Complexes of azobisindoles with π-organic acceptors

Complexes of azobisindoles with tetracyanoethylene and tetracyanoquinodimethane were studied by UV-Vis, FT-IR, Raman, NMR and X-ray spectroscopies. FT-IR and Raman spectra, as well as X-ray analysis, gave useful information on the participation of various sites to the association, through analysis of CN and N=N vibrational modes, while UV-Vis and NMR spectra were less helpful. The crystal structure of complexes 1-ethyl-2-phenyl-3-(1-ethyl-2-phenyl-3-azoindole)indole/TCNE,3a and 1,2-diphenyl-3-(1,2-diphenyl-3-azoindole)indole/TCNQ,5b are reported. In the two complexes, the distances between donor and acceptor planes range between 3.4 and 3.5 Å; in3a tetracyanoethylene faces the phenyl ring of the indole, while in5b the superposition of tetracyanoquinodimethane with the donor is negligible. Compound3a,P–1,a=9.504(2),b=9.513(3),c=8.941(2) Å, =97.81(4), =103.38(3), =84.14(2)°,Z=2,D _calc=2.55 g cm^–3; compound5b,P–1,a=12.648(3),b=12.205(2),c=7.263(3) Å, =103.69(2), =91.23(3), =110.61(2)°,Z=2,D _calc=2.53 g cm^–3.     

Molecular structures of quinuclidinic neurokinin antagonists: 2-(2-Phenylbenzylidene)-3-(2-X-benzylamino) derivatives

The solid-state molecular conformations and crystal structures of three analogues of the CP-96,345 molecule, an important nonpeptidic SP antagonist, namely the (±)-2-(3-phenylbenzilidene)-3-(2-benzylamino) quinuclidine, theo-chloro- and theo-methoxy-derivatives, have been determined by X-ray diffusion analyses and refined to finalR values of 0.055, 0.045, and 0.056, respectively. All three molecules in the solid state show the same disposition of the substituents of the double bond and differences in the conformation mainly caused by the need of releasing intramolecular strains and/or nonbonded interactions. The observed molecular structures are compared to the reported solid-state structure of the CP-96,345 and correlated to the biological activity as NK antagonists.     

Limits of stability of microcomputer-controlled scanning systems for strain-gage data readings

The zero-drift and the relative interval of uncertainty associated with two multichannel sequential automated systems for strain-gage data readings were examined. The strain-measurement systems are made up of a switch control unit (with mechanical relays), digital multimeters, power-supply unit and microcomputer. These devices are generally available in laboratories. Significant differences were observed by comparing the results obtained with the systems examined.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

Fabrication of plastic microchips by hot embossing

Plastic microchips with microchannels (100 microm wide, 40 microm deep) of varying designs have been fabricated in polymethylmethacrylate by a hot embossing process using an electroform tool produced starting with silicon chip masters. Hot-embossed chips were capped with a polymethylmethacrylate top using a proprietary solvent bonding process. Holes were drilled through the top of the chip to allow access to the channels. The chips were tested with fluid and shown to fill easily. The seal between the top of the chip and the hot embossed base was effective, and there was no leakage from the channels when fluid was pumped through the microchannels. The chips were also tested with a semen sample and the plastic chip performed identically to the previous silicon-glass and glass versions of the chip. This microfabrication technique offers a viable and potentially high-volume low cost production method for fabricating transparent microchips for analytical applications.     

Kinetics and Thermodynamics of Binding of a Model Tripeptide to Teicoplanin and Analogous Semisynthetic Antibiotics

The thermodynamics and kinetics of binding of model tripeptides epsilon-N-acetyl-alpha-N-dansyl-L-Lys-D-Ala-D-Ala (ADLAA) or alpha-N,epsilon-N-diacetyl-L-Lys-D-Ala-D-Ala (AALAA) to teicoplanin (1a) and a series of semisynthetic derivatives with (1b-f) or devoid of (2a-g) the glycidic side arms and modified at the terminal amino acids of the peptide backbone have been studied by fluorescence or UV spectroscopy. The binding process is suggested to occur via a two-step mechanism. The first, fast process is likely governed by an electrostatic interaction between the C- and N-termini of the peptide chain of the substrate and of the antibiotic, respectively, while the second slower one, accounts for the formation of the hydrogen bonds responsible of the major contribution to the overall binding energy. The binding constants with all modified derivatives are smaller than that with native teicoplanin. Larger modification of the overall binding constant are observed when the sugar residues are removed and, to a lower extent, when the N-terminus of the peptide chain is acylated. The kinetic process is very little affected by the modifications introduced.     

