bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Radicals Formed by Electron Transfer between inorganic ions and excited aromatic molecules in polar solvents
Authors: Mac Marek , Wirz Jakob , Najbar Jan
Published: December 2004

Fluorescence quenching of aromatic molecules by inorganic anions has been the subject of many investigations, yet the nature of the quenching mechanism is not fully understood. The fluorescence‐quenching rate constants correlate with electrochemical data, but the radicals expected to form upon transfer of an electron to the excited aromatic molecules have escaped observation. We report the first observation of radical‐ion species formed by electron‐transfer quenching with inorganic anions in acetonitrile. A decisive step leading to formation of separated radical ions is the trapping of the primary charge‐transfer complex by a second inorganic ion.
Radical Ions of a Bishomobinaphthylene Containing two 1,6‐methano[10]annulene moieties: An ESR and ENDOR study
Authors: Bachmann Rainer , Gerson Fabian , Kusch Andreas , Vogel Emanuel
Published: December 2004

The radical cation and the radical anion of ‘syn’‐cyclobuta[1,2‐c:3,4‐c′]di‐1,6‐methano[10]annulene (‘syn’‐4a,12a:6a, 10a‐bishomobinaphthylene; 3) have been characterized by their hyperfine data. The highly resolved ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} is dominated by a triplet splitting from the outer pair of methano β‐protons (Ho). In contrast, the ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} is poorly resolved with the largest coupling constants arising from perimeter α‐protons. The different hyperfine features of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} are rationalized by MO models. The SOMO of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{+ \atop \dot{}} $\end{document} ψSA(b1), has substantial LCAO coefficients of the same sign at the bridged atoms C(1), C(6), C(11), and C(16), whereas in the SOMO of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, ψSS(a1), the four atoms lie in the vertical nodal planes. The large width and the reluctance to saturation of the lines in the ESR spectrum of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} are attributed to the near‐degeneracy of the lowest antibonding MO's. Due to their similar nodal properties, the SOMO's of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} and the radical anions of binaphthylene (4), 1,6‐methano[10]annulene (1), and naphthalene (2) are interrelated. Moreover, because the cyclic π‐systems in 3 and 1 deviate in the same way from planarity, the effect of such distortions on the coupling constants, aHμ, of the perimeter α‐protons in \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{- \atop \dot{}} $\end{document} should be comparable. Indeed, on going from \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} to \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, the |aHμ| values are reduced exactaly by half as much as the corresponding values on passing from \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{- \atop \dot{}} $\end{document} to \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document}, of which the cyclic π‐systems are twice contained in \documentclass{article}\pagestyle{empty}\begin{document}$ 4^{- \atop \dot{}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{- \atop \dot{}} $\end{document} respectively.
Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part IV. Derivatives with monodentate ligands and edge‐bridging bidentate ligands
Authors: Strawczynski Andrès , Suardi Gianfranco , Ros Renzo , Roulet Raymond
Published: December 2004

The fluxionality of [Ir4(CO)8(μ2‐CO)3L] (L = Br−, I−, SCN−, NO2−, P(4‐ClC6H4)3, PPh3, P(4‐MeOC6H4)3, P(4‐Me2NC6H4)3), as studied by 2D‐13C‐NMR in solution, is due to two successive scrambling processes: the merry‐go‐round of six basal CO's and CO bridging to alternative faces of the Ir4 tetrahedron. The basicity of the ligand L has no significant effect on the activation parameters. The scrambling process of lowest activation energy in [Ir4(CO)7(μ2‐CO)3(PMePh2)2] correspond to the two possible synchronous CO bridging about a unique face of the metal tetrahedron swapping the relative axial and radial positions of the ligands L. The disubstituted clusters [Ir4(CO)10(μ2‐LL)] with one edge‐bridging ligand have a ground‐state geometry with three edge‐bridging CO's (LL = bis(diphenylphosphino)methane, bis(diphenylarsino)methane, bis(diphenylphosphino)propane) or with all terminal CO's (LL = CH3SCH2SCH3). In all cases, the fluxional process of lowest activation energy in the merry‐go‐round of six CO's about a unique triangular face. For the P and As donor ligands, this process is followed by the rotation of terminal CO's bonded to two Ir‐atoms residing on the mirror plane of the unbridged intermediate.
Homogeneous Catalysis with Dicationic PdII Complexes: Aldol reaction of methyl isocyanoacetate with benzaldehyde
Authors: Nesper Reinhard , Pregosin Paul S. , Püntener Kurt , Wörle Michael
Published: December 2004

A series of dicationic PdII‐acetonitrile complexes containing bi‐ and tridentate nitrogen and bidentate phosphine ligands (some of which are chiral) has been prepared as their BF4 salts. The molecular structures for two of these, [Pd(CH3CN)2(bipy)] (BF4)2 (4) and [Pd(CH3CN)((pybox)(i‐Pr))] (BF4)2((S,S)‐pybox(i‐Pr) = 2,6‐bis[(S)‐4′‐isopropyloxazolin‐2′‐yl]pyridine, 5) have been determined by X‐ray diffraction. All of these complexes are shown to be effective homogeneous catalysts for the aldol‐type condensation of the isonitrile, methyl isocyanoacetate, with benzaldehyde. Two isonitrile complexes, [Pd(2,2′‐bipyridyl)(CNCH2COOCH3)2] (BF4)2 and [Pd((S,S)‐pybox(i‐Pr))(CNCH2COOCH3)] (BF4)2, have also been prepared.
Ringerweiterung von sechs‐ zu neungliedrigen Heterocyclen: Umsetzung von 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirin mit 3,4‐Dihydro‐2H‐1,2,4‐benzothiadiazin‐3‐on‐1,1‐dioxiden
Authors: Schläpfer‐Dähler Marlise , Heimgartner Heinz
Published: December 2004

