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Effective assessment is an extremely important area of chemistry education. Typically tests measure students’ knowledge of critical thinking skills, chemistry vocabulary, and application of concepts from one chapter to another. While it is relatively straightforward to measure concepts such as chemical vocabulary and algorithmic problem solving during a regular session with paper-pencil based testing, an online test with no proctoring presents significant challenges to test administration. In the COVID-19 term, when instruction moved online, it was imperative that the authenticity of the tests administered to students was maintained, irrespective of an institution’s choice to allow students to select credit/noncredit or pass/fail options. This communication describes some of the challenges faced during online testing and some of the strategies implemented to successfully overcome them.

The synthesis and spectroscopic characterization of several methacryloxy-modified spiropyran dyes is reported. The dyes were found to have similar photochromic isomerization rates relative to a commercially available reference compound in solution. The methacryloxy-modified dyes were also successfully incorporated into polymer matrices, where they retained their ability to photoisomerize and complex with cobalt (II) and zinc (II) ions.

A quantitative and qualitative high-performance liquid chromatography (HPLC) analysis of single-origin chocolates is presented as a laboratory experiment for an advanced analytical chemistry course. The quantitative portion involves the determination of caffeine and theobromine content by an internal standard calibration method and then a validation by comparison to a certified reference material. The qualitative component introduces students to chemometrics through the use of discriminant analysis to determine the provenance of an unknown single-origin chocolate sample.

The mammalian olfactory system is able to detect many more odorants than the number of receptors it has by utilizing cross-reactive odorant receptors that generate unique response patterns for each odorant. Mimicking the mammalian system, artificial noses combine cross-reactive sensor arrays with pattern recognition algorithms to create robust odor-discrimination systems. The first artificial nose reported in 1982 utilized a tin-oxide sensor array. Since then, however, a wide range of sensor technologies have been developed and commercialized. This review highlights the most commonly employed sensor types in artificial noses: electrical, gravimetric, and optical sensors. The applications of nose systems are also reviewed, covering areas such as food and beverage quality control, chemical warfare agent detection, and medical diagnostics. A brief discussion of future trends for the technology is also provided.

This paper discusses the use of flow dynamics in a model nasal cavity as a novel way to expand the information available from a fiber optic vapor sensor. Nasal cavities are known to play an important role in vertebrate olfaction; however, they have not previously been incorporated into gas-phase sensor technology. By exposing identical sensors to different flow environments, we found that measurements of the combined sensor responses provided increased discrimination of a series of alcohols as compared to measurements obtained from a single sensor at the anterior of the cavity. This methodology is potentially useful for improving the discriminatory power of sensors employed in “artificial noses” and could be used to model the effects of flow dynamics in vertebrate olfaction.

An artificial nose based on microsphere sensor arrays has been developed for the discrimination of numerous volatile organic compounds. Sensor elements consist of 3-5 micron diameter silica and polymer spheres that have a fluorescent, solvatochromic dye adsorbed to the microsphere surface. These sensors respond to changes in the local polarity of the environment by shifting their excitation and/or emission characteristics, thereby indicating the presence of different volatile compounds. High-density microsphere arrays are fabricated which contain thousands of individual sensor elements and multiple copies of each sensor type. By monitoring the sensors temporal fluorescence responses with a CCD camera, unique patterns are recorded that identify individual analytes or are characteristic of a complex mixture. By summing over the redundant sensor elements within an array, the signal-to-noise ratio can be enhanced. These types of sensor arrays have been used to detect and discriminate between different bacterial strains such as Escherichia coli based on characteristic odors from the live and dead bacteria.

Conventional approaches to chemical sensors have traditionally made use of a “lock-and-key” design, wherein a specific receptor is synthesized in order to strongly and highly selectively bind the analyte of interest.1-6 A related approach involves exploiting a general physicochemical effect selectively toward a single analyte, such as the use of the ionic effect in the construction of a pH electrode. In the first approach, selectivity is achieved through recognition of the analyte at the receptor site, and in the second, selectivity is achieved through the transduction process in which the method of detection dictates which species are sensed. Such approaches are appropriate when a specific target compound is to be identified in the presence of controlled backgrounds and interferences. However, this type of approach requires the synthesis of a separate, highly selective sensor for each analyte to be detected. In addition, this type of approach is not particularly useful for analyzing, classifying, or assigning human value judgments to the composition of complex vapor mixtures such as perfumes, beers, foods, mixtures of solvents, etc.

