A Theoretical Study of Amine Bonding in Titanium Alkoxide Adducts

Summary. DFT calculations were carried out on Ti₂(OCH₃)₈ (NH₂CH₃)₂ and Ti₂(OCH₃)₈(NH₃)₂, which are model compounds for the previously isolated amine adducts Ti₂(OR)₈(NH₂ R′)₂. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on Ti t_2g-like orbitals.     

Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped metal-phthalocyanine compounds

We have performed a comparative study of the electronic properties of six different electron-doped metal-phthalocyanine (MPc) compounds (ZnPc, CuPc, NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by means of potassium intercalation. Despite the complexity of these systems, we find that the nature of the underlying molecular orbitals produces observable effects in the doping dependence of the electrical conductivity of the materials. For all the MPc's in which the added electrons are expected to occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping dependence of the conductivity has an essentially identical shape. This shape is different from that observed in MPc materials in which electrons are also added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The observed relation between the macroscopic electronic properties of the MPc compounds and the properties of the molecular orbitals of the constituent molecules clearly indicates the richness of the alkali-doped metal-phthalocyanines as a model class of compounds for the investigation of the electronic properties of molecular systems.     

Synthesis and catalytic properties of soluble platinum nanoparticles protected by a thiol monolayer

Several new platinum monolayer protected clusters (MPCs) have been synthesized and characterized. Two methods of platinum reduction were used depending on the solubility of the thiol: sodium borohydride for the water-soluble thiols and lithium triethylborohydride for the organic soluble thiols. In general, reactant solutions containing a 1:1 thiol/Pt ratio yielded the best particles in a single-phase reaction. Higher thiol/Pt ratios produced lower yields of MPCs, while much lower ratios produced gray-black precipitates. The Pt MPCs were used as catalysts to hydrogenate allyl alcohol to propanol by reducing the carbon-carbon double bond. The Pt-mercaptoammonium MPCs were also used as catalysts in the hydrogenation of maleic acid to succinic acid. Differences in the catalytic hydrogenation rates among the various monolayer coatings for MPCs are attributed to the variations in ligand chain length, branching, charged functional groups, packing density, and core size.     

Phase-fixed double-group 3-Γ symbols. IV. Real 3-Γ symbols and coupling coefficients for the group hierarchies T* ⊃ C 3 * and T* ⊃ C 2 *

We present sets of real 3- symbols which correspond to explicitly given irreducible matrix representations for the two double group hierarchies T* C ₃ ^* and T* C ₂ ^* . They fit into the formalism exposed in a previous paper [1] on the general theory of 3- symbols and coupling coefficients and illustrate much of the discussion in a subsequent one [2] treating the particular properties of the double groups.     

The crystal structure of CuSb2O3Br: Slabs from cubic Sb2O3 interspersed between puckered hexagonal CuBr-type layers

The new compound CuSb₂O₃Br crystallize in the monoclinic space group Cc. The unit cell parameters are , , , β=90°, Z=16. The crystal structure is solved from single crystal data, R=0.0490. The compound show a layered structure with slabs from cubic Sb₂O₃ interspersed in between puckered layers of CuBr. The Sb(III) atoms have tetrahedral [SbO₃E] coordination where E is the 5s² lone pair, these units build up Sb₄O₄E₆ cages. The CuBr layers resemble those in hexagonal CuBr but the Cu(I) ions have actually tetrahedral [CuBr₃O] coordination. The Cu-O bonds link the Sb₄O₆ cages with the CuBr layers.     

Übergangsmetall-silyl-komplexe: IV. Bildung eines ring-substituierten wolframocen dihydrid derivats durch reaktion von Cp2WCl2 MIT Li[Si(SiMe3)3]

In the reaction of Cp₂WGl₂ with Li[Si(SiMe₃)₃] the dihydrid tungstenocene derivative [(Me₃Si)₃SiC₅H₄]WH₂ (3) is formed with a 56% yield. 3 crystallizes in space group P$\text{1}$, with a 918.0(4), b 1580.9(4), c 1621.2(7) pm, α 117.63(2), β 89.95(3), γ 94.39(3)° at ?40° C. The dihedral angle between the Cp planes is 140.9°.     

