Presence Of Alkali Cations Research Articles

Role of Alkali Cations in DNA-Thioflavin T Interaction.

This study investigates the role of alkali cations in modulating the interaction between deoxyribonucleic acid (DNA) and Thioflavin T (ThT) in dilute and condensed phases. The emission characteristics of ThT were analyzed in the presence of double-stranded DNA and G-quadruplex structures with a focus on the effects of four cations: sodium, potassium, calcium, and magnesium. The ThT emission in double-stranded DNA was influenced by direct DNA binding and steric hindrance within the hydration shell of DNA, which was modulated by the presence of alkali cations. Lasing spectroscopy experiments further highlighted ThT sensitivity to the spatial arrangement of water molecules in the DNA hydration shell. Lasing was exclusively observed in the presence of Mg2+ in the G-quadruplex structure, suggesting that the parallel propeller configuration of G4 provides an optimal environment for ThT light amplification. This study highlights the critical role of cations in DNA-dye interactions and reaffirms the significance of ThT in biophysical studies.

Geopolymers made using organic bases. Part I: Synthesis and atomic structure

AbstractGeopolymers can act as a facile forming route to aluminosilicate ceramic composites due to being processed as fluids rather than as powders. However, the compositions available via typical alkali geopolymers are limited by the presence of alkali cations, introduced by the alkali silicate solution precursors. In order to expand the ceramic compositions that are accessible by geopolymer processing, this study explored the use of three strong organic bases (guanidine, tetramethylguanidine [TMG], and tetramethylammonium hydroxide [TMAOH]) as alternatives to inorganic alkali hydroxides in geopolymer synthesis. Silicate solutions were able to be produced with all three bases and favorable silica speciation was identified in the guanidine and TMG silicate solutions. Monolithic bodies were produced using guanidine and TMAOH, while no TMG samples hardened. By 27Al and 29Si nuclear magnetic resonance spectroscopy and powder X‐ray diffraction, the guanidine samples were determined to be structurally similar to those made using sodium hydroxide and hence can be called geopolymers, while the solids made with TMAOH were not structurally similar to sodium geopolymers and contained one or more unknown phases. This study has demonstrated that geopolymers can be made using organic bases rather than alkali hydroxides and that the speciation of dissolved silica alone does not indicate that an organic base silicate solution will be reactive.

Towards Responsive Spiroborate‐Based Assemblies of Podand‐Type Ligands Functionalized with Two Terminal/Peripheral Catecholate Moieties in the Presence of Alkali Cations

AbstractThe synthesis of two ligands bearing two terminal catecholate binding sites connected by an oligo(ethyleneglycol) bridge of two distinct lengths and their self‐assembly upon boron coordination and alkali cation binding (M=Li, Na, K, Cs) are reported. Attempts to synthesize positional isomers of the ligands are also described. Binding of the four alkali cations M+ through M−O interactions was studied depending on the length of the oligo(ethyleneglycol) chain in solution by 1H and DOSY NMR, mass spectrometry (MS) and in the solid‐state by X‐ray diffraction (XRD) on single crystals. MS spectrometry as well as 1H NMR revealed the presence of monomeric and oligomeric spiroborate compounds. Two monomeric macrocycles could be characterized by XRD, entrapping either lithium or cesium cations within the spiroborate macrocycle.

Amino-functionalization enhanced CO2 reduction reaction in pure water.

The electrochemical reduction of carbon dioxide (CO2RR) to carbon monoxide represents a cost-effective pathway towards realizing carbon neutrality. To suppress the hydrogen evolution reaction (HER), the presence of alkali cations is critical, which can however lead to precipitate formation on the electrode, adversely impacting the device stability. Employing pure water as the electrolyte in zero-gap CO2 electrolyzers can address this challenge, albeit at the cost of diminished catalyst performance due to the absence of alkali cations. In this study, we introduce a novel approach by implementing amino modifications on the catalyst surface to mimic the function of alkali metal cations, while simultaneously working in pure water. This modification enhances the adsorption of carbon dioxide and protons, thereby facilitating the CO2RR while concurrently suppressing the HER. Utilizing this strategy in a zero-gap CO2 electrolyzer with pure water as the anolyte resulted in an impressive carbon monoxide faradaic efficiency (FECO) of 95.5% at a current density of 250 mA cm-2, while maintaining stability for over 180 hours without any maintenance.

