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1.
The thermodynamic stability constants and thermodynamic parameters for the complexation reaction of Be2+, Mg2+ and Ca2+ with 3-hydroxy-2-naphthoic acid have been determined pH metrically in a 70% v/v dioxane-water medium in the presence of potassium nitrate. The study showed the formation 1:1 and 1:2 complexes of Be2+, Mg2+ and 1:1 complex of Ca2+ with 3-hydroxy-2-naphthoic acid. The order of overall stability is Be2+>Mg2+>Ca2+.  相似文献   

2.
Responsive or smart magnetic resonance imaging (MRI) contrast agents are molecular sensors that alter the MRI signal upon changes in a particular parameter in their microenvironment. Consequently, they could be exploited for visualization of various biochemical events that take place at molecular and cellular levels. In this study, a set of dual‐frequency calcium‐responsive MRI agents are reported. These are paramagnetic, fluorine‐containing complexes that produce remarkably high MRI signal changes at the 1H and 19F frequencies at varying Ca2+ concentrations. The nature of the processes triggered by Ca2+ was revealed, allowing a better understanding of these complex systems and their further improvement. The findings indicate that these double‐frequency tracers hold great promise for development of novel functional MRI methods.  相似文献   

3.
Optimum geometries and stabilization energies are determined for complexes of H2O, NH3, CH4, C2H4, CO, and N2 with metal cations including Li+, Na+, K+, Rb+, Be2+, Mg2+, Ca2+, Zn2+, and Al3+, for the complex (HO)2PO 2 ...Mg2+ and for the complexes of water with F, Cl, and Br by SCF calculations employing the MINI-1 minimal gaussian basis sets. The Boys-Bernardi method was used to evaluate the superposition error. Comparison with the extended basis set results revealed that the MINI-1 set gives uniformly good results for a broad variety of ionic complexes and therefore should be preferred to other small basis sets.  相似文献   

4.
The complex formation constants of polyacrylic (PAA) ligands (1.4≤log N≤2.4, N=number of monomer units) with calcium and magnesium ions were determined in different ionic media at different ionic strengths, 0≤I≤1 mol l−1, at t=25 °C. Experimental pH-metric data in the presence of Ca2+ or Mg2+ were firstly analysed in terms of apparent protonation constants, log KH*, using the “three parameter model” proposed by Högfeldt; differences in log KH*, determined in different ionic media, were interpreted in terms of complex species formation. The only species present in the system M-PAA (M=Ca2+ or Mg2+) is ML2: attempts to find species of different stoichiometry were unsuccessful. The stability dependence of this species on ionic strength, on the degree of neutralisation (α) and on PAA molecular weight is discussed using empirical equations. The formation constant, log β2, is significantly higher for Ca2+ than for Mg2+: at I=0.1 mol l−1 (NaCl), log N=1.8 and α=0.5, log β2Ca=4.43 and log β2Mg=4.24. The formation of polyacrylate-alkaline earth metal complexes is discussed in the light of sequestering effects in natural waters.  相似文献   

5.
The stoichiometry of the interaction of Ca2+ with sodium triphosphate was determined using a Ca2+ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca2+ and P3O5?10 is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O?310 and Ca2P3O?10 in aqueous solution.  相似文献   

6.
From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ca2+ (aq)+1·Sr2+ (nb) ⇆ 1·Ca2+ (nb) + Sr2+ (aq) taking place in the two-phase water-nitrobenzene system (1 = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (Ca2+, 1·Sr2+) = 2.4±0.1. Further, the stability constant of the valinomycin-calcium complex (abbrev. 1·Ca2+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β nb (1·Ca2+) = 8.3±0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Ca2+·2H2O complex species was predicted. In this complex, the “central” Ca2+ cation is bound by strong bonds to two oxygen atoms of the respective water molecules and to four ester carbonyl oxygens of the parent valinomycin ligand 1. Finally, the calculated binding energy of the considered complex 1·Ca2+·2H2O is −319.2 kcal/mol, which confirms the relatively high stability of this cationic complex species.  相似文献   

7.
Complete conformational analysis of chelate complex of oubaine molecule with Ca2+ in 1:1 stoichiometry is carried out. Complete ab initio optimization of geometric parameters of all possible structures of the complexes is performed in the framework of restricted Hartree-Fock method with 6–31G* basis using GAMESS program. Influence of the complex formation on the steric structure and electronic structure of oubaine molecule is analyzed. Oubaine molecule is found capable of binding Ca2+ by two modes. Mechanism of binding of oubaine molecule with transductor site of Na+,K+-ATPhase is proposed: ligand-receptor interaction is assumed to be realized in account of formation of trial complex oubaine-Ca2+-Na+,K+-ATPhase, with main contribution to the interaction energy of ion-ion bonds formation between Ca2+ and nucleophilic functional groups in the composition of the mentioned binding site of Na+,K+-ATPhase.  相似文献   

