Synthesis and characterization of a pH-sensitive conjugate of isoniazid with Fe3O4@SiO2 magnetic nanoparticles

The Letter describes the preparation and characterization of a conjugate of isoniazid (INH) with magnetic nanoparticles Fe₃O₄@SiO₂ 115 ± 60 nm in size. The INH molecules were attached to the surface of nanoparticles by a covalent pH-sensitive amidine bond. The conjugate was characterized by X-ray diffraction, SEM, dynamic light scattering, IR spectroscopy and microanalysis. The conjugate released isoniazid under in vitro conditions (pH = 4; 37 °C; t_1/2 ≈ 115 s). In addition, the cytotoxicity of the Fe₃O₄@SiO₂–INH conjugate was evaluated in SK-BR-3 cells using the xCELLigence system.     

Exposure of rainbow trout (Oncorhynchus mykiss) to magnetite (Fe3O4) nanoparticles in simplified food chain: Study on ultrastructural characterization

The widespread exposure of metallic nanoparticles to the aquatic ecosystem and its adverse impact on human life is the colossal concern worldwide. In view of this, this context was investigated to analyze microscopically the bioaccumulation and localization of magnetite (Fe₃O₄) nanoparticles in the cellular organelles of rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) in aquatic conditions. Initially, Fe₃O₄ nanoparticles were absorbed on to Elodea (Elodea canadensis) and fed to molluscs (Melanopsis praemorsa). Fish were fed with the same molluscs, and then the intestines and liver were examined using light and transmission electron microscopy. Results showed that nanoparticles were present in the cytoplasm and other organelles of cells (mitochondrion and lysosome) by absorbing through microvilli of the epithelial cells of the tunica mucosa in the intestine. Further, nanoparticles passed through the vessels of the lamina propria of the tunica mucosa and reached to the sinusoids of the liver via blood circulation. It was then accumulated from the endothelium of the sinusoid to the cytoplasm of liver hepatocytes and to mitochondria and lysosome. The accumulation of nanoparticles in the epithelial cells, cytoplasm, mitochondria, and lysosome revealed the degree of transparency of the pattern with slight hesitation. In summary, this investigation contributed towards the understanding of the physiological effects of Fe₃O₄ nanoparticles on O. mykiss, which ascertains essentiality for sustainable development of nanobiotechnology in the aquatic ecosystem.     

High activity and selectivity immobilized lipase on Fe3O4 nanoparticles for banana flavour synthesis

Lipase (E.C.3.1.1.3) from Thermomyces lanuginosus (TL) was directly bonded, through multiple physical interactions, on citric acid functionalized monodispersed Fe₃O₄ nanoparticles (NPs) in presence of a small amount of hydrophobic functionalities. A very promising scalable synthetic approach ensuring high control and reproducibility of the results, and an easy and green immobilization procedure was chosen for NPs synthesis and lipase anchoring. The size and structure of magnetic nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The samples at different degree of functionalization were analysed through thermogravimetric measurements. Lipase immobilization was further confirmed by enzymatic assay and Fourier transform infrared (FT-IR) spectra. Immobilized lipase showed a very high activity recovery up to 144% at pH = 7 and 323% at pH = 7.5 (activity of the immobilized enzyme compared to that of its free form). The enzyme, anchored to the Fe₃O₄ nanoparticles, to be easy recovered and reused, resulted more stable than the native counterpart and useful to produce banana flavour. The immobilized lipase results less sensitive to the temperature and pH, with the optimum temperature higher of 5 °C and optimum pH up shifted to 7.5 (free lipase optimum pH = 7.0). After 120 days, free and immobilized lipases retained 64% and 51% of their initial activity, respectively. Ester yield at 40 °C for immobilized lipase reached 88% and 100% selectivity.     