Recycled waste glass as precursor for synthesis of slag-based geopolymer

The current study assesses the effectiveness of recycled waste glass as a precursor in the synthesis of slag-based geopolymer. Fractional substitution of slag was made with powdered waste glass (WG) with 10%, 20%, 30% and 40%-part replacement. The early age, hardened and microstructural properties of slag-waste glass-based binary geopolymer synthesized with 6 M sodium hydroxide solution were assessed. The hardened and microstructural properties were examined on the 28 days cured specimens subjected to 24 h initial heat curing at 60 °C. The presence of alkali cations in the WG speeds up the setting time of the binary geopolymer as slag is partly replaced with WG. The mix proportion with 10% WG achieved a peak 28-day compressive strength of 42.7 MPa. Further, it also attains a low pore volume in the hardened matrix, confirming sorptivity index values and microstructural images. However, the incorporation of higher WG contents causes a significant decrease in mechanical strength with high pore volumes. The energy dispersive spectroscopic analysis showed an enhancement in Si/Al ratio with the incorporation of WG. In addition, the development of calcium silicate hydrates and sodium aluminosilicate hydrates in slag-WG geopolymer was identified from mineralogical studies. These results confirm that WG has a substantial influence on the gel formation mechanism in the matrix and alters the mechanical behaviour. The outcomes of the present study encourage the incorporation of WG as a fractional substitute of slag in the manufacturing process of sustainable geopolymer binders.

Effect of Surface Curvature on Colloidal Stability of Silver Nanoparticles with Monomolecular and Mixed Thiol Ligand Layers in the Presence of Alkali Cations.

Colloidal stability of silver nanoparticles is the critical parameter while designing colloidal colorimetric biosensors. Here, we examined colloidal stability of 11-mercaptoundecanoate-capped quasi-spherical silver nanoparticles and silver nanoplates in 0.02 M phosphate buffers with pH 8.0 containing Li+ , Na+ , K+ , or Cs+ cations. While quasi-spherical nanoparticles demonstrate a good colloidal stability in the presence of all studied cations, nanoplates aggregate in the presence of Na-phosphate buffer. The mechanism of aggregation consists in the ion-specific nanoparticle-cation bridging interaction, which is sensitive to the nanoparticle surface curvature. Increased apparent dissociation constant of carboxyl groups on the zero-curvature nanoplates' surface enhances bridging interactions and makes nanoplates colloidally unstable. Bridging interactions can be eliminated by using mixed bimolecular 11-mercaptoundecanoate-11-mercaptoundecanol surface ligand layer. Silver nanoplates with mixed ligand layer show an enhanced colloidal stability at a standard carbodiimide bioconjugation protocol.

The Solvation-Induced Onsager Reaction Field Rather than the Double-Layer Field Controls CO2 Reduction on Gold.

The selectivity and activity of the carbon dioxide reduction (CO2R) reaction are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in situ-generated CO on Au in the presence of alkali cations, we quantify the total electric field present at catalytic active sites and deconvolute this field into contributions from (1) the electrochemical Stern layer and (2) the Onsager (or solvation-induced) reaction field. Contrary to recent theoretical reports, the CO2R kinetics does not depend on the Stern field but instead is closely correlated with the strength of the Onsager reaction field. These results show that in the presence of adsorbed (bent) CO2, the Onsager field greatly exceeds the Stern field and is primarily responsible for CO2 activation. Additional measurements of the cation-dependent water spectra using vibrational sum frequency generation spectroscopy show that interfacial solvation strongly influences the CO2R activity. These combined results confirm that the cation-dependent interfacial water structure and its associated electric field must be explicitly considered for accurate understanding of CO2R reaction kinetics.

