Rohini M. de Silva

Push–pull porphyrins as non-linear optical materials: ab initio quantum chemical calculations

Abstract We report accurate ab initio quantum chemical calculations of the first static hyperpolarizability ( β ) of porphyrin systems containing porphyrin moiety as the electron donor and quinone and pyromellitimide as the electron acceptors separated by a spacer which influence the electronic communication between donor and acceptor. Geometries of all porphyrin molecules were optimised at the Hartree–Fock level with STO-3G minimal basis set and with the 3-21G split valence basis set using gaussian 98W. In addition to non-linear properties, polarizabilities ( α ) of these molecules are also reported. The calculated values of β were compared with β of tertraphenyl porphyrin derivatives reported in the literature. We examine the HOMO and LUMO generated via gaussian 98W in order to explain the variation of β in these highly conjugated molecular systems. The study suggested that these porphyrin molecules in general may have potential applications in the development of non-linear optical materials.

A new role for surfactants in the formation of cobalt nanoparticles

During wet-chemical synthesis of nanoparticles it is believed that surfactants interact with the particles after their nucleation thereby controlling their crystal structure, shape and size. Contrary to this, our investigations presented in this paper reveal a new role for surfactants: influencing the reaction pathways, prior to nucleation, leading to the formation of cobalt nanoparticles. The results from the mechanistic investigation of the influence of various surfactants on the formation of cobalt nanoparticles carried out using time dependent FT-IR spectroscopy support this observation. The utilization of different surfactants such as oleic acid (OA), trioctylphosphine oxide (TOPO), octadecylamine (ODA), and trioctylphosphine (TOP) led to differences in reaction pathways and reaction intermediates, prior to the nucleation, leading to the formation of Co nanoparticles with very different properties. The particle size and size distribution were obtained from transmission electron microscopy (TEM). The electronic and geometric properties of the cobalt nanoparticles obtained were determined using synchrotron radiation based X-ray absorption spectroscopy (XAS) and the magnetic properties were measured using SQUID magnetometry.

pH responsive controlled release of anti-cancer hydrophobic drugs from sodium alginate and hydroxyapatite bi-coated iron oxide nanoparticles

Graphical abstract Figure. No caption available. HighlightsSynthesis of a pH sensitive bilayer coated nano iron oxide drug carrier.Nanocomposite was characterized using various techniques.Loading efficiency and capacity of curcumin and 6‐gingerol were examined.In‐vitro drug releasing behavior of curcumin and 6‐gingerol was studied.Mechanism of drug release from the nanocomposite of each situation was studied. ABSTRACT Developing a drug carrier system which could perform targeted and controlled release over a period of time is utmost concern in the pharmaceutical industry. This is more relevant when designing drug carriers for poorly water soluble drug molecules such as curcumin and 6‐gingerol. Development of a drug carrier system which could overcome these limitations and perform controlled and targeted drug delivery is beneficial. This study describes a promising approach for the design of novel pH sensitive sodium alginate, hydroxyapatite bilayer coated iron oxide nanoparticle composite (IONP/HAp‐NaAlg) via the co‐precipitation approach. This system consists of a magnetic core for targeting and a NaAlg/HAp coating on the surface to accommodate the drug molecules. The nanocomposite was characterized using FT‐IR spectroscopy, X‐ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The loading efficiency and loading capacity of curcumin and 6‐gingerol were examined. In vitro drug releasing behavior of curcumin and 6‐gingerol was studied at pH 7.4 and pH 5.3 over a period of seven days at 37 °C. The mechanism of drug release from the nanocomposite of each situation was studied using kinetic models and the results implied that, the release is typically via diffusion and a higher release was observed at pH 5.3. This bilayer coated system can be recognized as a potential drug delivery system for the purpose of curcumin and 6‐gingerol release in targeted and controlled manner to treat diseases such as cancer.

Reactivity of cyclo-(PhX)6 (X = As, P) towards [M3L2(CO)10] (M = Ru, L = CO or NCMe; M = Fe, L = CO)

Abstract Reaction of [Ru3(CO)10(NCMe)2] with cyclo-(PhX)6 (X=As 1a, P 1b) in toluene at ambient temperature gives [Ru3{μ-cyclo-(PhX)6}(CO)10] (X=As 2a, P 2b), in which the intact six-membered rings adopt chair conformations and bridge metal–metal edges via either two arsine (2a) or two phosphorus (2b) atoms in the 1,5 positions of the respective rings. Conversely, treatment of [Ru3(CO)12] with cyclo-(PhX)6 (X=As 1a, P 1b) in toluene at elevated temperature results in fragmentation of the six-membered rings to afford [Ru4(μ3-AsPh)2(CO)13] (3) and [Ru6(μ4-PPh)3(μ3-PPh)2(CO)12] (4), respectively. Fragmentation of the cyclo-hexaarsane ring in 1a also occurs on reaction with [Fe3(CO)12] in toluene at elevated temperature to furnish [Fe3(μ3-AsPh)2(CO)9] (5) as the sole product. However, treatment of 1b with [Fe3(CO)12] gives [Fe3(μ3-PPh2)2(CO)9] (6), the phosphorus analogue of 5, along with [Fe2{μ-η2-catena-(P4Ph4)}(CO)6] (7) and [Fe2{μ4-(P2Ph2)}(CO)6]2 (8). In addition, the mixed phosphinidene–arsenidene complex [Fe3(μ3-PPh)(μ3-AsPh)(CO)9] (9) can be obtained on treatment of 1 with a 1:1 mixture of 1a and 1b. Single crystal X-ray diffraction studies have been performed on 2a, 3, 4·2CH2Cl2, and 8.

