Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (22 results)

  • Multimedia
  • Peer Reviewed
UC Berkeley Previously Published Works (2017)
X-ray absorption spectroscopy (XAS) is an electronic absorption technique for which the initial state is a deeply buried core level. The photon energies corresponding to such transitions are governed primarily by the binding energies of the initial state. Because the binding energies of core electrons vary significantly among atomic species, this makes XAS an element-selective spectroscopy. Proper interpretation of XA spectra can provide detailed information on the local chemical and geometric environment of the target atom. The introduction of liquid microjet and flow cell technologies into XAS experiments has enabled the general study of liquid samples. Liquids studied to date include water, alcohols, and solutions with relevance to biology and energy technology. This Review summarizes the experimental techniques employed in XAS studies of liquid samples and computational methods used for interpretation of the resulting spectra and summarizes salient experiments and results obtained in the XAS investigations of liquids.
  • 1 supplemental file
  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2016)

X-ray Absorption Spectroscopy (XAS) is a powerful atom-selective probe of the local chemical environment of a target atom. Streaming liquid microjets, created by forcing liquid at high pressures (ca. 20-100 atm.) through a capillary tube of inner diameter 30-100 µm, allow for liquids to be introduced into a vacuum chamber and interrogated with soft X-rays generated by synchrotron light sources. This technique has enabled the study of many liquids and solutions. In this dissertation, the use of soft X-ray XAS for the study of the solvation of ions in electrolyte solutions is discussed. The majority of chemical reactions occur in the solution phase. The thermodynamics and kinetics of these reactions are explicitly dependent upon the local chemical environments of the reactants. Consequently, knowledge of the solvation of ions in solution is critical to understanding their chemistry in this phase. By interpreting XAS measurements with ab initio Density Functional Theory (DFT)-based electronic structure calculations, it is possible to acquire valuable knowledge about the local chemical environment of ions and molecules in solution, such as the solvation number and geometry and propensity to form ion pairs.

Commercial lithium ion batteries typically contain a liquid electrolyte comprising a lithium salt dissolved in a mixture of alkyl carbonates such as propylene carbonate, dimethyl carbonate, and ethylene carbonate. The solvation environment of the lithium ion in these solutions is thought to direct the formation of the Solid Electrolyte Interphase (SEI), which in turn is believed to play a critical role in determining essential cell properties including power output, recharging rate, and cycle life. Consequently, understanding this solvation environment is of critical importance. Here I report the a study of the solvation of Li+ in solutions of LiBF4 in alkyl carbonates via XAS on the carbon and oxygen K-edges. In collaboration with Dr. David Prendergast, we have performed electronic structure calculations within the eXcited electron and Core Hole (XCH) approximation and extracted a solvation number for Li+ in propylene carbonate.

I also report the study of aqueous solutions sodium nitrate and nitrite on the nitrogen K-edge utilizing similar experimental and theoretical methods. Aqueous nitrate and nitrite salts are important commercial reagents and play a critical role in the global nitrogen cycle. A detailed understanding of their chemical environment of solution would be beneficial in understanding and modeling reactivity. Unfortunately, the nitrogen K-edge XAS spectra of these species are found to be largely insensitive to ion pairing and solvation geometry around the anion, such that limited chemical information was extracted from this study.