Spectroscopic and bond-topological investigation of interstitial volatiles in beryl from Slovakia

Nine beryl samples from Western Carpathians, Slovakia, were investigated by infrared and Raman spectroscopy and differential thermal analysis. Two types of water H2O I and H2O II were detected. Infrared spectroscopy proved the presence of water type I and II in the presence of alkali cations with several bands: (1) symmetric stretching vibration—ν1; (2) antisymmetric stretching mode—ν3; (3) bending vibration—ν2. The presence of singly and doubly coordinated type II water (IIs and IId) was confirmed by single-crystal IR spectroscopy. From Raman spectra a band at 3606 cm−1 was assigned to ν1 of water type I and the range of 3597–3600 cm−1 to water type II. The presence of doubly coordinating water indicates a relatively highly hydrated environment with the presence of alkali ions including Na as the dominant cation coordinated by H2O II. CO2 bands were detected only by single-crystal IR spectroscopy. Thermal analysis proved total water loss in the range of 1.4–2.0 wt% and three main dehydration events. Based on the study of bond-topological arrangements two molecules of H2O IId are each bound with two H···O1 bonds and one Na–OW bond with an angular distortion, and by releasing one H2O molecule more stable H2O IIs is produced. The H2O I molecule is bound only by two equivalent hydrogen bonds. The H2O IIs molecule with a Na–OW bond strength of 0.28 vu and two H···O1 bonds of 0.14 vu without any forced angular distortion is the most stable of all.

Electrical conductivity of iron-bearing silicate glasses and melts. Implications for the mechanisms of iron redox reactions

The electrical conductivity of a series of glasses and melts of the system SiO2–CaO–MgO–M2O–“FeO” (M=Li and Na) and of a borosilicate has been measured from room temperature to about 1820K. For samples with predominantly reduced iron, the conductivity increases markedly upon addition of Na+ and still more of Li+, which is consistent with the increasing order Mg2+, Na+, Li+ order of cation mobility. For the oxidized samples the conductivity is in contrast almost not affected by the presence of alkali cations, which agrees with the low mobility of alkali cations that are then serving as charge compensators of tetrahedrally coordinated Al3+. The conductivity is higher for oxidized than for reduced samples. As indicated by polarization electrode phenomena and complementary continuous current measurements, this difference is due to an important contribution of electronic conduction caused by electronic charge transfer between iron species that exists in the oxidized samples. The diffusivities of oxygen and divalent cations were then determined from Eyring relationship and the measured conductivities, respectively and compared with the redox diffusivies determined for the same samples. The good agreement found between both kinds of data confirms the controlling role of divalent cations and of oxygen species in the redox kinetics near the glass transition and at high temperatures, respectively. In addition it illustrates that describing melt properties in an integrated manner is becoming possible.

The Role of Sulfur in the Atmospheric Corrosion of Silver

X-ray photoelectron spectroscopy was used to investigate the corrosion products formed on silver (Ag) samples that were exposed at various outdoor sites. Silver chloride (AgCl) and silver sulfide (Ag2S) were identified, as well as silver sulfite (Ag2SO3) and silver sulfate (Ag2SO4). The presence of these oxidized sulfur species on field-exposed Ag samples has been contested. Yet, evidence here suggests that Ag2SO3 is a stable intermediate in the formation of Ag2SO4. Furthermore, the presence of alkali cations, such as Na+, correlates with the final oxidation state of the sulfur species found on the Ag samples. When cations were present, Ag2SO4 was the final state, whereas Ag2SO3 was found in the absence of alkali cations. In addition, silver carbonate (Ag2CO3) was identified on samples exposed at one site with higher altitude. Here, we present for the first time the detection of Ag2SO3, in addition to Ag2CO3, on field-exposed Ag. These findings improve the ability to use Ag as an atmospheric corrosion monitor for the simultaneous detection of AgCl and Ag2S as well as Ag2SO3 and Ag2SO4.

Alkali cation specific adsorption onto fcc(111) transition metal electrodes.

The presence of alkali cations in electrolyte solutions is known to impact the rate of electrocatalytic reactions, though the mechanism of such impact is not conclusively determined. We use density functional theory (DFT) to examine the specific adsorption of alkali cations to fcc(111) electrode surfaces, as specific adsorption may block catalyst sites or otherwise impact surface catalytic chemistry. Solvation of the cation-metal surface structure was investigated using explicit water models. Computed equilibrium potentials for alkali cation adsorption suggest that alkali and alkaline earth cations will specifically adsorb onto Pt(111) and Pd(111) surfaces in the potential range of hydrogen oxidation and hydrogen evolution catalysis in alkaline solutions.

