Accurate standard enthalpies of formation of 115 isolated pentagon rule (IPR) fullerenes with 60-180 carbon atoms have been derived from energies of isodesmic interconversion reactions computed at the B3LYP/6-31G* level of theory. The calculated values of ∆H°f, which may serve as benchmarks for both calorimetric measurements and less sophisticated theoretical studies, are reproduced within 3 kcal/mol by a simple scheme based upon counts of 30 distinct structural motifs composed of hexagons together with their first and second neighborhoods. The extremely low computational cost of such a scheme makes it ideally suited for a rapid prescreening for thermodynamically viable IPR fullerenes with cages composed of hundreds of carbon atoms. With the inclusion of a global curvature term, this scheme is expected to be equally successful for small and large carbon clusters.

We have performed large-scale molecular dynamics simulations of the polymerization of silicic acid in aqueous solution using the potential developed by Fueston and Garofalini [J. Phys. Chem. 1990, 94, 5351]. Seventeen simulations, with different water-to-silicon ratios and silicic acid concentrations, were each run for between 1.6 and 12.5 ns, at temperatures of 1500, 2000, and 2500 K. Water clearly acts as a catalyst in these simulations. When the water-to-silicon ratio is large, we find that the initial stages of the polymerization process are dominated by the conversion of monomers to dimers and addition of monomers to small clusters, while at longer times cluster−cluster aggregation is observed. Using data from simulations at different temperatures, the activation energies of condensation between silicic acid monomers were calculated at different water-to-silicon ratios and found to compare favorably with experimental results; an extrapolation (at constant density) of simulated reaction rates to ambient conditions (a temperature difference of more than 1200 K) agrees with experimental rates to within one order of magnitude.

The extraction kinetics and equilibrium concentrations of caffeine and 3-chlorogenic acid (3-CGA) in cold brew coffee were investigated by brewing four coffee samples (dark roast/medium grind, dark roast/coarse grind, medium roast/medium grind, medium roast/coarse grind) using cold and hot methods. 3-CGA and caffeine were found at higher concentrations in cold brew coffee made with medium roast coffees, rather than dark roast. The grind size did not impact 3-CGA and caffeine concentrations of cold brew samples significantly, indicating that the rate determining step in extraction for these compounds did not depend on surface area. Caffeine concentrations in cold brew coarse grind samples were substantially higher than their hot brew counterparts. 3-CGA concentrations and pH were comparable between cold and hot brews. This work suggests that the difference in acidity of cold brew coffee is likely not due to 3-CGA or caffeine concentrations considering that most acids in coffee are highly soluble and extract quickly. It was determined that caffeine and 3-CGA concentrations reached equilibrium according to first order kinetics between 6 and 7 hours in all cold brew samples instead of 10 to 24 hours outlined in typical cold brew methods.

The acidity and antioxidant activity of cold brew coffee were investigated using light roast coffees from Brazil, two regions of Ethiopia, Columbia, Myanmar, and Mexico. The concentrations of three caffeoylquinic acid (CQA) isomers were also determined. Cold brew coffee chemistry was compared to that of hot brew coffee prepared with the same grind-to-coffee ratio. The pH values of the cold and hot brew samples were found to be comparable, ranging from 4.85 to 5.13. The hot brew coffees were found to have higher concentrations of total titratable acids, as well as higher antioxidant activity, than that of their cold brew counterparts. It was also noted that both the concentration of total titratable acids and antioxidant activity correlated poorly with total CQA concentration in hot brew coffee. This work suggests that the hot brew method tends to extract more non-deprotonated acids than the cold brew method. These acids may be responsible for the higher antioxidant activities observed in the hot brew coffee samples.

Standard enthalpies of formation, ionization potentials, electron affinities, and band gaps of finite-length [5,5] armchair and [9,0] zigzag single-walled carbon nanotubes (SWNTs) capped with C(30) hemispheres obtained by halving the C(60) fullerene have been computed at the B3LYP/6-311G* level of theory. Properties of SWNTs are found to depend strongly on the tube length and, in the case of the [9,0] zigzag species, on the relative orientation of the caps. The metallic character of an uncapped infinite-length [5,5] armchair SWNT manifests itself in the oscillatory dependence of the properties of capped finite-length tubes on their size. An infinite-length [9,0] zigzag SWNT is predicted to be a semiconductor rather than a metal irrespective of the presence of caps. The present results underscore the slow convergence of SWNT properties with respect to the tube length and uncover small but significant radial distortions along the long axes of SWNTs.