Browsing by Author "Putikam, Raghunath"

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A fully-aqueous red-fluorescent probe for selective optical sensing of Hg2+ and its application in living cells
(2016-07)
Pola, Murali Krishna
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Raju, Mandapati V. Ramakrishnam
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Lin, Chein-Ming
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Putikam, Raghunath
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Lin, Ming-Chang
A new red-fluorescent mercury ion sensor material is designed and synthesized, which is composed of at weezer-shaped hydrophilic probe containing bifurcated soft-base atoms N and S coupled with 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) unit. By virtue of the strong electron-accepting nature of TCF unit (as a push pull chromophore), this designed sensor material can selectively detect Hg2+ over various tested metal ions in a 100% aqueous medium via naked-eye and photoluminescence (PL) observations. Theoretical and time-resolved photoluminescence measurements further confirmed the selectivity and reversibility of the probe towards Hg2+ via intramolocular charge transfer mechanism in this sensor material. Moreover, the living cell tests by confocal fluorescence images of this sensor material towards Hg2+ were also investigated. Finally, distinguished absorption changes and fluorescence quenching spectral appearances allowed us to present the selective optical indicator of Hg2+ via TCF moiety for the first time. (C) 2016 Elsevier Ltd. All rights reserved.
A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states
(2015-03-28)
Trong-Nghia Nguyen
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Putikam, Raghunath
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH2OO and anti/syn-CH3C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH2OO and anti-CH3C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH3C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C-H bonds. For syn-CH3C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH3 group by the terminal O atom producing CH2C(H)O-OH. At 298 K, the intramolecular insertion process in CH2OO was found to be 600 times faster than the commonly assumed ring-closing reaction. (c) 2015 AIP Publishing LLC.
A novel mechanism for the isomerization of N2O4 and its implication for the reaction with H2O and acid rain formation
(2018-06-15)
Putikam, Raghunath
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Lin, Ming-Chang
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應用化學系分子科學碩博班
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Institute of Molecular science
We have discovered, by high-level quantum-chemical calculations, a new and predominant isomerization mechanism for N2O4 -> ONONO2 via a roaming-like transition state occurring unimolecularly or bimolecularly during collision with H2O. The new mechanism allows N2O4 to react with H2O with a significantly lower barrier (< 13.1 kcal/mol) than the commonly known tight transition state (similar to 30-45 kcal/mol) by concurrent stretching of the N-N bond and rotation of one of the NO2 groups to form trans-ONONO2, which then undergoes a rapid metathetical reaction with H2O in the gas phase and in aqueous solution. The results have a significant implication for the hydrolysis of N2O4 in water to produce HONO and HNO3. Rate constants for the isomerization and hydrolysis reactions have been predicted for atmospheric modeling applications.
Anion receptors based on 4-nitrophenylhydrazone
(2016-07-20)
Jo, Jaeyoung
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Putikam, Raghunath
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Lin, M. C.
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Kang, Jongmin
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應用化學系
We have designed and synthesized new chromogenic anion receptors 1 and 2, which utilized 4-nitrophenylhydrazone as anion recognition moiety. UV-vis and H-1 NMR titration showed that receptors 1 and 2 bound anions utilizing two hydrazone N-H hydrogen bond and two C-H hydrogen bond. Despite the weak hydrogen bonding abilities of binding motifs, receptor 1 showed affinities for dihydrogen phosphate and acetate and receptor 2 showed relatively strong affinities for dihydrogen phosphate in polar solvent such as 5% DMSO in CH3CN. (C) 2016 Elsevier Ltd. All rights reserved.
Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light
(2018-01-12)
Shown, Indrajit
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Samireddi, Satyanarayana
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Chang, Yu-Chung
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Putikam, Raghunath
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Chang, Po-Han
Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an L-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS2 (SnS2-C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS2 lattice, resulting in different photophysical properties as compared with undoped SnS2. This SnS2-C photocatalyst significantly enhances the CO2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS2-C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO2 reduction under visible light, where the in situ carbon-doped SnS2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.
Extremely rapid self-reaction of the simplest Criegee intermediate CH2OO and its implications in atmospheric chemistry
(2014-06-01)
Su, Yu-Te
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Lin, Hui-Yu
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Putikam, Raghunath
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Matsui, Hiroyuki
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Lin, M. C.
Criegee intermediates, which are carbonyl oxides produced when ozone reacts with unsaturated hydrocarbons, play an important role in the formation of OH and organic acids in the atmosphere, but they have eluded direct detection until recently. Reactions that involve Criegee intermediates are not understood fully because data based on their direct observation are limited. We used transient infrared absorption spectroscopy to probe directly the decay kinetics of formaldehyde oxide (CH2OO) and found that it reacts with itself extremely rapidly. This fast self-reaction is a result of its zwitterionic character. According to our quantum-chemical calculations, a cyclic dimeric intermediate that has the terminal O atom of one CH2OO bonded to the C atom of the other CH2OO is formed with large exothermicity before further decomposition to 2H(2)CO + O-2 ((1)Delta(g)). We suggest that the inclusion of this previously overlooked rapid reaction in models may affect the interpretation of previous laboratory experiments that involve Criegee intermediates.
Reaction dynamics of O(D-1) + HCOOD/DCOOH investigated with time-resolved Fourier-transform infrared emission spectroscopy
(2014-10-21)
Huang, Shang-Chen
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Nghia, N. T.
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Putikam, Raghunath
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Nguyen, Hue M. T.
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Lin, M. C.
We investigated the reaction dynamics of O(D-1) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O-3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 <= upsilon <= 4, J <= 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrometer. In the reaction of O(D-1) + HCOOD, the rotational distribution of product OH is nearly Boltzmann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 +/- 0.05. In the reaction of O(D-1) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O(D-1) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient intramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O(D-1) + HCOOD and 4.08 for O(D-1) + DCOOH; the former agrees satisfactorily with experiments. We also observed the upsilon(3) emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol(-1) of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively. (C) 2014 AIP Publishing LLC.