Ischemic stroke is often accompanied by neuronal hyperexcitability (i.e., seizures), which aggravates brain damage. Therefore, suppressing stroke-induced hyperexcitability and associated excitoxicity ...is a major focus of treatment for ischemic insults. Both ATP-dependent and Ca2+-activated K+ channels have been implicated in protective mechanisms to suppress ischemia-induced hyperexcitability. Here we provide evidence that the localization and function of Kv2.1, the major somatodendritic delayed rectifier voltage-dependent K+ channel in central neurons, is regulated by hypoxia/ischemia-induced changes in metabolic state and intracellular Ca2+ levels. Hypoxia/ischemia in rat brain induced a dramatic dephosphorylation of Kv2.1 and the translocation of surface Kv2.1 from clusters to a uniform localization. In cultured rat hippocampal neurons, chemical ischemia (CI) elicited a similar dephosphorylation and translocation of Kv2.1. These events were reversible and were mediated by Ca2+ release from intracellular stores and calcineurin-mediated Kv2.1 dephosphorylation. CI also induced a hyperpolarizing shift in the voltage-dependent activation of neuronal delayed rectifier currents (IK), leading to enhanced IK and suppressed neuronal excitability. The IK blocker tetraethylammonium reversed the ischemia-induced suppression of excitability and aggravated ischemic neuronal damage. Our results show that Kv2.1 can act as a novel Ca2+- and metabolic state-sensitive K+ channel and suggest that dynamic modulation of IK/Kv2.1 in response to hypoxia/ischemia suppresses neuronal excitability and could confer neuroprotection in response to brief ischemic insults.
Puri City is situated on the east coast of India and receives water supply only from the groundwater sources demarcated as water fields. The objective of this paper is to assess and evaluate the ...groundwater quality due to impact of anthropogenic activities in the city. Groundwater samples were collected from the water fields, hand pumps, open wells, and open water bodies during post-monsoon 2006 and summer 2007. Groundwater quality was evaluated with drinking water standards as prescribed by Bureau of Indian Standards and Environmental Protection Agency to assess the suitability. The study indicated seasonal variation of water-quality parameters within the water fields and city area. Groundwater in the water fields was found to be suitable for drinking after disinfection. While in city area, groundwater quality was impacted by onsite sanitary conditions. The study revealed that groundwater quality was deteriorated due to the discharge of effluent from septic tanks, soak pits, pit latrines, discharges of domestic wastewater in leaky drains, and leachate from solid waste dumpsite. Based on observed groundwater quality, various mitigation measures were suggested to protect the water fields and further groundwater contamination in the city.
Straight chain amide N,N-dihexyloctanamide (DHOA) has been found to be a promising alternative extractant to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated uranium- and thorium-based ...fuels. Unlike TBP, DHOA displays preferential extraction of Pu(IV) over U(VI) at higher acidities (≥3 M HNO3) and poor extraction at lower acidities. Density functional theory (DFT) based calculations have been carried out on the structures and relative binding energies of U(VI) and Pu(IV) with the extractant molecules. These calculations suggest that the differential hardness of the two extractants is responsible for the preferential binding/complexation of TBP to uranyl, whereas the softer DHOA and the bulky nature of the extractant lead to stronger binding/complexation of DHOA to Pu(IV). In conjunction with quantum chemical calculations, small angle neutron scattering (SANS) measurements have also been performed for understanding the stoichiometry of the complex formed that leads to relatively lower extraction of Th(IV) (a model for Pu(IV)) as compared to U(VI) using DHOA and TBP as the extractants. The combined experimental and theoretical studies helped us to understand the superior complexation/extraction behavior of Pu(IV) over U(VI) with DHOA.
Infection with human immunodeficiency virus-1 (HIV-1) within the brain has long been known to be associated with neurodegeneration and neurocognitive disorder (referred as HAND), a condition ...characterized in its early stages by declining cognitive function and behavioral disturbances. Mechanistically, the HIV-1 coat glycoprotein 120 (gp120) has been suggested to be a critical factor inducing apoptotic cell death in neurons via the activation of p38 mitogen-activated protein kinase (MAPK), upon chronic exposure to the virus. Here we show that acute exposure of neurons to HIV-1 gp120 elicits a homeostatic response, which provides protection against non-apoptotic cell death, involving the major somatodendritic voltage-gated K⁺ (Kv) channel Kv2.1 as the key mediator. The Kv2.1 channel has recently been shown to provide homeostatic control of neuronal excitability under conditions of seizures, ischemia and neuromodulation/neuroinflammation. Following acute exposure to gp120, cultured rat hippocampal neurons show rapid dephosphorylation of the Kv2.1 protein, which ultimately leads to changes in specific sub-cellular localization and voltage-dependent channel activation properties of Kv2.1. Such modifications in Kv2.1 are dependent on the activation of the chemokine co-receptors CCR5 and CXCR4, and subsequent activation of the protein phosphatase calcineurin. This leads to the overall suppression of neuronal excitability and provides neurons with a homeostatic protective mechanism. Specific blockade of calcineurin and Kv2.1 channel activity led to significant enhancement of non-apoptotic neuronal death upon acute gp120 treatment. These observations shed new light on the intrinsic homeostatic mechanisms of neuronal resilience during the acute stages of neuro-HIV infections.