Supported ionic liquid asymmetric catalysis. A new method for chiral catalysts recycling. The case of proline-catalyzed aldol reaction

A new method for chiral catalysts recycling, based on the supported ionic liquid asymmetric catalysis concept, has been developed. This concept involves the treatment of a monolayer of covalently attached ionic liquid on the surface of silica gel with additional ionic liquid. These layers serve as the reaction phase in which the homogeneous chiral catalyst is dissolved. As first application of this concept the L-proline-catalyzed aldol reaction has been carried out. Good yields and ee values, comparable with those obtained under homogeneous conditions have been obtained. Moreover, this material shows high regenerability.     

Acid-base equilibria in organic solvents : Part 3. An Absolute pH Scale from Proton Basicity Evaluated by Cyclic Voltammetry

The relative basicity of some organic solvents of electroanalytical interest (propylene carbonate, sulfolane, 2-methyltetrahydrofuran, methyl formate and morpholine) is evaluated by cyclic voltammetry. Anhydrous perchloric acid is electrogenerated in these solvents and the half-wave potentials of the redox couple H⁺/H₂ are recorded by referring them to a reference system, here bis(biphenyl)chromium (I)/bis(biphenyl)chromium(0), which is independent of the nature of the solvent. The data obtained, together with those found previously for other solvents by following the same procedure, are used to draw an absolute pH scale covering a wide range of basicities from nitromethane to morpholine. The same approach is also utilized to evaluate and compare, on the basis of this absolute pH scale, the strength in the solvents studied of some nitrogen bases which are suitable as titrants in nonaqueous media. The proposed proton basicity scale is compared with other basicity series defined in the literature.     

A preliminary study on the migration mechanism of heavy metals into the vadose zone of soils of a dismissed industrial site

Within the framework of the site assessment of a dismantled steel-making plant area contaminated by Electric Arc Furnace dust (EAF dust), the actual migration of Cr, Cu, As, Cd, Pb, Zn and Ni (contaminants) from an industrial waste layer towards the vadose zone of the underlying soil has been evaluated. The crystalline phases and contaminant abundance of samples of the industrial waste layer and the surrounding soils were analysed, while the release of contaminants was evaluated by leaching tests. Results indicate the migration of pollutants from the industrial waste layer into the subsurface soil, but the high leachability of soil hides its real degree of contamination, with the consequent possibility of underestimating the hazardous characteristics of the actual situation.     

Fast atom bombardment mass spectrometry of neutral methanide and ionic carbene platinum(II) derivatives

The fast atom bombardment mass spectra of a series of neutral methanide and ionic carbene platinum(II) complexes of formula dPePtL₂ and [dPePt(LH)₂](BF₄)₂ (dPe = (C₆H₅)₂PCH₂CH₂P(C₆H₅)₂; L = ? C(OCH₃)-NCH₃, ? C(OCH₃) ? NC₆H₁₁, ? C(OCH₃) ? NC₆H₄p ? CH₃), respectively are reported. Glycerol, 3-mercapto-1,2-propanediol, bis (2-hydroxyethyl)sulphide, 3-nitrobenzyl alcohol, and 2,4-di-tert-pentylphenol have been used as matrices. Neutral and ionic derivatives containing the same ligand behave similarly and give the same quasi-molecular [dPePtL(L + H)]⁺ ion by different primary processes. Stepwise breakdown of the ligands L with retention or further loss of atoms or molecules of hydrogen is observed for all these complexes, followed by ejection of radicals from the dPe ligand. Elimination of CH₃OH from [dPePtL(L + H)]⁺ also occurs. The highest ionic yields of both neutral methanide and ionic carbene complexes are observed in 3-mercapto-1,2-propanediol, in bis(2-hydroxyethyl)sulphide, and in 3-nitrobenzyl alcohol with respect to glycerol. The [dPePt(LH)₂]²⁺ doubly charged ions are present in the spectra obtained with 3-nitrobenzyl alcohol and are rather strong when L is ? C(OCH₃) ? NCH₃ and ? C(OCH₃) ? NC₆H₄p ? CH₃. Substitution of ligands L with a molecule or with a fragment of a sulphur containing matrix takes place very seldom with this series of complexes.