Acylierung von Heterocyclen mit Kohlensäurederivaten. I. Kinetik und Mechanismus der Reaktion von 2-Aminobenzimidazolen mit Arylcyanaten

Acylation of Heterocycles with Carbonic Acid Derivatives. I. Kinetics and Mechanism of the Reaction of 2-Aminobenzimidazoles with Aryl Cyanates The second order rate constants for the reaction of 2-amino-benzimidazoles (2-ABI) with aryl cyanates forming 2-amino-benzimidazole aryl ester imide 3 have been determined in dependence on substituent effects by u. v. measurements. The results are interpreted by a six-membered cyclic transition state in which the electrophilic attack of the cyanate on the endocyclic N atom is catalyzed by an H bridge interaction of the exocyclic amino group of 2-ABI with the OCN group.     

A rapid spectroscopic method for quantification of P57 in Hoodia gordonii raw material

The feasibility of quantifying the perceived active ingredient (P57) in Hoodia gordonii raw material using Fourier transform near- and mid-infrared spectroscopy combined with chemometric techniques was investigated. The concentration of P57 (a triterpene glycoside) was determined in 146 plant samples with liquid chromatography coupled to mass spectrometry and these values were used to develop a calibration model based on the partial least squares projections to latent structures (PLS) and orthogonal projections to latent structures (O-PLS) regression algorithms. The performance of each calibration model was evaluated according to the root mean square error of prediction (RMSEP) and correlation coefficient (R²). The PLS model with 2nd derivative pre-processing predicted P57 content based on the FT-NIR spectra with the best accuracy and a correlation coefficient (R²) value of 0.9629 and the lowest RMSEP of 0.03%. These results demonstrated that FT-NIR spectroscopy can be used to rapidly quantify P57 in H. gordonii raw material with high accuracy.     

Reaction mechanism of poly(vinyl chloride) degradation. Molecular orbital calculations

Semiempirical Molecular Orbital Calculations (MNDO AM1) support kinetic results concerning the molecular mechanism of thermal degradation of PVC and show that under special conditions radical and ionic mechanisms are also possible. The degradation of poly(vinyl chloride) is a complex chain dehydrochlorination that consists of an initiation process to generate an active intermediate followed by chain reactions that generate additional active intermediates with progressively increased numbers of double bonds. Each intermediate partitions between an intermediate with one more double bond and a stable conjugated polyene with the same number of double bonds. At low and moderate temperatures thermal degradation of PVC in an inert atmosphere is a succession of molecular concerted reactions. The initiation process is a 1,2-elimination through a four center transition state requiring a synperiplanar conformation. There are two main chain reactions: the first is a 1,4-elimination from allylic chlorine atoms and methylenes cis to a double bond through a transition state of six centers; the second is a 1,3-rearrangement of hydrogen atoms catalyzed by hydrogen chloride. The chain reaction is interrupted when a relatively stable trans double bond is formed and no hydrogen chloride is present to catalyze trans-cis isomerization or 1,3-rearrangement. Macro carbocations formed by heterolysis of carbon-halogen bonds in the presence of strong Lewis acids react much faster than does the original PVC in concerted elimination by 1,2-syn or 1,4-cis mechanisms, promoting a so-called catastrophic, very fast degradation. Macro radicals formed by thermal homolysis, irradiation or reaction with promoters can also promote very fast hydrogen chloride elimination because of a special mechanism consisting of a 1,2-rearrangement of a chlorine atom followed by a concerted 1,3-elimination through a five center transition state.     

Process and technology challenges in swift-starting virtual teams

Virtual teams often face tight schedules and a need to start quickly and perform instantly. The goal of our study was to enhance understanding of the challenges faced by such teams. We used time–interaction–performance theory as the framework for following the processes and functions within virtual teams working on a systems development task. Our study provided a detailed examination of the group process, applied to virtual teams working under time pressure. The challenges faced by virtual teams in such settings showed that teams must work to enhance their effectiveness in multiple dimensions.     

