Enhancement Of Cl Research Articles

Role of Dielectric Drag in Circumventing the Solubility-Diffusivity Trade-off in Zwitterionic Copolymer Membranes.

Recent experiments have revealed that random zwitterionic amphiphilic copolymer (r-ZAC) membranes exhibit excellent Cl-/F- permselectivity circumventing the solubility-diffusivity trade-off. We conducted molecular dynamics simulations to investigate the origin of the experimental results on the transport of sodium halides in r-ZAC membranes. Our results indicate that the enhancement of Cl-/F- diffusivity selectivity in r-ZAC membranes (relative to that in bulk water) stems from the increase in dielectric drag dominating over the increase in Stokes drag, zwitterionic group-induced steric hindrance, and ion-polymer interactions. The importance of dielectric drag is further demonstrated by showing that reduction in ionic charges leads to a complete reversal of the diffusivity selectivity trends. We conclude that leveraging the impact of hydrophilic nanoconfinement on the dynamics of water can be utilized as a strategy to simultaneously augment solubility selectivity and diffusivity selectivity for separations, wherein the flux of the larger ionic species is desired over that of the smaller.

Numerical investigation of aerodynamic characteristics of a flying wing aircraft controlled by reverse dual synthetic jets

In this work, to explore the control potential of reverse dual synthetic jets (RDSJs) in a flying wing aircraft (FWA), reverse dual synthetic jet actuators (RDSJAs) are integrated into a FWA with a hybrid flow mode of rollers and streamers. The aerodynamic characteristics and control mechanism are investigated using numerical simulations. The results show that the aerodynamic loads follow a nonlinear trend, and the overall process can be divided into three stages with an increasing angle of attack (AOA). In the first stage (AOA = 0°–8°), the RDSJs can improve the reverse pressure gradients and form alternate recirculation zones or even a large-area separation. The pressure rises before and falls after the exits, causing an increase in Cd and a drop in CL. The decrease in the leading-edge suction and the pressure envelope area results in a further increase with the increasing AOA, resulting in a reduction in ΔCL and an improvement in ΔCd. In the second stage (AOA = 8°–24°), the energy of the RDSJs is too low to form a strong disturbance over the leeward surface, and the promotion of favorable pressure gradients along the lower surface can weaken the control effects of the RDSJAs, causing a decrease in the narrowing degree of the pressure envelope. The leading-edge vortex (LEV) is weakened, and ΔCL increases as Cd experiences a drop. In the third stage (AOA = 24°–32°), the RDSJs interact with the larger separation and are capable of accelerating the flow over the wing section, elevating the longitudinal velocity of the LEV through entrainments and improving the strength and stability of the LEV. The accelerated flow creates negative pressures behind RDSJAs, causing a further reduction in the decrement of the pressure envelope area. An enhancement of CL and Cd appears under the influence of the above factors.

Ag and N-doped carbon dot-enhanced H2O2–Co2+ chemiluminescence and its application for the determination of Co2+ and hydroquinone

Exploiting the Co2+ enhancement of CL in the Ag–NCDs–H2O2 system and HQ’s proficient quenching in the Ag–NCDs–H2O2–Co2+ system, we devised a CL method for sequential Co2+ and HQ analysis in real samples.

Bromovalerylurea modulates GABAA receptor-mediated inhibitory neurotransmission while inducing sleep

