Computational studies of pandemic 1918 and 2009 H1N1 hemagglutinins bound to avian and human receptor analogs

<div><p>The purpose of this work was to study the binding properties of two pandemic influenza A virus 1918 H1N1 (SC1918) and 2009 H1N1 (CA09) hemagglutinin (HA) with avian and human receptors. The quantum chemical calculations have been performed to analyze the interactions of 130 loop, 190 helix, 220 loop region, and conserved residues 95,145,153–155, of pandemic viruses’ HA with sialo-trisaccharide receptor of avian and human using density functional theory. The HA’s residues Tyr 95, Ala 138, Gln 191, Arg 220, and Asp 225 from the above regions have stronger interaction with avian receptor. The residues Thr 136, Trp 153, His 183, and Asp 190 of HA are important and play a significant role to bind with human receptor. The residues Tyr 95, Ala 138, Lys 145, Trp 153, Gln 192, and Gln 226 of HA of CA09 virus have found more interaction energies with human than avian receptors. Due to mutations in the active residues of HA of CA09 virus comparing with SC1918, the binding capabilities of HA with human have been increased. The molecular dynamics simulation was made to understand the different dynamical properties of HA and molecular interactions between HA of these two viruses with sialo-trisaccharide receptors of avian and human receptors. The interaction energy of HA of CA09 virus with human receptor decreases due to the human receptor far away from conserved residue region of HA protein. This reveals that the conserved residues particularly Lys 145 play major contribution to interaction with human receptor in HA of CA09 virus.</p></div

The inhibitory performance of flavonoid cyanidin-3-sambubiocide against H274Y mutation in H1N1 influenza virus

<p>Oseltamivir (Tamiflu) is the most accepted antiviral drug that targets the neuraminidase (NA) protein to inhibit the viral release from the host cell. Few H1N1 influenza strains with the H274Y mutation creates drug resistance to oseltamivir. In this study, we report that flavonoid cyanidin-3-sambubiocide (C3S) compound acts as a potential inhibitor against H274Y mutation. The drug resistance mechanism and inhibitory activity of C3S and oseltamivir against wild-type (WT) and H274Y mutant-type (MT) have been studied and compared based on the results of molecular docking, molecular dynamics, and quantum chemical methods. Oseltamivir has been found less binding affinity with MT. C3S has more binding affinity with WT and MT proteins. From the dynamical study, the 150th loop of the MT protein has found more deformation than WT. A single H274Y mutation induces the conformational changes in the 150th loop which leads to produce more resistance to oseltamivir. The 150th cavity is more attractive target for C3S to stop the conformational changes in the MT, than 430th cavity of NA protein. The C3S is stabilized with MT by more number of hydrogen bonds than oseltamivir. The electrostatic interaction energy shows a stronger C3S binding with MT and this compound may be more effective against oseltamivir-resistant virus strains.</p

Study of mutation and misfolding of Cu-Zn SOD1 protein

<div><p>The main objective of this work is to determine the mechanism for misfolding and aggregation as a result of mutations in Cu-Zn superoxide dismutase1. The quantum mechanical approach is beneficial for investigating the early stages of mutation, misfolding, and loss of protection of the native structures involved in the neuro-degeneration disease Amyotrophic Lateral Sclerosis. All the structures were optimized using density functional theory (B3LYP) with 6–31G* and LANL2DZ basis sets. The binding energies of the metal ions with their associated residues in the active site loop and metal binding loop have been investigated for native and metal-bound mutated structures. The metal ion affinity (MIA) was computed for all the structures. The binding energy and MIA in gas phase reveal the nature of interaction of active site residues with the metal cations. The electronic effect prevailing between the side chains of the residues in the active site governing the intermolecular interactions is given by the polarizability studies. The role of the bridging residue His 63 in the active site of the protein in the native and metal-bound mutated structures have been studied using ONIOM method to reveal the changes that takes place in the structural parameters during mutation. The molecular dynamics simulation is used to explore different dynamic properties of active site in native and metal-bound mutated structures. The structural information provided by the molecular dynamics simulation illustrates the structural consequences in the mutated structures.</p></div

A theoretical perspective of the nature of hydrogen-bond types – the atoms in molecules approach

