Sylwia Ptasinska

University of Notre Dame, South Bend, Indiana, United States

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Publications (74)219.61 Total impact

  • Xueqiang Zhang, Sylwia Ptasinska
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    ABSTRACT: Water adsorption and dissociation on a GaP(111) crystal surface are investigated using Near-Ambient Pressure X-ray Photoelectron Spectroscopy (NAP XPS) in a wide range of pressures (~10-10-5 mbar) and temperatures (~300-773 K). Dynamic changes in chemical evolution at the H2O/GaP(111) interface are reflected in Ga 2p3/2, O 1s, and P 2p spectra. In the pressure-dependent study performed at room temperature, an enhancement of surface Ga hydroxylation and oxidation with an increase in H2O pressure is observed. In the temperature-dependent study performed at elevated pressures, two distinct regions can be defined in which drastic changes occur in the surface chemistry. Below 673 K, the surface Ga hydroxylation and oxidation progress continuously. However, above 673 K, a large-scale conversion of surface O‒Ga‒OH species into non-stoichiometric Ga hydroxide along with oxidation of surface P atoms occurs through an intermediate state. The NAP XPS technique enabled us to experimentally track the chemistry at the H2O/GaP interface under near-realistic conditions, thereby providing evidence to compare with recent theoretical efforts to improve the understanding of water-splitting mechanisms and photo-corrosion on semiconductor surfaces.
    Physical Chemistry Chemical Physics 12/2014; · 4.20 Impact Factor
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    ABSTRACT: Electron ionization of the DNA nucleobase, adenine, and the tRNA nucleobase, hypoxanthine, was investigated near the threshold region (~5-20 eV) using a high-resolution hemispherical electron monochromator and a quadrupole mass spectrometer. Ion efficiency curves of the threshold regions and the corresponding appearance energies (AEs) are presented for the parent cations and the five most abundant fragment cations of each molecule. The experimental ionization energies (IEs) for adenine and hypoxanthine were determined to be 8.70 ± 0.3 eV and 8.88 ± 0.5 eV, respectively. Quantum chemical calculations (B3LYP/6 311+G(2d,p)) yielded a vertical IE of 8.08 eV and an adiabatic IE of 8.07 eV for adenine and a vertical IE of 8.51 eV and an adiabatic IE of 8.36 eV for hypoxanthine, and the lowest energy optimized structures of the fragment cations and their respective neutrals were calculated. The enthalpies of the possible reactions from the adenine and hypoxanthine cations were also determined computationally, which assisted in determining the most likely electron ionization pathways leading to the major fragment cations. Our results suggest that the imidazole ring is more stable than the pyrimidine ring in several of the fragmentation reactions from both adenine and hypoxanthine. This electron ionization study contributes to understanding the biological effects of electrons on nucleobases and contributes to the database of electronic properties of biomolecules, which is necessary for modeling damage of DNA in living cells that is induced by ionizing radiation.
    Physical Chemistry Chemical Physics 10/2014; · 4.20 Impact Factor
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    ABSTRACT: In this study we have investigated the plasma-air boundary of an atmospheric pressure discharge by exposing samples of dry plasmid DNA to a plasma jet. While visible emission from excited plasma species suggested that the plasma jet had dimensions approximately 5.5 cm long and 0.4 cm wide, damage to DNA samples was detected at distances of up to 20 cm from the tip of the jet with observable effects far outside the luminous plasma volume. Reactive oxygen species were identified as the most likely cause of DNA damage at these long distances. These results provide a novel method for determining the extent of any kind of plasma jet generated in the open atmosphere.
    The European Physical Journal D 06/2014; 68(6). · 1.40 Impact Factor
  • Chemical Physics Letters 06/2014; s 605–606:51–55. · 1.99 Impact Factor
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    ABSTRACT: The manipulation of semiconductor surfaces by tuning their electronic properties and surface chemistry is an essential ingredient for key applications in areas such as electronics, sensors, and photovoltaic devices. Here, in-situ surface reactions on gallium arsenide (GaAs) are monitored for two morphologies: a simple planar crystalline surface with (100) orientation and an ensemble of GaAs nanowires, both exposed to oxygen environment. A variety of oxide surface species, with a significant enhancement in oxidation states in the case of nanowires, are detected via near ambient pressure X-ray photoelectron spectroscopy. This enhancement in oxidation of GaAs nanowires is due to their higher surface area and the existence of more active sites for O2 dissociation.