Ring Enlargement of Six‐ to Nine‐Membered Heterocycles: Reaction of 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirine with 3,4‐Dihydro‐2H‐1,2,4‐benzothiadiazin‐3‐one 1,1‐Dioxides

Reaction of 3‐(dimethylamino)‐2,2‐dimethyl‐2H‐azirine (1) and N‐substituted 3,4‐dihydro‐2H‐1,2,4‐benzothiadiazin‐3‐one 1,1‐dioxides (4) in CHCl3 yields 3‐(dimethylamino)‐4,5,6,7‐tetrahydro‐1,2,5,7‐benzothiatriazonin‐6‐one 1,1‐dioxides 5, a novel nine‐membered heterocyclic system, by ring enlargement (Schemes 2 and 4). In refluxing MeOH, the heterocycle 5a rearranges to give the N‐[1‐methyl‐1‐(1,1‐dioxo‐4H‐1,2,4‐benzothiadiazin‐3‐yl)ethyl]‐N′, N′‐dimethylurea 10. The three isomeric 2‐(methylamino)benzenesufonamides 8,9, and 11 (Scheme 3) are obtained by naBH4 reduction of 5a and 10, respectively. Mechanisms for the thermal isomerization 5a → 10 and the NaBH4 reduction of 5a are proposed in Schemes 5 and 6.
Synthesis of Certain 5‐Substituted 2′‐Deoxytubercidin Derivatives
Authors: Seela Frank , Thomas Horst
Published: December 2004

The synthesis of the 7‐deaza‐2′‐deoxy‐adenine derivatives 7b–3 with chloro, bromo, or methyl substituents at C(5) is described. Glycosylation of the 5‐substituted 4‐chloropyrrolo[2,3‐d]pyrimidines 4b–d with 2‐deoxy‐3,5‐di‐O‐(4‐toluoyl)‐α‐D‐erythro‐pentofuranosyl chloride (3) gave the β‐D‐nucleosides 5b–d, exclusively. They were deblocked (→6b–d) and converted into the tubercidin derivatives 7b–d.
Herstellung von Analoga von Polyamin‐Spinnentoxinen
Authors: Benz Herbert , Hesse Manfred
Published: December 2004

Synthesis of Polyamine Analoga of Spider Toxins

Within the last few years, polyamine toxins derived from various arthropods raised increasing interest due to their interaction with glutamate receptors of insects and invertebrates. Compounds 51 and 52 (Scheme 5) were prepared together with 53–58 to study a new pathway to Ala‐, Lys‐, and Gln‐derived polyamine toxins according to Scheme 6.
Photocycloaddition of Benzothiazole‐2‐thiones to Alkenes
Authors: Nishio Takehiko , Mori Yo‐Ichi , Iida Ikuo , Hosomi Akira
Published: December 2004

The photocycloaddition of benzothiazole‐2‐thiones to electron‐rich and aryl‐substituted alkenes are described. Irradiation of N‐unsubstituted benzothiazole‐2‐thione (1) in the presence of alkenes 3 gave 2‐(2′‐mercaptoalkyl)benzothiazoles 4, and 2‐substituted benzothiazoles 5 and 6 (in the case of 3a and 3h, resp.) through the ring cleavage of an intermediate 2‐aminothietane (Schemes 1 and 3). The latter was formed by [2+2] cycloaddition of the CS bond of 1 and the CC bond of 3. Irradiation of N‐methylbenzothiazole‐2‐thione (2) and 2‐methylpropene (3a) gave the spiro‐1,3‐dithiane 8, 1,2,6‐benzodithiazocin‐5‐one 9, and disulfide 10. The structure of 9 was established by X‐ray crystal‐structure analysis.
Efficient Preparation and X‐Ray Structure Analyses of (2R)‐N‐pyruvoyl‐ and (2R)‐N‐(phenylglyoxyloyl)bornane‐10,2‐sultam
Authors: Bauer Tomasz , Chapuis Christian , Kiegiel Jaroslaw , Krajewski Janusz W. , Piechota Katarzyna , Urbanczyk‐Lipkowska Zofia , Jurczak Janusz
Published: December 2004

An efficient synthesis of the two title compounds is reported, as well as their X‐ray crystal‐structure analyses. A discussion based on stereoelectronic considerations rationalizes the first example of a crystalline SO2/C(O) syn‐periplanar conformer of a N‐acylbornane‐10,2‐sultam.
Glycosylidene Carbenes. Part 23. Regioselective glycosidation of deoxy‐ and fluorodeoxy‐myo‐inositol derivatives
Authors: Zapata Amparo , Bernet Bruno , Vasella Andrea
Published: December 2004

