bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of counterion binding and alkyl chain length on the phase transition behaviour of DI‐n‐alkyl phosphate vesicles
Authors: Wagenaar Anno , Streefland Lisette , Hoekstra Dick , Engberts Jan B. F. N.
Published: January 2005

This paper describes a fluorescence depolarization and 31P NMR spectroscopic study of the phase transition behaviour of a series of identical and mixed‐chain di‐n‐alkyl phosphate vesicles in the presence of different counterions (Na+,K+,Me4N+,Ca2+). Using trans, trans, trans‐1, 6‐diphenyl‐1, 3, 5‐hexatriene (DPH) as a fluorescent probe, the fluorescence polarization (P) was measured for the identical‐chain vesicles (Na+, K+, Me4N+) as a function of temperature. The temperature for the main phase transition (Tm) only responded to variation of the counterion in the case of the longer‐chain di‐n‐alkyl phosphates, with Tm decreasing in the sequence Na+ > K+ > Me4N+. This result is rationalized in terms of a decreasing counterion binding, which affects chain ordening in the core of the bilayer. Peak intensities and line widths of the 31P NMR resonances for the bilayer vesicles suggest a more complex phase behaviour, but the overall results are reconcilable with the picture emerging from the fluorescence depolarization experiments. Fluorescence depolarization measurements were also carried out with vesicles formed from the sodium di‐n‐alkyl phosphates and in the presence of various concentrations of Ca2+ (0‐6 mM) at temperatures above Tm. For both the identical‐chain and mixed‐chain di‐n‐alkyl phosphate vesicles, a steep increase in P was found between ca 1.0 and 1.4 mM Ca2+, indicative of a strong Ca2+‐induced ordening of the alkyl chains.
Self‐organizing systems based on amphiphilic cyclodextrin diesters
Authors: Zhang Ping , Parrot‐lopez Hélène , Tchoreloff Pierre , Baszkin Adam , Ling Chang‐chun , de Rango Colette , Coleman Anthony W.
Published: January 2005

The formation of micelles, vesicles and monomolecular layers by amphiphilic cyclodextrins possessing hydrophobic ester groups on the secondary hydroxyl face is described. The physico‐chemical properties of these self‐organizing systems were studied by dynamic light scattering, variable‐temperature 1H NMR, the use of lanthanide shift reagents, deposition of Langmuir layers, variable‐temperature solubility measurements and aqueous and non‐aqueous surface tension activity measurements. The results are interpreted in terms of the cylindrical geometry of the compounds which, coupled with the presence of a large planar polar head group, lead to the formation of self‐organized systems both in polar organic solvents and also at the air–water interface.
Structure and conformation of pyridino‐ and diesterpyridino‐18‐crown‐6 complexes with primary ammonium salts in solution and crystalline states
Authors: Izatt Reed M. , Zhu Cheng Y. , Dalley N. Kent , Curtis Janet C. , Kou Xiaolan , Bradshaw Jerald S.
Published: January 2005

Structures in CD3ODCDCl3 mixtures of pyridino‐18‐crown‐6 and diesterpyridino‐18‐crown‐6 complexes with primary ammonium cations containing an α‐phenyl group were found to be significantly different. The π–π overlap between the α‐phenyl group of the ammonium cation and the pyridine ring of the ligand occurs in the pyridino‐18‐crown‐6 complexes but not in the diesterpyridino‐18‐crown‐6 complexes. The solution structure of a diesterpyridino‐18‐crown‐6 complex with an α‐phenyl‐containing primary ammonium cation was also found to differ markedly from the corresponding crystal structure in that π–π overlap occurs in the crystal structure, but not in the solution structure.
Supramolecular effects on photochromism—properties of crown ether‐modified dihydroindolizines
Authors: Dürr H. , Thome A. , Kranz C. , Kilburg H. , Bossmann S. , Braun B. , Janzen K.‐P. , Blasius E.
Published: January 2005

Photochromic molecules such as dihydroindolizines (DHI) containing crown ether units can be ‘tuned’, as far as their properties are concerned, by supramolecular ion binding. Inclusion of the ion in the crown ether cavity yields a new supramolecular species. This species shows special properties of the excited state after guest addition: (a) bathochromic shifts of the photochromic crown ethers and also hyperchromic effects in the UV spectra; (b) fluorescence intensity of one of the photochromic crown ethers is either increased (crown excitation) or decreased (DHI excitation) after addition of alkali metal ions; and (c) in the ground state a large change in reaction rate for the reaction 1,5‐electrocyclization betaine (coloured form) to dihydroindolizine is observed in the supramolecular complexes.
Metal ion‐promoted hydrolysis of uridine 2′, 3′ ‐ cyclic monophosphate: Effect of metal chelates and uncomplexed aquo ions
Authors: Kuusela Satu , Lönnberg Harri
Published: January 2005

The effect of a wide variety of metal ious and metal ion complexes on the hydrolysis of uridine 2′,3′‐cyclic monophosphate was studied over the pH range 4.5–8.0. The greatest rate accelerations observed were 107–108‐fold. The kinetic data obtained are interpreted in terms of a mechanism involving arapid monodentate binding of the metal ion to the monoanionic phosphodiester and a subsequent intracomplex participation of the metal‐bound hydroxo ligand, either as a nucleophile attacking the tetracoordinated phosphorus or as a base facilitating an intermolecular attack of a water molecule. No effect on the product distribution between uridine 2′‐ and 3′‐monophosphates was observed.
Alkaline hydrolysis of substituted benzyl substituted benzoates
Authors: Yoh Soo‐dong , Cheong Duk‐young , Tsuno Yuho
Published: January 2005