Uptake of dissolved inorganic and organic nitrogen by the benthic toxic dinoflagellate Ostreopsis cf. ovata

Environmental factors that shape dynamics of benthic toxic blooms are largely unknown. In particular, for the toxic dinoflagellate Ostreopsis cf. ovata, the importance of the availability of nutrients and the contribution of the inorganic and organic pools to growth need to be quantified in marine coastal environments. The present study aimed at characterizing N-uptake of dissolved inorganic and organic sources by O. cf. ovata cells, using the ¹⁵N-labelling technique. Experiments were conducted taking into account potential interactions between nutrient uptake systems as well as variations with the diel cycle. Uptake abilities of O. cf. ovata were parameterized for ammonium (NH₄⁺), nitrate (NO₃⁻) and N-urea, from the estimation of kinetic and inhibition parameters. In the range of 0 to 10 μmol N L⁻¹, kinetic curves showed a clear preference pattern following the ranking NH₄⁺ > NO₃⁻ > N-urea, where the preferential uptake of NH₄⁺ relative to NO₃⁻ was accentuated by an inhibitory effect of NH₄⁺ concentration on NO₃⁻ uptake capabilities. Conversely, under high nutrient concentrations, the preference for NH₄⁺ relative to NO₃⁻ was largely reduced, probably because of the existence of a low-affinity high capacity inducible NO₃⁻ uptake system. Ability to take up nutrients in darkness could not be defined as a competitive advantage for O. cf. ovata. Species competitiveness can also be defined from nutrient uptake kinetic parameters. A strong affinity for NH₄⁺ was observed for O. cf. ovata cells that may partly explain the success of this toxic species during the summer season in the Bay of Villefranche-sur-mer (France).     

Improvement of biodegradation in compact co-current biotrickling filter by high recycle liquid flow rate: Performance and biodegradation kinetics of ammonia removal

As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH₃ and absorption of O₂ with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50 s, almost complete removal of NH₃ was obtained with recycle liquid flow rates of 103 and 205 L m⁻³ day⁻¹ for 20 days while the inlet NH₃ concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m⁻³ day⁻¹ the removal efficiency remained above 95% for 57 days while the inlet NH₃ concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH₃ removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate.     

The effects of NH4+ and NO3− on growth,resource allocation and nitrogen uptake kinetics of Phragmites australis and Glyceria maxima

The effects of NH₄⁺ or NO₃⁻ on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 μM the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g⁻¹ d⁻¹), whereas the growth rate of Glyceria was 16% higher in NH₄⁺-N cultures than in NO₃⁻-N cultures (mean = 66.7 and 57.4 mg g⁻¹ d⁻¹ of NH₄⁺ and NO₃⁻ treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH₄⁺ cultures than in NO₃⁻ cultures, 123.5 and 129.7%, respectively.Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH₄⁺ treated plants by 16%. The tissue NH₄⁺ concentration (mean = 1.6 μmol g fresh wt⁻¹) was not affected by N treatment, whereas NO₃⁻ contents were higher in NO₃⁻ (mean = 1.5 μmol g fresh wt⁻¹) than in NH₄⁺ (mean = 0.4 μmol g fresh wt⁻¹) treated plants. In Phragmites, NH₄⁺ (mean = 1.6 μmol g fresh wt⁻¹) and NO₃⁻ (mean = 0.2 μmol g fresh wt⁻¹) contents were not affected by the N regime. Species did not differ in NH₄⁺ (mean = 56.5 μmol g⁻¹ root dry wt h⁻¹) and NO₃⁻ (mean = 34.5 μmol g⁻¹ root dry wt h⁻¹) maximum uptake rates (V_max), and V_max for NH₄⁺ uptake was not affected by N treatment. The uptake rate of NO₃⁻ was low in NH₄⁺ treated plants, and an induction phase for NO₃⁻ was observed in NH₄⁺ treated Phragmites but not in Glyceria. Phragmites had low K_m (mean = 4.5 μM) and high affinity (10.3 l g⁻¹ root dry wt h⁻¹) for both ions compared to Glyceria (K_m = 6.3 μM, affinity = 8.0 l g⁻¹ root dry wt h⁻¹). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH₄⁺-N source may participates in the observed success of Glyceria at NH₄⁺ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites.     

