bluuebunny/crossref_metadata_2025 huggingface dataset:
Der oxydative Abbau von Roridin A, ein weiterer Beweis für die Art der Verknüpfung der Roridinsäure mit Verrucarol. Verrucarine und Roridine, 17. Mitteilung [1]
Authors: Achini R. , Tamm Ch.
Published: December 2004

Epoxidation of di‐O‐acetyl‐roridin A (2) gave the two mono‐epoxides 3 (not pure) and 4 (main product) and the di‐epoxide 5. Subsequent treatment of 4 with ozone and NaBH4 led to the esters 6 and 8. They yielded the acetylderivatives 7 and 9 respectively. Since the degradation products prove the sites of the ester linkages also in roridin A (1), the structure of this antibiotic is proved beyond any doubt.
Ringöffnung von Nitrothiazolen
Authors: Ilvespää Atso O.
Published: December 2004

The reaction between 2‐halogeno‐5‐nitro‐thiazoles and amines has been studied. Especially the sterically hindered strongly basic secondary aliphatic amines tend to cause opening of the thiazole ring system, resulting in the formation of the heretofore unknown (1‐nitro‐2‐amino‐vinyl)‐thiocyanates. The ring opening is favored by a highly polar solvent, such as dimethyl sulfoxide. A simple reaction mechanism is proposed and some properties of these new compounds are discussed.
Menschliches Calcitonin I. Isolierung und Charakterisierung
Authors: Riniker B. , Neher R. , Maier R. , Kahnt F. W. , Byfield P. G. H. , Gudmundsson T. V. , Galante L. , Macintyre I.
Published: December 2004

Two highly active calcitonin peptides, M with 32 amino acids, and D a dimer of M, were isolated from a large human mediastinal C cell tumour. D can easily be transformed into M by the action of 1N ammonia; D and M afford two different sulphoxides, but all four peptides yield the same product upon oxidation with performic acid. Both D and M have a potency of about 120 MRC units/mg dry weight; their sulphoxides, by contrast, are almost inactive. Tryptic digestion of M produces an N‐terminal octadecapeptide (TrI) and a C‐terminal tetradecapeptide (TrII), the latter being also obtained from D. Amino acid analysis and other analytical data are presented. The structure of the human calcitonin peptides D and M is thus very different from that of porcine α‐thyrocalcitonin.
Beiträge zur Chemie der Si‐N‐ Bindung, XVI [1] Umsilylierungen an 1,3‐Bis‐dimethylchlorsilyl‐1,3‐diaza‐2,2,4,4‐tetramethyl‐cyclodisilazan
Authors: Fink Walter
Published: December 2004

Die Umsetzung von Diphenyldichlorsilan mit 1, 3‐Bis‐dimethylchlorsilyl‐1, 3‐diaza‐2,2,4,4‐tetramethyl‐cyclodisilazan in den molaren Verhältnissen 1:1 bis 4:1 führt zu isomeren partiell und per‐phenylierten 1, 3‐diorganochlor‐funktionellen Cyclodisilazanen, die isoliert und identifiziert werden.
Untersuchungen an Kobalt‐Zink‐Hydroxid, Co3Zn2(OH)10, 2H2O
Authors: Günter J. R. , Oswald H. R.
Published: December 2004

A new cobalt‐zinc‐hydroxide with the composition Co3Zn2(OH)10 · 2 H2O is described. The X‐ray powder diffraction pattern can be indexed with a monoclinic cell, a = 5.49 Å, b = 6.22 Å, c = 15.45 Å, β = 100.7º. A possible structure of this new compound, with cobalt ions in octahedral and zinc ions in tetrahedral coordination, is proposed.
Photochemische Reaktionen. 48. Mitteilung [1]. Photolytische Substitutionen von Aromaten mit α‐Sulfonyloxyketonen. Vorläufige Mitteilung
Authors: Tuinman A. , Iwasaki [2] S. , Schaffner K. , Jeger O.
Published: December 2004

Photo‐excited arenes have been found to initiate a substitution reaction in which the sulfonyloxy group of α‐sulfonyloxyketones is displaced, and the corresponding β‐arylketones are formed. Evidence is presented that the electronically excited arene need not be involved directly in the substitution step. It would seem to be more likely that upon interaction with the sulfonyloxyketone a reactive species derived from the latter is produced which is capable of aromatic substitution.
Kupferkomplexe von Bisamiden, III Oxamidsäurederivate als dreizähnige Liganden
Authors: Kaden Th. , Zuberbühler A.
Published: December 2004

By potentiometry and spectrophotometry Cu2+ and N‐(2‐dimethylaminoethyl)‐oxamide are shown to form different mononuclear complexes and a binuclear species containing a hydroxo bridge. Visible absorption spectra of each species were obtained by an interactive process and used to assign definite structures to them. Stability constants and concentrations of each complex were calculated from the potentiometric data. The ligand behaves as a tridentate chelating agent, and hydrolysis of one coordinated water molecule predominates over deprotonation of the second amid group.
Zur Thermodynamik der Metallcarbonate. 2. Mitteilung [1]. Löslichkeitskonstanten und Freie Bildungsenthalpien von Cu2(OH)2CO3 (Malachit) und Cu3(OH)2(CO3)2 (Azurit) bei 25°C
Authors: Schindler P. , Reinert M. , Gamsjäger H.
Published: December 2004

The solubilities of Cu2(OH)2CO3 (malachite) and Cu3(OH)2(CO3)2 (azurite) have been studied at 25° C in solutions of the constant ionic strength 0,2 M consisting primarily of sodium perchlorate. From experimental data the following values for equilibrium constants and Gibbs energies of formation are deduced:

