| 1. |
- Amombo Noa, Francoise Mystere, 1988, et al.
(författare)
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Metal-Organic Frameworks with Hexakis(4-carboxyphenyl)benzene: Extensions to Reticular Chemistry and Introducing Foldable Nets
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:20, s. 9471-9481
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Tidskriftsartikel (refereegranskat)abstract
- Nine metal-organic frameworks have been prepared with the hexagon-shaped linker 1,2,3,4,5,6-hexakis(4-carboxyphenyl)-benzene (H(6)cpb) by solvothermal reactions in dimethylformamide (dmf) or dimethylacetamide (dmac) with acetic acid or formic acid as modulators: [Bi-2(cpb)(acetato)(2)(dmf)(2)]center dot 2dmf CTH-6 forms a rtl-net; 2(H2NMe2)[Cu-2(cpb)] CTH-7 forms a kgd-net; [Fe-4(cpb)-(acetato)(2)(dmf)(4)] CTH-8 and [Co-4(cpb)(acetato)(2)(dmf)(4)] CTH-9 are isostructural and form yav-nets; 2(HNEt3)[Fe-2(cpb)] CTH-10 and the two polymorphs of 2(H2NMe2)[Zn-2(cpb)]center dot 1.5dmac, Zn-MOF-888 and CTH-11, show kgd-nets; [Cu-2(cpb)-(acetato)(2)(dmf)(2)]center dot 2dmf, CTH-12, forms a mixed coordination and hydrogen-bonded sql-net; and 2(H2NMe2)[Zn-2(cpb)] CTH-13, a similarly mixed yav-net. Surface area values (Brunauer-Emmett-Teller, BET) range from 34 m(2) g(-1) for CTH-12 to 303 m(2) g(-1) for CTH-9 for samples activated at 120 degrees C in dynamic vacuum. All compounds show normal (10-fold higher) molar CO2 versus N-2 uptake at 298 K, except the 19-fold CO2 uptake for CTH-12 containing Cu(II) dinuclear paddle-wheels. We also show how perfect hexagons and triangles can combine to a new 3D topology laf, a model of which gave us the idea of foldable network topologies, as the laf-net can fold into a 2D form while retaining the local geometry around each vertex. Other foldable nets identified are cds, cds-a, ths, sqc163, clh, jem, and tfc covering the basic polygons and their combinations. The impact of this concept on "breathing" MOFs is discussed. I-2 sorption, both from gas phase and from MeOH solution, into CTH-7 were studied by time of flight secondary ion mass spectrometry (ToF-SIMS) on dried crystals. I-2 was shown to have penetrated the crystals, as layers were consecutively peeled off by the ion beam. We suggest ToF-SIMS to be a method for studying sorption depth profiles of MOFs.
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| 2. |
- Axelsson, Martin, et al.
(författare)
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Small Organic Molecule Based on Benzothiadiazole for Electrocatalytic Hydrogen Production
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:50, s. 21229-21233
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Tidskriftsartikel (refereegranskat)abstract
- A small organic molecule 2,1,3-benzothiadiazole-4, 7-dicarbonitrile (BTDN) is assessed for electrocatalytic hydrogen evolution on glassy carbon electrode and shows a hydrogen production Faradaic efficiency of 82% in the presence of salicylic acid. The key catalytic intermediates of reduced species BTDN-. and protonated intermediates are characterized or hypothesized by using various spectroscopic methods and density functional theory (DFT)-based calculations. With the experimental and theoretical results, a catalytic mechanism of BTDN for electrocatalytic H-2 evolution is proposed.
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| 3. |
- Azam, M. S., et al.
(författare)
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Silica Surface Charge Enhancement at Elevated Temperatures Revealed by Interfacial Water Signals
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:2, s. 669-673
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Tidskriftsartikel (refereegranskat)abstract
- The structure of water adjacent to silica is sensitive to the degree of deprotonation of surface silanol groups. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. We have used nonlinear vibrational spectroscopy of the water O-H stretching band over a temperature range of 10-75 °C to account for the increase in surface potential from deprotonation. We demonstrate that the behavior at the silica surface is a balance between increasing surface charge and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, we use our data to report the changes in enthalpy and entropy for deprotonation at each site. This is the first experimental determination of these thermodynamic parameters for hydrated silanol groups at the silica surface, critical to a wide range of geochemical and technological applications.
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| 4. |
- Baladi, Tom, 1991, et al.
