One‐Pot Decarboxylative Acylation of N‐, O‐, S‐Nucleophiles and Peptides with 2,2‐Disubstituted Malonic Acids

Monocarbonyl activation of 2,2‐disubstituted malonic acids with benzotriazole leads to decarboxylation of one of the carboxy groups and formation of a C?H bond. Intermediate carbonyl benzotriazoles then readily acylate nucleophilic reagents and peptides resulting in libraries of conjugates and peptidomimetics.     

Scattering Theory for Jacobi Operators with Quasi-Periodic Background

We develop direct and inverse scattering theory for Jacobi operators which are short range perturbations of quasi-periodic finite-gap operators. We show existence of transformation operators, investigate their properties, derive the corresponding Gel'fand-Levitan-Marchenko equation, and find minimal scattering data which determine the perturbed operator uniquely. Work supported by the Austrian Science Fund (FWF) under Grant No. P17762, the Austrian Academy of Sciences under DOC-21388, and INTAS Research Network NeCCA 03-51-6637.     

Gold-Catalyzed 1,2-Aryl Shift and Double Alkyne Benzannulation

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2-aryl shift is described. Harnessing the unique electron-rich character of 1,4-dihydropyrrolo[3,2-b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2-aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π-expanded, centrosymmetric pyrrolo[3,2-b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six-membered rings accompanied with a 1,2-aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7-membered rings. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time-dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities.     

Stereoselective bile pigment binding to polypeptides and albumins: a circular dichroism study

Stereoselective recognition of bilirubin and biliverdin by poly(L-lysine) (PLL), poly(D-lysine) (PDL), and poly(L-arginine) (PLA) and their micelles with dodecanoate ions (C(12)) at different pH has been studied using a combination of vibrational and electronic circular dichroism. Biliverdin has been found to be more sensitive to pH in its complexes with the polypeptides. In acidic media in the complexes with PLL-C(12) and PDL-C(12) the conformation becomes more closed than the characteristic one found at physiological pH. Partial flattening and chiral self-association of bilirubin molecules takes place at higher concentrations with PLL and PDL. For both pigments, inversions of the ECD signals are observed in the systems with PLA at pH > or = 8.5. This study was carried out in order to clarify the role of Lys and Arg residues in pigment binding to serum albumin. The circular dichroism spectra obtained for bilirubin bound to different mammalian serum albumins have been compared with the homology within the IIA principal ligand-binding structural domains. Analysis suggests that the chiroptical properties of the pigment in the complexes with serum albumins depend on the location of Lys and/or Arg at positions 222 and 199 in the binding site.     

Phase diagram and domain structure of the Rb2 x Tl2(1− x )Cd2(SO4)3 solid solutions

From measurements of temperature dependences of the birefringence and from observations of the domain structure the x, T–phase diagram for the Rb_{2 x} Tl_{2(1? x )}Cd₂(SO₄)₃ solid solutions have been obtained. Ferroelastic domain structure and movement of phase boundaries have been studied in the course of phase transitions in Rb_{2 x} Tl_{2(1? x )}Cd₂(SO₄)₃ crystals. Possible reasons for the appearance of mechanically non-compatible (‘forbidden’) ferroelastic domain walls are given.     

Catecholase activity of a copper(II) complex with a macrocyclic ligand: unraveling catalytic mechanisms

We report the structure, properties and a mechanism for the catecholase activity of a tetranuclear carbonato-bridged copper(II) cluster with the macrocyclic ligand [22]pr4pz (9,22-dipropyl-1,4,9,14,17,22,27,28,29, 30-decaazapentacyclo[22.2.1.1(4,7).1(11,14). 1(17,20)]triacontane-5,7(28),11(29),12,18, 20(30),24(27),25-octaene). In this complex, two copper ions within a macrocyclic unit are bridged by a carbonate anion, which further connects two macrocyclic units together. Magnetic susceptibility studies have shown the existence of a ferromagnetic interaction between the two copper ions within one macrocyclic ring, and a weak antiferromagnetic interaction between the two neighboring copper ions of two different macrocyclic units. The tetranuclear complex was found to be the major compound present in solution at high concentration levels, but its dissociation into two dinuclear units occurs upon dilution. The dinuclear complex catalyzes the oxidation of 3,5-di-tert-butylcatechol to the respective quinone in methanol by two different pathways, one proceeding via the formation of semiquinone species with the subsequent production of dihydrogen peroxide as a byproduct, and another proceeding via the two-electron reduction of the dicopper(II) center by the substrate, with two molecules of quinone and one molecule of water generated per one catalytic cycle. The occurrence of the first pathway was, however, found to cease shortly after the beginning of the catalytic reaction. The influence of hydrogen peroxide and di-tert-butyl-o-benzoquinone on the catalytic mechanism has been investigated. The crystal structures of the free ligand and the reduced dicopper(I) complex, as well as the electrochemical properties of both the Cu(II) and the Cu(I) complexes are also reported.     

