The “Missing Link”, Allostery and Synergism─Hosting of Metal Cations by Regular and Partial Cone Calix[4]arene Isomers

Since details on metal cation transport proteins and on the allocation mechanisms for transition metals are provided elsewhere in this book, I will present aspects of transition metal homeostasis in a hopefully novel overview. We will start with a microbial look at the transition metal Periodic Table, cation speciation, and availability in the environment. This information provides rules that might govern microbial metal cation homeostasis from the outside of the cell. The fate of metal cations inside the cell is influenced by redox potentials and affinities to ligands in complex compounds. Understanding this topic requires study of interactions between metal cations and the consequences thereof. External availability and internal binding equilibria are connected by transport reactions. These lead to metal cation concentrations in cellular compartments, which are in flow equilibrium of import and export reactions. Thus, cellular cation homeostasis may be described as an interplay of transport flow backbone and competitive binding reactions. Both together provide an energy landscape for each metal cation and cellular compartment. As a recent part of the transport flow backbone in Gram-negative bacteria, efflux across the outer membrane from the periplasm to the outside has been identified. Active outer membrane efflux might indeed be taking place in Gram-negative bacteria. Thus, the periplasm is important in bacterial metal cation homeostasis.

Adsorption characteristics of both cationic and oxyanionic metal ions on hexadecyltrimethylammonium bromide-modified NaY zeolite

Multiple strong field ionization of metallocenes: Applicability of ADK rates to the production of multiply charged transition metal (Cr, Fe, Ni, Ru, Os) cations

Extensive research efforts have been concentrated into the conversion of CO2 into value-added chemicals as it provides a route to a circular carbon economy. Electroreduction of CO2 on Au surfaces allows for the selective transformation of CO2 into CO via carbon dioxide reduction reaction (CO2RR), and the catalytic activity depends on the concentration and identity of cations present at the electrode-electrolyte interface. Experimental reports performed under typical CO2RR-operating conditions have widely shown that the CO2RR is enabled by the presence of metal or organic cations in the cathodic interfacial microenvironment. A remaining question is to address if CO2RR can occur in the absence of metal or organic cations and, if so, what the mechanism may be. Here, we show that CO2 can be electrochemically reduced to CO on Au in acidic electrolytes rigorously controlled to avoid the presence of metal and organic cations and systematically suggest the important contributions allowing this reaction to proceed. The formation of CO is confirmed by both qualitative and quantitative methods using potentiodynamic CO-stripping scans and chromatography-assisted constant potential electrolysis. Calculations indicate that H3O+ is able to stabilize the formation of *CO2 -, albeit at more negative potentials than when an alkali metal cation is present. Spectroelectrochemical experiments show that the electric field at the interface is reduced when metal cations are not added, indicating that the decreased field stabilization of intermediates could play an important role in increased overpotential required for the CO2RR to occur.

Endohedral metallofullerene has novel properties because of the interaction between the encapsulated metal atom or cation and fullerene. Experiments have demonstrated that the insertion of Li(+) into C60 can greatly promote the reactivity of the Diels-Alder (DA) cycloaddition of cyclopentadiene (CpH) to C60. However, the reaction is sufficiently fast that its quantitative kinetic data cannot be obtained experimentally. In addition, knowledge regarding the effects of other alkali metal cations and metal cations with more charges on the reactivity and regioselectivity of C60 is almost nonexistent. In the current study, DA cycloadditions of CpH to M(+)@C60 (where M = Li, Na, K, Rb, and Cs) and Ca(2+)@C60 were investigated via density functional theory in the gas phase and in solvent. Via careful discussion and comparison with the results of C60, we concluded the following for the DA reaction of CpH to C60 and, more generally, for DA reactions of other fullerenes: (1) the encapsulated metal cations enhance the reactivity; (2) among alkali metal cations, Na(+) could be the best catalyst; (3) Ca(2+) is more favorable in promoting the reactivity than any alkali metal cation; (4) encapsulated metal cations with more positive charges enhance the reactivity of the 6-5 bond in C60, which is significant when the 6-5 adduct is the target product.

The complexing properties of a thiacalix[2]thianthrene 1 and its disulfoxide derivative 2 toward alkali metal, alkaline earth metal, some transition metal and some heavy metal cations have been investigated in acetonitrile by means of UV spectrophotometry. At the concentrations suited to this technique, complexation of the alkali metal cations by the sulfoxide but not the thiacalixthianthrene was detectable, whereas the converse was true for both transition metal and lanthanide cations. Complexation of the alkaline earth cations was not detectable. The strongest binding observed was that of Hg(II) to ligand 1 but in no case was complexation sufficiently strong for either ligand to function as a useful metal ion extractant. The complexing properties of a thiacalix[2]thianthrene 1 and its disulfoxide derivative 2 toward alkali metal, alkaline earth metal, some transition metal and some heavy metal cations have been investigated in acetonitrile by means of UV spectrophotometry. At the concentrations suited to this technique, complexation of the alkali metal cations by the sulfoxide but not the thiacalixthianthrene was detectable, whereas the converse was true for both transition metal and lanthanide cations. Complexation of the alkaline earth cations was not detectable. The strongest binding observed was that of Hg(II) to ligand 1 but in no case was complexation sufficiently strong for either ligand to function as a useful metal ion extractant.

