Density functional study of lanthanide complexes (η-C5H5)2LnX·OC4H8 (Ln=La-Lu; X=F, Cl, Br and I)

Density functional calculations were performed on a series of mixed-ligand organolanthanide complexes, (η⁵-C₅H₅)₂LnX·OC₄H₈ (η⁵-C₅H₅=Cp; Ln=La-Lu; X=F, Cl, Br and I; OC₄H₈=THF). The calculated geometrical parameters are in reasonable agreement with the experimental data. The distances between Ln and ligands follow linearity along the ionic radius of lanthanide metal, as the same as that observed in experiment. In the mixed-ligand complexes, Ln-Cp and Ln-THF bonds are more covalent compared to Ln-X. The lanthanide contraction of various bond and the metal-ligand interaction energy followed the order of Ln-X>Ln-Cp>Ln-OC₄H₈. The orbital population and dipole moment were also discussed.     

Proton-Induced Tuning of Electrochemical and Photophysical Properties in Mononuclear and Dinuclear Ruthenium Complexes Containing 2,2'-Bis(benzimidazol-2-yl)-4,4'-bipyridine: Synthesis, Molecular Structure, and Mixed-Valence State and Excited-State Properties

A series of mono- and dinuclear Ru(bpy)(2) complexes (bpy = 2,2'-bipyridine) containing 2,2'-bis(benzimidazol-2-yl)-4,4'-bipyridine (bbbpyH(2)) were prepared. The mononuclear complex [Ru(bpy)(2)(bbbpyH(2))](ClO(4))(2).CH(3)OH.4H(2)O was characterized by an X-ray structure determination. Crystal data are as follows: triclinic, space group P&onemacr;, a = 14.443(4) ?, b = 15.392(4) ?, c = 11.675(2)?, alpha = 101.44(2) degrees, beta = 107.85(2) degrees, gamma = 96.36(2) degrees, V = 2380(1) ?(3), Z = 2. The coordination geometry of the ruthenium(II) ion is approximately octahedral. The dihedral angle between the two pyridyl rings in bbbpyH(2) is 9.4(3) degrees, which is close to coplanar, in the complex. Mono- and dinuclear complexes exhibit broad charge-transfer absorption bands at 420-520 nm and emission at 660-720 nm in CH(3)CN solution with lifetimes of 200-800 ns at room temperature. Transient difference absorption spectra and resonance Raman (rR) spectra were used to assign the charge-transfer bands in the 420-520 nm region and to identify the lowest excited states. Both absorption and emission spectra are sensitive to solvent and solution pH. Deprotonation of the dinuclear complex raises the energies of the pi orbitals of the bbbpyH(2) ligand, so that they become closer in energy to the pi orbitals of bpy. The intervalence band of [(bpy)(2)Ru(bbbpyH(2))Ru(bpy)(2)](5+)()()is observed at 1200 nm ( epsilon = 170 M(-)(1) cm(-)(1)) in CH(3)CN. The value of the electronic coupling matrix element, H(AB), was determined as 120 cm(-)(1). Upon deprotonation, the IT band was not observed. It is therefore concluded that a superexchange pathway occurs predominantly via the Ru(II) dpi-bbbpyH(2) pi interaction, since deprotonation decreases the interaction. The role of the intervening fragments in the bridging ligand is discussed from the viewpoint of orbital energies and their orbital mixing with Ru dpi orbitals.     

Discovery of (E)-9,10-dehydroepothilones through chemical synthesis: on the emergence of 26-trifluoro-(E)-9,10-dehydro-12,13-desoxyepothilone B as a promising anticancer drug candidate