Role of alkali cations for the excited state dynamics of liquid water near the surface

Time-resolved liquid jet photoelectron spectroscopy was used to explore the excited state dynamics at the liquid water surface in the presence of alkali cations. The data were evaluated with the help of ab initio calculations on alkali-water clusters and an extension of these results on the basis of the dielectric continuum model: 160 nm, sub-20 fs vacuum ultraviolet pulses excite water molecules in the solvent shell of Na(+) or K(+) cations and evolve into a transient hydrated complex of alkali-ion and electron. The vertical ionization energy of this transient is about 2.5 eV, significantly smaller than that of the solvated electron.

Preparation and photoluminescent properties of Eu(III) containing M-layered silicates (M = Li, Na, K, Rb, Cs)

Eu(III) containing M-layered silicates (M = Li, Na, K, Rb, Cs) were prepared using the layered silicates, such as ilerite, magadiite, and kenyaite, as a host matrix and the luminescence properties were investigated. The results from the luminescence measurements indicated that the luminescence properties in the EuM-layered silicate system depended strongly on the types of host matrices and alkali cations. Among the EuM-layered silicates, EuM-ilerite exhibited the strongest luminescence intensity for all alkali cations, whereas EuM-kenyaite exhibited relatively weak luminescence intensity. The luminescence intensity was significantly increased by heat treatment at high temperature, mainly due to the phase change of host matrices and the presence of alkali cations in the host matrices. Particularly, the luminescence intensity of EuM-layered silicate calcined at 1,000 °C increased with the increase of the ion size of alkali cations.

Nitroxide Radicals as Probes for Exploring the Binding Properties of the Cucurbit[7]uril Host

EPR spectroscopy was used for the first time to explore the binding properties of cucurbit[7]uril (CB7), a representative member of the cucurbituril family. Evidence for the formation of a complex between nitroxide radicals and the host system in an aqueous solution was provided by large changes in the nitrogen hyperfine splitting, attributed to the different polar environments experienced by the included radical. In the presence of alkali cations, the EPR spectra of benzyl tert-butyl nitroxide were characterised by new signals attributed to the radical hosted in the CB7 cavity in which one metal cation is in close contact with the nitroxidic oxygen. The formation of the coordination complex results in a substantial increase in the electron spin density on the nitrogen in inverse order with respect to the size of the cation owing to increased localisation of negative charge on the oxygen atom from bonding to the alkali cation. The EPR spectra showed selective line-broadening effects as a result of metal exchange between bulk water and the coordination complex. Analysis of the EPR linewidth variations allowed us to measure the corresponding kinetic rate constants for the first time. NMR spectroscopy showed that this behaviour is not peculiar to nitroxides but is also exhibited by the related carbonyl compounds. These data allowed us to quantify the template effect and to reach the conclusion that, in the presence of a guest having a coordinating lone pair, the formation of ternary metal-guest-CB complexes must be taken into account when discussing the complexation behaviour of cucurbituril derivatives in the presence of salts.

Effect of template concentration and gel dilution on crystallization and particle size of zeolite beta in the absence of alkali cations

Zeolite beta was hydrothermally synthesized in the SiO 2:Al 2O 3:TEAOH:H 2O system without the presence of alkali cations. The effects of TEAOH/SiO 2 molar ratio, and gel dilution on the crystallization kinetics, particle size, and framework SiO 2/Al 2O 3 of synthesized zeolite beta were studied. The as-synthesis and calcinated zeolites were characterized by XRD, TEM, N 2 adsorption, TG/DTA. When TEAOH/SiO 2 molar ratio was increased, the induction time, particle size, and framework SiO 2/Al 2O 3 of zeolites decrease. Concentrated gel favoured the increase of nucleation rate and framework SiO 2/Al 2O 3 of zeolites, and the reduction of particle sizes.

Effect of Cs impregnation on the properties of platinum in Pt/Na-BEA and Pt/Cs-BEA catalysts

The presence of alkali cations in zeolite framework provides peculiar basic properties that influence the characteristics and reactivity of supported metal particles. Particularly, the addition of increasing amounts of cesium in Pt/Na-BEA and Pt/Cs-BEA catalysts, by CsOH impregnation, leads to changes of the oxidation state and reducibility of Pt species present in the zeolite microporosity. For similar contents of impregnated Cs, the metal dispersion is higher in Pt/Cs-BEA than in Pt/Na-BEA series, showing that both the amount of Cs excess and the nature of the compensating cation affect the characteristics of the Pt species. In the case of Cs-overloaded Pt/Cs-BEA, the size of Pt nanoclusters is below 10 Å. The very small Pt nanoparticles in reduced Cs-overloaded Pt/Cs-BEA are particularly active in aromatization of n-hexane.

