Stoichiographic determination of the composition and concentration of phases encapsulated in the bulk of a solid matrix phase

A two-step method of stoichiographic calculations used in the determination of the formulas of phases encapsulated in the bulk of matrices of another composition is proposed. At the first stage of calculations, the stoichiometric composition of the encapsulated phase is determined and, at the second step, the concentrations of this phase and the matrix are found. The use of this method in the analysis of oxide La–Cu catalysts by the method of differential dissolution ensures the detection of the phase La₁Cu₁ (La₂Cu₂O₅), incorporated within the matrix La₁Cu_0.5 (La₂CuO₄) phase.     

Determination of the chemical composition of supported vanadium-containing oxide catalysts by the differential dissolution method

The results of the application of the stoichiographic method of differential dissolution (DD) in the determination of the chemical composition of vanadium-containing catalysts are presented. In the studied catalyst series, amounts of vanadium were deposited onto TiO₂, SiO₂, Al₂O₃, ZrO₂, and Nb₂O₅. The catalysts were prepared by the impregnation method or by the spray drying method and thermally treated at different temperatures. The DD method was used for the precise correction of the phase composition of the V₂O₅/TiO₂ catalyst samples in order to determine the nature of the active component of these catalysts and obtain the correct information on their structure using the NMR method.     

Giant correlation effects in the photoelectron spectrum of Ni(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>: clues from accurate calculation of ionization cross-sections

Several general issues relating to the strong correlation effects present in the ionic states and the interpretation of molecular photoelectron spectra are discussed in the context of the Ni(C₃H₅)₂ molecule, and the problematic assignment of its spectrum is considered. Accurate calculations of photoionization cross-sections relative to all the valence ionizations are computed and compared with the available experimental evidence. It is shown that most ambiguities are resolved by a careful analysis of cross-section profiles and branching ratios, which reveal a wealth of details on the complex electronic structure of this molecule.     

Mass spectrometric and quantum mechanical analysis of gas-phase formation, structure, and decomposition of various b2 ions and their specifically deuterated analogs

B ions represent an important type of fragment ions derived from protonated peptides by cleavage of an amide bond with N-terminal charge retention. Such species have also been discussed as key intermediates during cyclic peptide fragmentation. Detailed structural information on such ion types can facilitate the interpretation of multiple step fragmentations such as the formation of inner chain fragments from linear peptides or the fragmentation of cyclic peptides. The structure of different b₂ ion isomers was investigated with collision-induced dissociations (CID) in combination with hydrogen/deuterium (H/D) exchange of the acidic protons. Special care was taken to investigate fragment ions derived from pure gas-phase processes. Structures deduced from the results of the CID analysis were compared with structures predicted on the basis of quantum chemical density functional theory (DFT) calculations to be most stable. The results pointed to different types of structures for b₂ ion isomers of complementary amino acid sequences. Either the protonated oxazolone structure or the N-terminally protonated immonium ion structure were proposed on the basis of the CID results and the DFT calculations. In addition, the analysis of different selectively N-alkylated peptide analogs revealed mechanistic details of the processes generating b ions.     

Multiisotopic modeling of fragmentation ion patterns in mass spectra of organometallic and coordination compounds

Investigation of hardly interpretable complex patterns can lead to an explanation of details of fragmentation and, therefore, the identification of ion clusters can be a significant procedure of mass spectra interpretation. The modeling presented remains a simple tool for mass spectra interpretation and determination of parameters of complex cluster components. Good adjustment of model to experimental data suggests that such components must be considered in the pattern interpretation; approach results in the model fits within a 1% precision for the cluster of two or more components. Applications of the Multiisotopic Modeling of Fragmentation Ion Patterns (MMFIP method) are presented for bis(dibutyldithiophosphate)‐zinc(II)‐[(C₄H₉O)₂PS₂]₂Zn, 1′,1‴‐dibenzylbiferrocene‐C₃₄H₃₀Fe₂ and 1,1′,2,2′,3,3′‐hexachloroferrocene‐C₁₀H₄Cl₆Fe as examples. It seems that the isotopic cluster modeling based on the least squares method can be a helpful aid for determination of the complex pattern components. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 354–365, 2001     