BackgroundAntimicrobial agents (AMAs) are essential for treating infections. A part of AMAs chelate with metal cations (MCs), reducing their blood concentrations. That drug-drug interaction could lead to a reduction of therapeutic efficacy and the emergence of drug-resistant bacteria. However, prescriptions ordering concomitant intake (co-intake) of AMAs and MCs are frequently seen in clinical settings. A method for preventing such prescriptions is urgently needed.MethodsWe implemented pop-up alerts in the hospital's ordering and pharmacy dispensation support system to notify the prescriptions ordering co-intake of AMAs and MCs for physicians and pharmacists, respectively. To assess the effectiveness of the pop-up alerts, we investigated the number of prescriptions ordering co-intake of AMAs and MCs and the number of pharmacist inquiries to prevent co-intake of AMAs and MCs before and after the implementation of pop-up alerts.ResultsBefore the implementation of pop-up alerts, 84.5% of prescriptions containing AMA and MCs ordered co-intake of AMAs and MCs. Implementing pop-up alerts time-dependently reduced the proportion of prescriptions ordering co-intake of AMAs and MCs to 43.8% and 29.5% one year and two years later, respectively. The reduction of tetracycline-containing prescriptions was mainly significant. Before the implementation of pop-up alerts, the proportion of prescriptions in which pharmacists prevented co-intake of AMAs and MCs was 3.4%. Implementing pop-up alerts time-dependently increased proportions of such prescriptions to 20.9% and 28.2% one year and two years later.ConclusionImplementing pop-up alerts reduced prescriptions ordering co-intake of AMAs and MCs and accelerated pharmacists to prevent co-intake of AMAs and MCs. The implementation of dual pop-up alerts in the hospital's ordering and pharmacy dispensation support system could help prevent co-intake of AMAs and MCs.

Two [(bpy)Re(CO)3L]+ complexes (bpy = 2,2'-bipyridine), where L contains an aza-15-crown-5 ether which is linked to Re via an alkenyl- or alkynyl-pyridine spacer, have been synthesised along with model complexes. Solutions of the complexes in acetonitrile have been studied by UV-Vis absorption spectroscopy, and by 1D and 2D 1H NMR spectroscopy. Strong UV-Vis bands, assigned to intraligand charge-transfer transitions localised at the L ligands, blue shift on protonation of the azacrown nitrogen atom or on complexation of alkali-metal (Li+, Na+ and K+) or alkaline-earth metal (Mg2+, Ca2+ and Ba2+) cations to the azacrown; the magnitude of the blue shift is dependent on the cation, with protonation giving the largest shift of ca. 100 nm. Cation binding constants in the range of log K= 1-4 depend strongly on the identity of the metal cation. Protonation or cation complexation causes downfield shifts in the 1H NMR resonances from most of the azacrown and L ligand protons, and their magnitudes correlate with those of the blue shifts in the UV-Vis bands; shifts in the azacrown 1H NMR resonances report on how the different metal cations interact with the macrocycle. UV-Vis and 1H NMR spectra of the free L ligands enable the effect of the Re centre to be assessed. Together, the data indicate that the alkene spacer gives a more responsive sensor than the alkyne spacer by providing stronger electronic communication across the L ligand.

Prediction and optimization of the separation of metal cations by capillary electrophoresis with indirect UV detection

SiAlON ceramics have found applications in many different areas due to their excellent engineering properties such as high hardness, fracture toughness, good thermal shock and oxidation resistance. SiAlON exist mainly in two different polymorphs: a (MxSi12-(m+n)Al(m+n)OnN16-n; M: metal and rare earth cations, x≈0,35 and n≤1,35) and β (β-Si6-zAlzOzN8-z; 0≤z≤4). In general, stable alpha and beta phases separately as well as in combination of α and β are obtained by incorporation of metal and rare earth cations as sintering additives. The metal cations such as Li, Mg, Ca, Y, and most lanthanide cations with the exception of La, Ce, Pr and Eu are able to stabilise α-SiAlON structure. Ekstrom et al. 1991 found that cerium can not occupy interstitial sites in α-SiAlON structure due to the fact that ionic radius of Ce3+ (0.103 nm) is too large, whereas ionic radius of Ce4+ (0.080 nm) is too small to stabilise α-SiAlON structure. After this work, several studies carried out to incorporate cerium cations into α-SiAlON structure. It was shown that cerium cation alone can be incorporated into α-SiAlON if the samples are either fast cooled after sintering, or when the samples are spark plasma sintered. On the other hand, cerium can also be incorporated into the α-SiAlON structure when it is used as a sintering additive together with a smaller α-SiAlON stabiliser cation such as Yb or Ca. Similar results were observed in other multi-cation doped SiAlONS that non α-SiAlON stabiliser cations like Sr2+ (0.112 nm) and La3+ (0.106 nm) are able to stabilise α-SiAlON when used together with α-SiAlON stabiliser cations such as Ca or Yb. Although it was shown that cerium existed in mixed valance state at domain boundaries in Ce-doped and spark plasma sintered α-SiAlON, there is no work on the valance determination of cerium in sintered α-SiAlON which has no domain boundaries. Therefore, in this study; it was aimed to incorporate cerium into α-SiAlON structure by combining with Yb3+ and the determination of possible cerium valence states (Ce3+/Ce4+) in both α-SiAlON grains and secondary phases.