The kinetics and mechanism of the alkaline hydrolysis of both acyl‐ and aryl‐substituted benzyl benzoates were studied in 80% (v/v) aqueous acetone at 20, 34, and 40 °C. Each of the substituted benzyl alcohols generated an independent σ–ρ plot which was correlated well with the Hammett equation (R = 0·996−0·999). The values of ρ for the acyl moiety showed no tendency either to increase or to decrease with the intrinsic reactivity of the parent benzyl alcohol and were all within ±0·098 of the mean of 2·236. However, the Hammett ρ values for the leaving groups decreased from H to p‐NO2 substituents of the acyl part, in which the values were smaller than those of acyl moieties and fairly accurately obeyed the σ0 values rather than the σ values. The rate data for benzyl‐substituted benzoates were correlated by the Yukawa–Tsuno equation, log k/k0 = 1·72(σ0 + 0·49Δ) − 0·020, R = 0·996. The results suggested that the alkaline hydrolysis of benzyl benzoates showed a greater sensitivity to acyl than aryl activation, and the rates and activation parameters were largely determined by the addition step. The results are attributed to the preferential partitioning of an unstable tetrahedral intermediate to the products.
Acidity constants of benzamide and some Ortho‐substituted derivatives
Authors: García Begoña , Casado Rosa M. , Castillo Julio , Ibeas Saturnino , Domingo Inmaculada , Leal José M.
Published: January 2005

Acidity constants of benzamide and seven ortho‐substituted derivatives were determined. Except for o‐nitrobenzamide, all the amides exhibit medium effects. The data were treated by vector analysis. o‐Aminobenzamide displays two protonation equilibria. The second acidity constant was determined by vector analysis and by the excess acidity function, since the acid strength provided by perchloric acid is insufficient for complete protonation. Different acidity functions and the ortho substituent effect on ionization of the amide group are compared.
Determination of the existence, value and uncertainty of the compensation or isokinetic temperature
Authors: Alper Joseph S. , Gelb Robert I.
Published: January 2005

The demonstration of the existence of a compensation effect, the linear dependence of the enthalphy on the entropy for a series of chemical reactions, is often complicated by an apparent linear dependence arising solely from experimental errors. A non‐linear least squares method has been developed for establishing the existence or non‐existence of a compensation effect and for determining the value of the compensation temperature if the effect exists. The uncertainty in the value of the compensation temperature can be determined by means of a Monte Carlo procedure. If a compensation effect does not exist, three cases can be distinguished: (1) the relationship between the enthalpy and entropy is linear, but the compensation temperature is 0 K; (2) the various reactions cannot be distinguished from each other because of experimental errors; and (3) the reactions do differ, but the relationship (if one exists) between the enthalpy and entropy is not linear. The method is illustrated using both hypothetical and experimental examples.
Evidence for the presence of the CH–π‐interacted ap‐conformers of benzyl formates
Authors: Suezawa Hiroko , Mori Akiyoshi , Sato Masayuki , Ehama Ritsuko , Akai Ikuo , Sakakibara Kazushisa , Hirota Minoru , Nishio Motohiro , Kodama Yoshio
Published: January 2005

In order to examine the preferred conformations of benzyl, 1‐phenylethyl and cumyl formates, lanthanoid‐induced shifts (LIS) of 1H and 13C NMR and difference NOE spectra of these esters were measured. The measurements showed that a folded conformer capable of forming intramolecular CH–π interaction are predominant with all three series of formate esters. The LIS and other experiments suggested the coexistence of considerable amounts of extended conformers, however. As the ester group is enforced to take supposedly unfavourable ap‐conformation in the CH–π contiguous folded conformer, the predominance of the conformer was a surprise and needed explanation. The NOE experiments on a series of para‐substituted benzyl formates, XC6H4CH2OCHO (X = CH3O, CH3, H, Cl, NO2), showed that the enhancement of aromatic proton signals (ortho and meta) induced by the irradiation of formyl proton increases gradually as the substituent becomes more electron donating, whereas the enhancement of benzylic (α) proton signal remains constant irrespective of the nature of the substituent. This can be explained by assuming that the CH–π contiguous folded conformer is in equilibrium with the extended conformer. The trend of the substituent effect supports the hydrogen bond‐like nature of the CH–π interaction. A similar trend was also observed with substituted 1‐phenylethyl formates. Hence the unexpected stability of the ap‐conformer of benzyl formates could be ascribed to the stabilization due to the CH–π interaction.
Structural study on 1‐phenyl‐ and 1‐(2‐naphthyl)‐8‐tropylionaphthalene hexafluoroantimonates
Authors: Tsuji Ryotaro , Komatsu Koichi , Takeuchi Ken'ichi , Shiro Motoo , Cohen Shmuel , Rabinovitz Mordecal
Published: January 2005

The molecular structures of 1‐phenyl‐ (5) and 1‐(2‐naphthyl)‐8‐tropylionaphthalene (6) hexafluoroantimonates were determined by x‐ray crystallography and compared with those of 1,8‐diphenylnaphthalene and related compounds. In these compounds, the two aromatic substituents face each other in a nearly parallel conformation with a splayed‐out arrangement. In the cations 5 and 6, the distance between the facing rings is appreciably shorter than that of other 1,8‐diarylnaphthalenes, suggesting the presence of some attractive force. This attraction is ascribed to an intramolecular charge‐transfer interaction, and seems to bring about a slight inward bending of the 2‐naphthyl substituent in the cation 6. AM1 calculations were carried out for these cations and the results are discussed in comparison with the results of x‐ray crystallography.
Photoreaction of 2‐benzoylcyclohexanones on a silica gel surface: Deviation from their solution photochemistry
Authors: Hasegawa Tadashi , Imada Manabu , Yoshioka Michikazu
Published: January 2005

