Chemistry - A European Journal

The cover picture shows a representation of two pathways for the hydrolysis of phosphotriesters, which are represented by tris(phenyl)phosphate (TPP). The catalytic hydrolysis is represented by a novel bimetallic nickel(II) complex that contains a double phosphodiester bridge, prepared from the reaction of TPP with the hydroxo–nickel(II) complex [Ni(Me₃[12]aneN₃)(μ-OH)]₂[PF₆]₂ (top right) The enzymatic hydrolysis (bottom left) is represented by the phosphotriesterase from Pseudomonas diminuta (PDB ID: 1EYW), a zinc-containing enzyme. The cover picture was created by A. Abel Lozano. For more details please see the article by G. García, M. D. Santana et al. on p. 1738ff.

Itinerant electrons: A novel material—an “inorganic electride”—with a stoichiometic trapped or itinerant electron as anion is illustrated. Inorganic electrides are stable at room-temperature. The alkali metals in inorganic electrides form continuous zigzag chains along the narrow pore channels of zeolites and the released electrons are delocalized from the alkali metals.

Cool and calculating! A novel computational model for the study of crystal structures both on their own and in conjunction with inhibitor molecules is reported. This extended MC model has been applied to the study of antifreeze proteins (AFPs) and their effects on ice formation. The technique successfully models the AFP-induced ice-growth inhibition with concurrent changes to ice morphology that mimic experimental results.

Adequately designed β-peptides can be stabilized by electrostatic interactions which was shown with 1. The β³-heptapeptide was assembled by solid-phase synthesis from β³-homoarginine derivatives and investigated both in methanol and aqueous solutions using CD- and NMR-structural methods.

Remote control of binding is achieved by triggering the reaction center in a π-conjugated molecule (see scheme). Theoretical analysis shows why, in certain systems, the signal sent out by the reaction center does not die out with long distances.

A stable, nontoxic, and non-genotoxic antimalarial agent, compound 1 (DU1302 c), is a trioxaquine that was prepared from α-terpinene. It exhibited high antimalarial activity in vitro against Plasmodium falciparum, as well as in vivo activity after being orally administered to infected mice.

Catalytic destruction of CCl₄ in the presence of steam was investigated at 200–350 °C over a series of lanthanide (La, Ce, Pr, and Nd) and alkaline-earth metal (Mg, Ca, Sr, and Ba) oxide-based catalysts by kinetic experiments, various spectroscopic techniques and DFT calculations. For example, approach of a CCl₄ molecule to the surface of La₂O₃ results in the elongation of a CCl bond, and the Cl gets a partial negative charge, while the hydrocarbon fragment becomes partially positively charged (see picture).

The extent of incorporation of magnesium in the calcite crystal lattice depends on the type of co-anion present in the precipitation system. For the appropriate initial molar ratios c_i(Mg²⁺)/c_i(Ca²⁺), the magnesium content in calcite crystals decreases in the series Mg(OH)₂>MgSO₄>Mg(NO₃)₂>MgCl₂, as illustrated.

A high-speed experimentation exploration of the hydrolytic condensation of trichlorosilanes in highly polar solvents (see figure) has led to the identification of new silsesquioxane precursors for homogeneous and heterogeneous titanium catalysts active in the epoxidation of alkenes.

Unexplored ligands: Substituted naphthalene-1,8-dichalcogenoles are an unexplored class of ligands. A systematic series of novel platinum complexes have been prepared and characterised (see scheme).

An acid rather than an enzyme as the active additive to trigger conversion of alkenes to iodohydrins by reaction with NaI and hydrogen peroxide in aqueous media (see scheme). This simple and efficient procedure is based on biomimetic considerations.

Remarkable ability for hydrogen bonding (primarily CH⋅⋅⋅Cl; also CH⋅⋅⋅O and OH⋅⋅⋅Cl) and π–π stacking interactions is displayed by neutral M^IICl₂-containing coordination building blocks, varying in the type and denticity of heterocyclic N-donor ligands, metal ion (Co, Cu, Zn) and their geometry (tetrahedral, distorted square pyramidal/trigonal bipyramidal, and trans-octahedral). Such noncovalent interactions afford novel supramolecular architectures.

A novel family of monoanionic Cu^IIIcomplexes of bis(pyrazine-1,2-dichalcogenene)ligands (picture, top left) is reported. The side-coordination capability of the pyrazine moieties towards alkali metal cations (dots in picture, right) was demonstrated to be a new tool for fine 3D tuning and crystal engineering of these and other systems. The innocence of the ligands was experimentally and theoretically addressed, by DFT calculations of MOs (picture, bottom left).

A new optical trigger: A new series of photocleavable protein cross-linking reagents based on bis(maleimide) derivatives of diaryl disulfides have been synthesised. They have been functionalised with cysteine and transient absorption spectra for the photolysis reaction have been recorded by using the pump-probe technique with a time resolution of 100 femtoseconds (see scheme).

Work with nature! Dynamic combinatorial carbohydrate libraries can easily be generated by acylhydrazone interchange from a range of carbohydrate aldehydes and structural hydrazide elements. In the present study, such libraries were used to probe carbohydrate–lectin interactions by using Concanavalin A as a target species. The libraries allowed the efficient identification of the structural features required for binding to Concanavalin A and the selection of a tritopic mannoside as a strong binder (see picture).

Accommodating capsules! The capability of the dinuclear complex fragment [(L^Me)Ni₂]²⁺ to accommodate a range of small molecules L′ in its bowl-shaped cavity is demonstrated herein (see picture). Owing to the confined environment in the binding pocket only one of possible coordination modes of L′ is realized. The coligands influence many properties of the dinuclear complex fragment, such as complex stability, redox potential, and spin ground state.