To demonstrate the relevance of the kinetic acidity of individual OH groups for the regioselectivity of glycosylation by glycosylidene carbenes, we compared the glycosylation by 1 of the known triol 2 with the glycosylation of the diol D‐3 and the fluorodiol L‐4. Deoxygenation with Bu3SnH of the phenoxythiocarbonyl derivative of 5 (Scheme 1) or the carbonothioate 6 gave the racemic alcohol (±)‐7. The enantiomers were separated via the allophanates 9a and 9b, and desilylated to the deoxydiols D‐ and L‐3, respectively. The assignment of their absolute configuration is based upon the CD spectra of the bis(4‐bromobenzoates) D‐ and L‐10. The (+)‐(R)‐1‐phenylethylcarbamates 13a and 13b (Scheme 2) were prepared from the fluoroinositol (±)‐11 via (±)‐4 and the silyl ether (±)‐12 and separated by chromatography. The absolute configuration of 13a was established by X‐ray analysis. Decarbamoylation of 13a ( → L‐12) and desilylation afforded the fluorodiol L‐4. The H‐bonds of D‐3 and L‐4 in chlorinated solvents and in dioxane were studied by IR and 1H‐NMR spectroscopy (Fig. 2). In both diols, HOC(2) forms an intramolecular, bifurcated H‐bond. There is an intramolecular H‐bond between HOC(6) and F in solutions of L‐4 in CH2Cl2, but not in 1,4‐dioxane; the solubility of L‐4 in CH2Cl2 is too low to permit a meaningful glycosidation in this solvent. Glycosidation of D‐3 in dioxane by the carbene derived from 1 (Scheme 3) followed by acetylation gave predominantly the pseudodisaccharides 18/19 (38%), derived from glycosidation of the axial OH group besides the pseudodisaccharides 16/17 (13%) and the epoxides 20/21 (7%), derived from protonation of the carbene by the equatorial OH group. Similarly, the reaction of L‐4 with 1 (Scheme 4) led to the pseudodisaccharides 28/29 (46%) and 26/27 (14%), derived from deprotonation of the axial and equatorial OH groups, respectively. Formation of the epoxides involved deprotonation of the intramolecularly H‐bonded tautomer, followed by intramolecular alkylation, elimination, and substitution (Scheme 4). The regio‐ and diastereoselectivities of the glycosidation correlate with the H‐bonds in the starting diols.
Synthesis and transformations of methyl (E)‐2‐(acetylamino)‐3‐cyanoprop‐2‐enoate und methyl (E)‐2‐(benzoylamino)‐3‐cyanoprop‐2‐enoate, versatile reagents for the preparation of polyfunctional heterocyclic systems
Authors: Pizzioli Lucija , Ornik Brina , Svete Jurij , Stanovnik Branko
Published: December 2004

Methyl (E)‐2‐(acetylamino)‐3‐cyanoprop‐2‐enoate (2a), and its 2‐benzoyl analog 2b ere prepared from the corresponding methyl (Z)‐2‐(acylamino)‐3‐(dimethylamino)propenoates 1 Multifunctional compounds 2 are versatile synthons for preparation of polysubstituted heterocyclic systems such as pyrroles 4, pyrimidines 5 and 6, pyridazines 7, pyrazoles 8, 9, and 11, and isoxazoles 10.
Intrinsic and Intramolecular Lipophilicity Effects in O‐Glucuronides
Authors: Giroud Yvan , Carrupt Pierre‐Alain , Pagliara Alessandra , Testa Bernard , Dickinson Ronald G.
Published: December 2004

In this study, we compared the lipophilicity of O‐glucuronides and their aglycones. Distribution coefficients (log D) and P values of neutral species (log P) were determined by centrifugal partition chromatography (CPC) in octanol/buffer systems. Two‐phase potentiometry was also used to measure the log P value of some lipophilic solutes. The experimentally determined global influence of glucuronidation on lipophilicity, obtained as the difference (decrement) log P(glucuronide) − log P(aglycone), was found to be −1.30 ± 0.16 (n = 4) for glucuronides of alcohols (methyl, menthyl, neomenthyl, and chloramphenicol O‐glucuronide). The mean decrement was −2.06 ± 0.31 (n = 9) for glucuronides of phenols (phenyl, p‐nitrophenyl, 1‐naphthyl, 6‐bromo‐2‐naphthyl, 4‐methylumbelliferyl, 3‐coumarinyl, phenolphthalein, 4′‐benzophenonyl O‐glucuronide, and diflunisal phenolic glucuronide). For the acylglucuronide of diflunisal and its rearrangement isomers, the mean decrement was −1.80 ± 0.08 (n = 4; range −1.7 to −1.9). Differences in through‐bond proximity effects as parametrized in the CLOGP algorithm seem to account for much of this difference. Conformational factors may also play a role, although it appears modest and unassessable for the glucuronides investigated here. The results imply that in vivo glucuronidation should have a stronger influence on the excretion of phenols than on that of alcohols.
Zur Krystallstruktur einiger Sterine und verwandter Verbindungen. 2. Hochtemperatur‐Modifikation von 17‐Iso‐desoxy‐corticosteron‐acetat
Authors: Nowacki W.
Published: December 2004

Die Hochtemperatur‐Modifikation von 17‐Iso‐desoxy‐corticosteron‐acetat krystallisiert in der Raumgruppe D–P212121 mit den Gitterkonstanten a = 19,267 ± 0,05, b = 9,888 ± 0,027, c = 10,664 ± 0,015 Å und Z = 4 Molekeln pro Zelle [d(röntgen.) = 1,210]. Der Strukturvorschlag ist in Fig. 2 abgebildet worden. Eine Beziehung zur Struktur von Desoxy‐corticosteron‐acetat hat sich nicht ergeben. Die Frage nach der Stellung der langen Seitenkette am C17 bleibt offen.
Notice sur la prise, en photographie en couleurs, de spectres d'émission, de spectres d'absorption et spécialement de spectres Raman
Authors: Briner E. , Kundig J. J. , Berenstein M.
Published: December 2004

