Showing papers by "Richard J. Saykally published in 2011"
TL;DR: The first X-ray absorption spectra of aqueous carbonate have been measured at three different pH values to characterize the evolution of electronic structure of carbonate, bicarbonate, carbonic acid and dissolved CO2 as mentioned in this paper.
121 citations
TL;DR: Simulations reveal that water is arranged nearly isotropically around boric acid and sodium borate, but the calculations also indicate that the boron K-edge NEXAFS spectra are insensitive to hydrogen bonding, molecular environment, or salt interactions.
Abstract: Near edge x-ray absorption fine structure (NEXAFS) spectra at the boron K-edge were measured for aqueous boric acid, borate, and polyborate ions, using liquid microjet technology, and compared with simulated spectra calculated from first principles density functional theory in the excited electron and core hole (XCH) approximation. Thermal motion in both hydrated and isolated molecules was incorporated into the calculations by sampling trajectories from quantum mechanics/molecular mechanics simulations at the experimental temperature. The boron oxide molecules exhibit little spectral change upon hydration, relative to mineral samples. Simulations reveal that water is arranged nearly isotropically around boric acid and sodium borate, but the calculations also indicate that the boron K-edge NEXAFS spectra are insensitive to hydrogen bonding, molecular environment, or salt interactions.
43 citations
Journal Article•
18 citations
TL;DR: The simulations indicate that water preferentially associates with borohydride on the tetrahedral corners and edges, causing transitions to excited states with p character to become more intense and a sharp feature, uncharacteristic of tetrahed molecules, to emerge.
Abstract: Borohydride salts have been considered as good prospects for transportable hydrogen storage materials, with molecular hydrogen released via hydrolysis. We examine details of the hydration of sodium borohydride by the combination of X-ray absorption spectroscopy and first principles' theory. Compared to solid sodium borohydride, the aqueous sample exhibits an uncharacteristically narrow absorption feature that is shifted to lower energy, and ascribed to the formation of dihydrogen bonds between borohydride and water that weaken the boron–hydrogen covalent bonds. Water also acts to localize the highly excited molecular orbitals of borohydride, causing transitions to excited states with p character to become more intense and a sharp feature, uncharacteristic of tetrahedral molecules, to emerge. The simulations indicate that water preferentially associates with borohydride on the tetrahedral corners and edges.
17 citations
TL;DR: P pH dependence of surface behavior of the β-amyloid is confirmed, with largest surface affinity found at pH = 7.4, and it follows from the simulations that phenylalanine is the most surface exposed residue, followed by tyrosine and histidine in their neutral form.
Abstract: The adsorption and aggregation of β-amyloid (1−16) fragment at the air−water interface was investigated by the combination of second harmonic generation (SHG) spectroscopy, Brewster angle microscopy (BAM), and molecular dynamics simulations (MD). The Gibbs free energy of surface adsorption was measured to be −10.3 kcal/mol for bulk pHs of 7.4 and 3, but no adsorption was observed for pH 10−11. The 1−16 fragment is believed not to be involved in fibril formation of the β-amyloid protein, but it exhibits interesting behavior at the air−water interface, as manifested in two time scales for the observed SHG response. The shorter time scale (minutes) reflects the surface adsorption, and the longer time scale (hours) reflects rearrangement and aggregation of the peptide at the air−water interface. Both of these processes are also evidenced by BAM measurements. MD simulations confirm the pH dependence of surface behavior of the β-amyloid, with largest surface affinity found at pH = 7. It also follows from the si...
10 citations
Journal Article•
TL;DR: Radiative transitions between neutral H3 Rydberg states were calculated at wavelengths near 7 μm and could be compared with mid-infrared laser lines observed in hydrogen/rare gas discharges, and the investigation is extended to wavelengths near 10–13 μm.
Abstract: The triatomic hydrogen ion (H3(+)) has spurred tremendous interest in astrophysics in recent decades, and Rydberg states of H3 have also maintained an important role for understanding H3(+) experiments. In a previous study (J. Chem. Phys. 2010, 133, 234302), radiative transitions between neutral H3 Rydberg states were calculated at wavelengths near 7 μm and could be compared with mid-infrared laser lines observed in hydrogen/rare gas discharges. The present study extends the investigation to wavelengths near 10–13 μm. Rydberg states of D3 are also treated.