Presence Of Alkali Metal Ions Research Articles

α-D Nucleoside Based Self-Healing Supramolecular Hydrogels Derived from the α-D Anomers of 2'-Deoxyguanosine and Fluorescent 8-Azapurine 2'-Deoxyribofuranosides.

Self-assembly of α-D nucleosides to supramolecular hydrogels is described in detail. Hydrogel formation is studied on α-D 2'-deoxyguanosine (α-dG), and the fluorescent 8-azapurine α-D nucleosides 2-amino-8-aza-2'-deoxyadenosine (α-2-NH2-z8Ad) and 8-aza-2'-deoxyisoguanosine (α-z8iGd). These compounds were prepared from α-D 8-aza-2'-deoxyguanosine by an activation/amination protocol followed by deamination. Protonation and deprotonation pKa values of monomeric nucleosides were determined. Fluorescence measurements displayed the pH-dependent fluorescence intensity of α-D 8-azapurine nucleosides. α-dG and α-z8iGd self-assemble to gels that are selective for K+-ions. The α-dG gel is transparent and the α-z8iGd gel shows fluorescence. α-2-NH2-z8Ad forms fluorescent gels in the presence of alkali metal ions of different size. SEM images expose a large condensed and flat structure for the α-dG gel, whereas the α-2-NH2-z8Ad gel consists of flakes that are connected to bundles. A porous structure generated by helical cylindric fibers was found for the α-z8iGd gel. All α-D hydrogels show long-term lifetime stability. The α-z8iGd hydrogel in KCl solution has the highest Tgel value. The minimum gelation concentration of the hydrogels is 0.3-0.5 mg nucleoside/100 μL alkali ion solution. In periodical step-strain experiments, the hydrogels of α-dG, α-2-NH2-z8Ad and α-z8iGd displayed thixotropy. Based on their self-healing and shear-thinning properties the hydrogels are injectable.

Secondary metal ion-induced electrochemical reduction of U(VI) to U(IV) solids

Recent studies have shown that aqueous U(VI) ions can be transformed into U(VI) precipitates through electrocatalytic redox reactions for uranium recovery. However, there have been no reports of U(IV) solids, such as UO2, using electrochemical methods under ambient conditions since low-valence states of uranium are typically oxidized to U(VI) by O2 or H2O2. Here we developed a secondary metal ion-induced strategy for electrocatalytic production of U(IV) solids from U(VI) solutions using a catalyst consisting of atomically dispersed gallium on hollow nitrogen-doped carbon capsules (Ga-Nx-C). This method relies on the presence of secondary metal ions, e.g., alkaline earth metals, transition metals, lanthanide metals, and actinide metals, which promote the generation of UO2 or bimetallic U(IV)-containing oxides through a two-electron transfer process. No U(IV) solid products were generated in the presence of alkali metal ions. Mechanistic studies revealed that the strong binding affinity between U(IV) and alkaline earth metals (Ca2+/Mg2+/Sr2+/Ba2+), transition metals (Ni2+/Zn2+/Pb2+/Fe3+, etc.) and lanthanide/actinide metals (Ce4+/Eu3+/Th4+/La3+) suppressed re-oxidation of U(IV) to U(VI), leading to the generation of U(IV)O2 and Mx(M = Ce, Eu, Th, La)U(IV)yO2. This work provides fundamental insights into the electrochemical behavior of uranium in aqueous media, whilst guiding uranyl capture from nuclear waste and contaminated water.

Direct Cation Stabilization Effects of CO Dimerization for Boosting C2 Pathways of CO2 Reduction on Noble Metal Surfaces

The carbon dioxide reduction reaction (CO2RR) is one of the most promising solutions for realizing carbon neutralization via converting the emitted CO2 into value‐added chemicals. The CC coupling step for CO dimerization is the rate‐determining step for C2 pathways, which have not been thoroughly investigated. Herein, the direct cation stabilization effects on CO dimerization for *OCCO formation on the representative Cu(100) and Pt(100) surfaces are investigated. Density functional theory calculations show that the presence of alkali metal ions plays a vital role in promoting the coupling of *CO monomers on both metal surfaces, where Cu shows a stronger stabilization effect. More importantly, a strong linear correlation (R2 ≈ 0.9) between the dimer stabilization energy and the reaction energy is revealed for the first time, which is a promising indicator for the selectivity of C2 pathways. Further investigations on electronic structures reveal that the promoting effect on *OCCO formation is strongly related to the negative charges of the molecules, in which the negative charge accumulation is favored by the directional electron transfer due to the chemisorption of *OCCO on Cu(100) surface. This work offers insights into the understanding of CC coupling reactions for CO2RR mechanisms.