On irradiation on a dry silica gel surface, 2‐benzoylcyclohexanones which have the lowest n, π* state and are devoid of methyl substituents on their cyclohexanone rings, undergo an oxidative cleavage to give adipic acid and subsituted benzoic acid along with the Norrish Type II product. Irradiation of 2‐chlorocylohexanone and cyclohexane‐1,2‐dione on silica gel also gives adipic acid. The cyclohexanonyl radical on the surface, which is produced from the α‐cleavage of the 2‐benzoyl group of the 2‐benzoylcyclohexanones or the cleavage of the CCl bond of 2‐chlorocyclohexanone, is suggested as the precursor of adipic acid; the radical is probably converted into cyclohexane‐1,2‐dione, which undergoes a secondary photoreaction to give adipic acid on the surface.
Using theoretical descriptors in structure–activity relationships: Solubility in supercritical CO2
Authors: Famini George R. , Wilson Leland Y.
Published: January 2005

The use of quantitative structure–activity relationships (QSAR) in correlating biological phenomena to chemical structure, and the use of linear free energy relationships (LFER) and linear solvation energy relationships (LSER) for correlating physical phenomena are becoming standard occurrences. In this work the empirical LSER solvatochromic descriptors were replaced with a computationally derived set to aid in a priori property prediction. This paper deals with the application of this descriptor set to correlating the solubilities of 22 compounds in super critical CO2. A reasonable correlation, consistent with previous correlations by other researchers, was found.
Nucleophilic catalysis in deoxymercuration: The beta effect of mercury
Authors: Lambert Joseph B. , Emblidge Robert W.
Published: January 2005

Deoxymercuration was examined in the antiperiplanar stereochemistry of trans‐2‐acetoxycyclohexylmercury(II) acetate (6). The presence of the mercury group accelerates the departure of the beta leaving group by a factor of about 1010. This beta effect is larger than that of silicon and comparable to that of germanium. In contrast to these latter cases, the rate for 6 was found to increase with the nucleophilicity of the solvent. It is concluded that a molecule of solvent is coordinated with mercury in the transition state. This nucleophilic assistance raises the polarizability and nucleophilicity of the mercury group, enhancing its ability to stabilize the developing positive charge or to form a bridged intermediate.
Stereochemical structures of (8,8‐ethylenedioxy‐2‐oxo‐)‐ and (8,8‐ethylenedioxy‐2‐hydroxy‐)‐6‐phenylsulphonylbicyclo[3·3·0]octanes
Authors: Tinant Bernard , Declercq Jean Paul , Wynants Chantal , Demillequand Marc
Published: January 2005

Cyclopentannulation of 4‐tert‐butyldimethylsilyloxy‐2‐cyclopenten‐1‐one from a β‐metallated dioxolane‐type orthoester affords 4‐tert‐butyldimethylsilyloxy‐8,8‐ethylenedioxy‐6‐phenylsuiphonyl‐2‐oxobicyclo [3·3·0] octanes as a mixture of two diastereoisomers. Their stereochemical structures were established by NMR and x‐ray analysis. The minor product possesses a cis ring fusion, the sulphonyl and the tert‐butyldimethylsilyloxy groups being endo and exo, respectively. The major isomer also has a cis ring fusion but an exo position for both dimethylsilyloxy and sulphonyl groups. Both cyclopentannulation products result from an anti addition with respect to the 4‐tert‐butyldimethylsilyloxy group on the enone.
Cationic and anionic halochromism
Authors: Zanotto Sandra P. , Scremin Marivania , Machado Clodoaldo , Rezende Marcos Caroli
Published: January 2005

The spectral changes of organic solutions of N,N,N′,N′‐tetramethylenediaminoacetylacetonatocopper(II) perchlorate and a merocyanine dye in the presence of NaI or LiClO4 provide examples of anionic and cationic halochromism, respectively. The observed changes are interpreted as arising from all possible interactions in the three‐component system of the dye, the salt and the solvent.
Nucleophilic participation in the solvolyses of 2‐aryl‐2‐halopropanes and the previously claimed advantage of using YBnX scales
Authors: Kevill Dennis N. , D'Souza Malcolm J.
Published: January 2005

Contrary to a recent report, the specific rates of solvolyses of five 2‐aryl‐2‐chloropropanes give only marginally (not significantly) better correlations with use of the YBnCl scale rather than the YCl scale. With the use of the extended (two‐term) Grunwald–Winstein equation, some evidence for a weak nucleophilic solvation is obtained, but at a low confidence level. The specific rates of 2‐bromo‐2(p‐trifluoromethylphenyl)propane solvolysis are significantly better correlated using YBr (rather than YBnBr) values and, indeed, the use of NT values in conjunction with YBr values leads to an l value of 0·17 ± 0·06 and evidence for a weak nucleophilic participation at a 98·7% confidence level.
Potentiometric evaluation of the ion‐selective characteristics of 1,4‐bridged cubyl diester crown ethers
Authors: Moriarty Robert M. , Rao M. Suresh Chander , Tuladhar Sudersan M. , Gilardi Richard , D'Silva Claudius , Williams Gwyn
Published: January 2005

