student picts

Mindy Cushing
College: Colorado College
Tolbert Group Project Abstract: Tropospheric aerosols are studied for their impact both on climate and human health. Recent field evidence shows that up to 50% of these aerosols are organic. This study looks at water-soluble organics, which are internally mixed in the aerosol, and may change the conditions of water uptake by the aerosol. Di-carboxylic acids are chosen here to represent the organic component of aerosols because of their solubility and presence in the atmosphere. Although deliquescence and efflorescence (phase changes) are well defined for pure ammonium sulfate, a modified model is needed to account for the presence of organic. Deliquescence relative humidity (RH) over saturated bulk solution was measured to map out a simple phase diagram for a multi-component system in water. Results were in agreement with flow tube FTIR data, and depicted the lowest deliquescence RH at the eutectic composition. A decrease in temperature depressed the eutectic deliquescence RH, and the magnitude of this depression was found to increase with decreased solubility in ammonium sulfate. Di- carboxylic acids more soluble in ammonium sulfate were observed to exhibit a shift toward higher organic weight percent at the eutectic composition.

Robert Diaz
College: University of Puerto Rico- Rio Piedros Campus
Leone Group

Karari Hanks
College: Carnegie- Mellon University
Birks Group

Project Abstract: This study is the basis for examining the history of the ozone layer, specifically the amount of ultraviolet light that is coming through the ozone layer and reaching the surface of the earth. Pollen grains were exposed to 254 nm of ultraviolet light so that the pollen would become oxidized. The carbonyl groups formed were then reacted with dansylhydrazine (DNSH) to derivatize the pollen and allow it to fluoresce. The derivatized pollen's fluorescence can be observed using a fluorescence spectrometer and by studying the grains under a fluorescent microscope. The optimal derivatization conditions were to react 15-20 mg of exposed pollen with a 25 mg/mL solution of DNSH/acetonitrile. The solution was heated for 30 minutes while adding a drop of 85% H₃PO₄ to acidify the solution to a pH of 3-4, a few minutes into the heating process. The derivatized pollen is best viewed with a 4,6-diamidino-2-phenylindole filter with a fluorescent microscope. The excitation wavelengths used to achieve the greatest emission spectrum for the fluorescence spectrophotometer were 340, 425, and 465nm.

Jason Keith
College: University of North Texas
Michl Group

Project Abstract: The observed and reproducible changes in the monomer footprints on the mercury surface induced by different applied potentials indicates the difference in their orientations. This demonstrates that the LB method applied to the mercury surface is suitable for studying electroactive compounds. It provides a method of distinguishing between different conformations and alignments of molecules on a liquid metal subphase acting as a large electrode. Obviously, further work is required to prove the effect of the applied potentials on the orientation of the molecules in the adsorbed monolayer. We see this furthered in the development of infrared reflection-adsorption spectroscopic techniques, which are directly applicable for in situ investigations of molecules adsorbed to highly reflective surfaces such as the mercury surface in our work. The interaction of infrared radiation with adsorbed molecules, when it is applied at a grazing incidence, distinguishes between molecules with electronic dipoles perpendicular to the surface with those that do not. Thus molecules aligned perpendicular to the surface can be distinguished from those that have only a horizontal orientation.

Jamie Lucia
College: University of San Diego
Jonas Group

Project Abstract: Photosynthesis is one of the most complex processes in nature. Many living systems use this process to acquire energy. The electrochemical energy that is gained from photosynthesis is used to drive chemical reactions within the organism. One of the current focuses of ultrafast laser experimentation is the analysis of energy transfer processes in photosynthetic bacteria, the most commonly studied being thc membranes that contain unique pigment-protein complexes, which are given the name reaction centers. These reaction centers can be found in any organism that relies on photosynthesis to obtain its photochemical energy. In plant cells and algae, the reaction centers can be found within chloroplasts, which are special organelles that absorb sunlight, while in bacteria they are found in the cytoplasmic membrane that surrounds and protects cells. The reaction centers were first discovered to be present in cells when light-induced absorbance changes were observed in organisms that undergo photosynthesis. This was further supported by the discovery that bacteria whose growth depends on respiration due to the absence of reaction centers do not exhibit the same absorbance changes. In the natural photosynthesis process, the first receptor of the energy from the antenna is the special pair. However, in studies of these reaction centers there is no sunlight present, so laser light is used as a substitute. In this substitution, one of the accessory bacteriochlorophylls absorbs a flash of laser light. Electronic Energy Transfer (EET), which is not a natural process, transfers the energy from the bacteriochlorophyll to the special pair, which initiates Electron Transfer (ET). Although the bacteriochlorophylls are necessary in the experimentation, the goal of studies of this system is to determine the role, if any, that the accessory bacteriochlorophylls play in the natural ET process.

