| 1. |
- Alam, Rauful, et al.
(författare)
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Stereoselective allylboration of imines and indoles under mild conditions. An in situ E/Z isomerization of imines by allylboroxines
- 2014
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:7, s. 2732-2738
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Tidskriftsartikel (refereegranskat)abstract
- Direct allylboration of various acyclic and cyclic aldimine, ketimine and indole substrates was performed using allylboronic acids. The reaction proceeds with very high anti-stereoselectivity for both E and Z imines. The allylboroxines formed by dehydration of allylboronic acids have a dual effect: promoting E/Z isomerization of aldimines and triggering the allylation by efficient electron withdrawal from the imine substrate.
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| 2. |
- Bryan, Thomas, et al.
(författare)
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The robust electrochemical detection of a Parkinson's disease marker in whole blood sera
- 2012
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 3:12, s. 3468-3473
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Tidskriftsartikel (refereegranskat)abstract
- Protein aggregation, leading to amyloid deposition in the brain, is implicated in the pathology of a number of increasingly prevalent neurodegeneration states such as Parkinson's disease (PD), Alzheimer's disease and prion diseases. The body's protective response to the formation of such deposits is to generate specific autoimmune antibodies. Alpha-synuclein, a natively unfolded protein relatively abundant in the brain, is the main constituent of Lewy body amyloid dispositions in PD. Previous assays determining content of alpha-synuclein in bodily fluids have proven to be largely inconclusive. Here we have taken a novel approach in utilising alpha-synuclein modified electrodes to sample the autoantibodies generated as the body responds to changes in its homeostasis. We show that these electroanalytical assays not only robustly distinguish between disease state and control individuals but also map out disease progression with unprecedented sensitivity and clarity. The impedimetric electrode surfaces are highly specific, reusable, exhibit a linear range from 0.5 to 10 nM and a detection limit of 55 +/- 3 pM. We believe electroanalyses such as these, possible with less than 10 microlitres of fluid and a total assay time of only a few minutes, to be of value for early diagnosis of PD and possibly other alpha-synucleinopathies, and for monitoring disease progression and effects of possible disease modifying interventions.
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| 3. |
- Czyzewski, Michal, et al.
(författare)
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Silene equivalents through the rhodium-catalysed reactions of alpha-hypersilyl diazoesters : a computational and experimental study
- 2011
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 2:12, s. 2367-2372
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Tidskriftsartikel (refereegranskat)abstract
- The generation of silenes through the rhodium-catalysed decomposition of alpha-hypersilyl diazocarbonyl compounds has been explored both computationally and experimentally. This transformation proceeds via a pathway involving initial formation of the carbene, followed by rearrangement, initially to a silene and ultimately to a ketene. Density functional theory (DFT) calculations of model compounds suggested that silene formation was most preferential with electron donating substituents attached to the carbonyl group. The predictions were experimentally evaluated and hypersilyl diazoacetates provided an unusually long-lived species (t(1/2) > 40 h) that reacts as a formal silene equivalent. Further DFT calculations support the formation of an internally stabilised silene in the form of a 1,2-silaoxetene. Importantly the acylsilene-silaoxetene reaction is reversible and consequently this silene equivalent reacts with alpha,beta-unsaturated carbonyl compounds to form cyclic silyl enol ethers which have considerable potential for further synthetic transformations.
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| 4. |
- Dreiser, Jan, et al.