Cubane diester crown ethers were tested as ion‐selective electrodes in poly(vinyl chloride) (PVC) membranes. The four ionophores studied proved to be good K+ neutral carriers, showing Nernstian and near‐Nernstian responses to this ion, in the range 10−4–10−1 M. The fixed interferences method was used to determine relative selectivity coefficients for all the electrodes. The highest selectivity for potassium relative to sodium, lithium, calcium and magnesium ions using potassium tetrakis(p‐chlorophenyl)borate (KTpClPB) as a resistance modifier and NPOE as a plasticizer was obtained with the 1,4‐cubyl diester‐25‐crown‐7 ether ionophore. The effects of KTpCIPB on membrane selectivity were assessed; its removal was found to increase the selectivity of the four ionophores for potassium relative to cesium, sodium, calcium and magnesium ions with minimal effects on lithium and ammonium ions. The compounds tested exhibited a fast Nernstian response to changes in K+ concentration which was stable to within <100 μV h−1.
Orbital‐controlled reactions catalysed by zeolites: Electrophilic alkylation of aromatics
Authors: Corma A. , Zicovich‐Wilson C. , Viruela P.
Published: January 2005

The role of orbital control in product selectivity during electrophilic aromatic alkylation catalysed by zeolites was studied both theoretically and experimentally. In order to discuss this, the alkylation of toluene and m‐xylene by methanol was carried out on a series of large‐pore zeolites (HY). The changes in the para to ortho ratio observed on changing the framework Si/Al ratio of the zeolites were related to ab initio molecular orbital calculations of the LUMO energy of structurally alike model clusters but containing different tetrahedral cations around the active site. The observed correlation is discussed in terms of the HSAB principle by taking into account the influence of the catalyst composition on the reactivity of the electrophilic reagent.
An E ⇌ Z isomerization of an electrophilic vinyl azide by 15N. A probe for internal rotation processes in the carbanionic intermediate of nucleophilic vinylic substitution
Authors: Jonas Jaroslav , Mazal Ctibor , Rappoport Zvi
Published: January 2005

The label incorporation and Z → E isomerization in the reaction of 3‐azidomethylenedihydro‐(3H)‐furan‐2‐one with Na15NN2 in 1:1 water–acetone were measured as a probe for internal clockwise vs anticlockwise rotation in the intermediate carbanion.
Topological analysis of electronic charge densities as a tool to study protonation effects on thiocarbonyl compounds
Authors: Yáñez O. MÓ M. , Esseffar M. , Abboud J.‐L. M.
Published: January 2005

The substituent effects on the intrinsic basicity of a wide variety of thiocarbonyl compounds were investigated by means of a topological analysis of the electronic charge densities and their Laplacians for the neutral and the protonated species, and also by means of their harmonic vibrational frequencies. For the sake of comparison, a similar analysis was carried out for a reduced set of carbonyl compounds with similar substituents. The results show that the behaviour of the thiocarbonyl group with regard to the protonation process is similar to that predicted for the carbonyl group, in the sense that both groups are not much affected by protonation. The charge transferred to the proton results basically in a polarization and, in some cases, in a depopulation of the bonds in which the thiocarbonyl carbon atom participates. Accordingly, the intrinsic basicities of these kinds of compounds depend strongly on the ability of the substituents to be polarized. This conclusion seems to be ratified also by the shiftings undergone by the C=S stretching frequencies on protonation.
Linear solvation energy relationships between electrolyte pK values and solvent properties for several 2‐methylpropan‐2‐Ol–cosolvent mixtures
Authors: Bosch Elisabeth , Rived Fernando , Rosés Martí
Published: January 2005

The dissociation pK values of picric acid, tetrabutylammonium picrate, bromide and hydroxide and tetramethylammonium hydroxide in some 2‐methylpropan‐2‐ol–cosolvent mixtures were determined and correlated with the Taft and Kamlet solvatochromic parameters π*, δ, α and β. The results show the most important solvent properties that affect electrolyte dissociation are polarity, polarizability and hydrogen bond acidity. These results were confirmed by analysis of published literature data.
Interrelations Of the energetics of amides and alkenes: Enthalpies of formation of N,N‐dimethyl derivatives of pivalamide, 1‐adamantylcarboxamide and benzamide, and of styrene and its α‐, trans‐β‐ and β,β‐methylated derivatives
Authors: Abboud José‐Luis M. , Jiménez Pilar , Roux M. Victoria , Turrión Concepcióon , Lopez‐Mardomingo Carmen , Podosenin Andrew , Rogers Donald W. , Liebman Joel F.
Published: January 2005

The enthalpies of formation of the condensed phase and gaseous N,N‐dimethyl derivatives of pivalamide, 1‐adamantylcarboxamide and benzamide were determined by combustion calorimetry and the associated enthalpies of vaporization and sublimation. The enthalpies of formation of styrene and its α‐, trans‐β‐ and β,β‐methylated derivatives were determined from measurements of their enthalpies of hydrogenation in dilute hydrocarbon solution. Strain and resonance effects of amides and alkenes are discussed in terms of the exo‐/endothermicity of the following reactions:

equation image

and in terms of the difference of enthalpies of formation of the isomeric (Z)‐ and E‐RCHCHCH3.
Photoisomerization of 3‐benzoylacrylates on a silica gel surface: Effect of reaction environment on selectivity
Authors: Hasegawa Tadashi , Yamazaki Yuko , Yoshioka Michikazu
Published: January 2005

