Metal Ions Drive Thermodynamics and Photochemistry of the Bis(styryl) Macrocyclic Tweezer

UV/Vis and NMR spectroscopy were used for the structural elucidation and thermodynamic and photochemical studies of the metal‐coordinated crown‐containing macrocyclic tweezer (E,E)‐ 1 . The bis(styryl) tweezer (E,E)‐ 1 formed two types of complexes with magnesium(II): a 1:1 intramolecular asymmetric sandwich complex [(E,E)‐ 1 ]?Mg²⁺ and a 1:2 complex [(E,E)‐ 1 ]?(Mg²⁺)₂. In the former case, there is direct cation intramolecular exchange (0.299 s^?1, ΔG^≠=69.4 kJ mol^?1) between two parts of the bis(styryl) tweezer (E,E)‐ 1 . Addition of barium(II) to the bis(styryl) tweezer (E,E)‐ 1 led to an intramolecular centrosymmetric sandwich 1:1 complex [(E,E)‐ 1 ]?Ba²⁺. Irradiation of [(E,E)‐ 1 ]?Ba²⁺ afforded reversible intramolecular [2π+2π] photocyclization with excellent stereoselectivity and quantitative yield. In contrast, irradiation of [(E,E)‐ 1 ]?(Mg²⁺)₂ resulted in reversible stepwise E,Z‐isomerization.     

A new sulfonamide derivative as magnesium ion receptor: N-tosyl-2,6-diisopropyl-4-(2,3-dimethoxylbenzoylamide)aniline

N-Tosyl-2,6-diisopropyl-4-(2,3-dimethoxylbenzoylamide)aniline (1) has been synthesized and its metal ion (Na⁺, K⁺, Ca²⁺, Mg²⁺) coordinating properties investigated by FT-IR, ESI-MS, and ¹H NMR methods. Among the tested metal ions, the overall stability constant (log K) for Mg²⁺ (6.89) is the highest (Na⁺, 5.64; K⁺, 5.43; Ca²⁺, 5.51) in 10% water/THF at 25.0 ± 0.5 °C determined by UV-vis spectroscopy, indicating that 1 is a potent ionophore for Mg²⁺ ion.     

Cation exchange behaviour of mercury (II) on Dowex 50W-X8

Summary Quantitative studies are reported on the behaviour of mercury at milligram level, using cation exchange resin Dowex 50W-X8. Various eluants such as nitric acid, hydrochloric acid, sulphuric acid, ammonium acetate, sodium nitrate solutions, sodium nitrate-nitric acid mixtures, ammonium acetate-acetic acid mixture are used for column operation. The elution constants are evaluated. Mercury(II) is separated from different cations, i.e., Ca²⁺, Ba²⁺, Sr²⁺, Mg²⁺, Fe³⁺, Al³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cu²⁺ by selective elution.

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Zusammenfassung Das Verhalten von mg-Mengen Quecksilber am Kationenaustauscher Dowex 50W-X8 wird quantitativ untersucht. Dabei werden folgende Eluierungsmittel benutzt: Salpetersäure, Salzsäure, Schwefelsäure, Lösungen von Ammoniumacetat und Natriumnitrat sowie die Gemische Salpetersäure-Natriumnitrat und Essigsäure-Ammoniumacetat. Die Elutionskonstanten werden berechnet. Durch selektive Eluierung kann Quecksilber von mehreren Kationen (Ca²⁺, Ba²⁺, Sr²⁺, Mg²⁺, Fe³⁺, Al³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cu²⁺) getrennt werden.

     

H NMR study of interparticle interactions in the system rare-earth element-acetic acid-diamagnetic salt

Complexation of acetic acid in 5.0 M NaNO₃ at 298 K with yttrium-group rare-earth ions (Dy³⁺, Er³⁺, Tm³⁺, Yb³⁺) in the absence and in the presence of Mg²⁺ ions was studied by ¹H NMR spectroscopy in combination with mathematical simulation of complex equilibria. In the presence of Mg²⁺, the stability constants of monoacetate complexes of rare-earth ions decrease relative to the Mg-free systems.     

Effect of ionic charge on energy contributions to the interaction of an ion with a polar molecule: ab initio calculations for MH2O (M = Mg, Mg, Mg, Ca, Ca, Ca)

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.     