Bromovalerylurea (BU), an acyl urea derivative, was originally developed as a hypnotic/sedative. We recently reported that BU at a dose of 50 mg/kg ameliorates sepsis, Parkinson's disease, and traumatic brain injury in Wistar rat models through its anti-inflammatory actions on microglia and macrophages. However, since BU was developed more than 100 years ago, its hypnotic mechanism and characteristics are poorly understood. Herein, we conducted an electroencephalogram (EEG) study and found that BU, when administered at a dose of more than 125 mg/kg but not at a dose of 50 mg/kg in Wistar rats, significantly increased non-rapid eye movement (NREM) sleep duration and dose-dependently decreased rapid eye movement (REM) sleep duration. This characteristic of sleep induced by BU is similar to the effect of compounds such as barbiturate, benzodiazepine, and z-drugs, all of which require γ-aminobutyric acid A receptors (GABAAR) for hypnotic/sedative activity. To investigate whether BU could potentiate GABAAergic neurotransmission, we conducted a whole-cell patch-clamp recording from pyramidal neurons in rat cortical slices to detect spontaneous GABAAR-mediated inhibitory postsynaptic currents (IPSCs). We found that BU dose-dependently prolonged IPSCs. Importantly, the prolonged IPSCs were not attenuated by flumazenil, a benzodiazepine receptor antagonist, suggesting that modulation of IPSCs by BU is mediated by different mechanisms from that of benzodiazepine. Taken together, these data elucidate the basic characteristics of the hypnotic effects of BU and suggest that the enhancement of GABAAR-mediated Cl− flux may be a possible mechanism that contributes to its hypnotic/sedative activity.

Surface solvation of Martian salt analogues at low relative humidities.

Salt aerosols play important roles in many processes related to atmospheric chemistry and the climate systems on both Earth and Mars. Complicated and still poorly understood processes occur on the salt surfaces when interacting with water vapor. In this study, ambient pressure X-ray photoelectron spectroscopy (APXPS) is used to characterize the surface chemical environment of Martian salt analogues originating from saline lakes and playas, as well as their responses to varying relative humidities. Generally, APXPS shows similar ionic compositions to those observed by ion chromatography (IC). However, XPS is a surface-sensitive method while IC is bulk-sensitive and differences are observed for species that preferentially partition to the surface or the bulk. Element-selective surface enhancement of Cl− is observed, likely caused by the presence of SO42−. In addition, Mg2+ is concentrated on the surface while Na+ is relatively depleted in the surface layer. Hence, the cations (Na+ and Mg2+) and the anions (Cl− and SO42−) show competitive correlations. At elevated relative humidity (RH), no major spectral changes were observed in the XPS results, except for the growth of an oxygen component originating from condensed H2O. Near-edge X-ray absorption fine structure (NEXAFS) measurements show that the magnesium and sodium spectra are sensitive to the presence of water, and the results imply that the surface is fully solvated already at RH = 5%. The surface solvation is also fully reversible as the RH is reduced. No major differences are observed between sample types and sample locations, indicating that the salts originated from saline lakes commonly have solvated surfaces under the environmental conditions on Earth.

Adsorbable organic halogens formed during treatment of Cl−-containing wastewater by sulfate and hydroxyl radical-based advanced oxidation processes

The formation of adsorbable organic halogens (AOX) in two typical advanced oxidation processes (AOPs), OH-based (UV/H2O2) and SO4−-based (UV/potassium persulfate (PDS)) processes, was investigated during the treatment of Cl−-containing wastewater. Compared with the original AOX concentration (0.08 mg/L), a significant increase in the AOX concentration was observed in both AOPs under the condition that TOC concentration was minimized. Higher concentration of AOX was formed in the UV/PDS process than that in the UV/H2O2 process under all experimental conditions, although the former showed a better performance on TOC removal. An increase of effluent AOX concentration from 0.4 mg/L to 1.1 mg/L in the UV/H2O2 process and from 1.9 mg/L to 3.4 mg/L in the UV/PDS process was observed, respectively, when the Cl− concentration increased from 1800 mg/L to 10000 mg/L. This enhancement of high Cl−concentration on the AOX formation was attributed to the reactive halogen species generated in the AOP treatment. The term AOXMFP was created to determine the AOX formation potential of wastewater and AOPs system. The results showed that organic matters with a molecular weight (MW) between 1 k ∼ 100 k Da tend to form AOX more easily than those with a MW lower than 1 k Da and higher than 100 k Da. In addition, eight and fourteen kinds of formed organic halogens were identified in UV/H2O2 and UV/PDS treated wastewater, respectively. Five kinds of them have been proved to be toxic, which partially contributed to the increase of acute toxicity of effluent. The results of this work provides a new perspective to evaluate, in terms of eco-safety and efficiency, the application of AOPs to wastewater containing high concentration of Cl−.

