A triazole‐based fluorescence probe for detecting Hg2+ ions and its biological application

A new compound, ethyl 5‐phenyl‐2‐(p‐tolyl)‐2H‐1,2,3‐triazole‐4‐carboxylate was successfully introduced and synthesized as a novel rhodamine B derivative named REPPC, and characterized by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, and high resolution mass spectrometry (HRMS). It showed an obvious fluorescence and UV–visible light absorption enhancement towards Hg²⁺ ion without interference from common metal ions in N,N‐dimethylformamide–H₂O (pH 7.4). The spirolactam ring moiety of rhodamine in REPPC was converted to the open‐ring form generating a 1:1 complex with the intervention of a mercury ion, verified by electrospray ionization‐mass spectroscopy testing and density functional theory calculation. REPPC was used to visualize the level of mercury ions in living HeLa cells with encouraging results.     

Evaluation of electrocoagulation,flocculation, and sedimentation harvesting methods on microalgae consortium grown in anaerobically digested abattoir effluent

Microalgae dewatering is a major bottleneck for biomass production in a large-scale microalgal production system which accounts for 20–60% of production cost. In this study, three dewatering systems of electrocoagulation, flocculation, and pH-induced flocculation were evaluated for microalgal consortium grown in anaerobically digested abattoir effluent at pH 6.5 and 9.5. At the shortest time (15 min) and the highest current density (0.08 A cm^?2), the highest microalgae recoveries of 78 and 84% were obtained with the corresponding power consumptions of 1.25 and 1.07 kWh kg^?1 for cultures at pH 6.5 and 9.5. For microalgae suspension at pH 6.5, the highest biomass recovery of 77% was obtained when 100 mg L^?1 of FeCl₃·6H₂O (after 15 min) or 100 mg L^?1 of Al₂(SO₄)₃·18H₂O (after 30 min) was added. However, microalgal recoveries significantly increased when FeCl₃·6H₂O or Al₂(SO₄)₃·18H₂O was used with the culture at pH 9.5. pH-Induced experiments showed that cultures adjusted at pH 10.5 had 36% higher biomass recovery compared to that in cultures at pH 8.5 after 2 h. The results of this study showed that cultures at higher pH (9.5) had a better microalgae recovery in all dewatering systems than cultures at lower pH (6.5).

     

Erratum to “Conformations of NhaA, the Na/H Exchanger from Escherichia coli, in the pH-Activated and Ion-Translocating States” [J. Mol. Biol. 386 (2009) 351-385]: Conformations of NhaA, the Na/H Exchanger from Escherichia coli, in the pH-Activated and Ion-Translocating States

NhaA, the main sodium-proton exchanger in the inner membrane of Escherichia coli, regulates the cytosolic concentrations of H⁺ and Na⁺. It is inactive at acidic pH, becomes active between pH 6 and pH 7, and reaches maximum activity at pH 8. By cryo-electron microscopy of two-dimensional crystals grown at pH 4 and incubated at higher pH, we identified two sequential conformational changes in the protein in response to pH or substrate ions. The first change is induced by a rise in pH from 6 to 7 and marks the transition from the inactive state to the pH-activated state. pH activation, which precedes the ion-induced conformational change, is accompanied by an overall expansion of the NhaA monomer and a local ordering of the N-terminus. The second conformational change is induced by the substrate ions Na⁺ and Li⁺ at pH above 7 and involves a 7-Å displacement of helix IVp. This movement would cause a charge imbalance at the ion-binding site that may trigger the release of the substrate ion and open a periplasmic exit channel.     

Sensitive and selective detection of Cu(II) ion: A new effective 1,8‐naphthalimide‐based fluorescence ‘turn off’ sensor

The present study reports the development of a new 1,8‐naphthalimide‐based fluorescent sensor V for monitoring Cu(II) ions. The sensor exhibited pH independence over a wide pH range 2.52–9.58, and indicated its possible use for monitoring Cu(II) ions in a competitive pH medium. The sensor also showed high selectivity and sensitivity towards the Cu(II) ions over other competitive metal ions in DMSO–HEPES buffer (v/v, 1:1; pH 7.4) with a fluorescence ‘turn off’ mode of 79.79% observed. A Job plot indicated the formation of a 1:1 binding mode of the sensor with Cu(II) ions. The association constant and detection limit were 1.14 × 10⁶ M^–1 and 4.67 × 10^–8 M, respectively. The fluorescence spectrum of the sensor was quenched due to the powerful paramagnetic nature of the Cu(II) ions. Potential application of this sensor was also demonstrated when determining Cu(II) ion levels in two different water samples.     