Julius Lucks
College: UNC- Chapel Hill
Lineberger Group

Project Abstract: In the past few years, studies of photoelectrons have proven to be more than just a tool for obtaining gas-phase spectra of a variety of substances. Although the information contained in a photoelectron spectrum corresponds very closely to the information obtained in gas-phase infrared spectroscopy, new techniques, especially in the study of negative ions have provided a wealth of information on other aspects of species such as transition state studies and non-adiabatic systems.
The scope of this paper is to briefly outline the principles behind photoelectron spectroscopy, and to provide an overview of traditional and modern techniques used to perform these studies. Threshold Photoelectron Spectroscopy (TPES) and Dispersive Photoelectron Spectroscopy (DPES) will be discussed in detail followed by the techniques of Zero Kinetic Energy Spectroscopy (ZEKE) as applied to neutral systems and Resonance Enhanced Multiphoton Ionization Photoelectron Spectroscopy (REMPI-PES). After a discussion of the principles behind each technique, experimental considerations will be discussed and the applicability of certain experimental methods to each of the techniques will be mentioned.

Charissa PettyJohn

College: St. Olaf College Rowlen Group Project Abstract: Second harmonic generation (SHG) studies were utilized in order to determine the mean orientation angle of a trifunctional silane. This covalently bound silane with a surface coverage of approximately 29% was determined to sit at 52.9 +/- 0.3 degrees with respect to normal. This approach to studying molecular orientation through SHG can provide a submonolayer sensitive technique that will give researchers information about the optical and mechanical properties of monolayer and multilayer organic thin films, as well as the molecular function of biological systems.

Jacklyn Ripley

College: Mesa State College Kuchta Group Project Abstract: It is not known exactly how mutant p49 primases affect primase activity in human cells. My project has focused on the primase p49 subunit, and its role in the DNA checkpoint/repair mechanism. In order to do this, mutant p49 subunits were synthasized with the hope of studying the mutants' effects on primase activity. Two mutants of p49 were synthasized. Each mutant plasmid was inserted into a RNA oligonucleotide primers for the two different mutants were inserted into a DNA template, where the mutation was synthesized by the inserted mutant primers.
A polymerase chain reaction (PCR) was performed in order to amplify the mutated DNA sequence. Once the DNA was amplified sufficiently, the mutant plasmid was transformed into supercompetent JM105 E. coli bacterial cells. To make these cells "supercompetent" they were treated with rubidium chloride and heat shocked in a water bath in order to partially degrade their cell walls so that the cell could readily take up the plasmid. These E. coli cells were grown on LB agar plates and then in LB liquid media in the presence of ampicillin. The mutant plasmid was engineered to be resistant to ampicillan; therefore, only the cells containing the mutant plasmid grew. Once these cells were grown up, a plasmid miniprep procedure was done in which the cells were lysed and the mutant plasmid was recovered.

Amy Roberts

College: University of North Texas George Group Project Abstract: Using an infrared laser resonant desorption technique that has been demonstrated previously, this study investigated pre-diffusion (initial) depth-profiles in addition to post-diffusion depth-profiles of annealed isotopic ice multilayers. This IR LRD method employs an Er: YAG rotary Q-switched laser with an output wavelength of 2.94µm. The Er: YAG radiation excites the O-H stretching vibrations in the H₂O molecules that form ice. This energy heats the ice surface, enabling desorption. Optimal experimenhown to depth-profile into ice multilayers with sub-micron spatial resolution. The experiment performed gained accurate initial profiles of H₂¹⁶O/H₂¹⁸O ice sandwiches. After annealing, the ice films were resistant to the Er: YAG resonant heating, and could not be profiled. This resistance was probably due to optical scattering off the frosty ice surface and future studies will address this problem.

Shantanu Sharma

College: California State University, Los Angeles Nesbitt Group Project Abstract: Crossed supersonic jets and high resolution infrared laser direct absorption techniques were used to study state-to-state reactive scattering. Our experimental setup is structured to only permit single collision conditioption profiles. Summed over all product rotational levels, the nascent vibrational quantum state populations for HF(v) [v=2:0.520(10); v=1:0.480(16); 2 sigma error bars] seem to be in disagreement with previous flow cell studies by Setser and co-workers. Density-to-flux transformation has not been determined as of yet, and work continues in a range of vibrational manifolds.

Kristina Treanor

College: Brown University Vaida Group Project Abstract: We measured the morphology, permeability, spectroscopic properties, and solubility of organic acid monolayers. We found that the morphology is affected by varying the pH of the bulk aqueous solution. The organic acid monolayer is permeable to SO₂, though we were unable to acquire quantitative results. The apparatus will be modified, and then the amount of SO₂ introduced to the cells can be regulated. The spectra of the several acids tested display different properties depending on whether the molecules are in gaseous or liquid phase. These spectra will be used as reference in later research. These findings are important to achieve a preliminary understanding of the structural, chemical, and optical properties of organic aerosols. According to the proposed model of organic aerosols, the surface of the aerosol is composed of a single layer of organic acids. These properties of monolayers that we investigated help govern the extent to which the Earth’s climate is affected.
We are also interested in these features of organic aerosols in relation to the possibility that these inverted-micelle structures could provide the perfect environment for key chemical transformations in the prebiotic world [Dobson et al., in print].