Subphthalocyanines (SubPcs) and their aza-analogues (SubTPyzPzs) are fluorophores with strong orange fluorescence emission; however, their sensing ability towards metal cations remains uncharted. To fill this gap, we have developed an efficient method for introducing aza-crown moieties at the axial position of SubPcs and SubTPyzPzs to investigate the structure-activity relationship for sensing alkali (Li+, Na+, K+) and alkaline earth metal (Ca2+, Mg2+, Ba2+) cations. SubPcs showed better photostability than SubTPyzPzs and even a commonly utilized dye, 6-carboxyfluorescein. Selectivity toward metal cations was driven by the size of the aza-crown, irrespective of the counter anion. The stoichiometry of binding was found to be 1 : 1 in all cases, and the interaction between SubPcs and cations was characterized by the corresponding apparent binding constants (Ka). Notably, an unusually strong interaction of all sensoric SubPcs with Ba2+ compared to other studied cations was demonstrated. The role of the surrounding environment, i.e. the addition of water or methanol, in sensing cations is shown in detail as well. Selectivity towards K+ over Na+ was demonstrated in aqueous media with SubPcs bearing the 1-aza-6-crown-18 moiety in Tween 80 micelles. In this case, a 5-fold increase of the fluorescence quantum yield was observed upon binding K+ ions. The high brightness, photostability, and sensing activity in aqueous media make SubPc macrocycles promising fluorophores for metal cation sensing.

Structures and energetics of complexes between the guanine−cytosine Watson−Crick DNA base pair and pentahydrated Mg2+, Ca2+, Sr2+, Ba2+, Zn2+, Cd2+, and Hg2+ metal cations were studied. Comparison has been made with the data for the unsolvated cations. The complexes were fully optimized within the Hartree−Fock approximation applying the 6-31G* basis set of atomic orbitals, while relativistic pseudopotentials were used for the cations except magnesium. The energetics have been studied with the inclusion of electron correlation using the full second-order Møller−Plesset perturbation theory. The cation with its hydration sphere has been considered as one subsystem in the calculations of interaction energy. Thus, the complete system for a calculation would include the hydrated cation−guanine−cytosine trimer. The interaction between hydrated cation and guanine is significantly reduced compared to the guanine−unsolvated cation interaction. Though the stabilizing three-body contribution has been reduced by almost 50% by hydration, it still remains significant. The stability of the guanine−cytosine Watson−Crick base pair is enhanced by ca. 20−30% due to the coordination of the hydrated cation. All the transition metal and Mg2+ cations are tightly bound to the N7 atom of guanine, constituting an octahedral coordination sphere. The Ca2+, Sr2+, and Ba2+ cations are coordinated simultaneously to the N7 and O6 atoms of guanine and the base−cation distance increases with the row number in this series. However, the energy difference between the N7 and N7−O6 types of coordination is rather small. The calculations show a different balance between the transition metal and alkaline earth cations with respect to the cation−base and cation−water interactions. Zn2+ compared to Mg2+ is bound more tightly to the base, and the hydration shell around Zn2+ is more flexible. The replacement of Mg2+ by Zn2+ can be viewed, to some extent, as a shift from the interaction between nucleobase and a hydrated cation toward hydration of a metalated base. This is likely to contribute to the different biological role of Zn2+ and Mg2+.

Effect of copper cation on electrochemical behaviour of steel in presence of imidazole in acid medium

Separation of alkali and alkaline-earth metal and ammonium cations by capillary electrophoresis using poly(ethylene glycol) and tartaric acid

Two EAA (Ethylene/acrylic acid) copolymers from Dow Chemical Company have been studied. Primacor resin (5980), having a mol wt of about 30,000 and an acrylic acid content of 19.2%, was converted into 10 and 20 denier per filament fibers to create a high surface area. Cold drawing and use of a fiber lubricant helped prevent sticking and blocking during spinning. The fiber was optimally swollen in a 0.5 N caustic at 55°C to produce an ion exchange fiber. Primacor resin (5980) in pellet form was reacted with alkali and was subsequently hammermilled into an ion exchange porous particulate. Physical and chemical properties, such as thermal properties, swelling, cation exchange activity and selectivity, tensile and elongation properties, among others, were determined on the fiber before and after conversion to specific metal (cationic) forms. The swollen fibers appeared to have more cation binding capacity than hammermilled pellets. The EAA polymers were colored by some metal cations. Some metal cations could be preferentially removed from solutions of mixed cations. Most fibers were weak, even after exchanging with multivalent ions, and did not have a precise melting point. Fiber tension and solution pH during the cationic exchange had an effect on the cation uptake, as well as on the physical properties obtained. © 1993 John Wiley & Sons, Inc.