Solvation effect of the cation of the supporting electrolyte in hexamethylphosphoramide

Polarographic reductions of sodium and potassium ions in hexamethylphosphoramide (HMPA) have been examined in various supporting electrolytes. The supporting electrolytes, which have much the same solvated radii and much the same electrocapillary curves, sometimes have a significantly different influence on the polarographic reductions of metal ions. The Li⁺ and Hex₄N⁺ ions provide a typical example. Their effective radii are seen to have much the same characteristics. However, the polarographic reduction of the sodium ion shows a difference in shape between that occurring in Li⁺ solution and that in Hex₄N⁺ solution. Another example is found in the case of Et₄N⁺, Me₄N⁺ and 5N6⁺, whose r_eff and the electrocapillary curves are much the same. However, the polarographic reductions of the sodium and potassium ions are different in these solutions. The solvation number of the solvent molecule of the supporting electrolyte cation seems to exert a great influence on these reductions. The electrocapillary curves were also examined with the tetradodecylammonium ion, tetradecylammonium ion and tetraphenylphosphonium ion used as the supporting electrolytes. The inhibition of the reduction of metal ion for these cations is evidence for their lack of solvation. The effects of the solvated asymmetrical tetraalkylammonium ions on the polarographic behaviour were also examined. When some methyl groups cooperate with the tetraalkylammonium ion, the chemical character is between that of the Et₄N⁺ ion and that of the Me₄N⁺ ion.     

The Remarkable Effect of the Manganese Ion with Dioxygen on the Stability of π‐Conjugated Radical Cations

In this paper, nanosecond laser flash photolysis has been used to investigate the influence of metal ions on the kinetics of radical cations of a range of carotenoids (astaxanthin (ASTA), canthaxanthin (CAN), and β‐carotene (β‐CAR)) and various electron donors (1,4‐diphenyl‐1,3‐butadiene (14DPB), 1,6‐diphenyl‐1,3,5‐hexatriene (16DPH), 4‐methoxy‐trans‐stilbene (4 MeOSt), and trans‐stilbene (trans‐St)) in benzonitrile. Radical cations have been generated by means of photosensitized electron‐transfer (ET) using 1,4‐dicyanonaphthalene (14DCN) and biphenyl (BP). The kinetic decay of CAR ^{. +} shows a strong dependence on the identity of the examined metal ion. For example, whereas NaClO₄ has a weak effect on the kinetics of CAR ^{. +}, Ni(ClO₄)₂ causes a strong retardation of the decay of CAR ^{. +}. It is also interesting to note that Mn²⁺, which is a biologically relevant metal ion, shows the strongest effect of all the investigated metal ions (e.g., in the presence of Mn²⁺ ions, the half‐life (t_1/2) of CAN ^{. +} (t_1/2>90 ms) is more than three orders of magnitude higher than in the absence of the metal ions (t_1/2≈16 μs)). Furthermore, the influence of metal‐ion and oxygen concentrations on the kinetics of CAR ^{. +} reveals their pronounced effect on the kinetic decay of CAR ^{. +}. However, these remarkable effects are greatly diminished if either oxygen or metal ions are removed from the investigated solutions. Therefore, it can be concluded that oxygen and metal ions interact cooperatively to induce the observed substantial effects on the stabilities of CAR ^{. +}. These results are the first direct observation of the major role of oxygen in the stabilization of radical cations, and they support the earlier mechanism proposed by Astruc et al. for the role of oxygen in the inhibition of cage reactions. On the basis of these results, the factors that affect the stability of radical cations are discussed and the mechanism that shows the role of oxygen and metal ions in the enhancement of radical‐cation stability is described.     

Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M₁ + Cat + M₂)⁺, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M₁ + Cat)⁺ and (M₂ + Cat)⁺ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li⁺, Na⁺, and K⁺ than the larger ions such as Cs⁺ and Rb⁺. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.     