On irradiation on a dry silica gel surface, 2‐(N, N‐dialkylamino)ethyl 3‐benzoylacrylates undergo selective E‐Z isomerization. Competing processes, such as remote‐hydrogen abstraction via a charge‐transfer state, with the photoisomerization in solution are completely suppressed on the surface. The yield of the Z ‐ from the E‐ isomer increases with increase in the coverage of the E‐isomer on the surface, reaching a limiting value. Thermal isomerization of the Z‐ to the E‐ isomer occurs easily on the silica gels surface when the alkyl group on the nitrogen atom is small. Benzoylacrylates without any amino group also undergo selective photoisomerization.
Living polymerization of methacrylic esters with aluminium porphyrin initiators. Axial ligand exchange activities of alkyl‐ and enolate‐aluminium porphyrins in relation to the polymerization Mechanism
Authors: Aida Takuzo , Sugimoto Hiroshi , Kuroki Masakatsu , Inoue Shohei
Published: January 2005

Polymerization of methacrylic esters such as benzyl methacrylate using as initiator an‐equimolar mixture of methylaluminium 5,10,15,20‐tetraphenylporphine [(TPP)AlMe] and 2,7,12,17‐tetramethyl‐3,8,13,18‐tetramethylporphine [(EtioP)AlMe] proceeded from both initiators, affording a unimodal polymer of narrow molecular weight distribution, although the reactivities of (TPP)AlMe and (EtioP)AlMe are very different from each other. 1H NMR studies on a mixture of two different (porphinato)aluminium enolates, the growing species, and a mixture of a (porphinato)aluminium enolate and an alcoholate, in the absence and presence of methyl methacrylate (MMA or MMA‐d8), indicated an acyclic transition state polymerization mechanism by the participation of two aluminium porphyrin molecules, where the growing species always exchange their enolate ligands whenever it grows.
‘Living’ and controlled radical polymerization
Authors: Matyjaszewski Krzysztof , Gaynor Scott , Greszta Dorota , Mardare Daniela , Shigemoto Takeo
Published: January 2005

Radical polymerizations cannot truly be ‘living’ because of the inevitable termination between growing radicals. However, relatively good control of molecular weights, polydispersities and terminal functionalities can be achieved by using either unimolecular or bimolecular exchange between growing radicals and dormant chains. The dormant chains can be in the form of either covalent species or organometallic compounds. Some systems based on alkoxyamines, organochromium compounds, organoaluminum compounds and alkyl iodides were studied and are discussed in detail.
Oscillations of electrical potential differences across the interface in phase‐transfer catalytic systems
Authors: Srivastava R. C. , Agarwala V. , Upadhyay S. , Varghese V. A. , Sahney R.
Published: January 2005

Oscillations of electrical potential differences across the liquid–liquid interface in phase‐transfer catalyst systems are reported. The occurrence of the oscillations is consistent with the Starks' shuttling mechanism.
Tributylammonium cyanamidate BU3N+–N−–C≡N: A ‘super‐basic’ nitrile group more basic, on the hydrogen‐bond basicity scale, than any amine or pyridine
Authors: Chardin Aurélie , Berthelot Michel , Laurence Christian , Morris David G.
Published: January 2005

An IR spectroscopic study of the hydrogen bonding of Bu3N+N−C≡N with 4‐fluorophenol showed that the site of complexation is the nitrogen of the nitrile function. THe formation constant of the 1:1 complex in CCl4 indicates that this cyanamidate is a stronger hydrogen‐bond base than is any nitrile, amine or pyridine. The Bu3N+–N− group increases the basicity of the nitrile group very efficiently because of the conjugation of two lone pairs on the anionic nitrogen with the π systems of the cyano group. This conjugation is also exemplified by the very low ν(C≡N) wavenumber (2104 cm−1).
Substitutent effects in monosubstituted benzenes: Semi‐empirical SCF studies of the Hammett constants
Authors: Monaco Regina R. , Gardiner William C.
Published: January 2005

Semi‐empirical SCF calculations using the AM1 Hamiltonian were shown to account for the Hammett σ constants and other properties of a representative series of 22 monosubstituted benzenes in terms of the atomic charges at the ipso, ortho, meta and para positions. The trends of the correlations with experimental σ constants were found to follow the normal expectations of physical organic chemistry. Additional support for the AM1 charge distributions was obtained in correlations with the 13C chemical shifts of 12 of the test molecules. On the other hand, no correlations were found between σ constants and computed force constants for bending peripheral H atoms out of the plane of the aromatic ring, supporting the view that Hammett σ constants reffect charge distributions and not secondary effects expressed in the stiffness of bonds.
Influence of Tester Geometry, Speed and Procedure on the Results from a Ring Shear Tester
Authors: Schmitt Rüdiger , Feise Hermann
Published: January 2005

Automated ring shear testers have gained widespread acceptance in the chemical industry. In this paper, comparative measurements with different shear testers are described and possible factors influencing the measurement of flowability, are discussed. The measurement results presented show a dependency on the bulk solid investigated. No significant influence of the shear tester was measured for easy flowing bulk solids. An influence of the shear tester is observed for poor flowing, compressible bulk solids. Experiments have shown that test procedure and shear cell design (tester geometry) affect the measurements considerably.
Nonlinear current–voltage characteristics and recombination current instability in p‐Ge(Au)
Authors: Kamilov I. K. , Ibragimov Kh. O. , Aliev K. M. , Abakarova N. S.
Published: January 2005

