has been attached covalently to an amino-functionalized MIL-101(Cr) through an amide bond. Chemical reduction experiments reveal that the MOF channels can be clogged by ion pairs that are formed between the oxidized reductant and the reduced catalyst. This effect is lessened in MIL-101-NH-[FeFe] with lower [FeFe] loadings. On longer timescales, it is shown that large proportions of the [FeFe] catalysts within the MOF engage in photochemical hydrogen production and the amount of produced hydrogen is proportional to the catalyst loading.
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| 13. |
- Roy, Souvik, et al.
(författare)
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Electrocatalytic Hydrogen Evolution from a Cobaloxime-Based Metal-Organic Framework Thin Film
- 2019
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:40, s. 15942-15950
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Tidskriftsartikel (refereegranskat)abstract
- Molecular hydrogen evolution catalysts (HECs) are synthetically tunable and often exhibit high activity, but they are also hampered by stability concerns and practical limitations associated with their use in the homogeneous phase. Their incorporation as integral linker units in metal-organic frameworks (MOFs) can remedy these shortcomings. Moreover, the extended three-dimensional structure of MOFs gives rise to high catalyst loadings per geometric surface area. Herein, we report a new MOF that exclusively consists of cobaloximes, a widely studied HEC, that act as metallo-linkers between hexanuclear zirconium clusters. When grown on conducting substrates and under applied reductive potential, the cobaloxime linkers promote electron transport through the film as well as function as molecular HECs. The obtained turnover numbers are orders of magnitude higher than those of any other comparable cobaloxime system, and the molecular integrity of the cobaloxime catalysts is maintained for at least 18 h of electrocatalysis. Being one of the very few hydrogen evolving electrocatalytic MOFs based on a redox-active metallo-linker, this work explores uncharted terrain for greater catalyst pathways.
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| 14. |
- Roy, Souvik, et al.
(författare)
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Light-driven hydrogen evolution catalyzed by a cobaloxime catalyst incorporated in a MIL-101(Cr) metal-organic framework
- 2018
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 2:6, s. 1148-1152
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Tidskriftsartikel (refereegranskat)abstract
- A cobaloxime H-2 evolution catalyst with a hydroxo-functionalized pyridine ligand, Co(dmgH)(2)(4-HEP)Cl [dmgH = dimethylglyoxime, 4-HEP = 4-(2-hydroxyethyl)pyridine] was immobilized on a chromium terephthalate metal-organic framework (MOF), MIL-101(Cr), to construct a MOF-catalyst hybrid which displays good photocatalytic H-2 evolution activity. The longevity of the cobaloxime catalyst is increased by MOF incorporation, but limited by the stability of the cobalt-pyridine bond under turnover conditions.
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| 15. |
- Roy, Souvik, et al.
(författare)
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Synthesis and Electrocatalytic Activity of [FeFe]-Hydrogenase Model Complexes with Non-Innocent Chelating Nitrogen-Donor Ligands
- 2017
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Ingår i: European Journal of Inorganic Chemistry. - : WILEY-V C H VERLAG GMBH. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :23, s. 2942-2950
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Tidskriftsartikel (refereegranskat)abstract
- To probe the influence of redox non-innocent ligands on a well-known class of [FeFe]-hydrogenase models, three new asymmetrically disubstituted diiron complexes of the general formula (mu-SRS)[Fe(CO)(3)][Fe(CO)(N-N)] {SRS = propane-1,3-dithiolate (pdt) or benzene-1,2-dithiolate (bdt), and N-N = 2,2-bipyridine (bipy) or 2,2-bipyrimidine (bpym)} have been synthesized from their parent hexacarbonyls and characterized. The new complexes, (mu-pdt)Fe-2(CO)(4)((2)-bpym) (2), (mu-bdt)Fe-2(CO)(4)((2)-bipy) (3), and (mu-bdt)Fe-2(CO)(4)((2)-bpym) (4), were fully characterized by spectroscopic and electrochemical techniques, and the results are compared to those of a related complex, (mu-pdt)Fe-2(CO)(4)((2)-bipy) (1). The crystal structures of 2-4 show that, in each complex, the two iron units are in an eclipsed orientation, and the N-N ligand lies in the basal plane. IR spectra and electrochemical analyses indicate that electron density at the iron centers decreases in the order 1 > 2 > 3 > 4. Furthermore, compound 2 undergoes a ligand-centered reduction at the same potential that the hexacarbonyl precursor undergoes its first reduction. However, unlike the 2,2-bipy derivatives 1 and 3, the 2,2-bpym complexes 2 and 4 are not effective catalysts for electrochemical proton reduction from acetic acid.