<p>Hydrogen bonds and their strength were analysed based on their X–H proton–donor bond properties and the parameters of the H–Y distance (Y proton acceptor). Strong, moderate and weak interactions in hydrogen-bond types were verified through the proton affinities of bases (PA), deprotanation enthalpies of acids (DPE) and the chemical shift (σ). The aromaticity and anti-aromaticity were analysed by means of the NICS (0) (nucleus-independent chemical shift), NICS (1) and ΔNICS (0), ΔNICS (1) of hydrogen-bonded molecules. The strength of a hydrogen bond depends on the capacity of hydrogen atom engrossing into the electronegative acceptor atom. The correlation between the above parameters and their relations were discussed through curve fitting. Bader's theory of atoms in molecules has been applied to estimate the occurrence of hydrogen bonds through eight criteria reported by Popelier <i>et al</i>. The lengths and potential energy shifts have been found to have a strong negative linear correlation, whereas the lengths and Laplacian shifts have a strong positive linear correlation. This study illustrates the common factors responsible for strong, moderate and weak interactions in hydrogen-bond types.</p

Mechanism and Kinetics of the Atmospheric Oxidative Degradation of Dimethylphenol Isomers Initiated by OH Radical

Dimethylphenols are highly reactive in the atmosphere, and their oxidation plays a vital role in the autoignition and combustion processes. The dominant oxidation process for dimethylphenols is by gas-phase reaction with OH radical. In the present study, the reaction of OH radical with dimethylphenol isomers is studied using density functional theory methods, B3LYP, M06-2X, and MPW1K, and also at the MP2 level of theory using 6-31G­(d,p) and 6-31+G­(d,p) basis sets. The activation energy values have also been calculated using the CCSD­(T) method with 6-31G­(d,p) and 6-311+G­(d,p) basis sets using the geometries optimized at the M06-2X/6-31G­(d,p) level of theory. The reactions subsequent to the principal oxidation steps are studied, and the different reaction pathways are modeled. The positions of the OH and CH₃ substituents in the aromatic ring have a great influence on the reactivity of dimethylphenol toward OH radical. Accordingly, the reaction is initiated in four different ways: H-atom abstraction from the phenol group, H-atom abstraction from a methyl group, H-atom abstraction from the aromatic ring by OH radical, or electrophilic addition of OH radical to the aromatic ring. Aromatic peroxy radicals arising from initial H-atom abstraction and subsequent O₂ addition lead to the formation of hydroperoxide adducts and alkoxy radicals. The O₂ additions to dimethylphenol–OH adduct results in the formation of epoxide and bicyclic radicals. The rate constants for the most favorable reaction pathways are calculated using canonical variational transition state theory with small curvature tunneling corrections. This study provides thermochemical and kinetic data for the oxidation of dimethylphenol in the atmosphere and demonstrates the mechanism for the conversion of peroxy radical into aldehydes, hydroperoxides, epoxides, and bicyclic radicals, and their lifetimes in the atmosphere

Role of 6-Mercaptopurine in the potential therapeutic targets DNA base pairs and G-quadruplex DNA: insights from quantum chemical and molecular dynamics simulations

<p>The theoretical studies on DNA with the anticancer drug 6-Mercaptopurine (6-MP) are investigated using theoretical methods to shed light on drug designing. Among the DNA base pairs considered, 6-MP is stacked with GC with the highest interaction energy of –46.19 kcal/mol. Structural parameters revealed that structure of the DNA base pairs is deviated from the planarity of the equilibrium position due to the formation of hydrogen bonds and stacking interactions with 6-MP. These deviations are verified through the systematic comparison between X–H bond contraction and elongation and the associated blue shift and red shift values by both NBO analysis and vibrational analysis. Bent’s rule is verified for the C–H bond contraction in the 6-MP interacted base pairs. The AIM results disclose that the higher values of electron density (<i>ρ</i>) and Laplacian of electron density (∇²<i>ρ</i>) indicate the increased overlap between the orbitals that represent the strong interaction and positive values of the total electron density show the closed-shell interaction. The relative sensitivity of the chemical shift values for the DNA base pairs with 6-MP is investigated to confirm the hydrogen bond strength. Molecular dynamics simulation studies of G-quadruplex DNA d(TGGGGT)₄ with 6-MP revealed that the incorporation of 6-MP appears to cause local distortions and destabilize the G-quadruplex DNA.</p

Oxidation and Nitration of Tyrosine by Ozone and Nitrogen Dioxide: Reaction Mechanisms and Biological and Atmospheric Implications