Cation Complexation by a Lower Rim Calix(4)arene Derivative: Structural,Electrochemical and Thermodynamic Studies

The synthesis and characterization (¹H and ¹³C NMR) of a partially substituted lower rim p-tert-butylcalix(4)arene, namely, 5,11,17,23-tetra-4-tert-butyl-25,27-bis(diethylphosphate amino)ethoxy-26,28-dihydroxycalix[4]arene (1), are reported. The solution thermodynamics of the ligand in a variety of solvents at 298.15?K was investigated through solubility (hence standard Gibbs energy of solution) measurements while the calorimetric technique was used to derive the standard solution enthalpy. These data were used to calculate the standard entropy of solution. An enthalpy–entropy compensation effect is shown and, as a result, slight variations are observed in the transfer Gibbs energies of this ligand from the reference to other solvents. ¹H NMR, conductance and calorimetric measurements were carried out to establish the degree of interaction of the ligand with univalent (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ and Ag⁺) and bivalent (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, Zn²⁺) cations in acetonitrile, methanol, N,N-dimethylformamide and propylene carbonate. No complexation was found between this ligand and univalent cations in these solvents. As far as the bivalent cations are concerned, interaction between 1 and these cations was found only in acetonitrile. The versatile behaviour of this ligand with bivalent cations in this solvent is reflected by the formation of complexes of different stoichiometry. Thus the interaction of 1 with alkaline-earth (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) and Pb²⁺ metal cations leads to the formation of 1:2 (cation:ligand) complexes. However, for other bivalent metal cations (Cu²⁺, Zn²⁺, Cd²⁺ and Hg²⁺) the complex stoichiometry was found to be 1:1. The results are discussed in terms of the key role played by acetonitrile in processes involving calix[4]arene derivatives.     

Effect of ionic charge on energy contributions to the interaction of an ion with a polar molecule: ab initio calculations for M⋯H2O (M = Mg,Mg+, Mg2+, Ca,Ca+, Ca2+)

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.     

Silver selective benzimidazol-2(1H)-one based,sulphur-containing podands

Podands based on benzimidazol-2(1H)-one, containing S and terminal NH₂ groups, selectively transport and extract silver picrate over Mg²⁺, Ca²⁺, Sr²⁺, Ph²⁺ and Tl⁺ picrates.     

The mechanism of electroreduction of nitrobenzene and 3-nitropyridine in DMF in the presence of divalent cations

The differences in electrochemical behaviour of nitrobenzene and 3-nitropyridine connected with a change of supporting electrolyte are discussed. It is shown that in the presence of alkaline earch metal cations a deposit of composition (NB^?. Me²⁺) is formed at the electrode surface. The cations: Ba²⁺, Ca²⁺ and Mg²⁺ cause the instability of the nitrobenzene radical anion formed in the first electroreduction step. It was found that in the presence of Ba²⁺ and Ca²⁺ the NOB/NO^?. couple is stabilized.     

Theoretical evaluation of the possibility of hydrogen release during the thermal activation of hydrated magnesium oxide surfaces

The hydrated MgO surface has been simulated by the linear atomic chain (MgOHV″_MgHOMg)²⁺ and the total energy of this system has been evaluated ab initio as a function of the HH (or OH) distance. A symmetrical motion of both hydrogen nuclei with respect to the central Mg²⁺ vacancy was assumed. Two potential minima are found which correspond to systems that can be formally described as (2Mg²⁺, 2OH^?) (I, lower energy system) and (2Mg²⁺, 2O^?, H₂) (II, lying 140.9 kcal above I). These theoretical calculations show that the reaction 2OH^? → 2O^? + H₂ will occur on MgO with a thermal activation energy of about 145.0 kcal, while the chemisorption of hydrogen as hydrexyls on O^? sites has a very low activation energy (4.1 kcal).     

Calculation of the equilibrium constants and binding cooperativity parameters of ammonia with Group II metal cations in solution

The matrix model was used to analyze the distribution diagrams and formation functions of ammonia complexes [M(NH₃) _n ]²⁺ (n = 0−4) of Group II metal ions (Mg²⁺, Ca²⁺, Zn²⁺, Cd²⁺, and Hg²⁺) in solution. Intrinsic binding constants of the ligand (K _in) and mutual influence corrections (ω) for complex formation with aqua ions in solution were calculated. The equilibrium constants were calculated by the matrix method. The coordination sphere of Mg²⁺, Ca²⁺, and Zn²⁺ by ammonia in a cooperative manner; with Cd²⁺ and Hg²⁺, both cooperative and anticooperative binding occur concurrently. Possibilities for differentiation between tetrahedral and square planar coordination polyhedra on the basis of the characteristic features of ligand binding, determined by the matrix model, are discussed.     

