Effects of Carboxylic Acids on Calcite Formation in the Presence of Mg2+ Ions

The effects of seven carboxylic acids on calcite formation in the presence of Mg2+ ions, whose molar concentration ratio Mg2+/Ca2+ = 0.5 exclusively induced aragonite precipitation in the absence of carboxylic acids, were studied using a double diffusion technique. The presence of carboxylic acids, acrylic acid, maleic acid, tartaric acid, malonic acid, malic acid, succinic acid, and citric acid in the gel medium favored the formation of magnesian calcite relative to the amount of the additives. Induction time and the positions of the first precipitation were measured to analyze the behavior of crystallization based on the equivalency rule. The formation of magnesian calcite was also studied with the help of Avrami's equation (solid-state model for transformation). The results of applying this equation suggested that aragonite transformed into calcite through a solid-to-solid process. The formation of magnesian calcite was interpreted as the following process: aragonite nuclei, formed owing to Mg2+ ions at the initial stage of CaCO3 crystallization, transformed into calcite nuclei through a solid-to-solid process while their growth was inhibited by the adsorption of carboxylic acids. The magnesian calcite crystals grew on crystal seeds of calcite formed from aragonite nuclei. Copyright 1999 Academic Press.     

土壤颗粒表面电场作用下固-液界面Mg~(2+)-K~+与Ca~(2+)-K~+交换动力学的比较研究

通过恒流法研究了不同表面电场作用下Mg2+、Ca2+吸附动力学.结果发现:(1)实验初期阶段是强静电力作用下的零级动力学过程和一定反应时间后的弱静电力作用下的一级动力学过程,且零级速率过程和一级速率过程之间存在明显的转折点;(2)不同电解质构成中Ca2+的吸附速率明显快于Mg2+的,平衡吸附量也大于Mg2+的,且Ca2+在土壤颗粒表面的覆盖度比Mg2+在土壤颗粒表面的覆盖度高;(3)离子的相对有效电荷系数与土壤颗粒表面电场作用的不同是各体系中Ca2+、Mg2+吸附动力学有差别的根本原因;(4)根据离子吸附的理论模型可以分别计算出速率系数、平衡吸附量、离子在土壤颗粒表面的覆盖度以及固定液的体积,这些参数可以定量评估土壤颗粒表面电场对离子吸附动力学的影响.     

土壤颗粒表面电场作用下固-液界面Mg2+-K+与Ca2+-K+交换动力学的比较研究

通过恒流法研究了不同表面电场作用下Mg2+、Ca2+吸附动力学. 结果发现: (1)实验初期阶段是强静电力作用下的零级动力学过程和一定反应时间后的弱静电力作用下的一级动力学过程, 且零级速率过程和一级速率过程之间存在明显的转折点; (2)不同电解质构成中Ca2+的吸附速率明显快于Mg2+的, 平衡吸附量也大于Mg2+的, 且Ca2+在土壤颗粒表面的覆盖度比Mg2+在土壤颗粒表面的覆盖度高; (3)离子的相对有效电荷系数与土壤颗粒表面电场作用的不同是各体系中Ca2+、Mg2+吸附动力学有差别的根本原因; (4)根据离子吸附的理论模型可以分别计算出速率系数、平衡吸附量、离子在土壤颗粒表面的覆盖度以及固定液的体积, 这些参数可以定量评估土壤颗粒表面电场对离子吸附动力学的影响.     

Role of Vitamins B-3 and C in the Fashioning of Granules in UASB Reactor Sludge

Whereas a myriad of possible factors have been reported which effect the formation of granules in a upflow anaerobic sludge blanket (UASB) reactor and influence their properties, there is no study on the effect of vitamins on the granulation of UASB reactor sludge. The present study was undertaken to bridge this gap. It was seen that vitamins helped in better granule formation??as reflected by favorable size distribution, sludge volume index, and settling velocity??compared to controls. The vitamin-spiked reactors also achieved >85?% COD removal efficiency in half the number of days the unspiked reactors took. The vitamin supplements were effective at concentrations????1?mg/l. Hence, their use in expediting granule formation as also in developing better-quality granules appears economically viable.     

Properties of (Mg2 + Ca2+)-ATPase of erythrocyte membranes prepared by different procedures: influence of Mg2+, Ca2+, ATP, and protein activator.