Probing the proton release by Photosystem II in the S1 to S2 high-spin transition

The stoichiometry and kinetics of the proton release were investigated during each transition of the S-state cycle in Photosystem II (PSII) from Thermosynechococcus elongatus containing either a Mn₄CaO₅ (PSII/Ca) or a Mn₄SrO₅ (PSII/Sr) cluster. The measurements were done at pH 6.0 and pH 7.0 knowing that, in PSII/Ca at pH 6.0 and pH 7.0 and in PSII/Sr at pH 6.0, the flash-induced S₂-state is in a low-spin configuration (S₂^LS) whereas in PSII/Sr at pH 7.0, the S₂-state is in a high-spin configuration (S₂^HS) in half of the centers. Two measurements were done; the time-resolved flash dependent i) absorption of either bromocresol purple at pH 6.0 or neutral red at pH 7.0 and ii) electrochromism in the Soret band of P_D1 at 440 nm. The fittings of the oscillations with a period of four indicate that one proton is released in the S₁ to S₂^HS transition in PSII/Sr at pH 7.0. It has previously been suggested that the proton released in the S₂^LS to S₃ transition would be released in a S₂^LSTyr_Z^? → S₂^HSTyr_Z^? transition before the electron transfer from the cluster to Tyr_Z^? occurs. The release of a proton in the S₁Tyr_Z^? → S₂^HSTyr_Z transition would logically imply that this proton release is missing in the S₂^HSTyr_Z^? to S₃Tyr_Z transition. Instead, the proton release in the S₁ to S₂^HS transition in PSII/Sr at pH 7.0 was mainly done at the expense of the proton release in the S₃ to S₀ and S₀ to S₁ transitions. However, at pH 7.0, the electrochromism of P_D1 seems larger in PSII/Sr when compared to PSII/Ca in the S₃ state. This points to the complex link between proton movements in and immediately around the Mn₄ cluster and the mechanism leading to the release of protons into the bulk.     

A Model for Calcium Permeation into Small Intestine

An in vitro model was used to simulate the intestinal permeation of calcium ions depending on the type of salt (carbonate, fumarate, citrate, or gluconate), its concentration (1.0, 2.5, 5.0, or 10 mM/l), and pH (1.3, 4.2, 6.2, or 7.5). To simulate the conditions for calcium permeation in a patient in a fasting state, the solutions were placed in contact with segments of small intestine of pig: stomach, duodenum, jejunum, and ileum. The percent permeation, its rate, and half-time were measured in each case. In all cases, the maximum permeation was seen at 1 mM concentration, depending on pH: 100% for carbonate at pH 1.3; 82% for fumarate, pH 6.2; 79.5% for citrate at pH 4.2, and 81% for gluconate at pH 7.4. The maximum rate of permeation (% h⁻¹) was also observed at 1 mM: 2.16 for carbonate at pH 1.3, 0.29 for fumarate at pH 6.2, 0.26 for citrate at pH 4.2, and 0.28 for gluconate at pH 7.4. The shortest half-time permeation (t _1/2, h) for 1 mM solutions depended also on pH (in parentheses): carbonate 0.3 (1.3), fumarate 2.4 (6.2), citrate 2.6 (4.2), and gluconate 2.5 (7.4). The results suggest that calcium carbonate and citrate can be recommended to patients with normal gastric acidity and hyperacidity while fumarate and gluconate to patients with hypoacidity.     

Lanthanide ions promote the hydrolysis of 2,3-Bisphosphoglycerate

The ³¹P NMR studies showed that lanthanide ions promote the site-specific hydrolysis of 2,3-Bisphosphoglycerate (BPG) at pH 7.4 by cleaving the 2 phosphomonoester bond. The effect of fourteen trivalent lanthanide ions and Sc³⁺, and Y³⁺ were compared by the percentage of hydrolysis obtained by determining the inorganic phosphate produced. All the trivalent lanthanide ions promote the hydrolysis, but Sc³⁺ not. Among them, Ce³⁺ affects the reaction mostly. This was mainly attributed to the autooxidation of Ce³⁺ to Ce⁴⁺, since the promoting effect of Ce³⁺ is related to the increasing Ce⁴⁺ amount in the solution and depressed by adding sulphite. Ce⁴⁺ promotes the hydrolysis more efficiently than Ce³⁺ do. The pseudo first-order rate constant for the hydrolysis of BPG by Ce(SO₄)₂ (18.7 mM) at pH 1 and pH 2, 37 °C is 3.1 h^–1 and 0.65 h^–1 respectively. A mechanism with a hydroxo species as reactive intermediate was proposed for the trivalent lanthanide ions. The site-specificity was explainable by this mechanism.     

