Exhaustive extraction of peptides by electromembrane extraction

This fundamental work illustrates for the first time the possibility of exhaustive extraction of peptides using electromembrane extraction (EME) under low system-current conditions (<50 μA). Bradykinin acetate, angiotensin II antipeptide, angiotensin II acetate, neurotensin, angiotensin I trifluoroacetate, and leu-enkephalin were extracted from 600 μL of 25 mM phosphate buffer (pH 3.5), through a supported liquid membrane (SLM) containing di-(2-ethylhexyl)-phosphate (DEHP) dissolved in an organic solvent, and into 600 μL of an acidified aqueous acceptor solution using a thin flat membrane-based EME device. Mass transfer of peptides across the SLM was enhanced by complex formation with the negatively charged DEHP. The composition of the SLM and the extraction voltage were important factors influencing recoveries and current with the EME system. 1-nonanol diluted with 2-decanone (1:1 v/v) containing 15% (v/v) DEHP was selected as a suitable SLM for exhaustive extraction of peptides under low system-current conditions. Interestingly, increasing the SLM volume from 5 to 10 μL was found to be beneficial for stable and efficient EME. The pH of the sample strongly affected the EME process, and pH 3.5 was found to be optimal. The EME efficiency was also dependent on the acceptor solution composition, and the extraction time was found to be an important element for exhaustive extraction. When EME was carried out for 25 min with an extraction voltage of 15 V, the system-current across the SLM was less than 50 μA, and extraction recoveries for the model peptides were in the range of 77–94%, with RSD values less than 10%.     

Oxygen Quenching of nπ* Triplet Phenyl Ketones: Local Excitation and Local Deactivation

We have studied the charge‐transfer‐induced deactivation of nπ* excited triplet states of benzophenone derivatives by O₂(³Σ), and the charge‐transfer‐induced deactivation of O₂(¹Δ_g) by ground‐state benzophenone derivatives in CH₂Cl₂ and CCl₄. The rate constants for both processes are described by Marcus electron‐transfer theory, and are compared with the respective data for a series of biphenyl and naphthalene derivatives, the triplet states of which have ππ* configuration. The results demonstrate that deactivation of the locally excited nπ* triplets occurs by local charge‐transfer and non‐charge‐transfer interactions of the oxygen molecule with the ketone carbonyl group. Relatively large intramolecular reorganization energies show that this quenching process involves large geometry changes in the benzophenone molecule, which are related to favorable Franck‐Condon factors for the deactivation of ketone‐oxygen complexes to the ground‐state molecules. This leads to large rate constants in the triplet channel, which are responsible for the low efficiencies of O₂(¹Δ_g) formation observed with nπ* excited ketones. Compared with the deactivation of ππ* triplets, the non‐charge‐transfer process is largely enhanced, and charge‐transfer interactions are less important. The deactivation of singlet oxygen by ground‐state benzophenone derivatives proceeds via interactions of O₂(¹Δ_g) with the Ph rings.     

Multi-multigrid solution of modified Poisson–Boltzmann equation for arbitrarily shaped molecules

A new multi-multigrid method is presented for solving the modified Poisson–Boltzmann equation based on the Kirkwood Hierarchy of equations, with Loeb's closure, on a three-dimensional grid. The results are compared with standard Poisson–Boltzmann calculations, which are known to underestimate the local concentration of counterions near charged parts of molecules, mainly due to neglect of fluctuations in the ionic concentrations. In the present study, the Kirkwood hierarchy of equations is discretized with the finite volume method and solved using multigrid techniques. The new possibility for solution of the three-dimensional modified Poisson–Boltzmann equation, for the first time within a model including a dielectric discontinuity, and within reasonable computational time, enables the calculation of higher valence ion distributions around arbitrarily shaped biological macromolecules. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 893–901, 1998     

Bimetallic assemblies, [Ni(en)2]3[M(CN)6]2·3H2O (en = H2NCH2CH2NH2; M = Fe,Co)

The reaction between tris(ethyl­enedi­amine)­nickel(II) cations and hexa­cyanometallate(III) anions (M = Fe, Co) yields ordered bimetallic assemblies, catena‐poly­[[tris­(ethyl­enedi­amine)­nickel‐bis(μ‐hexa­cyano­iron‐N,N′)] trihydrate] and catena‐poly­[[tris­(ethyl­enedi­amine)­nickel‐bis(μ‐hexa­cyano­cobalt‐N,N′)] trihydrate], [{Ni(C₂H₈N₂)₂}₃{M(CN)₆}₂]·3H₂O, in which both cis and trans [Ni(en)₂] and [M(CN)₆] moieties are linked to give S‐shaped Ni–NC–M–CN–Ni–NC–M–CN–Ni units which are cross­linked to give ribbons parallel to the b axis. The two compounds are isomorphous with mean metal–ligand distances Fe—C = 1.940 (3), Co—C = 1.844 (3) and Ni—N = 2.102 (2) Å for the iron, and 2.105 (3) Å for the cobalt compound. These compounds appear to be identical with those formulated as [Ni(en)₂]₃[M(CN)₆]₂·2H₂O [Ohba, Maruona, Okawa, Enoki & Latour (1994). J. Am. Chem. Soc. 116 , 11566–11567; Ohba, Fukita & Okawa (1997). J. Chem. Soc. Dalton Trans. pp. 1733–1737] which were indexed on a smaller unit cell and described as disordered.     

Model order reduction for nonlinear problems in circuit simulation

Electrical circuits usually contain nonlinear components. Hence we are interested in MOR methods that can be applied to a system of nonlinear Differential-Algebraic Equations (DAEs). In particular we consider the TPWL (Trajectory PieceWise Linear) and POD (Proper Orthogonal Decomposition) methods. While the first one fully exploits linearity, the last method needs modifications to become efficient in evaluation. We describe a particular technique based on Missing Point Estimation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of power ultrasound for azo dye degradation

Power ultrasound of 850 kHz at 60, 90 and 120 W was used for the degradation of industrial azo dyes Acid Orange 5 and 52, Direct Blue 71, Reactive Black 5 and Reactive Orange 16 and 107. The results show that power ultrasound is able to mineralize azo dyes to non-toxic end products, which was confirmed by respiratory inhibition test of Pseudomonas putida. All investigated dyes have been decolorized and degraded within 3-15 h at 90 W and within 1-4 h at 120 W, respectively. Mass spectrometric investigations show, that hydroxyl radicals attack azo dyes by simultaneous azo bond scission, oxidation of nitrogen atoms and hydroxylation of aromatic ring structures. A volumetric scale-up showed a correlation between the energy input and the absolute amount of degraded dye. Up to an energy input of about 90 W no enzymatic deactivation of laccase was observed which might be helpful for a simultaneous action of sonochemical and enzymatic treatments.