    Applied Physics Letters 05/2014; 104(18):181602-181602-4. · 3.52 Impact Factor
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    ABSTRACT: Conventional wisdom tells us that interfacial thermal transport is more efficient when the interface adhesion energy is enhanced. In this study, we demonstrate that molecular bridges consisting of small molecules chemically absorbed on solid surfaces can enhance the thermal transport across hard-soft material interfaces by as much as 7 folds despite a significant decrease in the interface adhesion energy. This work provides an unconventional strategy to improve thermal transport across material interfaces.
    Advanced Materials 05/2014; · 15.41 Impact Factor
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    ABSTRACT: X-ray irradiation of plasmid DNA in presence of platinum (II)-based compounds was carried out in order to assess the radiosensitization capabilities of these drugs. In present investigations pBR322 plasmid DNA was used to monitor the effectiveness of chosen compounds in inducing strand breaks. Samples were incubated in the presence of potential radiosensitisers: platinum (II) bromide and cis-diamminedibromoplatinum (II). The results were examined against a common cancer chemotherapy drug cis-diamminedichloroplatinum (II). It was found that platinum (II) bromide can greatly increase the levels of single- and double-strand break formation observed in the irradiated samples with respect to the samples containing platinum as a radiosensitizer only, possessing very little chemotherapeutic activity. The suggested drugs exhibit much higher level of radiosensitivity than widely used cisplatin and thus may be good candidates for cancer treatment.
    The European Physical Journal D 04/2014; 68(4):1-5. · 1.40 Impact Factor
  • Xueqiang Zhang, Sylwia Ptasinska
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    ABSTRACT: Ultra-thin silicon oxynitride (SiOxNy) layers were deposited by direct interaction of plasma species formed in an atmospheric pressure plasma jet (APPJ) with a silicon wafer. APPJs have been ignited in mixtures of helium (He) together with several nitrogen-based compounds. The chemical composition of the APPJ treated silicon surfaces was analysed by ultra-high vacuum x-ray photoelectron spectroscopy (XPS). The obtained N 1s XPS spectra showed that even 5 min of APPJ treatment is sufficient to fabricate SiOxNy films with a few nanometre thickness. A Si substrate exposed to an APPJ generated in a mixture of He/NH3 resulted in the most efficient growth of SiOxNy films, indicated by the strongest N 1s XPS signal among all studied gas mixtures. Moreover, the N 1s spectra exhibited two major characteristics of chemical bonding structures attributed to nitrogen bonded to three silicon surface atoms, N─(S)3, and nitrogen bonded to two silicon surface atoms and one oxygen atom, (Si)2─N─O.
    Journal of Physics D Applied Physics 03/2014; 47(14). · 2.52 Impact Factor
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    ABSTRACT: Soft X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to probe the electronic and adsorption properties of two cyclic dipeptides, i.e. cyclo(glycyl-histidyl) and cyclo(phenylalanyl-prolyl), on Au(111) and Cu(110) surfaces. The core level spectra show chemical shifts which indicate weak chemisorption on Au(111), and stronger chemisorption on the Cu(110) surface, mainly via one of the nitrogen atoms in the central rings of both molecules, and nitrogen in the imidazole ring of cyclo(glycyl-histidyl). From the angular dependence of the NEXAFS spectra at the O and N K-edges, we conclude that both dipeptides have a preferred orientation on the two surfaces.
    Physical Chemistry Chemical Physics 03/2014; · 4.20 Impact Factor
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    ABSTRACT: A helium atmospheric pressure plasma jet (APPJ) is applied to induce damage to aqueous plasmid DNA. The resulting fractions of the DNA conformers, which indicate intact molecules or DNA with single- or double-strand breaks, are determined using agarose gel electrophoresis. The DNA strand breaks increase with a decrease in the distance between the APPJ and DNA samples under two working conditions of the plasma source with different parameters of applied electric pulses. The damage level induced in the plasmid DNA is also enhanced with increased plasma irradiation time. The reactive species generated in the APPJ are characterized by optical emission spectra, and their roles in possible DNA damage processes occurring in an aqueous environment are also discussed.