(författare)
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Stealth Fluorescence Labeling for Live Microscopy Imaging of mRNA Delivery
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 143:14, s. 5413-5424
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Tidskriftsartikel (refereegranskat)abstract
- Methods for tracking RNA inside living cells without perturbing their natural interactions and functions are critical within biology and, in particular, to facilitate studies of therapeutic RNA delivery. We present a stealth labeling approach that can efficiently, and with high fidelity, generate RNA transcripts, through enzymatic incorporation of the triphosphate of tCO, a fluorescent tricyclic cytosine analogue. We demonstrate this by incorporation of tCO in up to 100% of the natural cytosine positions of a 1.2 kb mRNA encoding for the histone H2B fused to GFP (H2B:GFP). Spectroscopic characterization of this mRNA shows that the incorporation rate of tCO is similar to cytosine, which allows for efficient labeling and controlled tuning of labeling ratios for different applications. Using live cell confocal microscopy and flow cytometry, we show that the tCO-labeled mRNA is efficiently translated into H2B:GFP inside human cells. Hence, we not only develop the use of fluorescent base analogue labeling of nucleic acids in live-cell microscopy but also, importantly, show that the resulting transcript is translated into the correct protein. Moreover, the spectral properties of our transcripts and their translation product allow for their straightforward, simultaneous visualization in live cells. Finally, we find that chemically transfected tCO-labeled RNA, unlike a state-of-the-art fluorescently labeled RNA, gives rise to expression of a similar amount of protein as its natural counterpart, hence representing a methodology for studying natural, unperturbed processing of mRNA used in RNA therapeutics and in vaccines, like the ones developed against SARS-CoV-2.
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| 5. |
- Benitez-Martin, Carlos, 1994, et al.
(författare)
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Toward Two-Photon Absorbing Dyes with Unusually Potentiated Nonlinear Fluorescence Response
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:35, s. 14854-14858
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Tidskriftsartikel (refereegranskat)abstract
- The combination of two two-photon-induced processes in a Förster resonance energy transfer (FRET)-operated photochromic fluorene-dithienylethene dyad lays the foundation for the observation of a quartic dependence of the fluorescence signal on the excitation light intensity. While this photophysical behavior is predicted for a four-photon absorbing dye, the herein proposed approach opens the way to use two-photon absorbing dyes, reaching the same performance. Hence, the spatial resolution limit, being a critical parameter for applications in fluorescence imaging or data storage with common two-photon absorbing dyes, is dramatically improved.
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| 6. |
- Biler, Michal, et al.
(författare)
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Ground-State Destabilization by Active-Site Hydrophobicity Controls the Selectivity of a Cofactor-Free Decarboxylase
- 2020
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 142:47, s. 20216-20231
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial arylmalonate decarboxylase (AMDase) and evolved variants have become a valuable tool with which to access both enantiomers of a broad range of chiral arylaliphatic acids with high optical purity. Yet, the molecular principles responsible for the substrate scope, activity, and selectivity of this enzyme are only poorly understood to date, greatly hampering the predictability and design of improved enzyme variants for specific applications. In this work, empirical valence bond and metadynamics simulations were performed on wild-type AMDase and variants thereof to obtain a better understanding of the underlying molecular processes determining reaction outcome. Our results clearly reproduce the experimentally observed substrate scope and support a mechanism driven by ground-state destabilization of the carboxylate group being cleaved by the enzyme. In addition, our results indicate that, in the case of the nonconverted or poorly converted substrates studied in this work, increased solvent exposure of the active site upon binding of these substrates can disturb the vulnerable network of interactions responsible for facilitating the AMDase-catalyzed cleavage of CO2. Finally, our results indicate a switch from preferential cleavage of the pro-(R) to the pro-(S) carboxylate group in the CLG-IPL variant of AMDase for all substrates studied. This appears to be due to the emergence of a new hydrophobic pocket generated by the insertion of the six amino acid substitutions, into which the pro-(S) carboxylate binds. Our results allow insight into the tight interaction network determining AMDase selectivity, which in turn provides guidance for the identification of target residues for future enzyme engineering.
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| 7. |
- Boström, Hanna, et al.
(författare)
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Probing the Influence of Defects, Hydration, and Composition on Prussian Blue Analogues with Pressure
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:9, s. 3544-3554
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Tidskriftsartikel (refereegranskat)abstract
- The vast compositional space of Prussian blue analogues (PBAs), formula A(x)M[M'(CN)(6)](y)center dot nH(2)O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties-e.g., flexibility and propensity for phase transitions-is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus (B-0 approximate to 6 GPa) for defective PBAs. Interstitial water increases B-0 and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN)(6), but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN)(6) (A(I) = Rb, Cs) transition from F (4) over bar 3m to P (4) over bar n2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb0.87Mn[Co(CN)(6)](0.91) is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.
