Nornicotine aqueous aldol reactions: synthetic and theoretical investigations into the origins of catalysis

The recent discovery that nornicotine 1, a minor nicotine metabolite, can catalyze the aldol reaction under physiologically relevant conditions has initiated research efforts into the potential chemical roles of nicotine metabolites. Herein, we disclose studies aimed at determining the origin and thus mechanism of the nornicotine-catalyzed aqueous aldol reaction. Conformationally constrained compounds designed to mimic the low-energy conformations of nornicotine were synthesized and tested for aldol catalysis; however, none showed rate enhancements on par with nornicotine. To further explore the mechanism of this process, a density functional theory (DFT) study was performed by using a variety of compounds previously tested for catalysis. These in silico studies have uncovered an unprecedented mechanistic subtlety of aqueous aldol reactions. Unlike the single transition state model observed for aldol reactions in organic solvent, the nornicotine-catalyzed reaction in water proceeds via a two-step mechanism in which a water molecule is utilized in both steps and a stable intermediate is generated. In total, these studies validate the proposed enamine-based mechanism of nornicotine-catalyzed aqueous aldol reactions and also provide the basis for future studies into the stereoelectronic nature of individual catalyst structures.     

2,5-diphenyl-3-morpholinofuran and its 2-hydro, 2-bromo and 2-hydroxymorpholinofurylium salts

2,5-Diphenyl-3-morpholinofuran ( 1 ) reacts with bromine and trifluoroacetic acid, giving respectively 2-bromo and 2-hydro furylium salts ( 2,3 ). The 2-hydroxy furylium bromide ( 4 ) was obtained by reaction of cis-morpholino-1,2-dibenzoylethylene ( 5 ) with hydrogen bromide. The nmr spectra of these salts show differences between the two morpholino dimethylene moieties of each caused by restricted rotation at the 3-immonium group. Chemical relationships studied include reductions to the morpholinofuran, conversions to 3-furanones, and the slow reaction of morpholinodibenzoylethylene with phenylmagnesium bromide to give cis-dibenzoylstyrene (13).     

Great expectations: Specific lexical anticipation influences the processing of spoken language

Background  

Recently several studies have shown that people use contextual information to make predictions about the rest of the sentence or story as the text unfolds. Using event related potentials (ERPs) we tested whether these on-line predictions are based on a message-level representation of the discourse or on simple automatic activation by individual words. Subjects heard short stories that were highly constraining for one specific noun, or stories that were not specifically predictive but contained the same prime words as the predictive stories. To test whether listeners make specific predictions critical nouns were preceded by an adjective that was inflected according to, or in contrast with, the gender of the expected noun.     

Microwave heating of ceramic composites

The microwave heating of a ceramic composite is modelled andanalysed. The composite consists of many small ceramic particlesembedded in a ceramic cement. The composite is assumed to bewell insulated, and each particle is assumed to be in imperfectthermal contact with the surrounding cement. Based on thesetwo assumptions an asymptotic theory exploiting the small Biotnumber and small non-dimensional contact conductance is developed.Our asymptotic theory yields a set of nonlinear partial differentialequations which govern the temperature in the composite. Theseare reduced to a set of coupled nonlinear ordinary differentialequations in which the surface area of each particle entersas a parameter. Recent experiments with such composites haveshown that the steady-state temperature of the composite isstrongly dependent upon the radii of the embedded particles.Our model captures this effect. In fact, our analysis showsthat the assumption of imperfect thermal contact between theparticles and the ceramic cement is essential for this trendto be established.