-
[show abstract]
[hide abstract]
ABSTRACT: Reactions of sesamol with different free radicals, in lipid and aqueous media, have been studied at the M05-2X/6-311+G(d,p) level of theory in conjunction with the SMD continuum model. Different mechanisms of reaction have been considered as well as polar and nonpolar environments. According to the overall rate coefficients, sesamol is predicted to react significantly faster in aqueous solution than in nonpolar media. The polarity of the environment also changes the relative importance of the reaction mechanisms. The anionic form of sesamol was found to be particularly reactive toward peroxyl radicals by transferring one electron. This mechanism was found responsible for the exceptional peroxyl radical scavenging activity of sesamol in aqueous solution, which was found to be even better than carotenoids, 2-propenesulfenic acid, and glutathione under physiological conditions. The agreement between experimental and calculated data supports the presented results as well as the methodology used in this work.
The Journal of Physical Chemistry B 10/2011; 115(44):13101-9. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Water complexes involving methanol, ethanol, formaldehyde, formic acid, acetone, ammonia, acetylene, ethylene, chloroethene, trichloroethene, 1,1,1-trichloroethane, hydroxyl radical, and hydroperoxyl radical have been studied. Enthalpies, entropies, and Gibbs free energies of association have been estimated, as well as the concentrations of the complexes under lower-troposphere conditions. The influence of the relative air humidity on the complexation processes has been analyzed. The association processes yielding water complexes of methanol, ethanol, formic acid, ammonia, acetone, hydroxyl radical, and hydroperoxyl radical were found to be more exothermic than that of the water dimer. General trends for the reactivity of the studied water complexes, compared to those of the corresponding free species, are proposed based on global reactivity indexes. The previously reported increased reactivity of the (*)OOH self-reaction, when there is water present, has been explained. The IR spectra of the complexes have been analyzed and compared with those of the free species.
The Journal of Physical Chemistry A 05/2010; 114(18):5796-809. · 2.95 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of different functional groups on the free radical scavenging capability of single-walled carbon
nanotubes (SWCNT) is investigated using density functional theory calculations. The reaction mechanism
that is considered in this study is the radical adduct formation. The reactions of a •OH radical with eight
different functionalized SWCNTs (armchair and zigzag) were studied. All of them were found to be exothermic
and exergonic. Different sites of reaction were considered, and the increase on reactivity with respect to
pristine tubes was found to be site-dependent. The presence of functional groups on the sidewalls of SWCNTs
is predicted to increase their OH radicals scavenging activity. To enhance this property, the best functional
groups are -CH2-OH for the armchair (3,3) SWCNT and -CONH-CH3 for the zigzag (5,0) fragment. The
major conclusion from this work is that functionalized SWCNTs, in addition to be soluble in different media,
are also very good free radical scavengers, being the armchair tubes better than the zigzag ones, when they
are ultrashort fragments.
The Journal of Physical Chemistry C 01/2010; 114:14734. · 4.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of point defects on the free-radical scavenging activity of armchair and zigzag single-walled carbon
nanotubes (SWCNTs), through a radical adduct formation mechanism, has been studied using density functional
theory calculations. SWCNTs with different vacancy (V), adatom (AA), and Stone-Wales (SW) defects
have been considered, as well as their pristine partners. All the studied reactions were found to be significantly
exothermic and exergonic, which supports their viability. The presence of point defects in the carbon lattice
of SWCNTs is predicted to increase their free-radical scavenging activity. The AA and V point defects,
involving C atoms with dangling bonds, are expected to cause a larger increase on the SWCNTs’ reactivity
toward free radicals than the SW and vacancy defects without C atoms with dangling bonds. The studied
Stone-Wales point defect shows the largest site-dependent effect on the free-radical scavenging activity of
SWCNTs. The presence of nonpolar environments is not expected to change the proposed trends. Characteristic
infrared bands in the 3300 and 900-1100 cm-1 regions have been assigned to the νO-H and νC-O vibrations
of the OH radical adducts.