Methodology and procedure of the stoichiographic analysis of solid inorganic substances and materials

The technical and experimental aspects of creating the conditions of differential dissolution in a flow stoichiographic system are discussed; the scheme of the experimental apparatus, stoichiograph, is presented. The construction, operation conditions of the main units of the stoichiograph, and sample treatment issues are considered. The principles of the creation and optimization of the conditions of the dynamic differential dissolution for the analysis of compounds and materials of the known and unknown phase composition are discussed: the composition of solvents and temperature, and the principles of their variation in time, including those in the processes of stoichiographic titration.     

Molecular conformations of a partially halogenated ether: A study based on infrared spectroscopy and density functional theory calculations

A new partially halogenated ether (ClCF₂CF(CF₃)OCF₂CH₃) has been synthesized and characterized using DSC, GC, ¹H and ¹⁹F NMR, IR. The experimental infrared spectra of this “flexible” molecule have been successfully interpreted on the basis of reliable Density Functional Theory calculations. An efficient method useful for the identification of the many stable conformers has been developed and applied. Infrared spectra of the stable conformers have been simulated after full geometry optimization. The results obtained allow detection of conformation-sensitive bands, making possible the interpretation of fine details in the spectra.     

Efficient Routes to Racemic and Enantiomerically Pure (S)-BINOL Diesters

A systematic study for esterification procedures to the synthesis of BINOL diesters is described. Reaction conditions with trifluoracetic acid anhydride (TFAA) and 85% H₃PO₄ were selected as the best procedure to prepare enantiomerically pure (S)-1,1′-bi-2-naphthol (BINOL) diesters VIII to XI with almost quantitative yields and very short reaction times.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications^® for the following free supplemental resources: Full experimental and spectral details.]     

Crystalline inclusion compounds of a new diol host featuring a combination of anthracene and 9-fluorenol units

The diol host compound 2 has been synthesised and its behaviour to form crystalline inclusion compounds is discussed in comparison with an analogous ethynylene spaced host compound 1. The rotation around the fluorenol–anthracene bonds in 2 is highly restricted as indicated by solution NMR spectroscopy, molecular mechanics and semi-empirical calculations. Single-crystal X-ray structures of the inclusion complexes of 2 with 1-BuOH (2a), morpholine/H₂O (2b) and DMSO (2c) are in agreement with the bent geometry of the anthracene ring system suggested by the calculations. The structures exhibit specific modes of hydrogen bond interactions.     

系列三核钼硫簇合物的合成、结构表征和性质研究

系统地报道了9个三核钼硫簇合物的合成和结构表征. 晶体结构分析表明, 其中化合物1和6具有[Mo₃(μ₃-S)(μ-S)₃]簇芯, 化合物2和3具有不对称的簇芯[Mo₃(μ₃-S)(μ-O)(μ-S)₂], 化合物4, 5, 7和8具有少见的[Mo₃(μ₃-O)(μ-S)₃]簇芯, 而化合物9则具有[Mo₃(μ₃-S)(μ-S₂)₃]簇芯. 这一系列不同的簇芯以及桥配体和“松散”配位的端配体造成了不同的堆积结构. 讨论了前三种簇芯的电子结构, 并根据它们的立体构型和电子结构对某些重要的谱学表征结果做了合理的诠释. 测定了化合物4的变温电导率, 表明其具有半导体导电性能.     

A new SCF procedure and its applications to ab initio calculations of the states of the fluorosulphate radical

Ab initio calculations using a small Gaussian basis set, including 3d orbitals on the sulphur atom, have been performed on the fluorosulphate radical and the related ions SO₃F⁺ and SO₃F^?. A new SCF procedure is described and applied to the open shell cases discussed here. The results are compared with recent CNDO calculations and with the experimental transition energies of the radical.     