Selex: An expert system for evaluating published data on selenium in foods

Providing consistent and objective evaluation of published data on nutrient composition is critical for planning future analytical studies and for effective use of data. Based on a commercial expert system shell, a computer system of approximately 200 rules has been created to evaluate and ratre quantitatively published data on selenium in foods. The evaluation scheme uses five general categories for its rule-making process: number of samples, analytical method, sample handling, sampling plan, and analytical quality control. For each selenium value to be evaluted, rating ar assigned in each category by the expert system based on input which is derived from the information reportedin a given paper. A quality index, which is derived from the ratings, is a measure of the reliability of a given selenium value over all categories for a given study. The concepts used in developing SELEX have the potential of establishing criteria for evaluation of proposed analytical methods prior to their publication.     

Theoretical exploration of structure-reactivity relationships in organometallic chemistry: butadiene insertion into the organyltransition-metal bond and conversion of the allyltransition-metal fragment in the [Ni(η-Cp)(η-phenyl)(η-butadiene)] complex

We have theoretically examined the reaction course of the butadiene insertion into the arylNi^II bond in the [Ni^II(η⁵-Cp)(η¹-phenyl)(η²-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η¹-σ→η³-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η³- and syn-η³-allyl isomers of the [Ni^II(η⁵-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η³-allyl isomer. Butadiene preferably inserts in η²-mode into the η¹-phenylNi^II bond, initially giving rise to the η¹(C³)-allyl product species, 3σ. The direct formation of the η³-allyl product species, 3π, along the alternative path for η⁴-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η²-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η³-allylNi^II coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η³-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η³-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η³-allyl→syn-η³-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η³-allylNi^II coordination.     

Alkylation studies on 6-ethyl-2,3-dihydrothiazolo-[3,2-A] pyrimidine-5,7-diones

The title compound 7b undergoes alkylation with ethyl iodide or ethyl sulfate at the 7-position yielding the O-ethylated product 10 rather than 6,6-diethyl product 8 as reported previously. Reaction of 7b with mesyl chloride gives 13b which on reaction with potassium carbonate in absolute ethanol also gives 10. Treatment of 7b with phosphorus oxychloride gives 11b which on reaction with potassium carbonate or sodium ethoxide in ethanol produced a mixture from which no 10 was isolated. Authentic 8 was prepared by the reaction of 2-amino-thiazoline with ethyl diethylmalonyl chloride (20) in THF containing triethylamine or by the reaction of 5,5-diethyl-2-thiouracil (18) with excess 1,2-dibromoethane.     

Simultaneous determination of albumin and immunoglobulin G with fluorescence spectroscopy and multivariate calibration

A method is proposed for the simultaneous determination of albumin and immunoglobulin G (IgG1) with fluorescence spectroscopy and multivariate calibration with partial least squares regression (PLS). The influence of some instrumental parameters were investigated with two experimental designs comprising 19 and 11 experiments, respectively. The investigated parameters were excitation and emission slit, detection voltage and scan rate. When a suitable instrumental setting had been found, a minor calibration and test set were analysed and evaluated. Thereafter, a larger calibration of albumin and IgG1 was made out of 26 samples (0-42 μg ml⁻¹ albumin and 0-12.7 μg ml⁻¹ IgG1). This calibration was validated with a test set consisting of 14 samples in the same concentration range. The precision of the method was estimated by analysing two test set samples for six times each. The scan modes tested were emission scan and synchronous scan Δ60 nm. The results showed that the method could be used for determination of albumin and IgG1 (albumin, root mean square error of prediction (RMSEP) <2, relative standard error of prediction (RSEP) <6% and IgG1, RMSEP <1, RSEP <8%) in spite of the overlapping fluorescence of the two compounds. The estimated precision was relative standard deviation (R.S.D.) <1.7%. The method was finally applied for the analysis of some sample fractions from an albumin standard used in affinity chromatography.