The Journal of Physical Chemistry C 01/2010; 114:8302. · 4.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Density functional theory calculations have been used to model the efficiency of carboxylated single-walled
carbon nanotubes (SWCNT) to act as free radical scavengers, relative to that of their corresponding
nonfunctionalized partners. The exergonicity of the reactions between carboxylated SWCNTs and the studied
free radicals was found to be dependent on the site of functionalization as well as on the site of reaction. The
major conclusion from this work is that carboxylated SWCNTs are at least as good, or even better, free
radical scavengers than their nonfunctionalized partners. It is proposed that the presence of -COOH groups
would increase the free radical scavenging activity of SWCNTs, provided that the coverage occurs in such
an amount that there is enough free space on the walls for the reactions to take place. The reliability of the
calculations reported in the present work has been tested by comparison with different levels of theory.
The Journal of Physical Chemistry C 01/2010; 114:6363. · 4.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The OOH radical reactions with allicin and its Cope elimination products (2-propenesulfenic acid and thioacrolein) in aqueous solution have been studied. The CBS-QB3 quantum chemistry method has been used, with geometries and frequencies at BHandHLYP/6-311++G(d,p) level and conventional transition state theory. 2-Propenesulfenic acid is predicted to be over 1000 times more reactive toward OOH radical than allicin (2.60 x 10(7) vs 7.38 x 10(3) L mol(-1) s(-1), at 298 K). Accordingly, our results strongly support the novel suggestion by Vaidya et al. (Angew. Chem., Int. Ed. 2009, 48, 157) that the active ingredient responsible for the free radical scavenging activity of garlic is actually 2-propenesulfenic acid and not allicin. In addition, direct reaction branching ratios and product distribution for the three studied reactions are proposed for the first time.
The Journal of Physical Chemistry B 11/2009; 113(49):16077-81. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The relative free radical scavenging activity of beta-carotene, lycopene, and torulene toward OOH radicals has been studied using density functional theory. Hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms have been considered. All the possible reaction sites have been included in the modeling, and detailed branching ratios are reported for the first time. The reactions of hydrocarbon carotenoids (Car) with peroxyl radicals, in both polar and nonpolar environments, are predicted to proceed via RAF mechanism, with contributions higher than 98% to the overall OOH + Car reactions. Lycopene and torulene were found to be more reactive than beta-carotene. In nonpolar environments the reactivity of the studied carotenoids toward peroxyl radical follows the trend LYC > TOR > BC, whereas in aqueous solutions it is TOR > LYC > BC. OOH adducts are predicted to be formed mainly at the terminal sites of the conjugated polyene chains. The main addition sites were found to be C5 for beta-carotene and lycopene and C30 for torulene. The general agreement between the calculated magnitudes and the available experimental data supports the predictions from this work.
The Journal of Physical Chemistry B 08/2009; 113(32):11338-45. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Density functional theory has been used to model the OH reaction with Gly-Met-Gly and Gly-Nle-Gly tripeptides. The first one is predicted to be about 100 times faster than the second one. Therefore, if a methionine fragment is replaced by norleucine, the overall reactivity of the peptide toward free radicals is expected to be significantly reduced, which is in agreement with previous experimental findings. Since the most reactive sites were found to be located in the central backbone for Nle and in the terminal fragment of the side chain for Met, this decrease is expected to be even more critical for large-sized free radicals. The S atom seems to activate not only those alkyl sites next to it but also those located an odd number of bonds apart. In addition the viability of different paths explaining the formation of methionine sulfoxide has been tested, and it is proposed that this process involves the formation of R-SO radical and formaldehyde. The results from the present work offer an explanation to the role of sulfur atom on the reactivity of methionine toward free radicals. They also support the preponderant role of Met35 on the development of the Alzheimer disease.
The Journal of Physical Chemistry B 05/2009; 113(14):4947-52. · 3.70 Impact Factor
