Human frataxin: iron and ferrochelatase binding surface

The coordinated iron structure and ferrochelatase binding surface of human frataxin have been characterized to provide insight into the protein's ability to serve as the iron chaperone during heme biosynthesis.     

Covalent strategy for immobilization of DNA-microspots suitable for microarrays with label-free and time-resolved optical detection of hybridization

Sequence-specific detection and quantification of nucleic acids are central steps in many molecular biology procedures which have also been transferred to chip-based procedures. Hybridization-based assays can be used to quantify and discriminate between DNA target sequences down to the level of single base mismatches. Arrays of DNA probes immobilized on a support enable simultaneous testing of multiple sequences of a single sample. DNA arrays can be produced either by in-situ synthesis of oligonucleotides or by immobilization of pre-assembled DNA probes. Covalent and directed immobilization improves the reproducibility and stability of DNA arrays. This is especially interesting with repeated use of transducers or chips. Procedures are described for effective covalent immobilization of pre-assembled amino-linked oligonucleotides, by use of ink-jet techniques, on a modified and heated glass surface, with addressable surface areas ranging from 0.01 mm2 to a few mm2. Almost immediate evaporation of the spotted droplets on the heated surfaces leads to very high surface hybridization capacities. The surfaces are suitable for use with a label-free detection method - reflectometric interference spectroscopy (RIfS). It is shown that hybridization capacity and non-specific interaction at these DNA-surfaces can be characterized by use of RIfS. With a consumption of less than 80 ng mm(-2) oligonucleotide and a specific hybridization capacity of more than 300 fmol mm(-2), the activated aminodextran procedure was usually suitable for setting up a DNA array with label-free detection. Non-specific interactions with random oligomers or protein (ovalbumin) were low. Up to 150 repeated regenerations (stripping) of the surfaces by acid treatment and denaturing agents, and 50 days of storage, have been possible without significant loss of hybridization capacity.     

Preparation of site-differentiated mixed ligand and mixed ligand/mixed metal metallacrowns

Assembly reactions that can prepare reliably regioselective metallamacrocyclic complexes have been a target in the development of metallacrowns. To this end, a series of mixed ligand and mixed ligand/mixed metal metallacrowns have been synthesized in high yield and structurally characterized. Two distinct connectivities have been observed in these types of metallacrowns. The monomeric, vacant metallacrown with mixed ligand composition [12-MC(Ni(II)N(Hshi)2(pko)2-4)] (1a) shows the connectivity pattern [-O-Ni-O-N-Ni-N-]2 while the other Ni metallacrowns, [12-MC(Ni(II)N(shi)2(pko)2-4)] (2a) and the coupled [12-MC(Ni(II)N(shi))2(pko)2-4)][12-MC(Ni(II)N(shi))3(pko)-4)] (3a) fused metallacrowns as well as the mixed metal Mn-Ni metallacrown [12-MC(Ni(II)Mn(III)N(shi)2(pko)2-4)] (4a), follow the pattern [-Ni-O-N-]4. Also, three distinct arrangements of the chelate rings around the metal ions have been observed. The syntheses are completely general, allowing for the substitution of different ligands into the metallacrown core. Compounds 1 and 4 show the 6-5-6-5-6-5-6-5 arrangement, compounds 2 and 3(1) the 6-6-5-5-6-6-5-5, and the 3(2) component the 6-6-5-5-6-5-6-5. The obtained structures can be rationalized by balancing the charge at each metal site in the metallacrown. Variable temperature magnetic susceptibility measurements show that exchange interactions for all the compounds are weak and dominantly antiferromagnetic (e.g., 2a gives an exchange coupling of J = -1.2 cm(-1) with g = 2.2). In solution, the metallacrowns are shown to be stable both to decomposition and ligand exchange.     

Numerical continuation of degenerate homoclinic orbits in planar systems

In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.