Approaching High-Performance TS-1 Zeolites in the Presence of Alkali Metal Ions via Combination of Adjusting pH Value and Modulating Crystal Size.

Lewis acid zeolites play an important role in industrially important green reactions closely related to fine chemical and biomass conversion. Titanium-doped TS-1 zeolite is a milestone Lewis acid zeolite widely used in industrially significant green oxidation processes with hydrogen peroxide as an oxidant under mild conditions. TS-1 zeolites are normally synthesized in basic conditions under hydrothermal treatment. Up to now, there has still been no success in synthesizing active TS-1 Lewis acid zeolites by using inorganic alkali, e.g., NaOH or KOH as base, which is cheaper and more stable compared to the quaternary ammonium hydroxide or organic amines used in traditional synthesis. Here, an inorganic base of NaOH was employed in synthesizing active TS-1 zeolites for the first time. The crucial factor was the control of adverse effects of sodium cations on the incorporation of active titanium cations. Higher catalytic activity was achieved by further reducing the size of the TS-1 crystal by using the seed-added strategy, which uses the catalytic activity of a commercial catalyst, the production cost being much lower than commercial TS-1 catalysts, indicating great commercial potential and the possibility of preparing other cheap Lewis acid catalysts by using inorganic alkali.

1, 10-phenanthroline derivative as colorimetric and ratiometric fluorescence probe for Zn2+ and Cd2+

A colorimetric and ratiometric fluorescent probe 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (probe 1), was designed and synthesized for sensitive and selective detection of Zn2+ and Cd2+ ions in methanol, test paper and actual water samples. When probe 1 was excited at 350 nm in methanol solution, in the presence of alkali metal ions, alkali-earth metal ions and a variety of transition metal ions, it showed sensitive fluorescence selectivity to Zn2+ and Cd2+ ions. With the addition of Zn2+, the color of the solution changed from purple to cyan with the naked eye, and with the addition of Cd2+, the color of the solution changed from purple to blue. The fluorescence intensity of probe 1 showed a good linear relationship with Zn2+ and Cd2+ concentrations, and the detection limits were 0.04 μM and 0.11 μM, respectively. The binding mode of probe 1 and Cd2+ was discussed according to the 1-Cd single X-ray crystal structure. In addition, the results of strip test and real water sample test showed that probe 1 has potential application in environmental metal ion recognition and detection.

Phenanthroline-based ligand scaffold as an efficient colorimetric and ratiometric fluorescence probe for Zn2+ and Cd2+ ion detection

A colorimetric and ratiometric fluorescent probe 2-(naphthalen-2-yl)-2,11b-dihydro-1H-imidazo[4,5-f][1,10]phenanthroline (probe 1), was designed and synthesized for sensitive and selective detection of Zn2+ and Cd2+ in methanol, test paper and actual water samples. When probe 1 was excited at 350 nm in methanol solution, in the presence of alkali metal ions, alkali-earth metal ions and a variety of transition metal ions, it showed sensitive fluorescence selectivity to Zn2+ and Cd2+. With the addition of Zn2+, the color of the solution changed from purple to green with the naked eye, and with the addition of Cd2+, the color of the solution changed from purple to cyan. The fluorescence intensity of probe 1 showed a good linear relationship with Zn2+ and Cd2+ concentrations, and the detection limits were 0.09 μM and 0.06 μM, respectively. The binding mode of probe 1 and Zn2+ was discussed according to the 1-Zn single X-ray crystal structure. In addition, the results of strip test and real water sample test showed that probe 1 has potential application in environmental metal ion recognition and detection.

