If the protein-folding problem were solved, the folded structure of a protein and its stability could be deduced from the sequence of amino acids. Today it is possible to construct proteins that differ in one or more amino acids. The determination of their three-dimensional structure by X-ray crystallography and NMR spectroscopy contributes substantially to the understanding of protein folding and stability. For these reasons, several proteins are being studied by these techniques today. One of them is the enzyme ribonuclease T1, whose structure is sketched to the right.

The almost unlimited potential for variation is the astounding feature of metallo-mesogens. They combine the variety of coordination chemistry with the exceptional properties of liquid crystals. The incorporation of metals into mesophases intensifies useful characteristics such as polarizability and birefringence, but the increase in melting point (the temperature at which the phase transition crystal → liquid crystal takes place) is a disadvantage. For practical applications it should be close to room temperature. As a result of asymmetry in the ligand sphere, which disturbs the packing in the crystal, the olefin-platinum complexes 1 adopt the smectic A phase at low temperature.

Enantioselective catalytic oxidations of nonfunctionalized alkenes (Equation (a), X = H, alkyl, aryl) remained a challenge long after Sharpless and co-workers developed the enantioselective epoxidation of allyl alcohols (Equation (a), X = OH) ten years ago. Designer catalysts based on porphyrins recently brought new progress, while poly-L-leucine proved attractive as catalyst for the epoxidation of diverse chalcones with H₂O₂/NaOH in up to 92% ee.

Supramolecular chemistry does not stop at organometallic compounds, as two recent articles of Gokel and co-workers show. Redox-controlled vesicles can be formed from cholesteryl-substituted ferrocenes, and the linking of two ferrocene units as in 1 affords novel receptors. The spacer R allows different diamines to be bound to 1. The required spatial orientation of the carboxylic acid residues is achieved by rotation of the cyclopentadienyl rings.

Bonds and lone electron pairs can be made “visible” when the electron density distribution is used to calculate the electron localization function (ELF). This paper presents a computer-graphics image of ELF in colors which represent the extent of the localization (at the right a black-and-white picture of N₂).

In an in vitro tubulin test, the depolymerization of tubulin was shown to be inhibited also by less functionalized taxol analogues such as 1. The α ring formation at C8 is achieved by a stereoselective de Mayo reaction of cyclohexene on a suitable functionalized 1,3-diketone.

Five from one!—this is the bottom line in the transformation of 1 into 4, where one stereocenter induces four new ones. The allyl alcohol 1 is converted into the ester 2 with sorbic acid, which then cyclizes to 3 in an intramolecular Diels–Alder reaction (“CO → CC induction”). In a simple reaction sequence compound 3 opens to 4, which contains five distinct hydroxy functions and is therefore an attractive building block for synthesis.

The enol 2, produced by a Norrish type II photoelimination from 1, is protonated enantioselectively to ketone 3 in the presence of (–)-ephedrine. Best optical yields are obtained at 0^oC using small amounts of the chiral aminoalcohol. There is still wide scope for optimization.

A simple intercalating group like a naphthyl substituent increases the ability of unsaturated sulfones such as 1 to cleave DNA, as demonstrated by compounds 2 and 3. A selective attack on the guanine residue has been proven for 1. The mechanism of action of this class of compounds involves an alkylation reaction.

Only one of eight possible diastereomers of the sodium salt of the tricarboxylic acid 1 is formed in high yield in the novel title reaction. Compound 1 cannot be prepared in solution, by thermolysis or by UV irradiation of crystalline sodium trans-2-butenoate. The trimerization is interesting as a model reaction for the early stages of oligomer formation in a solid-state polymerization reaction.

Hydrothermal synthesis is used to prepare the Me₄N^⊕ salt of the title anion. The structure of this VV polyoxovanadate anion is characterized by crystallographic C₄ symmetry and may be described as consisting of four vanadium oxygen tetramers which are covalently linked by four CH₃PO units to resemble chains on a tire. The diameter of the opening is 4 Å and is thus about as big as the larger Si/Al-O ring in zeolite A. The sketch on the right shows the V₄O₈ tetramer and four CH₃PO units.

A novel type of autocatalytic growth, which is distinguishable from exponential growth and has implications for theories on the origin of life, is revealed by self-replication experiments based on nonenzymatic template-directed reactions of oligonucleotide derivatives. The sketch on the right shows the general mechanism of a minimal system for self-replication.

