A simplified View of δ → δ* Transition Energies in Compounds with multiple metal-metal bonds: The isolated δ — δ* manifold model

The energetics of the * transition in quadruply bonded complexes are investigated using a very simple valence-bond formalism, called the isolated * manifold (IDDM) model. In this model all electrons except for those that occupy the or * molecular orbitals are ignored, as are explicit metal-ligand interactions. The resulting equations allow the calculation of transition energies very inexpensively, albeit with poor quantitative agreement: the * transition in prototypical quadruple-bond systems is predicted to occur at energies greater than 70,000 cm¹. The model incorporates configuration interaction between the two¹ A _1g configurations (|| and |**|) to roughly the same extent as do correlated all-electron calculations. The application of the method to systems that involve relative changes in * transition energies, such as the torsional twisting of quadruple bonds, is more successful quantitatively.     

Differentiation of δ, μ, and κ opioid receptor agonists based on pharmacophore development and computed physicochemical properties

Compounds that bind with significant affinity to the opioid receptor types, , , and , with different combinations of activation and inhibition at these three receptors could be promising behaviorally selective agents. Working on this hypothesis, the chemical moieties common to three different sets of opioid receptor agonists with significant affinity for each of the three receptor types , , or were identified. Using a distance analysis approach, common geometric arrangements of these chemical moieties were found for selected , , or opioid agonists. The chemical and geometric commonalities among agonists at each opioid receptor type were then compared with a non-specific opioid recognition pharmacophore recently developed. The comparison provided identification of the additional requirements for activation of , , and opioid receptors. The distance analysis approach was able to clearly discriminate -agonists, while global molecular properties for all compounds were calculated to identify additional requirements for activation of and receptors. Comparisons of the combined geometric and physicochemical properties calculated for each of the three sets of agonists allowed the determination of unique requirements for activation of each of the three opioid receptors. These results can be used to improve the activation selectivity of known opioid agonists and as a guide for the identification of novel selective opioid ligands with potential therapeutic usefulness.     

Charge control of phenol complexation with unsaturated compounds containing group IVB organometallic substituents. Interpretation of NMR spectra of acetylenic derivatives

²⁹Si and ¹¹⁹Sn chemical shifts in the NMR spectra of acetylenic derivatives Me₃ECCX (E = Si or Sn; X — organic substituents) and shifts of frequencies () of stretching vibrations of OH groups in the IR spectra of phenol when hydrogen-bonded to these compounds have been analyzed. In each of two series (E = Si or Sn), the and values are connected by a linear relationship; this indicates that there is virtually no effect of the magnetic anisotropy of the X substituents on the chemical shifts. It has been established that the shifts of the frequencies and the ²⁹Si and ¹¹⁹Sn chemical shifts are the relative characteristics of the effective negative charge on the carbon atoms of the triple bond in Me₃ECCX compounds.For the previous communication of this series, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2069–2073, December, 1993.     

The μ-and δ-opioid pharmacophore conformations of cyclic β-casomorphin analogues indicate docking of the Phe3 residue to different domains of the opioid receptors

Summary Cyclic -casomorphin analogues with a d-configured amino acid residue in position 2, such as Tyr-c[-Xaa-Phe-Pro-Gly-] and Tyr-c[-Xaa-Phe-d-Pro-Gly-] (Xaa=d-A₂bu, d-Orn, d-Lys) were found to bind to the -opioid receptor as well as to the -opioid receptor, whereas the corresponding l-Xaa² derivatives are nearly inactive at both. Low-energy conformers of both active and nearly inactive derivatives have been determined in a systematic conformational search or by molecular dynamics simulations using the TRIPOS force field. The obatained conformations were compared with regard to a model for -selective opiates developed by Brandt et al. [Drug Des. Discov., 10 (1993) 257]. Superpositions as well as electrostatic, lipophilic and hydrogen bonding similarities with the -opioid receptor pharmacophore conformation of t-Hpp-JOM-13 proposed by Mosberg et al. [J. Med. Chem., 37 (1994) 4371, 4384] were used to establish the probable -pharmacophoric cyclic -casomorphin conformations. These conformations were also compared with a -opioid agonist (SNC 80) and the highly potent antagonist naltrindole. These investigations led to a prediction of the -and -pharmacophore structures for the cyclic -casomorphins. Interestingly, for the inactive compounds such conformations could not be detected. The comparison between the -and -pharmacophore conformations of the cyclic -casomorphins demonstrates not only differences in spatial orientation of both aromatic groups, but also in the backbone conformations of the ring part. In particular, the differences in ² and ² (70°,-80°; 165°,55°) cause a completely different spatial arrangement of the cyclized peptide rings when all compounds are matched with regard to maximal spatial overlap of the tyrosine residue. Assuming that both the -and -pharmacophore conformations bind with the tyrosine residue in a similar orientation at the same transmembrane domain X of their receptors, the side chain of Phe³ as a second binding site has to dock with different domains.This paper is based on a presentation given at the 14th Molecular Graphics and Modelling Society Conference, held in Cairns, Australia, August 27–September 1, 1995.     

