Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired electron appears to be delocalized as much as possible over the whole aromatic ring, especially in the bromine substituent. The O-H bond dissociation energies (BDEs) and ionization potential energies (IPs) are reported at the B3LYP level of theory, providing the first complete series of BDEs and IPs for bromophenols. The observations are compared to those of other antioxidants for which BDEs and IPs have been previously obtained.
Understanding the nature of the interaction between metal
nanoparticles
and biomolecules has been important in the development and design
of sensors. In this paper, structural, electronic, and bonding properties
of the neutral and anionic forms of glutathione tripeptide (GSH) complexes
with a Au3 cluster were studied using the DFT-B3LYP with
6-31+G**-LANL2DZ mixed basis set. Binding of glutathione with the
gold cluster is governed by two different kinds of interactions: Au–X
(X = N, O, and S) anchoring bond and Au···H–X
nonconventional hydrogen bonding. The influence of the intramolecular
hydrogen bonding of glutathione on the interaction of this peptide
with the gold cluster has been investigated. To gain insight on the
role of intramolecular hydrogen bonding on Au–GSH interaction,
we compared interaction energies of Au–GSH complexes with those
of cystein and glycine components. Our results demonstrated that,
in spite of the ability of cystein to form highly stable metal–sulfide
interaction, complexation behavior of glutathione is governed by its
intramolecular backbone hydrogen bonding. The quantum theory of atom
in molecule (QTAIM) and natural bond orbital analysis (NBO) have also
been applied to interpret the nature of interactions in Au–GSH
complexes. Finally, conformational flexibility of glutathione during
complexation with the Au3 cluster was investigated by means
of monitoring Ramachandran angles.
The radical cations of DNA constituents generated by the ionizing radiation initiate an alteration of the bases, which is one of the main types of cytotoxic DNA lesions. These cation radical spices are known for their role in producing nucleic acid strand break. In this study, the gas-phase intrinsic chemical properties of the gaseous radical cations of cytosine and its base pair with guanine were examined by employing density functional theory (B3LYP) with the 6-311++G(d,p) basis set. Structures, geometries, adiabatic ionization energies, adiabatic electron affinities, charge distributions, molecular orbital analysis and proton-transfer process of these molecules were investigated. The influence of cation radical formation on acidities of multiple sites in cytosine molecule was investigated. Results of calculations revealed that cytosine radicals formed by deprotonation of cytosine cation radicals can exothermically abstract hydrogen atoms from thiol groups, phenol, and α-positions of amino acid. Furthermore, comparison of acidity value of N–H sites of cytosine cation radical with the known proton affinities (PA) of organic and biological molecules implied that cytosine cation radical can exothermically transfer onto basic sites of amino acids and peptides.
Copper(II) efficiently catalyzes the aerobic oxidation of aryl thioacetamides into the corresponding a-keto aryl thioamides in moderate to high yields in the presence of K 2 CO 3 under O 2 atmosphere. This protocol is simple, clean, and generates water as the only byproduct. A mechanism is proposed for the reaction course.
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