Ozone as an endogenous compound? The discovery of 5,6-secosterol, a characteristic product of the in vitro ozonolysis of cholesterol, in atherosclerotic tissue (see picture) suggests that ozone is formed by biochemical processes. This and other typical products of oxidation may serve as indicators (“biomarkers”) of endogenous ozone.

Now a quarter of a century since its serendipitous discovery, the Belluš–Claisen rearrangement of ketenes with allylic ethers, amines, and thioethers has been developed into a simple and reliable [3,3] bond reorganization reaction. This rearrangement, which proceeds via a zwitterionic intermediate, is especially powerful for the ring expansion of cyclic allylic substrates by four carbon atoms (see scheme). R¹, R²=alkyl, Cl.

A diverse range of biomolecules, including steroids and glycosaminoglycans, are sulfonated enzymatically by the cosubstrate PAPS in the presence of sulfotransferases (see scheme). As these enzymes have been implicated in several crucial pathophysiological events (regulation of estrogen sulfate synthesis and leukocyte adhesion, viral entry) they have emerged as promising therapeutic targets.

A DNA aptamer structure is the basis of a molecular machine that can be instructed to grab or release the human blood-clotting factor α-thrombin, depending on the operator DNA sequence addressing it. In the picture the aptamer structure, which assumes a conformation characterized by two stacked guanine quadruplex structures, is linked to thrombin (gray ellipse).

The power of life: An autonomous DNA nanomotor powered by an RNA-cleaving DNA enzyme (see figure) has been constructed that works in the same way as cellular protein motors: it continuously extracts chemical energy from fuel molecules to power mechanical motions. The fuel for the DNA nanomotor is the RNA substrate of the DNA enzyme.

Selective guest ejection: Up to eight guest molecules are assembled at the periphery of a third-generation dendrimer. Collision-induced dissociation mass spectrometry has demonstrated that the guests are removed very selectively in a one-by-one manner (see spectrum).

Titanium(III) pyrochlores with Ti^III centers at up to 90 % of the B sites of the A₂B₂O₆O′ pyrochlore structure (see picture; blue: BO₆, green: A, red: O′), which is well-known for supporting high oxidation states at the octahedral B sites, were obtained by the low-temperature reduction of lanthanide pyrochlores Ln₂Ti₂O₇ with CaH₂. This leads to significant rearrangement of the anion sublattice and introduces antisite disorder between the two distinct cation arrays.

Magic probes: The geometry of strongly hydrogen bonded silanols in octosilicate can be probed by exploiting the ¹H NMR distance correlations together with the joint effects of ²⁹Si chemical shielding and dipolar ¹H–²⁹Si interactions. Dipolar-modulated, slow magic-angle spinning ²⁹Si NMR spectra allow the determination of Si⋅⋅⋅H distances, the magnitude of the ²⁹Si chemical-shielding tensor, and its orientation in the molecular frame.

Stable oil-in-water emulsions are obtained in alkaline solution in the absence of any conventional surfactant. The oil droplets are charged by hydroxide ions (see picture). The surface charge density is obtained by measuring the size of the emulsion droplets by electroacoustics and the quantity of NaOH required to keep the pH constant during homogenization.

Classical organometallic chemistry was used to prepare the dinuclear iron complex 1 with two protected cysteinyl-S ligands. Oxidative addition of the thiol to [Fe₃(CO)₁₂] gave complex 1, which undergoes an unusual intramolecular nucleophilic cyclization with inversion of the configuration to form the chiral carbon-bridged diiron complex 2.

Excellent activity and selectivity in the copolymerization of CO₂ with epoxides at extremely mild temperature and pressure are observed in the presence of binary nucleophile–electrophile catalyst systems based on chiral [(salcy)Co^IIIX] complexes and quaternary ammonium salts (see scheme). Completely alternating copolymers are obtained with >95 % head-to-tail linkages.

An infinite network is formed by the hydrogen bonding of a cluster of 12 hydrogen-bonded water molecules (see picture) to the secondary amino nitrogen atoms of a laterally nonsymmetric azacryptand. This mode of association had not previously been predicted or found experimentally.

Diazoacetates in coupling reactions: CuI serves as an effective catalyst for coupling terminal alkynes with diazo compounds to generate 3-alkynoates (see scheme). This method is efficient (1:1 ratio of reactants), mild (room temperature), and simple (no additional ligand), and a range of functional groups are tolerated (e.g., CC double bonds, heteroatoms, and hydroxy groups).

Spontaneous trimerization of fluoro(triisopropylsilyl)acetylene, prepared from 1,1-difluoroethylene in one step, gives the corresponding fluorinated Dewar benzene derivative, whose structure was determined by X-ray diffraction (see picture).

Quantitative conversion: Reaction of the 14-electron complex [RuCl₂{(2,6-Me₂C₆H₃)PPh₂}₂] with CH₂O in the presence of NEt₃ gave a five-coordinate cyclometalated complex with a δ-agostic interaction of one ortho-methyl group (see X-ray crystal structure). Displacement of one phosphane group with 2-(aminomethyl)pyridine gave a highly active catalyst for the quantitative conversion of ketones into alcohols.

Quick reactions: The gas-phase nucleophilic displacement reaction of fluoride ions with nitrobenzene proceeds with a rate constant close to the collision limit. The calculated energy profile indicates that the reaction proceeds by an out-of-plane attack, with the Meisenheimer complex being the local transition state for the reaction (see picture).

Programmable bisintercalators: Symmetric synthetic DNA bisintercalators (see picture) based on the H-pin polyamide motif afford high affinity and programmable sequence specificity.

A wide range of oxidative reactions are mediated by novel, nonpolymeric, and recyclable hypervalent I^III reagents (e.g. 2). In all cases, tetraiodide 1 was recovered nearly quantitatively in pure form after a simple workup. Reoxidation of 1 to 2 with m-chloroperbenzoic acid also proceeded quantitatively, without loss of oxidative activity.

Desulfuration as a source of alkyl radicals: The addition of alkylsulfanyl radicals to isocyanides gives the corresponding alkyl radicals. This methodology can replace the usual tin-mediated radical procedures and allows for the generation of tertiary, secondary, and even nonstabilized primary radicals that can be used efficiently in reductive defunctionalizations and intermolecular additions to electron-rich olefins (see scheme).

The vacuolar-type (H⁺)-adenosine triphosphatase inhibitor oximidine III and its enamide and epoxide stereoisomers have been synthesized enantioselectively. A relay ring-closing metathesis (RCM) strategy was employed to facilitate the macrocyclization of a well-defined substrate possessing two differentially functionalized RCM alkene partners (see scheme).

The formation of a CC and a CN bond in a reaction between γ-(N-arylamino) alkenes and aryl bromides results in the stereoselective synthesis of substituted pyrrolidine derivatives (see scheme). Preliminary studies suggest these reactions proceed by intramolecular alkene insertion into the PdN bond of intermediate [Pd(Ar)(amido)] complexes. dba=dibenzylideneacetone, dppb=1,3-bis(diphenylphosphanyl)butane.