Results of an experimental study of short and long p‐Ge(Au) samples are presented and compared qualitatively with data furnished by the one‐dimensional theoretical model describing the evolution of domain instability in a two‐parametric space “voltage V–emission coefficient β”. According to the theory, single, double‐ and multi‐subdomain states and order–disorder–order transitions via intermittency have been observed in the system with increasing voltage. Three operation regimes of the system are found, depending on the region of the parametric space: ohmic, quenched (pulsing) and transit‐time. In short samples a second portion with S‐switching is revealed in the current–voltage characteristic. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionic conduction studies in P(VDF–HFP)–LiAsF6–(PC + DEC)–fumed SiO2 composite gel polymer electrolyte system
Authors: Saikia D. , Kumar A.
Published: January 2005

In the present work, thin polymer electrolyte films of P(VDF–HFP) copolymer containing LiAsF6 salt dissolved in PC and DEC and fumed SiO2 submicron particles as dispersed phase prepared by solution casting technique are characterized by ac impedance measurements in the temperature range 303 K–373 K. Maximum ionic conductivity for P(VDF–HFP)–(PC + DEC)–LiAsF6–SiO2 fumed composite gel polymer electrolyte is found to be of the order of 10–3 S/cm at room temperature. XRD patterns show the increased amorphicity in the electrolytes. The degree of crystallinity is decreased from 30% in pure polymer to 17.7% in composite gel polymer electrolyte. Scanning electron micrographs show uniform dispersion of SiO2 particles and suggest that SiO2 supports formation of porous microstructures and increases the retaining capability of liquid electrolyte in the polymer gel network. FTIR spectral analyses confirm the polymer/salt/filler interaction. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bonding of Cr and V in FeAl B2 phase
Authors: Fuks D. , Strutz A. , Kiv A.
Published: January 2005

Ab initio calculations of the properties of the FeAl B2 phase alloyed by Cr or V are performed on the basis of the full potential augmented plane‐wave (APW) + local orbitals (lo) method. The site preference occupation for Cr and V atoms in this compound is investigated. We studied the changes in the site preference for Cr and V substituting for Fe or Al when the vacancy on the Fe site is formed. Existence of the vacancy significantly changes the site occupation preference for Cr that transits from the Al site to the Fe site. The site occupation preference for these alloying elements in the compound is explained in terms of the electronegativity of surrounding atoms and the effective charges of transition metals. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Refractive index and third‐order nonlinear susceptibility of C60 in the condensed phase calculated with the discrete solvent reaction field model
Authors: Jensen L. , Van Duijnen Piet Th.
Published: January 2005

We have calculated the frequency‐dependent refractive index and the third‐order nonlinear susceptibility for C60 in the condensed phase, which is related to third‐harmonic generation (THG) and degenerate four‐wave mixing (DFWM) experiments. This was done using the recently developed discrete solvent reaction field (DRF) model, which combines a time‐dependent density functional theory (TD‐DFT) description of the central C60 molecule with a classical polarizable MM model for the rest of the fullerene cluster. Using this model, effective microscopic properties can be calculated that, combined with calculated local field factors, give macroscopic susceptibilities. The largest calculation was for a cluster of 63 C60 molecules in which the central molecule was treated with TD‐DFT. For this molecule, the effective polarizability was increased with about 15% and the effective second hyperpolarizability with about 60% compared with the gas phase. The calculated refractive index was found to be in good agreement with experiments and other theoretical results. The agreement with THG experiments was within a factor of two, whereas for DFWM the agreement was less good due to the neglect of vibrational contributions in the calculations. It was found that it is more important to account for the dispersion in the third‐order susceptibilities than in the corresponding second hyperpolarizability. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Computational study of dimethyl phosphate anion and its complexes with water, magnesium, and calcium
Authors: Petrov Anton S. , Funseth‐Smotzer Joni , Pack George R.
Published: January 2005

Dimethyl phosphate anion (DMP−) is often used to simulate the properties of the phosphate group, an important structural fragment of nucleic acids and phospholipids. Besides its functional importance, DMP− has a strong affinity for metal cations and is often considered to be their binding site. In this study we reevaluate the binding properties of DMP− with water molecules and with explicitly hydrated magnesium and calcium cations in the presence of a polar continuum solvent. We analyze the stability of the DMP− in different conformations that represent possible inner‐ and outer‐sphere binding modes. Our previous work (Petrov et al. J Phys Chem B 2004) has shown that electrostatic calculations, particularly those using a point‐charge model, are wholly inadequate for this purpose. Calculations were performed at the B3LYP/6‐31G(d,p) level of theory within the framework of the COSMO polarized continuum model (CPCM). Our data indicate that magnesium prefers outer‐sphere coordination with DMP−, whereas calcium binds directly. The effect of cation binding on vibrational infrared and Raman spectra are also discussed. We found that the inclusion of polar solvent in the computations improves the agreement between calculated spectral data and experimental results. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Theoretical studies on cosolvation of Li ion and solvent reductive decomposition in binary mixtures of aliphatic carbonates
Authors: Wang Yixuan , Balbuena Perla B.
Published: January 2005

We use density functional theory to investigate the interactions of Li+ and aliphatic carbonates such as ethylene carbonate and three linear carbonates (dimethyl, diethyl, and ethyl methyl), and the reductive decomposition mechanisms of these carbonates. On the basis of theoretical results and analyses, some phenomena relevant to the formation of a solid electrolyte interphase layer at the electrode surface of lithium ion batteries are well explained. This study also illustrates that theoretical analyses and calculations are able to provide useful insights into the design of components for modern power systems. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
New unitary transformation for the three coupled oscillators
Authors: Hong‐Yi Fan
Published: January 2005

