CCSD(T), W1, and other model chemistry predictions for gas-phase deprotonation reactions

A series of CCSD(T) single-point calculations on MP4(SDQ) geometries and the W1 model chemistry method have been used to calculate ΔH° and ΔG° values for the deprotonation of 17 gas-phase reactions where the experimental values have reported accuracies within 1 kcal/mol. These values have been compared with previous calculations using the G3 and CBS model chemistries and two DFT methods. The most accurate CCSD(T) method uses the aug-cc-pVQZ basis set. Extrapolation of the aug-cc-pVTZ and aug-cc-pVQZ results yields the most accurate agreement with experiment, with a standard deviation of 0.58 kcal/mol for ΔG° and 0.70 kcal/mol for ΔH°. Standard deviations from experiment for ΔG° and ΔH° for the W1 method are 0.95 and 0.83 kcal/mol, respectively. The G3 and CBS-APNO results are competitive with W1 and are much less expensive. Any of the model chemistry methods or the CCSD(T)/aug-cc-pVQZ method can serve as a valuable check on the accuracy of experimental data reported in the National Institutes of Standards and Technology (NIST) database.

Culture's Calling: Mobile Phones, Gender, and the Making of an African Migrant Village in Lisbon

In this article, I explore how immigrants from the West African nation of Guinea-Bissau living in Portugal use mobile phones in their daily lives in Lisbon. Whereas one might assume that mobile phones and other new information technologies facilitate transnational communication between Africa and Portugal, the ethnographic fieldwork that I conducted in Lisbon from 1999 to 2003 revealed a different scenario. Instead, mobile phones as imagined and used by the Guinean immigrants I met in Lisbon revealed less about transnationalism and globalization than they did about constructing community and identity in a new locale. As Guinean immigrants in Portugal reconfigured their relationship to their former colonizers and struggled to make their way in a new, multicultural Europe, they used their mobile phones to engage local networks, shape local identities, and transform Lisbon's sprawl into an African migrant village. Here, I highlight the gendered dimensions of this process and contend that Guinean men's and women's varied uses of mobile phones in Lisbon underscore contrasting experiences of migration, mobility, and belonging.

Culture's Calling: Mobile Phones, Gender, and the Making of an African Migrant Village in Lisbon

In this article, I explore how immigrants from the West African nation of Guinea-Bissau living in Portugal use mobile phones in their daily lives in Lisbon. Whereas one might assume that mobile phones and other new information technologies facilitate transnational communication between Africa and Portugal, the ethnographic fieldwork that I conducted in Lisbon from 1999 to 2003 revealed a different scenario. Instead, mobile phones as imagined and used by the Guinean immigrants I met in Lisbon revealed less about transnationalism and globalization than they did about constructing community and identity in a new locale. As Guinean immigrants in Portugal reconfigured their relationship to their former colonizers and struggled to make their way in a new, multicultural Europe, they used their mobile phones to engage local networks, shape local identities, and transform Lisbon's sprawl into an African migrant village. Here, I highlight the gendered dimensions of this process and contend that Guinean men's and women's varied uses of mobile phones in Lisbon underscore contrasting experiences of migration, mobility, and belonging.

Comparison of Model Chemistry and Density Functional Theory Thermochemical Predictions with Experiment for Formation of Ionic Clusters of the Ammonium Cation Complexed with Water and Ammonia; Atmospheric Implications

The G2, G3, CBS-QB3, and CBS-APNO model chemistry methods and the B3LYP, B3P86, mPW1PW, and PBE1PBE density functional theory (DFT) methods have been used to calculate ΔH° and ΔG° values for ionic clusters of the ammonium ion complexed with water and ammonia. Results for the clusters NH4+(NH3)n and NH4+(H2O)n, where n = 1−4, are reported in this paper and compared against experimental values. Agreement with the experimental values for ΔH° and ΔG° for formation of NH4+(NH3)n clusters is excellent. Comparison between experiment and theory for formation of the NH4+(H2O)n clusters is quite good considering the uncertainty in the experimental values. The four DFT methods yield excellent agreement with experiment and the model chemistry methods when the aug-cc-pVTZ basis set is used for energetic calculations and the 6-31G* basis set is used for geometries and frequencies. On the basis of these results, we predict that all ions in the lower troposphere will be saturated with at least one complete first hydration shell of water molecules.

Sensitivity Gains, Linearity, and Spectral Reproducibility in Nonuniformly Sampled Multidimensional MAS NMR Spectra of High Dynamic Range

Recently, we have demonstrated that considerable inherent sensitivity gains are attained in MAS NMR spectra acquired by nonuniform sampling (NUS) and introduced maximum entropy interpolation (MINT) processing that assures the linearity of transformation between the time and frequency domains. In this report, we examine the utility of the NUS/MINT approach in multidimensional datasets possessing high dynamic range, such as homonuclear C-13-C-13 correlation spectra. We demonstrate on model compounds and on 1-73-(U-C-13,N-15)/74-108-(U-N-15) E. coli thioredoxin reassembly, that with appropriately constructed 50 % NUS schedules inherent sensitivity gains of 1.7-2.1-fold are readily reached in such datasets. We show that both linearity and line width are retained under these experimental conditions throughout the entire dynamic range of the signals. Furthermore, we demonstrate that the reproducibility of the peak intensities is excellent in the NUS/MINT approach when experiments are repeated multiple times and identical experimental and processing conditions are employed. Finally, we discuss the principles for design and implementation of random exponentially biased NUS sampling schedules for homonuclear C-13-C-13 MAS correlation experiments that yield high-quality artifact-free datasets.