Predominance area diagrams for the ternary system Cu2+H2O‐CO2(g), including CuO, Cu(OH)2, Cu2(OH)2CO3, Cu3(OH)2(CO3)2, Cu2+ and Cu (CO3)22−, are given.
Contribution à l'étude du système quaternaire K+—NH4+—CrO4−−—SO4−−—H2O: I. les isothermes de 25° des systèmes ternaires limites
Authors: Flatt R. , Brunisholz G. , Merbach A.
Published: December 2004

The four ternary limiting isotherms of the system K+− NH4+CrO4−−SO4−−H2O are given for 25° C. In the systems K2SO4(NH4)2SO4H2O and K2SO4K2CrO4H2O only one solid phase has been encountered; both systems belong to the type I of the ROOZEBOOM classification. A miscibility gap is present in the systems (NH4)2CrO4K2CrO4H2O and (NH4)2CrO4(NH4)2SO4H2O; they belong to ROOZEBOOM'S type V.
Sur les constituants odorants de l'essence absolue de Cassie (Acacia farnesiana WILLD.)
Authors: Demole E. , Enggist P. , Stoll M.
Published: December 2004

The absolute oil of cassie (Acacia farnesiana WILLD.) has been thoroughly investigated by using several combined chromatographic techniques. Among the 38 new constituents which were thus identified in this oil, four deserve a particular mention, namely, the cis‐3‐methyldec‐3‐en‐1‐ol (I), the related acid III, the trans‐3‐methyl‐dec‐4‐enoic acid (IV), and the homoterpene lactone dihydroactinidiolide (II). With the exception of the last one, these unusual C11 compounds play a prominent role in the characteristic fragrance of cassie oil.
Contribution à l'étude du système quaternaire KCI‐RbCI‐H2O: I. Les isothermes de 25° des systèmes ternaires limites
Authors: Merbach A. , Gonella J.
Published: December 2004

The three ternary limiting isotherms of the system KCI‐RbCI‐CsCI‐H2O are given for 25°. The system KCI‐RbCI‐H2O, with only one solid phase present, belongs to the type I of the ROOZEBOOM classification. A large miscibility gap is present in the systems RbCI‐CsCI‐H2O and KCI‐CsCI‐H2O; in the latter the incorporation is almost negligible; they belong to ROOZEBOOM's type IV.
Darstellung und spektroskopische Untersuchungen von Kupferkomplexen mit verschiedenen Mikrostrukturen. I. Halogeno‐Stickstoffbasen‐Kupfer (II)‐Komplexe
Authors: Ludwig W. , Gasser F.
Published: December 2004

Es wird über Darstellung und spektroskopische Untersuchungen von Kupfer (II)‐Komplexen CuL2X2 und CuL4X2 mit grösstenteils unidentaten Stickstoffbasen berichtet. Durch Ausnützung der Einflüsse von Substitutenten am Pyridin‐ bzw. Piperidinring der Liganden L wurden Komplexe verschiedener Stereometrie erhalten, an denen sich der Zusammenhang zwischen Mikrosymmetrie und Elektronenspektren studieren liess. Insbesondere konnte die Stauchung eines pseudotetraedrischen Teilchens über eine Reihe von Zwischenstufen bis zur planaren Anordnung der 4 Ligandatome anhand einer Anzahl von Verbindungen des Type CuL2X2 verfolgt werden. Die Arbeit befasst sich dabei im wesentlichen mit den Ligandenfeldspektren (über die Elektronentransfer‐Übergange sol1 später berichtet werden). Der letzte Ligandenfeldübergang tritt bei den planaren Komplexen ‐ offenbar wegen. Abschirmung des Zentral‐Ions vor Störungen längs der z‐achse bei unerwartet hoher Energie auf.
Stoffwechselprodukte von Mikroorganismen 73. Mitteilung [1] Chlorothricin und Des‐chlorothoricin
Authors: Keller‐Schierlein W. , Muntwyler R. , Pache W. , Zähner H.
Published: December 2004

A crystalline mixture of the antibiotics chlorothricin and dechlorothricin was isolated from a strain of Streptomyces antibioticus. By degradation 5‐chloro‐6‐methylsalicylic acid methyl ether (from chlorothricin) and 6‐methylsalicylic acid methyl‐ether (from dechlorothricin) were isolated. Common degradation products of both antibiotics were 2‐deoxy‐D‐rhamniose and an aglycone, C30H38O8, of unknown structure. The antibiotic mixtures was active against GRAM positive bacteria on syntheitc, but not on complex media.
Niederdruck‐Oligomerisation von Mono‐Olefinen mit löslichen Nickel/Aluminium‐Bimetallkatalysatoren, Teil II Reaktionskinetische Untersuchungen über die Dimerisation von Propen
Authors: Onsager Olav‐Torgeir , Wang Hagbarth , Blindheim Ulf
Published: December 2004

The kinetics of the dimerization of propene in organic solvents under the influence of a homogeneous catalyst containing π‐tetramethylcyclobutadiene‐nickel dichloride and a prereacted mixture of ethylaluminiumdichloride and tri‐n‐butylphosphin are reported. The primary reaction products are: 2‐methyl‐1‐pentene, 4‐methyl‐2‐pentene (cis/trans), 2,3‐dimethyl‐1‐butene and 2‐Hexene (cis/trans) The results are in accordance with a coordinative mechanism on nickel. New results on the reaction between ethylaluminiumdichloride and O, N and P containing electrondonors are also discussed.
Allongement de la chaîne carbonée d'un aldéhydosucre à groupements hydroxyles bloqués par l'utilisation d'ylides du phosphore non stabilisés
Authors: Tronchet J. M. J. , Doelker E. , Baehler Br.
Published: December 2004

The action of the unstabilized WITTIG reagents methylene triphenylphosphorane and methoxymethylene triphenylphosphorane on 2,3:4,5‐di‐O‐isopropylidene aldehydo‐L‐arabinose led with acceptable yields to the corresponding unsaturated sugars, providing a direct route for a one‐carbon chain extension in the carbohydrate series.
Synthèse de quelques dérivés de l'amino‐3‐désoxy‐3‐érythrose et l'amino‐3‐désoxy‐3‐érythrose D‐3
Authors: Tronchet J. M. J. , Graf R. , Tronchet Mme J.
Published: December 2004