A new unitary operator U, which can transform the Fock space of a three‐dimensional isotropic harmonic oscillator into the space in which the Hamiltion of three coupled oscillators is diagonized, is found. The coordinate representation of U is presented and is used to directly derive the wave function of the energy eigenstate of the coupled oscillators.
Explicit density–potential relation for 4‐electron atoms in 2‐orbital S states
Authors: Hunter G. , March N. H.
Published: January 2005

An explicit relation is derived between the one‐body potential energy and the electron density for the ground state of the Be atom in a nonrelativistic framework. This same relation applies to any four‐electron atomic ion (or to Be itself) in a state where the electrons occupy two doubly filled orbitals. The relation is interpreted as an exact Hartree‐like model of the Hohenberg–Kohn theorem within the general context of N electrons and a potential that is not necessarily spherically symmetrical.
Electronic structure of helium‐trapped vacancy in aluminum using multiple scattering Xα method
Authors: Iyakutti K. , Sankar S. , Thiagarajan M.
Published: January 2005

The self‐consistent multiple scattering Xα (MSXα) method is used to arrive at the electronic structure of a helium‐trapped vacancy in aluminum using a cluster model. The calculated orbital energies, electron density, and charge distributions are compared with the available theoretical results. It is shown that helium trapping causes the reshuffling and upward movement of the cluster levels (with vacancy).
Analysis of degeneracy in the spectrum of a class of molecular graphs
Authors: Ojha P. C.
Published: January 2005

We consider the Hückel approximation to the π‐electron spectrum of molecules which are built by linking a number of identical fragments to a central atom in an identical manner. The Hückel matrix H of the composite molecule (or equivalently the adjacency matrix of the molecular graph) is simply related to the Hückel matrix h of the fragment and a vector \documentclass{article}\pagestyle{empty}\begin{document}$ vec{f} $\end{document} which encodes the bonding of a fragment to the central atom. The eigenvalues and eigenvectors of H are obtained from those of h. The orbitals of the composite molecule are of three types: (1) a molecular orbital of the fragment localized on one of the fragments, (2) a molecular orbital of the fragment spread over more than one fragment, and (3) orbitals spread over the entire molecule including the central atom. The orbital energies Λ of the first two types of orbitals are same as the orbital energies λ of the fragment. Energies of the third type of orbitals separate a subset of orbital energies of the fragment and, barring accidental degeneracy, they are distinct from all orbital energies of the fragment. It is only through the third type of orbitals that the composite molecule manifests itself as a new entity rather than an aggregate of noninteracting fragments. It is shown that the graph group of H fails to explain its degeneracy if any eigenvector of the subgraph, not orthogonal to the connection vector \documentclass{article}\pagestyle{empty}\begin{document}$ vec{f} $\end{document}, belongs to a degenerate manifold of h. This solves a long‐standing puzzle regarding degeneracy in the Hückel spectrum of triphenylmethyl.
Algebrants in many‐electron quantum mechanics: Applications of generalized determinants or matrix functions
Authors: Poshusta R. D. , Kinghorn D. B.
Published: January 2005

We define the algebrant, a mathematical generalization of the determinant, the immanant, the permanent, and the Schur functions. Algebrants are classified as multilinear matrix functions or multicomponent symmetrized tensors. In applications, such as N‐electron quantum mechanics, where extensive computation is required, it is vital to reduce computational effort, e.g., the well‐known N‐factorial problem. We derive certain mathematical properties that can be incorporated in efficient computing algorithms for algebrants. Foremost is our “elimination theorem,” which allows (in important special cases) zeros to be introduced into an algebrant in close analogy with Gaussian elimination for determinants. Savings accruing from such elimination can be substantial. We show examples from Matsen's spin‐free quantum chemistry where elimination effectively removes the N‐factorial problem that has hitherto stifled possible applications.
Symmetric‐group algebraic variational solutions for Heisenberg models at finite temperature
Authors: Klein D. J. , Seitz W. A.
Published: January 2005

The Heisenberg spin Hamiltonian for a collection of N spin‐1/2 sites is viewed, as favored by Professor Matsen, to be an element of the group algebra of the symmetric group 𝒮N. Several computationally tractable, variational group–algebraic approximations for the finite‐temperature density matrix are made so as to minimize the Gibb's free–energy functional. Relations to previous quite differently motivated approximations are identified, though improvements are noted with the present approach.
The Berry phase in molecular physics
Authors: Bohm A. , Kendrick B. , Loewe Mark E.
Published: January 2005

The geometric phase of quantum mechanics is introduced, and its physical effects are then studied in the context of molecular physics. By performing the most general Born–Oppenheimer procedure, we show how gauge groups appear in the study of molecules. This method is then applied to the doubly degenerate Λ‐levels of a diatomic molecule. The resulting dynamics for the slow angular motion of the dumbbell is equivalent to that of a Dirac monopole.
On the internally contracted multireference CI method with full contraction
Authors: Siegbahn Per E. M. , Svensson Mats
Published: January 2005

The configuration interaction (CI) method where the efficiency of the generators of the unitary group is most fully exploited is the internally contracted multireference CI method. In the most recent version of this method the semi‐internal configurations were kept uncontracted, which means that the number of configurations can still be quite large. In the present study the necessary formulas are derived for the case where the semi‐internal states are also contracted. The highest density matrix that appears in these formulas is of order 5, and the computational treatment of this large matrix is discussed in detail.
Improved quadrature methods for the Fourier transform of a two‐center product of exponential‐type basis functions
Authors: Homeier Herbert H. H. , Steinborn E. Otto
Published: January 2005

