Theoretical investigation of the backbone···π and π···π stacking interactions in substituted-benzene||3-methyl-2′-deoxyadenosine: a perspective to the DNA repair

<p>The π-stacking effects of substituted benzenes on the <i>N</i>-glycosidic bond strength of 3-methyl-2'-deoxyadenosine (3-MDA) were studied by quantum mechanical calculations. Although all substituents enhance the stacking interactions, enhancement is higher for the electron-donating (ED) substituents. When the overall binding energy is separated into the π···π (Δ<i>E_π</i>_···<i>_π</i>) and backbone···π (Δ<i>E</i>_bb···<i>_π</i>) contributions, the ED and electron-withdrawing (EW) substituents increase those contributions, respectively. Both the ED and EW substituents decrease the distance between the centres of stacked rings, while the EW ones increase the <i>N</i>-glycosidic bond length. The electron charge density calculated at the C--N bond critical point (ρ_C–N) is in linear correlation with the backbone···π interaction, not with the π···π interaction. This study also shows that the charge transfer from X-Ben to 3-MDA is in linear correlation with the Δ<i>E_π</i>_···<i>_π</i> and the change in the charge on the sugar ring is in better accordance with the backbone···π interaction. The N7 proton affinity (PA_N7), with a key role in the depurination process, is highly affected by the π···π interactions. Thus, both interactions must be considered because of the balance between the backbone···π and π···π contributions in these biomolecular systems.</p> <p></p

A systematic study on interplay between intermolecular hydrogen bonding and aromaticity

In this study, the interplay between aromaticity and intermolecular hydrogen bonding was investigated in some heterocyclic compounds using quantum mechanical calculations. The NH … O intermolecular hydrogen bonds between formamide and NH and CO functional groups of the selected compounds enhance the delocalisation of the six-membered ring electron cloud, resulting in an increase in the aromaticity of the ring. The contribution of various factors to the binding energy, including the stabilisation energy of the interplay between aromaticity and H-bonding, was estimated using two model systems. The relative binding energies and the estimated stabilisation energies of the aforementioned interplay can be explained by the weights of resonance structures calculated using the natural resonance theory (NRT) analysis with the natural bond orbitals (NBO) method. These weights reflect the tendency of ring nitrogen lone pairs to contribute to the π electron cloud of the ring. The results of the topological analysis of electron charge densities using the atoms in molecules (AIM) method were used to estimate the aromaticity of the ring. Aromaticity indices, particularly nucleus-independent chemical shifts (NICS) calculated one angstrom above the ring plane, are in good linear correlation with the estimated stabilisation energies and electron density at the H-bond critical points. The sum of the total nuclear spin–spin coupling 1J of adjacent atoms of the ring (Σ1J), and the J values of H-bond donor and H-bond acceptor atoms, 1HJNO, which are in good agreement with the energy data and aromaticity indices, can be used as measures of the interplay between aromaticity and H-bonding. The interplay between H-bonding and the aromaticity of the ring is clearly evident from the changes in the pattern of the molecular electrostatic potential (MEP) contour maps at 1.7 Å above the plane of the molecule upon H-bond complexation.</p

Publications on Islamic Studies from 1980 to 2015: An Overview

In this study we evaluated global publication of Islamic studies from 1980 to 2015 of all subject category of the Science Citation Index based (SCI) on the Web of Science (WoS)

Urinary MicroRNA Biomarkers of Drug-induced Kidney Injury (DIKI) Demonstrate Differences in Sensitivity within Exosomal Fraction Compared to Whole Urine

Poster presented to the Society of Toxicology (SOT) 63rd Annual Meeting and ToxExpo March 2024Search for CCTE records in EPA’s Science Inventory by typing in the title at this link.https://cfpub.epa.gov/si/si_public_search_results.cfm?advSearch=true&showCriteria=2&keyword=CCTE&TIMSType=&TIMSSubTypeID=&epaNumber=&ombCat=Any&dateBeginPublishedPresented=07/01/2017&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&DEID=&personName=&personID=&role=Any&journalName=&journalID=&publisherName=&publisherID=&sortBy=pubDate&count=25</p