Jihye Lee

One-Step Peptide Backbone Dissociations in Negative-Ion Free Radical Initiated Peptide Sequencing Mass Spectrometry

Peptide dissociation behavior in TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-based FRIPS (free radical initiated peptide sequencing) mass spectrometry was analyzed in both positive- and negative-ion modes for a number of peptides including angiotensin II, kinetensin, glycoprotein IIb fragment (296-306), des-Pro(2)-bradykinin, and ubiquitin tryptic fragment (43-48). In the positive mode, the ·Bz-C(O)-peptide radical species was produced exclusively at the initial collisional activation of o-TEMPO-Bz-C(O)-peptides, and two consecutive applications of collisional activation were needed to observe peptide backbone fragments. In contrast, in the negative-ion mode, a single application of collisional activation to o-TEMPO-Bz-C(O)-peptides produced extensive peptide backbone fragmentations as well as ·Bz-C(O)-peptide radical species. This result indicates that the duty cycle in the TEMPO-based FRIPS mass spectrometry can be reduced by one-half in the negative-ion mode. In addition, the fragment ions observed in the negative-ion experiments were mainly of the a-, c-, x-, and z-types, indicating that radical-driven tandem mass spectrometry was mainly responsible for the TEMPO-based FRIPS even with a single application of collisional activation. Furthermore, the survival fraction analysis of o-TEMPO-Bz-C(O)-peptides was made as a function of the applied normalized collision energy (NCE). This helped us to better understand the differences in FRIPS behavior between the positive- and negative-ion modes in terms of dissociation energetics. The duty-cycle improvement made in the present study provides a cornerstone for future research aiming to achieve a single-step FRIPS in the positive-ion mode.

MALDI In-Source Decay Mass Spectrometry of Polyamidoamine Dendrimers

We report using MALDI-ISD (in-source decay) mass spectrometry (MS) to characterize highly branched synthetic polymers of polyamidoamine (PAMAM) dendrimer. This inherently monodisperse polymer possesses dendritic branches networked by tertiary amines and an amide functionality in each repeating unit. Among various ISD matrices examined, 2,5-DHB was the most efficient, yielding 33 fragments produced by single- or multiple-bond cleavages. Detailed analysis revealed that cleavages at tertiary amine sites (S- and E-type fragments) were the most pronounced, with various other cleavages around amide groups. The fragmentation mechanism appeared to follow the radical-induced dissociation pathway. In addition, the matrix dependence of PAMAM MALDI-ISD differed from that of peptides/proteins. The observed fragments provided rich structural information, which was suitable to characterize dendritic polymers.

Characterization of Natural Dyes and Traditional Korean Silk Fabric by Surface Analytical Techniques

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are well established surface techniques that provide both elemental and organic information from several monolayers of a sample surface, while also allowing depth profiling or image mapping to be carried out. The static TOF-SIMS with improved performances has expanded the application of TOF-SIMS to the study of a variety of organic, polymeric and biological materials. In this work, TOF-SIMS, XPS and Fourier Transform Infrared (FTIR) measurements were used to characterize commercial natural dyes and traditional silk fabric dyed with plant extracts dyes avoiding the time-consuming and destructive extraction procedures necessary for the spectrophotometric and chromatographic methods previously used. Silk textiles dyed with plant extracts were then analyzed for chemical and functional group identification of their dye components and mordants. TOF-SIMS spectra for the dyed silk fabric showed element ions from metallic mordants, specific fragment ions and molecular ions from plant-extracted dyes. The results of TOF-SIMS, XPS and FTIR are very useful as a reference database for comparison with data about traditional Korean silk fabric and to provide an understanding of traditional dyeing materials. Therefore, this study shows that surface techniques are useful for micro-destructive analysis of plant-extracted dyes and Korean dyed silk fabric.