The synthesis of derivatives of 3‐amino‐3‐deoxy‐L‐erythrose by LAH or LAD reduction of the oxime of 1,2‐O‐isopropylidene α‐L‐glycero‐tetros‐3‐ulofuranose is described.
Solvolyse von 3,17‐Dioxo‐19‐mesyloxy‐Δ4‐androsten. Über Steroide, 216. Mitteilung
Authors: Wieland P. , Anner G.
Published: December 2004

3,17‐Dioxo‐19‐mesyloxy‐Δ4‐androstene was reacted with lithiumchloride in isopropanol. In addition to the mainly formed 3,17‐dioxo‐19‐chloro‐Δ4‐androstene two side products were isolated and identified as 6ß‐methylestrone and 3,17‐dioxo‐B‐homo‐Δ4,6‐19‐norandrostadiene.
Sur les carbonates basiques de fer (III): III. Préparation, radiocristallographie et spectres IR. du (NH4)4Fe2(OH)4(CO3)3·3H2O
Authors: Dvořák V. , Feitknecht W.
Published: December 2004

The obtention of the crystalline basic carbonate of iron (III) and ammonium, (NH4)4Fe2(OH)4(CO3)3 · 3 H2O, is described, and its formula is established by chemical analysis and infrared spectroscopy. The compound is probably monoclinic, but it was not possible to index with certainty all X‐ray reflections. The compound is similar to (NH4)2Fe2(OH)4(CO3)2 · H2O and its infrared spectrum leads to the assumption that in both the CO group is linked in the same fashion.
Contribution à l'étude du dosage de traces d'acide borique par luminescence
Authors: Marcantonatos M. , Gamba G. , Monnier D.
Published: December 2004

A highly sensitive luminescent reaction is proposed for the determination of submicrotraces of boric acid by complexation with dibenzoylmethane in ether‐concentrated sulfuric acid. The optimal conditions of complex formation between boric acid and dibenzoylmethane are investigated, luminescence spectral caracteristics of the solutions of the complex are described, and the phosphorescence mean lifetime of the dibenzoylmethane‐boric acid system is evaluated. Analytical curves, established by fluorimetry and phosphorimetry, are satisfactory. 0.0005 μg B/ml is the minimum detectable concentration.
Cuprous complexes and dioxygen, VII. Competition between one‐ and two‐electron reduction of O2 in the autoxidation of Cu(1‐methyl‐2‐hydroxymethyl‐imidazole)2+
Authors: Zuberbühler Andreas D.
Published: December 2004

The complexation of 1‐methyl‐2‐hydroxymethyl‐imidazole (L) with Cu(I) and Cu(II) has been studied in aqueous acetonitrile (AN). Cu(I) forms three complexes, Cu(AN)L+, CuL2+, and Cu(AN)H−1L, with stability constants logK(Cu(AN)+ + L ⇌ Cu(AN)L+) = 4.60 ± 0.02, logβ2 = 11.31 ± 0.04, and logK(Cu(AN)H−1L+H+ ⇌ Cu(AN)L+) = 10.43 ± 0.08 in 0.15M AN. The main species for Cu(II) are CuL2+, CuH−1L+, CuH−1L2+, and CuH−2L2.

The autoxidation of CuL2+ was followed with an oxygen sensor and spectrophotometrically. Competition between the formation of superoxide in a one‐electron reduction of O2 and a path leading to H2O2 via binuclear (CuL2)2O was inferred from the rate law

with ka = (2.31 ± 0.12) · 104M−2S−1, kb = (1.0 ± 0.2) · 103M−1, kc = (2.85 ± 0.07) · 102M−2S−1, kd = 3.89 ± 0.14M−1S−1, ke = 0.112 ± 0.004, kf = (2.06 ± 0.24) · 10−10M S−1, kg = (1.35 ± 0.07) · 10−7 S−1, and kh = (6.8 ± 1.4) · 10−7M−1 S−1.
Structural Studies of 1,8‐Disubstituted Naphthalenes as Probes for nucleophile‐electrophile interactions
Authors: Schweizer W. Bernd , Procter Garry , Kaftory Menahem , Dunitz Jack D.
Published: December 2004

Results of crystal structure analyses of seven 1, 8‐disubstituted naphthalenes (2a, 8‐(N,N‐dimethylamino)‐1‐naphthyl methyl ketone; 2b, 8‐(N, N‐dimethylamino)naphthalene‐1‐carboxylic acid; 2c, methyl 8‐(N, N‐dimethylamino)naphthalene‐1‐carboxylate; 2d, 8‐methoxy‐1‐naphthyl methyl ketone; 2e, 8‐methoxynaphthalene‐1‐carboxylic acid; 2f, N, N‐dimethyl‐8‐methoxynaphthalene 1‐carboxamide; 2g, N, N‐dimethyl‐8‐hydroxynaphthalene‐1‐carboxamide) with a nucleophilic centre (N(CH3)2, OCH3, OH) at one of the peri positions and an electrophilic centre (carbonyl C) at the other are described. All seven molecules show a characteristic distortion pattern: the exocyclic bond to the electrophilic centre is splayed outward, and the one to the nucleophilic centre is splayed inward; the carbonyl C is displaced from the plane of its three bonded atoms towards the nucleophile. This distortion pattern differs from that found in other 1,8‐disubstituted naphthalenes and is interpreted as an expression of incipient nucleophilic addition to a carbonyl group. The crystal structure of 2b contains an ordered arrangement of equal numbers of amino acid and zwitterionic molecules.
Persistent inward currents in motoneuron dendrites: Implications for motor output
Authors: Heckman C. J. , Gorassini Monica A. , Bennett David J.
Published: December 2004