Erythrocyte membranes prepared by three different procedures showed (Mg2+ + Ca2+)-ATPase activities differing in specific activity and in affinity for Ca2+. The (Mg2+ + Ca2+)-ATPase activity of the three preparations was stimulated to different extents by a Ca2+-dependent protein activator isolated from hemolysates. The Ca2+ affinity of the two most active preparations was decreased as the ATP concentration in the assay medium was increased. Lowering the ATP concentration from 2 mM to 2-200 microM or lowering the Mg:ATP ratio to less than one shifted the (Mg2+ + Ca2+)-ATPase activity in stepwise hemolysis membranes from mixed "high" and "low" affinity to a single high Ca2+ affinity. Membranes from which soluble proteins were extracted by EDTA (0.1 mM) in low ionic strength, or membranes prepared by the EDTA (1-10 mM) procedure, did not undergo the shift in the Ca2+ affinity with changes in ATP and MgCl2 concentrations. The EDTA-wash membranes were only weakly activated by the protein activator. It is suggested that the differences in properties of the (Mg2+ + Ca2+)-ATPase prepared by these three procedures reflect differences determined in part by the degree of association of the membrane with a soluble protein activator and changes in the state of the enzyme to a less activatable form.     

Role of Mg2+ and Ca2+ in DNA bending: evidence from an ONIOM-based QM-MM study of a DNA fragment

The binding of hydrated Mg2+ and Ca2+ ions with a DNA fragment containing two phosphate groups, three sugar units, and a G.C base pair is modeled in the anion and dianion states using a three-layer ONIOM approach. A monodentate binding mode was the most stable structure observed for both the ions in the anion model. However, the interactions of Mg2+ and Ca2+ with the dianion model of the DNA fragment gave rise to a large structural deformation at the base pair region, leading to the formation of "ring" structures. In both anion and dianion models, Mg2+-bound structures were considerably more stable than the corresponding Ca2+-bound structures. This feature and the formation of ring structures in the dianion models strongly supported the higher coordination power of the Mg2+ toward DNA systems for its compaction. The charge of the DNA fragment appeared to be crucial in deciding the binding strength as well as the binding mechanism of the metal ions. To the best of our knowledge, this is the first theoretical investigation of the interaction of a comparatively larger DNA model system with the biologically important Mg2+ and Ca2+ ions.     

Studies of polyfunctional O-ligands: Formation and stability of Mg(2+) and Ca(2+) complexes of 1,2,4,5-benzenetetracarboxylic acid in aqueous solution at 25 degrees

The stabilities of the Ca(2+) and Mg(2+) complexes with 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid) were studied potentiometrically, at 25 degrees . The species ML, MHL, MH(2)L, and M(2)L [L = pyromellitate(4-); M = Ca(2+), Mg(2+)] were found to be present in solution (for Mg(2+) the species MH(3)L was also found). The dependence of the formation constants on ionic strength, and the stability trends of the Ca(2+) and Mg(2+) complexes with carboxylate ligands, are discussed.     

Factors governing the substitution of La3+ for Ca2+ and Mg2+ in metalloproteins: a DFT/CDM study

Trivalent lanthanide cations are extensively being used in biochemical experiments to probe various dication-binding sites in proteins; however, the factors governing the binding specificity of lanthanide cations for these binding sites remain unclear. Hence, we have performed systematic studies to evaluate the interactions between La3+ and model Ca2+ - and Mg2+ -binding sites using density functional theory combined with continuum dielectric methods. The calculations reveal the key factors and corresponding physical bases favoring the substitution of trivalent lanthanides for divalent Ca2+ and Mg2+ in holoproteins. Replacing Ca2+ or Mg2+ with La3+ is facilitated by (1) minimizing the solvent exposure and the flexibility of the metal-binding cavity, (2) freeing both carboxylate oxygen atoms of Asp/Glu side chains in the metal-binding site so that they could bind bidentately to La3+, (3) maximizing the number of metal-bound carboxylate groups in buried sites, but minimizing the number of metal-bound carboxylate groups in solvent-exposed sites, and (4) including an Asn/Gln side chain for sites lined with four Asp/Glu side chains. In proteins bound to both Mg2+ and Ca2+, La3+ would prefer to replace Ca2+, as compared to Mg2+. A second Mg2+-binding site with a net positive charge would hamper the Mg2+ --> La3+ exchange, as compared to the respective mononuclear site, although the La3+ substitution of the first native metal is more favorable than the second one. The findings of this work are in accord with available experimental data.     

