Toward a Formyl-to-Phenyl Conversion: An Unexpected Photochemical Fulvene Rearrangement

Toward a conversion of aldehydes into arenes, we designed a sequence involving the initial reaction of an aldehyde to give a fulvene, followed by photochemical and platinum-catalyzed rearrangements into a Dewar benzene derivative, which finally isomerizes into the targeted arene. While computational studies support the plausibility of this route, we found that fulvene irradiation resulted in an unexpected isomerization into a spiro[2.4]heptadiene. This unusual photorearrangement has been investigated mechanistically and provides access to a variety of spiro[2.4]heptadienes with different substituents.     

Kinetics of cation distribution in cobalt-containing olivine, (Co0.6Mg0.4)2)SiO4

In olivines, (A,B)(2)SiO(4), the A and B cations are distributed over two non-equivalent sites of octahedral coordination, M1 and M2. In the case of temperature dependent cation distributions, the kinetics of cation redistribution between these two sublattices can be studied by means of temperature-jump experiments. In situ experiments of this type are reported for a cobalt-containing olivine single crystal, (Co(0.6)Mg(0.4))(2)SiO(4). The relaxation experiments were performed by means of optical spectroscopy under in situ conditions in the temperature range between 480 and 690 degrees C yielding an activation energy of about 2.0 eV. The results are discussed in the framework of microscopic models of cation sublattice exchange. Implications for quench experiments are addressed.     

Stereochemistry and rearrangement reactions of hydroxylignanolactones

Various conflicting data on the rearrangement and absolute stereochemistry of hydroxylignano-9,7'-lactones are resolved using 18O labeled compounds, also confirmed by an X-ray analysis of a pure lignano-9,7'-lactone enantiomer, obtained for the first time. Under NaH/DMF rearrangement conditions a silyl protected hydroxylignano-9,9'-lactone underwent an unexpected silyl migration.     

Solid-phase synthesis of a cyclodepsipeptide: cotransin

The first solid-phase synthesis of cotransin--a cyclic depsipeptide having high pharmacological potential--was achieved, by a proper choice of coupling reagents and use of either TBAF or DBU for Fmoc removal to suppress the otherwise dominating, sequence-derived diketopiperazine formation. Starting the assembly from C-terminal lactic acid allowed fast and epimerization-free cyclization in solution. Novel conditions for orthogonal use of the Fmoc/Bsmoc-protection system were discovered, and an unexpected nucleophilic behavior of DBU was observed.     

Development of electrochemical biosensors based on sol-gel enzyme encapsulation and protective polymer membranes

Protective polymer coatings have been used to enhance the retention of enzymes in sol-gel films as immobilisation phases in electrochemical biosensors. Carbon film electrodes were electrochemically modified with poly(neutral red) (PNR). These electrodes were coated with oxysilane sol-gels incorporating glucose oxidase and an outer coating of carboxylated PVC (CPVC) or polyurethane (PU), with and without Aliquat-336 or isopropyl myristate (IPM) plasticizer, was applied. The biosensors were characterised electrochemically using cyclic voltammetry and amperometry, electrochemical impedance spectroscopy and scanning electron microscopy. Impedance spectra showed that the electrode surface is most active when the sol-gel–GOx layer is not covered with a membrane. However, membranes without plasticizer extend the lifetime of the biosensor to more than 2 months when PU is used as an outer membrane. The linear range of the biosensors was found to be 0.05–0.50 mM of glucose and the biosensor with PU outer membrane exhibited higher sensitivity (ca.117 nA mM⁻¹) in the region of linear response than that with CPVC. The biosensors were applied to glucose measurement in natural samples of commercial orange juice.     

Energy Efficient Emulsion Polymerization Strategies

Polymerization strategies aiming at further reducing the environmental impact of the already “green” emulsion polymerization process were investigated. Life cycle assessment showed that non‐isothermal strategies starting at low temperature resulted in an environmental impact lower than the isothermal ones. Nevertheless, the major part of the environmental impact was due to raw materials. The effect of the polymerization strategy on polymer microstructure was investigated.

     

Cyanometallate incorporated supramolecular networks based on a nitroalkyl-substituted CuN4 precursor: Synthesis, crystal structure, thermal and electrochemical studies