The nitration of tyrosine by atmospheric oxidants, O₃ and NO₂, is an important cause for the spread of allergenic diseases. In the present study, the mechanism and pathways for the reaction of tyrosine with the atmospheric oxidants O₃ and NO₂ are studied using DFT-M06-2X, B3LYP, and B3LYP-D methods with the 6-311+G­(d,p) basis set. The energy barrier for the initial oxidation reactions is also calculated at the CCSD­(T)/6-31+G­(d,p) level of theory. The reaction is studied in gas, aqueous, and lipid media. The initial oxidation of tyrosine by O₃ proceeds by H atom abstraction and addition reactions and leads to the formation of six different intermediates. The subsequent nitration reaction is studied for all the intermediates, and the results show that the nitration affects both the side chain and the aromatic ring of tyrosine. The rate constant of the favorable oxidation and nitration reaction is calculated using variational transition state theory over the temperature range of 278–350 K. The spectral properties of the oxidation and nitration products are calculated at the TD-M06-2X/6-311+G­(d,p) level of theory. The fate of the tyrosine radical intermediate is studied by its reaction with glutathione antioxidant. This study provides an enhanced understanding of the oxidation and nitration of tyrosine by O₃ and NO₂ in the context of improving the air quality and reducing the allergic diseases

A theoretical study on the reaction mechanism and kinetics of allyl alcohol (CH₂ = CHCH₂OH) with ozone (O₃) in the atmosphere

<p>Volatile organic compounds (VOCs) play a major role in the physical and chemical process of the tropospheric chemical reactions in both polluted and remote environments. A theoretical work has been presented on the VOC of allyl alcohol with O₃ molecule is investigated using density functional theory methods. The reaction profile is initiated through the cycloaddition of ozone which leads to the formation of primary ozonide with minimal relative energy barrier of 1.31 kcal/mol which decomposes to form carbonyl molecule and carbonyl oxide. Carbonyl oxide, i.e. criegee intermediates reacts with various atmospheric species to produce more hazardous and toxic end products to the environment. The condensed form of Fukui function was calculated to predict reactive sites of the primary and secondary reaction profile. The rate coefficient using CVT with SCT over the temperature range of 258–358K is analysed and also to study the atmospheric effects of allyl alcohol in the atmosphere. The predicted rate coefficient for the favourable reaction pathway of <i>k</i>_p1 found to be 1.190 ×10⁻¹⁵ cm³/molecule/sec and comparable with the experimental result at 298 K. The atmospheric lifetime of allyl alcohol was found to be around 10 hours in addition to that global warming potentials are compared with the CO₂.</p

Mechanism and kinetics of the atmospheric degradation of 2-formylcinnamaldehyde with O₃ and hydroxyl OH radicals – a theoretical study

<p>In the present investigation, the reaction mechanism and kinetics of 2-<b>f</b>ormylcinnamaldehyde (2-FC) with O₃ and hydroxyl OH radicals were studied. The reaction of 2-FC with O₃ radical are initiated by the formation of primary ozonide, whereas the reaction of 2-FC with the hydroxyl OH radical are initiated by two different ways: (1). H-atom abstraction by hydroxyl OH radical from the –CHO and –CH = CHCHO group of 2-FC (2). Hydroxyl OH addition to the –CH = CHCHO group to the ring-opened 2-FC. These reactions lead to the formation of an alkyl radical. The reaction pathways corresponding to the reactions between 2-FC with O₃ and hydroxyl OH radicals have been analysed using density functionals of B3LYP and M06-2X level of methods with the 6-31+G(d,p) basis set. Single-point energy calculations for the most favourable reactive species are determined by B3LYP/6-311++G(d,p) and CCSD(T)/6-31+G(d,p) levels of theory. From the obtained results, the hydroxyl OH addition at C8 position of 2-FC are most favourable than the C9 position of 2-FC. The subsequent reactions of the alkyl radicals, formed from the hydroxyl OH addition at C8 position, are analysed in detail. The individual and overall rate constant for the most favourable reactions are calculated by canonical variational transition theory with small-curvature tunnelling corrections over the temperature range of 278–350 K. The calculated theoretical rate constants are in good agreement with the available experimental data. The Arrhenius plot of the rate constants with the temperature are fitted and the atmospheric lifetimes of the 2-FC with hydroxyl OH radical reaction in the troposphere calculate for the first time, which can be applied to the study on the atmospheric implications. The condensed Fukui function has been verified for the most favourable reaction sites. This study can be regarded as an attempt to investigate the O₃-initiated and hydroxyl OH-initiated reaction mechanisms of 2-FC in the atmosphere.</p