Characterization of synthetic N-acetylcysteine conjugates by positive- and negative-ion 252Cf plasma desorption mass spectrometry

N-Acetylcysteine and nine N-acetylcysteine conjugates of synthetic origin were characterized by positive- and negative-ion plasma desorption mass Spectrometry. For sample preparation the electrospray technique and the nitrocellulose spin deposition technique were applied. The fragmentation of these compounds, which are best seen as S-substituted desaminoglycylcysteine dipeptides, shows a similar behaviour to that of linear peptides. In the positive-ion mass spectra intense protonated molecular ion peaks are observed. In addition, several sequence-specific fragment ions (A⁺, B⁺, [Y + 2H]⁺, Z⁺), immonium ions (I⁺) and a diagnostic fragment ion for mercap-turic acids (R_M⁺) are detected. The negative-ion mass spectra exhibit deprotonated molecular ions and in contrast only one fragment ion corresponding to side-chain specific cleavage ([R_XS]^?) representing the xenobiotic moiety. In the case of a low alkali metal concentration on the target, cluster molecular ions of the [nM + H]⁺ or [nM - H]^? ion type (n = 1-3) are observed. The analysis of an equimolar mixture of eight N-acetylcysteine conjugates shows different quasi-molecular ion yields for the positive- and negative-ion spectra.     

Stability constants of diaza-crown-ether complexes of univalent metal ions and free energies of transfer of ligand and complexes from acetonitrile to several solvents

1:1 complexes of 1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (2,2) with Ag⁺ and T1⁺ have been determined by potentiometric pAg measurements in several polar nonaqueous solvents at 25°C. A comparison of the results with those for the cryptand (2,2,2) including alkali metal ions shows that interactions for a given ion with the two ligands are similar but differ considerably for different ions. The free energies of transfer of ligand (2,2) and its complexes have been determined from distribution measurements and are around zero between acetonitrile and aprotic solvents.     

Effects of Alkali Metal Ion Cationization on Fragmentation Pathways of Triazole-Epothilone

The collisionally activated dissociation mass spectra of the protonated and alkali metal cationized ions of a triazole-epothilone analogue were studied in a Fourier transform ion cyclotron resonance mass spectrometer. The fragmentation pathway of the protonated ion was characterized by the loss of the unit of C₃H₄O₃. However, another fragmentation pathway with the loss of C₃H₂O₂ was identified for the complex ions with Na⁺, K⁺, Rb⁺, and Cs⁺. The branching ratio of the second pathway increases with the increment of the size of alkali metal ions. Theoretical calculations based on density functional theory (DFT) method show the difference in the binding position of the proton and the metal ions. With the increase of the radii of the metal ions, progressive changes in the macrocycle of the compound are induced, which cause the corresponding change in their fragmentation pathways. It has also been found that the interaction energy between the compound and the metal ion decreases with increase in the size of the latter. This is consistent with the experimental results, which show that cesiated complexes readily eject Cs⁺ when subject to collisions.     

Application of an Ion Beam Technique for the Design of Visible Light-Sensitive, Highly Efficient and Highly Selective Photocatalysts: Ion-Implantation and Ionized Cluster Beam Methods

As a new concept for the design of effective photocatalysts, an ion beam technology using accelerated metal ions, a metal ion implantation and an ionized cluster beam (ICB) method, have been applied to design unique photocatalysts. The metal ion implantation of TiO₂ and Ti-containing zeolites with highly accelerated metal ions (V⁺, Cr⁺, etc.) is useful in designing photocatalysts that can operate efficiently under visible light irradiation. Also, an ICB method with a low acceleration energy is useful in preparing transparent TiO₂ thin films on various types of substrates for the efficient photocatalytic degradation of pollutants diluted in water and air. The combination of the ICB method and metal ion implantation can develop the TiO₂ thin films that are able to operate not only under UV light but also under visible light irradiation.     

