Silver(I) 3-aminomethylpyridine complexes, part 2: effect of ligand ratio, hydrogen bonding, and pi-stacking with an interacting anion

Reaction of 3-aminomethylpyridine (3-amp) with silver(I) salts of triflate (OTf-) and trifluoroacetate (tfa-) produce a variety of multidimensional coordination networks whose structures depend on the stoichiometry of the components present. A 1:1 ratio of 3-amp to AgX produces a linear polymer, 1, when X = tfa- and a planar sheet, 2, when X = OTf-. Addition of a second equivalent of ligand increases the dimensionality of both structures by one to form a two-dimensional sheet, 3, and a three-dimensional system, 4, for their respective anions. Addition of 2,2'-bipyridine (bipy) to solutions of any of the previous compounds produces the fixed-ratio complexes 5 (tfa- salt) and 6 (OTf- salt). The bipyridyl ligand halts the polymerization of compounds 1-4 by cutting the chain after each silver(I) link and forcing a 1:2:2 ratio of 3-amp to AgX to bipy. Compound 5, however, remains polymeric in nature due to the closed-shell Ag-Ag interactions of the planar metals holding the monomers together. Differences between structures of each ratio stem from the differences in basicity and in the extra degree of H-bonding ability that the OTf- anion has over tfa-.     

Stereoselective synthesis of methyl monate C

[Structure: see text] The stereoselective synthesis of methyl monate C 2 is described using as a key step an ene-intramolecular modified Sakurai cyclization (IMSC) reaction to prepare tetrahydropyran 5. An asymmetric allylic alkylation, followed by a cross-metathesis, enables the insertion of the right-hand side chain.     

Enhancing aperiodic stochastic resonance through noise modulation

We show that the conventional stochastic resonance (SR) effect for aperiodic signals in a model neuron can be enhanced by modulating the intensity of the input noise (which could be introduced artificially in bioengineering applications) with either the input signal or the unit's output rate signal. We analyze SR enhancement theoretically and numerically. We discuss how this work provides the theoretical foundation for the development of an optimal noise-based technique for enhancing sensory function. (c) 1998 American Institute of Physics.     

Curtius rearrangement in the 5-phenyl-1,4-benzodiazepine series. Unprecedented participation by an imine nitrogen

The previously unknown 3-aminomethyl-1,3-dihydro-5-(2′-fluorophenyl)-2H,4-benzodiazepin-2-one, 3a, was synthesized in two steps as a racemate. In the chiral series, 3(S)-azidocarbonylmethyl-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, 12b, was prepared from Nα-Cbz-β-methylaspartate in five synthetic operations and subjected to Curtius rearrangement. The intermediate isocyanate was trapped intramolecularly by the 5-imine nitrogen of the benzodiazepine ring in 12b. This unanticipated result runs counter to the generally held dictum that the isocyanate group has a strictly linear shape.     

Evaluation of the BAX system for detection of Listeria monocytogenes in foods: collaborative study

A multilaboratory study was conducted to compare the automated BAX system and the standard cultural methods for detection of Listeria monocytogenes in foods. Six food types (frankfurters, soft cheese, smoked salmon, raw, ground beef, fresh radishes, and frozen peas) were analyzed by each method. For each food type, 3 inoculation levels were tested: high (average of 2 CFU/g), low (average of 0.2 CFU/g) and uninoculated controls. A total of 25 laboratories representing government and industry participated. Of the 2335 samples analyzed, 1109 were positive by the BAX system and 1115 were positive by the standard method. A Chi square analysis of each of the 6 food types, at the 3 inoculation levels tested, was performed. For all foods, except radishes, the BAX system performed as well as or better than the standard reference methods based on the Chi square results.     

The thermal,spectral and magnetic studies ofp-tolylacetic acid compounds of cobalt,nickel and copper

The preparation and some properties of complexes ofp-tolylacetic acid with cobalt, nickel and copper are described. Magnetic measurements, electronic and far infrared spectra show that the metal complexes have octahedral structures. Infrared spectra indicate that coordination takes place through the carboxyl group to the metal ions and that the water molecule in each of the complexes is present as water of crystallisation. Thermogravimetry studies also show that the water molecules in each of the complexes do not form a coordinate bond with the metal ion. Differential thermal analysis show that the dehydration processes are accompanied by endothermic reactions. In each case the anhydrous metal complex undergoes an exothermic reaction to give the metal oxide.This work was supported by the Carnegie Trust for the Universities of Scotland and the Hungarian OTKA foundation (T-4096).     

Asymmetric proliferation with optically active polyanilines

Thin optically active polyaniline layers have been shown to function as platforms to induce optical activity in polyanilines (containing achiral dopants) that are formed by subsequent electrodeposition.     

Nanocomposites of Polyaniline/Poly(2‐methoxyaniline‐5‐sulfonic acid)

Summary: Poly(2‐methoxyaniline‐5‐sulfonic acid) (PMAS) is a water‐soluble derivative of polyaniline that carries negatively charged sulfonate groups. This self‐doped conducting polymer also behaves like a polyelectrolyte that can subsequently function as a dopant in polyaniline (PAn). The chemical synthesis of PAn/PMAS is presented describing the preparation of a highly stable composite dispersion. TEM images reveal a mixture of well‐defined nanofibres and nanoparticles with diameters between 20 and 100 nm. The UV‐vis spectra of the PAn/PMAS composite in water and in alkaline media indicate that both PAn and PMAS are present in the composite. Electrochemical studies show that both of the conducting polymer components are capable of undergoing oxidation and reduction. The novel PAn/PMAS nanocomposite has enhanced electrical conductivity and stability compared to PAn/HCl nanofibres prepared under equivalent conditions, making it a promising material for applications in areas such as batteries, electronic textiles, electrochromics, and chemical sensors.

Transmission electron micrograph of a PAn/PMAS nanocomposite.     

Acoustic generation of bubbles in excised canine urinary bladders

A high-intensity, 555-kHz acoustic field was used to generate bubbles within urinary bladders excised from dogs. Following the exposure, bubbles were visualized on a diagnostic ultrasound scanner with a 5-MHz in-line mechanical sector scanhead. Scattering of the high-intensity ultrasound by the bubbles was also observed during the exposure as high-amplitude scan lines. The bladders used had been surgically removed after tying off the ureters and urethra to prevent urine loss and exposure to external contaminants. Each bladder was sealed in a plastic bag filled with a degassed saline solution. The bladder was centered in a sealed degassed water path at the common focus of a 7-cm-diam transducer and a 10-cm-diam brass reflector. The 555-kHz transducer and reflector were both focused at 10 cm and were aligned coaxially. Using various acoustic pressure amplitudes, two, 10-s low-frequency exposures, separated by approximately 30 s, occurred at approximately 2-min intervals. Experiments on a single bladder lasted as long as 45 min. The sizes of the largest bubbles, which were easily imaged, were estimated from rise velocity measurements as 50-70 microns in radius, and pressure amplitudes used to generate those large bubbles were estimated as 10-20 bars. The detection of smaller bubbles was limited by the inability to clearly distinguish bubble echoes from artifacts caused by the reverberant field within the bladder. Visual inspection of the exterior and interior bladder wall showed no significant discoloration within the high intensity beam path.(ABSTRACT TRUNCATED AT 250 WORDS)