    The European Physical Journal D 02/2014; 68(3). · 1.40 Impact Factor
  • Xueqiang Zhang, Sylwia Ptasinska
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    ABSTRACT: Dissociative water adsorption on a GaAs(100) surface is demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under near-ambient conditions. These in situ XPS studies enable us to monitor the evolution of water dissociation on GaAs under elevated pressures and temperatures for the first time. In pressure-dependent XPS studies, the GaAs surface was exposed to room-temperature water vapor at pressures ranging from UHV to 5 mbar. With an increase in H2O pressure, enhancement of oxygenation and hydroxylation of surface Ga atoms is observed. In addition, strong XPS signals are also detected that originate from water molecules that are molecularly adsorbed onto the GaAs surface and hydrogen-bonded to surface OH species. Peak broadening and shifts in the As 2p XPS spectra are correlated with the signal increase resulting from surface HO–Ga species, suggesting the formation of surface H–As bonds. In temperature-dependent XPS studies, the GaAs surface was annealed from room temperature up to 773 K at a water vapor pressure of 0.1 mbar. The temperature increase leads to desorption of weakly adsorbed water molecules or their dissociation, resulting in surface Ga oxidation. However, no changes in chemical state of the surface As atoms are observed at higher temperatures.
    The Journal of Physical Chemistry C 02/2014; 118(8):4259–4266. · 4.84 Impact Factor
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    ABSTRACT: The formation of monocarbon cluster ions has been investigated by electron ionization mass spectrometry of cold helium nanodroplets doped with nitrogen/methane mixtures. Ion yields for two groups of clusters, CHmN2+ or CHmN4+, were determined for mixtures with different molecular ratios of CH4. The possible geometrical structures of these clusters were analyzed using electronic structure computations. Little correlation between the ion yields and the associated binding energies has been observed indicating that in most cases kinetic control is more important than thermodynamic control for forming the clusters.
    The Journal of Chemical Physics 12/2013; 140(3). · 3.12 Impact Factor
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    ABSTRACT: We report gas phase studies on NCO(-) fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO(-) production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO(-) upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO(-) formation in DEA. Site selectivity in the NCO(-) yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO(-) ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation.
    Journal of the American Society for Mass Spectrometry 09/2013; · 3.59 Impact Factor
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    ABSTRACT: The nitrogen atmospheric pressure plasma jet (APPJ) was applied to induce DNA damage of SCC-25 oral cancer cells. Optical emission spectra were taken to characterize the reactive species produced in APPJ. In order to explore the spatial distribution of plasma effects, cells were placed onto photo-etched grid slides and the antibody H2A.X was used to locate double strand breaks of DNA inside nuclei using an immunofluorescence assay. The number of cells with double strand breaks in DNA was observed to be varied due to the distance from the irradiation center and duration of plasma treatment.
    Applied Physics Letters 06/2013; 102(23). · 3.52 Impact Factor
  • Matej Klas, Sylwia Ptasinska
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    ABSTRACT: Due to its richness in various active species a nitrogen plasma discharge is a promising tool for many applications. However, owing to the difficulties in igniting and sustaining this type of discharge, the construction of plasma sources operating in nitrogen gas is still very challenging. In this work we describe and characterize two home-built plasma sources with two different electrode configurations able to work in a nitrogen atmosphere. For this purpose, the jets of plasma species formed are studied by emission spectroscopy, and thermal and electrical measurements. It is noted that the addition of a small amount of oxygen to the nitrogen flow changes the optical and thermal properties of the jet and these results are also discussed.
    Plasma Sources Science and Technology 03/2013; 22(2):025013. · 3.06 Impact Factor
  • M. Michele Dawley, Sylwia Ptasińska
