Neighbor games and the leximax solution

Neighbor games arise from certain matching or sequencing situations in which only some specific pairs of players can obtain a positive gain. As a consequence, the class of neighbor games is the intersection of the class of assignment games (Shapley and Shubik (1972)) and the class of component additive games (Curiel et al. (1994)). We first present some elementary features of neighbor games. After that we provide a polynomially bounded algorithm of order p ³ for calculating the leximax solution (cf. Arin and Iñarra (1997)) of neighbor games, where p is the number of players. This authors work has been supported by CentER and the Department of Econometrics, Tilburg University and by the Foundation for the Hungarian Higher Education and Research (AMFK).     

Internal rotation in squaramide and related compounds. A theoretical ab initio study

The structural and energetic changes associated with C–N bond rotation in a squaric acid derivative as well as in formamide, 3-aminoacrolein and vinylamine have been studied theoretically using ab initio molecular orbital methods. Geometry optimizations at the MP2(full)/6-31+G* level confirmed an increase in the C–N bond length and a smaller decrease in the C=O length on going from the equilibrium geometry to the twisted transition state. Other geometrical changes are also discussed. Energies calculated at the QCISD(T)/6-311+G** level, including zero-point-energy correction, show barrier heights decreasing in the order formamide, squaric acid derivative, 3-aminoacrolein and vinylamine. The origin of the barriers were examined using the atoms-in-molecules approach of Bader and the natural bond orbital population analysis. The calculations agree with Pauling's resonance model, and the main contributing factor of the barrier is assigned to the loss of conjugation on rotating the C–N bond. Finally, molecular interaction potential calculations were used to study the changes in the nucleophilicity of N and O (carbonyl) atoms upon C–N rotation, and to obtain a picture of the abilities of the molecules to act in nonbonded interactions, in particular hydrogen bonds. The molecular interaction potential results confirm the suitability of squaramide units for acting as binding units in host–guest chemistry. Received: 13 March 2002 / Accepted: 23 June 2002 / Published online: 21 August 2002     

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999     

Squaramido-based receptors: applicability of molecular interaction potential to molecular recognition of polyalkylammonium compounds

 A computational study of the mechanism of host–guest complexation between quaternary ammonium compounds and squaramido-based tripodal receptors has been carried out. Semiempirical molecular orbital calculations, which are in qualitative agreement with experimental results have been performed using the PM3 Hamiltonian. Molecular interaction potential (MIP) maps were used to analyze the suitability of both host and guest binding units for a high-affinity recognition process. MIP calculations were computed from PM3 wavefunctions of the corresponding ammonium cations and dimethyl squaramide as a model compound for the hydrogen-bond-acceptor unit of the receptors. MIP analyses are helpful for understanding the host–guest process from the point of view of the double-complementarity principle. Received: 23 June 1999 / Accepted: 22 September 1999 / Published online: 17 January 2000     

Morita Equivalence for Rings with Involution

We develop the theory of Morita equivalence for rings with involution, and we show the corresponding fundamental representation theorem. In order to allow applications to operator algebras, we work within the class of idempotent nondegenerate rings. We also prove that two commutative rings with involution are Morita *-equivalent if and only if they are *-isomorphic.     

A ‘naked-eye’ chemosensor system for phytate

We report the synthesis of two new anion receptors of a covalently linked 1,3,5-triarylbenzoamido-crown ether. Our results show that combined with a picrate salt they act by means of an intermolecular charge transfer process (EDA complex), as naked-eye sensors for basic anions, especially for sodium phytate in DMSO/H₂O (1:1).     

Magneto-Structural Correlations in Trinuclear Cu(II) Complexes: A Density Functional Study

Summary.  Density functional theoretical methods have been used to study magneto-structural correlations for linear trinuclear hydroxo-bridged copper(II) complexes. The nearest-neighbor exchange coupling constant shows very similar trends to those found earlier for dinuclear compounds for which the Cu–O–Cu angle and the out of plane displacement of the hydrogen atoms at the bridge are the two key structural factors that determine the nature of their magnetic behavior. Changes in these two parameters can induce variations of over 1000 cm⁻¹ in the value of the nearest-neighbor coupling constant. On the contrary, coupling between next-nearest neighbors is found to be practically independent of structural changes with a value for the coupling constant of about −60 cm⁻¹. The magnitude calculated for this coupling constant indicates that considering its value to be negligible, as usually done in experimental studies, can lead to considerable errors, especially for compounds in which the nearest-neighbor coupling constant is of the same order of magnitude. Corresponding author. E-mail: eliseo.ruiz@qi.ub.es Received June 28, 2002; accepted July 22, 2002