Analysis of Decomposition Algorithms with Benders Cuts for p-Median Problem

In this paper the algorithms for solving the p-median problem based on the Benders decomposition are investigated. A family of problems hard for solving with such algorithms is constructed and then generalized to a special NP-hard case of the p-median problem. It is shown that the effectiveness of the considered algorithms depends on the choice of the optimal values of the dual variables used in Benders cuts. In particular, the depth of the cuts can be equal to one.     

Theoretische Betrachtung der Diels-Alderschen Reaktion auf Grund der LCAO-MO-Theorie

Zusammenfassung Vorliegende Arbeit bietet eine theoretische Betrachtung derDiels-Alderschen Reaktion mit Hilfe der LCAO-MO-Methode in derHückelschen Näherung unter der grundsätzlichen Voraussetzung der dem aktiven Komplex vorausgehenden -Komplexbildung zwischen dem Dien und Dienophil. Die als Resultat der Wechselwirkung zwischen Dien und Dienophil auftretende, im Bereich des Energieminimums berechnete Delokalisationsenergie steht in linearer Korrelation zur Aktivierungsenergie.Am Beispiel der Wechselwirkung des Cyclopentadiens mit unterschiedlichen Dienophilen wird gezeigt, daß die Delokalisationsenergie inendo-Stellung des Diens und Dienophils stets kleiner ist als inexo-Stellung, was den Satz vonAlder erklärt.

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TheDiels-Alders reaction has been studied theoretically using the conventionalHückel LCAO-MO method. The investigation is based on regarding the formation of a -complex from the diene and dienophil as a forerunner of the transition state. A linear correlation exists between the energy of delocalization resulting from the diene—dienophil interaction and calculated for the region of the energy minimum and the energy of activation. The interaction of cyclopentadiene with various dienophils is used as an example showing that the delocalization energy of theendo situated diene and dienophil is always lower than the delocalization energy of theexo oriented ones, a fact that explainsAlders rule.

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Mit 5 Abbildungen     

Structure and properties of nonclassical polymers

Utilizing an extended Hubbard-type Hamiltonian which incorporates both nearest-neighbour Coulomb repulsion and exchange interactions, we have studied the energy dispersion of the lowest elementary excitation from the ferromagnetically aligned state of quasi one-dimensional alternant hydrocarbon networks. It was found that the main effect of the long range Coulomb interaction may be thought of as a renormalization (screening) of the on-site Hubbard integral. This implies an enhancement of the kinetic exchange term and impairs the stability of the ferromagnetic state towards single spin inversions. However, for physically relevant values of the parameters entering the model Hamiltonian, the collective spin excitation represents a magnon, whose energy band lies above the reference value pertaining to the magnetically saturated configuration.Dedicated to Prof. Dr. Adolf Neckel on the occasion of his 60th birthday     

Rational incorporation of defects within metal–organic frameworks generates highly active electrocatalytic sites

The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control. An emerging strategy to generate coordinatively-unsaturated active sites is through the use of organic linkers that lack a functional group that would usually bind with the metal nodes. To execute this strategy, we synthesize a model MOF, Ni-MOF-74 and incorporate a fraction of 2-hydroxyterephthalic acid in place of 2,5-dihydroxyterephthalic acid. The defective MOF, Ni-MOF-74D, is evaluated vs. the nominally defect-free Ni-MOF-74 with a host of ex situ and in situ spectroscopic and electroanalytical techniques, using the oxidation of hydroxymethylfurtural (HMF) as a model reaction. The data indicates that Ni-MOF-74D features a set of 4-coordinate Ni–O₄ sites that exhibit unique vibrational signatures, redox potentials, binding motifs to HMF, and consequently superior electrocatalytic activity relative to the original Ni-MOF-74 MOF, being able to convert HMF to the desired 2,5-furandicarboxylic acid at 95% yield and 80% faradaic efficiency. Furthermore, having such rationally well-defined catalytic sites coupled with in situ Raman and infrared spectroelectrochemical measurements enabled the deduction of the reaction mechanism in which co-adsorbed *OH functions as a proton acceptor in the alcohol oxidation step and carries implications for catalyst design for heterogeneous electrosynthetic reactions en route to the electrification of the chemical industry.