A highly selective and sensitive turn‐on fluorescent probe for the detection of Al3+ and its bioimaging

A novel fluorescent sensor, 1‐((2‐hydroxynaphthalen‐1‐yl)methylene)urea (ocn) has been designed and applied as a highly selective and sensitive fluorescent probe for recognition of Al³⁺ in Tris–HCl (pH = 7.20) solution. The probe ocn exhibits an excellent selectivity to Al³⁺ over other examined metal ions, anions and amino acids with a prominent fluorescence ‘turn‐on’ at 438 nm. ocn binds to Al³⁺ with a 2:1 binding stoichiometry and the detection limit was 0.3 μM. Furthermore, its capability of biological application was evaluated and the results showed that the sensor could be used to detect Al³⁺ in living cells.     

Helix VIII of NhaA Na(+)/H(+) antiporter participates in the periplasmic cation passage and pH regulation of the antiporter

The crystal structure of Escherichia coli NhaA determined at pH 4 has provided insights into the mechanism of activity of a pH-regulated Na⁺/H⁺ antiporter. However, because NhaA is active at physiological pH (pH 6.5-8.5), many questions related to the active state of NhaA have remained unanswered. Our Cys scanning of the highly conserved transmembrane VIII at physiological pH reveals that (1) the Cys replacement G230C significantly increases the apparent K_m of the antiporter to both Na⁺ (10-fold) and Li⁺ (6-fold). (2) Variants G223C and G230C cause a drastic alkaline shift of the pH profile of NhaA by 1 pH unit. (3) Residues Gly223-Ala226 line a periplasmic funnel at physiological pH as they do at pH 4. Both were modified by membrane-impermeant negatively charged 2-sulfonatoethyl methanethiosulfonate and positively charged 2-(trimethyl ammonium)-ethylmethanethiosulfonate sulfhydryl reagents that could reach Cys replacements from the periplasm via water-filled funnels only, whereas other Cys replacements on helix VIII were not accessible/reactive to the reagents. (4) Remarkably, the modification of variant V224C by 2-sulfonatoethyl methanethiosulfonate or 2-(trimethyl ammonium)-ethylmethanethiosulfonate totally inhibited antiporter activity, while N-ethyl maleimide modification had a very small effect on NhaA activity. Hence, the size—rather than the chemical modification or the charge—of the larger reagents interferes with the passage of ions through the periplasmic funnel. Taken together, our results at physiological pH reveal that amino acid residues in transmembrane VIII contribute to the cation passage of NhaA and its pH regulation.     

Preliminary Investigation on the Development of Diltiazem Resin Complex Loaded Carboxymethyl Xanthan Beads

The objective of this study was to develop a multiunit sustained release dosage form of diltiazem using a natural polymer from a completely aqueous environment. Diltiazem was complexed with resin and the resinate-loaded carboxymethyl xanthan (RCMX) beads were prepared by interacting sodium carboxymethyl xanthan (SCMX), a derivatized xanthan gum, with Al⁺³ ions. The beads were evaluated for drug entrapment efficiency (DEE) and release characteristics in enzyme free simulated gastric fluid (SGF, HCl solution, pH 1.2) and simulated intestinal fluid (SIF, USP phosphate buffer solution, pH 6.8). Increase in gelation time from 5 to 20 min and AlCl₃ concentration from 1 to 3% decreased the DEE respectively from 95 to 79% and 88.5 to 84.6%. However, increase in gum concentration from 1.5 to 2.5% increased the DEE from 86.5 to 90.7%. The variation in DEE was related to displacement of drug from the resinate by the gel forming Al⁺³ ions. While 75–82% drug was released in 2 h in SGF from various beads, 75 to 98% drug was released in 5 hour in SIF indicating the dependence of drug release on pH of dissolution media. Although the beads maintained their initial integrity throughout the dissolution process in both media, as evident from scanning electron microscopic studies, the faster release in SGF was accounted for higher swelling of the beads in SGF than in SIF. When release data (up to 60%) was fitted in power law expression, the drug release was found to be controlled by diffusion with simultaneous relaxation phenomena.     