The dendrites of motoneurons are not, as once thought, passive conduits for synaptic inputs. Instead they have voltage‐dependent channels that provide the capacity to generate a very strong persistent inward current (PIC). The amplitude of the PIC is proportional to the level of neuromodulatory input from the brainstem, which is mediated primarily by the monoamines serotonin and norepinephrine. During normal motor behavior, monoaminergic drive is likely to be moderately strong and the dendritic PIC generates many of the characteristic features of motor unit firing patterns. Most of the PIC activates at or below recruitment threshold and thus motor unit firing patterns exhibit a linear increase just above recruitment. The dendritic PIC allows motor unit derecruitment to occur at a lower input level than recruitment, thus providing sustained tonic firing with little or no synaptic input, especially in low‐threshold units. However the dendritic PIC can be readily deactivated by synaptic inhibition. The overall amplification due to the dendritic PIC and other effects of monoamines on motoneurons greatly increases the input–output gain of the motor pool. Thus the brainstem neuromodulatory input provides a mechanism by which the excitability of motoneurons can be varied for different motor behaviors. This control system is lost in spinal cord injury but PICs nonetheless recover near‐normal amplitudes in the months following the initial injury. The relationship of these findings to the cause of the spasticity syndrome developing after spinal cord injury is discussed. Muscle Nerve, 2005
Symmetry properties of natural orbitals and geminals I. Construction of spin‐ and symmetry‐adapted functions
Authors: McWeeny R. , Kutzelnigg W.
Published: December 2004

Natural spin‐orbitals (NSO), natural spin‐geminals (NSG) and their spinless counterparts are not always adapted to the symmetry group of the Hamiltonian. Alternative orbitals and geminals that are always symmetry adapted and as close as possible to the NSO and NSG are defined and their properties are discussed. The expansion of the one‐ and two‐ particle density matrices ρ1 and ρ2 in irreducible tensor components is considered and the relations between the tensor components of ρ2 and the spin coupling functions introduced previously are established. The totally symmetric components ρ and ρ of ρ1 and ρ2 are of particular interest, because their eigenfunctions are the required symmetry‐adapted NSO'S and NSG'S, respectively.
Semiempirical molecular‐orbital calculations of the basicities of pyrazole, imidazole, and methyl‐substituted pyrazoles and imidazoles: Inductive model of electron release
Authors: Vaughan John D. , Fullerton David C. , Chang Chin‐An
Published: December 2004

This work is concerned with the interpretation of the relative base strengths of pyrazole, imidazole, and some of their methyl derivatives. The LACO‐SCF method of Pariser, Parr, and Pople was used to calculate the π energies of protonation of the bases. We found that the usual treatments of the core attraction integrals failed to order the basicities of pyrazole and imidazole, but this failing could be corrected by using a scaling factor with the core penetration integrals. The electronic effect of the methyl substituents was assumed to be wholly inductive, and the inductive modification of the core integrals αp was found to be highly sensitive to the scaling parameter for the core penetration integrals. A good correlation was obtained between the pKa values and the π protonation energies of seven diazoles, but this correlation could not be extended quantitatively to triazoles.
Etudes en methode de Hartree–Fock avec projection. I. Fonctions propres de S2. Evaluation de l'energie
Authors: Lefebvre R. , Prat R. F.
Published: December 2004

The rotational projection operator previously introduced [12] serves here to build up an explicit formula for the non‐relativistic energy associated with a spin‐projected determinant. Corresponding orbitals are used throughout, and interchange of configuration space and Euler angles integrations provides rapidly an energy expression previously obtained either by use of Löwdin's projector (via first‐ and second‐order density matrices (8)) or by mixed space and spin permutation operator (GF method (9)).
Lattice dynamics with second‐neighbor interactions. III. Green's matrix
Authors: McIntosh Harold V. , Hehenberger Michael , Reyes‐Sanchez Rodolfo
Published: December 2004

The theory of pth‐order singular differential equations is adaptable to the study of the system of recurrence relations occurring in the problem of a one‐dimensional chain with pth‐neighbor interactions. By using Green's formula, a mapping is defined between the space Vn of eigenvectors to the dynamical matrix and the symplectic space V2p of boundary conditions for the recurrence equations. The properties of the resolvent are obtained from an analysis of the solutions of a system of inhomogeneous equations and Green's matrix is constructed for the case of standard Sturm–Liouvilletype boundary conditions. The Weyl surface is discussed and its properties used for the construction of square summable sequences which in turn can be employed in expansion formulas. The generalization of Weyl's m‐function in the second‐order case (p = 1) becomes for p ≥ 2 a p × p matrix M(λ), where λ is a complex parameter. The imaginary part Im {M(λ)} is related to the spectral properties and serves as basis for the discussion of different concepts of spectral density for the normal modes of lattice dynamical problems. An important practical result is the equation M = −ΨΦa valid in the limit point case, generalizing the corresponding second‐order formula.
MO‐LCAO‐Calculations on polymethines. V. PPP‐type calculations and configuration analyses of simple prototype dyes in terms of molecular subsystems
Authors: Fabian J. , Tröger‐Naake G.
Published: December 2004

In order to elucidate certain controversies in interpreting the π‐electronic structure of some simple quinone and indigo dyes the Pariser–Parr–Pople SCβ,γ‐wave‐functions have been subjected to configuration analyses. Whereas 2,5‐diamino‐quinone (1) can be excellently represented by coupling of two trimethine‐merocyanine chains, the analogous consideration is less appropriate with bispyrrolindigo (2). In this case the results of the configuration analyses indicate clearly the limited applicability of the Longuet/Higgins–Murrell–method.
The interference in the decay of two ½ spins in a molecular medium, studied by the Nakajima–Zwanzig technique
Authors: Hardisson A. , Lefebvre R. , Mauricio F. , Velasco S.
Published: December 2004