Hartree-Fock calculations and photoelectron spectra of SSO and NSF

Results from ab initio Hartree-Fock calculations on the ground states of SSO and NSF are reported. The calculations employ large basis sets of Gaussian functions of essentially double zeta quality. The photoelectron spectra of the bent triatomic molecules with 18 valence electrons, i.e. SSO, NSF, O₃, SO₂, NSCl are compared. Further experimental details of the photoelectron spectrum of SSO are presented and an assignment of the observed ionic states of SSO⊕ is attempted. The calculated dissociation energies, dipole moments and the population analyses are given. The correlation effect is qualitatively discussed in connection with the applicability of Koopmans' theorem for the bent tri-atomic molecules.     

Spectroscopic and Theoretical Investigations on Supramolecular Interaction of a Newly Designed Monoporphyrin with Fullerenes and Functionalized Fullerenes in Solution

The present paper reports the results of a photophysical investigation of a designed monoporphyrin (1) and its supramolecular complexes with C₆₀, C₇₀ and derivatized fullerenes, namely tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl C₇₁ butyric acid methyl ester (3) in toluene. UV–vis studies reveal appreciable ground state interaction between the fullerenes and compound 1. Steady state fluorescence studies show quenching of fluorescence of 1 in the presence of fullerenes. The binding constants of the C₆₀/1, C₇₀/1, 2/1 and 3/1 complexes are estimated to be 300, 20770, 1150 and 13170 dm³⋅mol⁻¹, respectively. Molecular mechanics calculations in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and allow interpretation of the stability difference among various fullerene complexes of 1 in terms of their enthalpies of formation.     

On the structure of the intermediate phases in the praseodymium oxide system

The defect crystal structures for two phases in the praseodymium oxide system (Pr₉O₁₆, ζ phase; and Pr₄₀O₇₂, ε phase) are proposed on the basis of the results of a high-resolution transmission electron microscope (HRTEM) study. Dynamical n-beam electron scattering calculations are used to provide a more accurate and reliable interpretation of the experimental micrographs. In addition, electron diffraction studies reveal the unit-cell dimensions for the n = 11 member in the homologous series of phases in this system. The structural relationships among the related praseodymium oxide phases are discussed.     

Galvanic Stripping Analysis in Trace Determination of Gallium

Abstract

A galvanic stripping analysis procedure is described for the trace determination of gallium. This determination involves (i) pre-concentration of gallium onto mercury film coated glassy carbon electrode and (ii) re-oxidation in open circuit position by advantageously utilizing the localized galvanic couple formation (in the absence of external electrical field or oxidant in solution). The details of the development of such a procedure for the determination of 7–700 ppb of gallium are discussed.     

Novel Aspects in the Synthesis of Carbenoids Containing P/C-pπ-Bonds

Abstract

The synthesis and x-ray structure analysis of a novel type of carbenoids, aryl-P(=E)=C(Cl)Li(thf)₃ (E=N-aryl, C(SiMe₃)₂), as well as the first example of a 1,3-diphosphetane-2,4-diyl, (aryl-PCCl)₂, is reported and on the basis of quantum chemical calculations its bonding situation is discussed. Furthermore, selected examples for the varying reaction behavior of both types of compounds are presented.     

Conformational Transmission in 5′-PV and 5′-PV TBP Phosphorylated Nucleosides. Implications For DNA Structure and Dynamics

Abstract

Specific conformational changes in DNA and RNA can be induced via a transient pentacoordination of the phosphorus atoms in the helix backbone. The details of this conformational transmission mechanism are discussed briefly, using experimental data that were obtained with a set of 5′-pIV and 5′-pV phosphorylated tetrahydrofurfuryl systems. A conformational study on the more realistic model system, the dinucleotide 2 in which a stabilized pentacoordinated phosphorus forms the internucleoside linkage, is presented. Furthermore, it has been found that methylation of the phosphate groups in d(T_pT_pT_pT_pT_pT) results in the formation of a non-Watson & Crick type parallel duplex DNA structure, in which the two strands are joined via hydrogen bonding between the thymidine bases. Various physico-chemical techniques (e.g. NMR methods and UV hyperchromicity) were used to elucidate the structural details of the parallel duplex. Characteristic properties (parallellity, slimness, symmetry) are presented.