This paper describes the use of a microsphere sensor technology that allows simple fabrication of vapor sensor arrays with reproducible response patterns. Microsphere sensor fabrication protocols are uncomplicated and yield billions of highly reproducible sensors. Microsphere sensor arrays combined with a generalized Whitney−Mann−Wilcoxen (GWMW) classifier were used to discriminate between the presence and absence of nitroaromatic compounds in high background vapor mixtures. The classifier was trained on one sensor array and then used to obtain 98.2 and 93.7% correct classification rates with data collected using two subsequent arrays made up to six months after the initial training was performed. These results represent an advance in the ability to transfer training data between multiple sensor arrays with a fluorescence-based artificial nose.

Three hexadentate, podand-type, polypyridyl ligands, (5-bpy-2C)(3)Bz, (4-bpy-2C-Ph)(3)Et, and (4-phen-2C-Ph)(3)Et, and their Ru(II) and Fe(II) complexes have been prepared. Reaction of these ligands with Fe(II) produces only the monometallic hemicage species, while monometallic, bimetallic, and polymetallic Ru(II) complexes are formed. These species are separable by column chromatography, and NMR and ESI mass spectrometry demonstrate that with each ligand the first band to elute corresponds to the monometallic species, [RuL](2+). The ESI mass spectra show peaks for [RuL](2+) and [RuL](PF(6))(+) with expected m/z values and isotope peak spacings. (1)H NMR spectroscopy shows that [Ru(5-bpy-2C)(3)Bz](2+) is trigonally symmetric and contains a rigid methylene bridge between the capping group and the bipyridines. The excited-state lifetimes and emission quantum yields for the hemicage complexes, [Ru(5-bpy-2C)(3)Bz](2+), [Ru(4-bpy-2C-Ph)(3)Et](2+), and [Ru(4-phen-2C-Ph)(3)Et](2+), are significantly enhanced (tau = 2800, 1470, and 3860 ns, and Phi(em) = 0.271, 0.104, 0.202, respectively) relative to the model compounds and to the polymetallic complexes with the same ligand. An Arrhenius fit of temperature-dependent lifetime data for [Ru(5-bpy-2C)(3)Bz](2+) indicates a high activation energy for crossover to the dd state (DeltaE = 4960 cm(-)(1)) as well as the existence of an additional pathway for deactivation via a "4th MLCT" state. Only after extensive photolysis of [Ru(5-bpy-2C)(3)Bz](2+) is any decrease in emission intensity observed; this is accompanied by the formation of a bimetallic photoproduct, [Ru(2)L(2)](4+), with a quantum yield of 7.4 x 10(-)(6). Quenching studies with a variety of quenchers show that the useful excited-state redox and energy-transfer properties characteristic of Ru(II) polypyridyls are retained, but with improved photoinertness and photophysical properties arising from the rigidity of the hemicage complex.

Conventional approaches to chemical sensors have traditionally made use of a “lock-and-key” design, wherein a specific receptor is synthesized in order to strongly and highly selectively bind the analyte of interest.1-6 A related approach involves exploiting a general physicochemical effect selectively toward a single analyte, such as the use of the ionic effect in the construction of a pH electrode. In the first approach, selectivity is achieved through recognition of the analyte at the receptor site, and in the second, selectivity is achieved through the transduction process in which the method of detection dictates which species are sensed. Such approaches are appropriate when a specific target compound is to be identified in the presence of controlled backgrounds and interferences. However, this type of approach requires the synthesis of a separate, highly selective sensor for each analyte to be detected. In addition, this type of approach is not particularly useful for analyzing, classifying, or assigning human value judgments to the composition of complex vapor mixtures such as perfumes, beers, foods, mixtures of solvents, etc.