Oxidative condensation and chemiluminescence of 5-amino-2,3-dihydro-1,4-phtalazinedione

The oxidative condensation of (5-amino-2,3-dihydro-1,4-phtalazinedione) luminol was carried out under their oxidation by (NH₄)₂S₂O₈ and KIO₃ in the mixed water-organic (namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidinone (MPD)) solvent under the volume ratio 1:9. The structure of the products was studied by IR and Raman spectroscopy, elemental analysis and the derivatographic method. It was determined that oxidation by KIO₃ (E = 1.085 V) occurs on the amide nitrogen atoms, while in the case of (NH₄)₂S₂O₈ (E = 2.05 V) it occurs on the amino-group. The structure and thermal stability of the obtained products is determined by the nature of the oxidant. The active decomposition of luminol begins at t_d = 334.5 °C, while for the specimens of the polyluminols, which were synthesized in the water-DMSO and water-MPD mixtures, t_d equals 356.7 and 409.1 °C respectively. The worst thermal stability has products of luminol oxidation by KIO₃ (t_d = 282.5 °C). The mechanism of the luminol oxidative polymerization by (NH₄)₂S₂O₈ and KIO₃ has been proposed.     

Polyimides reinforced with the sol‐gel derived organosilicon nanophase as low dielectric permittivity materials

Polyimide (PI) nanocomposites prepared by the in situ generation of crosslinked organosilicon nanophase (ON) through the sol‐gel process were characterized by densities, thermally stimulated depolarization currents and dielectric relaxation spectroscopy. Both a looser molecular packing of PI chain fragments adjacent to the ON and a loose inner structure of the spatial aggregates of ON were assumed to be responsible for a non‐additive decrease of the experimental values of dielectric permittivity for the nanocomposites. The pattern of composition dependence of the apparent dielectric permittivity of the ON suggested a probability of a morphological change around the composition PAAS/MTS = 100/16 (presumably, a sort of percolation transition from small‐size, individual clusters into large‐size, infinite clusters). Thus, PI reinforced with the sol‐gel derived nanophase may have a reasonably good potential as low dielectric permittivity materials. Copyright © 2004 John Wiley & Sons, Ltd.     

Bio-mimicking galactose oxidase and hemocyanin, two dioxygen-processing copper proteins

The modelling of the active sites of metalloproteins is one of the most challenging tasks in bio-inorganic chemistry. Copper proteins form part of this stimulating field of research as copper enzymes are mainly involved in oxidation bio-reactions. Thus, the understanding of the structure-function relationship of their active sites will allow the design of effective and environmental friendly oxidation catalysts. This perspective illustrates some outstanding structural and functional synthetic models of the active site of copper proteins, with special attention given to models of galactose oxidase and hemocyanin.     

Coalescence-induced coalescence and dimensional crossover during the phase separation in ternary surfactant/polymer/water mixtures

We studied the separation process in the ternary mixtures of nonionic surfactant (C(12)E(6), hexaethylene glycol monododecyl ether), polymer (PEG = poly(ethylene glycol)), and water. The separation process of PEG/water rich domains from the surfactant rich matrix was observed by the optical microscopy. From the morphological analysis, we determined the size of the domains as a function of time. On this basis we identified a dominating mechanisms of domains growth, that is the coalescence-induced coalescence mechanism. The coalescence (collision) event of two droplets induces a flow or a change of concentration distribution around droplets which pushes other droplets together inducing further growth. We also observed the evaporation-condensation (Lifshitz-Slyozov) mechanism of growth, but it did not affect the growth of large domains appreciably. We determined two regimes of the coalescence-induced coalescence associated with the dimensionality of the system. When the domains were smaller or comparable in size to the sample thickness we observe a three-dimensional growth. When the domains became larger than the sample thickness, a two-dimensional growth was observed. In the first regime, the size of the domains, L(t), grew linearly with t, while in the second regime, L(t) approximately t(0.3). In the binary, surfactant/water system, water domains grew by the geometrical coalescence-induced coalescence as L(t) approximately t in three dimensions.