An algorithm to recognize a middle graph

A graph F is called middle if there exists a graph G such that there is a one-to-one correspondence between the vertices of F and the vertices and edges of G such that two vertices of F are adjacent if and only if the corresponding elements (considered as subsets of the set of vertices) have a non-empty intersection.In this paper we present a linear time algorithm for the recognition of the middle graphs. The algorithm is based on a computer-oriented characterization of middle graphs. We show also how the algorithm can be generalized to recognize the middle graphs of hypergraphs.     

Investigation of the influence of nickel content on the correlation between the hydrogen equilibrium pressure for hydrogen absorbing alloys and the capacity of MH electrodes in open and closed cells

Two series of overstoichiometric AB_2.4 alloys [(Zr_0.35Ti_0.65)(V_1.33Cr_0.4Fe_0.27)_{2– x} Ni_{0.4+ x} and (Zr_0.5Ti_0.5)(V_0.8Mn_0.8Cr_0.4)_{2– x} Ni_{0.4+ x} ], differing in the Zr to Ti ratios in group A and the presence of Mn or Fe in group B, were examined to consider the influence of various amounts of nickel on the structural parameters following the sorption of hydrogen. To predict the electrochemical behaviour of the prepared alloys as negative electrodes for Ni-MH cells, the pressure-composition isotherms (PCT) determined for the gas/solid phase system were correlated with the electrochemical pressure-composition (EPC) isotherms estimated from the rest potential of the alloy electrode. For preliminary assessment of the practical usefulness of the prepared samples, the electrodes made of all the alloys were subjected to charge/discharge measurements in a half-cell in 6 M KOH solution and the discharge capacities were estimated. Of the alloys with Fe and Mn components, the samples (Zr_0.35Ti_0.65)(V_0.93Cr_0.28Fe_0.19Ni_1.0) and (Zr_0.5Ti_0.5)(V_0.68Mn_0.68Cr_0.34Ni_0.7) provided the highest capacities. These alloys were chosen for testing the charge/discharge cycleability in closed Ni-MH cells. The reversibility of the cell with the former sample decreased significantly around the 25th cycle, whereas the discharge capacity of the cell with the latter sample remained almost unchanged during 100 cycles of testing. Electronic Publication     

Mass spectrometric investigation of gallium and zirconium complexes with octaethylporphyrin and tetraphenylporphyrin

Gallium and zirconium octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) were examined by electrospray ionization (ESI) mass spectrometry. All systems were prepared in dichloromethane with addition of a stabilizing lipophilic anionic agent, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB). In the solutions examined both monomeric and dimeric metalloporphyrins were observed. In the gallium-OEP mass spectrum the ion registered at m/z 601 was attributed to monomeric [Ga(OEP)](+) and that at m/z 1219 to the dimeric form, [[Ga(OEP)](2)OH](+). Peaks appearing in the ESI mass spectra of zirconium systems were substantially less intense, probably owing to the relatively low stability of complexes of this metal caused by its different geometry preferences. The most abundant monomeric zirconium-OEP complexes were [[Zr(OEP)OH]](+) (m/z 639) and [Zr(OEP)Cl](+) (m/z 657), and dimeric [[Zr(OEP)OH](2)](2+) (m/z 639). Analogous species were observed in the Zr(TPP) system: monomeric [[Zr(OEP)OH]](+) (m/z 719) and [Zr(TPP)Cl](+) (m/z 737) and dimeric [[Zr(TPP)OH](2)](2+) (m/z 719). In both cases series of other dimers, e.g. [[Zr(OEP)](2)O(2)H](+) (m/z 1277), [[Zr(OEP)OH](2)Cl](+) (m/z 1313), [Zr(TPP)(2)O(2)H](+), (m/z 1437), [[Zr(TPP)OH](2)OH](+) (m/z 1455) and [[Zr(TPP)OH](2)Cl](+) (m/z 1473), appeared. The results obtained confirmed the hypothesis concerning the formation of dimeric metalloporphyrins in solutions containing stabilizing lipophilic anions. It also allowed us to explain the super-Nernstian slopes of the calibration curves towards primary anions of ion-selective electrodes with membranes containing the examined metalloporphyrins.     

Effective basis sets for calculations of exchange-repulsion energy

Usefulness of different Gaussian basis sets for reproducing the “tail” region of the SCF wavefunctions employed in calculations of the exchange-repulsion effect is investigated for the model He-He interaction. It has been shown that extension of the monomer-centered basis set in the scheme of regularized even-tempered basis sets [M. W. Schmidt and K. Ruedenberg, J. Chem. Phys. 71 , 3951 (1979)] can be more efficient than augmentation of the fully energy-optimized basis set with diffuse basis functions. It has been also found that Landshoff term vanishes and the “tail” region is well reproduced if monomer wavefunctions are calculated with the basis set of the dimer.     

Dissolution of a base (RbOH) by water clusters

Density functional and ab intio calculations are employed in order to understand the base dissociation of rubidium hydroxide by water molecules. The hydrated structures, stabilities, thermodynamic quantities, dissociation energies, infrared spectra, and electronic properties of RbOH(H2O)(n = 0-5) are investigated. With the successive addition of water molecules to RbOH, the Rb-OH bond lengthens significantly from 2.45 angstroms for n = 0 to 3.06 angstroms for n = 5. It is interesting to note that four water molecules are needed for the stable dissociation of RbOH (as an almost dissociate conformation) and five water molecules are needed for the complete dissociation without any Rb-OH stretch mode, in contrast to the same group base of CsOH which requires only three water molecules for an almost dissociate conformation and four water molecules for the complete dissociation.     