(författare)
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Direct observation of a ferri-to-ferromagnetic transition in a fluoride-bridged 3d-4f molecular cluster
- 2012
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520. ; 3:4, s. 1024-1032
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, crystal structure and magnetic characterisation of the trinuclear, fluoride-bridged, molecular nanomagnet [Dy(hfac)(3)(H2O)-CrF2(py)(4)-Dy(hfac)(3)(NO3)] (1) (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone, py = pyridine) and a closely related dinuclear species [Dy(hfac)(4)-CrF2( py)(4)]center dot 1/2 CHCl3 (2). Element-specific magnetisation curves obtained on 1 by X-ray magnetic circular dichroism (XMCD) allow us to directly observe the field-induced transition from a ferrimagnetic to a ferromagnetic arrangement of the Dy and Cr magnetic moments. By fitting a spin-Hamiltonian model to the XMCD data we extract a weak antiferromagnetic exchange coupling of j -0.18 cm(-1) between the Dy-III and Cr-III ions. The value found from XMCD is consistent with SQUID magnetometry and inelastic neutron scattering measurements. Furthermore, alternating current susceptibility and muon-spin relaxation measurements reveal that 1 shows thermally activated relaxation of magnetisation with a small effective barrier for magnetisation reversal of Delta(eff) 3 cm(-1). Density-functional theory calculations show that the Dy-Cr couplings originate from superexchange via the fluoride bridges.
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| 5. |
- Falenczyk, C., et al.
(författare)
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Chromo-pharmacophores: Photochromic diarylmaleimide inhibitors for sirtuins
- 2014
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:12, s. 4794-4799
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Tidskriftsartikel (refereegranskat)abstract
- © the Partner Organisations 2014. Controlling the activity of sirtuins is of high biomedical relevance as the enzymes are involved in cancer, neurodegeneration and other diseases. Therefore structural elements of 3,4-bisindoylmaleimides (BIMs), which are known NAD+-dependent histone deacetylase (sirtuin) inhibitors, were merged with photochromic diarylmaleimides to yield photoswitchable enzyme inhibitors. The new inhibitors show excellent photophysical properties, are switchable even in polar solvents, and subtype selective against hSirt2. The inhibitory activity changes up to a factor of 22 for the two photoisomers and physiological properties can therefore be effectively toggled by irradiation with light of different wavelengths. Docking experiments using the enzyme crystal structure explain the observed activity changes based on the steric demand of the thiophene substitution and the rigidity of the molecular structure. This journal is
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| 6. |
- Göransson, Erik, et al.
(författare)
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Charge transfer through cross-hyperconjugated versus cross-pi-conjugated bridges : an intervalence charge transfer study
- 2013
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 4:9, s. 3522-3532
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Tidskriftsartikel (refereegranskat)abstract
- Recently there has been much interest in electron transfer and transport through cross-conjugated molecules as interesting test cases for the interplay between molecular and electronic structure as well as potential motifs in the design of new compounds for molecular electronics. Herein we expand on this concept and present the synthesis and characterization of a series of four organic mixed-valence dyads to probe the effect of the bridge structure on the electronic coupling. The electronic coupling between two triarylamine units could be mediated either by cross-hyperconjugation through a saturated ER2 bridge (E = C or Si, R = alkyl or silyl group), or via a cross-conjugated pi-system. The aim of the study is to compare the electron transfer through the various saturated bridges to that of a cross-pi-conjugated bridge. The electronic coupling in these mixed-valence compounds was determined by analysis of intervalence charge transfer bands, and was found to be in the range of 100-400 cm(-1). A complementary DFT and TD-DFT study indicated that the electronic coupling in the dyads with saturated ER2 segments is highly conformer dependant. Furthermore, the calculations showed that two types of interactions contribute to the electronic coupling; a through-bond cross-(hyper)conjugation mechanism and a through-space mechanism. Taken together, these findings suggest the possibility for new architectures for molecular electronics applications utilizing cross-hyperconjugation through properly selected saturated segments which have comparable electron transfer characteristics as regular cross-pi-conjugated molecules.
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| 7. |
- Hansen, Malte, et al.
