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Lewis acid sites in zeolites catalyze aqueous-phase sugar isomerization at higher turnover rates when confined within hydrophobic rather than within hydrophilic micropores; however, relative contributions of competitive water adsorption at active sites and preferential stabilization of isomerization transition states have remained unclear. Here, we employ a suite of experimental and theoretical techniques to elucidate the effects of coadsorbed water on glucose isomerization reaction coordinate free energy landscapes. Transmission IR spectra provide evidence that water forms extended hydrogen-bonding networks within hydrophilic but not hydrophobic micropores of Beta zeolites. Aqueous-phase glucose isomerization turnover rates measured on Ti-Beta zeolites transition from first-order to zero-order dependence on glucose thermodynamic activity, as Lewis acidic Ti sites transition from water-covered to glucose-covered, consistent with intermediates identified from modulation excitation spectroscopy during in situ attenuated total reflectance IR experiments. First-order and zero-order isomerization rate constants are systematically higher (by 3–12×, 368–383 K) when Ti sites are confined within hydrophobic micropores. Apparent activation enthalpies and entropies reveal that glucose and water competitive adsorption at Ti sites depend weakly on confining environment polarity, while Gibbs free energies of hydride-shift isomerization transition states are lower when confined within hydrophobic micropores. DFT calculations suggest that interactions between intraporous water and isomerization transition states increase effective transition state sizes through second-shell solvation spheres, reducing primary solvation sphere flexibility. These findings clarify the effects of hydrophobic pockets on the stability of coadsorbed water and isomerization transition states and suggest design strategies that modify micropore polarity to influence turnover rates in liquid water.

2 nm PdIn intermetallic alloy (cubic, CsCl type) nanoparticle catalyst was near 100% selective to ethane dehydrogenation at 600 °C (at 15% conversion) with a dehydrogenation TOR almost 10 times higher than that of monometallic Pd.

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We examine the puzzling displacement in various Spanish dialects of a plural suffix from a verb where it is motivated semantically, syntactically, and morphologically onto a following clitic. We present previously unreported data and a new analysis of this material that succeeds where earlier efforts fail to provide a unified account of related phenomena. Our solution, which employs recent work on reduplication and metathesis, allows us to account for seemingly disparate phenomena as special cases of a single general framework and demonstrates that these operations are more versatile than previously thought. Directions for future research are indicated.

We compared omeprazole and mephenytoin as probes for the CYP2C19 metabolic polymorphism. Single oral doses of omeprazole (20 mg) or mephenytoin (100 mg) were administered at least 1 week apart to 167 healthy volunteers. Mephenytoin metabolism was measured using the amount of 4'-hydroxymephenytoin and the S/R ratio of mephenytoin in an 8-hour urine collection. Omeprazole hydroxylation was measured using the ratio of omeprazole to 5'-hydroxyomeprazole in serum 2 hours after dosing. All three methods separated poor- or extensive-metabolizer phenotypes with complete concordance. Omeprazole hydroxylation correlated with the S/R ratio of mephenytoin in extensive metabolizers (r2 = 0.681; p < 0.001). Genotyping tests showed that six poor metabolizers of omeprazole were homozygous for a single base pair mutation in exon 5 of CYP2C19. These results support the hypothesis that omeprazole 5'-hydroxylation cosegregates with the CYP2C19 metabolic polymorphism.

Measurements of turnover rates of gas-phase bimolecular ethanol dehydration to diethyl ether (404–438 K) on a suite of hydrophobic and hydrophilic Sn-zeolites (Sn-Beta, Sn-BEC, Sn-MFI) of varying Sn content, together with quantitative titration of active Sn sites by pyridine during catalysis, identify two types of Sn sites with reactivity differing by more than an order of magnitude (>20×). Apparent activation entropies to form bimolecular dehydration transition states from predominantly ethanol monomer-covered sites are less negative (ΔΔS app ⧧ = 48 ± 22 J mol–1 K–1) at the more reactive subset of Sn sites, which are present in amounts equivalent to 17–26% of the Sn sites quantified by the peak centered at 2308 cm–1 in CD3CN IR spectra (Sn2308) but not correlated with that at 2316 cm–1 (Sn2316). Synthetic and postsynthetic treatments to prepare Sn-zeolites containing Sn sites hosted within diverse local coordination environments suggest that Sn2316 sites are not associated with Sn bound to residual fluoride anions or Sn sited at external crystallite surfaces, amorphous domains, or among the diverse T-site locations contained within CHA, MFI, BEC, and STT frameworks. Treating Sn-Beta in HF or NH4F solutions, which dissolve zeolitic domains preferentially at defect grain boundaries, decreased the number of Sn2316 sites but not Sn2308 sites. These data indicate that Sn2316 sites are preferentially located at stacking faults in zeolite Beta, which provide tetrahedral coordination environments for Sn in defect-open configurations ((HO)–Sn–(OSi)3) with proximal Si–OH groups that do not permit condensation to tetrahedral closed configurations (Sn–(OSi)4). A computational model was developed for stacking fault defect-open Sn sites, which predict apparent activation free energies for bimolecular ethanol dehydration that are 65–74 kJ mol–1 higher (at 404 K) than those at framework-closed Sn sites that are capable of stabilizing transition states via Sn site opening and closing as part of the catalytic cycle, consistent with the lower experimentally measured ethanol dehydration reactivity for Sn2316 sites. In contrast, defect-open sites possess Si–OH groups that preferentially stabilize hydride shift transition states involved in glucose–fructose isomerization catalytic cycles. These findings highlight the ability of a given zeolite framework to confer structural diversity to nominally site-isolated Lewis acid centers, thus generating configurations with distinct reactivity for different chemical transformations.

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