Synthesis and Surface‐Spectroscopic Characterization of Photoisomerizable glyco‐SAMs on Au(111)

Photoisomerizable glyco‐SAMs (self‐assembled monolayers), utilizing synthetic azobenzene glycoside derivatives were fabricated. The ultimate goal of this project is to assay the influence of the 3D arrangement of sugar ligands on cell adhesion, and eventually make cell adhesion photoswitchable. However, it is a prerequisite for any biological study on the spatial conditions of carbohydrate recognition, that photoisomerization of the surface molecules can be verified. Here, we employed IRRAS and XPS to spectroscopically characterize glyco‐SAMs. In particular and unprecedented to date, we prove reversible E→Z→E isomerization of azobenzene glycoside‐terminated SAMs.     

Multivalent Inhibitors for Carbohydrate‐Processing Enzymes: Beyond the “Lock‐and‐Key” Concept

During the last decades, tremendous chemical efforts have been dedicated to design monovalent inhibitors of carbohydrate‐processing enzymes, with comparatively few rewards in terms of marketed drugs. Recently, an alternative to the traditional “lock and key” approach has emerged. Multivalency, a widely used strategy for lectin inhibition, has been successfully applied to specific glycosidases and glycosyltransferases.     

Self‐Assembly of a Highly Organized,Hexameric Supramolecular Architecture: Formation,Structure and Properties

Two derivatives, ³ L and ⁹ L , of a ditopic, multiply hydrogen‐bonding molecule, known for more than a decade, have been found, in the solid state as well as in solvents of low polarity at room temperature, to exist not as monomers, but to undergo a remarkable self‐assembly into a complex supramolecular species. The solid‐state molecular structure of ³ L , determined by single‐crystal X‐ray crystallography, revealed that it forms a highly organized hexameric entity ³ L ₆ with a capsular shape, resulting from the interlocking of two sets of three monomolecular components, linked through hydrogen‐bonding interactions. The complicated ¹H NMR spectra observed in o‐dichlorobenzene (o‐DCB) for ³ L and ⁹ L are consistent with the presence of a hexamer of D₃ symmetry in both cases. DOSY measurements confirm the hexameric constitution in solution. In contrast, in a hydrogen‐bond‐disrupting solvent, such as DMSO, the ¹H NMR spectra are very simple and consistent with the presence of isolated monomers only. Extensive temperature‐dependent ¹H NMR studies in o‐DCB showed that the L ₆ species dissociated progressively into the monomeric unit on increasing th temperature, up to complete dissociation at about 90 °C. The coexistence of the hexamer and the monomer indicated that exchange was slow on the NMR timescale. Remarkably, no species other than hexamer and monomer were detected in the equilibrating mixtures. The relative amounts of each entity showed a reversible sigmoidal variation with temperature, indicating that the assembly proceeded with positive cooperativity. A full thermodynamic analysis has been applied to the data.     

Inorganic–Organic Heteropolyacid–Gold(I) Hybrids: Structures and Catalytic Applications

Gold(I)‐polyoxometalate hybrid complexes 1 – 4 ([PPh₃AuMeCN]_xH_4?xSiW₁₂O₄₀, x=1–4) were synthesized and characterized. The structure of the primary gold(I)–polyoxometalate 1 (x=1) was fully ascertained by XRD, FTIR, ³¹P and ²⁹Si magic‐angle spinning (MAS) NMR, mass spectroscopy, and SEM–energy dispersive X‐ray spectroscopy (EDX) techniques. Moreover, this complex exhibited better catalytic activity and selectivity compared with standard, homogeneous, gold catalysts in the new rearrangement of propargylic gem‐diesters.     

Dual Catalysis with Copper and Rhenium for Trifluoromethylation of Propargylic Alcohols: Efficient Synthesis of α‐Trifluoromethylated Enones

Trifluoromethylation of propargylic alcohols to provide (Z)‐α‐trifluoromethylated enones and β‐unsubstituted α‐trifluoromethylated enones proceeded with high yield and selectivity in the presence of CuI/Re₂O₇. The Z isomer was formed under kinetic control, though it is less stable than the E isomer in terms of steric repulsion.     

A Multifunctional Photoswitch: 6π Electrocyclization versus ESIPT and Metalation

A terthiazole‐based molecular switch associating 6π electrocyclization, excited state intramolecular proton transfer (ESIPT), and strong metal binding capability was prepared. The photochemical and photophysical properties of this molecule and of the corresponding nickel and copper complexes were thoroughly investigated by steady‐state and ultrafast absorption spectroscopy and rationalized by DFT/TDDFT calculations. The switch behaves as a biphotochrome with time‐dependent photochemical outcome and displays efficient ESIPT‐based fluorescence photoswitching. Both photochemical reactions are suppressed by nickel or copper metalation, and the main factors contributing to the quenching of the electrocyclization are discussed.     

Sponge Phase Producing Porous CeO2 for Catalytic Oxidation of CO

The aggregation behavior of mixtures of the alkaline amino acid L ‐Arginine (L ‐Arg) and bis(2‐ethylhexyl)phosphoric acid (DEHPA) in water was studied in detail. At a fixed L ‐Arg concentration, a phase sequence of micellar phase (L₁ phase), vesicle phase (L_αv phase), planar lamellar phase (L_αl phase), and sponge phase (L₃ phase) was obtained with increasing DEHPA concentration due to changes in the packing parameter. The phase transition of the lamellar structures was determined by freeze‐fracture TEM and ²H NMR spectroscopy. Rheological measurements reflected the phase transition through significant variations of both the elastic modulus and the viscous modulus. Porous CeO₂ materials were produced by utilizing the L₃ phase as template, and the porous CeO₂ exhibited excellent catalytic oxidation activity toward CO due to its high surface area, which provides more active sites for CO conversion.     

Insertion of a Single‐Molecule Magnet inside a Ferromagnetic Lattice Based on a 3D Bimetallic Oxalate Network: Towards Molecular Analogues of Permanent Magnets

The insertion of the single‐molecule magnet (SMM) [Mn^III(salen)(H₂O)]₂²⁺ (salen^2?=N,N′‐ethylenebis‐(salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [Mn^III(salen)(H₂O)]₂[Mn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 1 ). This cationic Mn₂ cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn^III(salen)(H₂O)]₂[Zn^IICr^III(ox)₃]₂ ? (CH₃OH) ? (CH₃CN)₂ ( 2 ) and [In^III(sal₂‐trien)][Mn^IICr^III(ox)₃] ? (H₂O)_0.25 ? (CH₃OH)_0.25 ? (CH₃CN)_0.25 ( 3 ), which are used as reference compounds. In 2 it has been shown that the magnetic isolation of the Mn₂ clusters provided by their insertion into a paramagnetic oxalate network of Cr^III affords a SMM behavior, albeit with blocking temperatures well below 500 mK even for frequencies as high as 160 kHz. In 3 the onset of ferromagnetism in the bimetallic Mn^IICr^III network is observed at T_c=5 K. Finally, in the hybrid compound 1 the interaction between the two magnetic networks leads to the antiparallel arrangement of their respective magnetizations, that is, to a ferrimagnetic phase. This coupling induces also important changes on the magnetic properties of 1 with respect to those of the reference compounds 2 and 3 . In particular, compound 1 shows a large magnetization hysteresis below 1 K, which is in sharp contrast with the near‐reversible magnetizations that the SMMs and the oxalate ferromagnetic lattice show under the same conditions.