Browsing by Author "Wang, Yi-Sheng"

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Analysis of Initial Reactions of MALDI Based on Chemical Properties of Matrixes and Excitation Condition
(1970-01-01)
Lai, Yin-Hung
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Wang, Chia-Chen
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Chen, Chiu Wen
;
Liu, Bo-Hong
;
Lin, Sheng Hsien
"This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with alpha-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions."
Contribution of thermal energy to initial ion production in matrix-assisted laser desorption/ionization observed with 2,4,6-trihydroxyacetophenone
(2014-08-15)
Lai, Yin-Hung
;
Chen, Bo-Gaun
;
Lee, Yuan Tseh
;
Wang, Yi-Sheng
;
Lin, Sheng Hsien
RATIONALE: Although several reaction models have been proposed in the literature to explain matrix-assisted laser desorption/ionization (MALDI), further study is still necessary to explore the important ionization pathways that occur under the high-temperature environment of MALDI. 2,4,6-Trihydroxyacetophenone (THAP) is an ideal compound for evaluating the contribution of thermal energy to an initial reaction with minimum side reactions. METHODS: Desorbed neutral THAP and ions were measured using a crossed-molecular beam machine and commercial MALDI-TOF instrument, respectively. A quantitative model incorporating an Arrhenius-type desorption rate derived from transition state theory was proposed. Reaction enthalpy was calculated using GAUSSIAN 03 software with dielectric effect. Additional evidence of thermal-induced proton disproportionation was given by the indirect ionization of THAP embedded in excess fullerene molecules excited by a 450 nm laser. RESULTS: The quantitative model predicted that proton disproportionation of THAP would be achieved by thermal energy converted from a commonly used single UV laser photon. The dielectric effect reduced the reaction Gibbs free energy considerably even when the dielectric constant was reduced under high-temperature MALDI conditions. With minimum fitting parameters, observations of pure THAP and THAP mixed with fullerene both agreed with predictions. CONCLUSIONS: Proton disproportionation of solid THAP was energetically favorable with a single UV laser photon. The quantitative model revealed an important initial ionization pathway induced by the abrupt heating of matrix crystals. In the matrix crystals, the dielectric effect reduced reaction Gibbs free energy under typical MALDI conditions. The result suggested that thermal energy plays an important role in the initial ionization reaction of THAP. Copyright (C) 2014 John Wiley & Sons, Ltd.
Contribution of thermal energy to initial ion production in matrix-assisted laser desorption/ionization observed with 2,4,6-trihydroxyacetophenone
(2014-08-15)
Lai, Yin-Hung
;
Chen, Bo-Gaun
;
Lee, Yuan Tseh
;
Wang, Yi-Sheng
;
Lin, Sheng Hsien
RATIONALE: Although several reaction models have been proposed in the literature to explain matrix-assisted laser desorption/ionization (MALDI), further study is still necessary to explore the important ionization pathways that occur under the high-temperature environment of MALDI. 2,4,6-Trihydroxyacetophenone (THAP) is an ideal compound for evaluating the contribution of thermal energy to an initial reaction with minimum side reactions. METHODS: Desorbed neutral THAP and ions were measured using a crossed-molecular beam machine and commercial MALDI-TOF instrument, respectively. A quantitative model incorporating an Arrhenius-type desorption rate derived from transition state theory was proposed. Reaction enthalpy was calculated using GAUSSIAN 03 software with dielectric effect. Additional evidence of thermal-induced proton disproportionation was given by the indirect ionization of THAP embedded in excess fullerene molecules excited by a 450 nm laser. RESULTS: The quantitative model predicted that proton disproportionation of THAP would be achieved by thermal energy converted from a commonly used single UV laser photon. The dielectric effect reduced the reaction Gibbs free energy considerably even when the dielectric constant was reduced under high-temperature MALDI conditions. With minimum fitting parameters, observations of pure THAP and THAP mixed with fullerene both agreed with predictions. CONCLUSIONS: Proton disproportionation of solid THAP was energetically favorable with a single UV laser photon. The quantitative model revealed an important initial ionization pathway induced by the abrupt heating of matrix crystals. In the matrix crystals, the dielectric effect reduced reaction Gibbs free energy under typical MALDI conditions. The result suggested that thermal energy plays an important role in the initial ionization reaction of THAP. Copyright (C) 2014 John Wiley & Sons, Ltd.
Dissociation of heme from gaseous myoglobin ions studied by infrared multiphoton dissociation spectroscopy and Fourier-transform ion cyclotron resonance mass spectrometry
(2006-10-07)
Wang, Yi-Sheng
;
Sabu, Sahadevan
;
Wei, Shih-Chia
;
Kao, C. -M. Josh
;
Kong, Xianglei
Detachment of heme prosthetic groups from gaseous myoglobin ions has been studied by collision-induced dissociation and infrared multiphoton dissociation in combination with Fourier-transform ion cyclotron resonance mass spectrometry. Multiply charged holomyoglobin ions (hMb(n+)) were generated by electrospray ionization and transferred to an ion cyclotron resonance cell, where the ions of interest were isolated and fragmented by either collision with Ar atoms or irradiation with 3 mu m photons, producing apomyoglobin ions (aMb(n+)). Both charged heme loss (with [Fe(III)-heme](+) and aMb((n-1)+) as the products) and neutral heme loss (with [Fe(II)-heme] and aMb(n+) as the products) were detected concurrently for hMb(n+) produced from a myoglobin solution pretreated with reducing reagents. By reference to E-a=0.9 eV determined by blackbody infrared radiative dissociation for charged heme loss of ferric hMb(n+), an activation energy of 1.1 eV was deduced for neutral heme loss of ferrous hMb(n+) with n=9 and 10. (c) 2006 American Institute of Physics.
