Ca2+ selectivity of the sarcoplasmic reticulum Ca2+-ATPase at the enzyme-water interface and in the Ca2+ entrance channel

The sarcoplasmic reticulum (SR) Ca(2+)-ATPase, a P-type transmembrane protein, can transport Ca(2+) from the cytoplasmic to the luminal side over other cations specifically. The proposed Ca(2+) entrance channel, composed of the main-chain carbonyl oxygen and side-chain carboxyl oxygen atoms of the amino acids, opens on the enzyme surface, just above the biphospholipid layer membrane-water interface, where Trp residues are frequently found. In this work, the physicochemical nature of Ca(2+) selectivity over Mg(2+) on the surface of the SR Ca(2+)-ATPase has been investigated using the density functional theory (DFT) method. The selection process can be regarded as the first step of the specificity of the enzyme to transport Ca(2+). Subsequently, the specificity of the entrance channel to conduct Ca(2+) over other cations has also been explored. As revealed by thermodynamic analyses, either the aromatic or the aliphatic amino acid residues distributed on the surface of Ca(2+)-ATPase have a bigger affinity to Mg(2+) than to Ca(2+), resulting in a concentration decrease of free Mg(2+) in the local region. Thus, Ca(2+) can transport into the Ca(2+)-entrance channel more easily. Whereafter, for a small quantity of Mg(2+) entering this channel accompanying the Ca(2+) current, the strong electrostatic interactions between Mg(2+) and the ligands will limit the activity of this metal ion, which facilitates the weakly bonded Ca(2+) passing through the channel at a relatively high rate, as suggested by the "sticky-pore" hypothesis. Furthermore, the corresponding theoretical investigations have demonstrated that the increase of the ligand electronegativity can enhance their discrimination between these two cations effectively.     

Catalytic hydrolysis of esters of 2-hydroxypyridine derivatives for Cu2+ detection

Hydrolysis of activated esters, e.g., picolinic acid and alpha-amino acid esters, in the presence of Cu(2+) salts is a stoichiometric process because products of this reaction bind the catalytic metal ion substantially stronger than starting materials do. Herein we report improved ester substrates, which are cleaved in the presence of catalytic amounts of Cu(2+); 55 turnovers of hydrolysis are observed for the best substrate, acetic acid 2-hydroxypyridine ester. We demonstrate that this reaction can be used for sensitive and selective detection of Cu(2+) by using both absorption and fluorescence spectroscopy.     

Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: effect of citric acid

Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca(2+) and Mg(2+) on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing 10(-3)mol/L of Ca(2+), Mg(2+) and Fe(3+) with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of 5 x 10(-4)mol/L citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of 10(-3)mol/L Ca(2+) and Mg(2+) cations at pH approximately 10, and at pH approximately 8 for Fe(3+). It was found that hydrolyzable metal cations enhanced bitumen-kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal-citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.     

热动力学研究L-抗坏血酸和Cu~2+对过氧化氢酶的协同抑制

在310．15K，pH=7．0的0．1mol·L~(-1)Na_2HPO_4-NaH_2PO_4缓二者同时存 在时，过氧化氢酶催化H_2O_2分解反应的动力学规律。发现L-抗坏血酸和C~(2+)单 独存在时对酶反应没有明显的抑制作用，二者共存时，对反应有非线性抑制作用。 在一定的酶和底物浓度下，L-抗坏血酸和Cu~(2+)不影响率方程的形式，只减小了一级 反应速率常数．酶活性随抑制剂浓度变化关系呈S形曲线．结合实验结果和文献，提出 了一L-抗坏血酸和Cu~(2+)协同抑制过氧化氢酶的可能机理.     

Adsorption of Pb2+, Zn2+, and Cd2+ from waters by amorphous titanium phosphate

In the current study, amorphous titanium phosphate (TiP) was prepared as an adsorbent for heavy metals from waters. Uptake of Pb(2+), Zn(2+), and Cd(2+) onto TiP was assayed by batch tests; a polystyrene-sulfonic acid exchanger D-001 was selected for comparison and Ca(2+) was chosen as a competing cation due to its ubiquitous occurrence in waters. The pH-titration curve of TiP implied that uptake of heavy metals onto TiP is essentially an ion-exchange process. Compared to D-001, TiP exhibits more preferable adsorption toward Pb(2+) over Zn(2+) and Cd(2+) even in the presence of Ca(2+) at different levels. FT-IR analysis of the TiP samples laden with heavy metals indicated that the uptake of Zn(2+) and Cd(2+) ions onto TiP is mainly driven by electrostatic interaction, while that of Pb(2+) ions is possibly dependent upon inner-sphere complex formation, except for the electrostatic interaction. Moreover, uptake of heavy metals onto TiP approaches equilibrium quickly and the exhausted TiP particles could be readily regenerated by HCl solution.     

