The stereochemistry and biosynthesis of hybridalactone,an eicosanoid from laurencia hybrida

The stereochemistry of the marine eicosanoid, hybridalactone, has been determined experimentally to be as in 2, in accord with a proposed scheme of biosynthesis from eicosapentaenoic acid.     

RFA as control method of the reactive sputtering process of TiN films

In-situ X-ray fluorescence (XRF) analysis has been used to control the deposition process of Ti-N films on steel substrates during reactive sputtering. The analysis system consisted of a tungsten X-ray tube, secondary targets of Cu, Fe and Cr and a Si (Li) detector. The sputtering off the Ti target has been determined indirectly by plasma monitoring using optical emissions spetroscopy (OES) of the Ti atoms, and the film growth has been measured directly by XRF analysis of the surface mass of Ti atoms deposited on the substrate. For zero bias voltage and varying N₂ flow the increment of surface mass per deposition time has been found to incrase linearly with the intensity of the OES signal of Ti. A negative bias voltage U_B100 V changes strongly the growth rate by resputtering effects, especially in the range where stoichiometric TiN is formed.     

How the Co-C bond is cleaved in coenzyme B12 enzymes: a theoretical study

The homolytic cleavage of the organometallic Co-C bond in vitamin B12-dependent enzymes is accelerated by a factor of approximately 10(12) in the protein compared to that of the isolated cofactor in aqueous solution. To understand this much debated effect, we have studied the Co-C bond cleavage in the enzyme glutamate mutase with combined quantum and molecular mechanics methods. We show that the calculated bond dissociation energy (BDE) of the Co-C bond in adenosyl cobalamin is reduced by 135 kJ/mol in the enzyme. This catalytic effect can be divided into four terms. First, the adenosine radical is kept within 4.2 angstroms of the Co ion in the enzyme, which decreases the BDE by 20 kJ/mol. Second, the surrounding enzyme stabilizes the dissociated state by 42 kJ/mol using electrostatic and van der Waals interactions. Third, the protein itself is stabilized by 11 kJ/mol in the dissociated state. Finally, the coenzyme is geometrically distorted by the protein, and this distortion is 61 kJ/mol larger in the Co(III) state. This deformation of the coenzyme is caused mainly by steric interactions, and it is especially the ribose moiety and the Co-C5'-C4' angle that are distorted. Without the polar ribose group, the catalytic effect is much smaller, e.g. only 42 kJ/mol for methyl cobalamin. The deformation of the coenzyme is caused mainly by the substrate, a side chain of the coenzyme itself, and a few residues around the adenosine part of the coenzyme.     

On diffusion-controlled dissociation

The theory of diffusion-controlled association is used to determine the time development of the corresponding dissociation process. The departure from a pure exponential decay will influence the entire time course, and not just the initial transient as in the case of an association process. It is also shown how this departure enters the results from temperature- jump experiments and alike. The effect is predicted to be most apparent in the case of ligand binding to a macromolecule with a large number of binding sites.     

Electroporation of cell membranes supporting penetration of photodynamic active macromolecular chromophore dextrans

The aim is to demonstrate that macromolecular chromophore dextrans (Cibacron-dextran) acting as photosensitizers can be transported easily into cancer cells by electroporation of their membranes (short electric pulses on cell suspension between electrodes). There are two possibilities, either:(A)irradiation starts with the electropulse-showed with easily penetrating thiopyronin-yielding nearly 100% dead cells;(B)irradiation starts after a resealing time of membrane pores during which macromolecular photosensitizers can penetrate into cells. In this way, fractions of Cibacron-dextran with molecular weights (Mw) 3300, 10,900 and 500,000 are now able to kill. This combination of bioelectrochemistry and photobiology will be suitable also for other biopolymers, connected with photodynamic active chromophores (e.g. chromopeptides) to transport them through cell walls and membranes into cells and tissues. The human cancer cells U-935 and K-562 (pulsed by 1.15 kV/cm field strength) additionally or synergistically reach high rates of necrotic cells (colored by trypan blue) by this combination.     

First Synthesis of 2-Vinylindole and its diels-Alder Reactions with CC-Dienophiles

By means of an intramolecular Wittig process, 2-vinylindole ( 2 ) was prepared. The indole 2 functions as a heterocyclic, donor-activated 1,3-diene and undergoes [4+2] cycloaddition reactions with dimethyl acetylenedicarboxylate, N-phenylmaleimide, and p-benzoquinone leading to the novel carbazole dervatives 3 , 4 , 5c , 6 and 7 respectively. The reaction of 2 with acceptor (A)-Substituted dienophiles (e.g.) ACH?CH₂, AC≡(CH) does not yield products that can be isolated.     

Hybrids of silver nanoparticles with amphiphilic hyperbranched macromolecules exhibiting antimicrobial properties

Hybrids of silver particles of 1 to 2 nm in size with highly branched amphiphilically modified polyethyleneimines adhere effectively to polar substrates providing environmentally friendly antimicrobial coatings.