μSr studies of free radicals in the gas phase

1995 ◽  
Vol 190 (2) ◽  
pp. 493-503 ◽  
Author(s):  
M. Senba ◽  
D. J. Arseneau ◽  
J. J. Pan ◽  
M. Shelley ◽  
D. G. Fleming
Keyword(s):  
Free Radicals ◽  
Gas Phase

Photochemical oxidation of atmospheric sulphur dioxide

1979 ◽  
Vol 290 (1376) ◽  
pp. 543-550 ◽  
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Sulphur Dioxide ◽  
Heterogeneous Reactions ◽  
Photochemical Oxidation ◽  
Gas Phase Reactions ◽  
Oxidation Rates ◽  
Polluted Atmosphere ◽  
Gas Phase Oxidation ◽  
Background Troposphere

Oxidation of atmospheric sulphur dioxide can occur by homogeneous photochemically initiated gas-phase reactions as well as by heterogeneous reactions in cloud and fog droplets. Gas phase oxidation can result from reactions of excited SO 2 molecules formed by absorption of solar u.v. radiation by ground state SO 2 , from reactions of SO 2 with photochemically generated OH and RO 2 free radicals, and from its reaction with transient species produced in thermal ozone—alkene reactions. Evaluation of the available mechanistic and rate data reveals that, of these three processes, oxidation by free radicals, particularly OH, is likely to be the most important in the atmosphere. Oxidation rates of up to 4 % h -1 are predicted for a hydrocarbon-NO x polluted atmosphere under western European summertime conditions. This can lead to the formation of elevated concentrations of sulphuric acid and sulphate aerosol in polluted air. In the natural background troposphere oxidation rates are much less, ca . 0.3 % h -1 averaged over 24 h, but probably still significant as a source of atmospheric sulphates.

scholarly journals Theoretical Study about the Effect of Halogen Substitution on the Reactivity of Antitumor 3-Formylchromones and Their Free Radicals

2017 ◽  
Vol 2017 ◽  
pp. 1-5
Author(s):  
Maximiliano Martínez-Cifuentes ◽  
Boris Weiss-López ◽  
Ramiro Araya-Maturana
Keyword(s):  
Free Radicals ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Theoretical Study ◽  
Computational Study ◽  
Bond Dissociation Enthalpy ◽  
Radical Species ◽  
Anticancer Compounds ◽  
Dissociation Enthalpy ◽  
Polarizable Continuum

The mandatory presence of a chlorine atom on the aromatic ring of 6-hydroxy-3-formyl angular chromones, on the respiration inhibition of mammary carcinoma mouse, is explained through a computational study of these compounds. This study analyzes the reactivity of the neutral molecules and their free radicals, in gas phase and with water solvation, incorporated by the polarizable continuum medium (PCM) approach. Electrophilic reactivities were evaluated using Fukui (f+) and Parr (P+) functions. The stabilities of radical species formed by the abstraction of a hydrogen atom from the O-H bond were evaluated by bond dissociation enthalpy (BDE) and spin density (SD) calculations. This study has potential implications for the design of chromone analogues as anticancer compounds.

Scavenging Effects of Plant Antioxidants on Gas-Phase Free Radicals in Mainstream Cigarette Smoke

2010 ◽  
Vol 43 (3) ◽  
pp. 446-454 ◽  
Author(s):  
Xin Shen ◽  
Kejun Zhong ◽  
Xianjun Sun ◽  
Hongbing Lu ◽  
Yu Shen ◽  
...  
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Cigarette Smoke ◽  
Plant Antioxidants ◽  
Mainstream Cigarette Smoke

A KINETIC STUDY OF THE METATHETICAL AND ADDITION REACTIONS CHARACTERISTIC OF ALLYL POLYMERIZATION

1962 ◽  
Vol 40 (4) ◽  
pp. 796-803 ◽  
Author(s):  
A. C. R. Brown ◽  
D. G. L. James
Keyword(s):  
Experimental Data ◽  
Free Radicals ◽  
Gas Phase ◽  
Rate Constants ◽  
Allyl Alcohol ◽  
Reasonable Agreement ◽  
Chain Transfer ◽  
Addition Reactions ◽  
Radical Reactivity ◽  
Transfer Processes

The rate constants of the reactions[Formula: see text]have been measured in the gas phase between 50° and 142 °C:[Formula: see text]where ki is the (known) rate constant for the reaction[Formula: see text]The significance of these values is discussed in relation to the propagation and chain transfer processes in the polymerization of allyl alcohol. A consideration of the rates of addition of free radicals to a series of monomers of diverse reactivity reveals that a correlation exists between the rate constants for the addition of the ethyl radical in the gas phase and of certain polymer radicals in the liquid phase.An application of the general equation proposed by Bamford, Jenkins, and Johnston for radical reactivity leads to the conclusion that kp ≈ 2k7 and that kP/kf ≈ k7/k6 = 1.8 for allyl alcohol at 60 °C. Predictions based upon these relationships are compared with experimental data for the propagation and degree of homopolymerization of allyl alcohol and for inhibition and propagation in copolymerization; reasonable agreement is found in all cases.

scholarly journals ANTIOXIDANT PROPERTIES OF FOLIC ACID: A DFT STUDY

2018 ◽  
Vol 56 (4A) ◽  
pp. 39 ◽  
Author(s):  
Dao Duy Quang
Keyword(s):  
Free Radicals ◽  
Folic Acid ◽  
Gas Phase ◽  
Antioxidant Properties ◽  
Hydrogen Atom Transfer ◽  
Single Electron Transfer ◽  
To Receive ◽  
Antioxidant Mechanisms ◽  
Insight Into ◽  
Free Radicals Scavenging

Antioxidant activity of folic acid (FA) was investigated via two main antioxidant mechanisms: hydrogen atom transfer (HAT) and single electron transfer (SET) at the DFT/B3LYP/6-311G(d,p) level of theory. The characterizing thermochemical properties such as bond dissociation enthalpies (BDEs), ionization energy (IE) and electron affinity (EA) were calculated in the gas phase. Analyses of HOMOs distribution shows that the postions which easily donate electrons to free radicals are essentially found at C ring, while the positions which easily accept electrons (LUMOs) from radicals are mainly situated at B ring. The lowest BDE values equal to 76.5 and 80.1 kcal/mol are obtained at C19-H and C9–H position, respectively. It is showed that FA represents a potential antioxidant via HAT mechanism. In addition, the IE and EA values calculated in the gas phase are equal to 5.45 eV and 1.87 eV, respectively. This result shows that FA has higher ability to donate electrons into free radicals, while the ability to receive electrons is quite weak. Finally, the HAT reaction between FA and reactive radical like HOO• was also calculated at the same level of theory. This provides more insight into its mechanism on free radicals scavenging.

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