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| 8. |
- Canton, Martina, et al.
(författare)
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Improving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination Cage
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:34, s. 14557-14565
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Tidskriftsartikel (refereegranskat)abstract
- Photochromic molecules undergo reversible isomerization upon irradiation with light at different wavelengths, a process that can alter their physical and chemical properties. For instance, dihydropyrene (DHP) is a deep-colored compound that isomerizes to light-brown cyclophanediene (CPD) upon irradiation with visible light. CPD can then isomerize back to DHP upon irradiation with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimolecular events involving this unstable intermediate thus result in rapid decomposition and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a (PdIIL4)-L-6 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although molecular confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic molecules, but may also increase the amount of product obtainable from traditionally low-yielding organic reactions.
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| 9. |
- Castner, Ashleigh T., et al.
(författare)
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Mimicking the Electron Transport Chain and Active Site of [FeFe] Hydrogenases in One Metal-Organic Framework : Factors That Influence Charge Transport
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:21, s. 7991-7999
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe] hydrogenase (H2ase) enzymes are effective proton reduction catalysts capable of forming molecular dihydrogen with a high turnover frequency at low overpotential. The active sites of these enzymes are buried within the protein structures, and substrates required for hydrogen evolution (both protons and electrons) are shuttled to the active sites through channels from the protein surface. Metal–organic frameworks (MOFs) provide a unique platform for mimicking such enzymes due to their inherent porosity which permits substrate diffusion and their structural tunability which allows for the incorporation of multiple functional linkers. Herein, we describe the preparation and characterization of a redox-active PCN-700-based MOF (PCN = porous coordination network) that features both a biomimetic model of the [FeFe] H2ase active site as well as a redox-active linker that acts as an electron mediator, thereby mimicking the function of [4Fe4S] clusters in the enzyme. Rigorous studies on the dual-functionalized MOF by cyclic voltammetry (CV) reveal similarities to the natural system but also important limitations in the MOF-enzyme analogy. Most importantly, and in contrast to the enzyme, restrictions apply to the total concentration of reduced linkers and charge-balancing counter cations that can be accommodated within the MOF. Successive charging of the MOF results in nonideal interactions between linkers and restricted mobility of charge-compensating redox-inactive counterions. Consequently, apparent diffusion coefficients are no longer constant, and expected redox features in the CVs of the materials are absent. Such nonlinear effects may play an important role in MOFs for (electro)catalytic applications.
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| 10. |
- Chatgilialoglu, C., et al.
(författare)
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Oxygen Dependent Purine Lesions in Double-Stranded Oligodeoxynucleotides: Kinetic and Computational Studies Highlight the Mechanism for 5 ',8-Cyclopurine Formation
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:12, s. 5825-5833
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Tidskriftsartikel (refereegranskat)abstract
- The reaction of HO center dot radical with DNA is intensively studied both mechanistically and analytically for lesions formation. Several aspects related to the reaction paths of purine moieties with the formation of 5',8-cyclopurines (cPu), 8-oxopurines (8-oxo-Pu), and their relationship are not well understood. In this study, we investigated the reaction of HO center dot radical with a 21-mer double-stranded oligodeoxynucleotide (ds-ODNs) in gamma-irradiated aqueous solutions under various oxygen concentrations and accurately quantified the six purine lesions (i.e., four cPu and two 8-oxo-Pu) by LC-MS/MS analysis using isotopomeric internal standards. In the absence of oxygen, 8-oxo-Pu lesions are only similar to 4 times more than cPu lesions. By increasing oxygen concentration, the 8-oxo-Pu and the cPu gradually increase and decrease, respectively, reaching a gap of similar to 130 times at 2.01 x 10(-4) M of O-2. Kinetic treatment of the data allows to estimate the C5' radical competition between cyclization and oxygen trapping in ds-ODNs, and lastly the rate constants of the four cyclization steps. Tailored computational studies by means of dispersion-corrected DFT calculations were performed on the CGC and TAT in their double-strand models for each cPu diastereoisomer along with the complete reaction pathways of the cyclization steps. Our findings reveal unheralded reaction mechanisms that resolve the long-standing issues with C5' radical cyclization in purine moieties of DNA sequences.
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