Sorption Studies in DMSO-NITRIC Acid and DMSO-Acetic Acid Systems and Separation of Metal Ions on TIN(IV)-Iodophosphate

Abstract

Some new samples of tin(IV)-iodophosphate have been synthesized and their ion exchange properties have been studied. Adsorption behaviour of different metal ions on tin(IV)-iodophosphate (TIP₅), in H⁺ form, in different solvent systems have been examined. Kd values of few metal ions, in 4M DMSO medium, have also been determined on the same ion-exchanger in NH⁺ ₄ form. Effect of particle size of tin(IV)-iodophosphate (TIP₅), in H⁺ form, on the Kd values of metal ions has been studied. Separations of a number of metal ions have been achieved on tin(IV)-iodophosphate (TIP₅) columns.     

Resonant laser ablation as a selective metal ion source for gas-phase ion molecule reactions

Resonant laser ablation (RLA) is used as a source to selectively generate multiple metal ion species from the same sample. The capability of rapidly changing metal ions for gas-phase ion chemistry studies is a significant advantage in ion-molecule chemistry. The simple experimental arrangement uses relatively modest laser pulse energies (≤ 25 µJ/pulse) from a tunable dye laser to desorb and selectively ionize different metal atoms from a multicomponent sample. In turn, this allows the chemistry of several components to be investigated without breaking vacuum or altering the experimental geometry. This work demonstrates the use of RLA as a selective source of several reagent metal ions for gas-phase ion chemistry investigations. In particular, the reactivity of acetone with Cr⁺, Fe⁺, Ni⁺, and Cu⁺ was examined for metal ions selectively created by RLA from a standard steel sample.     

Lattice polarization effects in electrochromic switching in WO3−x films studied by pulse-nanogravimetric technique

The interactions of various types of cations with the tungsten trioxide lattice have been investigated to evaluate possible intercalation of these cations and the occurrence of lattice polarization leading to the near-surface structural lattice damage. The interactions of cations, such as the large monovalent cations (K⁺, Et₄N⁺, CtMe₃N⁺ cations), transition metal dications (Ni²⁺), heavy metal ions (Cd²⁺), and representative lanthanides (La³⁺) and actinides (Th⁴⁺), in competition with intercalation of H⁺ ions have been investigated using pulse-nanogravimetric technique. The effects of these cations in electrochromic processes of WO₃ proceeding during cathodic reduction have been assessed. For all of the metal ions studied, a large increase in the apparent mass uptake (up to eightfold) in comparison to pure H⁺ ion ingress was observed upon the film coloration induced by a cathodic potential pulse. The experiments indicate that the apparent mass gains, although large, are insufficient to confirm predominant contribution of metal ions in the ion transport along the channels in WO₃ lattice. The lower decoloration rate in the case of Ni²⁺ ions, in comparison to H⁺ and other transition metal cations (Cd²⁺), has been attributed to a slow dissociation of Ni²⁺ ions from lattice-bound oxygen atoms. For et₄N⁺ cation, which is too large to enter channels in WO₃, a dissociative reduction of the WO₃ and severe lattice damage was observed. Among the metal ions investigated, only K⁺ ions have been found to cause a dissociative reduction of WO₃ and near-surface lattice damage. Strong lattice polarization effects and irreversible binding have been found for La³⁺ and Th⁴⁺ cations.     

Gas-phase reactions of Sc+, Y+, and Lu+ with alcohols. Effects of the class and chain length of alcohols on the nature of primary products

The primary gas-phase reactions between methanol, ethanol, propan-1-ol, propan-2-ol, and 2-methyipropan-2-ol and the isovalent rare earth metal ions Sc⁺, Y⁺, and Lu⁺ generated by laser desorption-ionization of metal targets have been investigated by using a Fourier transform ion cyclotron resonance mass spectrometer. The three metal ions react exothermically with all the alcohols. The overall reactivity is controlled by the high oxophilicity of these metals, and the primary metallated ions obtained are principally oxygenated species. However, the number and the nature of these primary products depends on the electronic configuration of the metal ions as well as on the class and the principal chain length of alcohols. The order of reactivity is Y⁺ > Sc⁺ > Lu⁺. The Y⁺ and Sc⁺ ions principally react via C—O and O—H insertions, whereas Lu+ reacts by direct abstraction or via various five-center electrocyclic mechanisms as a function of the class and the alcohol chain length.     