We provide a full account of the discovery of the (E)-9,10-dehydro derivatives of 12,13-desoxyepothilone B (dEpoB), a new class of antitumor agents with promising in vivo preclinical properties. The compounds, which are to date not available by modification of any of the naturally occurring epothilones, were discovered through total chemical synthesis. We describe how our investigations of ring-closing metathesis reactions in epothilone settings led to the first and second generation syntheses of (E)-9,10-dehydro-12,13-desoxyepothilone congener 6. With further modifications, the synthesis was applied to reach a 26-trifluoro derivative compound (see compound 7). To conduct such studies and in anticipation of future development needs, the total synthesis which led to the initial discovery of compound 7 was simplified significantly. The total synthesis methodology used to reach compound 7 was then applied to reach more readily formulated compounds, bearing hydroxy and amino functionality on the 21-position (see compounds 45, 62, and 63). Following extensive in vitro evaluations of these new congeners, compound 7 was nominated for in vivo evaluations in xenograft models. The data provided herein demonstrate a promising therapeutic efficacy, activity against large tumors, nonrelapseability, and oral activity. These results have identified compound 7 as a particularly promising compound for clinical development. The excellent, totally synthetic, route to 7 makes such a program quite feasible.     

Racemic D,L-asparagine causes enantiomeric excess of other coexisting racemic D,L-amino acids during recrystallization: a hypothesis accounting for the origin of L-amino acids in the biosphere

When recrystallizations were performed using a mixture of 12 D,L-amino acids (alanine, aspartic acid, arginine, glutamic acid, glutamine, histidine, leucine, methionine, serine, valine, phenylalanine, and tyrosine) with excess D,L-asparagine, all amino acids with the same configuration as asparagine were preferentially co-crystallized, indicating that it is the nature of a mixture of racemic amino acids to produce a spontaneous high enantiomeric excess.     

Determination of Drugs in Blood Samples by High Performance Liquid Chromatography Using On-Line Sample Pretreatment Technique

The flow diagram of this on-line sample pretreatment system is shown in Fig. I.     

Determination of rhenium in molybdenite by neutron-activation analysis

A neutron-activation method is described for the determination of rhenium in molybdenite. Radiochemical separation by a carrier technique was carried out very rapidly by means of successive liquid-liquid extraction processes. The recovery of rhenium, which was determined by a spectrophotometric method, was about 93%. About 10 samples could be analysed within 6 hr in parallel runs.     

Optimising oxygen-sensitivity of optical sensor using pyrene carboxylic acid by myristic acid co-chemisorption onto anodic oxidized aluminium plate

Optical oxygen-sensitivity using pyrene carboxylic acid with long alkyl chain (1-pyrenedecanoic acid and 1-pyrenedodecanoic acid) and myristic acid co-chemisorption layer was controlled by varying the molar ratio of myristic acid to pyrene carboxylic acid. The ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities from a substrate exposed to 100% argon and 100% oxygen, respectively, is used as an indicator of the sensitivity of the sensing film. At a composition ratio of 1 pyrene carboxylic acid to 10 myristic acids, the I₀/I₁₀₀ attained its maximum value and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The Stern-Volmer constant (K_SV) also attained its maximum value at a composition ratio of one pyrene carboxylic acid to ten myristic acids and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The oxygen-sensitivity of optical sensor using pyrene carboxylic acid is optimized by myristic acid co-chemisorption.     

Miniaturization of batch- and flow-type chemiluminescence detectors in capillary electrophoresis

Glass and PTFE tubes as detection cells were put in small light-tight boxes to achieve miniaturization of batch-and flow-type chemiluminescence detectors for capillary electrophoresis. These light-tight boxes which included a detection cell and a photosensor module were successfully designed. In the batch-type detector using a glass tube as a detection cell, the influences of a repeated injection of sample and a reagent volume of the detection cell on chemiluminescence intensity were examined in detail. By using 3.8 mm I.D. glass tube including 400 microl chemiluminescence reagent solution, the chemiluminescence peaks were reproducibly observed for the repeated injection experiment up to the eight injection with each run time of 3.0 min. Dansyl-Trp was determined over the range 3 x 10(-8)-1 x 10(-5) M with the detection limit of 0.43 fmol (S/N=3). In the flow-type detector using a PTFE tube as a detection cell, both ends of the PTFE tube were connected to three-way joints; a chemiluminescence reagent solution was delivered into the cell and a capillary was inserted through one of the joints while an electrode was inserted through the other one. Dansyl-Trp was determined over the range 1 x 10(-7)-1 x 10(-5) M with the detection limit of 1.3 fmol (S/N=3). By using the compact flow-type detector, a mixture of dansyl-amino acids was separated and detected in micellar electrokinetic chromatography mode.