Single molecular multianalyte (Ca2+, Mg2+) fluorescent probe and applications to bioimaging

Intracellular signal transduction relies on spatial and temporal signal transmitter dynamics. To clarify the correlations of these transmitter molecules, multicolor-imaging has been widely used. However, in the case of applying multiple indicators in a cell, spectral overlap of the indicators prevents accurate quantitative analysis. Moreover, the invasive (toxic) effect, the localization, the metabolism, as well as photobleaching of these indicators complicate the situation. Here, we show that single-molecular multifluorescent probes can overcome these problems. While intracellular calcium plays a critical role as a signal transmitter and magnesium acts as a cofactor in many situations, the correlations between the two cations are now the main issue. We designed and synthesized a Ca2+-Mg2+ responsive multifluorescent probe, KCM-1. KCM-1 shows a spectral blue shift upon complexation to Ca2+ and a red shift to the presence of Mg2+. With data analyzed at different excitation wavelengths, the concentrations of Ca2+ and Mg2+ are simultaneously quantified. Furthermore, by using the AM-ester method, intracellular Ca2+ and Mg2+ concentrations are simultaneously imaged. Such a type of intracellular multiple analyte imaging by a single-molecular multifluorescent probe is successfully demonstrated for the first time.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.     

Modulator binding protein antagonizes activation of (Ca2+ + Mg2+)-ATPase and Ca2+ transport of red blood cell membranes.

Red blood cells contain a protein that activates membrane-bound (Ca2+ + Mg2+)-ATPase and Ca2+ transport. The red blood cell activator protein is similar to a modulator protein that stimulates cyclic AMP phosphodiesterase. Wang and Desai [Journal of Biological Chemistry 252:4175--4184, 1977] described a modulator-binding protein that antagonizes the activation of cyclic AMP phosphodiesterase by modulator protein. In the present work, modulator-binding protein was shown to antagonize the activation of (Ca2+ + Mg2+)-ATPase and Ca2+ transport by red blood cell activator protein. The results further demonstrate the similarity between the activator protein from human red blood cells and the modulator protein from bovine brain.     

尖吻蝮蛇毒抗凝血因子(ACF)含量和钙离子含量的定量测定及钙离子结合位点的初步研究

由紫外光谱法测定蛋白质浓度,用ICP测定Ca含量,从而确定一个ACF分子中含一个钙离子.ACF中分子中除一个高亲和性钙结合位点外,至少还有一个低亲和性钙结合位点,只有当过量钙离子存在时,才可能在低亲和性钙结合位点上进一步结合钙离子.Tb~(3+)具有比Ca~(2+)离子更强的键合ACF能力,能定量结合在ACF中的两个位点上,且能全部取代ACF中Ca~(2+).文中提及的金属离子对ACF的抗凝血活性没有显著的影响.     

Carboxylate binding to be(2+) in proteins and influence of the dielectric environment

To gain insight into the interaction of Be2+ ions with negatively charged protein residues, the free energy changes associated with the replacement of water molecules in the first hydration shell of with one and two acetate anions were computed for the gas phase reactions using ab initio methods at the MP2 and DFT-B3LYP computational levels. Both unidentate and bidentate modes of coordination of the carboxylate group with the Be2+ ion are considered. Continuum dielectric calculations were then performed to estimate the corresponding free energy changes in several environments of varying dielectric strength. Environments with dielectric constants of 2 and 4, which represent a protein interior, and 78, which corresponds to water, were used. It is found that the free energy changes for the substitution reactions decrease in magnitude with increasing dielectric strength, in agreement with similar results reported for Mg2+, Ca2+, and Zn2+ (Dudev et al. J. Phys. Chem. B 2000, 104, 3692). However, unlike Mg2+, Ca2+, and Zn2+, the free energy change for single-anion or concerted two-anion substitution reactions with remains negative and indicates the reactions are still favorable in the high dielectric aqueous environment. It is also found that the unidentate mode of binding is favored over the bidentate mode, and this is attributed, in part, to the introduction of hydrogen bonds between one carboxylate oxygen and a water molecule within the cluster when unidentate binding with Be2+ is involved.     

