Current theories of astringency propose that this sensation is a result of delubrication in the oral cavity due to precipitation of salivary proteins. Astringency, commonly described as a drying or puckering sensation, is a main driving factor for rejection of certain foods. Previous studies have shown that fat plays a role in moderating astringency in foods. To investigate the role that polyphenols and fat play in astringency perception, we used modified cocoa powders to produce pseudo-cocoa liquor systems that were rated for taste and flavor attributes on generalized Labeled Magnitude Scales by semi-trained consumers. Our results show significant differences among the cocoa liquors, resulting from acetone-water extraction of free polyphenols and fat content variation. No significant differences resulted from training with oil-based vis-à-vis water-based reference solutions. Practical ApplicationsAstringency is a prominent sensation commonly experienced by individuals who consume cocoa and chocolate products. It is of the utmost importance to the cocoa and chocolate industry because consumers typically reject products that are highly astringent. Therefore, study of the perception of astringency and the role that polyphenols and fat play would benefit our understanding of these fat-based products. Training with aqueous-based references, which was easier than oil-based references, yielded equivalent results.

Quantum dots (QDs) are useful for demonstrating the particle-in-a-box (PIB) model utilized in quantum chemistry, and can readily be applied to a discussion of both thermodynamics and kinetics in an undergraduate laboratory setting. Modifications of existing synthetic procedures were used to create QDs of different sizes and compositions (CdS passivated with polymer, and CdSe passivated with oleic acid/ trioctylphosphine). These were investigated by spectroscopy, to which standard 3D PIB mathematical models were applied to determine their effective size. The data were compared to those from other methods for students to see the validity of the PIB model. For CdSe QDs, an empirical formula was applied to the spectroscopic data. In the case of CdS, the synthesized QDs were studied with X-ray diffraction, from which one can also estimate the size of the QDs. Finally, the QDs were utilized as the light-harvesting layer in photovoltaic cells by attachment to a layer of surface-modified titania (TiO 2 ) nanoparticles on conductive glass, and the surface chemistry tested via water contact-angle measurements. The photoresponse of these cells was measured using basic electrochemistry equipment for a selection of QDs, and these results were considered in relation to the light source used for excitation (CdS QDs absorb UV light, and a voltage was only measurable upon exposure to UV light). Students are able to synthesize, characterize, and apply their materials to a functional purpose. Ultimately, students drafted reports in the form of an ACS-style communication, allowing for a tie-in of typical lab reports to real-world journal publications.

The principles of chemical kinetics comprise one of the core topics that appear throughout chemistry. Standard kinetics lessons typically cover reaction rates and relative rates, rate laws, integrated rate laws, half-lives, collision theory, and the Arrhenius equation. They can also introduce a discussion of mechanisms as well, which may be the first time students become aware of the importance of actual reaction path in general chemistry. Such concepts are grounded in mathematical descriptions of molecular movement and probability factors, and the convergence of various new topics with mathematics can be challenging. In an attempt to make these concepts less abstract, we developed analogies utilizing dice in a can that provide a tangible way to experience the realistic meaning behind kinetics, and briefly introduce students to statistical thermodynamics. One version is designed as a general science workshop, whereas the other is aimed at physical chemistry courses. Kinetic energy is put into the system via shaking the can of dice, which is used to represent temperature in our model. The dice are tossed, and “products” are removed before the procedure is repeated. In a first-order kinetic simulation, a reaction is symbolized by dice facing “6” up after tossing. To simulate second-order kinetics, a hook and loop fastener is attached to the dice and a successful reaction is represented by the formation of a pair having two “6”s facing up. Students are able to experience the difference between first- and second-order mechanisms and to reason through the parameters that affect reaction rates and rate constants. The overall goal is to allow for self-discovery of the purpose behind the intersecting topics in kinetic theory by incorporating data collection, dimensional analysis, plotting, and derivation of equations.

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