    Cover page: Investigating Ion Solvation in Electrolyte Solutions via X-ray Absorption Spectroscopy
    • Article
    • Peer Reviewed
    Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 37 (2015)
    We introduce a novel class of visual illusion -- motion pareidolia -- in which sequential presentations of random textures can trigger percepts of coherent apparent motion. In two experiments we presented observers with sequences of random 140x140 pixel arrays refreshing at 2.5Hz. In Experiment 1, observers were primed with a coherent motion pattern, such as fixed texture shifting up-and-down across frames. After 8 priming frames, the textures became completely random from frame to frame. Participants were instructed to indicate when they could no longer perceive the primed motion pattern. Participants' responses were delayed by an average of 6 frames (or 2.4 seconds). In Experiment 2, observers detected motion patterns in 6-frame sequences under different noise levels and falsely identified coherent motion in 39% of the purely random sequences. To account for this phenomenon, we propose a selective visual attention process that is biased to detect expected motion.
      Cover page: The suggestible nature of apparent motion perception
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2021)
      Inhalation of dry powder synthetic lung surfactant may assist spontaneous breathing by providing noninvasive surfactant therapy for premature infants supported with nasal continuous positive airway pressure. Surfactant was formulated using spray-drying with different phospholipid compositions (70 or 80 total weight% and 7:3 or 4:1 DPPC:POPG ratios), a surfactant protein B peptide analog (KL4, Super Mini-B, or B-YL), and Lactose or Trehalose as excipient. KL4 surfactant underperformed on initial adsorption and surface activity at captive bubble surfactometry. Spray-drying had no effect on the chemical composition of Super Mini-B and B-YL peptides and surfactant with these peptides had excellent surface activity with particle sizes and fine particle fractions that were well within the margins for respiratory particles and similar solid-state properties. Prolonged exposure of the dry powder surfactants with lactose as excipient to 40 °C and 75% humidity negatively affected hysteresis during dynamic cycling in the captive bubble surfactometer. Dry powder synthetic lung surfactants with 70% phospholipids (DPPC and POPG at a 7:3 ratio), 25% trehalose and 3% of SMB or B-YL showed excellent surface activity and good short-term stability, thereby qualifying them for potential clinical use in premature infants.
        Cover page: Aerosol, chemical and physical properties of dry powder synthetic lung surfactant for noninvasive treatment of neonatal respiratory distress syndrome.
        • Multimedia
        • Peer Reviewed
        UC Berkeley Previously Published Works (2016)
        While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measured negative excess entropy is a result of clustering or micro-immiscibility.
        • 1 supplemental PDF
        • Multimedia
        • Peer Reviewed
        UC Berkeley Previously Published Works (2017)
        The fractionation of ions at liquid interfaces and its effects on the interfacial structure are of vital importance in many scientific fields. Of particular interest is the aqueous carbonate system, which governs both the terrestrial carbon cycle and physiological respiration systems. We have investigated the relative fractionation of carbonate, bicarbonate, and carbonic acid at the liquid/vapor interface finding that both carbonate (CO32-) and carbonic acid (H2CO3) are present in higher concentrations than bicarbonate (HCO3-) in the interfacial region. While the interfacial enhancement of a neutral acid relative to a charged ion is expected, the enhancement of doubly charged, strongly hydrated carbonate anion over the singly charged, less strongly hydrated bicarbonate ion is surprising. As vibrational sum frequency generation experiments have concluded that both carbonate and bicarbonate anions are largely excluded from the air/water interface, the present results suggest that there exists a significant accumulation of carbonate below the depletion region outside of the area probed by sum frequency generation.
        • 1 supplemental PDF
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2015)
        Nitrate and nitrite ions are of considerable interest, both for their widespread use in commercial and research contexts and because of their central role in the global nitrogen cycle. The chemistry of atmospheric aerosols, wherein nitrate is abundant, has been found to depend on the interfacial behavior of ionic species. The interfacial behavior of ions is determined largely by their hydration properties; consequently, the study of the hydration and interfacial behavior of nitrate and nitrite comprises a significant field of study. In this work, we describe the study of aqueous solutions of sodium nitrate and nitrite via X-ray absorption spectroscopy (XAS), interpreted in light of first-principles density functional theory electronic structure calculations. Experimental and calculated spectra of the nitrogen K-edge XA spectra of bulk solutions exhibit a large 3.7 eV shift between the XA spectra of nitrate and nitrite resulting from greater stabilization of the nitrogen 1s energy level in nitrate. A similar shift is not observed in the oxygen K-edge XA spectra of NO3 (-) and NO2 (-). The hydration properties of nitrate and nitrite are found to be similar, with both anions exhibiting a similar propensity towards ion pairing.
          Cover page: Properties of aqueous nitrate and nitrite from x-ray absorption spectroscopy
          • Multimedia
          • Peer Reviewed
          UC Berkeley Previously Published Works (2017)
          • 1 supplemental PDF
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2018)
          Hepatic steatosis is a hallmark feature of kwashiorkor malnutrition. However, the pathogenesis of hepatic steatosis in kwashiorkor is uncertain. Our objective was to develop a mouse model of childhood undernutrition in order to test the hypothesis that feeding a maize vegetable diet (MVD), like that consumed by children at risk for kwashiorkor, will cause hepatic steatosis which is prevented by supplementation with choline. A MVD was developed with locally sourced organic ingredients, and fed to weanling mice (n = 9) for 6 or 13 days. An additional group of mice (n = 4) were fed a choline supplemented MVD. Weight, body composition, and liver changes were compared to control mice (n = 10) at the beginning and end of the study. The MVD resulted in reduced weight gain and hepatic steatosis. Choline supplementation prevented hepatic steatosis and was associated with increased hepatic concentrations of the methyl donor betaine. Our findings show that (1) feeding a MVD to weanling mice rapidly induces hepatic steatosis, which is a hallmark disturbance of kwashiorkor; and that (2) hepatic steatosis associated with feeding a MVD is prevented by choline supplementation. These findings support the concept that insufficient choline intake may contribute to the pathogenesis of hepatic steatosis in kwashiorkor.
            Cover page: Choline Supplementation Prevents a Hallmark Disturbance of Kwashiorkor in Weanling Mice Fed a Maize Vegetable Diet: Hepatic Steatosis of Undernutrition
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2015)
            Abstract The dissolution of carbon dioxide in water and its subsequent hydrolysis reactions comprise one of the most central processes in all of science, yet it remains incompletely understood despite enormous effort. We report the detailed characterization of dissolved CO2 gas through the combination of X-ray spectroscopy and first principles theory. The molecule acts as a hydrophobe in water with an average hydrogen bond number of 0.56. The carbon atom interacts weakly with a single water at a distance of >2.67 Å and the carbonyl oxygens serve as weak hydrogen bond acceptors, thus locally enhancing the tetrahedral water hydrogen bonding structure.
              Cover page: The hydration structure of dissolved carbon dioxide from X-ray absorption spectroscopy
              Top