Elucidation of artefacts in proton transfer reaction time‐of‐flight mass spectrometers

We present an effective procedure to differentiate instrumental artefacts, such as parasitic ions, memory effects, and real trace impurities contained in inert gases. Three different proton transfer reaction mass spectrometers were used in order to identify instrument‐specific parasitic ions. The methodology reveals new nitrogen‐ and metal‐containing ions that up to date have not been reported. The parasitic ion signal was dominated by [N₂]H⁺ and [NH₃]H⁺ rather than by the common ions NO⁺ and O₂⁺. Under dry conditions in a proton transfer reaction quadrupole interface time‐of‐flight mass spectrometer (PTR‐QiTOF), the ion abundances of [N₂]H⁺ were elevated compared with the signals in the presence of humidity. In contrast, the [NH₃]H⁺ ion did not show a clear humidity dependency. On the other hand, two PTR‐TOF1000 instruments showed no significant contribution of the [N₂]H⁺ ion, which supports the idea of [N₂]H⁺ formation in the quadrupole interface of the PTR‐QiTOF. Many new nitrogen‐containing ions were identified, and three different reaction sequences showing a similar reaction mechanism were established. Additionally, several metal‐containing ions, their oxides, and hydroxides were formed in the three PTR instruments. However, their relative ion abundancies were below 0.03% in all cases. Within the series of metal‐containing ions, the highest contribution under dry conditions was assigned to the [Fe(OH)₂]H⁺ ion. Only in one PTR‐TOF1000 the Fe⁺ ion appeared as dominant species compared with the [Fe(OH)₂]H⁺ ion. The present analysis and the resulting database can be used as a tool for the elucidation of artefacts in mass spectra and, especially in cases, where dilution with inert gases play a significant role, preventing misinterpretations.     

A study of vitamin A as a probe in critical micelle concentration determinations of surfactants

The effects of the heteroatom donor on the complexation of various metal ions by macrocyclic polyethers were qualitatively examined by application of the ligand exchange technique in a quadruple ion trap mass spectrometer. The metal ions, including K⁺, Cs⁺, Al⁺, Mg⁺, Cu⁺ and Ni⁺, were generated by laser desorption and allowed to react with 12-crown-4 and its nitrogen and sulfur analogs, cyclen and 1,4,7,10-tetrathiacyclododecane. The orders of gas-phase basicities were established as a comparison. The relative K⁺ and Cs⁺ binding affinities of 12-crown-4 are greatest, whereas cyclen has the highest binding affinity for all the other metal ions and also the highest gas-phase basicity.     

Comparative study of [Xe]+ and [Ar]+ bombardment in secondary ion mass spectrometry for bioorganic compounds

Secondary ion mass spectra obtained by [Xe]⁺ bombardment are compared with those obtained by [Ar]⁺ bombardment. Although [Ar]⁺ ions are commonly used as primary ions in secondary ion mass spectrometry for organic compounds, [Xe]⁺ ions seem better as primary ions because they give a larger sputtering yield for a metal substrate than [Ar]⁺ ions. Cationized molecular intensities of sucrose, raffinose and stachyose, and quasimolecular ion intensities of tuftsin and eledoisin related peptide are investigated using [Xe]⁺ and [Ar]⁺ bombardments. The observed molecular species are 2–4 times more intense for [Xe]⁺ bombardment than for [Ar]⁺ bombardment, although the secondary ion mass spectra are almost the same in both cases.     

Imaging Endogenous Metal Ions in Living Cells Using a DNAzyme–Catalytic Hairpin Assembly Probe

DNAzymes are a promising platform for metal ion detection, and a few DNAzyme-based sensors have been reported to detect metal ions inside cells. However, these methods required an influx of metal ions to increase their concentrations for detection. To address this major issue, the design of a catalytic hairpin assembly (CHA) reaction to amplify the signal from photocaged Na⁺-specific DNAzyme to detect endogenous Na⁺ inside cells is reported. Upon light activation and in the presence of Na⁺, the NaA43 DNAzyme cleaves its substrate strand and releases a product strand, which becomes an initiator that trigger the subsequent CHA amplification reaction. This strategy allows detection of endogenous Na⁺ inside cells, which has been demonstrated by both fluorescent imaging of individual cells and flow cytometry of the whole cell population. This method can be generally applied to detect other endogenous metal ions and thus contribute to deeper understanding of the role of metal ions in biological systems.     