THE EFFECT OF OXYGEN DEPRIVATION ON INORGANIC NITROGEN UPTAKE IN AN ANTARCTIC MACROLICHEN

Snow meltwater containing 36 ng ml⁻¹NO₃⁻-N (raised here to between 95–101 ng ml⁻¹NO₃⁻-N) and 112 ng ml⁻¹NH₄⁺-N was sprayed onto illuminatedUsnea sphacelataat 2°C in a 2-1 capacity transparent perspex chamber force-ventilated with either air or O₂- (and CO₂-) free N₂. The NO₃-concentration in meltwater recirculated through a layer ofU. sphacelatafell toc. 8 ng ml⁻¹after 1·25 h. Although the pattern of decline was broadly comparable in both air and N₂, the initial rate of decline was lower in N₂. When undepleted meltwater was continuously sprayed onto the lichen and the effluent collected for analysis, the lichen was found to retain 55% of the wet deposited NO₃⁻in air but only 27% under N₂. Up to 90% of NH₄⁺supplied in a continuous spray of meltwater was retained by the lichen but this was affected little by O₂and CO₂deprivation.     

Acetato complexes of molybdenum(V): A novel tetranuclear core based on the metal–metal bonded {Mo2O4}2+ units

A series of acetato complexes of molybdenum(V), based on the singly metal–metal bonded {Mo₂O₄}²⁺ structural fragment, has been prepared. A dinuclear (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) (PyH⁺ = pyridinium cation, C₅H₅NH⁺) was obtained upon the reaction of (PyH)₅[MoOCl₄(H₂O)]₃Cl₂ with the equimolar solution of pyridine and acetic acid in acetonitrile at ambient conditions. The acetato ligand in 1 is coordinated to a pair of molybdenum atoms in a syn–syn bidentate bridging manner. (PyH)_n[MoOBr₄]_n afforded in an analogous synthetic procedure a tetranuclear cluster, [Mo₄O₈(OOCCH₃)₃(OH)Py₄] · 1/2CH ₃CN · 1/2H₂O (3), with a novel core which may be envisioned as the acetate- and hydroxide-assisted assembly of {Mo₂O₄}²⁺ building blocks. Its structure is presented in terms of known tetranuclear clusters which are also composed of two {Mo₂O₄}²⁺ units. The acetato ligands in 3 adopted apart from bidentate bridging binding modes also a monodentate one. Partial substitution of chlorido ligands in (PyH)₃[Mo₂O₄Cl₄(OOCCH₃)] · CH₃CN (1) with pyridine resulted in a neutral [Mo₂O₄Cl(OOCCH₃)Py₃] · PrⁱOH · Py (2) which retained the original acetate coordination. The title compounds were fully characterized by X-ray diffraction studies and infrared vibrational spectroscopy.     

Immobilization of lysine oxidase on a gold–platinum nanoparticles modified Au electrode for detection of lysine

A commercial lysine oxidase (LyOx) from Trichoderma viride was immobilized covalently onto gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs) electrodeposited onto Au electrode using 3-aminopropyltriethoxy silane (3-APTES) and glutaraldehyde cross linking chemistry. A lysine biosensor was fabricated using LyOx/3-APTES/AuNPs-PtNPs/Au electrode as a working electrode, Ag/AgCl (3 M KCl) as standard electrode and Pt wire as auxiliary electrode connected through a potentiostat. The enzyme electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The cumulative effect of AuNPs and PtNPs showed excellent electrocatalytic activity at low applied potential for detection of H₂O₂, a product of LyOx reaction. The sensor showed its optimum response within 4 s, when polarized at 0.2 V vs. Ag/AgCl in 0.1 M phosphate buffer, pH 7.5 at 30 °C. The linear range and detection limit of the sensor were 1.0–600 μM and 1.0 μM (S/N = 3), respectively. Biosensor measured lysine level in sera, milk and amino acid tablet, which correlated well with those by standard HPLC method. The enzyme electrode lost 50% of its initial activity after 200 uses over a period of 4 months.     