AT base pair anions versus (9-methyl-A)(1-methyl-T) base pair anions

The anionic base pairs of adenine and thymine, (AT)(-), and 9-methyladenine and 1-methylthymine, (MAMT)(-), have been investigated both theoretically and experimentally in a complementary, synergistic study. Calculations on (AT)(-) found that it had undergone a barrier-free proton transfer (BFPT) similar to that seen in other dimer anion systems and that its structural configuration was neither Watson-Crick (WC) nor Hoogsteen (HS). The vertical detachment energy (VDE) of (AT)(-) was determined by anion photoelectron spectroscopy and found to be in agreement with the VDE value predicted by theory for the BFPT mechanism. An AT pair in DNA is structurally immobilized into the WC configuration, in part, by being bonded to the sugars of the double helix. This circumstance was mimicked by methylating the sites on both A and T where these sugars would have been tied, viz., 9-methyladenine and 1-methylthymine. Calculations found no BFPT in (MAMT)(-) and a resulting (MAMT)(-) configuration that was either HS or WC, with the configurations differing in stability by ca. 2 kcal/mol. The photoelectron spectrum of (MAMT)(-) occurred at a completely different electron binding energy than had (AT)(-). Moreover, the VDE value of (MAMT)(-) was in agreement with that predicted by theory. The configuration of (MAMT)(-) and its lack of electron-induced proton transfer are inter-related. While there may be other pathways for electron-induced DNA alterations, BFPT in the WC/HS configurations of (AT)(-) is not feasible.     

Autoassociates and tautomerism of 2-oxo-5-halogenopyrimidines: theoretical and experimental investigations

Theoretical calculations (on a semi-empirical level) of energy and geometry of the autoassociates of two tautomeric forms of 2-oxo-5X-pyrimidines (X = H, Cl, Br) are presented. On the basis of the calculated energies of autoassociates it is possible to explain the enol—keto tautomeric transition between the gas phase and condensed phases. We propose a double-proton transfer reaction as a possible mechanism for the tautomeric transition.

Infrared absorption spectra of 2-oxo-5X-pyrimidines in the v(NH …) and v(C=O) regions in solid phases and in low-temperature argon matrices are also presented and discussed. Comparison of IR spectra and results of the theoretical calculations with known crystallographic structures of 2-oxo-5X-pyrimidines (X = H, F, Cl) lead to the conclusion that the crystal structure of the 5-bromo derivative should be similar to that of the 5-chloro derivative.     

Wavelet decompositions of Fourier multipliers

We show that in terms of its weak topology, the space of Fourier multipliers for , , can be decomposed by band-limited wavelets belonging to the Schwartz class.

     

Adsorption behavior of surface chemically pure N-cycloalkylaldonamides at the air/water interface

Equilibrium surface tension (sigma(e)) and electric surface potential (DeltaV(e)) versus concentration isotherms of the homologous series of N-cycloalkylaldonamides synthesized from cycloalkylamines (from cyclopentyl- to cyclododecylamine) and D-glucono-1,5-lactone (c-C(n)GA) or D-glucoheptono-1,4-lactone (c-C(n)GHA) (c-n(C) = 5-12) were investigated at the air/water interface. The measurements were performed with aqueous, surface chemically pure surfactant solutions. Equilibrium surface tension vs concentration isotherms were evaluated to get the adsorption parameters, i.e., standard free energy of adsorption, DeltaG degrees (ads), saturation surface concentration, Gamma(infinity), minimum surface area demand per molecule adsorbed, A(min), and interaction parameter, H(s). Increasing the size of the cycloalkyl moiety leads to a significant increase of the minimum surface area demand per molecule adsorbed. This fact, together with a decrease of the intermolecular interaction parameter suggests that the introduction of a more bulky cycloalkyl ring (c-n(C) = 7 and 8) causes an attenuation of the hydrogen-bond network. This goes in line with the exceptional finding that the higher homologues revealed improved solubility in water. In addition, surface tension investigations suggest occurrence of a phase transition for the N-cyclooctylaldonamides at relatively small surface coverage. This observation is well supported by the surface potential measurements, for which the effect of possible changes in the molecules' surface orientation is even more pronounced. Moreover, the concentration intervals of N-cyclooctylaldonamide in which the change in orientation is observed for either the surface tension or the surface potential isotherms are in very good agreement.     

Anion of the formic acid dimer as a model for intermolecular proton transfer induced by a pi* excess electron

The neutral and anionic formic acid dimers have been studied at the second-order Moller-Plesset and coupled-cluster level of theory with single, double, and perturbative triple excitations with augmented, correlation-consistent basis sets of double- and triple-zeta quality. Scans of the potential-energy surface for the anion were performed at the density-functional level of theory with a hybrid B3LYP functional and a high-quality basis set. Our main finding is that the formic acid dimer is susceptible to intermolecular proton transfer upon an excess electron attachment. The unpaired electron occupies a pi(*) orbital, the molecular moiety that accommodates an excess electron "buckles," and a proton is transferred to the unit where the excess electron is localized. As a consequence of these geometrical transformations, the electron vertical detachment energy becomes substantial, 2.35 eV. The anion is barely adiabatically unstable with respect to the neutral at 0 K. However, at standard conditions and in terms of Gibbs free energy, the anion is more stable than the neutral by +37 meV. The neutral and anionic dimers display different IR characteristics. In summary, the formic acid dimer can exist in two quasidegenerate states (neutral and anionic), which can be viewed as "zero" and "one" in the binary system. These two states are switchable and distinguishable.