Spectrophotometric and voltammetric characterization of a novel selective electroactive chemosensor for Mg2+

A novel azocalix[4]arene derivative, 5,11,17,23-tetrakis[(acetophenone)azo]-25,26,27,28-tetrahydroxycalix[4]arene (APC4), containing acetophenone azo groups at the upper rim was synthesized as a chemosensor. Its binding and sensing properties with alkali and alkaline earth metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) were investigated by UV-vis spectrophotometric and voltammetric techniques. The stoichiometric ratio and the association constant were determined spectrophotometrically as 1:1 and (1.94±0.31)×10⁵ L mol^?1 for the complex between Mg²⁺ and the chemosensor, respectively. Moreover, it was shown that the interaction between Mg²⁺ and the APC4 occurred by means of the phenol groups at the lower rim by voltammetric methods. The results of spectrophotometric and voltammetric experiments showed that the chromogenic chemosensor has high selectivity towards Mg²⁺ among the other used metal ions, especially the interfering Ca²⁺ ion.      

A Thermodynamic Study Between 18-Crown-6 with Mg2+, Ca2+, Sr2+and Ba2+ Cations in Water–Methanol and Water–Ethanol Binary Mixtures Using The Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations with the macrocyclic ligand, 18-Crown-6 (l8C6) in water–methanol (MeOH) binary systems as well as the complexation reactions between Ca²⁺ and Sr²⁺ cations with 18C6 in water–ethanol (EtOH) binary mixtures have been studied at different temperatures using conductometric method. The conductance data show that the stoichiometry of all the complexes is 1:1. It was found that the stability of 18C6 complexes with Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations is sensitive to solvent composition and in all cases, a non-linear behaviour was observed for the variation of log K _f of the complexes versus the composition of the mixed solvents. In some cases, the stability order is changed with changing the composition of the mixed solvents. The selectivity order of 18C6 for the metal cations in pure methanol is: Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺. The values of thermodynamic parameters (Δ H _c ° and Δ S _c °) for formation of 18C6–Mg²⁺, 18C6–Ca²⁺, 18C6–Sr²⁺ and 18C6–Ba²⁺complexes were obtained from temperature dependence of the stability constants. The obtained results show that the values of (Δ H _c ° and Δ S _c °) for formation of these complexes are quite sensitive to the nature and composition of the mixed solvent, but they do not vary monotonically with the solvent composition.This revised version was published online in July 2005 with a corrected issue number.     

Solid‐state nuclear magnetic resonance investigation of neurosteroid compounds and magnesium interactions

The neurosteroid trans‐dehydroandrosterone (DHEA) and its analogs with slightly different modifications in the side chain attached to C17, that is, (3S)‐acetoxypregn‐5‐en‐20‐one ( 1 ) and (3S,20R)‐acetoxypregn‐5‐en‐20‐ol ( 2 ), have been synthesized to investigate DHEA–cation interactions. In this study, we applied solid‐state ¹H/¹³C cross‐polarization/magic‐angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy to a series of DHEA analog/Mg²⁺ mixtures at different Mg²⁺ concentrations. The high‐resolution ¹³C NMR spectra of 1 /Mg²⁺ mixtures exhibit two distinct ¹³C spectral patterns, one attributable to 1 free from Mg²⁺, and the other attributable to 1 with bound Mg²⁺. For 2 , the ¹³C NMR spectra exhibit three distinct spectral patterns; besides that of the free form, the other two can be assigned to Mg²⁺‐bound forms. Based on the analysis of the chemical shift deviations (CSDs), we conclude that both 1 and 2 might be subject to a cation–π interaction via the C5–C6 double bond, in contrast to that observed previously for DHEA. As demonstrated, DHEA possesses two Mg²⁺ binding sites, that is, C17–O and C5–C6 double bond, in which the binding affinity of the former is at least three times stronger than that of the latter. The solid‐state ¹³C NMR investigation allows better understanding of the underlying cation binding effects of neurosteroid molecules in vitro.     

金属离子(Na~+、K~+、Ca~(2+)、Mg~(2+)、Zn~(2+))与鸟嘌呤异构体配合物的稳定性

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+.     

Heats of adsorption of water on vermiculite having large singly-charged cations in the exchange complex

The isotherms and differential heats of adsorption of water vapor on K-, NH₄-, Rb-, and Cs-vermiculites have been studied by means of a Calvet microcalorimeter having a microweighing adsorption attachment. The results are interpreted taking into account that the large cations K₊, NH₄ ⁺, Rb⁺, and especially Cs⁺, may not replace the initial exchange complexes (Na⁺ or Mg²⁺) of the mineral completely, so that besides hydration of the principal exchange cations the reaction of water molecules being adsorbed with the residual Na⁺ or Mg⁺ cations also takes place. The presence of a certain number of the initial cations (Na⁺ or Mg²⁺) in the Cs form of vermiculite is confirmed by the results of studying the ion exchange equilibria on the Na and natural (Mg) forms of the mineral involving the participation of the Cs₊ ions. The nature of the variation in the dependence of the differential heats of adsorption with an increase in the amount of adsorbed substance indicates the segregation (isolation) of the principal (K⁺, NH₄ ⁺, Rb⁺, Cs⁺) and the residual (Na⁺, Mg²⁺) exchange cation in the structure of the mineral.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 91–96, January–February, 1986.     