This paper studies the decay, due to the spin‐lattice coupling, of two ½ spins with slightly different Zeeman energies when the lattice is thermally excited. The analysis is based on obtaining, by means of the Nakajima–Zwanzig projection operator technique, an equation for the evolution of the reduced density operator of the spin system which manifests the influence of one spin on the relaxation process of the other. The zero‐order solutions obtained for the evolution of the expectation values of the spin dynamics operators are essentially equivalent to the Bloch equations; higher order solutions are also obtained.
The role of double antisymmetrization
Authors: Lim T. K.
Published: December 2004

With the basic equivalent transformation Pσ = ϵ(P)(Pr)−1 the dual bases of symmetric groups can be constructed. The importance of the double antisymmetrization is shown. The advantages of the use of the m basis as compared to the Wigner (matric) basis are discussed.
Clebsch–Gordan coefficients for chains of groups of interest in quantum chemistry. II. The chain SU(2) ⊃ D′∞ ⊃ D′4 ⊃ D′2
Authors: Kibler M. R. , Grenet G.
Published: December 2004

The formalism described in the first paper of this series is applied to the chain SU(2) ⊃ D′∞ ⊃ D′4 ⊃ D′2, the covering of SO(3) ⊃ D∞ ⊃ D4 ⊃ D2. The state vectors (|αJaΓγ) adapted to each link of the chain under consideration and the corresponding coupling coefficients \documentclass{article}\pagestyle{empty}\begin{document}$ f\left( {\begin{array}{*{20}c} {J_1 } & {J_2 } & J \\ {a_1 \Gamma _1 \gamma _1 } & {a_2 \Gamma _2 \gamma _2 } & {a\Gamma \gamma } \\ \end{array}} \right) $\end{document} are given in analytical form. The material reported here is very convenient for a quantum‐mechanical description of molecular and nuclear systems with linear, tetragonal, or orthorhombic symmetry. In this respect, we present an outline for its applications to the electronic and vibrational–rotational spectroscopy of molecular aggregates and to the rotational spectroscopy of molecules or nuclei. In addition, we briefly show how the material may simplify the second–order non‐Lie subgroup type approach to the representation theory of SU(2).
The symmetric groups and the Waller–Hartree spin‐free method
Authors: Lim T. K.
Published: December 2004

The relations between the Waller–Hartree spin‐free method and the symmetric group theory are given. It is shown that the Gallup method is a special case of ours with S = M. Furthermore, all the irreducible representation matrices and other matrices needed are written explicitly in terms of Sanibel coefficients which makes the method more useful. However, it was shown that the cases with S ≠ M for the spin‐free pure spin states might be beyond the power of the symmetric group theory.
The floating spherical gaussian orbital model and shape of B2H5 ion
Authors: Rastogi R. C. , Ray N. K.
Published: December 2004

The FSGO model has been used to make ab initio calculations of the geometry of B2H ion. The results indicate that the acetylenic structure has the lowest energy (−43.881 a.u.) and the planar structure has the highest energy (−43.838 a.u.). The energy of the non‐symmetric structure is only slightly higher (−43.879 a.u.) than that of the acetylenic one. Results of CNDO/2 calculations reported here also predict the acetylenic structure to be the most stable one.
The energetic effects of p, d, and f Gaussian polarization functions on closed‐shell AHn oxygen and sulfur hydrides
Authors: Kari Roy , Csizmadia Imre G.
Published: December 2004

A series of LCAO‐MO‐SCF calculations, using various basis sets of Gaussian‐type functions, has been made in order to study the effects of p, d, and f polarization functions for a 10‐electron isoelectronic series of oxygen hydrides and for an 18‐electron isoelectronic series of sulfur hydrides. Conclusions from these results suggest that meaningful proton affinities cannot be calculated without the inclusion of a d function on the heavy atom and a p function on the hydrogen atoms.
Conformational energy map for a pair of peptide units using the bond polarisability method
Authors: Sundaram Srinivasan K. A. R.
Published: December 2004

A method recently developed for the calculation of intramolecular nonbonded interactions based on experimental bond polarisabilities and atomic charges and transition π‐charges obtained from MO calculations has been applied to the alanyl dipeptide. The potential energy contours in the ϕ, ψ plane obtained by this method compare favourably with those derived from the frequency of occurrence of conformations in globular proteins. An analysis of the various components of the nonbonded interaction energy indicates that the fairly frequent occurrence of conformations around ϕ = −80°, ψ=0° is presumably due to a favourable interaction of the π‐polarisation.
A weakly bound, quantum‐mechanical buridan's ass
Authors: Moiseyev N. , Katriel J. , Trindle C.
Published: December 2004

The spherical limit of a single particle in the field of three nuclei is shown to exhibit a variety of phenomena associated with the stability of the various extrema involved. Some consequences with respect to the general problem of detecting broken symmetry solutions of variational problems are pointed out.
On convergence in many‐shell SCF theory
Authors: Firsht D. , Pickup B. T.
Published: December 2004

The effect of damping factors on convergence to general stationary solutions in many‐shell SCF theory is discussed using a first order perturbation analysis. Their bearing on the maximum overlap criterion is examined and a comparison made with Hartree damping. Examples are drawn from numerical experience with hole state and transition operator calculations, some of which lead to saddle point stationary conditions. The method of Hsu et al. is reviewed in the light of the foregoing arguments.
Exact calculations of Franck–Condon overlaps and of matrix elements of some potentials by means of the coherent state representation
Authors: Nishikawa Kiyoshi
Published: December 2004

Franck–Condon overlaps are described as the matrix elements of unitary operators related to the spatial displacement and the frequency shift. They are calculated exactly by means of the coherent state representation. Furthermore, the generalized matrix elements of xj, e−αx, and e−βx2 between two states with different equilibrium coordinates and frequency are evaluated in the same way.
Angular dependence of Gaussian‐Lobe orbitals. II. Set of axial Gaussian‐Lobe orbitals
Authors: Le Rouzo H. , Silvi B.
Published: December 2004