Alkali cation-mediated topology displayed by an exonic G-rich sequence of TRPA1 gene

G-rich sequences are intrinsic parts of the genome, widespread in promoters, telomeres, or other regulatory regions. The in vivo existence and biological significance have established the functional aspect of G-quadruplex structures and thus have developed immense interest in exploring their therapeutic aspects. Herein, using biophysical methods, we examined the structural status and comprehensive cation-dependence of a 17-bp G-rich genomic sequence (SKGT17) located in the coding region of the human TRPA1 gene, known to be associated with various neurovascular, cardiovascular, and respiratory conditions. TRPA1 is primarily seen as a therapeutic target for the development of novel analgesics. Bioinformatics analysis has suggested that 17-bp quadruplex motif is a binding site for transcription factor 'Sp1'. The formation and recognition of SKGT17 G-quadruplex might impact its regulatory functioning. Biophysical studies confirmed that the presence of alkali metal ions facilitated the formation of G-quadruplex in parallel topology. Native gel further substantiated the formation of a biomolecular species. Circular dichroism (CD), UV-thermal melting (Tm), and CD melting confirmed the formation of parallel G-quadruplex with metal ion-dependent stability. The stability of the G-quadruplex formed is found to be significantly high in the presence of K+ ions than that of other ions. Intriguingly, we have also established that this segment of the TRAP1 gene favors G-quadruplex formation over its participation in the corresponding duplex formation under K+ ions conditions. This study attempts to explain the rationale for the stabilization of G-quadruplex in the presence of alkali metal ions and may add to a better understanding and insights into DNA-metal ions interactions.

A colorimetric and ratiometric fluorescence probe for Zn2+ and Cd2+ with 1,10-phenanthroline derivative

A colorimetric and ratiometric fluorescent probe 2-([1, 1′-biphenyl]-4-yl)-2, 3b,11a,11b-tetrahydro-1H-imidazo[4,5-f][1,10]phenanthroline (probe 1), was designed and synthesized for sensitive and selective detection of Zn2+ and Cd2+ in methanol, test paper and actual water samples. When probe 1 was excited at 350 nm in methanol solution, in the presence of alkali metal ions, alkali-earth metal ions and a variety of transition metal ions, it showed sensitive fluorescence selectivity to Zn2+ and Cd2+. With the addition of Zn2+, the color of the solution changed from purple to green with the naked eye, and with the addition of Cd2+, the color of the solution changed from purple to cyan. The fluorescence intensity of probe 1 showed a good linear relationship with Zn2+ and Cd2+ concentrations, and the detection limits of both Zn2+ and Cd2+ were 0.11 μM. The binding mode of probe 1 and Zn2+ was discussed according to the 1-Zn single X-ray crystal structure. In addition, the results of strip test and real water sample test showed that probe 1 has potential application prospect in environmental ion recognition.

Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions.

The one-pot self-coupling reaction of 3-amino-5-bromo-BODIPY 9 under Buchwald-Hartwig amination conditions gave nitrogen-bridged cyclic BODIPY tetramer 10, pentamer 11, and hexamer 12. Oxidation of 10, 11, and 12 in the presence of alkali metal ions provided 13, 15, and 16, respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10-12 showed large association constants (104 -106 M-1 ) with K+ and Na+ , but the spontaneous complexations were not observed, indicating the extremely high affinities of 13-16 toward alkali metal ions, which can be ascribed to the multiple and effective ion-dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF2 walls surrounding the cavity. Importantly, 13, 14, and 15 show diatropic ring currents as a result of global aromaticity.

Expanded Azaporphyrins Consisting of Multiple BODIPY Units: Global Aromaticity and High Affinities Towards Alkali Metal Ions

AbstractThe one‐pot self‐coupling reaction of 3‐amino‐5‐bromo‐BODIPY 9 under Buchwald–Hartwig amination conditions gave nitrogen‐bridged cyclic BODIPY tetramer 10, pentamer 11, and hexamer 12. Oxidation of 10, 11, and 12 in the presence of alkali metal ions provided 13, 15, and 16, respectively, as the first examples of expanded azaporphyrins possessing more than six pyrrole rings. Curiously, the oxidation even in the absence of alkali metal ions gave the same complexes as a result of spontaneous complexation. 10–12 showed large association constants (104–106 M−1) with K+ and Na+, but the spontaneous complexations were not observed, indicating the extremely high affinities of 13–16 toward alkali metal ions, which can be ascribed to the multiple and effective ion–dipole interaction of the alkali metal ion with the negatively polarized F atoms of the BF2 walls surrounding the cavity. Importantly, 13, 14, and 15 show diatropic ring currents as a result of global aromaticity.

