When Mentos candies are dropped into a bottle of Diet Coke, a foamy fountain jets out of the beverage container. It has previously been argued that ingredients found in Mentos candies significantly enhance this fountaining effect. Other previous work has demonstrated that the kinetics of foam production can be quantitatively monitored using a device constructed from inexpensive, easily obtained materials. In the results reported here, students used this simple device to monitor the kinetics of foam production in the Diet Coke and Mentos experiment and to draw conclusions about the system. It was possible to model the kinetic data obtained using kinetic mechanisms that involve irreversible first-order steps. Furthermore, the data collected allowed students to acquire evidence that the kinetics of foam production appears to be unaffected by the presence of certain ingredients in candies and gums, in contrast to previous claims. Many of the protocols described herein can be carried out simply and inexpensively, making them useful for high school, introductory, and general chemistry courses. In addition, the kinetic data collected are of sufficient quality to allow for analysis sophisticated enough for use in student research projects and physical chemistry courses.

Oxygen evolution by photosystem II (PSII) is activated by chloride and other monovalent anions. In this study, the effects of iodide on oxygen evolution activity were investigated using PSII-enriched membrane fragments from spinach. In the absence of Cl(-), the dependence of oxygen evolution activity on I(-) concentration showed activation followed by inhibition in both intact PSII and NaCl-washed PSII, which lacked the PsbP and PsbQ subunits. Using a substrate inhibition model, the range of values of the Michaelis constant K(M) in intact PSII (0.5-1.5 mM) was smaller than that in NaCl-washed PSII (1.5-5 mM), whereas values of the inhibition constant K(I) in intact PSII (9-17 mM) were larger than those in NaCl-washed PSII (1-4 mM). Studies of I(-) inhibition of Cl(-)-activated oxygen evolution in intact PSII revealed that I(-) was primarily an uncompetitive inhibitor, with uncompetitive constant K(i)' = 37 mM and Cl(-)-competitive constant K(i) > 200 mM. This result indicated that the activating Cl(-) must be bound for inhibition to take place, which is consistent with the substrate inhibition model for I(-) activation. The S(2) state multiline and g = 4.1 EPR signals in NaCl-washed PSII were examined in the presence of 3 and 25 mM NaI, corresponding to I(-)-activated and I(-)-inhibited conditions, respectively. The two S(2) state signals were observed at both I(-) concentrations, indicating that I(-) substitutes for Cl(-) in formation of the signals and that advancement to the S(2) state was not prevented by high I(-) concentrations. A model is presented that incorporates the results of this study, including the action of both chloride and iodide.

Observations of the rapid release of CO 2 from carbonated beverages, also known as sodas, provide a rich assortment of experiments for chemical educators and their students to explore. For example, dropping Mentos candies into a freshly opened bottle of soda creates a fountain that can jet several meters into the air. The fountain is generated by rapid formation of CO 2 (g) bubbles on innumerable nucleation sites that exist on the rough surface of the candies. Interestingly, it is possible to create fountains of moderate height by dropping smooth objects into bottles of soda. Exploration of how smooth objects create such fountains provides new classroom demonstrations, laboratory experiments, and inquiry-based projects that can be tied to topics that include kinetics, density, and gas solubility.

In order to facilitate the development of the green subcritical water chromatography technique for vanillin and coumarin, the stability of the compounds under subcritical water conditions was investigated in this work. In addition, their extraction from natural products was also studied. The stability experiments were carried out by heating the mixtures of vanillin and water or coumarin and water at temperatures ranging from 100 °C to 250 °C, while subcritical water extractions (SBWE) of both analytes from vanilla beans and whole tonka beans were conducted at 100 °C to 200 °C. Analyte quantification for both stability and extraction studies was carried out by HPLC. After heating for 60 min, vanillin was found to be stable in water at temperatures up to 250 °C. While coumarin is also stable at lower temperatures such as 100 °C and 150 °C, it undergoes partial degradation after heating for 60 min at 200 °C and higher. The results of this stability study support green subcritical water chromatographic separation and extraction of vanillin and coumarin at temperatures up to 150 °C. The SBWE results revealed that the extraction efficiency of both analytes from vanilla beans and tonka beans is significantly improved with increasing temperature.

Organic solvents are widely used in pharmaceutical and chemical industry for chromatographic separations. In recent years, subcritical water chromatography (SBWC) has shown ability in replacing hazardous organic solvents used in traditional high-performance liquid chromatography (HPLC). In this work, a pain killer—aspirin—and an antidiabetic drug—metformin HCl—were successfully separated on an XBridge C18 column using no organic solvents in the subcritical water chromatography mobile phase. Both traditional HPLC and subcritical water chromatography were used for comparison purposes. SBWC separation of metformin HCl and aspirin were achieved at 95 °C and 125 °C, respectively. The recovery for both active pharmaceutical ingredients (APIs) obtained by SBWC is 99% in comparing with the stated content of each drug. The relative standard deviation is less than 1% for SBWC assays developed in this work. This level of accuracy and precision achieved by SBWC is the same as that resulted by the traditional HPLC analysis.