The topological properties of real spherical harmonic representations on the unit sphere have been found to provide a convenient tool to infer the lobe edifices which mimic these orbitals. The prohibitive number of lobes required in such an approach for l > 2, can be avoided in using only axial Gaussian‐lobe orbitals (AGLO). It is proved that 2l + 1 independent Ylo‐like functions correctly span the relevant Ylm (m = −l,l) subspace. The multipolar component analysis of any spatial arrangement of lobes is derived, and allows the optimization of the angular dependence of AGLOS. The cases of d‐ and f‐orbitals are studied in detail and accurate optimized functions are proposed. This method can be easily extended to obtain the atomic orbitals of any azimuthal quantum number l‐subspace.
An ab initio molecular orbital study of the deprotonation of amines
Authors: Hopkinson Alan C. , Lien Min H.
Published: December 2004

The geometries of the amines NH2X and amido anions NHX−, where X = H, CH3, NH2, OH, F, C2H, CHO, and CN have been optimized using ab initio molecular orbital calculations with a 4‐31G basis set. The profiles to rotation about the NX bonds in CH3NH−, NH2NH−, and HONH− are very similar to those for the isoprotic and isoelectronic neutral compounds CH3OH, NH2OH, and HOOH. The amines with unsaturated bonds adjacent to the nitrogen atoms undergo considerable skeletal rearrangement on deprotonation such that most of the negative charge of the anion is on the substituent. The computed order of acidity for the amines NH2X is X = CN > HCO > F ≈ C2H > OH > NH2 > CH3 > H and for the reaction NHX− + H+ → NH2X the computed energies vary over the range 373–438 kcal/mol.
Complex scaling: An introduction
Authors: Bardsley J. N.
Published: December 2004

The complex scaling method, also known as the complex coordinate or dilatation transformation method, is discussed in relation to the Stark effect and to the calculation of the position and width of resonant states of atoms or molecules. The significance of resonant scattering in atomic physics is briefly reviewed.
Extended virial theorem applied to predissociation phenomena. Interpretation of the nearly degenerate G1Π ∼ I1Π energy spectra in SiO
Authors: Brändas Erkki , Elander Nils , Froelich Piotr
Published: December 2004

The extended virial theorem, obtained from a Fourier–Laplace transformation of equations of motion, is applied to the phenomenon of predissociation. The underlying resonance energy model rigorously defined by means of the theory of dilation analytic operators prescribes in detail the balance between the various energy contributions in a way analogous to the situation prevailing in a stationary system. The extended virial theorem is applied to predissociation, particularly in connection with the interpretation of the nearly degenerate G 1Π ∼︁ I 1Π energy spectrum in SiO. It was previously found for the rovibronic spectra assigned to G 1Π – X 1Σ+ and I1Π – X1 Σ+, that every G – X band is accompanied by a I – X band. Whereas the I 1Π state does not seem to undergo predissociation, the G state shows increasing predissociation with increasing vibrational quantum number. We show that the virial theorem generalized to include continuum phenomena offers an interpretation of the nearly degenerate spectra of SiO as well as of the concomitant isotope shift of SiO16 and SiO18 with respect to both resonance positions and widths.
Time dependence, complex scaling, and the calculation of resonances in many‐electron systems
Authors: Nicolaides Cleanthes A. , Beck Donald R.
Published: December 2004

The theory of this paper deals with certain aspects of the formal properties of atomic and molecular highly excited nonstationary states and the problem of calculating their wave functions, energies, and widths. The conceptual framework is a decay theory based on the consistent definition and calculation of the t = 0 localized state, |Ψ. Given this framework, the following topics are treated: (a) The variational calculation of Ψ0 and E0 using a previously published theory that generalized the projection operator approach to many‐electron systems. (b) The exact definition of the resonance energy. (c) The possibility of bound states in the continuum. (d) The relation of Ψ0 to the resonance (Gamow) function Ψ and of the Hamiltonian to the rotated Hamiltonian H(θ) based on the notion of perturbation of boundary conditions in the asymptotic region. (e) The variational calculation of real and complex energies employing matrix elements of H and H2 with square‐integrable and resonance functions. (f) The mathematical structure of the time evolution of |Ψ0〉 and the possibility of observing nonexponential decays in certain autoionizing states that are very close to the ionization threshold. (g) A many‐body theory of atomic and molecular resonances that employs the coordinate rotation method.
Use of the overlap multipole expansion for approximating molecular electrostatic potentials
Authors: Goldblum A. , Perahia D. , Pullman A.
Published: December 2004

The molecular electrostatic potentials computed by the overlap‐multipole‐expansion procedure (OMTP) are compared to exact electrostatic potentials computed with the same Gaussian basis set, for different molecular species. It is shown that at distances of the molecule larger than 2.2 Å, the OMTP values compared to those of the exact ones are within an error of 0.5 kcal/mol. This error decreases with increasing distance. For distances below this limit the OMTP potentials may be used as a first indication of the trends of the molecule, provided the values to compare are not too close.
Contributions from inner and outer shell electron energies to reaction heats for C1, C2, and C3 hydrocarbons
Authors: George P. , Bock C. W. , Trachtman M.
Published: December 2004