Two new copper(II) complexes, viz. [Cu(nelin)(H₂O)₂]₂[Fe(CN)₆] · 6H₂O (2) and [{Cu(nelin)}₂Ni(CN)₄](ClO₄)₂ · 2H₂O (3), have been synthesized using [Cu(nelin)](ClO₄)₂ (1) (nelin = 1,9-diamino-5-methyl-5-nitro-3,7-diazanonane) as a nitroalkyl-substituted Cu^IIN₄ precursor, and their structures and supramolecular networks have been fully explored using the single crystal X-ray diffraction technique. The H-bonded 1D chains of 2 run along the a-axis, being generated from supramolecular synthons using cations and anions, and are further propagated into a 3D array to form irregular honeycomb-like channels which are divided into two halves, with each half accomodating a helical water chain running in opposite directions to each other. In complex 3, the trinuclear units are arranged in successive rows in a herringbone fashion and bifurcated hydrogen bonding through the uncoordinated terminals of the [Ni(CN)₄]²⁻ units give rise to a supramolecular (4,4) network. A comparison of the PXRD pattern of complex 2 and its dehydrated form indicate marked changes in the diffraction pattern with the development of a quasi glassy nature in the dehydrated form. The electrochemical properties of 1, 2 and 3 have been investigated in comparative ways using the cyclic voltammetric technique in aqueous and MeCN solutions with Ag/AgCl as a reference electrode. Electrochemical reduction generates the one-electron reduced nitro-radical anion. In water–alcohol glass at 77 K complex 2 exhibits a typical four-line hyperfine EPR spectra with g_|| = 2.11, g = 2.02, A_|| = 150 Oe and A = 5 Oe at ν = 9.45 MHz.     

Synthesis and crystal structure of a mixed valence heteropoly green compound, (PPh<Subscript>4</Subscript>)<Subscript>4</Subscript>[PMo<Subscript>12</Subscript>O<Subscript>40</Subscript>], and its use as a catalyst in olefin epoxidation

A green heteropolyblue compound, (PPh₄)₄[PMo₁₂O₄₀] · 3DMF(1), has been synthesized from MoO₃, H₂O₂ and H₃PO₄ in acetylacetone medium and crystallized from N,N-dimethylformamide. Compound 1 was characterized by analytical and spectroscopic methods, and X-ray structure analysis. The compound is a one-electron paramagnet and shows a featureless and cubic EPR spectrum with <g> = 1.95 in DMF glass. The complex shows a Mo(V)–Mo(IV) couple, which has been studied by cyclic voltammetric and coulometric methods. The compound acts as an efficient olefin epoxidation catalyst with H₂O₂ as oxidant and NaHCO₃ as co-catalyst. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Kinetic studies on promazine oxidation by FeIII/CuII in acidic aqueous bromide solutions. Spectroscopic and kinetic non-additivity as evidence for the CuII–Br–FeIII-type heterobimetallic complex formation

The formation of Cu^II–Br–Fe^III-type heterobimetallic complexes was observed spectrophotometrically, given the non-additivity of the spectra from the copper(II) and iron(III) complexes. The kinetics of the oxidation of promazine radical (ptz^+•) to promazine 5-oxide, by iron(III) bromides, copper(II) bromides, and a mixture of these complexes in acidic aqueous solutions, have been studied using UV–Vis spectroscopy at I = 1.0 M (H⁺, Cu²⁺, Fe³⁺, Br⁻) and T = 318 K. Copper(II) inhibits the oxidation of the promazine radical to promazine sulfoxide using iron(III) complexes. A rate retardation effect, characterized by the dependence of the pseudo second-order rate constant (k ^II) on the copper(II) concentration k ^II = a/(1 + b[Cu^II]), can be rationalized as a result of Cu^II–Br–Fe^III-type heterobimetallic complex formation.     

Characterization of globular protein solutions by dynamic light scattering, electrophoretic mobility, and viscosity measurements

In this work, physicochemical properties of two globular proteinsbovine serum albumin (BSA) having a molecular weight of 67 kDa and human serum albumin (HSA) having a molecular weight of 69 kDawere characterized. The bulk characteristics of these proteins involved the diffusion coefficient (hydrodynamic radius), electrophoretic mobility, and dynamic viscosity as a function of protein solution concentration for various pH values. The hydrodynamic radius data suggested an association of protein molecules, most probably forming compact dimers. Using the hydrodynamic diameter and the electropheretic mobility data allowed the determination of the number of uncompensated (electrokinetic) charges on protein surfaces. The electrophoretic mobility data were converted to zeta potential values, which allowed one to determine the isoelectric point (iep) of these proteins. It was found to be at pH 5.1 for both proteins, in accordance with previous experimental data and theoretical estimations derived from amino acid composition and p K values. To determine further the stability of protein solutions, dynamic viscosity measurements were carried out as a function of their bulk volume concentration for various pH values. The intrinsic viscosity derived from these measurements was interpreted in terms of the Brenner model, which is applicable to hard spheroidal particles. It was found that the experimental values of the intrinsic viscosity of these proteins were in good agreement with this model when assuming protein dimensions of 9.5 x 5 x 5 nm3 (prolate spheroid). The possibility of forming linear aggregates of association degree higher than 2 was excluded by these measurements. It was concluded that the combination of dynamic viscosity and dynamic light scattering can be exploited as a convenient tool for detecting not only the onset of protein aggregation in suspensions but also the form and composition of these aggregates.