A Kinetic and Mechanistic Study of the Reaction Between and Methionine: Evidence for the Formation of Water Soluble Colloidal MnO2

AbstractRadioprotectors for acute injuries caused by large doses of ionizing radiation are vital to national security, public health and future development of humankind. Here, we develop a strategy to explore safe and efficient radioprotectors by combining Hantzsch’s reaction, high-throughput methods and polymer chemistry. A water-soluble polymer with low-cytotoxicity and an excellent anti-radiation capability has been achieved. In in vivo experiments, this polymer is even better than amifostine, which is the only approved radioprotector for clinical applications, in effectively protecting zebrafish embryos from fatally large doses of ionizing radiation (80 Gy X-ray). A mechanistic study also reveals that the radioprotective ability of this polymer originates from its ability to efficiently prevent DNA damage due to high doses of radiation. This is an initial attempt to explore polymer radioprotectors via a multi-component reaction. It allows exploiting functional polymers and provides the underlying insights to guide the design of radioprotective polymers.

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Mechanistic study of a manganese porphyrin catalyst for on-demand production of chlorine dioxide in water

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424615500376 ◽

2015 ◽

Vol 19 (01-03) ◽

pp. 492-499 ◽

Cited By ~ 3

Author(s):

Scott D. Hicks ◽

Silei Xiong ◽

Curt J. Bougher ◽

Grigori A. Medvedev ◽

James Caruthers ◽

...

Keyword(s):

Electron Transfer ◽

Chlorine Dioxide ◽

Transfer Reaction ◽

Water Soluble ◽

Reaction Pathways ◽

Mechanistic Study ◽

Manganese Porphyrin ◽

Oxygen Atom Transfer ◽

On Demand ◽

Proton Coupled Electron Transfer

A water-soluble manganese porphyrin complex was examined for the catalytic formation of chlorine dioxide from chlorite under ambient temperature at pH 5.00 and 6.90. Quantitative kinetic modeling allowed for the deduction of a mechanism that accounts for all experimental observations. Catalysis is initiated via an OAT (Oxygen Atom Transfer) reaction resulting in formation of a putative manganese(V) oxo species, which undergoes ET (Electron Transfer) with chlorite to form chlorine dioxide. As chlorine dioxide accumulates in solution, chlorite consumption slows down and ClO 2 reaches a maximum as the system reaches equilibrium. In phosphate buffer at pH 6.90, manganese(IV) oxo accumulates and its reaction with ClO 2 gives ClO 3-. However, at pH 5.00 acetate buffer proton coupled electron transfer (PCET) from chlorite to manganese(IV) oxo is fast and irreversible leading to chlorate formation only via the putative manganese(V) oxo species. These differences underscore how PCET rates affect reaction pathways and mechanism. The ClO 2 product can be collected from the aqueous reaction mixture via purging with an inert gas, allowing for the preparation of chlorine dioxide on-demand.

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Kinetics of metribuzin degradation by colloidal manganese dioxide in absence and presence of surfactants

Chemical Papers ◽

10.2478/s11696-013-0424-7 ◽

2014 ◽

Vol 68 (1) ◽

Cited By ~ 17

Author(s):

Qamruzzaman ◽

Abu Nasar

Keyword(s):

Sodium Dodecyl ◽

Oxidative Degradation ◽

Activation Parameters ◽

Water Soluble ◽

Ionic Surfactant ◽

Ammonium Bromide ◽

Pseudo First Order Reaction ◽

First Order ◽

Colloidal Mno2 ◽

Kinetics Of

AbstractThe kinetics of the degradation of metribuzin by water-soluble colloidal MnO2 in acidic medium (HClO4) were studied spectrophotometrically in the absence and presence of surfactants. The experiments were performed under pseudo-first-order reaction conditions in respect of MnO2. The degradation was observed to be of the first order in respect of MnO2 while of fractional order for both metribuzin and HClO4. The rate constant for the degradation of metribuzin was observed to decrease as the concentration of MnO2 increased. The anionic surfactant, sodium dodecyl sulphate (SDS), was observed to be ineffective whereas the non-ionic surfactant, Triton X-100 (TX-100), accelerated the reaction rate. However, the cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), caused flocculation with oppositely-charged colloidal MnO2; hence further study was not possible. The catalytic effect of TX-100 was discussed in the light of the available mathematical model. The kinetic data were exploited to generate the various activation parameters for the oxidative degradation of metribuzin by colloidal MnO2 in the absence as well as the presence of the non-ionic surfactant, TX-100.

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