Cloning,purification, and characterization of β-galactosidase from <Emphasis Type="Italic">Bacillus licheniformis</Emphasis> DSM 13

The gene encoding homodimeric β-galactosidase (lacA) from Bacillus licheniformis DSM 13 was cloned and overexpressed in Escherichia coli, and the resulting recombinant enzyme was characterized in detail. The optimum temperature and pH of the enzyme, for both o-nitrophenyl-β-d-galactoside (oNPG) and lactose hydrolysis, were 50°C and 6.5, respectively. The recombinant enzyme is stable in the range of pH 5 to 9 at 37°C and over a wide range of temperatures (4–42°C) at pH 6.5 for up to 1 month. The K _m values of LacA for lactose and oNPG are 169 and 13.7 mM, respectively, and it is strongly inhibited by the hydrolysis products, i.e., glucose and galactose. The monovalent ions Na⁺ and K⁺ in the concentration range of 1–100 mM as well as the divalent metal cations Mg²⁺, Mn²⁺, and Ca²⁺ at a concentration of 1 mM slightly activate enzyme activity. This enzyme can be beneficial for application in lactose hydrolysis especially at elevated temperatures due to its pronounced temperature stability; however, the transgalactosylation potential of this enzyme for the production of galacto-oligosaccharides (GOS) from lactose was low, with only 12% GOS (w/w) of total sugars obtained when the initial lactose concentration was 200 g/L.     

Cold acclimation enhances the activity of plasma membrane Ca2+ ATPase in winter rye leaves

Exposure of plant cells and tissues to low or freezing temperatures often lead to uncontrolled and detrimental ion leakage. Therefore, when plants acclimate to low temperatures, processes that control ionic homeostasis are important. Here we characterized H⁺ ATPase and ATP-dependent Ca²⁺ transport activities in isolated plasma membranes of cold-acclimated and non-acclimated winter rye leaves (Secale cereale L. cv. Voima). Cold acclimation resulted in a two-fold higher Ca²⁺ transport activity, significantly different (P = 0.021) from that of non-acclimated rye, whereas only a small increase in H⁺ ATPase activity, measured as ATP hydrolysis, was observed in cold-acclimated compared to non-acclimated preparations. In plasma membranes, extensively washed with EDTA and Brij 58 to remove endogenous calmodulin, Ca²⁺ transport activity increased to about double by calmodulin addition, with both non-acclimated and cold-acclimated material. Uptake of Ca²⁺ was seen within the pHrange analyzed (pH 6–8), with an optimum at pH 7.2 with both materials, and both in the absence and in the presence of calmodulin. The increase in activity of ATP-dependent Ca²⁺ transport in cold-acclimated rye plasma membranes probably reflects the capacity needed to sustain the resting level of cytosolic Ca²⁺ concentration that is characteristic to the cold-acclimated situation.     

Purification of the alkaliphilic xylanases from Myceliophthora sp. IMI 387099 using cellulose-binding domain as an affinity tag

Ten xylanase isoforms produced by Myceliophthora sp. were characterized for their ability to bind to avicel. Three of the xylanases showing differential affinity for avicel were purified by column chromatography. The purified xylanase Xyl IIa, IIb and IIc showed molecular mass of 47, 41 and 30 kDa and pI of ∼3.5, 4.8 and 5.2, respectively. Xyl IIa was optimally active at pH 8.0 and temperature 70 °C, while Xyl IIb and IIc were optimally active at pH 9.0 and 60 °C and 7.0 and 80 °C, respectively. Xyl IIa and Xyl IIb showed higher stability under alkaline conditions (pH 9.0) and retained 80% of the original activity upto 1 h and 3 h respectively, at 50 °C. All three purified iso-xylanases showed enhanced activities in presence of Na⁺, Mg²⁺, Mn²⁺ and K⁺ ions, whereas, Zn²⁺ and Cu²⁺ showed negative effect on Xyl IIa. The activity of Xyl IIa increased in presence of reducing agents DTT and mercaptoethanol, however, SDS showed inhibitory effect. Kinetic studies showed that Xyl IIb and IIc degrade rye arabinoxylan, much more efficiently than oat spelt xylan, whereas, Xyl IIa showed much higher Kcat/Km value for birch wood xylan as compared to oat spelt xylan. The purified xylanases were apparently classified in family 10.     