The numerical properties of a one‐dimensional integral representation [H. P. Trivedi and E. O. Steinborn, Phys. Rev. A 27, 670 (1983)] for the Fourier transform of a two‐center product of certain exponential‐type orbitals (ETOs), the B functions [E. Filter and E. O. Steinborn, Phys. Rev. A 18, 1 (1978)], are examined. These functions span the space of ETOs. Hence, molecular integrals for other ETOs, like the more common Slater‐type orbitals, may be found as finite linear combinations of integrals with B functions. The main advantage of B functions is the simplicity of their Fourier transform that makes the derivation of relatively simple general formulas for molecular integrals with the Fourier transform method possible. The integrand of the integral representation mentioned above shows sharp peaks, making, in the cases of highly asymmetric charge distributions and/or large momentum vectors, usual quadrature methods rather slow. New quadrature schemes are presented that utilize Möbius‐transformation‐based quadrature rules. These rules are well suited for the numerical quadrature of functions possessing a sharp peak at or near one boundary of integration [H. H. H. Homeier and E. O. Steinborn, J. Comput. Phys. 87, 61 (1990)]. Numerical results are presented that illustrate the fact that the new quadrature schemes are much more efficient than are automatic quadrature routines.
Theoretical prediction of ionization potential, electron affinity, and electronic spectrum of the S2N radical
Authors: Sannigrahi A. B. , Peyerimhoff S. D.
Published: January 2005

Ab initio MRD–CI calculations using a basis set of near Hartree–Fock quality have been carried out to calculate the ground‐state electronic structure of S2N+, S2N, and S2N− and the ionization potential, electron affinity, and vertical electronic spectrum of S2N. At the highest level of theory (estimated full CI or FCI), S2N+ is predicted to have a linear structure with r(NS) = 1.51 Å. For S2N and S2N−, the minimum in energy at the FCI level corresponds to a quasi‐linear [with a barrier height to linearity of about 2.0 kcal mol−1, ] and a bent structure , respectively. The adiabatic/vertical ionization potential and electron affinity of S2N are predicted to be 7.26/7.82 and 1.60/0.79 eV, respectively. Of the several electronic transitions in S2N considered, the ones with the excitation energy of 1.87 eV (X2 A1 → 2B2) and 2.87 eV (X2A1 → 2B2) are somewhat intense (ƒ = 0.005 and 0.002) and likely to be observed.
Modification of the superposition of correlated configurations method
Authors: Firszt M. , Woźnicki W.
Published: January 2005

Introduction of a modified correlation factor in the place of r eliminates the problem of multiple infinite summations in Hamiltonian matrix elements. Calculations performed for several He states show that the introduction of the modified correlation factor does not change energies of the states by more than 1 cm−1.
A quantum chemical study of interchain hopping model of negatively charged solitons in polyacetylene
Authors: Tachibana Akitomo , Ishikawa Shigeru , Asai Yoshihiro , Katagiri Hideki , Yamabe Tokio
Published: January 2005

Phonon‐assisted interchain hopping of negatively charged solitons in polyacetylene has been studied using a local chemical reaction model CH + CH4 → CH4 + CH. Quantum chemical characteristics of the electron transfer process have been analyzed in terms of the dynamic electron density and the mutual polarization moment. The CH stretching vibrational motion of CH4, which is a local model of the sp3 defect, has been found to play a significant role for the electron transfer. The excitation of the corresponding vibrational mode of the sp3 defect would promote the interchain hopping of the charged soliton. The electron transfer process has also been studied in terms of the “regional” density functional theory. It has been shown that the driving force of the electron transfer is represented by the regional chemical potentials.
Accurate local spin‐polarized exchange potential: Reconciliation of generalized Slater and Kohn–Sham methods
Authors: Krieger J. B. , Li Yan , Iafrate G. J.
Published: January 2005

Using simple physical arguments, a local spin‐polarized exchange potential, Vxσ, is constructed from the single‐particle Hartree–Fock (HF) potentials (generalized Slater method) that reduces to the usual Kohn–Sham (KS) result in the uniform gas limit. Numerical results for 10 closed subshell atoms demonstrate that the total energy calculated employing this Vxσ is closer to the exact KS results than those of other standard exchange approximations with electron densities and highest occupied orbital eigenvalues that closely approximate the HF results.
Computational studies of the 3‐Dimensional structure of cyclopenta polycyclic aromatic hydrocarbons containing a gulf region
Authors: Venegas Ruben E. , Reggio Patricia H. , Rabinowitz James R.
Published: January 2005

Recently, some cyclopenta‐fused polyaromatic hydrocarbons, an environmentally relevant subclass of chemicals, have been shown to have carcinogenic activity in animals. It has been suggested that benz[l] aceanthrylene (I), an active member of this subclass with a gulf region, has a trans dihydrodiol metabolite that is nonplanar and has two distinct spatial configurations. We have used MMP2(85) and AM1 to investigate the three‐dimensional structure of this dihydrodiol and other similar derivatives of (I) and have found that although (I) is somewhat nonplanar the relevant derivatives are all nearly planar. Further, we have computed potential functions for the bending of the angular ring in the gulf region using MMP2(85), AM1, and ab initio computed energies for AM1 spatial configurations and find that these molecules all have only a single potential minimum. We have performed the same calculations for benzo[c]phenanthren and its 1,12 dimethyl derivative, molecules with a similar gulf region for which crystallographic data exists. In agreement with that data, we find that two distinct spatial configurations exist separated by significant barries. The differences between the results generated by the three different methods of computation will be discussed.