Hemant G. Salunke

Biocompatible phosphate anchored Fe3O4 nanocarriers for drug delivery and hyperthermia

We demonstrate the preparation of biocompatible, water-dispersible phosphate anchored Fe3O4 magnetic nanocarriers (PAMN) by a facile soft-chemical approach. The surface functionalization of Fe3O4 nanoparticles (∼10 nm) with bioactive phosphate molecules (sodium hexametaphosphate) was evident from infrared, thermal and light scattering measurements. These superparamagnetic nanoparticles show better aqueous colloidal stability, good magnetic response and excellent self-heating efficacy under an external AC magnetic field. The bioactive shell not only provides colloidal stability to the particles but also creates functionalized exteriors with high densities of phosphate moieties for conjugation of drug molecules. The drug loading and release behavior of PAMN was investigated using doxorubicin hydrochloride (DOX) as a model drug to evaluate their potential as a carrier system. The cell viability and hemolysis assay suggests that PAMN do not have adverse toxic effects for further in vivo use. Specifically, high loading affinity for DOX with their sustained release profile and self-heating capacity makes these novel nanocarriers suitable for drug delivery and magnetic hyperthermia.

Dzyaloshinskii-Moriya interaction and chiral magnetism in 3d − 5d zigzag chains: Tight-binding model and ab initio calculations

We investigate the chiral magnetic order in freestanding planar 3d-5d biatomic metallic chains (3d :F e, Co; 5d: Ir, Pt, Au) using first-principles calculations based on density functional theory. We find that the antisymmetric exchange interaction, commonly known as the Dzyaloshinskii-Moriya interaction (DMI), contributes significantly to the energetics of the magnetic structure. For the Fe-Pt and Co-Pt chains, the DMI can compete with the isotropic Heisenberg-type exchange interaction and the magnetocrystalline anisotropy energy, and for both cases a homogeneous left-rotating cycloidal chiral spin-spiral with a wavelength of 51 u A and 36 u A, respectively, was found. The sign of the DMI, which determines the handedness of the magnetic structure, changes in the sequence of the 5d atoms Ir(+), Pt(−), Au(+). We use the full-potential linearized augmented plane wave method and perform self-consistent calculations of homogeneous spin spirals, calculating the DMI by treating the effect of spin-orbit interaction in the basis of the spin-spiral states in first-order perturbation theory. To gain insight into the DMI results of our ab initio calculations, we develop a minimal tight-binding model of three atoms and four orbitals that contains all essential features: the spin canting between the magnetic 3d atoms, the spin-orbit interaction at the 5d atoms, and the structure inversion asymmetry facilitated by the triangular geometry. We find that spin canting can lead to spin-orbit active eigenstates that split in energy due to the spin-orbit interaction at the 5d atom. We show that the sign and strength of the hybridization, the bonding or antibonding character between d orbitals of the magnetic and nonmagnetic sites, the bandwidth, and the energy difference between occupied and unoccupied states of different spin projection determine the sign and strength of the DMI. The key features observed in the trimer model are also found in the first-principles results.

Folic acid conjugated Fe3O4 magnetic nanoparticles for targeted delivery of doxorubicin

The interfacial engineering of magnetic nanoparticles (MNPs) with specific functional groups or targeting ligands is important for their in vivo applications. We report here the preparation and characterization of bifunctional magnetic nanoparticles (BMNPs) which contain a carboxylic moiety for drug binding and an amine moiety for folate mediated drug targeting. BMNPs were prepared by introducing bioactive cysteine molecules onto the surface of undecenoic acid coated Fe3O4 magnetic nanoparticles (UMNPs) via a thiol-ene click reaction and then, folic acid was conjugated with these BMNPs through an EDC-NHS coupling reaction. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicate the formation of highly crystalline single-phase Fe3O4 nanostructures. The changes in the interfacial characteristics of the nanoparticles and the presence of an organic coating are evident from Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), zeta-potential measurement, and thermogravimetric analysis (TGA). These nanocarriers have an average size of 10 nm, and have a pH dependent charge conversional feature and protein resistance characteristic in physiological medium. These nanoparticles also show high loading affinity for an anticancer drug, doxorubicin hydrochloride (DOX) and its pH dependent release. This is highly beneficial for cancer therapy as the relatively low pH in tumors will specifically stimulate the drug release at the site of interest. Furthermore, our fluorescence microscopy and flow cytometry studies confirmed the higher cellular internalization capability of these folic acid conjugated nanoparticles in cancer cells over-expressing folate receptors.

Electronic structure of the 4H polytype of diamond

We report the core-level x-ray photoelectron spectrum (XPS) of 4H diamond - a higher polytype of the well-studied cubic diamond. Diamond polytype films were synthesized by laser-induced reactive quenching at a liquid - solid interface, and characterized by transmission electron micro-diffraction. Electronic energy bands and densities of states, calculated using the local-density-based tight-binding linear muffin-tin orbital method, have been used to interpret the XPS data.

Cohesive and electronic properties of ordered Li-Al intermetallic compounds

Self-consistent electronic structure calculations have been performed on ordered lithium-aluminium compounds using the tight-binding linear muffin-tin orbital (TBLMTO) method. The FCC-based ground-state superstructures (namely Ll2 and Ll0 structures) show some systematic trends in their cohesive and electronic properties, which are in reasonably good agreement with the available experimental data. We have also compared the density of states, band structures and total ground-state energies of equiatomic AlLi compounds, between the FCC-based Ll0 structure and the BCC-based B32 structure. While the former shows a two-dimensional metallic behaviour, the latter shows a resemblance to a tetrahedral-bonded covalent solid, and is more stable. After detailed comparison with some recent LAPW calculations, we conclude that the TBLMTO method can be used as an efficient and reasonably accurate first-principles tool for studying the phase stability and chemical bonding in ordered intermetallic compounds.