On expose les résultats observés dans la prise en couleur de divers spectres: spectres d'émission, spectres d'absorption et spécialement de spectres Raman.
The electronic structures and spectra of proflavine, acridine orange, and their DNA complexes
Authors: Ito Hirotoshi , I'Haya Y. J.
Published: December 2004

The electronic structure of the proflavine cation is studied by the SCF–ASMO–CI method using the Pariser–Parr–Pople approximations. It is shown that the band at 445 mμ may be assigned to the 1A1 → 1B1, transition polarized along the long axis of the molecule. The bands in the neighbourhood of 260 mμ, which are composed of three absorption bands, are tentatively assigned to the 1A1 → 1B1, 1A1 → 1B1, and 1A1 → 1A1 transitions, respectively, in order of decreasing wavelength. The spectrum of the acridine orange cation may be understood to have the same assignment as that of the proflavine cation.

The acridine dye cations are well known for their dimerization with concentration. The intermolecular distances in these dimers are estimated from the band shifts due to the formation of dimers, using the exciton theory. The main contribution to the molecular interaction is shown to be the electrostatic dipole–dipole interaction.

Since the first excitation band of the dye molecule which exhibits a remarkable change due to the formation of the DNA–acridine dye complex, is suggested to be polarized along the long axis, preference of the outside stacking or the intercalation model is qualitatively discussed from the spectral shift of the acridine dye bound to the DNA, assuming simple models.
Über eine Näherung zur Lösung des “Self‐consistent‐field” Verfahrens für Systeme mit ungepaarten Elektronen I. Die Methode
Authors: Diercksen G.
Published: December 2004

An approximate solution of the SCF problem for systems with unpaired electrons (open‐shell) is proposed. The equations are given and the results are discussed.
Proof of the linear independence of properly selected projected spin eigenfunctions
Authors: Gershgorn Z.
Published: December 2004

An inductive proof is given of Löwdin's theorem about the linear independence and completeness of a properly selected set of projected spin eigenfunctions.
Factorization of the secular determinant by constants of the motion
Authors: Gallup G. A.
Published: December 2004

A discussion of the factorization by constants of the motion of the secular equation is given and formulas are obtained which relate these factors to the traces of certain operators. These traces are independent of the specific basis in the vector space, and, hence, so are the factors of the secular equation. The results are also applied to the case of factoring by a finite symmetry group.
Computation of derivatives for parameter optimization in least‐squares fitting of linear combinations of Slater‐type orbitals by Gaussians
Authors: Lesk Arthur M.
Published: December 2004

The approximation of a linear combination of Slater‐type orbitals in terms of Gaussian functions is a many‐parameter optimization problem. Formulas for computation of the gradient of the overlap in parameter space are reported. An alternative method of computing the gradient is described, which is of general applicability. This technique permits the exact evaluation of a derivative, without derivation and programming of its analytic expression.
Lower bounds to eigenvalues of quantum mechanical systems
Authors: Bazley Norman , Fox David W.
Published: December 2004

Procedures are presented which are expected to produce good numerical lower bounds to eigenvalues for Hamiltonians having continuous spectra. Further, it is observed how these lower bounds can be utilized in other estimation methods.
The effect of electric field on the electronic structure of DNA. I. Calculation of the polarizability and of the permanent dipole moment for the nucleotide bases and base pairs
Authors: Seprödi L. , Biczó G. , Ladik J.
Published: December 2004

Generalizing the method of Hirschfelder, Curtiss and Bird for the calculation of the polarizability of molecules, we have calculated both the diagonal and off‐diagonal polarizability tensor elements of the nucleotide bases and base pairs. In the course of calculations also the components of the permanent dipole moments have been computed for these systems.

On the basis of the results obtained we have determined also the critical field strengths necessary to break off a base pair and thus to induce the unwinding of the DNA double helix. According to the data obtained, a field strength of the order 108 V/cm can induce the unwinding of DNA if its direction lies in the plane of the base pairs.
Theoretical study of the derivative hydrocarbons of biphenylene. I. Electronic spectrum of the biphenylene
Authors: Peradejordi F. , Domingo R. , Ferńndez‐Alonso J. I.
Published: December 2004

The electronic spectrum of biphenylene has been studied theoretically. The investigation is based on the semi‐empirical LCAO SCF MO method with various degrees of approximations. The results have been analysed with regard to the following two factors: (a) The difference in effective electronegativity between the carbon atoms in the four‐membered ring and the other carbon atoms in the molecule. (b) The inclusion of doubly excited configurations in the description of the π‐electronic molecular states. The theory satisfactorily interprets the excitation energies and the nature of the electronic transitions. The predictions are particularly affected by the inclusion of the doubly excited configurations. On the basis of these results, the empirical parameters used are discussed.
Brackets to the eigenvalues of the Schrödinger equation, part 1. Tridiagonal matrices
Authors: Weltin E.
Published: December 2004

The problem of upper and lower bounds to the first few eigenvalues of a very large or infinite tridiagonal matrix H is studied. Those eigenvalues of a comparison‐matrix Mn which are lower than a characteristic limit, together with the corresponding eigenvalues of the variational matrix Hn are shown to bracket exact eigenvalues of H. Mn differs from Hn only in the last off‐diagonal element and is easily obtained from H. Sufficient conditions for lower bounds are based on a low estimate of the characteristic limit. For increasing dimensions n, the lower bounds approach the exact eigenvalues from below. As a numerical illustration, brackets to the known eigenvalues of the harmonic oscillator with a linear perturbation are calculated.
A perturbed generalized eigenvalue equation for the helium atom
Authors: Laughlin C. , Amos A. T.
Published: December 2004