Electrochemical Transparency of Graphene.

In the present study, we used the electrochemical transparency of graphene to show that the direct intercalation of alkali-metal cations is not a prerequisite for the redox reaction of Prussian blue (PB). PB thin films passivated with monolayer graphene still underwent electrochemical redox reactions in the presence of alkali-metal ions (K+ or Na+) despite the inability of the cations to penetrate the graphene and be incorporated into the PB. Graphene passivation not only preserved the electrochemical activity of the PB but also substantially enhanced the stability of the PB. As a proof of concept, we showed that a transparent graphene electrode covering PB can be used as an excellent hydrogen peroxide transducer, thereby demonstrating the possibility of realizing an electrochemical sensor capable of long-term measurements.

Electrochemical Oscillations (Named Oscillations H and K) during H2O2 Reduction on Pt Electrodes Induced by a Local pH Increase at the Electrode Surface

The reduction of H2O2 on Pt electrodes in H2SO4 solution shows various electrochemical oscillations, named sequentially from A to J, as reported previously. The present work demonstrates that this electrochemical system also shows a new type of oscillation, called oscillation K, when an alkali metal sulfate is added to the H2SO4 solution containing H2O2. In the presence of alkali metal ions, the local pH at the electrode surface (pHs) becomes basic during H2O2 reduction, and, consequently, reduction and oxidation reactions of HO2 −, which is formed by dissociation of H2O2, take place at the electrode. Detailed studies reveal that oscillation K is caused by an N-shaped negative differential resistance (N-NDR) that is induced by the autocatalytic reduction of HO2 − and that the oscillation can be classified as a “hidden” N-NDR (HN-NDR) type. In this sense, oscillation K is similar to oscillation H which is induced by the autocatalytic reduction of H2O2 and is an HN-NDR oscillator. Besides, a numerical simulation was conducted to understand how HO2 − reduction and oxidation cause oscillation K. To estimate the change in pHs, our simulation employs a newly developed model in which the dissociation of water and that of H2O2 at the electrode are considered.

Trizbenzim, Cu-Trizbenzim and Zn-Trizbenzim as G-Quadruplex Inducing and Stabilizing Compounds on Human Telomeric Sequence and their Anticancer Properties.

The benzimidazole and their derivatives have rich biological relevance with respect to available natural amino acids and their role in protein folding and quaternary conformations. Thus the ligand trizbenzim and their Cu(II) and Zn(II) metal complexes were prepared to induce G-quadruplex conformation even under no-salt conditions with remarkable anticancer activities. The ligand N,N',N''-Tris-(1H-benzoimidazol-2-ylmethyl)-[1,3,5]triazine-2,4,6-triamine ( trizbenzim) and its Cu and Zn complexes (Cu-trizbenzim, Zn-trizbenzim) were synthesized and characterized by IR, NMR, and MALDI-TOF techniques. The pure ligand and its complexes interacted with human telomere DNA sequence d(TTAGGG), HTelo8and HTelo20and the interactions were followed by circular dichroism spectroscopy, FID assay, and molecular docking techniques. The compounds were tested for anticancer activity towards selected cell lines. All the three compounds stabilized the HTelo8 and HTelo20 in parallel and antiparallel G-quadruplex conformations with salt conditions. Under no-salt conditions, the compounds induce and stabilize the G-quadruplex conformation in antiparallel topology selectively. The pure ligand, Cu-trizbenzim, and Zn-trizbenzim were involved in partial or classical intercalation and some backbone interactions on the strand. The FID assay using thiazole orange intercalator supports the proposed intercalation mode of binding for the three compounds, especially for the pure ligand and the Cu-complex. The MOE docking experiments using X-ray and NMR derived G-quadruplex models with the title compounds extensively support the G-quadruplex induction and stabilization of the telomere sequence by these compounds. The guanines bases involved in the G-tetrad formation interact well with the triazine and the benzimidazole part of the ligand through strong π-π interactions. The primary mode of binding is described as end stacking and intercalation of the compounds to the G-quadruplex structures. The Cu-trizbenzim exhibited more anticancer property in comparison to the pure ligand and the Zntrizbenzim complex. The IC50 values were in the nanomolar range from 50 to 150nM in concentration. This novel self-induction of G-quadruplex is novel without the presence of alkali metal ions.