Groundwater recharge and evolution in the Wuwei Basin, northwestern China

Understanding the mechanisms and processes of groundwater recharge and evolution is critical for sustainable water resources management to meet human and agriculture needs under climate change, because groundwater is the primary water source in semiarid and arid regions, where the surface water resources are usually highly unstable and scarce. However, few studies investigated the recharge and evolution processes of groundwater combining with isotopic geochemistry and radiocarbon data, especially focused on the interactions among precipitation, surface water, groundwater, and rock. This study examined the recharge and evolution processes of groundwater in the Wuwei Basin based on stable isotopes, chemical indicators, and radiocarbon data. Our results showed that the Na+ (sodium ion) and K+ (potassium ion) concentrations of the groundwater were controlled by the dissolution of sylvite and halite origin from sediments, whereas the increase of Na+ and Cl− (chloride ion) concentrations were not in accordance with a ratio of 1:1, indicating that the Na+ and K+ concentrations in groundwater were barely affected by the dissolution of halite and sylvite. Meanwhile, we also found that bicarbonate ion (HCO3−) was the dominant ion with a decreased ratio in the groundwater. The SO42−/Cl− (sulfate ion/chloride ion) ratio decreased with the sample profile from Southwest to Northeast due mainly to the increases of Cl− concentration. The Ca2+/Cl− (calcium ion/chloride ion) ratio decreased with the enhancement of Cl− in the hydrodynamic sluggish belt. In addition, the δ18O (oxygen isotope) and δ2H (hydrogen isotope) values of groundwater gradually increased from Southwest to Northeast along the flow path. The heavy isotopic values were more strongly depleted than the isotopic values of precipitation in the ground water samples, suggesting that the recharge of ground water in the plain region was very limited from precipitation. Moreover, the groundwater in the phreatic aquifer was younger water with 3H (tritium isotope) values from 47 to 71 a.BP (before present), while the groundwater age in the confined aquifer was 1000–5800 BP evidenced by the 14C (carbon isotope) values between 48 and 88 pmc (percentage modern carbon content). Overall, these results suggested that the unconfined groundwater enriched along the overall groundwater flow path from the southwest to northeast of the Wuwei Basin and the melt water from the Qilian Mountains may determine the water isotopic composition and contributed to the steady long-term runoff of the Shiyang River. Our findings may have important implications for inter-basin water allocation programmes and groundwater management in the Wuwei Basin.

Electrochemical impedance spectroscopy of enhanced layered nanocomposite ion exchange membranes

This work presents the enhancement of Cl−/SO42− mono-selectivity of layered nanocomposite anion exchange membranes (AEMs) and the mechanism that supports this improvement. These nanocomposite membranes are based on commercial polyethylene AEMs and a nanocomposite negative thin layer composed of sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) and a functionalized nanomaterial, Fe2O3−SO42− nanoparticles or oxidized multi-walled carbon nanotubes CNTs-COO−. The mechanism for monovalent selectivity was confirmed by characterizing nanocomposite membranes and commercial heterogeneous ion exchange membranes (IEMs) using ζ-potential and electrochemical impedance spectroscopy (EIS). ζ-potential measurements confirmed the modification of the charge of surface of the membrane after being coated with the nanocomposite layer. EIS measurements showed a totally different electrical performance between layered nanocomposite membranes and commercial IEMs. The electrical data from EIS was fitted to a Maxwell-Wagner model providing an equivalent electric circuit (EEC) for each membrane. The observed differences in ECC were related to the structural differences of the membranes. A physical explanation of the phenomena that caused these differences is provided. The influence of ion concentration on EIS measurements was also studied. To the best of our knowledge, this is the first time that an ECC related to the structure of advanced layered IEMs is proposed.