Coumarin-derived transformable fluorescent sensor for Zn2+

We report a coumarin-derived fluorescent sensor for Zn(2+) termed CTS. CTS shows excellent binding selectivity for Zn(2+) over competing metal ions due to the transformable ability of CTS, that is the displacement of other metal ions by Zn(2+), which induces transformation of chelation from an amide to an imidic acid tautomeric form.     

A facile reduction of Eu3+ to Eu2+ in gadolinium monosulfide nanoparticles using a mixed solvent of oleic acid/hexadecylamine

We prepared GdS:Eu(3+) by simple thermal decomposition under 1-dodecanethiol. A reduction process was observed from Eu(3+) to Eu(2+) when oleic acid and hexadecylamine were injected into GdS:Eu(3+). Under UV excitation, GdS:Eu(3+) showed an intense orange-red emission and GdS:Eu(2+) showed a broad green band.     

Borondipyrromethene-derived Cu2+ sensing chemodosimeter for fast and selective detection

Here, we report a new Cu(2+)-selective fluorescent turn-on probe BODIPY-EP, in which the 2-pyridinecarboxylic acid is connected to a 6-hydroxyindole-based BODIPY platform through an ester linkage. The ester bond of BODIPY-EP is selectively hydrolyzed by the reaction with Cu(2+) under mild and neutral conditions to generate BODIPY-OH, showing strong characteristic fluorescence of BODIPY-OH. The favorable features of BODIPY-EP towards Cu(2+) include fast response, large fluorescence enhancement and high selectivity. We further demonstrated that the membrane-permeable probe reacts with intracellular Cu(2+) and exhibits bright fluorescence in living cells.     

Preparation of an ion-imprinted fiber for the selective removal of Cu2+

A novel Cu(2+)-imprinted fiber (IIF) was prepared by grafting acrylic acid (AA) onto the surface of a polypropylene (PP) fiber and subsequently modified with polyethylenimine (PEI). An examination by infrared spectroscopy and scanning electron microscopy confirmed that the ion-imprinted polymer was successfully introduced onto the surface of a PP fiber. The modification of PP fibers with AA was beneficial to the grafting of PEI onto the fibers. The highest grafting degree of PEI could reach 120 wt % under optimal grafting conditions. This IIF showed excellent tensile and chemical stability in acid solution, which qualified the IIF for practical applications. Besides having a high adsorption capacity for Cu(2+) (120 mg/g), the IIF adsorbent showed a high selectivity for Cu(2+) as compared with that of the non-ion-imprinted fiber (NIF). The dynamic adsorption results indicated that IIF can thoroughly remove Cu(2+) from the solution in a relatively short contact time. The effective treatment volume was about 910 bed volumes. The selectivity coefficient of IIF for Cu(2+) with respect to Zn(2+) could reach 76.4. IIF also has good regeneration performance and could maintain almost the same adsorption capacity for copper ions after 10 adsorption-desorption cycles.     

A new emission band of Eu2+ and its efficient energy transfer to Mn2+ in Sr2Mg3P4O15:Mn2+, Eu2+

Eu(2+) singly and Eu(2+), Mn(2+) co-doped Sr(2)Mg(3)P(4)O(15) exhibit not only the well known blue emission band of Eu(2+) peaking at 448 nm but also a new band at 399 nm in violet. They are attributed to Eu(2+) on different Sr(2+) sites. The Eu(2+) for the violet band can transfer energy to the red emitting Mn(2+) more efficiently than Eu(2+) for the blue band. The new Eu(2+) band could enable Sr(2)Mg(3)P(4)O(15):Mn(2+), Eu(2+) to be a promising phosphor for enriching the red component of white LEDs.     