The Schrödinger equation for helium is written as a generalized eigenvalue equation and this is solved perturbatively for the ground state. The zero order equation is taken to be that of a “six‐dimensional hydrogen atom” since, in generalized eigenvalue form, this has a discrete spectrum. Although the zero‐order wave function is very poor and gives only 86% of the energy the perturbation procedure is able to improve this to 99% through third‐order.
The electronic correlation problem and loge localization
Authors: Ludeña E. V.
Published: December 2004

The model of complete loge localization is employed here to develop a practical method for handling correlation effects in atomic and molecular many electron systems. Intraloge correlation is dealt with by an independent variational treatment of pair functions which are continuous and vanish outside a given loge. It is shown that in the context of the model it is possible to compute pair correlation energies for localized single and double bonds in molecules by evaluating only modified atomic integrals. We bypass in this manner the evaluation of multicenter integrals necessary in other formalisms. In addition, the corrections to the model are discussed and in particular it is shown that part of the interloge correlation effects are already described by the loge localized wave function.
A theory for the construction of the irreducible representations of finite groups
Authors: Blokker Esko
Published: December 2004

It is shown how the irreducible representations of a finite group can be calculated from the irreducible characters (the latter can be calculated exactly by using Dixon's method). All elements of the matrix, representing a group element, lie in the rational field of polynomials of ξ = exp (2πi/e), where e is the exponent of the group.
Stability conditions for the solutions of the hartree‐fock equations. VII. Stability of some closed‐shell nonalternant systems
Authors: Laidlaw W. G.
Published: December 2004

The instabilities of the solutions to the Hartree‐Fock equations for the nonalternants in the pentalene, heptalene, etc., series and in the azulene, etc., series are examined. The systems are found to have symmetry‐adapted solutions which are unstable for values of the core integral β close to the standard (spectroscopic) value; for example, the pentalene solution is unstable with β equal to 75% of its standard value. The “broken” symmetry solutions although exhibiting only a very slightly lower energy (0.01 eV) may exhibit dramatically different values for other properties, e.g., 30% changes in bond orders. The off‐diagonal charge‐density wave (CDW) appearing in the “broken” symmetry solutions at the onset of instability is amplified as the cooperative phenomena dominate, until in the “fully correlated” limit, the linked‐ethylenic (bond alternating) structure is obtained.
A theory for the construction of the irreducible representations of finite groups. II
Authors: Blokker Esko
Published: December 2004

The restriction on a method for computing irreducible representations of finite groups, requiring that in the irreducible representation to be constructed, at least one group element has at least one nondegenerate eigenvalue, is removed. The method is thus shown to be applicable to an arbitrary finite group and constitutes a practical algorithm for handling groups of order less than 400.
The loge theory as a starting point for variational calculations. I. General formalism
Authors: Aslangul C. , Constanciel R. , Daudel R. , Esnault L. , Ludeña E. V.
Published: December 2004

It is shown that any expectation value of any observable associated with a molecule is the sum of loge contributions and of loge pair contributions. This result provides a rigorous theoretical basis for the study of additive properties of molecules.

It is demonstrated that molecular wave functions (exact or approximate) can be expressed as a sum of functions corresponding to the various electronic events. Furthermore any of these event functions can be expressed in terms of correlated loge functions. This expression suggests many kinds of variational procedures of calculating wave functions (known methods and new ones).

The case in which noncorrelated completely localized loge functions are used is discussed. If continuous functions are used the variational equation reduces to a sum of independent variational equations, each one corresponding to a particular electronic event. This is not so when discontinuous functions are used or when a delocalized function is added to replace the correlation interloge function.

The noncorrelated completely localized loge model is analyzed in more detail. It is seen that local spin operators can be introduced and that each event density operator is the product of the loge density operators. Therefore that model is an independent loge model. The corresponding generalized self‐consistent field equations are derived. This treatment helps us to understand how a localized state of a molecule can produce an ion containing a delocalized region, a phenomenon which is sometimes at the origin of some misunderstanding in photoelectron spectroscopy. Finally it is seen how virtual loge functions can be introduced to describe excited states.
A study of the symmetry dilemma: Second‐order transitions
Authors: Katriel J. , Domany E.
Published: December 2004

Transitions from symmetry‐adapted to symmetry‐broken solutions of variational problems are classified according to the nature of the discontinuity involved. Two systems in which a second‐order transition occurs are studied.
Theoretical investigation of the π ‐electronic structure and spectra of protonated aromatic carbonyl compounds
Authors: Kiss A. I. , Joó F.
Published: December 2004

The π‐electronic structure and spectra of the protonated aromatic carboxylic acids, aldehydes and ketones have been calculated by the Pariser–Parr–Pople method. An essential modification was that the positive charge has been considered as delocalized within the substituent group. The best agreement for the cation of benzoic acid was obtained using a symmetric carboxy model with equal charges on both oxygen atoms. This model gave equally good results for the protonated fluoro‐, chloro‐ and methylbenzoic acids, as well. The delocalized charge model was successfully applied in the calculation of aromatic aldehydes and ketones. The methyl group was treated both as a one‐ and as a two‐centre substituent.
First‐Order perturbation treatment of the short‐range repulsion in a system of many closed‐shell atoms or molecules
Authors: Jeziorski Bogumił , Bulski Marek , Piela Lucjan
Published: December 2004