A novel approach towards crown-ether modified polyimides with affinity for alkali metal ions recognition

In the attempt to enlarge the family of imide-based materials suitable for sensor applications, novel five- and six-membered thermostable polyimides functionalized with benzo-15-crown-5 ether side chains were synthesized and thoroughly investigated with regard to their affinity for alkali metal ions recognition. For this purpose, a new diamine monomer containing as receptor triphenylmethane modified with 15-crown-5 ether (called by us crowned TPM) has been synthesized and structurally characterized. For the first time, we brought evidence for the occurrence of a ground-state intermolecular charge transfer (CT) complex between the donor crowned TPM diamine and the acceptor diimide segment which is actually responsible for the polyimides strong light emission in the green to yellow spectral range. All polyimides were electrochemically active in both anodic and cathodic regions, their voltammetric response being consistent with the coplanarity and electron accepting strength of the diimide segment. In the presence of alkali metal ions some changes appeared in the electronic absorption signals, although quite diffuse. Instead, these cations significantly altered the fluorescence response of polyimides in dependence on the excitation wavelength, cation type and polymer structure. These mostly caused the occurrence of a new emission band, when the green or yellow fluorescence turned in blue, thus proving the capability of our polyimides to detect alkali metal ions.

Alkali Metal Ions: A Secret Ingredient for Metal Nanocluster-Sensitized Solar Cells

The presence of alkali metal ions (AMIs) during the adsorption of thiolated Au nanoclusters (NCs) onto TiO2 plays a critical role in achieving high power conversion efficiency and suppressing anoma...

Metallo-responsive self-assembly of lipophilic guanines in hydrocarbon solvents: a systematic SAXS structural characterization.

Lipophilic guanines (LipoGs) in aprotic solvents undergo different self-assembly processes based on different H-bonded motifs. Cylindrical nanotubes made by π-π stacked guanine tetramers (G-quadruplexes) and flat, tape-like aggregates (G-ribbons) have been observed depending on the presence of alkali metal ions. To obtain information on the structural properties and stability of these LipoG aggregates, Small-Angle X-ray Scattering (SAXS) experiments have been performed in dodecane, both in the presence and in the absence of potassium ions. As a result, the occurrence of the two different metallo-responsive architectures (nanoribbons or columnar nanotubes) was confirmed and we reported here for the first time a systematic study on the dependence of the aggregate properties on composition, temperature and molecular unit structure. Even if dodecane was selected to favour LipoG solubility, a strong tendency to self-organize into ordered lyotropic phases was indeed detected.

Zeolite-Based Sorbent for CO2 Capture: Preparation and Performance Evaluation.

In this work, zeolite-based sorbents were developed from gasified rice husk. CO2 capture capacity of the sorbents was examined at various temperatures and pressures employing a fixed-bed flow reactor and simulated flue gas. Various physicochemical properties such as thermal stability, pore size distribution, morphology, chemical composition, etc. of the in-house-developed materials were characterized in detail and were also compared with two commercially available zeolites. Tetra-ethylenepentamine was impregnated in the in-house-developed zeolite supports to investigate its suitability to improve the CO2 adsorption capacity. The effects of reactor pressure, temperature, Si/Al ratio, and amine loading on CO2 uptake capacity were examined. A declining trend in CO2 adsorption capacity was observed with the increase in adsorption temperature and amine loading. At 30 °C, zeolite-Y (designated as Z-Y-3, silica to alumina ratio of 2.25) sample exhibited maximum adsorption capacity, and the obtained values were around 114 and 190 mg CO2/g sorbent under atmospheric and 5 bar pressure, respectively. It was also observed that the presence of alkali metal ions influenced the adsorption capacity of the zeolites. The study inferred that the adsorbent was efficient and promising for multiple adsorption-desorption cycles without much deterioration of the capture capacity.