Biochar application as a tool to decrease soil nitrogen losses (NH3 volatilization,N2O emissions,and N leaching) from croplands: Options and mitigation strength in a global perspective

Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil‐reactive nitrogen (N) to the air and water. However, the extent and spatial variability of biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH₃ volatilization, N₂O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha^?1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha^?1 wood biochar, <40 t ha^?1 straw biochar, or <10 t ha^?1 manure biochar for other soils) could achieve an increase in global crop yields by 222–766 Tg yr^?1 (4%–16% increase), a mitigation of cropland N₂O emissions by 0.19–0.88 Tg N yr^?1 (6%–30% decrease), a decline of cropland N leaching by 3.9–9.2 Tg N yr^?1 (12%–29% decrease), but also a fluctuation of cropland NH₃ volatilization by ?1.9–4.7 Tg N yr^?1 (?12%–31% change). The decreased sum of the three major reactive N losses amount to 1.7–9.4 Tg N yr^?1, which corresponds to 3%–14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions.     

Characterization of novel thermostable dextranase from Thermotoga lettingae TMO

Biochemical properties of a putative thermostable dextranase gene from Thermotoga lettingae TMO were determined in a recombinant protein (TLDex) expressed in Escherichia coli and purified to sevenfold apparent homogeneity. The 64-kDa protein displayed maximum activity at pH 4.3, and enzyme activity was stable from pH 4.3–10. The optimal temperature was 55–60°C during 15 min incubation, and the half-life of the enzyme was 1.5 h at 65°C. The enzyme showed higher activity against α-(1 → 6) glucan and released isomaltose and isomaltotriose as main products from dextran T2000. An unusual kinetic feature of TLDex was the negative cooperative behavior on the reaction of dextran T2000 cleavage. Enzyme activity was not significantly affected by the presence of metal ions, except for the strong inhibited by 1 mM Fe²⁺ and Ag²⁺. TLDex may prove useful as an enzyme for high temperature sugar milling processes.     

Phenothiazine–rhodamine‐based colorimetric and fluorogenic ‘turn‐on' sensor for Zn2+ and bioimaging studies in live cells

A phenothiazine–rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn²⁺ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn²⁺ ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn²⁺ ion binding to PTRH, the λ_em get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn²⁺ ion detection. The PTRH sensor had the lowest detection limit for Zn²⁺, found to be 2.89 × 10^?8 M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.     

Determination of lead(II) in food samples using a functionalized paper-based fluorescent sensor modified by carbon dots

This work discusses surface modification of cellulose paper specimens for compatibility with nitrogen and sulfur co-doped carbon dots (NSCDs) for lead ion sensing. The interaction of carbon dots (CDs) and cellulose fibers was investigated using silane or chitosan-modified cellulose papers. It was found that modified papers could reduce undesirable redistribution of CDs, during paper drying. Also, only chitosan-modified filter paper was suitable for the successful immobilization of NSCDs. The effect of paper type, chitosan amount, pH, and NSCDs concentration was also studied, and a Whatman No. 42 filter paper modified with chitosan (1% w/v), pH 8.0, and an NSCD concentration of 2.5 g L⁻¹ being selected for further studies. The sensor exhibited high selectivity for lead(II) compared with other metal ions because lead(II) resulted in the most significant changes in the emitted light intensity. Variations in NSCDs fluorescence were measured using a fluorescence imaging system. The NSCDs-paper sensor showed a linear relationship between mean fluorescence intensity and lead(II) in the concentration range of 5.00–1.25 × 10² μmol L⁻¹ with a correlation coefficient (R²) of 0.9988 and a detection limit of 4.50 μmol L⁻¹. The suggested method showed satisfying results for lead(II) determination in different samples as a fast and low-cost approach with on-site application.     