Assuming a determinantal form for the wave‐functions of free molecules, explicit formula for the first‐order interaction energy of many closed‐shell molecules has been derived. Provided that the determinants describing the free molecules are constructed from the Hartree‐Fock orbitals, the two‐, three‐, and four‐body effects predicted by the first‐order perturbation theory are closely related to those which one obtains in the framework of the Löwdin LCAO MO‐type approach. The results are illustrated by numerical calculations for the system of three ground‐state helium atoms.
Best optimized one‐electron wave‐functions. IV. Ionization energies of atoms
Authors: Jakubowski P.
Published: December 2004

On the basis of the previously described method for optimization of one‐electron wave‐functions, a simple procedure has been developed to determine the ionization energies in atomic cases. The procedure gives all the ionization energies at once with relatively high accuracy. This is possible due to optimal distribution of the total electron charge between the individual spin‐orbitals.
Theory of the infrared spectra of the hydrogen bond in molecular crystals
Authors: Wójcik Marek J.
Published: December 2004

A general model for the vibrational interactions of the hydrogen bonds in molecular crystals is presented. The energy and the intensity distributions of the IR spectra of the 1‐methylthymine and uracil crystals are correctly reproduced.
A comparison of orthogonalized plane wave and augmented plane wave methods for calculating photodetachment cross‐sections
Authors: Mohraz Manijeh , Lohr Lawrence L.
Published: December 2004

The orthogonalized plane wave (OPW) method of calculating electronic continuum wave‐functions is tested by the computation of photodetachment cross‐sections and angular distributions for gaseous halide anions. The results are compared to those obtained by a related augmented plane wave (APW) method involving the exact solution of a single‐particle Schrödinger equation containing a piecewise Coulombic potential energy. These comparisons, as well as other involving experimental and theoretical cross‐sections from the literature, indicate that OPW cross‐sections are, at best, only semi‐quantitatively reliable for describing photodetachment even at low photon energies, and that OPW cross‐sections should be calculated using the dipole length operator rather than the dipole velocity operator.
Reduced‐density‐matrix theory and algebraic structures
Authors: Kryachko Eugene S.
Published: December 2004

A survey of our recent work on algebraic structures and reduced‐density‐matrix theory is presented. Our approach leads to a method of classifying reduced density matrices and generalizes the notion of open and closed shells in many‐body theory.
Incompletely symmetric non‐bloch electron states in perfect cubic crystals. III. Density of dynamical observables in the FCC lattice
Authors: Kunert A.
Published: December 2004

The operators of dynamical observables of the crystal electron (velocity vector components. reciprocal mass tensor components and their functions) commute with the energy operator; hence, the averages of these observables can be adequately approximated by the eigenfunctions for the energy operator. Calculations of the averages were based on the LCAO eigenfunctions classified according to incompletely symmetric irreducible representations of the point group of the cubic crystal, and a similar classification was made for the averages.
Model quantum chemical studies of the electronic structure and aspects of reactivity of diol epoxides of aromatic hydrocarbons
Authors: Lavery Richard , Pullman Bernard
Published: December 2004

This paper offers a unified presentation of the main ring conformers of the diol expoxides, triol carbonium ions, and tetrols related to the “bay‐region” benzo ring of carcinogenic metabolites of PAH and brings forward quantitative information through ab initio SCF computations about their relative energies. It substantiates and evaluates the energy of the syn epoxide‐OH4 hydrogen bond and, on the contrary, refutes the significance of an O ⃛HO or an O− ⃛HO bond in the triol carbonium ions. It provides an explanation for the similar rates of acid‐catalyzed hydrolysis of the syn and anti diol expoxides. It evaluates the stabilization of the triol carbonium ions due to the presence of a neighboring double bond and accounts for the spontaneous opening of protonated epoxides. Finally it accounts for cis hydrolysis of the syn diol epoxide and trans hydrolysis of the anit diol epoxide under acid conditions.
Modified bielectronic potential method for correlation energy
Authors: Ruelle Jean‐Louis
Published: December 2004

Löwdin's correlation potential formalism has been used to define a modified bielectronic potential, allowing one to calculate the exact electronic energy, given the Hartree–Fock wave function. This modified potential is in principle peculiar to each electronic system, and is defined by a correlation factor depending on the interelectronic distance r2. The explicit calculation of the correlation factor has been performed for some two‐electron atoms, in the 11S and 23S states, and for the beryllium atom. Examination of the results so obtained leads us to conclude in favor of the nonexistence of a universal modified bielectronic potential.
Ab initio study of a purine nucleoside: Adenosine
Authors: Kwiatkowski J. S. , Pullman B.
Published: December 2004

The ab initio SCF LCAO‐MO method is used to compute the main electronic properties of a purine nucleoside, adenosine, in two specific conformational arrangements (3′‐endo conformation of the ribose, gt orientation of the extracyclic CH2OH group, anti orientation of the base with respect to the sugar and 3′‐endo conformation of the ribose, gg orientation of the extra‐cyclic CH2OH group, syn orientation of the base with respect to the sugar). The results are compared with those performed for the isolated component fragments, adenine and 3′‐endo riboses.
Natural orbital analysis of nonadiabatic H2+ wave functions
Authors: Bishop David M. , Cheung Lap M.
Published: December 2004