Metastable ion study of substituted cyclopentadienylmanganese cations in the gas phase

The behavior of some substituted cyclopentadienylmanganese ions has been studied by tandem mass spectrometry. This metastable ion study showed that only C₅H₅Mn⁺ and (C₅H₄CN)Mn⁺ ions retain their nido-cluster structure (1), which is characterized by a simple metal-ligand bond cleavage. Other substituted ions, RXC₅H₄Mn⁺, rearrange to a different extent, depending on the nature of the substituent. The first rearrangement step is R radical migration to the central metal atom, leading to RMnC₅H₄X⁺-type ions (2). These ions decompose by elimination of X (for X=CO) or with formation of RMnX⁺, but further rearrangements can also occur. These are the reverse migration of R from the metal atom to the π-ligand (for R=H, Ph) and cyclopentadienyl ring expansion (for X=CH₂). Collisional activation mass spectra contained an Mn⁺ ion peak, which can indicate the existence of stable type 1 structures for most cyclopentadienylmanganese ions. Carboxyl and hydroxymethyl derivatives exist, presumably as ions of type 2. The neutralization-reionization mass spectra of RXC₅H₄Mn⁺ ions are also discussed.     

Comparison of Fibrous Carboxylic Ion Exchangers in Water Treatment to Remove Heavy Metal Ions

Treatment of drinking water to remove heavy metal ions Pb^{2 +}, Cu^{2 +}, Cd^{2 +}, Co^{2 +}, Ni^{2 +}, and Zn^{2 +} with commercial fibrous carboxylic ion exchangers FIBAN Kh-1, K-3, K-4, and K-5 was studied. Features of metal ion sorption from two-component solutions were determined. A comparative evaluation of the sorption selectivity of FIBAN fibrous ion exchangers with respect to heavy metal ions was made.     

Regulation of metal ion recognition by allosteric effects in thiacalix[4]crown based receptors

Three new ditopic receptors 3a-c based on thiacalix[4]arene of 1,3 alternate conformation possessing two different complexation sites have been designed and synthesized for both soft and hard metal ions. The imino nitrogens bind soft metal ion (Ag⁺/Pb²⁺/Cu²⁺) and the crown moiety binds K⁺ ion. The preliminary investigations show that 3a-c behave as ditopic receptors for Ag⁺/K⁺, Pb²⁺/K⁺, and Cu²⁺/K⁺ ions, respectively. In all the three receptors it was observed that the formation of 3a·Ag⁺/3b·Pb²⁺/3c·Cu²⁺ complex triggers the decomplexation of K⁺ ion from crown moiety and acts as a gateway, which regulates the binding of alkali metal to crown moiety. Thus, allosteric binding between metal ions ‘switch off’ the recognition ability of crown ether ring.     

Kinetics and Determination of Some Transition Metals with Peri-Dihydroxynaphthindenone

Abstract

A simple sensitive and selective spectrophotometric method has been developed for determination of some transition metal ions. It is based on the reaction of the metal ions with excess peri-dihydroxynaphthindenone in 80% v/v ethyl alcohol-water mixture at 30°C. The colored products obtained display maximum absorption band at 560–590 nm depending upon the type of transition metal ion used, and E_{1 cm} ^1% in the range 70–480. Under the optimum conditions results with an average recovery of 96%, (mean standard deviation ±3% are obtained for 6 different transition metal ions without any significant interference from Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺, Ba²⁺, Sr²⁺, Ni²⁺, Bi³⁺, Co²⁺, Mn⁺², Cd⁺² and Al⁺³. Kinetic data reveal that the reaction proceeds via a second order route (first order with respect to either the metal cation or ligand). The activation parameters and a suggested mechanism have been presented, and the nature of bonding in the solid chelate products has been verified.