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71.
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73.
Larry A. Curtiss 《Chemical physics letters》1983,96(4):442-446
Ab initio molecular orbital methods have been used to study the first two adiabatic ionizations of the water dimer. Both ionizations cause considerable geometrical rearrangements in the water dimer structure. Good agreement is found with experiment on the difference between the vertical and adiabatic energies for the first ionization. 相似文献
74.
The isomerization of glyceraldehyde to dihydroxy acetone catalyzed by the active site of Sn-beta zeolite is investigated using the B3LYP density functional and MP2 levels of theory. Structural studies were aimed to understanding the binding modes of glyceraldehyde with the active site, and the detailed free energy landscape was computed for the isomerization process. The rate-limiting step for the isomerization is the 1,2-hydride shift, which is enhanced by the active participation of the hydroxyl group in the hydrolyzed Sn-beta active site analogues to the one seen in the xylose isomerase. On the basis of the assessment of the activation barriers for isomerization by the Sn, Zr, Ti, and Si zeolite models, the activity of the catalysts are in the order of Sn > Zr > Ti > Si in aqueous dielectric media. 相似文献
75.
Protein stability in ionic solutions depends on the delicate balance between protein-ion and ion-ion interactions. For molecular ions containing multiple charged groups, the role of ion-ion interactions is particularly important. In this study, we show how the interplay between homo- and heteroion pairing influences protein stability using polyarginine salts as a model system. For the chloride salts, protein thermostability decreases as the size of the peptide increases, indicating enhanced binding to the protein. Moreover, it indicates reduced homoion pairing between Gdm(+) and carboxylate groups that is largely responsible for aggregation suppression, rather than denaturation, in monomeric arginine solutions. However, for the sulfate salts, strong heteroion pairing between the Gdm(+) groups and the sulfate counterions compensates for the loss of homoion pairing and, in return, leads to enhanced thermostability and a dramatically reduced (up to 10-30 times) rate of protein aggregation. Molecular dynamics simulations reveal how this ion pairing enhances conformational stability and, at the same time, reduces protein association. This study provides insight into complex ion effects on protein stability and serves as an example of how these intrasolvent interactions can be leveraged to enhance protein stability. 相似文献
76.
Xiong G Elam JW Feng H Han CY Wang HH Iton LE Curtiss LA Pellin MJ Kung M Kung H Stair PC 《The journal of physical chemistry. B》2005,109(29):14059-14063
Anodic aluminum oxide (AAO) membranes were characterized by UV Raman and FT-IR spectroscopies before and after coating the entire surface (including the interior pore walls) of the AAO membranes by atomic layer deposition (ALD). UV Raman reveals the presence of aluminum oxalate in bulk AAO, both before and after ALD coating with Al2O3, because of acid anion incorporation during the anodization process used to produce AAO membranes. The aluminum oxalate in AAO exhibits remarkable thermal stability, not totally decomposing in air until exposed to a temperature >900 degrees C. ALD was used to cover the surface of AAO with either Al2O3 or TiO2. Uncoated AAO have FT-IR spectra with two separate types of OH stretches that can be assigned to isolated OH groups and hydrogen-bonded surface OH groups, respectively. In contrast, AAO surfaces coated by ALD with Al2O3 display a single, broad band of hydrogen-bonded OH groups. AAO substrates coated with TiO2 show a more complicated behavior. UV Raman results show that very thin TiO2 coatings (1 nm) are not stable upon annealing to 500 degrees C. In contrast, thicker coatings can totally cover the contaminated alumina surface and are stable at temperatures in excess of 500 degrees C. 相似文献
77.
Lin Y Wynveen A Halley JW Curtiss LA Redfern PC 《The Journal of chemical physics》2012,136(17):174507
We report results of development of a self consistent tight binding model for water. The model explicitly describes the electrons of the liquid self consistently, allows dissociation of the water and permits fast direct dynamics molecular dynamics calculations of the fluid properties. It is parameterized by fitting to first principles calculations on water monomers, dimers, and trimers. We report calculated radial distribution functions of the bulk liquid, a phase diagram and structure of solvated protons within the model as well as ac conductivity of a system of 96 water molecules of which one is dissociated. Structural properties and the phase diagram are in good agreement with experiment and first principles calculations. The estimated DC conductivity of a computational sample containing a dissociated water molecule was an order of magnitude larger than that reported from experiment though the calculated ratio of proton to hydroxyl contributions to the conductivity is very close to the experimental value. The conductivity results suggest a Grotthuss-like mechanism for the proton component of the conductivity. 相似文献
78.
Gaussian-2 (G2) theory for third-row non-transition elements is used to calculate energies of germanium clusters, Gen (n = 2−5). The G2 energies are used to derive accurate binding energies for the clusters. The results for Ge2 and Ge3 are in agreement with experiment while there is some disagreement for Ge4 and Ge5. The binding energies are also calculated using the B3LYP density functional method with the 6–311 + G(3df,2p) basis set and compared with the G2 results and experiment. 相似文献
79.
Larry A. Curtiss Carlos A. Melendres Alan E. Reed Frank Weinhold 《Journal of computational chemistry》1986,7(3):294-305
The interaction of superoxide ion O2? with up to four water molecules [O2?: (H2O)n, n = 1, 2, 4] has been investigated using ab initio molecular orbital theory. The binding energy of O2?: H2O is calculated to be ?20.6 kcal/mol in good agreement with gas phase experimental data. At the MP3/6-31G* level the O2?:H2O complex has a C2v structure with a double (cyclic) hydrogen bond between O2? and H2O. A Cs structure with a single hydrogen bond is only 0.7 kcal/mol less stable. Interaction of H2O with the doubly occupied π* orbital of O2? is preferred slightly over interaction with the singly occupied π* orbital. Natural bond orbital analysis suggests that both electrostatic and charge transfer interactions are important in anionic complexes. The charge transfer occurs predominantly in the O2? → H2O direction and is important in determining the relative stabilities of the different structures and states. Singly and doubly hydrogen-bonded structures for the O2?: (H2O)2 and O2?: (H2O)4 clusters were found to be similar in stability and the increase in binding of the cluster becomes smaller as each additional water molecule is added to the cluster. 相似文献