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    ABSTRACT: Gas-phase dissociative electron attachment (DEA) measurements to N-methylformamide (NMF, HC(O)NHCH3), a simple molecule containing the peptide linkage, were performed. The anion yields as a function of electron energy below 15 eV were obtained using a crossed molecular beam/Quadrupole Mass Spectrometer (QMS) setup. DEA to NMF produces CN̄, OCN̄, NH2̄, Ō, HCŌ, and NH̄, similar to formamide. Isotopic studies with N-methyl-d3-formamide (d3-NMF, HC(O)NHCD3) have confirmed and clarified assignments. Newly observed dissociation channels from NMF result in the formation of CH3NHC(O)̄/CH3NC(O)H̄, CH3NH̄, CŌ, and CH3̄. The dominant fragmentation pathways involve the formation of CN̄ and OCN̄ near 1.5 eV, which are produced from the electron capture by the π* orbital of the C = O combined with the scission of the N-CH3 bond and simultaneous formation of a C = N π bond. The methyl neutral by-product assists in lowering the thermodynamic threshold for CN̄ and OCN̄ production as compared with the DEA to formamide. The [Parent-H]̄ signal at m/z 61 from d3-NMF confirms site-selectivity for formation of this ion and excludes H loss from the methyl group of NMF. Peptide bond (O = C-N-H) dissociation is observed resulting in both CH3NH̄ and HCŌ, but these channels require higher energies (> 5 eV) to occur.
    International Journal of Mass Spectrometry 01/2013; · 2.23 Impact Factor
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    ABSTRACT: The results of an experimental investigation of 1 keV electron irradiation of ices (deposited at 30 K) of (i) pure methanol and (ii) of a 1:1 mixture of NH3:CH3OH are reported. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The products observed were methyl formate (H3COHCO), methane (CH4), hydroxymethyl (CH2OH), formamide (HCONH2), formic acid (HCOOH), formaldehyde (H2CO), formyl radical (HCO), cyanate ion (OCN−), isocyanic acid (HNCO), carbon monoxide (CO) and carbon dioxide (CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed.
    Chemical Physics Letters 01/2013; 556:359–364. · 1.99 Impact Factor
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    Chemical Physics Letters 11/2012; 551:144. · 1.99 Impact Factor
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    ABSTRACT: The adsorption of histidine (His), and its peptide glycyl-glycyl-histidine (Gly-Gly-His), on Au(111) and Au(110) has been studied by soft X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the nitrogen and oxygen K-edges. The molecules were adsorbed on surfaces from acidic (pH 3) solution. The results are compared with our previous studies of the adsorption of histidine and its peptides on Au(111) deposited on Au(111) from neutral solutions. When deposited from acidic solution, His adsorbs as carboxylic and carboxylate forms on both Au(111) and Au(110) surfaces, whereas its peptide is present mainly in the carboxylic form. In contrast, both molecules deposited from neutral solution adsorbed mainly as carboxylates. The imino nitrogen atom of the imidazole ring plays a crucial role in the interaction with gold surfaces. The Au 4f core level shift indicates that a chemisorption rather than a physisorption process occurs.
    The Journal of Physical Chemistry C 10/2012; 116(43):22960–22966. · 4.84 Impact Factor
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    ABSTRACT: In this work a low-energy electron beam is used to irradiate mixtures of nitrogen and methane in helium droplets. The formation of heterogeneous ionic species due to ionization is observed and the corresponding chemical structures and binding energies are calculated. Formation of a CN bond in CH3N2+ is shown computationally, which indicates the possibility of synthesis of true chemical bonds. The formation of CN bonds in organic molecules is of relevance for understanding atmospheric chemistry, for example in Titan's atmosphere.
    RSC Advances 10/2012; 2(28):10492-10495. · 3.71 Impact Factor

Publication Stats

1k Citations
219.61 Total Impact Points

Institutions

  • 2011–2014
    • University of Notre Dame
      • Department of Physics
      South Bend, Indiana, United States
  • 2008–2013
    • The Open University (UK)
      • Department of Physical Sciences
      Milton Keynes, England, United Kingdom
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 2008–2011
    • Milton Keynes College
      Milton Keynes, England, United Kingdom
  • 2003–2011
    • University of Innsbruck
      • Institut für Ionenphysik und Angewandte Physik
      Innsbruck, Tyrol, Austria
  • 2006–2010
    • Université de Sherbrooke
      • Department of Nuclear Medicine and Radiobiology
      Sherbrooke, Quebec, Canada
    • University of Nebraska at Lincoln
      • Department of Physics and Astronomy
      Lincoln, NE, United States