Promotional effects of Fe on manganese oxide octahedral molecular sieves for alkali-resistant catalytic reduction of NOx: XAFS and in situ DRIFTs study

Currently, selective catalytic reduction (SCR) of NOx with NH3 in the presence of alkali metal ions by using vanadium-free catalysts is still a big challenge for the removal of NOx for stationary sources. In this work, improved reduction of NOx with NH3 in the presence of alkali metal ions over novel Fe-doped manganese oxide octahedral molecular sieve (OMS-2) catalysts has been demonstrated and the promotional effects of Fe have been clarified. The Fe-doped OMS-2 (Fe-OMS-2) catalysts exhibited excellent NH3-SCR activity, improved N2 selectivity and enhanced alkali resistance. The X-ray absorption fine structure spectroscopy (XAFS) results indicated that the trapped K+ ions could make the catalyst structure more stable. In situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTs) results revealed that the Fe doping could enhance adsorption of NH3 species and adsorb various types of NOx species namely monodentate nitrate, bridged nitrate, bidentate nitrate and chelating nitrite. These formed intermediates on the Fe-OMS-2 catalysts were more reactive and thus more effectively participated in the SCR reactions. Superior alkali resistance of the Fe-OMS-2 catalysts was due to improved redox species, more acid sites and stronger adsorption of NOx species. The present investigations in this work may lead to an alternative development of high-performance non-vanadium catalysts for alkali-resistant NOx reduction.

Enhanced upconversion and downshifting emissions from Tm3+, Yb3+ co-doped CaZrO3 phosphor in the presence of alkali ions (Li+, Na+ and K+)

The Tm3+, Yb3+ co-doped CaZrO3 phosphor samples have been synthesized through solid state reaction method in the absence and presence of alkali metal ions (i.e. Li+, Na+, K+). The X-ray diffraction (XRD) study shows the formation of CaZrO3 crystal with orthorhombic phase. The Tm3+, Yb3+ co-doped CaZrO3 phosphor emits intense upconversion emission in blue (474 nm) and NIR (799 nm) regions due to 1G4 → 3H6 and 3H4 → 3H6 transitions of Tm3+ ions, respectively on excitation with 980 nm radiation. The emission intensity is significantly enhanced in the presence of alkali ions due to charge compensation and asymmetry in the crystal field. The emission intensity in the case of Na+ co-doped phosphor is maximum and at 1 W pump power, it is increased by ∼44 and ∼31 times in blue and NIR regions, respectively as compared to without alkali ions co-doped phosphor. The downshifting emission in blue region has been observed due to oxygen vacancy and Tm3+ ions on excitation with 277 and 360 nm radiations which is enhanced significantly in the presence of alkali ions. Thus, the intense blue emission by this material is suitable for blue and white light emitting phosphors.

Потенциометрическое определение метионина в щелочных растворах с помощью мембран Nafion и МФ-4СК, подвергшихся обработке и модификации

Разработаны массивы перекрестно чувствительных ПД-сенсоров (аналитический сигнал – потенциал Доннана) на основе мембран Nafion и МФ‑4СК, подвергшихся модификации и обработке, для определения анионов и цвиттерионов метионина совместно с катионами калия в щелочных растворах. Выявлено влияние кислотно-основных свойств и объемной доли наночастиц гидратированных оксидов ЭO2 (Э=Ce, Zr, Si), вводимых в мембраны разными методами, на перекрестную чувствительность ПД-сенсоров в исследуемых растворах. Выявлена зависимость чувствительности ПД-сенсоров к анионам и цвиттерионам метионина от диффузионной проницаемости мембран, подвергшихся обработке при различных температуре и относительной влажности. Выбраны образцы, обеспечивающие достаточно низкие значения относительной погрешности и относительного стандартного отклонения определения анионов и цвиттерионов метионина совместно с катионами калия в диапазоне концентраций от 1.0·10‑4 до 5.0·10‑2 М, не смотря на переменные значения рН растворов, изменяющиеся в широком диапазоне (от 8 до 11).