Study of additive compatibility with poly (vinyl chloride). 1: Dynamic mechanical analysis (DMA) of impact modified rigid PVC containing ester lubricants

The glass transition temperatures of impact modified PVC with different amounts of lubricants have been used to define two new parameters of lubrication: the saturation concentration and the efficiency constant. The use of lubricants at significantly lower concentration than the saturation concentration ensures their permanence in the polymer. They then act as internal lubricants reducing the viscosity of the melt. The use of lubricants at much higher concentrations ensures their release at the surface of the polymer, giving them an external character. The efficiency constant characterizes the capability of the lubricant to modify the properties of the polymer and increase flow. Polyacrylate impact modifiers form distinct polymer phases and consequently the effect of lubricants on impact modifier may be characterized in the same way by the two constants. The choice of impact modifier and lubricant for a given application can be rationally made by using the two characteristic parameters. The described procedure can be applied to any polymer and all the additives that can migrate in the polymeric phase as long as their glass transition temperatures can be measured.     

Managing strategic contradictions in hybrid teams

It has become a common practice to organize work teams to include members in multiple geographic locations. In contrast to co-located teams and purely virtual teams, these ‘hybrid’ teams combine face-to-face communication with computer-mediated interaction. In this paper, we report a qualitative study of management practices in three hybrid teams in one organization. We adopt the theoretical approach of strategic contradiction, in which apparently contradictory pairs of elements can be managed by attending to their possible synergies or clarifying their distinctions so as to make balanced trade-offs over time. Our data reveal four sets of paradoxical frames in hybrid teams: remoteness–closeness, cultural uniformity–cultural diversity, rationality–emotionality, and control–empowerment. In referencing these paradoxical frames, teams engaged in three cognitive processes: (a) integrating to produce synergies between opposing tensions, (b) differentiating to clarify distinctions between opposing tensions and to balance trade-offs over time, and (c) polarizing to remove tensions between opposing elements by using one element to reduce the effects of another. Both integrating and differentiating processes were found to be instrumental to sustaining contradictions as interdependent dualities, whereas polarizing processes were found to preserve contradictions as dualisms. Our findings advance the understanding of managing strategic contradictions by showing how managers influence cognitive processes that paradoxically emphasize remoteness and closeness, cultural uniformity and cultural diversity, rationality and emotionality, and control and empowerment.     

Nucleophile Substitutionen an Kohlensäurederivaten. XII. Kinetik und Mechanismus der Reaktion von N-Nitro-N-alkylurethanen mit primären aliphatischen Aminen

Nucleophilic Substitutions to Carbonic Acid Derivates. XII. Kinetics and Mechanism of the Reaction of N-Nitro-N-alkyl-urethanes with Primary Aliphatic Amines The aminolysis of N-alkyl-N-nitrourethanes takes place, as the kinetical studies demonstrate, by means of several consecutive steps. The nucleophilic attack of the amine (first step; reaction B), as well as the proton-transfere (second step; reaction C), are quick pre-equilibres, followed by the slow, rate-determining elimination of the nitramino-group (reaction D). During the deprotonation, an intermediate with two to the nitramino-group antiperiplanar orbitals is formed, providing the necessary mesomeric assistance of the elimination.     

Ultraviolet radiation as a non-thermal treatment for the inactivation of microorganisms in fruit juice

Fruit juices can be processed using ultraviolet (UV-C) light to reduce the number of microorganisms. The UV-C wavelength of 254 nm is used for the disinfection and has a germicidal effect against microorganisms. A novel turbulent flow system was used for the treatment of apple juice, guava-and-pineapple juice, mango nectar, strawberry nectar and two different orange and tropical juices. In comparison to heat pasteurization, juices treated with UV did not change taste and color profiles. Ultraviolet dosage levels (J L^− 1) of 0, 230, 459, 689, 918, 1 148, 1 377, 1 607 and 2 066 were applied to the different juice products in order to reduce the microbial load to acceptable levels. UV-C radiation was successfully applied to reduce the microbial load in the different single strength fruit juices and nectars but optimization is essential for each juice treated. This novel UV technology could be an alternative technology, instead of thermal treatment or application of antimicrobial compounds.

Industrial relevance

This novel UV-C system can be applied successfully to the Food Industry. UV-C can be effectively used to reduce the number of spoilage and pathogenic bacteria, as well as yeasts and moulds in different kinds of fruit juices.