Syntheses,structures of N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes and their application as redox sensor for Cu2+ ion

Rigid N‐(substituted)‐2‐aza‐[3]‐ferrocenophanes L1 and L2 were easily synthesized from 1,1 ‐dicarboxyaldehydeferrocene and the corresponding amines. Ligands L1 and L2 were characterized by ¹H NMR, ¹³C NMR and single‐crystal X‐ray crystallography. The coordination abilities of L1 and L2 with metal ions such as Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ were evaluated by cyclic voltammetry. The electrochemical shift (ΔE_1/2) of 125 mV was observed in the presence of Cu²⁺ ion, while no significant shift of the Fc/Fc + couple was observed when Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Cd²⁺ metal ions were added to the solution of L1 in the mixture of MeOH and H₂O. Moreover, the extent of the anodic shift of redox potentials was approximately equal to that induced by Cu²⁺ alone when a mixture of Cu²⁺, Mg²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ was added to a solution of L1. Ligand L1 was proved to selectively sense Cu²⁺ in the presence of large, excessive first‐row transition and late‐transition metal cations. The coordination model was proposed from the results of controlled experiments and quantum calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Metal-ion-dependent folding of a uranyl-specific DNAzyme: insight into function from fluorescence resonance energy transfer studies

Fluorescence resonance energy transfer (FRET) has been used to study the global folding of an uranyl (UO₂²⁺)‐specific 39E DNAzyme in the presence of Mg²⁺, Zn²⁺, Pb²⁺, or UO₂²⁺. At pH 5.5 and physiological ionic strength (100 mM Na⁺), two of the three stems in this DNAzyme folded into a compact structure in the presence of Mg²⁺ or Zn²⁺. However, no folding occurred in the presence of Pb²⁺ or UO₂²⁺; this is analogous to the “lock‐and‐key” catalysis mode first observed in the Pb²⁺‐specific 8–17 DNAzyme. However, Mg²⁺ and Zn²⁺ exert different effects on the 8–17 and 39E DNAzymes. Whereas Mg²⁺ or Zn²⁺‐dependent folding promoted 8–17 DNAzyme activity, the 39E DNAzyme folding induced by Mg²⁺ or Zn²⁺ inhibited UO₂²⁺‐specific activity. Group IIA series of metal ions (Mg²⁺, Ca²⁺, Sr²⁺) also caused global folding of the 39E DNAzyme, for which the apparent binding affinity between these metal ions and the DNAzyme decreases as the ionic radius of the metal ions increases. Because the ionic radius of Sr²⁺ (1.12 Å) is comparable to that of Pb²⁺ (1.20 Å), but contrary to Pb²⁺, Sr²⁺ induces the DNAzyme to fold under identical conditions, ionic size alone cannot account for the unique folding behaviors induced by Pb²⁺ and UO₂²⁺. Under low ionic strength (30 mM Na⁺), all four metal ions (Mg²⁺, Zn²⁺, Pb²⁺, and UO₂²⁺), caused 39E DNAzyme folding, suggesting that metal ions can neutralize the negative charge of DNA‐backbone phosphates in addition to playing specific catalytic roles. Mg²⁺ at low (<2 mM ) concentration promoted UO₂²⁺‐specific activity, whereas Mg²⁺ at high (>2 mM ) concentration inhibited the UO₂²⁺‐specific activity. Therefore, the lock‐and‐key mode of DNAzymes depends on ionic strength, and the 39E DNAzyme is in the lock‐and‐key mode only at ionic strengths of 100 mM or greater.     

A dipyrenyl calixazacrown chemosensor for Mg

A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg²⁺. When Mg²⁺ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by ¹H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg²⁺ by the amide functions to form a 1:1 complex.     

Studies on systems of salts and mixed solvents. XXXIII. On the solvation of cations (Li+, Mg2+, Al3+) in dimethylsulphoxide-water mixtures (Raman spectroscopic investigations into concentrated electrolyte solutions)

Starting from pure DMSO (DMSO-d₆) the solvent-solvent interactions detectable in the aqueous systems were investigated by means of v_SO and v_CS. On the basis of the results obtained the solvation behaviour of cations (Li⁺, Mg²⁺, Al³⁺) in DMSO (DMSO-d₆)? H₂O mixtures is discussed. In spite of the prevailing solvent-solvent interactions direct cation-DMSO (DMSO-d₆) interactions can still be proved in solutions rich in water, which suggest preferred cation solvation by the organic molecule.