Capacitive properties of polypyrrole/activated carbon composite

Electrochemical synthesis of polypyrrole (PPy) and polypyrrole / activated carbon (PPy / AC) - composite films, with a thickness between 0.5 and 15 ?m were performed in a three electrode cell containing 0.1 mol dm-3 Py, 0.5 mol dm-3 NaClO4 dissolved in ACN, and dispersed particles of AC (30 g dm-3). Electrochemical characterization of PPy and PPy / AC composites was performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The linear dependences of the capacitance (qC), redox capacitance (qred), and limiting capacitance (CL) of PPy and PPy / AC - composite films on their thickness (L), obtained by electrochemical and impedance analysis, indicate a nearly homogeneous distribution of the incorporated AC particles in the composite films (correlation coefficient between 0.991 and 0.998). The significant enhancement of qC, qred, and CL, was observed for composite films (for ?40 ? 5%) in respect to that of the ?pure? PPy. The decreased values of a volume resistivity in the reduced state of the composite film, ? = 1.3 ? 106 ? cm (for L = 7.5 ?m), for two orders of magnitude, compared to that of PPy - film with the same thickness, ? ? 108 ? cm, was also noticed.

Influence of salt stress on growth, pigments, soluble sugars and ion accumulation in three pistachio cultivars

In this study, three pistachio cultivars were treated with different concentration of salt solution to provide a reference for the cultivation of salt tolerant rootstocks. The results revealed that increasing the salinity stress resulted in decreasing growth performances of the plants in the three pistachio cultivars. This decrease was not significant in salinity of 100 mM but was significant in other salinities compared to control. In all salinity levels and control conditions, Akbari (Ak) cultivar exhibited larger growth performances of the plants in comparison with the other two cultivars; this state is more sensible in salinities of 200 and 300 mM. Ak cultivar assumed significantly higher pigment amount than the other two cultivars in high salinities. Impact of salinity on reduction of chlorophyll amount was significant in all cultivars starting from salinity of 200 mM. Moderate and high salinity led to an increase in amount of total soluble sugars in Ak cultivar while no significant contrast was achieved between the other two cultivars compared to control conditions. The impacts of different salinities on Na and Cl were nearly similar and the amounts of these elements increased with exceeding salinity stress in different cultivars compared to control condition. The high stress level resulted in remarkable enhancement of Cl and Na amounts in Ouhadi (Ou) and Kalehghouchi (Ka) cultivars. However, the low and moderate salinities increased the concentration of potassium in AK cultivar compared to the other two cultivars. Therefore, higher plant growth and photosynthetic pigments, lower Na and Cl content, greater accumulation of soluble sugars and K could explain the greater salt-tolerance of AK compared to that of Ka and Ou. Key words: Pistachio cultivars, salinity, growth, ion accumulation.

Local Electronic Properties of the Passive Film on Nickel Studied by Scanning Tunneling Spectroscopy

Scanning tunneling spectroscopy has been applied to characterize the electronic properties of the granular and intergranular sites of the passive film grown on Ni(111) single-crystal surfaces in acid solution. The passive film, essentially consisting of NiO, shows p-type grains (valence band edge at 0.54 ± 0.03 eV below Fermi level) with unoccupied Ni 3d surface states at 0.5–1.5 eV above Fermi level in the bandgap. At grain boundaries, the p-type semiconductivity is attenuated as evidenced by a downward shift of 0.12 ± 0.06 eV of the valence band edge, and the density of surface states is markedly reduced, both effects indicating the presence of oxygen vacancies in these sites. The dominant point defect in the film is metallic vacancies but oxygen vacancies attenuate locally the resulting p-type property at the grain boundaries. The implications of these local electronic properties on oxidative and reductive electronic transfer and on the corrosion resistance are discussed. The oxygen vacancies at intergranular boundaries imply local changes of the properties of anionic mass transport through the passive film and enhancement of Cl− adsorption and/or penetration, which is consistent with the view of passive film grain boundaries playing a key role in passivity breakdown.