Previously determined nonadiabatic wave functions for H2+ (containing several hundred terms) are analyzed by using natural orbitals. This is the first time that the natural orbital concept has been applied to other than purely electronic wave functions. We find that the natural orbital expansion converges rapidly and that five or six terms are sufficient to reproduce the exact expectation values. Several plots are given of the orbitals so found and these allow a visualization of the somewhat abstract nonadiabatic wave function in a format more reminiscent of everyday quantum‐mechanical pictures.
A nonlinear expression of the North Atlantic Oscillation in the North Pacific
Authors: Zhao Hongxu , Moore G. W. K.
Published: December 2004

The North Atlantic Oscillation (NAO) has been identified as an important mode of variability in the climate system. Our knowledge of its impacts is based largely on linear analysis techniques. As a result, nonlinearities associated with it are largely unknown. In this study, we use recently proposed nonlinear compositing and one‐sided regression techniques as well as a new rectified regression technique to show that the nonlinear expression of the NAO is fundamentally different from its linear expression. In particular, we show that its nonlinear expression is amplitude but not sign dependent and has a center of action in the North Pacific sector that is associated with the East Asia jet stream (EAJS) and the Aleutian Low.
Investigation of height gradient in vertical plasma drift at equatorial ionosphere using multifrequency HF Doppler radar
Authors: Prabhakaran Nayar S. R. , Sreehari C. V.
Published: December 2004

A multifrequency HF Doppler radar installed at the magnetic equatorial station Trivandrum provides an opportunity to study the height gradient in vertical plasma drift at the bottomside of equatorial F region during evening time. The multifrequency radar gives near‐simultaneous observation of vertical plasma drift at three close by F region heights above the sounding station. The height gradient of the vertical drift shows a negative value during the prereversal enhancement (PRE) period and turns to positive value after the prereversal enhancement. The average height gradient in vertical plasma drift remains negative around PRE and its magnitude decreases with altitude, below F peak. This could be a clear‐cut manifestation of the curl‐free nature of the low‐latitude electric field, and it could also indicate a partial signature of the postsunset velocity vortex at the equatorial F region. The magnitude of the mean height gradient around PRE exhibits a seasonal variation.
Low‐frequency electrical properties of peat
Authors: Comas Xavier , Slater Lee
Published: December 2004

Electrical resistivity/induced polarization (0.1–1000 Hz) and vertical hydraulic conductivity (Kv) measurements of peat samples extracted from different depths (0–11 m) in a peatland in Maine were obtained as a function of pore fluid conductivity (σw) between 0.001 and 2 S/m. Hydraulic conductivity increased with σw (Kv ∝ σw0.3 between 0.001 and 2 S/m), indicating that pore dilation occurs due to the reaction of NaCl with organic functional groups as postulated by previous workers. Electrical measurements were modeled by assuming that “bulk” electrolytic conduction through the interconnected pore space and surface conduction in the electrical double layer (EDL) at the organic sediment‐fluid interface act in parallel. This analysis suggests that pore space dilation causes a nonlinear relationship between the “bulk” electrolytic conductivity (σel) and σw (σel ∝ σw1.3). The Archie equation predicts a linear dependence of σel on σw and thus appears inappropriate for organic sediments. Induced polarization (IP) measurements of the imaginary part (σ″surf) of the surface conductivity (σ*surf) show that σ″surf is greater and more strongly σw‐dependent (σ″surf ∝ σw0.5 between 0.001 and 2 S/m) than observed for inorganic sediments. By assuming a linear relationship between the real (σ′surf) and the imaginary part (σ″surf) of the surface conductivity, we develop an empirical model relating the resistivity and induced polarization measurements to σw in peat. We demonstrate the use of this model to predict (a) σw and (b) the change in Kv due to an incremental change in σw from resistivity and induced polarization measurements on organic sediments. Our study has implications for noninvasive geophysical characterization of σw and Kv with potential to benefit studies of carbon cycling and greenhouse gas fluxes as well as nutrient supply dynamics in peatlands.
Efficacy of Percutaneous Electrical Nerve Stimulation for the Treatment of Chronic Low Back Pain in Older Adults
Authors: Weiner Debra K. , Rudy Thomas E. , Glick Ronald M. , Boston J. Robert , Lieber Susan J. , Morrow Lisa A. , Taylor Stephen
Published: December 2004

OBJECTIVES: To determine the efficacy of a complementary analgesic modality, percutaneous electrical nerve stimulation (PENS), for the treatment of chronic low back pain (CLBP) in community‐dwelling older adults.

DESIGN: Randomized, controlled clinical trial.

SETTING: University of Pittsburgh Pain Evaluation and Treatment Institute.

PARTICIPANTS: Thirty‐four English speaking, community‐dwelling adults aged 65 and older with CLBP of at least moderate intensity experienced every day or almost every day.

INTERVENTION: Subjects were randomized to receive twice‐weekly PENS and physical therapy (PT) or sham PENS and physical therapy for 6 weeks.

MEASUREMENTS: At baseline, immediately after the 6‐week intervention period, and 3 months later, the primary outcome measures pain intensity and pain‐related disability were assessed. The secondary outcome measures physical performance (timed chair rise, functional reach, gait speed, static and isoinertial lifting), psychosocial factors (mood, sleep, and life control), and cognitive function (measures of attention, concentration, and mental flexibility) were also collected.