Theoretical study on the gas-phase acidity of multiple sites of Cu+-adenine and Cu2+-adenine complexes

The acidities of multiple sites in Cu(+)-adenine and Cu(2+)-adenine complexes have been investigated theoretically. To compare, the acidities of adenine (A) and adenine radical cation (A(*+)) have also been included. The results clearly indicate that the acidities of C-H and N-H groups in Cu(+/2+)-adenine are significantly enhanced relative to the neutral adenine. The acidic order for a given site on adenine and adenine derivatives is as follows: Cu(2+)-adenine > A(*+) > Cu(+)-adenine > A. For Cu(+)-adenine and Cu(2+)-adenine, N3-coordination exhibits N9-H acid, and N1- and N7-coordination exhibits N6-H(a) and N6-H(b) acid, respectively. Additionally, it is found that C2-H group is surprisingly acidic in the coordination complexes. Calculations in aqueous solution reveal that our results can be extrapolated to aqueous solution. Analyses of the electronic properties interpret the highest acidity of Cu(2+)-adenine among the adenine derivatives studied. Also, Electrostatic potential calculations of [A(-H(+))](-) and [A(-H(+))](*) indicate that the removal of H(a) or H(b) from the amino group favors the bidentate coordination, which provides a dative bond from the deprotonated N and the original coordination ligand to copper ion besides the electrostatic interaction between them and thereby stabilizes the [A(-H(+))](-)/[A(-H(+))](*). NBO analysis confirms the electrostatic potential result.     

Single molecular colorimetric probe for simultaneous estimation of Cu2+ and Ni2+

The different optical responses in chromogenic sensor stimulated by addition of Cu(2+) (red to blue) and Ni(2+) (red to green) allow simultaneous estimation of Cu(2+) and Ni(2+).     

Colorimetric assay for parallel detection of Cd2+, Ni2+ and Co2+ using peptide-modified gold nanoparticles

A colorimetric assay has been developed for parallel detection of Cd(2+), Ni(2+) and Co(2+) utilizing peptide-modified gold nanoparticles (P-AuNPs) as a sensing element based on its unique surface plasmon resonance properties. The functional peptide ligand, CALNNDHHHHHH, was self-assembled on gold nanoparticles (AuNPs) to produce P-AuNPs probe. The P-AuNPs probe could be used to simultaneously detect and showed different responses to the three ions Cd(2+), Ni(2+) and Co(2+) in an aqueous solution based on the aggregation-induced color change of AuNPs. The method showed good selectivity for Cd(2+), Ni(2+) and Co(2+) over other metal ions, and detection limit as low as 0.05 μM Cd(2+), 0.3 μM Ni(2+) or 2 μM Co(2+). To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA and imidazole were applied to mask Co(2+) and Ni(2+) for detecting Cd(2+), glutathione and EDTA were applied to mask Cd(2+) and Co(2+) for detecting Ni(2+), and glutathione and imidazole were applied to mask Cd(2+) and Ni(2+) for detecting Co(2+). Finally, the simple and cost-effective probe could be successfully applied for simultaneously detecting Cd(2+), Ni(2+), and Co(2+) in river water. Because this novel P-AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies, the sensing system shows potential application in the developing region for monitoring water quality.     

Molecular view of the anomalous acidities of Sn2+, Pb2+, and Hg2+

Experimental results taken from both the condensed and gaseous phase show that, when associated with water, the three dications Sn(2+), Pb(2+), and Hg(2+) exhibit a facile proton-transfer reaction. In the gas phase, no stable [M.(H(2)O)(n)](2+) ions are observed; but instead the cations appear to undergo rapid hydrolysis to give ions of the form M(+)OH(H(2)O)(n-1). A series of ab initio calculations have been undertaken on the structures and proton-transfer reaction profiles associated with the complexes [M.(H(2)O)(2,4)](2+), where M is one of Sn, Pb, Hg, and Ca. The latter has been used as a reference point both in terms of comparisons with previous calculations, and the fact that Ca(2+) is a very weak acid. The calculations show that for Sn(2+), Pb(2+), and Hg(2+), the only barriers to proton transfer are those associated with the movement of water molecules. In the gas phase, these barriers could be overcome through energy gained during ion formation, and in the condensed phase the thermal motion of water molecules would be sufficient. In contrast, the calculations show that for Ca(2+) it is the proton-transfer step that provides the most significant reaction barrier. Proton transfer in Sn(2+) and Pb(2+) is further assisted by distortions in the geometries of [M.(H(2)O)(2,4)](2+) complexes due to voids created by the 5s(2) (6s(2)) inert lone pair. For Hg(2+), ease of proton transfer is derived partly from the high degree of covalent bonding found in both the reactants and products.     