(–)-Epigallocatechin-3-O-Gallate Augments Pentobarbital-Induced Sleeping Behaviors Through Cl− Channel Activation

This experiment investigated whether (-)-epigallocatechin-3-O-gallate (EGCG) (5-20 mg/kg, p.o.) has hypnotic effects and/or enhances pentobarbital-induced sleeping behaviors and whether these effects are mediated by γ-aminobutyric acid (GABA) receptors. EGCG prolonged sleeping time induced by pentobarbital (42 mg/kg, i.p.) and reduced sleeping latency induced by pentobarbital similarly to muscimol (0.2 mg/kg, i.p.), a GABA(A) receptor agonist in mice. EGCG also increased sleeping rate and sleeping time when co-administered with pentobarbital (28 mg/kg, i.p.) at a subhypnotic dosage. In addition, EGCG and pentobarbital increased chloride (Cl(-)) influx in primary cultured cerebellar cells. EGCG and pentobarbital decreased GABA(A) receptors α-subunit expression and had no effect on the expression of β- and γ-subunits and of glutamic acid decarboxylase in the hippocampus of rats. In conclusion, the EGCG enhancement of Cl(-) influx may play an important role in pentobarbital-induced sleeping behaviors.

Cyclopeptide alkaloid fraction from Zizyphi Spinosi Semen enhances pentobarbital-induced sleeping behaviors

This study aimed to investigate effects of cyclopeptide alkaloid fraction of ZSS (CAFZ) on pentobarbital-induced sleeping behaviors and to determine whether these effects were mediated by γ-aminobutyric acid (GABA) receptors Cl − channel activation, using a Western blot technique and Cl − sensitive fluorescence probe. GABA receptors subunits expression and Cl − influx were investigated in cultured cerebellar granule cells. CAFZ shortened sleeping onset and prolonged sleeping time induced by pentobarbital (42 mg/kg). It also significantly increased the falling asleep rate and duration of sleeping time at a sub-hypnotic dosage of pentobarbital (28 mg/kg). In addition, CAFZ in combination with GABA A receptors agonist, muscimol, synergistically prolonged pentobarbital-induced sleeping time. Both of CAFZ and pentobarbital treatment decreased GABA A receptors α-subunit expression, but did not change β- and γ-subunit expression. However, we found CAFZ and pentobarbital increased Cl − influx, CAFZ showed similar effects with muscimol in potentiating Cl − influx inducing effects of low-dose pentobarbital. In conclusion, it is suggested that the enhancement of Cl − influx by CAFZ may play an important role in the potentiation of pentobarbital-induced sleeping behaviors.

Enhanced production of ionic photofragments of Si(CH 3) 2Cl 2 following core-to-valence excitation

The state-selective positive-ion and negative-ion dissociation pathways for gaseous and condensed Si(CH 3) 2Cl 2 following the Cl 2p and Si 2p core-level excitations have been characterized using synchrotron radiation. The Si 2 p → 15 a 1 ∗ excitation of Si(CH 3) 2Cl 2 induces an enhancement of the Cl + desorption yield in the condensed phase and the Si ( CH 3 ) 2 + and SiCH 3 + yields in the gaseous-phase. The Cl −desorption yields are notably enhanced at the 15 a 1 ∗ resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl − yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide an insight into the comprehensive understanding of the state-selective fragmentation of molecules via core-level excitation.

Enhancement of P2Y6-Induced Cl- Secretion by IL-13 and Modulation of SK4 Channels Activity in Human Bronchial Cells

Expression of functional P2Y₆ receptors was demonstrated in primary cultures of human bronchial cells (NHBE cells). P2Y₆ receptors were located only on the apical membranes of NHBE cells. Their stimulation by UDP induced a chloride secretion (short-circuit current) reflected by the development of two I_sc components (I_fast and I_late). A pharmacological characterization of those two I_sc components showed the involvement of CaCC and CFTR channel activity in I_fast and I_late respectively. I_fast was also found to be under control of basolateral SK4 channels. Indeed, inhibition of SK4 channels opening by clotrimazole dramatically reduced I_fast amplitude. The epithelial ion transporting phenotype depends on the cellular state of differentiation. As previously reported, we observed that Ultroser G increased the epithelial tightness and Na⁺-transport capacity while IL-13 switch the epithelial ion transport phenotype from a Na⁺-absorbing to a Cl^--secreting one. In our study, we report for the first time a change in the K⁺ cell permeability associated to IL-13-induced cell differentiation. IL-13 treatment increased the-resting K⁺ permeability as well as the Ca²⁺-dependent K⁺ permeability stimulated by UDP or ionomycin. SK4 channels activity, underlying the Ca²⁺-dependent K⁺ permeability was in particular increased by IL-13. The on/off effect of IL-13 on P2Y₆-induced Cl-secretion may help to identify the molecular determinants responsible for the CaCC channel activity.

Dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed Si(CH3)2Cl2 via Si 2p, Cl 2p, and Cl 1s core-level excitations

The state-selective positive-ion and negative-ion dissociation pathways of gaseous and condensed Si(CH(3))(2)Cl(2) following Cl 2p, Cl 1s, and Si 2p core-level excitations have been characterized. The excitations to a specific antibonding state (15a(1) (*) state) of gaseous Si(CH(3))(2)Cl(2) at the Cl 2p, Cl 1s, and Si 2p edges produce significant enhancement of fragment ions. This ion enhancement at specific core-excited states correlates closely with the ion kinetic energy distribution. The results deduced from ion kinetic energy distribution are consistent with results of quantum-chemical calculations on Si(CH(3))(2)Cl(2) using the ADF package. The Cl(-) desorption yields for Si(CH(3))(2)Cl(2)Si(100) at approximately 90 K are notably enhanced at the 15a(1) (*) resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl(-) yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide insight into the state-selective ionic fragmentation of molecules via core-level excitation.

Enhancement of substrate-gated Cl− currents via rat glutamate transporter EAAT4 by PMA

Glutamate transporters (also called excitatory amino acid transporters, EAAT) are important in extracellular homeostasis of glutamate, a major excitatory neurotransmitter. EAAT4, a neuronally expressed EAAT in cerebellum, has a large portion (approximately 95% of the total L-aspartate-induced currents in human EAAT4) of substrate-gated Cl(-) currents, a distinct feature of this EAAT. We cloned EAAT4 from rat cerebellum. This molecule was predicted to have eight putative transmembrane domains. L-glutamate induced an inward current in oocytes expressing this EAAT4 at a holding potential -60 mV. Phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, significantly increased the magnitude of L-glutamate-induced currents but did not affect the apparent affinity of EAAT4 for L-glutamate. This PMA-enhanced current had a reversal potential -17 mV at extracellular Cl(-) concentration ([Cl(-)](o)) 104 mM with an approximately 60-mV shift per 10-fold change in [Cl(-)](o), properties consistent with Cl(-)-selective conductance. However, PMA did not change EAAT4 transport activity as measured by [(3)H]-L-glutamate. Thus PMA-enhanced Cl(-) currents via EAAT4 were not thermodynamically coupled to substrate transport. These PMA-enhanced Cl(-) currents were partially blocked by staurosporine, chelerythrine, and calphostin C, the three PKC inhibitors. Ro-31-8425, a PKC inhibitor that inhibits conventional PKC isozymes at low concentrations (nM level), partially inhibited the PMA-enhanced Cl(-) currents only at a high concentration (1 microM). Intracellular injection of BAPTA, a Ca(2+)-chelating agent, did not affect the PMA-enhanced Cl(-) currents. 4alpha-Phorbol-12,13-didecanoate, an inactive analog of PMA, did not enhance glutamate-induced currents. These data suggest that PKC, possibly isozymes other than conventional ones, modulates the substrate-gated Cl(-) currents via rat EAAT4. Our results also suggest that substrate-gated ion channel activity and glutamate transport activity, two EAAT4 properties that could modulate neuronal excitability, can be regulated independently.