Preparation of alkaline earth phosphates with sol containing sodium alginate and sodium diphosphate

Magnesium hydrogen phosphate, calcium hydroxyapatite, and strontium hydroxyapatite were successfully prepared from sol consisting of sodium alginate and Na4P2O7 with Mg2+, Ca2+, and Sr2+ in the corresponding nitrates, respectively. It is revealed that the order of the addition of those substrates and the role of sodium alginate are important factors for the preparation of desired phosphate compounds. According to the previous paper on the preparation of calcium hydroxyapatite, sodium alginate was mixed with aqueous Na4P2O7, followed by the addition of the aqueous divalent cations, resulting in the poor formation of the target phosphates. However, as a revised sol-gel technique, sodium alginate was added to the mixture of Na4P2O7 and aqueous Mg2+ and Sr2+, resulting in a rather favorable formation of MgHPO4 and strontium hydroxyapatite, respectively, while the sol thus obtained was stable within a few days. However for aqueous Ca2+, calcium hydroxyapatite could not be obtained through the revised sol-gel technique. In the preparation of magnesium hydrogen phosphate, sodium alginate contributes mainly to the sol formation of the precursor. The ion exchange between Na+ in sodium alginate and aqueous Ca2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na4P2O7 and aqueous Sr2+ afforded strontium hydroxyapatite at the specific ratio of those three substrates. The structure of calcium and strontium phosphates prepared from the revised sol-gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na4P2O7 and the corresponding divalent cations.     

Divalent cation dependent ATPase activities of red blood cell membranes: influence of the oxidation of membrane thiol groups close to each other

An Mg2+-dependent low ATPase activity can be detected in erythrocyte "white membranes," in addition to that of the well known (Ca2+ + Mg2+)-ATPase. The thiol oxidizing agent diamide affects both activities. The oxidation of neighboring thiols seems to leave the mechanism of the (Ca2+ + Mg2+)-ATPase amplification system evoked by Ca2+ largely unaffected. The perturbation caused by diamide in the membranes seems to affect primarily a step of the ATP hydrolysis mechanism that is common to both ATPase activities. The effectiveness of diamide seems to be the same when either Ca2+ and Mg2+, or Mg2+ alone are present during the reagent action. Reduction of disulfide bonds by DTE after diamide treatment restores the (Ca2+ + Mg2+)-ATPase activity but is unable to take the Mg2+-ATPase activity back to the original level. The hypothesis is discussed that the redox state of one (or more than one) couple of --SH close to each other and possibly connected to the active site, may be an important factor in optimizing the efficiency of Ca action on the (Ca2+ + Mg2+)-ATPase.     

Biosorption of Heavy Metal Ions (Cu2+, Mn2+, Zn2+, and Fe3+) from Aqueous Solutions Using Activated Sludge: Comparison of Aerobic Activated Sludge with Anaerobic Activated Sludge

The potential of using two different kinds of air drying of activated sludge (aerobic activated sludge and anaerobic activated sludge) for the removal of Cu²⁺, Mn²⁺, Zn²⁺, and Fe³⁺ from aqueous solutions was assessed. Results indicated that the maximum biosorption occurred at pH?=?5.0 for Cu²⁺, Zn²⁺, and Mn²⁺ and pH?=?3.0 for Fe³⁺. The kinetic parameters of biosorption data were found to be best fitted to the second-order equation. Also, it was found that the best dosage for biosorption was 0.2?g for both aerobic activated sludge and anaerobic activated sludge. The experimental results were fitted well to the Langmuir, Freundlich, and Dubinin?CRadushkevich (D-R) isotherms. The maximum biosorption capacities of Cu²⁺, Mn²⁺, Zn²⁺, and Fe³⁺ for aerobic activated sludge were 65.789, 44.843, 64.935, and 75.756?mg/g, respectively, while they were 59.880, 49.020, 62.500, and 69.444?mg/g for anaerobic activated sludge, respectively. The mean free energy values evaluated from the D-R model indicated that the biosorptions of studied heavy metal ions onto activated sludge were taken place by chemical interaction. The results of this study provided valuable information on the biosorption of heavy metals by activated sludge that may contribute in wastewater treatment.     

