Synthese, 13C-NMR-Spektren und räumliche Struktur von ‘Push-Pull’-Diacetylenen

Synthesis, ¹³C-NMR Spectra, and X-Ray Investigation of ‘Push-Pull’ Diacetylenes Phenyl-substituted ‘push-pull’ diacetylenes 1f and 1g have been prepared by acetylation and benzoylation of the appropriate lithiodiynylamines 4 (Scheme 2). ¹³C-NMR spectra of diacetylenes 1a–g (Table 1) are discussed with respect to the expected polarisation of the diacetylene unit by ‘push’ and ‘pull’ substituents. X-Ray investigations of 1c , 1e , and 1f have been performed in view of the planned solid-state polymerisation of ‘push-pull’ diacetylenes. In the crystalline state, diacetylenes 1c and 1f are stacked, however, the stacking parameters do not allow a solid-state polymerisation.     

Impact noise and the equal energy hypothesis

The equal energy hypothesis (EEH) was evaluated over a limited range of conditions by exposing four groups of chinchillas to impact noise (200-ms B duration) presented at a fixed rate of four impacts per second. The intensity of the impacts (107-125 dB peak SPL) and the duration (120-1.87 h) of the four exposure conditions were counterbalanced so that the four groups received the same total energy. The traumatic power of the exposures was assessed by measuring the threshold shift of the auditory evoked response and the amount of hair cell loss. Exposure between 107 and 119 dB were consistent with the EEH in that they produced roughly the same amount of permanent threshold shift (less than 20 dB) and hair cell loss (less than 20%). However, the 125-dB exposure produced substantially more threshold shift and hair cell loss than the three lower intensities. Thus, the EEH may be applicable only at lower impact intensities; above a "critical intensity" the amount of damage increases significantly.     

Study of process parameters for starch,gluten, and glycerol mixtures

This work involved a study of the effect of processing variables (temperature, water content, rotor speed, and time) on the mechanical properties of starch:gluten:glycerol mixtures in the weight ratio of 40:40:20. The properties of the materials were affected by the processing variables. The torque decreased with water content, indicating that water facilitates the plasticization of mixtures, whereas the increase in temperature accelerated the evaporation of water, thus increasing the torque. Ultimate tensile strength was achieved at the lowest temperature (110°C) and the highest water content (20%), whereas maximum elongation was achieved for the material processed at the highest temperature, 150°C, and the fastest rotor speed, 70 rpm. Copyright © 2007 John Wiley & Sons, Ltd.     

Ligand dynamics and reactivity in trimetallic clusters

The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to ₃-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in ₃-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth.     

Fast atom bombardment mass spectrometric analysis of the partial ozonolysis products of poly(isoprene) and poly(chloroprene)

The low molecular weight compounds formed by partial ozonolysis of poly(isoprene) and poly(chloroprene) were analyzed by fast atom bombardment mass spectrometry (FABMS). In the poly(chloroprene) case, the ozonized mixtures were treated with piperidine before the MS analysis to transform in amide end groups the reactive acyl chlorides formed by the cleavage of double bonds along the main chain. Only one family of compounds having carboxyl and ketone or carboxyl and amide end groups were obtained from the ozonolysis of poly(isoprene) and poly(chloroprene), respectively. The assigned structures were confirmed by FAB-MS analysis of the GPC separation fractions [poly(chloroprene)] or by FAB-MS of the KOH-doped ozonolysis mixtures [poly(isoprene)]. It has been also ascertained, by GPC experiments, that poly(chloroprene) decomposes more rapidly than poly(isoprene) and poly(butadiene).     

Iodine-poly(2-vinylpyridine-co-styrene-co-divinylbenzene) charge transfer complexes with antibacterial activity

In this work, we have developed three different copolymers based on 2-vinylpyridine, styrene and crosslinked with divinylbenzene (10-30 mol%). The copolymers were morphologically and chemically characterized by apparent density, swelling degree, elemental analysis, Fourier transform infrared spectrophotometry and optical microscopy. The formation of iodine complexes with these copolymers was carried out by two different procedures: with solvent, or not. The influence of the copolymers structure on the capacity of anchoring iodine has been investigated. The antibacterial properties of polymeric charge transfer complexes were determined towards 10³-10⁷ cells/mL dilutions from the auxotrophic AB1157 Escherichia coli strain.     