First proof of bismuth oxide nanoparticles as efficient radiosensitisers on highly radioresistant cancer cells

This study provides the first proof of the novel application of bismuth oxide as a radiosensitiser. It was shown that on the highly radioresistant 9L gliosarcoma cell line, bismuth oxide nanoparticles sensitise to both kilovoltage (kVp) or megavoltage (MV) X-rays radiation. 9L cells were exposed to a concentration of 50 μg.mL⁻¹ of nanoparticle before irradiation at 125 kVp and 10 MV. Sensitisation enhancement ratios of 1.48 and 1.25 for 125 kVp and 10 MV were obtained in vitro, respectively. The radiation enhancement of the nanoparticles is postulated to be a combination of the high Z nature of the bismuth (Z = 83), and the surface chemistry. Monte Carlo simulations were performed to elucidate the physical interactions between the incident radiation and the nanoparticle. The results of this work show that Bi₂O₃ nanoparticles increase the radiosensitivity of 9L gliosarcoma tumour cells for both kVp and MV energies. Monte Carlo simulations demonstrate the advantage of a platelet morphology.     

Two ways to achieve an anammox influent from real reject water treatment at lab-scale: Partial SBR nitrification and SHARON process

A comparative study to produce the correct influent for Anammox process from anaerobic sludge reject water (700–800 mg NH₄⁺-N L⁻¹) was considered here. The influent for the Anammox process must be composed of NH₄⁺-N and NO₂⁻-N in a ratio 1:1 and therefore only a partial nitrification of ammonium to nitrite is required. The modifications of parameters (temperature, ammonium concentration, pH and solid retention time) allows to achieve this partial nitrification with a final effluent only composed by NH₄⁺-N and NO₂⁻-N at the right stoichiometric ratio. The equal ratio of HCO₃⁻/NH₄⁺ in reject water results in a natural pH decrease when approximately 50% of NH₄⁺ is oxidised. A Sequencing batch reactor (SBR) and a chemostat type of reactor (single-reactor high activity ammonia removal over nitrite (SHARON) process) were studied to obtain the required Anammox influent. At steady state conditions, both systems had a specific conversion rate around 40 mg NH₄⁺-N g⁻¹ volatile suspended solids (VSS) h⁻¹, but in terms of absolute nitrogen removal the SBR conversion was 1.1 kg N day⁻¹ m⁻³, whereas in the SHARON chemostat was 0.35 kg N day⁻¹ m⁻³ due to the different hydraulic retention time (HRT) used. Both systems are compared from operational (including starvation experiments) and kinetic point of view and their advantages/disadvantages are discussed.     

Efficient production of S-(+)-2-chlorophenylglycine by immobilized penicillin G acylase in a recirculating packed bed reactor

(S)-(+)-2-Chlorophenylglycine 1 is an important intermediate in the synthesis of Clopidogrel. A recirculating packed bed reactor (RPBR) was constructed for efficient production of (S)-1 by kinetic resolution of racemic N-phenylacetyl-2- chlorophenylglycine 2 using immobilized penicillin G acylase (PGA). The immobilized PGA exhibited maximum activity at 50 °C and pH 8.0 with (R,S)-2 as substrate. The kinetic constants (K_m and v_max) of immobilized PGA were calculated to be 20.61 mM and 83.2 mM/min/g, respectively. The substrate displayed inhibitory effect on immobilized PGA with inhibition constant of 221.23 mM. The immobilized PGA showed a strict enantiospecificity for substrate at different temperature, pH and substrate concentration examined. The performance and productivity of RPBR were evaluated by several critical parameters, including immobilized PGA load, substrate feeding rate, height to diameter ratio and so on. The kinetic resolution process shows higher initial reaction rate and conversion by recycling 100 mL of substrate solution (80 mM) through RPBRs packed with 6.0 g immobilized PGA with a feeding rate of 1.5 mL/min while the H/D ratio was 4.0. The immobilized PGA-catalyzed kinetic resolution of (R,S)-2 was successfully operated in the RPBR for 60 batches, with an average productivity of 1.2 g/L/h for (S)-1 in high optical purity (>97% enantiomeric excess) in semi-continuous operation. The residual (R)-2 can be easily racemized and then used as substrate.     