[Ru(bpy)_2tpphz]~(2+)与Zn~(2+)形成的双核配合物的荧光性质研究

近年来,钌多吡啶配合物与DNA的作用得到了比较广泛的研究,并且发展了一系列具有特定功能的钌配合物犤1犦。如传统的DNA分子光开关犤Ru(bpy)2dppz犦2+和犤Ru(phen)2dppz犦2+犤2,3犦(bpy=2,2'-联吡啶,phen=1,10-菲咯啉,dppz=二吡啶犤3,2-a:2',3'-c犦吩嗪)。这些配合物与DNA具有较强的结合力,在水溶液中几乎不发光,但在DNA存在下则有强烈荧光发出。这是由于配合物插入DNA的碱基对之后,保护了dppz的吡嗪环上的N原子,使其免受水分子的进攻从而导致配合物荧光的恢复。但是对于大多数的多吡啶钌配合物来讲,由于其自身较强的背景荧光或与DN…     

Theoretical study of interaction of urate with li(+), na(+), k(+), be(2+), mg(2+), and ca(2+) metal cations

The geometries and energetics of complexes of Li(+), Na(+), K(+), Be(2+), Mg(2+), and Ca(2+)metal cations with different possible uric acid anions (urate) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Complexes of urate with Mg(2+), and Ca(2+)metal cations were also optimized at the MP2/6-31+G(d) level. Single point energy calculations were performed at the MP2/6-311++G(d,p) level. The interactions of the metal cations at different nucleophilic sites of various possible urate were considered. It was revealed that metal cations would interact with urate in a bi-coordinate manner. In the gas phase, the most preferred position for the interaction of Li(+), Na(+), and K(+) cations is between the N(3) and O(2) sites, while all divalent cations Be(2+), Mg(2+), and Ca(2+) prefer binding between the N(7) and O(6) sites of the corresponding urate. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi's polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between urate and the metal cations. It was revealed that aqueous solvation would have significant effect on the relative stability of complexes obtained by the interaction of urate with Mg(2+) and Ca(2+)cations. Consequently, several complexes were found to exist in the water solution. The effect of metal cations on different NH and CO stretching vibrational modes of uric acid has also been discussed.     

Modelling peptide-metal dication interactions: formamide-Ca(2+) reactions in the gas phase

The collision induced dissociation of formamide-Ca(2+) complexes produced in the gas phase through nanoelectrospray ionization yields as main products ions [CaOH](+), [HCNH](+), [Ca(NH(2))](+), HCO(+) and [Ca(NH(3))](2+) and possibly [Ca(H(2)O)](2+) and [C,O,Ca](2+), the latter being rather minor. The mechanisms behind these fragmentation processes have been established by analyzing the topology of the potential energy surface by means of B3LYP calculations carried out with a core-correlated cc-pWCVTZ basis set. The Ca(2+) complexes formed by formamide itself and formimidic acid play a fundamental role. The former undergoes a charge separation reaction yielding [Ca(NH(2))](+) + HCO(+), and the latter undergoes the most favorable Coulomb explosion yielding [Ca-OH](+) + [HCNH](+) and is the origin of a multistep mechanism which accounts for the observed loss of water and HCN. Conversely, the other isomer of formamide, amino(hydroxyl)carbene, does not play any significant role in the unimolecular reactivity of the doubly charged molecular cation.     

A confocal study of mechanism of 5-hydroxytryptamino induced intracellular calcium dynamics in cultured rat stomach fundus smooth muscle cells with a new Ca~(2+) indicator STDIn-AM

A new fluorescent Ca2+ indicator STDIn-AM for detecting [Ca2+]i transients in cultured smooth muscle cells is presented. By making a comparison, the difference between STDIn and fluo-3 is discussed in detail. Using the new Ca2+ indicator, the mechanism of 5-hydroxytryptamino (5-HT) induced intracellular calcium dynamics in stomach fundus smooth muscle cells (SFSMC) of rats is investigated. It is shown that in contrast with fluo-3, STDIn is uniformly distributed in the cytosolic compartment but excluded from the nucleus, when it is transfected into cells. This feature makes it a real cytosol Ca2+ indicator and can reflect changes of cytosol [Ca2+] more accurately than that of fluo-3. In addition, STDIn responds to the [Ca2+]i transients more sensitive and faster than fluo-3. The results also show that, the L-type Ca2+channel inhibitor Mn9202 and the PLC inhibitor Compound 48/80 can significantly inhibit the [Ca2+]i elevation induced by 5-HT, while the PKC inhibitor D-Sphingosine can enhance the effect of