Alkaline-earth cation transfer assisted by monensin across the water ∣ 1,2-dichloroethane interface in the presence of alkali cations

The electrochemical transfer of alkaline-earth cations (Me 2+) assisted by monensin (HX) across the water ∣ 1,2-dichloroethane (DCE) in the presence of alkali cations (M +) is reported. A shift in the peak potential for Ba 2+ transfer and an increase in Δ E p from 0.030 to 0.060 V are the principal effects produced by the presence of M +. These findings depend on pH and the relative concentrations of both cations. The following chemical exchange reaction M (w) ++HX (c)+H 2O⇄MX (o)+H 3O + coupled to the electrochemical transfer of Ba 2+ accounts for Δ E p=0.060 V of the peak observed as a consequence of the net charge transfer of +1 at the interface. These results are in agreement with the hyper-Nernstian slope of 60 mV found for Ca 2+ and Ba 2+ ion selective electrodes based on antibiotics with carboxylic groups at intermediate pH values. A theoretical equation for the dependence of Δ o w φ 1/2 for Me 2+ with pH and M + activity was developed.

Accelerated assembly of G-quadruplex structures by a small molecule.

In the presence of alkali cations, notably potassium and sodium, DNA oligomers that possess two G-rich repeats associate into either a tetrameric parallel G-quadruplex or a variety of dimeric antiparallel G-quadruplexes. The formation of such structures is normally a very slow process. Some proteins, such as the beta-subunit of the Oxytricha telomere-binding protein, promote the formation of G-quadruplex structures in a chaperone-like manner. In this report, we present data concerning the role of a perylene derivative, PIPER, in the assembly of G-quadruplex structures as the first example of a small ligand behaving as a driver in the assembly of polynucleotide secondary structures. Gel-shift experiments demonstrate that PIPER can dramatically accelerate the association of a DNA oligomer containing two tandem repeats of the human telomeric sequence (TTAGGG) into di- and tetrameric G-quadruplexes. In so doing, PIPER alters the oligomer dimerization kinetics from second to first order. The presence of 10 microM PIPER accelerates the assembly of varied dimeric G-quadruplexes an estimated 100-fold from 2 microM oligomer. These results imply that some biological effects elicited by G-quadruplex-interactive agents, such as the induction of anaphase bridges, may stem from the propensity such compounds have for assembling G-quadruplexes.

Properties of Ti-Beta Zeolites Synthesized by Dry-Gel Conversion and Hydrothermal Methods

The large-pore beta zeolite containing Ti has been synthesized in the presence of alkali cations (Na+) by a dry-gel conversion (DGC) technique using tetraethylammonium hydroxide (TEAOH) as a structure-directing agent. The obtained Ti-beta zeolites were compared with hydrothermally synthesized (HTS) Ti-beta. It was found that Ti-beta-DGC samples adsorbed less water (12−13 wt %) than Ti-beta-HTS (19 wt %), indicating that Ti-beta-DGC is more hydrophobic than Ti-beta-HTS. We propose that this leads to a higher activity for the former in the oxidation of cyclohexane. Upon being washed with H2SO4, the turnover number (TON) of DGC samples slightly increased for the oxidation of cyclohexane. DGC and HTS samples demonstrated no significant difference in the activity for oxidation reactions of unsaturated alcohols and C6−C8 cyclic alcohols.

A relation between the amounts of sorbed alkali cations and the stability of colloidal silica

The sorption of alkali cations, at various pH values and concentrations (0.1–4.0 mol dm −3), on colloidal silica was investigated by the potentiometric titration method. At the same time the colloidal silica stability in the presence of these cations was determined. The critical coagulation concentration of alkali cations decreases with increasing pH and for all studied cations a common “critical sorption curve” was obtained. The amount of sorbed cations at the critical coagulation concentration was found to correspond to a maximum value of the sorption at a given pH. Therefore, the coagulation of colloidal silica in the presence of alkali cations will occur with the sorption of the maximum possible amount of these ions at given pH values.