Natural polysaccharides leading to super adsorbent hydroxyapatite nanoparticles for the removal of heavy metals and dyes from aqueous solutions

Water pollution has created a major impact on the environment mainly due to contaminated industrial effluents with toxic substances such as heavy metals and textile dyes. Therefore finding effective methodologies for their removal are extremely important. Hydroxyapatite (HAp) is a biocompatible material and has been widely used in many biological and industrial applications. This study involves the synthesis of porous HAp polymer nanocomposites using chitosan (CTS@HAp) and carboxymethyl cellulose (CMC@HAp) to develop a potential adsorbent with high adsorption capacity for heavy metals and textile dyes. A facile in situ synthetic approach was followed to obtain nanoparticles without calcination or freeze drying. X-ray diffraction, Fourier transform infra-red spectroscopy, scanning electron microscopy, thermogravimetric analysis, X-ray fluorescence spectroscopy and BET surface area characterization techniques were applied to elucidate the crystallinity, surface chemistry, morphology and surface area of HAp nanoparticles. This simple approach has produced 25–30 nm and 10 nm spherical nanoparticles of HAp in the presence of chitosan (CTS) and carboxymethyl cellulose (CMC) respectively. These nanocomposites were used for the removal of Pb(II) ions and an industrial dye waste, acid yellow 220. The equilibrium sorption data were fitted according to the Freundlich and Langmuir isotherm models. For the CMC@HAp system the equilibrium for adsorption was achieved in 3 min, while CTS@HAp system required only 30 seconds. The maximum Pb(II) ion adsorption capacity (qm) was found to be 625.0 mg g−1 and 909.1 mg g−1 for CMC@HAp and CTS@HAp respectively. In the case of acid yellow 220, the equilibrium for adsorption was achieved in 90 minutes and 45 minutes for CMC@HAp and CTS@HAp respectively. The maximum acid yellow 220 adsorption capacity (qm) was found to be 200 mg g−1 and 303 mg g−1 for CMC@HAp and CTS@HAp respectively. Therefore this study has highlighted the possibility of developing a HAp nanocomposite material for the efficient and effective removal of both Pb(II) ions and acid yellow 220 from aqueous system.

Honey Mediated Green Synthesis of Nanoparticles: New Era of Safe Nanotechnology

With the advent of nanotechnology, many related industries rapidly developed over the recent past. Generally, top-down and bottom-up approaches are the two major processes used to synthesize nanoparticles; most of these require high temperatures, vacuum conditions, and harsh/toxic chemicals. As a consequence, adverse effects impacted organisms including humans. Some synthesis methods are expensive and time-consuming. As a corollary, the concept of “green nanotechnology” emerged with the green synthesis of nanoparticles commencing a new epoch in nanotechnology. This involves the synthesis of nanomaterial from microorganisms, macroorganisms, and other biological materials. Honey is documented as the world’s oldest food source with exceptional medical, chemical, physical, and pharmaceutical values. Honey mediated green synthesis is a relatively novel concept used during the past few years to synthesize gold, silver, carbon, platinum, and palladium nanoparticles. Honey acts as both a stabilizing and a reducing agent and importantly functions as a precursor in nanoparticle synthesis. This method usually requires room temperature and does not produce toxic byproducts. In conclusion, honey mediated green synthesis of nanoparticles provides a simple, cost effective, biocompatible, reproducible, rapid, and safe method. The special activity of honey functionalized nanoparticles may provide valuable end products with numerous applications in diverse fields.