Hydrogel Micropatch and Mass Spectrometry-Assisted Screening for Psoriasis-Related Skin Metabolites
(2016-08)
Dutkiewicz, Ewelina P.
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Hsieh, Kai-Ta
;
Wang, Yi-Sheng
;
Chiu, Hsien-Yi
;
Urban, Pawel L.
BACKGROUND: Psoriasis is a chronic, immune-mediated inflammatory skin disease. Screening skin metabolites could unravel the pathophysiology of psoriasis and provide new diagnostic approaches. Due to the lack of suitable methodologies for collecting scarce amounts of skin excretions, the psoriatic skin metabolome has not been extensively studied. METHODS: We implemented biocompatible hydrogel micropatch probes combined with mass spectrometry to investigate the skin metabolome. This noninvasive approach was applied to examine samples obtained from 100 psoriatic patients and 100 healthy individuals. We also developed custom data treatment tools and used chemometric and statistical tools to reveal the alterations in the skin metabolome caused by psoriasis. RESULTS: The proposed methodology enabled us to capture alterations in the composition of skin excretions caused by the disease. Chemometric analysis revealed the major differences between the metabolomes of psoriatic skin and healthy skin. Several polar metabolites were positively (choline and glutamic acid) or negatively ( urocanic acid and citrulline) correlated with the plaque severity scores. The amounts of these metabolites in the excretions sampled from psoriatic skin were significantly different (P < 0.001) from the excretions sampled from healthy skin. The role of biological variability and various confounding factors, which might affect the skin metabolome, was also investigated. CONCLUSIONS: Sampling lesional and healthy skin with the hydrogel micropatch probes and subsequent direct mass spectrometry scanning provided information on the alterations in the skin metabolome caused by psoriasis, increasing the understanding of the complex pathophysiology of this disease. (C) 2016 American Association for Clinical Chemistry
Hydrogel Micropatches for Sampling and Profiling Skin Metabolites
(2014-03-04)
Dutkiewicz, Ewelina P.
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Lin, Jia-Der
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Tseng, Te-Wei
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Wang, Yi-Sheng
;
Urban, Pawel L.
Metabolites excreted by skin have a huge potential as disease biomarkers. However, due to the shortage of convenient sampling/analysis methods, the analysis of sweat has not become very popular in the clinical setting (pilocarpine iontophoresis being a prominent exception). In this report, a facile method for sampling and rapid chemical profiling of skin metabolites excreted with sweat is proposed. Metabolites released by skin (primarily the constituents of sweat) are collected into hydrogel (agarose) micropatches. Subsequently, they are extracted in an online analytical setup incorporating nanospray desorption electrospray ionization and an ion trap mass spectrometer. In a series of reference measurements, using bulk sampling and electrospray ionization mass spectrometry, various low-molecular-weight metabolites are detected in the micropatches exposed to skin. The sampling time is as short as 10 min, while the desorption time is 2 min. Technical precision of micropatch analysis varies within the range of 3-42%, depending on the sample and the method of data treatment; the best technical precision (<= 10%) has been achieved while using an isotopically labeled internal standard. The limits of detection range from 7 to 278 pmol. Differences in the quantities of extracted metabolites are observed for the samples obtained from healthy individuals (intersubject variabilities: 30-89%; n = 9), which suggests that this method may have the potential to become a semiquantitative assay in clinical analysis and forensics.
Solid-Phase Thermodynamic Interpretation of Ion Desorption in Matrix-Assisted Laser Desorption/Ionization
(2010-11-04)
Lai, Yin-Hung
;
Wang, Chia-Chen
;
Lin, Sheng-Hsian
;
Lee, Yuan Tseh
;
Wang, Yi-Sheng
This work demonstrates a quantitative interpretation of ion desorption in matrix-assisted laser desorption/ionization (MALDI). The theoretical modeling incorporates transition state theory for the desorption of surface ions, assuming chemical and thermal equilibrium in the solid state prior to desorption. It is distinct from conventional models that assume chemical equilibrium in the gas phase. This solid-state thermodynamic interpretation was used to examine the desorption of pure 2,4,6-trihydroxyacetophenone (THAP) and of angiotensin I mixed with THAP. It successfully described the changes in ion yield with the effective temperature under various laser fluence and initial temperature conditions. The analysis also revealed the key role played by ion concentration in the modeling to provide the best fit of the model to observations. On the other hand, divergence of the ion beam with laser fluence was examined using an imaging detection method, and the signal saturation normally seen at high fluence was appropriately reduced by ion focusing. Simplified but deceptive theoretical interpretations were obtained when the analysis was conducted without adequate calibration of the instrument bias.