Two methods—one result: Through fluorescence energy transfer measurements and an X-ray structure analysis on ribozyme–substrate complexes, the groups of Eckstein and McKay independently arrived at a largely consistent structural model for hammerhead ribozymes. Three helices are arranged in a stretched Y shape (see picture) and are stabilized by unusual interactions besides the Watson-Crick base pairing.

As many as three stereogenic centers were introduced in one step in the preparatively simple cascade reaction of 1-benzothiopyrylium salts with 2-siloxy-1,3-butadienes. The cascade comprises 1,2-additions and subsequent intramolecular 1,4-additions and gives the all-cis-thioxanthon rac-3 in 91% yield from the starting compounds 1 and 2, formed in situ. A diastereoselective synthesis of such compounds was not previously known.

Double layers are formed by α,ω-docosanediol (C₂₂ diol) when it is spread on a water surface. The space group (a slightly relaxed form of P2₁/a) and the lattice parameters of the unit cell were determined by X-ray diffraction. Furthermore, multilayer formation was inhibited by addition of 10% of C₂₄H₄₉OH or 5% of HO(CH₂)₂₂OCH₂Ph to the spreading solution. The coverage with the double layer was reduced to less than 15%; the rest was occupied by a monolayer.

Not the aromatic form 1 a but the nonaromatic form 1b of the enzyme-inhibitor complex is preferred at the active site of urocanase. This can be observed in situ with ¹³C-labeled components by NMR spectroscopy. The enzyme-bound adducts were characterized by use of (4-¹³C)NAD⁺-containing urocanase and the labeled inhibitor (5′-¹³C)imidazolepropionate. • = ¹³C, R = adenosine diphosphate ribosyl.

σ Complex 1 or π complex 2? This is a controversial question for [R₃Si–arene]⁺ adducts. A crucial test based on their reactivity, toward selected nucleophiles provides convincing evidence for the existence of the σ complex 1 in the gas phase.

A versatile ligand system capable of acting as a two-four-, and six-electron ligand in Cp^* complexes of the cobalt triad is the bulky 1,1′-ferrocenedithiolato ligand [S₂fc]. In the Co₃ complex 1, [S₂fc] bridges the CoCo bonds symmetrically and functions as a six-electron donor. The unusual bent Co₃ chain in 1 has been structurally characterized.

The nonclassical characteristics of 1,5-dicarbapentaboranes 1 ( = 2,4,5-triborabicyclo-[1.1.1]pentanes) are lost only in part when a boron atom is exchanged for a carbon or a silicon atom (2–4). The CB hyperconjugation is replaced by CC or CSi hyperconjugation.

Readily available starting materials can be used to prepare silicon-bridged macrocycles of different ring sizes by deprotonation and reaction with Me₂SiCl₂. While heterocycles such as furan or thiophene gave sila[1₄]- and sila[1₆]phanes, para-(tert-butyl)methoxybenzene afforded the first silacalix-[4]arene 1.

An insoluble complex formed by self-assembly: Terephthalate and an acridine-substituted cyclen–Zn^II complex react to give the 2:1 complex 1, which results in a supramolecular chainlike aggregate, insoluble in water, that is held together by intermolecular hydrophobic interactions. Since the other phthalate isomers do not behave in this way, it is possible to separate terephthalate selectively.

Very strong antiferromagnetic coupling exists between the Fe centers in the N-bridged complexes 1 and 2. In 1 (shown on the right), which contains a symmetrical [Fe^IV = N = Fe^IV] unit, this results in an S = 0 ground state, while in 2, which has an unsymmetrical Fe^III–N = Fe^IV bridge, it leads to an S = 3/2 ground state. Compound 2 forms in the photolysis of [Fe^III(cat)N₃] and can be oxidized with Br₂ to give 1. L = trimethyltriazacyclononane, cat = tetrachlorocatecholate(2−).