m-Xylene conversion over dealuminated Y zeolites studied by the pulse method

m-Xylene conversion was studied over dealuminated Y type zeolites in hydrogen forms, SiO₂ to Al₂O₃ ratios were varied from 4.86 to 12.95.

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- . SiO₂/Al₂O₃ 4,86 12,95.

     

Configuration of benzoylpyridineoximes studied by 1H and 13C NMR. Effect of protonation of the pyridine nitrogen atom

A simple and convenient method is proposed for determining the configuration of E,Z-isomers of 2-, 3-, and 4-benzoylpyridines. The difference in chemical shifts (, ppm) in the system CCl₄-DMSO-D₆ and CCl₄-DMSO-CF₃COOD for the -H atoms or the , -C atoms of the pyridine ring can be used to determine the configuration. The shift () of the -H signals to weak field is greater for the Z-isomers than for the E-isomers due to protonation of the pyridine nitrogen atom. The reverse dependence is seen in the ¹³C NMR for the E,Z-isomers. The signals of the -C atoms shift to stronger field after protonation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1073–1077, August, 1990.     

Studies of the reaction mechanism between copper(I) sulphide and excess copper(II) sulphate

The reaction between copper(I) sulphide and excess copper(II) sulphate in the temperature range 600–750 K was investigated by methods of thermal analysis as well as by measuring the phase composition as a function of the fractional conversions. The reaction proceeds in four stages. The transient products are Cu₂S, a Cu₂SO₂ phase and CU₂SO₄, and the final product is CU₂O with the non-defect structure. The initial composition of the substrate mixture strongly influence the reaction kinetics.

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Zusammenfassung Die Reaktion zwischen Kupfer(I)-sulfid und überschüssigem Kupfer(II)-sulfat im Temperaturbereich von 600–750 K wurde mittels thermoanalytischer Methoden und durch Ermittlung der Phasenzusammensetzung in AbhÄngigkeit von der Konversion untersucht. Die Reaktion verlÄuft in vier Schritten. Als Zwischenprodukte treten CU₂S, eine Cu₂SO₂-Phase und Cu₃SO₄ auf, Endprodukt ist ein Cu₂O mit ungestörter Struktur. Die Reaktionskinetik wird stark von der Ausgangszusammensetzung des Substratgemisches beeinflu\t.

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600–750 K , . . Cu₂S, Cu₂SO₂ + Cu₂SO₄ — Cu₂O . .

     

A kinetic method for the determination of nanogram amounts of cadmium (II) by its catalytic effect on the complex formation of manganese(II) withα,β,γ,δ-tetra-(p-sulf onatophenyl) porphine

Summary Cadmium(II) accelerates the complex formation reaction of manganese (II) with, , , -tetra(p-sulfonatophenyl)porphine (H₂TPPS₄). Cadmium(II) concentration as low as 10^–7 mol dm^–3 can be determined from the decrease in absorbance at 413 nm (_max of H₂TPPS₄) at a fixed time after the start of the reaction of manganese(II) with H₂TPPS₄. After the separation of lead(II) by coprecipitation of manganese(IV) oxide, the method is highly selective and is free from interference of most substances usually encountered. Sandell's sensitivity calculated from the calibration curve at 30 min after the start of the reaction is 1.43×10^–1 ng cm^–2.