Stabilization of d-amino acid oxidase from Rhodosporidium toruloides by encapsulation in polyallylamine-mediated biomimetic silica

d-Amino acid oxidase from Rhodosporidium toruloides (RtDAO) and Fe₃O₄ magnetic nanoparticles were encapsulated simultaneously within biomimetic silica, as mediated by polyallylamine. The capacity for this enzyme reached 193 mg/g of biomimetic silica when 15 mg/ml RtDAO was used during encapsulation; the average encapsulation efficiency was approximately 74%. The T_m value (the temperature at which 50% of the initial activity was retained after 1 h of incubation) was increased from 44.3 °C of the free RtDAO to 57.7 °C, clearly indicating the thermal stability was improved by encapsulation. In the presence of 50 mM hydrogen peroxide, encapsulated RtDAO had a half-life of 148 min, an approximately 2-fold increase in resistance to hydrogen peroxide as compared to 78-min half-life of the free form. The encapsulation process is simple and can be completed within minutes; besides, the resultant enzymes can be recovered easily under magnetic field. Such preparation of encapsulated d-amino acid oxidase could be exploited for many potential applications.     

On the crystal structures and magnetism of some hybrid organic–inorganic metal organophosphonates

We review our recent work in the field of molecule-based magnets showing the structural and magnetic properties of a special class of hybrid organic–inorganic compounds, i.e. metal(II) organophosphonates. The synthesis, the crystal structures and, in particular, the magnetic studies of selected examples of compounds of formulas M(II)[(R–PO₃)(H₂O)], and M₂[(O₃P–R′–PO₃)(2H₂O)] M = Cr, Fe, Co; R = C_nH_2n+1, n = 1, 2, 3… and C₆H₅, R′ = (CH₂)₂ prepared in our laboratory are presented and discussed. Metal alkylphosphonates, except those of Co(II), are weak ferromagnets at low temperatures. The observed magnetic ordering temperature T_N varies from 4.2 to 25 K, depending on the transition metal ions and on crystal and molecular structure. Moreover, in the case of a bifunctional molecule like aminoethylphosphonic acid, NH₂(CH₂)₂PO₃H₂, or the carboxyethylphosphonic acid, HO₂C(CH₂)₂PO₃H₂, is used as a ligand, then a novel Cr(II) compound of formula Cr[NH₃(CH₂)₂PO₃(Cl)(H₂O)] and a microporous Fe(III) salt (NH₄)[Fe₂(OH){O₃P(CH₂)₂CO₂}₂] are isolated. The latter are both polar and, more interesting, Cr(II) ammoniumethylphosphonate chloride results to be a weak ferromagnet below T_N = 5.0 K.     

Effect of changing the nanoscale environment on activity and stability of nitrate reductase