Surface characterization of hydrophobic thin films deposited by inductively coupled and pulsed plasmas

Different fluorocarbon thin films were deposited on Si substrates using a plasma-polymerization method. Fluorine-containing hydrophobic thin films were obtained by inductively coupled plasma (ICP) and pulsed plasma (PP) with a mixture of fluorocarbon precursors C2F6, C3F8, and c-C4F8 and the unsaturated hydrocarbons of C2H2. The influence on the fluorocarbon surfaces of the process parameters for plasma polymerization, including the gas ratio and the plasma power, were investigated under two plasma-polymerized techniques with different fluorocarbon gas precursors. The hydrophobic properties, surface morphologies, and chemical compositions were elucidated using water contact angle measurements, field emission-scanning electron microscope, x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). In this study, the ICP technique provides coarser grained films and more hydrophobic surfaces as well as a higher deposi...

Expression of pituitary tumor-transforming gene in endometrial cancer as a prognostic marker

The pituitary tumor-transforming gene (PTTG) is a novel oncogene expressed abundantly in most tumors, regulates basic fibroblast growth factor secretion, and induces angiogenesis. The objective of this study is to compare the expression rate of PTTG in endometrial cells, to correlate the level of expression of PTTG with the clinicopathologic parameters and overall survival, and to evaluate the possible use of PTTG as a prognostic marker of endometrial cancer. Forty patients diagnosed with endometrial cancer, 20 patients with endometrial hyperplasia, and 20 patients with normal endometrial tissues were included in the study. Immunohistochemical analyses on paraffin-embedded blocks were performed using a polyclonal anti-PTTG antibody. The decrease in expression of cytoplasmic and nuclear PTTG seen for endometrial cancer cells was statistically significant (P< 0.05). Cytoplasmic PTTG expression correlated with expression of progesterone receptor (P= 0.009) and FGF-2 (P= 0.007) but not with other parameters such as the expression of estrogen receptor, tumor grade, and surgical stage. Nuclear PTTG expression did not correlate with any parameters. The mean survival of patients with positive and negative cytoplasmic PTTG expression was 40.8 and 48.6 months (P= 0.78). In nuclear PTTG expression, the survival was 20.0 and 51.8 months, respectively (P= 0.04). Cytoplasmic PTTG expression was not associated with survival. Patients with nuclear PTTG overexpression showed a significant decrease in survival. The use of PTTG as a prognostic marker for endometrial cancer needs further investigation.

Dynamics and mechanism of flame retardants in polymer matrixes: experiment and simulation.

We investigate the dynamics and the mechanism of flame retardants in polycarbonate matrixes to explore for a way of designing efficient and environment-friendly flame retardants. The high phosphorus content of organic phosphates has been considered as a requirement for efficient flame retardants. We show, however, that one can enhance the efficiency of flame retardants even with a relatively low phosphorus content by tuning the dynamics and the intermolecular interactions of flame retardants. This would enable one to design bulkier flame retardants that should be less volatile and less harmful in indoor environments. UL94 flammability tests indicate that even though the phosphorus content of 2,4-di-tert-butylphenyl diphenyl phosphate (DDP) is much smaller with two bulky tertiary butyl groups than that of triphenyl phosphate (TPP), DDP should be as efficient of a flame retardant as TPP, which is a widely used flame retardant. On the other hand, the 2-tert-butylphenyl diphenyl phosphate (2-tBuDP), with a lower phosphorus content than TPP but with a greater phosphorus content than DDP, is less efficient as a flame retardant than both DDP and TPP. Dynamic secondary ion mass spectrometry and molecular dynamics simulations reveal that the diffusion of DDP is slower by an order of magnitude at low temperature than that of TPP but becomes comparable to that of TPP at the ignition temperature. This implies that DDP should be much less volatile than TPP at low temperature, which is confirmed by thermogravimetric analysis. We also find from Fourier transform infrared spectroscopy that Fries rearrangement and char formation are suppressed more by DDP than by TPP. The low volatility and the suppressed char formation of DDP suggest that the enhanced flame retardancy of DDP should be attributed to its slow diffusivity at room temperature and yet sufficiently high diffusivity at high temperature.