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| 16. |
- Sain, Sunanda, et al.
(författare)
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Hydrophobic Shape-Memory Biocomposites from Tung-Oil-Based Bioresin and Onion-Skin-Derived Nanocellulose Networks
- 2020
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Ingår i: Polymers. - : MDPI. - 2073-4360. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- The fabrication of smart biocomposites from sustainable resources that could replace today’s petroleum-derived polymer materials is a growing field of research. Here, we report preparation of novel biocomposites using nanocellulose networks extracted from food residue (onion skin) and a vegetable oil-based bioresin. The resin was synthesized via the Diels-Alder reaction between furfuryl methacrylate and tung oil at various ratios of the components. The onion-skin-extracted cellulose nanofiber and cellulose nanocrystal networks were then impregnated with the resins yielding biocomposites that exhibited improved mechanical strength and higher storage modulus values. The properties of the resins, as well as biocomposites, were affected by the resin compositions. A 190-240-fold increase in mechanical strength was observed in the cellulose nanofiber (CNF) and cellulose nanocrystal (CNC)-reinforced biocomposites with low furfuryl methacrylate content. The biocomposites exhibited interesting shape-memory behavior with 80-96% shape recovery being observed after 7 creep cycles.
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| 17. |
- Topi, Geriolda, et al.
(författare)
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Combined Estrogen Alpha and Beta Receptor Expression Has a Prognostic Significance for Colorectal Cancer Patients
- 2022
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Ingår i: Frontiers in Medicine. - : Frontiers Media SA. - 2296-858X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We reported that high estrogen receptor beta (ERβ) expression is independently associated with better prognosis in female colorectal cancer (CRC) patients. However, estrogen receptor alpha (ERα) is expressed at very low levels in normal colon mucosa, and its prognostic role in CRC has not been explored. Herein, we investigated the combined role of ERα and ERβ expression in the prognosis of female patients with CRC, which, to the best of our knowledge, is the first study to investigate this topic. A total number of 306 primary CRCs were immunostained for ERα and ERβ expression. A Cox regression model was used to evaluate overall survival (OS) and disease-free survival (DFS). The combined expression of high ERβ + negative ERα correlates with longer OS (HR = 0.23; 95% CI: 0.11–0.45, P <0.0001) and DFS (HR = 0.10; 95% CI: 0.03–0.26, P < 0.0001) and a more favorable tumor outcome, as well as significantly higher expression of antitumorigenic proteins than combined expression of low ERβ + positive ERα. Importantly, we found that low ERβ expression was associated with local recurrence of CRC, whereas ERα expression was correlated with liver metastasis. Overall, our results show that the combined high ERβ + negative ERα expression correlated with a better prognosis for CRC patients. Our results suggest that the combined expression of ERα and ERβ could be used as a predictive combination marker for CRC patients, especially for predicting DFS.
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| 18. |
- Topi, Geriolda, et al.
(författare)
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High Oestrogen receptor alpha expression correlates with adverse prognosis and promotes metastasis in colorectal cancer
- 2024
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Ingår i: Cell Communication and Signaling. - 1478-811X. ; 22:1
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Tidskriftsartikel (refereegranskat)abstract
- In normal colon tissue, oestrogen receptor alpha (ERα) is expressed at low levels, while oestrogen receptor beta (ERβ) is considered the dominant subtype. However, in colon carcinomas, the ERα/β ratio is often increased, an observation that prompted us to further investigate ERα’s role in colorectal cancer (CRC). Here, we assessed ERα nuclear expression in 351 CRC patients. Among them, 119 exhibited positive ERα nuclear expression, which was significantly higher in cancer tissues than in matched normal tissues. Importantly, patients with positive nuclear ERα expression had a poor prognosis. Furthermore, positive ERα expression correlated with increased levels of the G-protein coupled cysteinyl leukotriene receptor 1 (CysLT1R) and nuclear β-catenin, both known tumour promoters. In mouse models, ERα expression was decreased in Cysltr1−/− CAC (colitis-associated colon cancer) mice but increased in ApcMin/+ mice with wild-type Cysltr1. In cell experiments, an ERα-specific agonist (PPT) increased cell survival via WNT/β-catenin signalling. ERα activation also promoted metastasis in a zebrafish xenograft model by affecting the tight junction proteins ZO-1 and Occludin. Pharmacological blockade or siRNA silencing of ERα limited cell survival and metastasis while restoring tight junction protein expression. In conclusion, these findings highlight the potential of ERα as a prognostic marker for CRC and its role in metastasis.
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