8.
The magnetic environments of Cu2+ doped Na+ complex have been identified by electron paramagnetic resonance (EPR) technique. The angular variation of the EPR spectra has shown that two different Cu2+ complexes are located in different chemical environments, and each environment contains one magnetic Cu2+ site occupying substantial positions in the lattice and showing very high angular dependence. The principal g, and the hyperfine structure parameter (A) values of two sets of Cu2+ complex groups are determined. The covalency parameter, mixing coefficients and Fermi-contact term of the complex are obtained, and the ground state wave function of the Cu2+ ion in the lattice has been constructed.  相似文献   

9.
10.
We have investigated the presence of foreign ions into the bulk structure and the external surfaces of aragonite using periodic ab-initio methods. Four cations isovalent to Ca2+ were studied: Mg2+, Sr2+, Ba2+ and Zn2+. The calculations were performed at structures (bulk, surface) that contain four and eight CaCO3 units. Our results, at the Hartree-Fock level, show that the incorporation of those ions into aragonite depends strongly on their size. Mg2+ and Zn2+, due to their smaller size, can substitute Ca2+ ions in the crystal lattice while the incorporation of Sr2+ and Ba2+ into aragonite is energetically less favoured. Examination of the [011], [110] and [001] surfaces of aragonite revealed that the surface incorporation reduces the energetic cost for the larger ions. These systems provide challenging examples for most shape analysis methods applied in Mathematical Chemistry.  相似文献   

11.
For M?H2O (M = Mg, Mg+, Mg2+, Ca, Ca+, Ca2+) various energy contributions (first-order, induction and charge-transfer, dispersion) are compared. Near the minimum, stability due to the first-order energy decreases and that due to dispersion increases from M2+ to M0. For M2+, dispersion represents only 1–7% of the total energy; it may reach 25% with M+ and is largely responsible for stability of the neutral complex.  相似文献   

12.
For MH2O (M = Mg, Mg+, Mg2+, Ca, Ca+, Ca2+) various energy contributions (first-order, induction and charge-transfer, dispersion) are compared. Near the minimum, stability due to the first-order energy decreases and that due to dispersion increases from M2+ to M0. For M2+, dispersion represents only 1–7% of the total energy; it may reach 25% with M+ and is largely responsible for stability of the neutral complex.  相似文献   

13.
Valinomycin is a well-known potassium-selective ion carrier, but the nature of its direct interaction with calcium ion, another biologically important cation, is also of considerable interest. We have determined the first crystal structure of a valinomycin–calcium complex, which crystallises exclusively as a 1:2 valinomycin:Ca2+ complex, [VCa2(OTf)2(H2O)2]2+ in the solid state (V = valinomycin, OTf = triflate). Along with the 1:2 complex, the solution phase 1:1 and 2:1 complexes have been characterised in acetonitrile by 1H NMR and UV–Vis titration experiments. The molar absorptivity curves and binding equilibrium constants for these complexes have been determined by the global analysis of the UV–Vis titration data using the program SIVVU?.  相似文献   

14.
Our electrospray ionization-ion funnel-rf hexapole (ESI-IF-6P) source is designed to produce ions for threshold collision-induced dissociation (TCID) studies in a guided ion beam mass spectrometer. This ion source forms an initial distribution of Ca2+(H2O) x ions where x is 6–9. A new in-source fragmentation technique within the hexapole ion guide of the source is described, which is easy to implement and of modest machining and electrical costs, and is able to generate smaller Ca2+(H2O) x complexes, where x=2–5. Fragmentation is achieved by biasing an assembly of six 0.25 in. long electrodes that are inserted between the hexapole rods. The assembly is positioned in the high-pressure region of the source such that newly formed Ca2+(H2O) x ions undergo enough collisions to become thermalized, as verified by TCID studies. From the initial distribution of ions, fragmentation proceeds along the lowest energy pathway, which corresponds to sequential water loss for most complexes. However, the Ca2+(H2O) complex cannot be formed using this method because charge separation into CaOH+ and H3O+ becomes the lowest energy pathway from the Ca2+(H2O)2 complex. Therefore, this fragmentation technique can be used to identify the critical size complex for M2+(H2O) x systems, which we define as the complex size (x) at which charge separation becomes a lower energy pathway compared with simple ligand loss.  相似文献   