TOF‐SIMS Analysis of Red Color Inks of Writing and Printing Tools on Questioned Documents

Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) is a well‐established surface technique that provides both elemental and molecular information from several monolayers of a sample surface while also allowing depth profiling or image mapping to be performed. Static TOF‐SIMS with improved performances has expanded the application of TOF‐SIMS to the study of a variety of organic, polymeric, biological, archaeological, and forensic materials. In forensic investigation, the use of a minimal sample for the analysis is preferable. Although the TOF‐SIMS technique is destructive, the probing beams have microsized diameters so that only small portion of the questioned sample is necessary for the analysis, leaving the rest available for other analyses. In this study, TOF‐SIMS and attenuated total reflectance Fourier transform infrared (ATR‐FTIR) were applied to the analysis of several different pen inks, red sealing inks, and printed patterns on paper. The overlapping areas of ballpoint pen writing, red seal stamping, and laser printing in a document were investigated to identify the sequence of recording. The sequence relations for various cases were determined from the TOF‐SIMS mapping image and the depth profile. TOF‐SIMS images were also used to investigate numbers or characters altered with two different red pens. TOF‐SIMS was successfully used to determine the sequence of intersecting lines and the forged numbers on the paper.

Digital and analog measurements of HTS SFQ RS flip-flops and shift register circuits

We fabricated reset-set (RS) flip-flops and shift registers by using YBCO bicrystal junctions and tested their operations by using a computer-controlled digital measurement set-up and an analog measurement set-up. The RS flip-flop circuits operated successfully at temperatures up to 71 K. The RS flip-flop circuit was observed over 600 computer-generated clock cycles with nearly no errors. The circuits were reset or set during each clock cycle. By using an analog measurement technique, we operated the RS flip-flop circuits at frequencies of up to 500 Hz. Since our probe was not designed for high speed operation, the test speed was limited to this frequency. Although we could not operate the shift register completely, we observed flux propagation in the shift register.

Tandem mass spectrometric analysis of isosorbide‐1,4‐cyclohexane‐dicarboxylic acid polyester oligomer cations using ion‐trap mass spectrometry

RATIONALEnIsosorbide is a promising biomass-derived molecule that can be used as a replacement for fossil resource-derived diol monomers used in polyester synthesis. Due to its increased use in sustainable development, it is useful to understand the tandem mass spectrometric (MS/MS) fragmentation pathways of the isosorbide-based copolymer as an aid to interpreting the MS/MS spectra of other isosorbide-containing copolymers.nnnMETHODSnCollision-activated dissociation (CAD) experiments were performed on the sodiated/protonated molecules, [(AB)(n)A+Na(or H)](+), n = 2-5, of isosorbide (A)-1,4-cyclohexanedicarboxylic acid (B) oligomers formed by ion-trap electrospray ionization (ESI).nnnRESULTSnProduct ions arose from cleavage of the bonds between isosorbide and 1,4-cyclohexanedicarboxylic acid. In the MS/MS spectra, f(n) product ions were most abundant, followed by e(n) ions. McLafferty rearrangement appeared to provide the most facile pathway to yield the abundant f(n) and e(n) ions. In addition, a(n), b(n), f(n)u(n), and en (+) ions were observed. Inductive cleavage and β-elimination were suggested to be the pathways involved in generating e(n)(+)- and e(n)/b(n)-type ions, respectively.nnnCONCLUSIONSnBased on the obtained CAD spectra, the alternating sequences of two copolymer building blocks, A and B, were unambiguously determined. The fragmentation pathways leading to the observed product ion types were also established.

Structural and compositional analyses of Cu(In,Ga)Se2 thin film solar cells with different cell performances

Copper indium gallium selenide (CIGS) absorber thin films were deposited on bilayer Mo back contacts with and without a SiOx film on a soda-lime glass substrate. This was done to control the quantity of alkali metals in the films and to apply the growth method to a substrate that does not contain alkaline elements. The average concentrations of major elements Cu, In, Ga, and Se in the CIGS solar cells were measured by electron probe microanalysis, secondary ion mass spectrometry (SIMS), and Auger electron spectrometry. The SIMS technique was also used to obtain and compare depth profiles of the relative ion intensities of sodium and potassium alkali metals for CIGS thin films with varying cell efficiencies. The CIGS/Mo interfaces also were investigated by transmission electron microscopy (TEM), whereby a cross-sectional view of Mo films prepared with and without an initial SiOx layer made possible the detection of a MoSe2/Mo bilayer with a columnar-type microstructure. Scanning TEM images and correspondin...