The binuclear complex [Cp₂Zr(μ-Cl)(μ-CH₂Me)AlMeEt] 1 attached to a support is formed by the reaction of [Cp₂ZrMe₂] and MgH₂ after the addition of the cocatalyst (Et₂AlCl)₂. Species 1 catalyzes the polymerization of ethylene by inserting ethylene molecules into the Zr–μ-alkyl bond. The intermediate steps in the formation of 1 and the polymerization could be observed by means of ¹³C CP/MAS NMR spectroscopy.

The reaction of an organic acid with solid metal hydroxides in hydrocarbon solvent in the presence of a Lewis base such as hexamethylphosphoric triamide (HMPA) affords the metal complexes of the title according to Equation (a). The complex Ox₂Ca^·2HMPA^·2H₂O can be prepared from Ca(OH)₂, 2-mercaptobenzoxazol (OxH) and HMPA in this direct synthesis. A striking feature of its structure is the intra- and intermolecular S…︁HO hydrogen bonds.

The cobalt-induced alkyne trimerization is absent when the coordinatively unsaturated cobalt complex fragment contains a fixed double bond as in 1, which can raise the activation barriers for the individual steps substantially. Depending on the alkyne substituents, several products can be formed such as 2 (R = SiMe₃) and 3.

Extreme deformation of the ethano bridge occurs during the isomerization of the chiral benzophenone derivative 1 to the yellow, reactive ortho-quinoid system 2 on irradiation. This is proved unambiguously by photoenolization experiments in [D₄]methanol. Whereas 2 is interesting as a reactive preparative intermediate, the fluorescence properties of 1 suggest a possible application as triplet sensitizer in photochemical reactions.

The auration of arylphosphanes by reaction with [(Ph₃PAu)₃O]BF₄ affords the triauriophosphonium salt 1, while reaction of P(SiMe₃)₃ with this oxonium salt yields 2, which has a hypercoordinated P center. The cation of 1 has an almost ideal tetrahedral geometry about the central P atom. The large radius of the P atom leads to large peripheral Au…︁Au distances of 3.7 Å. R = o-tolyl.

A cis configurated butadiene ligand which bridges two lanthanum nuclei, but forms a σ bond with one metal center and a π bond with the other, features in the title complex 1. Compound 1 can be prepared from “butadiene magnesium” as diene source (Equation (a)) and is isolated from pentane in the form of bright red, extremely air-sensitive crystals.

[6,4]Rotane 1 exists in a rigid chair form in the crystal as well as in solution, because it has the highest free energy of activation (ΔG^≠ = 156.8 ± 1.1 kJmol⁻¹) among the cyclohexanes for the chair-chair inversion. The cyclobutadiene rings are almost ideally staggered, approximately planar, and slightly kite-shaped.

rac-Tris(divinyldisiloxane)diplatinum(0) 1 is obtained on reaction of [Pt(cod)₂] with tetramethyldivinyldisiloxane. Detailed multinuclear NMR studies showed that solutions of 1 are almost identical to the catalytically active solution which is used in the hydrosilation of unsaturated compounds.

The mesophase type and the phase-change temperature of bolaamphiphilic triols such as 1 and tetrols such as 2 depend on the structure of the polar groups and the length of the polymethylene chain between them. But even addition of water modifies the phase type and the clearing temperature, because the polar bridge-head groups become hydrated.

Certain purine and pyrimidine bases form stable complexes with N-benzylated triscatechol macrobicycles (1), because the cavity is the right size and potential hydrogen bonding sites are present. The results stimulate the question whether siderophores play a role in the transport of nucleobases or nucleotides in biological systems.

“Dichloroneopentylsilaethene” 1 reacts with naphthalene in a surprising [4 + 2] cycloaddition to give the endo product 2. This can be reduced with LiAlH₄ to afford 3, which was analyzed by X-ray crystallography. A reaction of 1 with cyclohexa-1,3-diene forms bicyclic silacyclobutanes in a [2 + 2] cycloaddition.

The challenge of synthesizing the calicene parent compound remains, but now the higher homologues 1–3 (X, Y = H or StBu) exist. According to NMR data and an X-ray structure analysis of 2 (X; Y = StBu), both the polar resonance structures and the conjugated 16π electron systems (antiaromatic!) contribute to the description of the molecular structure.

No topochemical polymerization in the crystal and as a result no polymeric organic ferromagnets are observed for the radical substituted diacetylenes 1a–1d and an analogous series of compounds. Crystal structure analyses of two compounds illuminate the reason for the lack of polymerization on irradiation with electrons. a, R = H; b, R = OSO₂-p-C₆H₄CH₃; c, R = OSO²-p-C₆H₄OCH₃; d, R = CONHCH₂COnBu.