Diglycolamide (DGA)-functionalized poly(propyleneimine) diaminobutane dendrimers of the first (DGA-Den-I) or second (DGA-Den-II) generation and a room temperature ionic liquid (RTIL), viz., ...1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, based extraction chromatography resins were prepared for minor actinide separations from high level radioactive waste. The weight distribution coefficients (K d) of actinides on the two resins gave excellent and selective sorption of Am(III) and Pu(IV) over hexavalent uranyl ions, Sr(II) and Cs(I), over a wide range of acidity (0.01–6 M HNO3). The sorbed Am(III) and Pu(IV) could be efficiently desorbed with a buffered complexing solution of 1 M guanidine carbonate + 0.05 M EDTA. The sorption of metal ions on both the resins followed pseudo-second order rate kinetics and proceeded via a chemisorption phenomenon with a sorption energy of 13.4 ± 0.2 kJ/mol. The resin capacities were estimated to be 4.64 ± 0.18 and 4.19 ± 0.21 mg of Eu per g of DGA-Den-I and DGA-Den-II resins, respectively. The column loading of Eu(III) was about 85% of the theoretical value with a narrow elution profile using a buffered complexing solution. The resin affinity toward U(VI), Sr(II), and Cs(I) cations over Am(III) and Pu(IV) was poor, indicating the possible use of the resins for selective separation of Am(III) and Pu(IV) from other metal ions over a wide range of feed acidity.
Abstract
Modulation of photoluminescence of atomically thin transition metal dichalcogenide two-dimensional materials is critical for their integration in optoelectronic and photonic device ...applications. By coupling with different plasmonic array geometries, we have shown that the photoluminescence intensity can be enhanced and quenched in comparison with pristine monolayer MoS
2
. The enhanced exciton emission intensity can be further tuned by varying the angle of polarized incident excitation. Through controlled variation of the structural parameters of the plasmonic array in our experiment, we demonstrate modulation of the photoluminescence intensity from nearly fourfold quenching to approximately threefold enhancement. Our data indicates that the plasmonic resonance couples to optical fields at both, excitation and emission bands, and increases the spontaneous emission rate in a double spacing plasmonic array structure as compared with an equal spacing array structure. Furthermore our experimental results are supported by numerical as well as full electromagnetic wave simulations. This study can facilitate the incorporation of plasmon-enhanced transition metal dichalcogenide structures in photodetector, sensor and light emitter applications.
•Nd extraction by emulsion liquid membrane was studied.•DNPPA and TOPO mixture was used.•The extraction, demulsification and swelling aspects were studied.•The ELM method can be used for Nd recovery ...from acidic feeds.
The transport of Nd(III) from nitric acid medium across emulsion liquid membrane (ELM) using di-nonyl phenyl phosphoric acid (DNPPA) as the carrier extractant and Span 80 (sorbitol monoleate) as the surfactant in Petrofin as the diluent and sulphuric acid as the internal phase has been systematically investigated. The effect of different physical and chemical parameters such as stirring speed, neodymium concentration, external phase nitric acid concentration, extractant concentration, external to internal phase volume ratio, stripping agent concentration has been investigated on the extraction of Nd(III). The synergistic extraction of the metal ion has also been studied using mixtures of DNPPA and tri-n-octylphenyl phosphine oxide (TOPO) as the carrier extractants in the ELM. Quantitative extraction (>97%) of Nd(III) was observed with 0.3M DNPPA+0.13M TOPO and 1% (v/v) Span 80 liquid membrane at external to internal phase volume ratio of 10 for a feed having 500mg/L Nd(III) at 0.5M nitric acid concentration. The mechanism of extraction of Nd(III) has also been discussed in the light of the results obtained.