15.
Atrazine, a pesticide belonging to the s‐triazine family, is one of the most employed pesticides. Due to its negative impact on the environment, it has been forbidden within the European Union since 2004 but remains abundant in soils. For these reasons, its behavior in soils and water at the atomic scale is of great interest. In this article, we have investigated, using DFT, the adsorption of atrazine onto two different clay surfaces: a pyrophyllite clay and an Mg‐substituted clay named montmorillonite, with Ca2+ compensating cations on its surface. The calculations show that the atrazine molecule is physisorbed on the pyrophyllite surface, evidencing the necessity to use dispersion‐corrected computational methods. The adsorption energies of atrazine on montmorillonite are two to three times larger than on pyrophyllite, depending on the adsorption pattern. The computed adsorption energy is of about −30 kcal mol−1 for the two most stable montmorillonite‐atrazine studied isomers. For these complexes, the large adsorption energy is related to the strong interaction between the chlorine atom of the atrazine molecule and one of the Ca2+ compensating cations of the clay surface. The structural modifications induced by the adsorption are localized: for the surface, close to substitutions and particularly below the Ca2+ cations; in the molecule, around the chlorine atom when Ca2+ interacts strongly with this basic site in a monodentate mode. This study shows the important role of the alkaline earth cations on the adsorption of atrazine on clays, suggesting that the atrazine pesticide retention will be significant in Ca2+‐montmorillonite clays. © 2016 Wiley Periodicals, Inc.  相似文献   

16.
The photophysics of the complex forming reaction between Quin-2 and Ca2+ were investigated using steady-state and time-resolved fluorescence measurements. The fluorescence decay traces were analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution with EGTA as Ca2+ buffer: k01= 8.6 times 108 s?1, k21= 1 times 1011M?1 s?1, k02= 8.8 times 107 s?1, k12= 4 times 104 s?1. k01 and k02 denote the respective deactivation rate constants of the Ca2+ free and bound forms of Quin-2 in the excited state. The constant k21 represents the second-order rate constant of binding of Ca2+ and Quin-2 in the excited state while k12 is the first-order rate constant of dissociation of the excited Ca2+:Quin-2 complex. From the estimated values of k12 and k21 the dissociation constant Kd* in the excited state was calculated. It was found that pKd* (6.4) is slightly smaller than pKd (7.2). There was no interference of the excited-state complex forming reaction with the determination of Kd. Intracellular Ca2+ concentrations can thus accurately be determined from fluorometric measurements using Quin-2 as Ca2+ indicator.  相似文献   

17.
The inclusion complex of 2-hydroxy-1-naphthoic acid (2H1NA) with β-cyclodextrin (β-CD) has been investigated using UV-visible and fluorescence spectral techniques in liquid states, FTIR, NMR, XRD and SEM techniques in solid state, molecular docking techniques in virtual states. The binding constants of for the formation of 1:1 2H1NA:β-CD inclusion complex is estimated by UV-visible and fluorescence spectral techniques. The chemosensory power of 2H1NA:β-CD complex was investigated thoroughly for various metal cations and we found the emission of complex showed a drastic increase in the intensity for Ag+. Competition experiments of 2H1NA:β-CD complex with Ag+ in presence of other metal ions (Na+, K+, Hg+, Al2+, Ca2+, Ba2+, Cd2+, Co2+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+, Sn2+, Ti2+, Zn2+, Cr3+, Fe3+) showed that no significant variation was found in the fluoresce intensity of 2H1NA:β-CD complex upon adding all other cations. The linearity range, LOD and LOQ are determined from the selectivity and sensitivity studies for Ag+. Our result suggests that the 2H1NA:β-CD inclusion complex would be promising material for developing solid state sensory device for sensing Ag+.  相似文献   

18.
Analytical intermolecular potentials for the Fe+?H2O and Feo?H2O systems have been determined from ab initio calculations. Interaction energies for a lot of points along the two potential energy surfaces were calculated using Huzinga's MINI ?2 basis set. The results obtained were fitted to an analytical function containing 11 adjustable parameters that we have already used with success for the Fe2+?H2O system. The goodness of the generated intermolecular potentials is discussed.  相似文献   

19.
20.
在B3LYP/6-311++G**水平上用极化连续介质模型(PCM)系统研究了金属离子(M+/2+=Na+,K+,Ca2+,Mg2+,Zn2+)和十三种鸟嘌呤异构体形成的配合物GnxM+/2+(n为鸟嘌呤异构体的编号,x表示M+/2+与鸟嘌呤异构体的结合位点)在气(g)液(a)两相中的稳定性顺序.着重探讨了液相中配合物的稳定性差异,并且从溶质-溶剂效应、结合能、形变能及异构体的相对能量等几个方面分析了造成稳定顺序发生变化的原因.报道了溶液中这五种金属离子与鸟嘌呤异构体结合形成的六种基态配合物:aG1N2,N3Na+,aG1N2,N3K+,aG1O6,N7Ca2+,aG1N2,N3Mg2+(aG1O6,N7Mg2+),aG2N3,N9Zn2+.可以看出,除了在Zn2+配合物中鸟嘌呤异构体为G2外,构成其余四种金属离子配合物的鸟嘌呤异构体都是G1,但结合位点不同.同时对气相中各类配合物稳定性也进行了系统的排序,并报道了几种较稳定的配合物,如:gG3N1,O6K+,gG5N1,O6K+,gG3N1,O6Ca2+/Mg2+,gG4O6,N7Ca2+/Mg2+.  相似文献   

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