Cu(I) catalysed cyclopropanation with enantiopure scorpionate type ligands derived from (+)-camphor or (-)-menthone

One-pot syntheses of three new enantiopure heteroscorpionate ligands derived from (+)-camphor or (-)-menthone are described. The ligands are obtained by reacting pyrazoles derived from (+)-camphor or (-)-menthone with sodium hydride and thionyl chloride. Subsequent reactions with pyridine and various aldehydes afford the tripod ligands in multi-gram amounts. Especially the menthopyrazole based ligand 6 showed encouraging ee values up to 69% in the Cu(I) catalysed enantioselective cyclopropanation of styrene with ethyl diazoacetate.     

DMT-MM mediated functionalisation of the non-reducing end of glycosaminoglycans

Efficient functionalisation of the non-reducing end of uronic acid derivatives and glycosaminoglycan-derived disaccharides using peptide coupling has been achieved, mediated by the water-soluble agent DMT-MM.     

Structure and reactivity of the polarised liquid–liquid interface: what we know and what we do not

Charge transfer phenomena at the interface between two immiscible electrolyte solutions (ITIES) are electrochemical reactions taking place in soft media. Owing to their liquid nature, the ITIES shows a large panel of electrochemical reactions including electron transfer reactions, ion transfer reactions, coupled electron–ion transfer reactions or biomimetic redox reactions. Nevertheless, the mechanisms by which these reactions proceed are yet to be fully understood. The goal of this short review is to summarise the work accomplished over the past decades towards the elucidation of the structure and reactivity at the ITIES, highlighting the main questions still to be answered.     

Synthesis and microbial transformation of β-amino nitriles

Rhodococcus equi A4, Rhodococcus erythropolis NCIMB 11540 and Rhodococcus sp. R312 were investigated towards their ability to produce β-amino amides and acids from β-amino nitriles. The microorganisms show comparable trends: five-membered alicyclic 2-amino nitriles were transformed significantly faster than the six-membered compounds and the products of trans-2-amino nitriles (amides and acids) were formed considerably faster than the cis-counterparts (amides). The trans-five membered nitriles gave the amides (1b, 5b) in excellent enantiomeric excess (94-99%), the biotransformation of trans-six membered substrates resulted in the formation of the acid (3c, 7c) in excellent ee (87-99%). The ee's of the cis-compounds were throughout lower. Fifteen new substances were synthesized and characterized in the course of this work.     

An unprecedented tetranuclear niobium aqua ion with a capping mu4-sulfido ligand

The aqueous solution chemistry of niobium is rather unexplored, and well characterized aqua complexes are scarce. In this work, a new niobium aqua ion is obtained upon treatment of Zn-reduced ethanolic solutions of NbCl5 with HCl in the presence of a sulfide source. The red aqua ion, obtained upon cation-exchange chromatography, forms readily the thiocyanate complex which has been crystallized as Cs(4.26)Na(1.74)[Nb4SO5(NCS)10] . 0.33H2O. X-ray crystallography revealed an unprecedented metal-metal bonded tetranuclear Nb4(mu4-S)(mu2-O)5(4+) core with a capping mu4-S ligand.     

Determination of Spin Concentrations in ESR Tomography as Applied for the Spatial Distribution of Spin Labels in Human Skin

The spectral–spatial electron spin resonance (ESR) imaging experiment provides information about the spatial and spectral properties of the examined sample, as well as the intensity distribution. Obtaining quantitative statements of the respective sample requires the usage of reference standards such as diphenylpicrylhydrazyl (DPPH) or charcoal. By means of ultraviolet-visible spectroscopy a DPPH sample has been quantified to become the reference DPPH standard for the following experiments. Moreover, charcoal together with DPPH serves as a standard to determine the spatial dimension. An ESR tomographic device has been modified concerning the sample shaping and arranging in a TE₁₀₂ resonator to allow the spatially resolved quantitative determination of spin concentrations of spin probes (S = 1/2) with an acceptable error. Only standard ESR equipment has been used except the additional gradient coils and their computer-aided controls for recording the tomogram. The presented results, i.e., the spatially resolved determination of spin concentrations, seem to be useful to describe, e.g., transport processes in biological objects. As a first application of the developed method, the spatial resolution of the effect of ultraviolet irradiation on the concentration of a spin probe in human skin could be determined. Altogether, the newly introduced method widens the field of applications of ESR spectroscopy and tomography. Authors' address: Werner Herrmann, Institute of Pharmacy, Free University Berlin, Kelchstrasse 31, 12169 Berlin, Germany