Synthesis of quaternary amino acids bearing a (2'Z)-fluorovinyl alpha-branch: potential PLP enzyme inactivators

Protected alpha-formyl amino acids, themselves available from the corresponding alpha-vinyl amino acids, are stereoselectively transformed into the (Z)-configured alpha-(2'-fluoro)vinyl amino acids via a three-step sequence. The route employs McCarthy's reagent, diethyl alpha-fluoro-alpha-(phenylsulfonyl)methyl phosphonate, and proceeds via the intermediate (E)-alpha-fluorovinyl sulfones and (E)-alpha-fluorovinylstannanes. The latter may either be exploited as novel cross-coupling partners for fluorovinyl branch extension or be globally deprotected, to provide the title compounds. [structure: see text]     

Determination of salicylate in blood serum using an amperometric biosensor based on salicylate hydroxylase immobilized in a polypyrrole-glutaraldehyde matrix

The use of an amperometric biosensor for the salicylate determination in blood serum is described. The biosensor is based on salicylate hydroxylase (EC 1.14.13.1) electropolymerized onto a glassy carbon-working electrode with polypyrrole and glutaraldehyde, to improve the biosensor lifetime. The hexacyanoferrate (II) was also incorporated to work as a redox mediator to minimize possible interferences. The salicylate is enzymatically converted to catechol, which is monitored amperometrically by its electrooxidation at+0.170 V versus SCE (saturated calomel electrode). Salicylate determination was carried out maintaining the ratio between beta-NADH and salicylate at 4:1 (30 degrees C). The amperometric response of the biosensor was linearly proportional to the salicylate concentration between 2.3x10(-6) and 1.4x10(-5) mol l(-1), in 0.1 mol l(-1) phosphate buffer (pH 7.8), containing 0.1 mol l(-1) KCl and 5.0x10(-4) mol l(-1) Na(2)H(2)EDTA, as supporting electrolyte. The recovery studies, in the presence of several interfering compounds, showed recoveries between 96.4 and 104.8%. The useful lifetime of the biosensor in the concentration range evaluated was at least 40 days, in continuous use. Blood serum samples analyzed by this biosensor showed a good correlation compared to the spectrophotometric method (Trinder) used as reference, presenting relative deviations lower than 7.0%.     

Ring-opening Sn2'' reactions of 7-oxanorbornenes by organolithium reagents. Regio- and stereospecific synthesis of substituted cyclohexenediols

The nucleophilic Sn2' bridge opening of 7-oxabicyclo[2.2.1] hept-5-en-2-ols with organolithium reagents occurs in a regio- and stereospecific fashion to produce 6-substituted-cyclohex-4-en-1,3-diols, regardless of the stereochemistry at C-2. A free alcohol functionality is necessary to attain complete regiocontrol of the process. The methodology is utilized to prepare an optically pure cyclohexene derivative, (+)-(1S,3S,6R)-6-n-butyl-3-methyl-cyclohex-4-en-1,3-diol (5b), as a model system.     

Study of the ESI-mass spectrometry ionization mechanism of Fischer carbene complexes

By means of deuterium-labeling experiments, we have carried out a systematic ESI-MS study to determine the mechanism of ESI ionization of alkenyl and alkynyl group 6 Fischer carbene complexes. These compounds can be ionized under ESI conditions only in the presence of additives such as hydroquinone (HQ) or tetrathiafulvalene (TTF). Our results demonstrate that in the ESI source an anion-radical is formed after the initial HQ- or TTF-mediated electron transfer to the metallic carbene complex. For alkenyl carbene complexes, this species evolves by extrusion of a hydrogen radical to form an allenylchromium anion that is detected as the [M - H](-) ion in the mass spectrum. The preference for this mechanistic pathway could be rationalized by DFT calculations. In the case of alkynyl carbene complexes, experiments combining deuterated substrate, additive, and solvent demonstrate that the previously proposed allene-anion carbene complex is not formed. Instead, the H transfer from the ethoxy group in the anion radical, followed by extrusion of a hydrogen radical, leads to an allenyl anion that is detected in the ESI-MS as [M - H - CO](-).