Nitrate reductase (NR) is employed for fabrication of nitrate sensing devices in which the enzyme in immobilized form is used to catalyze the conversion of nitrate to nitrite in the presence of a suitable cofactor. So far, instability of immobilized NR due to the use of inappropriate immobilization matrices has limited the practical applications of these devices. Present study is an attempt to improve the kinetic properties and stability of NR using nanoscale iron oxide (nFe₃O₄) and zinc oxide (nZnO) particles. The desired nanoparticles were synthesized, surface functionalized, characterized and affixed onto the epoxy resin to yield two nanocomposite supports (epoxy/nFe₃O₄ and epoxy/nZnO) for immobilizing NR. Epoxy/nFe₃O₄ and epoxy/nZnO support could load as much as 35.8 ± 0.01 and 33.20 ± 0.01 μg/cm² of NR with retention of about 93.72 ± 0.50 and 84.81 ± 0.80% of its initial activity respectively. Changes in surface morphology and chemical bonding structure of both the nanocomposite supports after addition of NR were confirmed by scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Optimum working conditions of pH, temperature and substrate concentration were ascertained for free as well as immobilized NR preparations. Further, storage stability at 4 °C and thermal stability between 25–50 °C were determined for all the NR preparations. Analytical applications of immobilized NR for determination of soil and water nitrates along with reusability data has been included to make sure the usefulness of the procedure.     

Carbon and nitrogen metabolism of an eutrophication tolerative macrophyte,Potamogeton crispus,under NH4+ stress and low light availability

Submersed macrophytes in eutrophic lakes often experience high NH₄⁺ concentration and low light availability in the water column. This study found that an NH₄⁺–N concentration of 1 mg L^?1 in the water column apparently caused physiological stress on the macrophyte Potamogeton crispus L. The plants accumulated free amino acids (FAA) and lost soluble carbohydrates (SC) under NH₄⁺ stress. These stressful effects of NH₄⁺ were exacerbated under low light availability. Shading significantly increased NH₄⁺ and FAA contents and dramatically decreased SC and starch contents in the plant shoots. At an NH₄⁺–N concentration of 1 mg L^?1 in the water column, neither growth inhibition nor NH₄⁺ accumulation was observed in the plant tissues of P. crispus under normal light availability. The results showed that 1 mg L^?1 NH₄⁺–N in the water column was not toxic to P. crispus in a short term. To avoid NH₄⁺ toxicity, active NH₄⁺ transportation out of the cell may cost energy and thus result in a decline of carbohydrate. When NH₄⁺ inescapably accumulates in the plant cell, i.e. under NH₄⁺ stress and shading, NH₄⁺ is scavenged by FAA synthesis.     

Efficient nitrogen removal in a pilot system based on upflow multi-layer bioreactor for treatment of strong nitrogenous swine wastewater

In order to prevent the toxic effect caused by high strength ammonium in a swine wastewater treatment system, a patented upflow multi-layer bioreactor (UMBR) as a pre-anoxic tank was applied to a pilot-scale plant with a treatment capacity of 5 m³/d. This plant was operated for 4 months at a high IR ratio in the range of 10–17, in order to alleviate the toxic effects caused by high strength ammonium. A computational fluid dynamic (CFD) analysis was also conducted to design and configure the rotating distributors in the UMBR. At an IR ratio of about 17, the influent NH₄⁺-N (1169 mg N/L) was diluted to less than 80 mg N/L at the head of the UMBR, and then was completely nitrified (about 98.3%) in the aeration tank, without any inhibition caused by high strength ammonium. The nitrate at a concentration of about 58.2 mg N/L recycled from the aeration tank was completely denitrified in UMBR #1, which was operated at an actual hydraulic retention time (HRT) of 3.5 h.     

Effects of nutrients on arsenic accumulation by arsenic hyperaccumulator Pteris vittata L.