Step by step: Reactions of tBuP(NH₂)₂ with Group 13 trialkyls MR₃ (M=Al, Ga, In; R=Me, tBu) proceed stepwise with the formation of aminophosphane and iminophosphorane adducts and finally yield heterocyclic metallonitridophosphinates (see structure). The proposed reaction pathway was verified by variable-temperature NMR investigations and quantum-chemical calculations.

Bridging the gap: The bis(phosphatediester)-bridged and phosphinate-bridged complexes were prepared from the hydroxo complex [{Ni([12]aneN₃)(μ-OH)}₂](PF₆)₂ (see scheme). The eight-membered rings defined by the nickel atoms and the bridging ligands display different conformations, and the magnetic-exchange pathways involve the phosphate/phosphinate bridges (NiOPONi); these favour antiferromagnetic interactions. The kinetics for the hydrolysis of TNP (tris(4-nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex was studied by UV-visible spectroscopy.

Preferential ion pairing: The possibility to individually monitor the diffusion coefficient of multiple anionic and cationic species in mixtures allows us to evidence ion exchange. Thus when [(BuSn)₁₂O₁₄(OH)₆](PTS)₂ (PTS=p-toluenesulfonate) is mixed with two equivalents of [NMe₄]Ph₂PO₂, PTS⁻ is displaced by Ph₂PO₂⁻ (see scheme). This example clearly illustrates the potential of pulsed field gradient ¹H NMR spectroscopy in inorganic/organometallic chemistry, to follow preferential ion pairing in multi-ion systems at the level of each individually charged species.

A stereospecific intramolecular nucleophilic substitution of the selenonyl group by the nitrogen atom of the carbamate in a ring-closure reaction (see scheme; R=Ts or Bz) is the key step in the stereospecific synthesis of 5- and 4,5-substituted-1,3-oxazolidin-2-ones from β-hydroxyalkyl phenyl selenides.

The hydroxo complexes of Groups 6 and 7 [Mo(OH)(η³-C₃H₄Me-2)(CO)₂(phen)] and [Re(OH)(CO)₃(NN)] (NN=bipy, Me₂bipy) react with a variety of unsaturated organic electrophiles to yield the corresponding products of insertion into either the MO or OH bond. In addition, when the electrophile is dimethylacetylenedicarboxylate (DMAD), the activation of a carbonyl ligand gave rise to a cyclic hydroxycarbene (see scheme).

The total synthesis of a wide range of complex terpenoid skeletons, including monocyclic, bicyclic, and tricyclic natural products, is facilitated by employing a novel reaction cascade based on the combination of biomimetic strategies with titanocene catalysis. For example, the titanocene-catalyzed radical cyclization of 2,3-oxidosqualene mainly gave malabaricatrienes (see scheme). Mechanistically the reaction presumably occurs via discrete carbon-centered radicals.

Phase-tagged palladium–phosphine catalysts for Suzuki coupling: Soluble, polymeric catalysts for aryl chloride coupling are recycled efficiently by applying a biphasic reaction protocol. One catalyst batch can be used for numerous coupling reactions with almost constant activity (TOF). A typical ligand used in these studies is shown.

A one-pot reaction provides a simple route to novel tetraphenylborate salts of organolanthanoid(II) cations [Ln(C₆F₅)(thf)_n]⁺ (e.g. 1). These organolanthanoid(II) cations show remarkable stability, even forming part of a fortuitously isolated mixed-valent cation/anion pair (e.g. 2).

A three-step mechanism is predicted for the reaction between CO and [Ni(N₃)(′S₃′)]⁻ (′S₃′²⁻=bis(2-mercaptophenyl)sulfide (2−)) based on DFT (B3 LYP & BP86) calculations: 1) reaction with CO generates a pseudo “square-pyramidal” complex; 2) CO inserts into the NiN bond (1) and the apical NiS bond rebounds as the nickel forms a square-planar intermediate 2; 3) in a one-step process N₂ leaves as the remaining N atom and carbonyl rearrange to produce [Ni(NCO)(′S₃′)]⁻.

An electrosensor for magnesium: The structural characteristics of the novel ferrocenophane (illustrated here) prepared have proved to be of special interest in the study of intramolecular electron transfer, as a specific electrosensor for Mg²⁺ and as a model for explaining the special stability of α-ferrocenylcarbenium ions.

A double-cubane heptacopper core surrounded by a belt of six X⁻ ions is present in the compounds [{Cu₃(Hpz^tBu)₆(μ₃-X)(μ₃-OH)₃}₂Cu]X₆ (X⁻Cl⁻, Br⁻, or NO₃⁻ (see structure)). These are associated with the cluster core through a combination of very long axial Cu⋅⋅⋅X interactions, hydrogen bonding and hydrophobic interactions. Spin frustration results in the seven Cu spins coalescing into three mutually independent spin systems in their magnetic ground state.

Cool, radical discoveries! The combined action of ab initio IR predicted spectra of isotopomers and selective use of isotope-labeled reagents allowed the complete elucidation of the mechanism shown in the scheme (CF₃ radicals in the presence of CO and O₂). This led to the conclusion that acyloxy radicals can be substantially stabilized at temperatures close to 0 °C.

Hollowed ZnO hexagons of 0.15 μm width and 0.5 μm length filled with functionaliazed Fe₃O₄ nanoparticles were grown from a supersaturated solution of Zn(NO₃)₂ seeded with the magnetic nanoparticles. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements show that the surfactants induced the directional growth of the ZnO crystals. The figure shows an HR-SEM (high-resolution scanning electron microscopy) micrograph of the ZnO crystals that were grown on the magnetite nanoparticles.