Blockade of heavy metals accumulation in Chlorella vulgaris cells by 24-epibrassinolide

This study was conducted on the influence of 24-epibrassinolide (24-epiBL) mixed with varying concentrations of heavy metals (copper, lead, cadmium, zinc) upon the growth and accumulation of these heavy metals in the cell of the alga Chlorella vulgaris Beijerinck (Chlorophyceae). Heavy metals at the concentration of 10^–3 M, alone or mixed with 24-epiBL, showed a lethal effect on C. vulgaris. At metal concentrations of 10^–6–10^–4 M, a combination with 24-epiBL appeared to have a stronger stimulatory effect on a number of cells than a single metal (a stronger inhibitory effect). 24-EpiBL at the concentration of 10^–8 M in combination with heavy metals (in the range 10^–6–10^–4 M) blocked metal accumulation in algal cells. 24-EpiBL has an anti-stress effect on C. vulgaris contaminated by heavy metals. The inhibitory effect on metal accumulation of 24-epiBL mixed with different heavy metals was arranged in the following order: zinc > cadmium > lead > copper. This process is correlated with the stimulation of growth of C. vulgaris. The stimulatory effect of 24-epiBL mixed with heavy metals leading to an increased pH in the medium (5.28–6.20) was significantly higher than the impact due to the increased acidity in the medium due to metals alone (pH 3.10–5.85). Lower pH increased the toxicity of heavy metals in C. vulgaris cells.     

Influence of pH and micellar systems on the sensitized photo‐oxidation of bovine serum albumin

Photosensitized oxidation of bovine serum albumin (BSA), by using perinaphtenone as a sensitizer, has been studied at pH 7.4 and 11. The selected sensitizer does not present ground‐state complexation with BSA and ensures that the mechanism is mediated by O₂(¹△_g). Strong dependence between BSA–O₂(¹△_g) photo‐oxidation and the pH of the medium has been found. The relative oxygen uptake rate (v_? △ O2 ) and the total quenching rate constant (k_t) values are higher at pH 11 than pH 7.4. The enhancement in the alkaline condition is due to conformational changes in the protein and the reactivity of tyrosinate anion with O₂(¹△_g). Even when the tendency with the pH in the presence of sodium dodecyl sulfate (SDS) micelles is similar to that observed in homogeneous media, an increment on the k_t value is detected. This effect may be attributable to the strong interaction of BSA–SDS, which leads to the protein unfolding and could leave more exposed photo‐oxidizable amino acids. A protective effect against the O₂(¹△_g)‐mediated photo‐oxidation was observed in reverse micelles (RMs) of sodium bis(2‐ethylhexyl)sulfosuccinate (AOT) by comparing the k_t values obtained at W = 10 with respect to the one obtain in homogeneous media. The latter could be mainly explained by the modification in the solvent polarity. Also, another important observation was found, the internal pH inside RMs of AOT sensed through tyrosine absorption was independent of the one used for the formation of the water pool. Hence, the k_t values observed at both pH, are quite similar.     

Concentration dependence of luminescence efficiency of Dy3+ ions in strontium zinc phosphate glasses mixed with Pb3O4

In this work we synthesized SrO–ZnO–P₂O₅ glasses mixed with Pb₃O₄ (heavy metal oxide) and doped with different amounts of Dy₂O₃ (0.1 to 1.0 mol%). Subsequently their emission and decay characteristics were investigated as a function of Dy₂O₃ concentration. The emission spectra exhibited three principal emission bands in the visible region corresponding to ⁴F_9/2 → ⁶H_15/2 (482 nm), ⁶H_13/2 (574 nm) and ⁶H_11/2 (663 nm) transitions. With increase in the concentration of Dy₂O₃ (upto 0.8 mol%) a considerable increase in the intensity of these bands was observed and, for further increase, quenching of photoluminescence (PL) output was observed. Using emission spectra, various radiative parameters were evaluated and all these parameters were found to increase with increase in Dy₂O₃ concentration. The Y/B integral emission intensity ratio of Dy³⁺ ions evaluated from these spectra exhibited a decreasing trend with increase in the Dy₂O₃ concentration up to 0.8 mol%. Quenching of luminescence observed in the case of the glasses doped with 1.0 mol% is attributed to clustering of Dy³⁺ ions. The quantitative analysis of these results together with infra‐red (IR) spectral studies indicated that 0.8 mol% is the optimum concentration of Dy³⁺ ions needed to achieve maximum luminescence efficiency. Copyright © 2016 John Wiley & Sons, Ltd.