This research investigated the effects of various nutrients on arsenic (As) removal by arsenic hyperaccumulator Pteris vittata L. in a Hoagland nutrient solution (HNS). The treatments included different concentrations of Ca and K in 20% strength of HNS, different strengths of HNS (10, 20 and 30%), different strengths of HNS (10 and 20%) with and without CaCO₃, and different concentrations of Ca, K, NO₃, NH₄, and P in 20% strength of HNS. The plants were grown in nutrient solution containing 1 mg As L^?1 for 4 weeks except the Ca/K experiment where the plants were grown in nutrient solution containing 10 or 50 mg As L^?1 for 1 week. Adding up to 4 mM Ca or 3 mM K to 20% strength HNS significantly (P < 0.05) increased plant arsenic accumulation when the solution contained 10 mg As L^?1. Plant arsenic removal was reduced with increasing Ca and K concentrations at 50 mg As L^?1. Lower strength of HNS (10%) resulted in the greatest plant arsenic removal (79%) due to lower competition of P with As for plant uptake. Addition of CaCO₃ to 20% strength of HNS significantly increased arsenic removal by P. vittata. Among the nutrients tested, NO₃ and CaCO₃ were beneficial to plant arsenic removal while NH₄, P and Cl had adverse effects. This experiment demonstrated that it is possible to optimize plant arsenic removal by adjusting nutrients in the growth medium.     

Effect of hydraulic retention time on the treatment of secondary effluent in a subsurface flow constructed wetland

This study evaluates the potential of subsurface flow (SSF) constructed wetlands (CWs) for tertiary treatment of wastewater at four shorter HRTs (1–4 days). The CWs were planted with Typha angustata, which was observed in our earlier study to be more efficient than Phragmites karka and Scirpus littoralis. The CWs comprised four rectangular treatment cells (2.14 m × 0.76 m × 0.61 m) filled with layers of gravel of two different sizes (approximately 2.5 cm and 1.5 cm diameter) to a depth of 0.61 m. The inflow rates of the secondary effluent in the four cells were accordingly fixed at 300 L d^?1, 150 L d^?1, 100 L d^?1 and 75 L d^?1, respectively, for 1, 2, 3 and 4 days HRT. The hydraulic loads ranged between 59.05 mm d^?1 and 236.22 mm d^?1.The wastewater inflow into the CW system as well as the treated effluent were analyzed, using standard methods, at regular intervals for various forms of nitrogen (NH₄-N, NO₃-N and TKN), orthophosphate-P and organic matter (BOD and COD) concentrations over a period of five weeks after the development of a dense stand.The higher HRT of 4 days not only helped maximum removal of all the pollutants but also maintained the stability of the treatment efficiency throughout the monitoring period. For the nutrients (NH₄-N, NO₃-N and TKN), HRT played a more significant role in their removal than in case of organic matter (BOD₃ and COD). More than 90% of NO₃-N and TKN and 100% of NH₄-N were removed from the wastewater at 4 days HRT.At lower HRTs, the mass loading rate was higher with greater fluctuation. However mass reduction efficiency of the T. angustata CW for all forms of nitrogen was >80% with the HRTs of 2, 3 and 4 days.     

Tuning magnetic properties using targeted structural distortion: New additions to a family of Mn6 single-molecule magnets

We report the synthesis and magnetic properties of three hexametallic Mn clusters: [Mn₆O₂(Et-sao)₆(O₂C-Naphth)₂(EtOH)₄(H₂O)₂] (1) (HO₂C-Naphth = 1-naphthoic acid, Et-saoH₂ = 2-hydroxyphenylpropanone oxime), [Mn₆O₂(Et-sao)₆(O₂C-Anthra)₂(EtOH)₄(H₂O)₂] · 0.66EtOH · 0.33H₂O (HO₂C-Anthra = anthracene-9-carboxylic acid) (2 · 0.66EtOH · 0.33H₂O) and [Mn₆O₂(Et-sao)₆(O₂CPhCCH)₂(EtOH)₄(H₂O)₂] · 1.7EtOH · 0.3H₂O (HO₂CPhC  CH = 4-ethynylbenzoic acid) (3 · 1.7EtOH · 0.3H₂O). Clusters 1–3 exhibit ferromagnetic exchange between all six Mn^III centres resulting in S = 12 ground spin states. Ac magnetic susceptibility and single crystal micro-SQUID measurements on 1–3 confirm SMM behaviour with barriers to magnetisation reversal of 60.12 (1), 60.10 (2) and 66.79 (3) K.