X-ray initiated molecular photochemistry of Cl-containing adsorbates on a Si(1 0 0) surface using synchrotron radiation

X-ray initiated molecular photochemistry for SiCl 4 and CCl 4 adsorbed on Si(1 0 0) at ∼90 K following Cl 2p core-level excitation is investigated by photon stimulated ion desorption and ion kinetic energy distribution measurements. The Cl 2 p → 8 a 1 ∗ excitation of solid SiCl 4 induces the significant enhancement (∼900%) of the Cl + yield, while the Cl 2 p → 7 a 1 ∗ excitation of condensed CCl 4 leads to a moderate enhancement (∼500%) of the Cl + yield. The enhancement of Cl + yield at the specific core-excited states is strongly correlated to the ion escaped energy. Upon X-ray exposure for CCl 4 adsorbed on Si(1 0 0) (20-L exposure), the Cl + yields at 7 a 1 ∗ resonances decrease and new structures at higher photon energies are observed. Cl + yields at these new resonances are significantly enhanced compared to those at other resonances. These changes are the results of desorption and surface reaction of the CCl 4–Si surface complex due to X-ray irradiation. We have demonstrated that state-specific enhancement of ion desorption can be successfully applied to characterize the reaction dynamics of adsorbates adsorbed on surfaces by X-ray irradiation.

Mechanism of state-specific enhancement in photon-stimulated desorption as studied using a polarization-dependent technique

In the present study, we investigated the mechanisms of state-selective fragment-ion desorption from condensed chlorobenzene following C 1s, Cl 2s, and Cl 2p core-level excitations by measuring the polarization dependences of NEXAFS (near-edge X-ray absorption fine structure) spectra recorded with desorbed ion yields and total electron yields (TEY). TEY-based NEXAFS shows no significant polarization dependence at any edges. In contrast, ion-based NEXAFS demonstrates a variety of marked polarization dependences. Cl 2p → 3d π* excitation induces a significant enhancement of Cl + desorption yield at normal incidence (polarization ∥ surface), while Cl 2s → σ*(C–Cl) excitation stimulates a substantial enhancement of Cl + desorption at grazing incidence (polarization ⊥ surface). C 1s → σ*(C–Cl) enhances D + desorption at grazing incidence, while C 1s → π*(C C) suppresses D + desorption at all angles. All polarization dependences consistently reveal that excited molecules with upward-pointing bonds at top-most surfaces lead to efficient fragment desorption. This orientation effect is understood in terms of competing processes between the ultra-fast dissociation and charge-neutralization relaxation taking place during core-excited states. We demonstrate that the polarization-dependent ion-NEXAFS technique can distinguish direct state-specific fragmentation from indirect desorption caused by the collision of secondary electrons.

ASSESSMENT OF DRUG INTERACTIONS IN HEPATOBILIARY TRANSPORT USING RHODAMINE 123 IN SANDWICH-CULTURED RAT HEPATOCYTES

The purpose of the present study was to explore the utility of sandwich-cultured rat hepatocytes as an in vitro tool to examine drug interactions at the hepatic transport level. Rhodamine 123 was used as a model substrate for P-glycoprotein-mediated biliary excretion. Effects of various types of P-glycoprotein modulation on the biliary excretion index (BEI; a relative measure of the extent of biliary excretion) and the in vitro biliary clearance (CL(bile)) were determined. Significant reductions in rhodamine 123 BEI and CL(bile) were noted in the presence of the P-glycoprotein inhibitors verapamil (30-100 microM) and progesterone (100 microM). The P-glycoprotein activator quercetin (10-100 microM) enhanced rhodamine 123 CL(bile) by approximately 4-fold, with only a minor effect on BEI, suggesting that quercetin had a more pronounced effect on uptake at the basolateral membrane rather than excretion across the canalicular membrane. Treatment of hepatocytes for 48 h with dexamethasone (10 microM) resulted in significant enhancement of CL(bile), whereas rifampin (5-50 microM) increased both BEI and CL(bile), indicating that the inducing effects of dexamethasone and rifampin were occurring at the basolateral and canalicular membranes, respectively. Total rhodamine 123 uptake in sandwich-cultured rat hepatocytes was partly saturable and was affected by the presence of typical Oatp1a4 substrates (digoxin, quinine, d-verapamil, 17beta-estradiol-d-17beta-glucuronide). In summary, sandwich-cultured rat hepatocytes are a useful tool to study mechanisms of hepatobiliary drug disposition and to predict the potential for drug interactions in hepatic transport.