(författare)
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Photocatalytic water oxidation at soft interfaces
- 2014
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Ingår i: CHEM SCI. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:7, s. 2683-2687
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Tidskriftsartikel (refereegranskat)abstract
- Molecular water oxidation catalysts have been, for the first time, co-embedded with a photosensitizer into phospholipid membranes. The functionalized small unilamellar vesicles produce molecular oxygen by photocatalysis when irradiated with visible light in aqueous buffer. The two dimensional assembly of the catalysts at the lipid-water interface mimics photoactive membranes in biology and allows photocatalytic water oxidation at very low catalyst concentrations of 500 nM, which cannot be reached in homogeneous systems. Highest TONs are obtained below the membrane's main transition temperature indicating that phase separation, clustering and a limited dynamic enhance the photocatalytic activity of the assembly. The concept of membrane co- embedding can be applied to various combinations, ratios and concentrations of photosensitizers and water oxidizing catalysts, providing a new approach for artificial photosynthesis.
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| 8. |
- Hub, Jochen S., et al.
(författare)
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Thermodynamics of hydronium and hydroxide surface solvation
- 2014
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:5, s. 1745-1749
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Tidskriftsartikel (refereegranskat)abstract
- The concentration of hydronium and hydroxide at the water-air interface has been debated for a long time. Recent evidence from a range of experiments and theoretical calculations strongly suggests the water surface to be somewhat acidic. Using novel polarizable models we have performed potential of mean force calculations of a hydronium ion, a hydroxide ion and a water molecule in a water droplet and a water slab and we were able to rationalize that hydronium, but not hydroxide, is slightly enriched at the surface for two reasons. First, because the hydrogen bond acceptance capacity of hydronium is weaker than water and it is more favorable to have the hydronium oxygen on the surface. Second, hydroxide ions are expelled from the surface of the droplets, due to the entropy being lower when a hydroxide ion is hydrated on the surface. As a result, the water dissociation constant pK(w) increases slightly near the surface. The results are corroborated by calculations of surface tension of NaOH solutions that are in reasonable agreement with the experiment. The structural and thermodynamic interpretation of hydronium and hydroxide hydration provided by these calculations opens the route to a better understanding of atmospheric and surface chemistry.
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| 9. |
- Johnson, Magnus, et al.
(författare)
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Reactivity of NHC Au(I)-C sigma-bonds with electrophiles. An investigation of their possible involvement in catalytic C-C bond formation
- 2011
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Ingår i: CHEM SCI. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 2:12, s. 2373-2377
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Tidskriftsartikel (refereegranskat)abstract
- The first example of the reaction of an isolated gold(I) complex with an aryl halide to form a C-C bond is reported. The reactivity of (NHC) Au(I)-R complexes towards a wide range of electrophiles was investigated. The Au-C sigma-bond is shown to exhibit low nucleophilicity, but it is reactive towards MeI and MeOTf to form toluene, biphenyl and ethane, most likely through an oxidative mechanism. Carbon dioxide is completely unreactive. The experimental findings are supported by theoretical calculations.
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| 10. |
- Karim, Alavi, 1986, et al.
(författare)
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The nature of [N-Cl-N]+ and [N-F-N]+ halogen bonds in solution
- 2014
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Ingår i: Chemical Science. - 2041-6520 .- 2041-6539. ; 5, s. 3226-3233
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Tidskriftsartikel (refereegranskat)abstract
- Halonium ions are synthetically useful, transient species that may be stabilized by attachment to two electron donors. Whereas studies of [C–X–C]+-type ions have greatly contributed to the fundamental understanding of chemical bonding and reaction mechanisms, investigations of the corresponding [N–X–N]+ halogen bond complexes are only at an early stage. Herein we present solution NMR spectroscopic and theoretical evidence for the nature of [N–Cl–N]+ and [N–F–N]+ complexes, and we discuss their geometries and stabilities in comparison to their iodine and bromine-centered analogues as well as the corresponding three-center [N–H–N]+ hydrogen bond. We show the chlorine-centered halogen bond to be weaker but yet to resemble the symmetric geometry of the three-center bond of heavier halogens. In contrast, the [N–F–N]+ bond is demonstrated to prefer asymmetric geometry analogous to the [N–H–N]+ hydrogen bond. However, the [N–F–N]+ system has a high energy barrier for interconversion, and due to entropy loss, its formation is slightly endothermic.
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