Debajyoti Bhattacharjee

Mechanistic and kinetics study of the gas phase reactions of methyltrifluoroacetate with OH radical and Cl atom

Theoretical investigations are carried out on the title reactions by means of ab initio and DFT methods. The optimized geometries, frequencies and minimum energy path are obtained at MPWB1K/6-31+G(d,p) level. Single point energy calculations are performed at MP2 and QCISD(T) levels of theory. Energetics were further refined by calculating the energy of the species with a high level G2(MP2) method. The rate constant of the two reactions are calculated at 298 K and 1 atm using Canonical Transition State Theory (CTST) utilizing the ab initio data obtained during the present study. The rate constant values are found to be 5.5 × 10−14 and 5.9 × 10−14 cm3 molecule−1 s−1, respectively which are in good agreement with the experimental data.

Theoretical investigation of atmospheric chemistry of volatile anaesthetic sevoflurane: reactions with the OH radicals and atmospheric fate of the alkoxy radical (CF3)2CHOCHFO: thermal decomposition vs. oxidation†

A theoretical study on the mechanism and kinetics of the gas phase reactions of a volatile anaesthetic compound (CF3)2CHOCH2F (Sevoflurane) with the OH radicals has been carried out using the hybrid HF–density functional M06-2X/6-31+G(d,p) method. Three conformations are predicted for the Sevoflurane molecule. Among the three conformers, the most stable one is considered for a detailed study. Reaction profiles are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Single point energy calculations have been performed by using the 6-311++G(d,p) basis set. The hydrogen abstraction from the –CH2F group is found to be the dominant reaction channel for hydrogen abstraction by OH radicals. Theoretically the calculated rate constant is found to be in good agreement with the experimentally measured ones. Using group-balanced isodesmic reactions, the standard enthalpies of formation for (CF3)2CHOCH2F, (CF3)2COCH2F and (CF3)2CHOCHF radicals are also reported for the first time. The atmospheric fate of the alkoxy radical, (CF3)2CHOCHFO, is also investigated for the first time using the same level of theory. Out of four prominent plausible decomposition channels including oxidation, our results clearly point out that reaction with O2 is the dominant path for the decomposition of (CF3)2CHOCHFO in the atmosphere involving the lowest energy barrier which is in accord with recent experimental findings.

Catalytic oxidation of NO by Au2− dimers: a DFT study

Density functional theory (DFT) calculations are performed to study the mechanistic details of NO oxidation promoted by gold dimer anions. Furthermore, we studied a full catalytic cycle producing two NO2 molecules. The reaction is explored along three possible pathways. Our theoretical results show that anionic gold dimers present catalytic activity towards NO oxidation, as indicated by the calculated low energy barriers and high exothermicities. The present results enrich our understanding of the catalytic oxidation of NO by Au-cluster based catalysts. For the first time, we have presented a systematic study on the structure and energetics of various reaction intermediates involved in NO oxidation by Au2− clusters using density functional theory (DFT).

Iron(III)-Mediated Radical Nitration of Bisarylsulfonyl Hydrazones: Synthesis of Bisarylnitromethyl Sulfones

Iron(III)-mediated radical nitration of bisarylsulfonyl hydrazones is described. In this protocol, the nontoxic and inexpensive Fe(NO3)3·9H2O plays a dual role as catalyst as well as nitro source. The mild conditions, broad substrate scope, and the functional group compatibility are the significant features. The reaction pathway has been demonstrated using DFT calculations, and the products can be subsequently converted into oximes using SnCl2·2H2O in high yields.

A DFT study on structure, stabilities and electronic properties of double magnesium doped gold clusters

Density functional theory (DFT) with PW91PW91 functional has been applied to investigate the structures, relative stabilities and electronic properties of small bimetallic neutral, cationic and anionic AunMg2 (n = 1–5) clusters. The results show that doping with two Mg atoms dramatically affects the geometries of the ground-states of Aun (n = 1–7) clusters. The relative stabilities of the clusters are compared on the basis of average binding energies, fragmentation energies and second order difference of energies. These parameters show even-odd alternation phenomenon. The electronic properties are calculated using hardness values and this suggests that even numbered clusters are more stable than odd counterparts in both bare, as well as doped ones. The nature of the bonding interaction is also investigated using Baders quantum theory of atoms in molecules (QTAIM), which indicates the presence of covalent bonding in the studied clusters. The population analysis reveals the transfer of electrons from Mg to Au atoms, which is in turn responsible for the enhanced stability of doped clusters.

Theoretical investigation on unimolecular decomposition of malonic acid: a potential sink for ketene†

DFT and ab initio calculations are performed to study the unimolecular decmposition pathways of malonic acid. The reaction is explored along three plausible decomposition pathways. The calculated results shows that decarboxylation is a two step process with an energy barrier of 32.16 kcal mol−1 at the CCSD(T)/6-311++G(d,p) level which is in reasonable agreement with available data. In contrast to the usual interpretations, novel features of this study are dehydration and in situ decarboxylation–dehydration pathways that involve energy barriers of 67.13 and 44.75 kcal mol−1, respectively at the CCSD(T)/6-311++G(d,p) level leading to the formation of carbon-suboxide and ketene along with conventional H2O and CO2. The thermal rate constants for the above decomposition pathways are also evaluated using Canonical Transition State Theory at 298 K.