Extraction of Am super(3+) from acidic feed solutions was investigated using novel solvent systems containing a tripodal diglycolamide (T-DGA) in three room temperature ionic liquids (RTIL), viz.C ...sub(4)mimNTf sub(2 ), C sub(6)mimNTf sub(2) and C sub(8)mimNTf sub(2). Compared to the results obtained with N,N,N',N'-tetra-n-octyl diglycolamide (TODGA), T-DGA gave significantly higher distribution coefficients in these RTILs. The D sub(Am) values decreased with increasing carbon chain length in the RTILs, which was related to the solubility of the RTIL in the aqueous phase. The distribution studies included the effect of equilibration time, aqueous phase acid concentration variation and T-DGA concentration variation. In general, significantly higher equilibration times were observed for the extraction systems, which was partly due to the viscous RTIL phase and partly due to the slow conformational changes of the T-DGA ligand during complexation. Apart from Am super(3+), extraction of Pu super(4+), UO sub(2) super(2+), Eu super(3+), Sr super(2+) and Cs super(+) was also investigated, since they have significant implications in radioactive waste processing. Stripping studies indicated >99% stripping in three stages using 0.5 M EDTA or DTPA in 1 M guanidine carbonate. Slope analysis indicated the extraction of 1 : 1 complexed species of Am(iii) with T-DGA. Time resolved laser fluorescence spectroscopy (TRLFS) studies showed a strong complexation with no inner-sphere water molecules in the Eu(iii)-T-DGA complexes for C sub(4)mimNTf sub(2) as the diluent. Radiolytic degradation studies of the solvent systems containing T-DGA in the three RTILs were also carried out and while the D sub(Am) values decreased marginally when the solvents were exposed to 500 kGy absorbed dose, a relatively sharp decrease (60%) was seen when the solvents were exposed further to 1000 kGy absorbed dose, suggesting the possibility of recycling. Extraction studies were also carried out at varying temperatures and the thermodynamic parameters were calculated.
► When DGA moiety was appended on to a tripodal framework, extraction of U(VI) decreased spectacularly while Am(III) and Pu(IV) extraction did not show much change. ► With the tripodal ligand 100 ...times less concentration of the reagent was required as compared to TODGA which make the observations quite extraordinary. ► The transport rates are dependent on the strippant used in the receiver phase and a 0.01
M EDTA solution (pH 3.0) was found to yield quantitative transport of Am
3+ using T-DGA. ► The transport efficiency of the carrier solvent system was Am
3+
>
Pu
4+
≫
Np
4+
>
UO
2
2+ which can be exploited for the separation of the actinide ions.
A novel tripodal diglycolamide (T-DGA) extractant in a diluent mixture (10:1
n-dodecane–
iso-decanol) was evaluated for the extraction of actinide ions such as UO
2
2+, Np(IV), Pu(IV), and Am(III) and fission product element ions such as Cs
+ and Sr
2+ from acidic feed solutions. Conditions for quantitative extraction and stripping were found out for the actinide ions other than UO
2
2+ which is poorly extracted. Solvent extraction studies were carried out at varying concentrations of the extractant and nitric acid using Am(III) and were compared with the results obtained with TODGA (
N,
N,
N′,
N′-tetraoctyldiglycolamide), a representative diglycolamide extractant proposed for actinide partitioning. The extracted species was found out to be Am(NO
3)
3·2T-DGA
(o) at higher T-DGA concentrations, while mixed 1:1 and 1:2 species were observed at lower T-DGA concentrations. The prevalence of 1:2 species in the present case as compared to the 1:1 species reported in a similar system was attributed to the low dielectric constant diluent medium used in the present study.
Supported liquid membrane studies were also carried out using the T-DGA under varying feed acidities, carrier extractant concentration and compared with TODGA under identical conditions. The transport rates are dependent on the strippant used in the receiver phase and a 0.01
M EDTA solution (pH 3.0) was found to yield quantitative transport of Am(III) using T-DGA as compared to dilute nitric acid, which was efficiently used for the TODGA system in an earlier study. The transport efficiency of the carrier solvent system was Am(III)
>
Pu(IV)
≫
Np(IV)
>
UO
2
2+. The diffusion parameters were calculated for the T-DGA system and compared with the experimentally determined parameters.
Mutual separation of trivalent actinide (An(3+)) and lanthanide (Ln(3+)) using several soft (N) donor ligands (bis(5,6-dialkyl-1,2,4-triazinyl)pyridine (R-BTP)) is attempted for the first time in ...room temperature ionic liquid (RTIL) medium. The results indicate a spectacular enhancement in the selectivity as compared to that in molecular diluents with a separation factor (S.F.) of >3000 for Am(3+) over Eu(3+) using the methyl derivative (Me-BTP) in RTIL medium using C(n)mim·NTf2 as the diluents (where n = 2, 3, 4, 6 or 8). Such a high S.F. value has never been reported before with any of the R-BTP derivatives in molecular diluents. An opposite trend in the distribution ratio values of both Am(3+) and Eu(3+) with the increasing size of the alkyl (R) group is observed in RTIL medium when compared with that in molecular diluents. The differences in the extraction behaviour of R-BTPs in RTILs vis-à-vis molecular diluents are explained on the basis of the difference in the nature of complexes extracted in these two distinctly different media as supported by the time resolved fluorescence (TRFS) study. An unusually high extractability and selectivity for Am(3+) over Eu(3+) with Me-BTP was attributed to the formation of a 1 : 4 complex for Am(3+), which was never reported earlier with any of the R-BTP derivatives in molecular diluents. DFT studies indicated higher metal 'd' and 'f' orbital participation (covalence) in the bonding with R-BTP in the case of Am(3+) complexes as compared to that in the case of Eu(3+) complexes, which resulted in the selectivity of these classes of ligands. The observed results may have a great significance in the radioactive waste management involving the partitioning and transmutation strategy.
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