Metal and polymer-mediated synthesis of porous crystalline hydroxyapatite nanocomposites for environmental remediation

This study was focused on the preparation of metal and polymer-mediated porous crystalline hydroxyapatite (HAp) nanocomposites for environmental applications. Four different nano HAp systems were synthesized, namely, microwave irradiated HAp (M1), Zn doped HAp (M2), Mg-doped HAp (M3) and sodium alginate incorporated HAp (M4), and characterized using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, nuclear magnetic resonance (NMR), X-ray fluorescence, thermogravimetric analysis and Brunauer–Emmett–Teller (BET) analyses. Systems M1–M4 showed morphologies similar to coral shapes, polymer-like interconnected structures, sponges and feathery mycelium assemblies. Using XRD, selected area electron diffraction patterns and 1H and 31P CP/MAS solid-state NMR studies, crystallinity variation was observed from highest to lowest in the order of M4 > M1 > M3 > M2. Surface area estimates using BET isotherm reflected the highest surface area for M3, and M1 > M2 > M4. Four systems of M1–M4 were used as potential adsorbent materials for the removal of metal containing azo dye from aqueous system. Adsorption data were correlated to Freundlich and Langmuir isotherm models. According to the results, the highest capacity of 212.8 mg g−1 was exhibited by M4 having mycelium like morphology with alginate groups. This study highlights the possibility of developing HAp nanocomposites for the effective removal of dye contaminants in the environment.

Biocompatible nano hydroxyapatite – curcumin bi-coated antibacterial activated carbon for water purification

Activated carbon has been used for water purification since ancient times due to its well-known sorption properties. However it is not capable of disinfecting water borne pathogens such as bacteria. The main objective of this study was to incorporate antibacterial properties while maintaining the existing properties of Granular Activated Carbon (GAC). This was achieved by a biocompatible double coating on to GAC which consists of hydroxyapatite (HAP) nanoparticles and on top of those curcumin molecules. Coating of GAC with HAP was carried out using in situ precipitation of HAP under basic conditions. A layer of curcumin molecules was then attached on top of the HAP coating in order to obtain HAP-curcumin bi-coated GAC (HAP/C/GAC). Synthesized HAP/GAC and HAP/C/GAC were characterized using FT-IR spectroscopy, scanning electron microscopy (SEM), powder X-ray diffractometry (PXRD) and thermogravimetry (TGA). Characterization revealed that needle shaped HAP nanoparticles (50–100 nm in width and approximately 200–500 nm in length) can be anchored and immobilized successfully on GAC which in turn enhances the adhesion of curcumin on it. Antibacterial properties of pure GAC, HAP/GAC and HAP/C/GAC were then investigated using both Gram negative (Escherichia coli) and Gram positive (Staphylococcus aureus) bacteria. The results show that the antibacterial properties of HAP/C/GAC are remarkably higher than that of HAP/GAC and the antibacterial activity of pure GAC is negligible.

Fragmentation of a As4Ph4-chain on a tetranuclear cobalt cluster induced by thermolysis or by reaction with Fe2(CO)9

Abstract Thermolysis of the tetranuclear cobalt cluster [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)8] (1) at 60°C in benzene for two days gives [Co4(μ3-AsPh)2(μ3-η2:η1-As2Ph2)(μ-CO)(CO)9] (2), in which the tetraarsine chain in 1 has been cleaved to give the bridging As2Ph2 unit in 2. Similar fragmentation of the As4Ph4 chain occurs on treatment of 1 with [Fe2(CO)9] in benzene at room temperature for 3 days affording [Co4(μ3-AsPh)2{(μ3-η2:η1-As2Ph2)Fe(CO)4}(μ-CO)(CO)9] (3), in which one arsine atom of the As2Ph2 bridging ligand is additionally bound to an Fe(CO)4 unit. Conversely, reaction of 1 with excess P(OMe)3 at room temperature in benzene for 3 days gives the trisubstituted trimethylphosphite derivative [Co4(μ3-AsPh)(μ4-η2:η2:η1-As4Ph4)(μ-CO)2(CO)5{P(OMe)3}3] (4), in which the As4Ph4 unit remains intact. Single crystal X-ray diffraction studies have been performed on 2, 3 and 4 and possible reaction pathways for the formation of the new complexes are proposed and discussed.

Heterogeneous in situ polymerization of polyaniline (PANI) nanofibers on cotton textiles: Improved electrical conductivity, electrical switching, and tuning properties

Electrically conductive cotton fabric was fabricated by in situ one pot oxidative polymerization of aniline. Using a simple heterogeneous polymerization method, polyaniline (PANI) nano fibers with an average fiber diameter of 40-75 nm were grafted in situ onto cotton fabric. The electrical conductivity of the PANI nanofiber grafted fabric was improved 10 fold compared to fabric grafted with PANI nanoclusters having an average cluster size of 145-315 nm. The surface morphology of the cotton fibers was characterized using SEM and AFM. Electrical conductivity of PANI nanofibers on the cotton textile was further improved from 76 kΏ/cm to 1 kΏ/cm by increasing the HCl concentration from 1 M to 3 M in the polymerization medium. PANI grafted cotton fabrics were analyzed using FTIR, and the data showed the presence of polyaniline functional groups on the treated fabric. Further evidence was present for the chemical interaction of PANI with cellulose. Dopant level and morphology dependent electron transition behavior of PANI nanostructures grafted on cotton fabric was further characterized using UV-vis spectroscopy. The electrical conductivity of the PANI nano fiber grafted cotton fabric can be tuned by immersing the fabric in pH 2 and pH 6 solutions for multiple cycles.