Effect of support on the synergy in HDS of thiophene and HDN of pyridine over Mo sulfide catalysts promoted by Rh

The effect of support (SiO₂-Al₂O₃, Al₂O₃,MgO) of the Rh-Mo(S) sulfide catalysts on the synergy in hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine was studied. The synergy in HDS was between 7–10 regardless of the kind of support used. The synergy in HDN varied from none over the MgO supported sample to about 3 over SiO₂-Al₂O₃ supported catalyst, in accord with the positive effect of increasing support acidities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis and molecular structure of methyl 4-O-methyl-alpha-D-glucopyranuronate

A method for the preparation of methyl 4-O-methyl-alpha-D-glucopyranuronate and its single crystal X-ray structure determination are reported. The molecule adopts an almost ideal (4)C1 ((degree)C3) conformation.     

On-line preconcentration of trace copper for flame atomic absorption spectrometry using a spherical cellulose sorbent with chemically bound quinolin-8-ol

Preconcentration was effected using a 50 mm × 2 mm i.d. minicolumn packed with a spherical cellulose sorbent with chemically bound quinolin-8-ol function groups (Ostorb Oxin). The column was connected to the nebulizer of the atomic absorption spectrometer and the sample solution and eluent (2 M hydrochloric acid) were sucked through it at a flow-rate of 2–3 ml min^?1 by utilizing the negative pressure of the nebulizer. The experimental design was tested with the determination of traces of copper. Peak-area and peak-height measurements were compared. Owing to the simple calibration, the former method was used for quantification. The dynamic range was from 0.3 ng ml^?1 (detection limit) to 5 μg ml^?1 (breakthrough). The reproducibility in the concentration range 25 ng ml^?1-5 μg ml^?1 was better than 5%. Water-soluble inorganic salts, ammonia and sodium hydroxide were analysed. The accuracy of the results was checked by anodic-stripping voltammetry and by electrothermal AAS.     

Charge transfer across a polymer gel/liquid interface: determination of ionophores

An electrochemical method for the determination of the ionophores monensin and lasalocid was developed, based on the polarization of an agar gel/nitrobenzene electrolyte interface. The measured current corresponding to the facilitated ion transfer across this interface is directly proportional to the concentration of an ionophore dissolved in the organic phase. Using cyclic voltammetry in a three-electrode system the detection limit for both ionophores is about 3 × 10^?5 M.     

Projective algebras

Presented by R. Freese.     

Oscillatory criteria for nonlinearnth-order differential equations with quasiderivatives

Sufficient conditions are given for the existence of oscillatory proper solutions of a differential equation with quasiderivativesL _n y=f(t,L ₀ y, ..., L _n–1 y) under the validity of the sign conditionf(t,x ₁ ,...,x _n )x ₁0,f(t,0,x ₂ ,...,x _n )=0 on ₊ x ⁿ .     

On the accuracy of molecular properties by coupled-cluster methods for some difficult examples: Oxygen atom,iron atom,and cyano radical

Coupled-cluster (CC ) methods at the level of CCSD , CCSD +T (CCSD ), CCSD (T ), CCSDT -1, and CCSDT -3 are applied to calculations of the dipole moment and polarizability of the CN molecule, ionization potentials and electron affinities of the oxygen and iron atoms and CN molecule, and the energy splitting of the ⁵D and ⁵F states of the iron atom. Both UHF and ROHF references are applied. Extended basis sets are used in some comparison of CC data to experiment. All calculated atomic and molecular properties are known as challenging problems, suitable for a careful analysis of the performance of sophisticated versions of the CC approach. Attention is paid to energy terms distinguishing CCSD (T ) from CCSD +T (CCSD ). We exploit results from various iterative and noniterative high-level CC methods in the assessment of error bars in calculations of atomic and molecular properties. © 1994 John Wiley & Sons, Inc.     

Fourth-order diagrammatic MB-RSPT calculations of the interaction energy between two helium atoms

The efficiency of the MB-RSPT in the calculations of the correlation contributions to the interaction energies was investigated, using He₂ as a model Van der Waals system. The attention has been focused on the convergency of the perturbation expansion in the calculations of the interaction energy and on the analysis of the fourth-order terms of MB-RSPT. The rôle of the renormalization term in the correct long-range behaviour of the interaction potential has been emphasized.     

2,8'-disubstituted-1,1'-binaphthyls: a new pattern in chiral ligands

The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2'-(diphenylphosphino)-1,1'-binaphthyl (MOP, 19) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15-->18), followed by functional group transformations, involving C-P and C-N bond formation (18-->19 and 18-->23). Racemic intermediate 22 was resolved by co-crystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(-)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92% ee (after hydrolysis of the primary product).