RESULTS: Subjects randomized to PENS plus PT displayed significant reductions in pain intensity measures from pre‐ to posttreatment (P < .001), but the sham PENS plus PT group did not (P = .94). These pain reduction effects were maintained at 3‐month follow‐up. Similarly, significant reductions in pain‐related disability were observed at posttreatment (P = .002) for the PENS plus PT group and were maintained at follow‐up, but the sham PENS plus PT group did not show reductions in pain‐related disability (P = .81). Of the secondary outcome measures, psychosocial function, timed chair rise, and isoinertial lifting endurance also improved significantly at posttreatment for the PENS plus PT group, and their improvement was sustained at 3‐month follow‐up, but the sham PENS plus PT did not display significant changes on these measures after treatment.

CONCLUSION: This preliminary study suggests that PENS may be a promising treatment modality for community‐dwelling older adults with CLBP, as demonstrated by reduction in pain intensity and self‐reported disability, and improvement in mood, life control, and physical performance. Larger studies with longer duration of follow‐up are needed to validate these findings and support the use of PENS in clinical practice.
The effects of density‐dependence and local dispersal in individual‐based stochastic metapopulations
Authors: Kean John M. , Barlow Nigel D.
Published: December 2004

We describe simulation models for metapopulations of individual‐based random walk populations with local dispersal on a coupled map lattice. The models were used to assess the factors determining persistence time, in particular the incidence of density‐dependence required for long‐term persistence of a temporally and spatially stochastic metapopulation, the extent of persistence possible in the absence of density‐dependence, and the factors that affect this.  Metapopulation persistence depended on the overall rate of increase of the metapopulation mean. This was maximised by (in order of importance) high mean and variance in the local rate of increase, high dispersal rates (20% or more of individuals dispersing each generation), large lattice size, and large dispersal range (to at least 24 neighbouring subpopulations).  With density‐dependence, the emergent dynamics of the metapopulation mean following global perturbation (reduction in density) resembled those of the logistic growth model. However, the overall metapopulation rate of increase and equilibrium level bore no resemblance to those of the subpopulations: rate of increase was higher (negative mean local rates of increase may give positive overall growth), and equilibrium mean metapopulation density was well below the local carrying capacity. This highlights the need to sample populations at an appropriate scale when seeking to understand regulatory mechanisms.  Metapopulations with the strongest tendency to grow gave the highest equilibrium mean density, the highest incidence of density‐dependence, and the longest persistence time. However, long‐term persistence with low average density and very low incidence of density‐dependence was possible on a sufficiently large lattice. For example, with 40×40 subpopulations, mean metapopulation persistence time was around 104 generations, with mean subpopulation size of 2% of the carrying capacity, and local density‐dependence acting just once every 2500 generations on average. Metapopulation processes may explain our inability to detect density‐dependence in many real populations, and may also play an important part in the persistence of rare species.
Effects of phenological constraints on sex allocation in cosexual monocarpic plants
Authors: Sato Toshihiko
Published: December 2004

The effects of two phenological constraints in resource investment to reproduction – resource limitation at the flowering stage and unpredictability of resources gained after flowering – on the resource allocation between male and female functions in monocarpic plants are considered using the ESS (evolutionarily stable strategy) approach. The model predicts that the sex allocation including the seed maturation stage has a female bias, when the quantity of reproductive resources available at flowering is small compared with that which is obtained after flowering, or when the cost of seed maturation relative to ovule production is low. The fluctuation of the quantity of resources available for seed maturation favors overproduction of ovules. As a result, more resources are allocated to female function and less to male function at flowering. The ESS allocation depends on the variability of resources and the cost of seed maturation relative to ovule production. The probability that total resource allocation has a female bias becomes higher than 0.5, and it depends on the cost of seed maturation relative to ovule production rather than resource variability. On the other hand, the probability that resource allocation has a female bias decreases with resource variability if we assume that the floral sex ratio is fixed. Future studies of plant sex allocation would profit by taking account of the phenological process of reproduction such as ovule production or seed maturation.
Social facilitation affects longevity and lifetime reproductive success in a self‐fertilizing land snail
Authors: Baur Bruno , Baur Anette
Published: December 2004

Factors that reduce the reproductive output of self‐fertilizing hermaphrodites are receiving increasing attention. The combined effects of reduced fecundity of selfing parents and inbreeding depression of the progeny have been referred to as self‐fertilization depression. In isolated freshwater snails the reproductive output of selfing individuals also decreases due to the lack of social facilitation (absence of a conspecific). We examined the effect of social facilitation on lifetime reproductive success (number of young produced and longevity) over two generations in the simultaneously hermaphroditic land snail Balea
perversa. In a parallel study we showed that B. perversa kept
singly and in pairs reproduced exclusively by self‐fertilization. In the
parent generation, snails kept singly produced less offspring than snails
kept in pairs. The difference in lifetime number of young was mainly due
to differences in adult life span. Snails of the two groups did not
differ in reproductive rate (number of young produced per 100 d of
reproductive life) and hatchling size. In the offspring generation,
snails kept singly did not differ from individuals kept in pairs in the
lifetime number of young and hatchling survival. As in the parent
generation, snails kept singly reproduced during a shorter period than
snails kept in pairs. However, the shorter reproductive life span of
snails kept singly was compensated for by a slightly (but not
significantly) higher reproductive rate which resulted in a similar
number of offspring produced for both groups. In both generations, snails
of the two groups did not differ in size at first reproduction, adult
growth rate and size at death. These findings suggest that social
facilitation may affect longevity in selfing B. perversa.