Easy to synthesize and highly soluble are the new (1,4-diaza-1,3-diene) complexes 1 and 2, which can be considered as alternative starting materials to the frequently used cyclopentadienyl lanthanoid halides in organolanthanoid chemistry. The similarity of Cp ligands and the [(dad)Li]^- unit is apparent in the structure of 1 on the right; complexes 2 have a different structure as a result of the smaller ionic radius of the lanthanoid.

An azomethine ylide is invoked as an intermediate in the copper-catalyzed addition of diazoesters to imines [Eq. (a)]. Coordinated to the chiral copper(I)–bis(dihydrooxazole) catalyst, these intermediates cyclize to produce enantiomerically enriched 1,3-diaryl-2-carboxyethylaziridines (44–67% ee).

Remarkably high chemo- and regioselectivity was found in the intramolecular one-pot McMurray-type reaction between ketone and amide carbonyl groups. A simple preparative method is used by which the active low-valent titanium species is formed selectively at the site of the reductive coupling. For example, compound 2 is formed from 1 in 86% yield by a zipper-like series of carbonyl couplings.

A CpCo-induced hydrogen migration and elimination in 1 gives rise to the olive-green, paramagnetic triple-decker complex 2 with the new 1,3,5-triboratabenzene bridging ligand. The B₃C₃ ring is planar and the BC distances almost the same length. Compound 2 may be easily oxidized with AgBF₄ to the diamagnetic 2⁺BF.

Cyclotetramerization of a hydroxymethylphenanthropyrrole afforded a highly conjugated porphyrin 1 with four annelated phenanthrene rings. The 68 carbon atoms in the dication of this highly symmetrical heptadecacycle–the neutral compound is virtually insoluble in most organic solvents–produced only nine resonances in the ¹³C NMR spectrum.

The controlling function of the crystal lattice in many reactions in the solid state can be exercised by the rigid [2.2]paracyclophane spacer in photochemical processes in solution. For example, irradiation of the bisvinylogous cinnamophane 1 affords [5]ladderane 2 in good yield.

The alkali metal compounds MR (R = C(SiMe₃)₃, M = Rb, Cs), which are extremely air- and moisture-sensitive, can be synthesized from RH and MMe. Crystals of RbR consist of linear chains of Rb⁺ ions and distorted planar R^- ions, whereas those of CsR contain isolated ion pairs surrounded by lattice C₆H₆ solvent molecules (shown on the right).

The reduced electrophilicity of the Ti center resulting from Cp^* ligands and sp² hybridization of the ring-C atoms influences the stability of 1 (XN, P) in such a way that 1-aza- and 1-phospha-2-titanacclobut-4-enes could be characterized by X-ray structure analysis for the first time. The metallacycles 1 are formed by trapping the [CpTiCCH₂] intermediate with tBuCX (XN or P); however, the mechanisms of these reactions differ.

The polarization of the polymethine π-electron system by the unsymmetrically arranged BPhion in 1 is so strong that a distortion of the molecular structure of the dye cation could be proved in the solid state for the first time. The phenyl rings in the vicinity of the polymethine chain positivate the left-hand half of the molecule (shown on the right) with the result that bond length alternation is induced.

The resorcinol–octadecanal cyclotetramer 1 forms an ion channel in planar lipid bilayers. A stable conductance level is observed with well-defined transitions between open and closed states. The channel discriminates K⁺ from Na⁺ ions as well as cations from anions (for example, K⁺ from Cl⁻), as indicated by permeability ratios of 3 and 20, respectively. Rb⁺ ions block the K⁺ ion current.

An enhanced preference for complexing to an RNA complement on the Hoogsteen side of the nucleobase is the consequence of the sugar modification in oligonucleotides of bicyclodeoxyguanosine 3. Furthermore, oligonucleotides containing bicyclothymidine 1 and bicyclodeoxycytidine 2 provide evidence of specific differences in the preferred sugar conformation of the nucleosides in the third strand in DNA triple helices.