The expectation energy values EK, Vee, Vnn, Ven, and ET have been calculated for H2 and the C1, C2, and C3 hydrocarbons using a (9,5) basis set and the experimental geometries. Treating the theoretical reaction heat, ΔET, as the resultant of the nuclear repulsion term, ΔVnn, and the net electron energy term, ΔEelec = ΔEK + ΔVee + ΔVen, the contribution of inner and outer shell electron energies to ΔEelec, and hence to ΔET, has been calculated for a large number of hydrocarbon reactions by evaluating the Coulson–Neilson energies ηi, where Σηi = Eelec. For the vast majority of reactions, 67/84, the change in inner shell electron energy, (Σηi)inner, accounts for more than 10% of ΔEelec, in many cases being as high as 20–35%. Furthermore, in addition to these cases in which the change in inner shell electron energy serves to augment (significantly) the change in outer shell electron energy, there are other cases in which the change in inner shell electron energy either exceeds in magnitude the change in outer shell energy, or is even opposite in sign, indicative of inner and outer shell electrons acting contrariwise. Inner shell electron energies contribute to the reaction heats because they are structure dependent, like the more familiar orbital energies ε, but the dependence is of a different kind.
New iterative scheme for a simultaneous calculation of m first eigenstates of a real symmetric matrix
Authors: Gołȩiewski A.
Published: December 2004

A new iterative scheme for a simultaneous calculation of the m lowest eigenvalues together with their eigenvectors has been derived for a real symmetric matrix. The scheme is based on the orthogonal gradient method and is easy to use for large‐scale configuration‐interaction calculations of electronic wave functions. A variant of the scheme deals with nonorthogonal basis functions, which are particularly simple in the case of the bonded‐function method of Boys.
Space partitioning in multiple scattering techniques. I. Hydrogen molecular ion and hydrogen molecule
Authors: Garritz Andoni , Gázquez José Luis , Castro Miguel , Keller Jaime
Published: December 2004

The use of multiple scattering techniques combined with a statistical exchange potential for the description of the electronic structure of atoms, molecules, and solids depends strongly on the geometry (muffin tin, overlapping spheres, or cellular potentials) and on the form of the electron gas exchange. In this work we compare only the effects of using different geometries. For that purpose we have done calculations on the hydrogen molecular ion and Hartree‐type calculations on the hydrogen molecule so that no exchange effects are involved. To avoid arbitrariness in the choice of the sphere sizes we propose a nonempirical criterion that consists of using the set of radii that will minimize the charge in the interstitial region of the molecule or cluster. Some arguments are given to justify this criterion, and to clarify the differences between cellular, overlapping spheres, and muffin‐tin geometries. It is found that the cellular geometry gives a very good description around the equilibrium internuclear distance. However, for most systems of interest, exchange will be present. Thus, we have done, for comparison, the calculation on H2 using Xαβ statistical exchange. It is shown through this calculation that some of the correlation energy may be obtained by redefining the molecular orbitals in terms of non‐paired‐spins spatial orbitals, this formulation being required to obtain the correct free‐atom limit.
Difficulties in the computation of physical observables due to a truncated CI
Authors: Meunier A. , Levy B.
Published: December 2004

It is proved that the values of various types of physical observables issued from a truncated CI are not size consistent. These observables include electronic transitions, ionization potential, and all the quantities depending on the one‐electron density matrix γ. Numerical examples are given. It is found that the error due to this size inconsistency can be important for systems of moderate size (e.g., 16% on a matrix element of γ for a 20‐electron system).
Thermodynamic functions for vibronic systems
Authors: Crotov S. S. , Ischenko A. A. , Ivashkevich L. S.
Published: December 2004

A method is introduced which simplifies the derivation of equations for the calculation of statistical sums for vibronic systems. Within the “independent ordering approximation” analytical expressions are found for thermodynamic functions for molecules with degenerate electronic ground state (E−β and E − e types of degeneracies). Vibronic interactions are shown to yield an additional thermodynamic stabilization. The computations were carried out for VCl4 and VBr4 with doubly degenerate electronic ground states. For these molecules the effect is shown to be small.
Valence‐bond studies of four‐electron three‐center bonding units. II. FNO, HNO, LiNO, LiON, and HF2−
Authors: Harcourt Richard D. , Roso Walter
Published: December 2004

For each of HNO, FNO, LiNO, LiON and HF2−, ab initio valence‐bond wave functions are reported for the four‐electron three‐center bonding unit which involves one of the following sets of atomic orbitals: (a) NX σ‐bond (X = H, For Li) and oxygen 2pπ′; (b) LiO σ‐bond and nitrogen 2pπ′; (c) hydrogen 1s and fluorine 2pσ. Six S = 0 valence‐bond structures pertain for this type of bonding unit. For HF2− and FNO, the calculated bond‐eigenfunction coefficients for some of these valence‐bond structures differ appreciably according to whether the Slater determinants include only the electrons of the four‐electron three‐center bonding unit, or all of the valence‐shell ± inner‐shell electrons. For HNO, LiNO, and LiON, the all‐electron and all valence‐shell electron calculations generate similar sets of bond‐eigenfunction coefficients. For each of the nitrosyl systems, the bond‐eigenfunction coefficient with largest magnitude is calculated to be that for which zero atomic formal charges occur in the valence‐bond structure. Qualitative valence‐bond and “increased‐valence” descriptions of the bonding are presented.
Tautomerism of oxopyridines and oxopyrimidines: Theoretical study with complete optimization of geometry
Authors: Czermiński R. , Lesyng B. , Pohorille A.
Published: December 2004

The semiempirical MINDO/3 method is employed to calculate the energies of various tautomers of model tautomeric compounds— 2‐oxo‐ and 4‐oxopyridines and pyrimidines. The results are compared with experimental data in the gas phase, where the solute–solvent interactions not included in theoretical calculations are absent. Although the relative energies obtained by the MINDO/3 method appear to be superior to other semiempirical and ab initio calculations, the accuracy of the method was determined to be as low as 3–4 kcal/mol. It indicates that it is exceedingly difficult to account theoretically for intrinsic stabilities of the tautomers. The importance of various factors influencing calculated free‐energy differences is discussed. Particular attention is paid to the problem of geometry optimization.
Electronic absorption and emission spectra of nucleic acids and their components: Some questions of theory and experiment
Authors: Danilov V. I. , Pechenaya V. I. , Zheltovsky N. V.
Published: December 2004

