Chemistry - A European Journal

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The following papers are very important in the opinion of two referees. They will be published as soon as possible.

 

 

The Structural Basis for Optimal Performance of Oligothiophene-Based Fluorescent Amyloid Ligands: Conformational Flexibility is Essential for Spectral Assignment of Diverse Protein Aggregates

T. Klingstedt, H. Shirani, K. O. A. Åslund, N. J. Cairns, C. J. Sigurdson, M. Goedert, K. P. R. Nilsson*

Luminescent conjugated oligothiophenes (LCOs) have proven to be useful for optical identification of disease-associated protein aggregates. An anionic pentameric LCO was subjected to chemical engineering by either replacing thiophene units with selenophene or phenylene moieties, or alternating the anionic substituents along the thiophene backbone. Replacing the central thiophene ring with a phenyl moiety stopped the detection of nonthioflavinophilic and noncongophilic protein aggregates, as well as the spectral assignment of Aβ and tau aggregates. Overall, this study identified conformational freedom and extended conjugation of the backbone to be crucial determinants for obtaining superior thiophene-based ligands for spectral assignment of disease-associated protein aggregates.

Coming soon.

 

 

Transition-Metal Complexes of a Salen–Fullerene Diad: Redox and Catalytically Active Nanostructures for Delivery of Metals in Nanotubes

M. A. Lebedeva, T. W. Chamberlain, E. S. Davies, D. Mancel, B. E. Thomas, M. Suyetin, E. Bichoutskaia, M. Schröder,* A. N. Khlobystov*

A hybrid nanoscale ligand, salen–C₆₀ (H₂L), binds a range of transition-metal cations in close proximity to the fullerene cage to give complexes [M(L)] (M=Mn, Co, Ni, Cu, Zn, Pd), [MCl(L)] (M=Cr, Fe), and [V(O)L]. Coordination of metal cations to salen–C₆₀ introduces tunable optical and redox properties determined both by the fullerene and the transition metal. The presence of the fullerene cage enhances the affinity of these complexes for carbon nanostructures without having a detrimental effect on the catalytic activity of the metal center. This approach shows promise for applications of salen–C₆₀ complexes in heterogeneous catalysis.

Coming soon.

 

 

Sulfur Species in Graphene Oxide

S. Eigler,* C. Dotzer, F. Hof, W. Bauer, A. Hirsch

Graphene oxide (GO) prepared according to Hummers’ protocol contains organosulfate as part of its structure. The organosulfates are covalently bound to GO and are still present after extensive aqueous workup. These organosulfate groups decompose at between 200 and 300°C, whereas inorganic sulfur species decompose above 700°C. Furthermore, the organosulfates are responsible for the chemical properties of the graphene oxide. Therefore, the structural model of graphene oxide was extended to include the presence of organosulfate groups. The identification of organosulfate groups beneath epoxy groups makes new molecular architectures feasible and can be used to explain the properties of GO in various applications.

Coming soon.

 

 

The Toxicity of Graphene Oxides: Dependence on the Oxidative Method Used

E. L. K. Chng, M. Pumera*

The cytotoxicity of the graphene oxides (GOs) prepared by the four different oxidative treatments (Staudenmaier, Hofmann, Hummers, and Tour) was investigated by measuring the mitochondrial activity in adherent lung epithelial cells (A549) by using viability MTT and WST-8 assays. There is a strong dose-dependent cytotoxic response resulting from all four GO nanomaterials tested after exposure for 24 h, and it is suggested that there is a correlation between the oxygen content/amount of functional groups in GOs and their toxicological behavior.

Received March 04, 2013, published online April 29, 2013, DOI: 10.1002/chem.201300824 – read now.

 

 

Siamese-Twin Porphyrin: A Pyrazole-Based Expanded Porphyrin of Persistent Helical Conformation

L. K. Blusch (née Frensch), Y. Hemberger, K. Pröpper, B. Dittrich, F. Witterauf, M. John, G. Bringmann,* C. Brückner,* F. Meyer*

The [3+3]-type synthesis of a pyrazole-based expanded porphyrin 1H₄, a hexaphyrin analogue named the Siamese-twin porphyrin, and its homobimetallic diamagnetic nickel(II) and paramagnetic copper(II) complexes, 1Ni₂ and 1Cu₂, is described. The structure of the macrocycle composed of four pyrroles and two pyrazoles, all linked by single carbon atoms, can be interpreted as two conjoined porphyrin-like subunits, with the two opposing pyrazoles acting as the fusion points. Variable-temperature 1D and 2D NMR spectroscopic analyses suggested a conformationally flexible structure for 1H₄. NMR and UV/Vis spectroscopic evidence, as well as structural parameters, proved the macrocycle to be non-aromatic, although each half of the molecule is fully conjugated. UV/Vis and NMR spectroscopic titrations of the free base macrocycle with acid showed it to be dibasic. In the complexes, each metal ion is coordinated in a square-planar fashion by a dianionic, porphyrin-like {N₄} binding pocket. The solid-state structures of the dication and both metal complexes were elucidated by single-crystal diffractometry. The conformations of the three structures are all similar and strongly twisted, rendering the molecules chiral. The persistent helical twist in the protonated form of the free base and in both metal complexes permitted resolution of these enantiomeric helimers by HPLC on a chiral phase. The absolute stereostructures of 1H₆²⁺, 1Ni₂, and 1Cu₂ were assigned by a combination of experimental electronic circular dichroism (ECD) investigations and quantum-chemical ECD calculations. The synthesis of the first member of this long-sought class of expanded porphyrin-like macrocycles lays the foundation for the study of the cooperativity of the metal centers within their bimetallic complexes.

Received December 03, 2012, published online April 09, 2013, DOI: 10.1002/chem.201204296 – read now.

 

 

Facile Fabrication of Core–Shell-Structured Ag@Carbon and Mesoporous Yolk–Shell-Structured Ag@Carbon@Silica by an Extended Stöber Method

T.-Y. Yang, J. Liu,* Y. Zheng, M. J. Monteiro, S. Z. Qiao*

Core–shell-structured Ag,AgBr@resorcinol formaldehyde (RF) polymer spheres were successfully synthesized by an extended Stöber method. After coating a layer of mesoporous silica (meso-SiO₂) on the surface, rattle-type Ag,AgBr@meso-SiO₂ or yolk–shell-structured Ag@Carbon@meso-SiO₂ were selectively obtained by subsequent annealing under a flow of air or N₂, respectively. These complex core–shell and yolk–shell spheres with adjustable core and shell functionalities have potential applications in nanocatalysis, drug delivery, and energy conversion and storage.

Received February 09, 2013, published online April 15, 2013, DOI: 10.1002/chem.201300523 – read now.