Biswarup Pathak

Transverse conductance of DNA nucleotides in a graphene nanogap from first principles.

The fabrication of nanopores in atomically thin graphene has recently been achieved, and translocation of DNA has been demonstrated. Taken together with an earlier proposal to use graphene nanogaps for the purpose of DNA sequencing, this approach can resolve the technical problem of achieving single-base resolution in electronic nucleobase detection. We have theoretically evaluated the performance of a graphene nanogap setup for the purpose of whole-genome sequencing, by employing density functional theory and the nonequilibrium Greens function method to investigate the transverse conductance properties of nucleotides inside the gap. In particular, we determined the electrical tunneling current variation at finite bias due to changes in the nucleotides orientation and lateral position. Although the resulting tunneling current is found to fluctuate over several orders of magnitude, a distinction between the four DNA bases appears possible, thus ranking the approach promising for rapid whole-genome sequencing applications.

Calcium doped graphane as a hydrogen storage material

On the basis of first principle density functional theory, we have studied the stability, electronic structure, and hydrogen storage capacity of a monolayer calcium doped graphane (CHCa). The stability of CHCa was further investigated using the ab initio molecular dynamics study. The binding energy of Ca on graphane sheet was found to be higher than its bulk cohesive energy, which indicates the stability of CHCa. It was observed that with a doping concentration of 11.11% of Ca on graphane sheet, a reasonably good H2 storage capacity of 6 wt. % could be attained. The adsorption energies of H2 were found to be 0.1 eV, within the range of practical H2 storage applications.

Room-Temperature Chemoselective Reduction of Nitro Groups Using Non-noble Metal Nanocatalysts in Water

Purely aqueous-phase chemoselective reduction of a wide range of aromatic and aliphatic nitro substrates has been performed in the presence of inexpensive Ni- and Co-based nanoparticle catalysts using hydrazine hydrate as a reducing agent at room temperature. Along with the observed high conversions and selectivities, the studied nanoparticle catalysts also exhibit a high tolerance to other highly reducible groups present in the nitro substrates. The development of these potential chemoselective reduction catalysts also provides a facile route for the synthesis of other industrially important fine chemicals or biologically important compounds, where other highly reducible groups are present in close proximity to the targeted nitro groups.

Borane Derivatives: A New Class of Super‐ and Hyperhalogens

Super- and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well-known Wade-Mingos rule for describing the stability of closo-boranes B(n)H(n)(2-) and state-of-the-art theoretical methods, we show that a new class of super- and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade-Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B(12)H(13) and its isoelectronic cluster CB(11)H(12) as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane-like moiety is sufficient to give M(B(12)H(12)) clusters (M=Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B(12)H(13))(2) and M(CB(11)H(12))(2) (M=Li-Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.

Theoretical Study of Electronic Transport through DNA Nucleotides in a Double-Functionalized Graphene Nanogap

Graphene nanogaps and nanopores show potential for the purp ose of electrical DNA sequencing, in particular because single-base resolution ap pears to be readily achievable. Here, we evaluated from first principles the advantages of a nanoga p setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green’s function method to investigate the transverse cond uctance properties of the four nucleotides occurring in DNA when located between the opposin g fu ctionalized graphene electrodes. In particular, we determined the electrical tunnel i g current variation as a function of To whom correspondence should be addressed †Uppsala University ‡Nakhon Phanom University ¶Royal Institute of Technology 1 the applied bias and the associated differential conductan ce t a voltage which appears suitable to distinguish between the four nucleotides. Intriguingly , we observe for one of the nucleotides a negative differential resistance effect.

Mo- and N-doped BiNbO4 for photocatalysis applications

The electronic structure of pure BiNbO4 has been calculated and their electronic band positions have been aligned with respect to the water oxidation/reduction potential. The effect of cationic (Mo), anionic (N), and co-doping (Mo-N) on BiNbO4 has been studied and discussed with respect to the standard redox potential levels. Our results show that co-doping of Mo and N in BiNbO4 reduces the band gap up to 31.8%, thus making it a potential candidate for the photocatalysis of water for hydrogen production. The relative stability between the mono- and co-doped BiNbO4 materials show that co-doped material is more stable and feasible in comparison to the mono-doped materials.

Band gap engineering in BiNbO4 for visible-light photocatalysis

We have investigated the electronic structure of anionic mono- (S, N, and C) and co-doping (N-N, C-N, S-C, and S-N) on BiNbO4 for the visible-light photocatalysis. The maximum band gap reduction of pure BiNbO4 is possible with the (C-S) co-doping and minimum with N mono-doping. The calculated binding energies show that the co-doped systems are more stable than their mono-doped counterparts. Our optical absorption curves indicate that the mono- (C) and co-anionic doped (N-N and C-S) BiNbO4 systems are promising materials for visible light photocatalysis.

Ab initio study of lithium-doped graphane for hydrogen storage

Based on the first-principle density functional calculations we predict that Li-doped graphane (prehydrogenated graphene) can be a potential candidate for hydrogen storage. The calculated Li-bindin ...

Cardanol benzoxazines – interplay of oxazine functionality (mono to tetra) and properties

Cardanol, a sustainable origin phenol, was utilized as a reactive diluent to mediate solventless Mannich-type condensation reaction with para-formaldehyde and primary aromatic amines to form a homologous series of benzoxazine (Bz) monomers namely C-a, C-ddm, C-trisapm and C-tetraapm which differ in their degree of oxazine functionality as mono-, di-, tri- and tetra-oxazine respectively. A strong correlation is reflected between the number of oxazine rings in the monomer and the polymerization behavior, thermo-mechanical transitions, and properties of the polybenzoxazine synthesized. The monomer structure was confirmed by FTIR, 1H-, 13C-NMR spectroscopy and mass spectrometry. The curing, rheological, thermo-mechanical and thermal properties were determined using DSC, FTIR, rheometer, DMTA, LSS and TGA studies. The curing characteristic due to ROP of Bz monomers was supported both by DSC and FTIR studies. The presence of neighboring oxazine group in monomers (C-a to C-tetraapm) strongly attenuates the curing temperature (Ti = 225–140 °C), enhances Tg, thermal stability, and mechanical properties. Interestingly, DFT calculations also supported the lowest curing temperature for highest oxazine functionality monomer (C-tetraapm). The interplay between the degree of oxazine functionality in the monomer; extent of H-bonding and crosslink density values in sustainable origin synthesized polybenzoxazines is suggested. The thermoset showed an increasing trend (PC-a < PC-ddm < PC-trisapm < PC-tetraapm) in Tg (58–109 °C), thermal stability (355–391 °C), char yield (13–37%), LOI (23–31) and storage modulus (3.6–66.5 MPa) values. The monomers are liquid to semi-viscous paste at room temperature and showed potential for solventless processing in adhesive applications.

Semiconducting allotrope of graphene

From first-principles calculations, we predict a planar stable graphene allotrope composed of a periodic array of tetragonal and octagonal (4, 8) carbon rings. The stability of this sheet is predicted from the room-temperature molecular dynamics study and the electronic structure is studied using state-of-the-art calculations such as the hybrid density functional and the GW approach. Moreover, the mechanical properties of (4, 8) carbon sheet are evaluated from the Youngs modulus and intrinsic strength calculations. We find this is a stable planar semiconducting carbon sheet with a bandgap between 0.43 and 1.01 eV and whose mechanical properties are as good as graphenes.