The allure of metal–organic frameworks (MOFs) in heterogeneous electrocatalysis is that catalytically active sites may be designed a priori with an unparalleled degree of control.     

Quantenchemische Untersuchung der Reaktionsfähigkeit von π-Elektronen-Systemen in angeregtem Singulett- und Triplettzustand

Zusammenfassung Anhand der Methode der Konfigurationenwechselwirkung wurde die Ladungsdichteverteilung in einer Reihe von aromatischen Aminen und N-haltigen Heteroaromaten im angeregten Singulett- und Triplettzustand untersucht. Durch die Untersuchungen wurde die Formulierung der folgenden Regel ermöglicht: im angeregten Singulett- und Triplettzustand ist die Basizität bei den Aminen wesentlich vermindert; die N-haltigen Heteroaromaten weisen im angeregten Singulettzustand eine erhöhte Basizität auf, und im Triplettzustand tritt eine Verminderung der Basizität ein.

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The electron density distribution in excited singlet and triplet states of a number of aromatic amines and heterocyclic compounds containing nitrogen atoms is studied using the CI-method. The investigation allows the formulation of the following rule: in excited singlet and triplet states the amines possess significantly reduced basicity; the nitrogen heterocyclic compounds in excited singlet states increase their basicity, whereas in excited triplet states their basicity is decreased.

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Résumé Au moyen de la méthode d'interaction de configuration, on a étudié la répartition de la densité électronique dans un certain nombre d'aminés aromatiques et de composés hétérocycliques azotés dans l'état excité singulet et triplet.Les études effectuées ont permis d'établir la règle suivante: à l'état excité singulet ou triplet la basicité des aminés est sensiblement réduite; la basicité des composés N-hétérocycliques augmente dans l'état excité singulet et diminue dans le triplet.

     

Matrices with Heterogeneous Distribution of the Binding Sites for Immobilization of Biomacromolecules

The coupling of photosensitive reagents has been carried out with the goal of obtaining the predetermined distribution of binding sites either for “surface” or “spacial” immobilization of biomacromolecules. The correlation holds between light intensity and the number of readant groups emerged in a matrix.     

Ligand-protein docking using a quantum stochastic tunneling optimization method

A novel hybrid optimization method called quantum stochastic tunneling has been recently introduced. Here, we report its implementation within a new docking program called EasyDock and a validation with the CCDC/Astex data set of ligand-protein complexes using the PLP score to represent the ligand-protein potential energy surface and ScreenScore to score the ligand-protein binding energies. When taking the top energy-ranked ligand binding mode pose, we were able to predict the correct crystallographic ligand binding mode in up to 75% of the cases. By using this novel optimization method run times for typical docking simulations are significantly shortened.     

Structural characterisation of tyrosine-nitrated peptides by ultraviolet and infrared matrix-assisted laser desorption/ionisation Fourier transform ion cyclotron resonance mass spectrometry

Nitration of tyrosine residues in proteins may occur in cells upon oxidative stress and inflammation processes mediated through generation of reactive nitroxyl from peroxynitrite. Tyrosine nitration from oxidative pathways may generate cytotoxic species that cause protein dysfunction and pathogenesis. A number of protein nitrations in vivo have been reported and some specific Tyrosine nitration sites have been recently identified using mass spectrometric methods. High-resolution Fourier transform ion cyclotron resonance mass spectrometry (MALDI) FT-ICR-MS) is shown here to be a highly efficient method in the determination of protein nitrations. Following the identification of nitration of the catalytic site Tyr-430 residue of bovine prostacyclin synthase, we synthesised several model peptides containing both unmodified tyrosine and 3-nitro-tyrosine residues, using solid-phase peptide synthesis (SPPS). The structures of the nitrotyrosine peptides were characterised both by ESI- and by matrix-assisted laser desorption/ionisation (MALDI)-FT-ICR-MS, using a standard ultraviolet (UV) nitrogen nitrogen laser and a 2.97 microm Nd-YAG infrared laser. Using UV-MALDI-MS, 3-nitrotyrosyl-peptides were found to undergo extensive photochemical fragmentation at the nitrophenyl group, which may hamper or prevent the unequivocal identification of Tyr-nitrations in cellular proteins. In contrast, infrared-MALDI-FT-ICR-MS did not produce fragmentation of molecular ions of Tyr-nitrated peptides.