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Eine kinetische Methode zur Bestimmung von Nanogrammengen von Cadmium(II) mit Hilfe seines katalytischen Effekts bei der Komplexbildung von Mangan(II) mit , , , -Tetra-(p-sulfonatophenyl)-porphin

Zusammenfassung Cadmium (II) beschleunigt die Komplexbildung von Mangan (II) mit, , , -Tetra-(p-sulfonatophenyl)-porphin (H₂TPPS₄). Konzentrationen bis zu 10^–7 Mol/l können durch Messung des Rückganges der Absorbanz bei 413 nm (_max von H₂TPPS₄) nach einer bestimmten Zeit gemessen werden. Nach Abtrennung von Blei(II) durch Mitfällung mit Mangan (IV)oxid ist die Methode sehr selektiv und frei von Störungen durch die meisten üblicherweise vorliegenden Substanzen. Die Empfindlichkeit nach Sandell, ermittelt aus der Eichkurve 30 min nach dem Start der Reaktion, beträgt 1,43×10^–1 ng/cm².

     

Synthesis and structure of 1-benzoyl-2,5-dimethyl- and 1,2,5-trimethyl-4-arylpiperideins

Isomeric 1-benzoyl-2,5-dimethyl-³-piperidein and 1-benzoyl-2,5-dimethyl-⁴-piperidein were prepared from disubstituted -piperidols and were hydroxylated with osmium tetroxide. The isomeric 1,2,5-trimethyl-4-(p-nitrophenyl)-³- and-⁴-piperideins were obtained from trisubstituted -piperidols.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1200–1206, September, 1986.In conclusion, the authors would like to thank Yu. T. Struchkov and N. I. Lebedev for carrying out the x-ray structural study.     

Synthesis of unsaturated δ-amino ketones containing a macrocyclic fragment

Conclusions A number of dienic mono--dimethylamino ketones, containing a macrocylic fragment, was synthesized by the condensation of 1,1,3-trimethoxy-3-dimethylaminopropane and-dimethylaminoacrolein acetal aminal with macrocylic ketones. We were unable to obtain polyenic bis-,-dimethylamino ketones, containing a macrocyclic fragment, by this route.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1373–1376, June, 1980.The authors express their gratitude to S. Z. Taits and E. S. Balenkova for supplying the macroeyclic ketones.     

Oxidative dehydrogenation of n-butenes: Product effect in the reactions over tin-antimony mixed oxides

The addition of possible oxidation and/or isomerization products (butadiene, water, isomeric n-butenes) resulted in neither promotion nor inhibition in the oxidative dehydrogenation of n-butenes over tin-antimony mixed oxide catalysts. On the basis of these and other information on the influence of products an interpretation has been given to complete the reaction mechanism more realistic than those based on previous experimental results.

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(, ) ( -) , . , , .

     

Alumina as a nickel catalysts support for steam reforming of hydrocarbons

The coking resistance of six alumina supported nickel catalysts in n-butane steam reforming mainly depends on the average size of nickel crystallites. Thus, by using suitable preparative methods, it is possible to produce good, coking resistant nickel catalysts even with Al₂O₃ support.

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Al₂O₃ -, , . . ., , - Al₂O₃.

     

Lattice Dynamics in LaTa2-2xNb2xVO9-δ (x=0–0.1) Solid Solutions

The oxygen nonstoichiometry (x) of LaTa_2-2xNb_2xVO₉- (x = 0–0.1) solid solutions was studied using Xray phase analysis, vibrational spectroscopy, and radiospectroscopy. A correlation was found between (x) and the unit cell volume V(x) of the solid solutions. It was shown that the infrared spectra of LaTa₂VO₉- change in passing from = 0 to 0. The structural position of the oxygen vacancy in LaTa_2-2xNb_2xVO₉- is discussed.     

On the dissociation mechanism of carbonates and their isomorphous mixture

The thermal decomposition processes of carbonate minerals are analyzed by comparison of the notions on chemical bonds in crystals and modern concepts on solid-phase reactions. It is shown that depending on the mechanism of thermal dissociation, the carbonate minerals most widespread in nature may be divided into two groups: first, CaCO₃, SrCO₃ and BaCO₃, characterized by decomposition temperatures close to the equilibrium values and undergoing recombination on cooling; and second, MgCO₃, MnCO₃, FeCO₃ and ZnCO₃, with dissociation temperatures exceeding the equilibrium values by 250° and recombining only at high partial pressures of CO₂ (above 1000 bar).