Catalytic Reduction of Water Contaminant ‘4-Nitrophenol’ over Manganese Oxide Supported Ni Nanoparticles

Nitroaromatic compounds (NACs) are among the largest and most important groups of industrial chemicals in use nowadays (Ju and Parales 2010; Tomei et al. 2010). The NACs, such as nitrophenol, nitrobenzene, nitrotoluene, and nitrobenzoates, are of considerable industrial importance as the main raw materials in the manufacture of various dyes, pharmaceuticals, pesticides and explosives (Tomei et al. 2010; Yi et al. 2006; Aditya et al. 2015). 4-Nitrophenol (4-NP) is one of the most common and important NACs, both in terms of quantities used and potential environmental impacts (Yi et al. 2006; Podeh et al. 1995; Aditya et al. 2015; Sarkar et al. 2011). 4-NP is mainly used for the manufacture of drugs (e.g. acetaminophen) and pesticides (e.g. methyl and ethyl parathion) and is also used in leather treatment, in dyestuff production, and for military purposes. Because of its regular and extensive use, 4-NP can be found as a pollutant in industrial wastewater streams associated with its formulation, distribution and application (Yi et al. 2006; Pozun et al. 2013). Moreover, hydrolysis of pesticides and herbicides can also release 4-NP into the subsurface and then contaminate groundwater resources (Labana et al. 2005). As the 4-NP released into the environment, its contamination can cause a significant environmental and public health risk, due to its acute toxicity and mutagenic potential (Yi et al. 2006; Podeh et al. 1995; Labana et al. 2005; Aditya et al. 2015; Pozun et al. 2013). The acute exposing of 4-NP may lead to blood disorders along with methemoglobin formation, liver and kidney damage, anemia, skin and eye irritation, and systemic poisoning. In particular, it may cause deleterious effects to ecological systems, due to the 4-NP contamination of rivers and groundwater resources [Zieris et al. (1988), Aditya et al. (2015)]. Therefore, 4-NP containing industrial wastewater should be uncontaminated before being discharged into the environment.

Combined experimental and theoretical investigations on the encapsulation of nickel(II)tet-a complex in zeolite Y and its photocatalytic activity

The encapsulation of 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane [tet-a] nickel(II) in zeolite Y was executed by the “Flexible Ligand method”. The neat and encapsulated complexes were well characterized by DRS UV-Vis, FTIR, powder and single crystal X-ray diffraction studies, ICP-OES, cyclic voltammetry and FESEM. An observed blue shift in the absorption spectrum specified that the structural changes occurred after encapsulation. The energy levels and transition probability of the encapsulated complex varied from the neat metal complex due to the constrained environment of the zeolite. DFT and TDDFT studies were also performed and correlated with the experimental results for both the neat and encapsulated complexes. The obtained experimental UV-Vis spectra were consistent with the theoretically generated UV-Vis spectra. The influence of the zeolite framework on the changes in the structural parameters, energies of the HOMO and LUMO, and global hardness and softness of complex was found via DFT calculations. Fukui functions were used to determine the reactive sites of the complexes. The photocatalytic activity of the encapsulated complex on the degradation of Congo red was carried out under visible light irradiation. The rate constant of the photocatalytic reaction was calculated, and the mechanistic details were proposed.

Catalytic activity of anionic Au–Ag dimer for nitric oxide oxidation: a DFT study

Bimetallic nanoparticles composed of two different metals such as Au–Ag show novel catalytic behavior based on the effect of the second metal element added. Considering this fact, we have performed density functional theory (DFT) calculations to study the oxidation pathway of NO promoted by anionic Au–Ag− dimer. During our investigations, we have considered two most plausible pathways of NO oxidation. We found that the anionic Au–Ag− dimer can effectively catalyze NO oxidation reaction. In Au–Ag−, the Au site is more active than the Ag site, and the calculated energy barrier values for the rate determining step of the Au-site catalytic reaction are remarkably lower than those for both the Ag-site catalytic reactions. The present results enrich our understanding of the catalytic oxidation of NO by Au–Ag cluster based catalyst. For the first time, we have presented a systematic study on the structure and energetics of various reaction intermediates involved in NO oxidation by Au–Ag− dimer using DFT. The T1 diagnostic calculation suggests that the multi-reference character is not an issue for the present study.

Atmospheric chemistry of HFE-7000 (i-C3F7OCH3) and isofluoro-propyl formate (i-C3F7OC(O)H): reactions with OH radicals, atmospheric lifetime and fate of alkoxy radical (i-C3F7OCH2O•) – a DFT study

ABSTRACT The mechanism of hydrogen abstraction reaction between HFE-7000 (i-C3F7OCH3) and OH radicals using M06-2X functional in conjunction with 6-31+G(d,p) basis set is investigated. The pre-reactive and post-reactive complexes from intrinsic reaction coordinate calculations are validated at entrance and exit channels, respectively. The standard enthalpies of formation for the species and bond dissociation energy for C–H bond are also estimated. The rate constants of the titled reactions over the temperature range of 250–450 K are reported. The OH-driven atmospheric life time of i-HFE-7000 is computed to be 3.19 years. The atmospheric fate of the alkoxy radical (i-C3F7OCH2O•) is also explored here for the first time. Three prominent plausible decomposition channels including oxidation are considered in detail. The thermochemical data reveal that reaction with O2 is the dominant path for the decomposition of i-C3F7OCH2O• radical. Moreover, rate constant for the OH-initiated hydrogen abstraction of isofluoro-propyl formate (i-C3F7OC(O)H) is also reported. Graphical Abstract