A 1,8-naphthyridine-based fluorescent chemodosimeter for the rapid detection of Zn2+ and Cu2+

A novel fluorescent chemodosimeter based on 1,8-naphthyridine exhibits high selectivity to Zn(2+) and Cu(2+). When 1-(7-acetamino-1,8-naphthyridyl)-2-(6-diacetaminopyridyl)ethene was mixed with CuCl2, hydrolysis of the acetamino group catalyzed by Cu(2+) complex was first observed. Resulting from coordination and hydrolysis catalyzed by the corresponding complex of Zn(2+) or Cu(2+), the highly effective fluorescent detection of Zn(2+) and Cu(2+) is realized with Zn(2+)-selective dual-emission and Cu(2+)-selective ON-OFF behavior.     

Preparation of a [Ru(bpy)2(dppz)]2+-intercalated DNA cast film using a self-standing method and its luminescence tuning by Cu2+ ions and EDTA

In this correspondence, we report on the first preparation of [Ru(bpy)(2)(dppz)](2+)-intercalated (bpy = 2,2'-bipyridine; dppz = dipyrido[3,2-a:2',3'-c]phenazine) DNA films on an indium-tin oxide surface via a solution-based self-standing strategy, carried out by the direct mixing of aqueous solutions of both anionic DNA and cationic metallointercalator at a molar ratio of 5:6. The luminescence of a [Ru(bpy)(2)(dppz)](2+)-intercalated DNA cast film is studied and found to show excellent tunable characteristics by Cu(2+) ions and ethylenediaminetetraacetic acid addition.     

Development of a borondipyrromethene-based Zn2+ fluorescent probe: solvent effects on modulation sensing ability

A borondipyrromethene-based Zn(2+) fluorescent probe BODPAQ was designed and synthesized. The chelators in BODPAQ, 2,2'-dipicolylamine (DPA) and 8-aminoquinoline (AQ), coordinate to Zn(2+) in a synergic manner. As a result, BODPAQ displays high Zn(2+) selectivity with a dramatic enhanced emission accompanied by a notable hypsochromic shift due to the binary inhibition effect of PET and ICT mechanisms, enabling the detection of Zn(2+) by both ratiometric and normal turn-on fluorescence methods in acetonitrile. Interestingly, the sensitivity of BODPAQ towards Zn(2+) changes upon varying the compositions of buffer solutions. In 3-morpholinopropanesulfonic acid (MOPS) buffer aqueous solution (50% CH(3)CN), BODPAQ displays the highest sensitivity for Zn(2+), while in citrate-phosphate buffer, BODPAQ shows no response to Zn(2+).     

Porphyrin-based multi-signal chemosensors for Pb2+ and Cu2+

Two metal-free tetra(aryl)porphyrin derivatives modified by one and four N,N-bis(2-pyridylmethyl)amino group(s), namely porphyrin-1-DPA (1) and porphyrin-4-DPA (2) respectively, have been designed, synthesized, and characterized. Binding with Pb(2+) induces a significant change in their solution color and in the ratio of two absorption/fluorescence signal peaks, rendering them the first example of porphyrin-based triple-signal optical sensors for Pb(2+). Their dual-mode Cu(2+)-selective sensing properties via either the porphyrin fluorescence ON-OFF mechanism or metal displacement from the 1-Pb(2+) complex that results in a triple-signal change clearly reveals their potential application as excellent and versatile sensors.     

Removal of Cu2+ from aqueous solution by chitosan-coated magnetic nanoparticles modified with alpha-ketoglutaric acid

Chitosan-coated magnetic nanoparticles (CCMNPs), modified with a biodegradable and eco-friendly biologic reagent, alpha-ketoglutaric acid (alpha-KA), was used as a magnetic nanoadsorbent to remove toxic Cu(2+) ions from aqueous solution. The prepared magnetic nanoadsorbents were characterized by FTIR, TEM, VSM, XRD, and EDS. Factors influencing the adsorption of Cu(2+), e.g., initial metal concentration, initial pH, contact time and adsorbent concentration were investigated. TEM images show that the dimension of multidispersed circular particles is about 30 nm and no marked aggregation occurs. VSM patterns indicate superparamagnetic properties of magnetic nanoadsorbents. EDS pictures confirm the presence of the Cu(2+) on the surface of magnetic nanoadsorbents. Equilibrium studies show that Cu(2+) adsorption data follow Langmuir model. The maximum adsorption capacity (q(max)) for Cu(2+) ions was estimated to be 96.15 mg/g, which was higher than that of pure CCMNPs. The desorption data show no significant desorption hysteresis occurred. In addition, the high stability and recovery capacity of the chitosan-coated magnetic nanoparticles modified with alpha-ketoglutaric acid (alpha-KA-CCMNPs) suggest that these novel magnetic nanoadsorbents have potential applications for removing Cu(2+) from wastewater.