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Zusammenfassung Die thermischen Zersetzungsprozesse von Carbonatmineralien wurden auf der Basis der Vorstellungen über die chemischen Bindungen in Kristallen und moderner Konzeptionen über Festphasenreaktionen analysiert. Es wird gezeigt, dass die in der Natur weitverbreitetsten Carbonatmineralien, abhängig vom Mechanismus der thermischen Zersetzung, in zwei Gruppen unterteilt werden können: die erste umfasst CaCO₃, SrCO₃ und BaCO₃ und ist durch Zersetzungstemperaturen nahe den Gleichgewichtswerten und durch Rekombination beim Abkühlen charakterisiert, zur zweiten gehören MgCO₃, MnCO₃, FeCO₃ und ZnCO₃ mit Dissoziationstemperaturen, die die Gleichgewichtswerte um etwa 250° überschreiten, und die nur bei hohen CO₂-Partialdrücken (über 1000 bar) rekombinieren.

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, . , , . CaCO₃, SrCO₃, BaCO₃ , . MgCO₃, MnCO₃, FeCO₃, ZnCO₃ , 250°, ( 1000 .).

     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

Thermoanalytical studies of substances liberating aggressive gases

A modification to the derivatograph has been designed that allows thermoanalytical investigations of chemical compounds, including sulphides and acids, that evolve aggressive gases such as CO, SO₂, S, etc. during warming. Application of this modification is exemplified by studies on the thermal dehydrogenation of titanium hydride (TiH_1.85) and on the interaction of rhenium disulphide (ReS₂) with concentrated sulphuric acid.

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Zusammenfassung Es wird über die Modifizierung eines Derivatografen berichtet, die die Thermoanalyse von Stoffen ermöglicht, die wie z. B. Sulfide oder Säuren beim Erhitzen aggressive Gase wie z. B. CO, SO₂, S usw. freisetzen. Als Beispiel für die Anwendung dieser Modifizierung dienten Untersuchungen der thermischen Dehydrogenierung von Titanhydrid (TiH_1.85) und des Einwirkens von konzentrierter Schwefelsäure auf Rheniumsulfid (ReS₂).

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, , , , , SO₂, S . . 2- , - (³_1,85) (ReS₂) (H₂SO₄).

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Presented as a poster at ESTAC-4, Jena, GDR, 1987.     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Trends in the NMR chemical shifts of F19 and the NQR spectra of Cl35 and Br79 in halonitroalkanes

F¹⁹ NMR chemical shifts _F are reported for fluoronitroalkanes, which are found to show a nearly linear relation to the NQR shifts for the chlorine and bromine analogs. The spin-spin coupling constant J_F-N also indicates that the Hal-C-N angles vary little in the series Hal_nC(NO₂)_4-n. The empirical relation can be used to predict the properties of new halonitromethanes. The observed trends in _F and _Cl when H is replaced by X (with X=Cl, F, or NO₂) for the halonitromethanes indicate the sequence NO₂, F, Cl as regards shift _F towards weaker fields, but the sequence F, Cl, NO₂ as regards shift _Cl towards higher NQR frequencies. The deviations from a linear relation for mixed halonitromethanes containing electron-donor groups indicate either that the distortion of the tetrahedral angle varies with the halogen or that conjugation effects for F¹⁹ NMR are different from those for Cl³⁵ and Br⁷⁹ NQR.     

Kinetics and mechanism of the oxidation of methyl phenyl sulfoxide by peroxodiphosphate

The kinetics of the oxidation of methyl phenyl sulfoxide (MPSO) by potassium peroxodiphosphate (PP) in 50% aqueous acetic acid obeys the rate law.-d[PP]_T/dt=k[PP] [MPSO] at constant [H⁺]. The active species in the oxidation has been found to be H₃P₂O ₈ ^– . The kinetic results have been explained by a polar mechanism.

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() () 50%- (./.) -d[]^T/dt=k·[]·[] [H^*]. H₃P₂O ₈ ^– . .

     

Optical and electrical measurements on CO2 covered copper films

Thin polycrystalline copper films are deposited in a special UHV cell on glass substrates and are covered step by step with CO₂. The optical and electrical properties of the films are studied in-situ by means of ellipsometry and resistivity measurements. The properties of the clean films correspond to literature data. In the case of monolayer adsorption of CO₂, the changes in the ellipsometrical angles are +1° and +0.1°, similar to the Cu/O and Cu/CO systems. Three-dimensional island growth leads to a drastical increase of and by several orders of magnitude. The resistivity first quickly decreases and then slowly reapproaches the initial value. This marked kinetics is quantitatively interpreted on the basis of a diffusion model.