The results of calculations of the transition energies and polarization in nucleotide bases performed by the CNDO/S CI method are compared with experimental data for long‐wavelength and vacuumabsorption bands. The calculations and the analysis of experimental data testify to the existence of n − π* transitions in the first absorption bands of the bases. The study of double‐stranded polynucleotides and DNA hypochromism based on the theoretical electronic characteristics of the bases and perturbation theory is performed. The role of stacking and complementary interactions within the hypochromic effect is cleared up. Two mechanisms for the shift of the fluorescence band maximum are investigated: two‐proton transfer along H bonds and excimer formation. The study of H‐bond potential curves shows the disadvantage of two‐proton phototautomerism in the nucleotide base pairs in contrast to model systems. The possibility of excimer state formation in stacked homo‐ and heterodimers of nucleotide bases is shown within the extended‐Hückel treatment. The nature of excimer minimum for the excited‐state potential curve is analyzed.
π‐Orbital electron–energy contributions to chemical reaction heats, I. Reactions involving only linear molecules containing up to three first–row atoms
Authors: George Philip , Trachtman Mendel , Bock Charles W.
Published: December 2004

Ab initio calculations of various expectation energies have been made for the reactant and product species in six reactions that involve only small linear molecules. The reactions include fission by hydrogen, addition of hydrogen, exchange of triply bonded atoms, fluorination, and oxygen atom transfer. The change in total electronic energy is not invariably the result of changes in inner shell energy and outer shell σ‐ and π‐electron energies simply augmenting each other, but in several cases there is a complex interplay of opposing effects. This approach gives a different insight into the energetic aspects of changes in bonding from that derived from the concept of shared electron pairs in σ and π bonds together with lone pairs in valence shells. Changes in π‐electron energy are shown to be important in a reaction in which neither reactant nor product molecules contain π bonds in the usual chemical sense. While in a reaction in which there is a complete change in the nature of the triple bonds, and hence the π bonding, the change in π‐electron energy makes a smaller contribution than either the change in inner shell or the outer shell σ‐electron energies.
Variational principle for obtaining approximate analytical solutions of the temperature‐perturbed Thomas–Fermi equation for compressed atoms
Authors: Csavinszky P. , Tarr C. E. , Vosman F.
Published: December 2004

A temperature correction to the Thomas–Fermi (TF) model of a neutral compressed atom has been given by Marshak and Bethe. The aim of the present work is to point out that, by formulating a variational principle, one may obtain approximate analytical solutions of the temperature‐perturbed TF equation. As a test of the proposed theory, the total energy of a Ne atom, confined to a spherical container, has been calculated as a function of the container radius at T = 0°K. Comparison of the data obtained with energy values calculated by Ludeña, using a self‐consistent‐field Hartree–Fock approach, shows reasonable agreement. It is, therefore, concluded that the variational approach suggested in this paper is a sound one.
Investigation of tertiary structure of a series of DNA compact forms by the small‐angle X‐ray scattering method
Authors: Polivtsev O. F. , Osika V. D. , Tsvankin D. Ya.
Published: December 2004

This work describes the investigation of the space organization of DNA compact forms and DNA–protein complexes by the small‐angle x‐ray scattering method. A plane texture was disclosed in dehydrated DNP films. Compact DNA particles formed in the presence of poly(ethylene glycol) reveal ordered structures having a periodicity of 84 Å. Various morphological forms of crystals of CTA‐DNA were used to obtain small‐angle x‐ray patterns of the single‐crystal type.
Perturbation and SCF calculations for excited states
Authors: Chang Tse‐Chiang
Published: December 2004

One can treat the linear variation calculation by the perturbation expansion; on the other hand, one can also relate the perturbed wave function for the mth state to the mth eigenvector and justify the upper bound nature of the perturbation calculations for excited states. One can also associate a special type linear variation wave function to the SCF calculation. The upper bound nature of the excited‐state SCF calculation can then be accessed by the help of this special wave function.
Ab initio studies of 1,3‐sigmatropic rearrangements: Effect of basis set and electron correlation
Authors: Rodwell William R. , Bouma Willem J. , Radom Leo
Published: December 2004

Ab initio molecular‐orbital theory has been used to study the 1,3‐sigmatropic hydrogen rearrangements: propene → propene, formic acic → formic acid, and vinyl alcohol → acetaldehyde. Fully optimized structures of stable molecules and transition states have been determined using gradient procedures and the 4‐31G basis set. Improved energies have been obtained using a variety of techniques with basis sets up to the size of double‐ζ plus polarization (DZP) and electron correlation up to the CEPA/DZP level. Although both polarization functions and electron correlation lead to a lowering of the calculated barriers, the values remain substantial for all three rearrangements.
CNDO‐MO calculation of NnFm molecules
Authors: Chen Cheng
Published: December 2004

The s‐p separation model CNDO‐MO method has been introduced and developed for both the open‐ and closed‐shell systems since 1975. This method has two chief advantages over most of the other CNDO methods. (1) The ns and np bases of the same atom may be considered independent to infer different bonding behavior. (2) Pariser–Parr and Nishimoto–Mataga approximations are applied to the Coulombic repulsion integrals, which not only simplifies the calculation and saves computer time but also gives reliable computational results. A series of nitrogen fluoride molecules such as NF, NF2, NF3, cis‐N2F2, trans‐N2F2, and N2F2 have been selected for this MO calculation. In each case, both ionization potential and dipole moment were calculated. The results are closer to the observed values than those reported in other works.
Calculation of the determinant of the adjacency matrix and the stability of conjugated molecules
Authors: Yuan‐Sun Kiang
Published: December 2004

A new approach to evaluate the determinant of the adjacency matrix is presented in this paper.