β-D-核糖（ RI）与一价、二价金属离子相互作用的理论研究

在HF和MP2水平用全电子(AE)和相对论有效芯势(RECP)方法研究了Ⅰa、Ⅰb、Ⅱa和Ⅱb族金属离子与β D 核糖(RI)的相互作用. 结果表明, RECP能可靠地用于重金属离子;二价金属离子(M2＋)比一价金属离子(M＋)更易使β D 核糖(RI)变形;二价金属离子络合物(RI M2＋)比一价金属离子络合物(RI M＋)稳定. 电荷布居分析的结果支持上述结论.     

The Role of Binary and Many-centre Molecular Interactions in Spin Crossover in the Solid State. Part II. Non-ideality Parameters Defined via Binary Molecular Potentials

Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T_1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given.     

Redox troponization of (η5-cyclopentadienyl)(η4-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium as a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone seriesas a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone series

The possibility of redox troponization of a gem-polyhalomethylated semiquinoid system, π-coordinated to a metal atom, was shown in relation to the reaction of (η⁵-cyclopentadienyl)(η⁴-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium with Pd(PPh₃)₄. The reaction occurs with retention of the metal coordination affording a sevenmembered organometallic derivative of the nonbenzoid aromatic series, namely, (η⁵-cyclopentadienyl)(η⁴-4-chloro-5-menthylcyclohepta-2,4,6-trien-1-one)rhodium, whose structure was established by means of elemental analysis, NMR, and mass-spectral data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1255–1256, June, 1998.     

STUDIES ON THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY METAVANADATE-CONTAININ G ANION EXCHANGER-THIOUREA REDOX SYSTEM

The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by metavanadate-containing anion exchange resin (PV)-thiourea (TU) redox system at 20—40℃. has been investigated. The overall rate of polymerization (R_p) is given byR_p=1.92×10~4e~(-6.860/RT) [AN]~(1.2) [PV]~(0.44) [TU]~(1.0)[HNO_3]~(1.0)The kinetic parameters differed from those of V~(5+)-TU system indicated that the generation of the primary radicals is mainly a difffusion-controlled reaction. The effect of macromolecular field arisen from the polymer matrix exerts a great influence on the polymerization process.     

Initiation Mechanism of Polymerization of Acryl－amide by Ceric Ion／2－Benzoyl Acetanilide System

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Oxidative Transformations of Organic Compounds Mediated by Redox Molecular Sieves

Zeolites are viewed by some as the “philosopher's stone” of modern chemistry.^[1] They are more or less indispensable in oil refining and petrochemicals manufacture where they are widely applied as solid acid catalysts. More recently attention has been focused on their use in the manufacture of fine chemicals. The synthetic utility of zeolites and related molecular sieves (zeotypes) has been considerably extended by the incorporation of redox metals into their frameworks. The resulting redox molecular sieves catalyze a variety of selective oxidations under mild conditions in the liquid phase. Their structural diversity–including variation of the redox metal, incorporation of metal complexes, and the size and polarity of the micropores–provides the possibility of designing tailor-made solid catalysts (“mineral enzymes”) for liquid-phase oxidations with clean oxidants such as O₂, H₂O₂, and RO₂H. Hence, they have enormous potential in industrial organic synthesis as environmentally friendly alternatives to traditional oxidations employing inorganic oxidants in stoichiometric amounts. A primary aim of this review is to familiarize organic chemists with the synthetic potential of redox molecular sieves. An outline of their synthesis, structures, and chemical properties, highlighting their unique advantages, is followed by a discussion of general (mechanistic) features that influence the choice of a suitable catalyst for a particular type of oxidation. The main part of the review deals with the oxidation of various substrates of synthetic interest–such as alkanes, alkenes, (alkyl)arenes, alcohols, and amines–and emphasizes the advantages of redox molecular sieves (including selectivity and stability) over their homogeneous counterparts. New directions towards truly biomimetic solid catalysts, for example zeolite-encapsulated chiral metal complexes as heterogeneous catalysts for asymmetric oxidations, are high-lighted.     

Vinyl polymerization of acrylonitrile by the Ce(IV)-glucose redox system

Aqueous polymerization of acrylonitrile (M) initiated by the Ce(IV)-glucose (R) redox system has been studied under nitrogen in the temperature range of 30–40 °C. The rate of polymerization (Rp) is proportional to [M]², [R] and inversely proportional to [Ce(IV)]. The rate of ceric ion disappearance is proportional to [R] and [Ce(IV)]. The end group in the polymer is characterised by IR spectra. A suitable kinetic scheme has been proposed and explained in the light of these experimental findings.     

RP-HPLC study of redox equilibria in vanadium-PAR binary and ternary systems: Direct determination of vanadium in steel

The reversed-phase high-performance liquid Chromatographic (RP-HPLC) behaviour of the binary chelates of V(V) and V(IV) with 4-(2-pyridylazo) resorcinol (PAR) and ternary chelates of vanadium with PAR and auxiliary ligands: hydrogen peroxide, hydroxylamine, tartrate and citrate were studied using a C₁₈ column. The complex double-peak chromatograms of V(IV)/V(V)-PAR systems were studied and the origin of each peak was proved. Vanadium in ternary systems with PAR and hydrogen peroxide was found exclusively in V(V)-H₂O₂-PAR complex (single peak on the chromatogram) despite its initial oxidation state. The double role of hydroxylamine (complex agent and reductor) in vanadium systems with PAR was confirmed: in the V(V) system three species were identified (V(V)-PAR, V(V)-NH₂OH-PAR and V(IV)-PAR), but in the V(IV) system only two: V(IV)-PAR and V(V)-NH₂OH-PAR. Citrate and tartrate giving single peak were found as auxiliary ligands in ternary V(V) systems of analytical importance. Due to its masking potential towards iron (III) ions, citrate was chosen as the most suitable third component of a ternary vanadium system with PAR, to form the basis of an RP-HPLC method for direct determination of V in steel.