Photophysical, bandstructural, and textural properties of o-FeNbO4 in relation to its cocatalyst-assisted photoactivity for water oxidation

In this study, a relationship between physicochemical, photophysical and photocatalytic properties of hydrothermally synthesized orthorhombic iron niobate (FeNbO4) is investigated. o-FeNbO4 displayed a multi-regime optical absorbance, which was ascribed to at least two distinct phenomena: (i) bandgap (∼3.4 eV) excitation giving rise to UV absorbance and (ii) energy transitions involving disorder-induced sub-bandgap donor or acceptor states leading to visible light absorbance. The preparation-dependent distortion in the crystal lattice and the existence of closely spaced inter-bandgap energy states were corroborated by powder X-ray diffraction, photoluminescence, thermoluminescence, and Raman spectroscopy studies. The first principles electronic structure elucidation and photoelectrochemical measurements supported a wide bandgap for FeNbO4, in contrast to the narrow bandgap reported previously. Correspondingly, a small photocurrent density was observed for FeNbO4 (∼2 to 3 μA cm−2) under 1 sun illumination, suggesting the availability of a smaller cross section of photogenerated charge pairs. Following these band characteristics, while no H2 evolution was observed, FeNbO4 gave rise to particle size-dependent O2 evolution during visible light irradiation of water in the presence of electron scavengers, the samples loaded with NiO as cocatalyst showing better activity. Further, the transmission electron microscopy examination revealed the dominant exposure of (011) facets of FeNbO4, besides a significant heterogeneity of inter-domain boundaries. Overall, our results confirm that the photoactivity of metal/oxide nanocomposites is governed by a combination of factors, such as: grain morphology, microstructure, surface adsorption states, and the localized inter-bandgap energy states. Our study also reveals that, in contrast to prevalent assumptions, the wavelength at the absorption edge may not represent the true band-to-band energy gap of metal oxide semiconductors, which is relevant to their photocatalytic activity.

AN AUGMENTED SPACE RECURSION STUDY OF THE ELECTRONIC STRUCTURE OF ROUGH EPITAXIAL OVERLAYERS

In this communication we propose the use of the augmented-space recursion as an ideal methodology for the study of electronic and magnetic structures of rough surfaces, interfaces and overlayers. The method can take into account roughness, short-ranged clustering effects, surface dilatation and interdiffusion. We illustrate our method by an application to an Fe overlayer on a Ag(100) surface.

Preparation-method-dependent morphological, band structural, microstructural, and photocatalytic properties of noble metal–GaNbO4 nanocomposites

We report the distinct physicochemical and photophysical properties of gallium niobate photocatalysts (bandgap: ∼3.1 eV), prepared by a solid-state (SS) reaction and sol–gel (SG) method and dispersed with a noble metal (∼0.5% of Pt, Au, or RuOx) cocatalyst. SG–GaNbO4 comprised smaller size particles (∼20–50 nm) and a larger surface area (∼160 m2 g−1) compared to SS–GaNbO4 (particle size ∼30–150 nm, surface area ∼27 m2 g−1). XRD patterns revealed a preparation-dependent variation in the relative intensity of prominent reflections. In TEM examination, SG samples exhibited small-range grain boundaries and heterogeneous metal/substrate interfacial contacts, while SS–GaNbO4 had long-range ordering. Laser-Raman and thermoluminescence investigations revealed that lattice distortion, defect-induced inter-bandgap charge trapping states, and the local environment around the metal/semiconductor interfaces may also depend on the preparation method. Metal–GaNbO4 nanocomposites showed no activity for the dissociation of pure water under UV (>250 nm) irradiation, despite the favourable conduction and valence band potentials. This was attributed to the sharp Ga and Nb d-levels in the narrow conduction band of GaNbO4, as confirmed by ab initio electronic structure calculation. These photocatalysts, however, showed good activity for semiconductor-mediated photo-dissociation of aqueous methanol to produce H2; a cocatalyst-dependent activity trend, Pt > RuOx > Au, was observed. Doping of S at ∼5% of the oxygen sites led to decreased photoactivity, ascribed to the presence of localized S 3p states just above the O 2p valence level. In conclusion, besides band characteristics, certain morphological and microstructural properties play a crucial role in the photoactivity of the metal/oxide nanocomposites.

Multifunctional hybrid structures of ferromagnetic FePt and ferroelectric BaTiO3 nanoparticles: facile synthesis and characterization

Nanohybrid structures of FePt and BaTiO3 with bifunctional properties were synthesized by a two step synthesis procedure including solid state and solvothermal methods. Two different compositions of FePt and BaTiO3 nanoparticle samples were synthesized. The hybrid composite, having the lower FePt concentration, exhibited bifunctionality including superparamagnetism with a blocking temperature near room temperature and ferroelectricity at ambient conditions. Magnetocapacitive measurements of this bifunctional FePt–BiTiO3 sample showed behaviour typical of weak magnetoelectric coupling. This synthetic approach provides a general method for preparing advanced multifunctional and technologically important ceramic–alloy hybrids.

Electron - phonon coupling and related properties of C16-structured intermetallics

The self-consistent potential parameters obtained from LDA-based LMTO electronic structure calculations and phonon dispersion relations obtained from lattice dynamical model calculations have been used to estimate the electron - phonon coupling constant for using the McMillan - Hopfield formula within the rigid-muffin-tin approximation. The theoretically calculated heat capacity parameters compare well with those fitted to the experimental data. The superconducting transition temperature deviates from the experimental value, but is within the expectations of the strong-coupling theory.