J. Appl. Cryst.の発刊に際して

The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of β-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Cultures on corn of Fusarium moniliforme MRC 826 are known to cause leukoencephalomalacia in horses and to be toxic and hepatocarcinogenic in rats. Culture material of this F. moniliforme isolate has also been shown to exhibit cancer-promoting activity in a short-term cancer initiation-promotion bioassay with diethylnitrosamine-initiated rats and the induction of gamma-glutamyl-transpeptidase-positive (GGT+) foci as an endpoint after 4 weeks of promotion. This bioassay was used as a monitoring system to isolate cancer-promoting compounds from cultures of F. moniliforme MRC 826. Culture material was successively extracted with ethyl acetate and CH3OH-H2O (3:1). Most of the cancer-promoting activity was recovered in the CH3OH-H2O extract and remained in the aqueous phase following partitioning of this extract between CH3OH-H2O (1:3) and CHCl3. The CH3OH-H2O fraction was chromatographed on an Amberlite XAD-2 column, and the active fraction was eluted with CH3OH. This fraction was chromatographed on a silica gel column with CHCl3-CH3OH-CH3COOH (6:3:1) as eluent and further purified on a C18 reverse-phase column. Two pure compounds were isolated, and these have been chemically characterized and given the trivial names fumonisin B1 and B2. At least 2 g of the major compound fumonisin B1 was purified from 1 kg of culture material. Fumonisin B1 in the diet (0.1%) significantly (P less than 0.001) induced the formation of GGT+ foci in the livers of initiated as well as noninitiated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fumonisins--novel mycotoxins with cancer-promoting activity produced by Fusarium moniliforme.

This article sets out to review the chemistry relating to the synthesis of structural and functional analogues of the three classes of hydrogenases. This chemistry has grown explosively over the last 10 or so years since the first X-ray structures of [NiFe]- and [FeFe]-hydrogenase systems were published. There are now some 400 papers covering structural and functional aspects, with the majority of these associated with the di-iron system. As much emphasized in earlier papers

Structural and functional analogues of the active sites of the [Fe]-, [NiFe]-, and [FeFe]-hydrogenases.

σ,π-Bridging Ligands in Bimetallic and Trimetallic Complexes

The assignment of structure (1) to fusarin C, a mutagen isolated from cultures of Fusarium moniliforme is based on a detailed study of its high-field 1H and 13C n.m.r. spectra and X-ray crystallography of the 8Z isomer of (1) which defined the substitution pattern and relative configuration of the 2-pyrrolidone moiety; nuclear Overhauser enhancement experiments indicate that the 2E,4E,6E,8E,10E polyene chromophore of (1) exists in solution as an equilibrium between two conformers with s-cis and s-trans topology of the C-5–C-6 single bond.

Structure elucidation of fusarin C, a mutagen produced by Fusarium moniliforme

Synthesis and Crystal Structure of a Monocarbene Complex of Copper

Modeling and spectroscopic studies of bisphosphonate–bone interactions. The Raman, NMR and crystallographic investigations of Ca–HEDP complexes

A new indanone derivative (1) and two new diterpenoids (2 and 3), together with three known flavonoids, have been isolated from an ethanol extract of the leaves of Croton steenkampianus. The structure of 2 was solved by single-crystal X-ray diffraction analysis, whereas those of 1 and 3 were established mainly by 1D and 2D NMR spectroscopic methods. The isolated compounds were tested for their antiplasmodial activity and cytotoxicity. Antiplasmodial assays against chloroquine-susceptible strains (D10 and D6) and the chloroquine-resistant strains (Dd2 and W2) of Plasmodium falciparum showed that compound 2 gave moderate activities at 9.1−15.8 μM, while none of the compounds were cytotoxic against Vero cells.

Petrus H. van Rooyen

Papers

σ,π-Bridging Ligands in Bimetallic and Trimetallic Complexes

Structure elucidation of fusarin C, a mutagen produced by Fusarium moniliforme

Synthesis and Crystal Structure of a Monocarbene Complex of Copper

Modeling and spectroscopic studies of bisphosphonate–bone interactions. The Raman, NMR and crystallographic investigations of Ca–HEDP complexes

Bioactive Diterpenes and Other Constituents of Croton steenkampianus