Interaction Of Cations Research Articles

Interaction of Nitrogen-Rich Cations with Azotriazolone Anions through Ion Exchange Results in the Formation of Energetically Stable and Insensitive Compounds.

In our pursuit of promoting the green development of energetic materials and harnessing their functional benefits, we strive to address the inherent contradiction between energy and low sensitivity. In this regard, we have successfully constructed an azotriazole framework via environmentally friendly electrochemistry with a satisfactory yield of 62.3%. Through a simple ion-exchange process, we then synthesized nitrogen-rich salt derivatives of azotriazolone. These nitrogen-rich salts exhibit a wide range of nitrogen contents, ranging from 32.16 to 68.80%. Remarkably, crystallographic analysis of these green energy-containing salts reveals substantial advantages in terms of thermodynamic stability and low sensitivity. Experimental investigations have demonstrated a positive relationship between the nitrogen content and the pyrothermal performance of the azotriazolone derivatives. Of particular significance is compound 5, a triaminoguanidine salt, which exhibits an exceptionally high nitrogen content of 68.80%. It displays a detonation pressure of 28.2 GPa and a detonation velocity of 7939.4 m s-1. Moreover, the derivatives of azotriazolone salts demonstrate the formation of nitrogen-rich compounds, characterized by insensitive properties, attributed to the hydrogen-bonded network structures resulting from anion-cation interactions. With the exception of compound 5, which exhibits a friction sensitivity of 252 N, the remaining derivatives show a similar value of approximately 360 N. This suggests that azotriazolone serves as a promising material possessing both stabilizing properties and better detonation performance, thereby providing a favorable platform for the synthesis of novel compounds with advantageous properties.

D2/H2 separation by quantum sieving in LiNaA zeolites: the role of aperture size and strong guest–cation interactions

D2/H2 separation by quantum sieving in LiNaA zeolites: the role of aperture size and strong guest–cation interactions

DFT-details & atomic-scale MC/MD simulations and experimental exploration of the Silybum extract bio-molecules effectiveness in mitigating aggressive effects of simulated corrosive concrete pore solutions

The growing emphasis on sustainability and environmental awareness is paramount today. Corrosion control, often achieved through inhibitors, is a prominent approach, with plant extracts being favored for their accessibility and ease of extraction. Yet, their efficacy in alkaline environments, common in construction materials like cement and concrete, remains constrained. This study evaluates the potential of Silybum extract as a corrosion inhibitor within a simulated chloride-contaminated concrete setting, employing electrochemical and surface analyses to scrutinize the inhibitory characteristics and surface chemistry of the treated samples. Following the analysis of concentrations at 0.5%, 1%, and 2% Silybum extract in the simulated concrete solution, the optimal inhibition efficiency of 96.5% was obtained based on polarization measurements. The electrochemical impedance spectroscopy (EIS) confirmed that the log of impedance at low-frequencies (log|Z|10mHz) for the inhibited sample had a noticeable increment compared to the blank sample, rising from 4.60 to 5.13 after 48 h of exposure. The use of Silybum extract resulted in a remarkable 89% increase in total resistance after 5 h of immersion, as compared to the blank basic solution. Silybum exhibited a protective effect on metal substrates through three key mechanisms: forming a passive surface film via electron donation, inhibiting corrosion reactions through surface adsorption, and reducing corrosive species diffusion via physical surface coverage by heavy components. These mechanisms were supported by various surface studies which revealed the formation of a protective layer instead of corrosion products originating from Silybum components. Also, the interaction of cations in the basic solution with Silybum components and the adsorption of the obtained complex on the metal surface was demonstrated via computer modeling calculations. Theoretical studies revealed negative adsorption energies for the complexes (−1129.83 kcal/mol energy in molecular dynamics (MD) simulation for the [Ca(Silychristin)3]+2 complex), confirming their strong chemical affinity for interfacial attachment.

Role of WSOCs and pH on Ammonium Nitrate Aerosol Efflorescence: Insights into Secondary Aerosol Formation.

Efflorescence of ammonium nitrate (AN) aerosols significantly impacts atmospheric secondary aerosol formation, climate, and human health. We investigated the effect of representative water-soluble organic compounds (WSOCs) (sucralose (SUC), glycerol (GLY), and citric acid (CA) on AN:WSOC aerosol efflorescence using vacuum Fourier transform infrared spectroscopy. Combining efflorescence relative humidity (ERH) measurements, heterogeneous nucleation rates, and model predictions, we found that aerosol viscosity, correlating with molecular diffusion, effectively predicted ERH variations among the AN:WSOC aerosols. WSOCs with higher viscosity (SUC and CA) hindered efflorescence, while GLY with a lower viscosity showed a minor effect. At a low AN:CA molar ratio (10:1), CA promoted ERH, likely due to CA crystallization. Increasing the droplet pH inhibited AN:CA aerosol efflorescence. In contrast, for AN:SUC and AN:GLY aerosols, efflorescence is pH-insensitive. With the addition of trivial sulfate, AN:SUC droplets exhibited two-stage efflorescence, coinciding with ammonium sulfate and AN efflorescence. Given the atmospheric abundance, the morphology, phase, and mixing state of nitrate aerosols are significant for atmospheric chemistry and physics. Our results suggest that AN:WSOCs aerosols can exist in the amorphous phase in the atmosphere, with efflorescence behavior depending on the aerosol composition, viscosity, pH, and the cation and anion interactions in a complex manner.

Deep removal of dichloromethane using ionic liquids: Thermodynamic and molecular insights

In this work, the efficient capture of dichloromethane (DCM) with ionic liquids (ILs) was proposed and systematically investigated. The carboxylic acid-based anion and quaternary phosphonium cation were screened out, and on this basis the designed tetrabutylphosphonium hexanoate ([P4444][C5COO]) and tetrabutylammonium hexanoate ([N4444][C5COO]) ILs were finally synthesized. The results demonstrate that [P4444][C5COO] exhibits the optimal absorption performance (1400 mg·g−1 at 30 °C and 0.3 bar). Notably, the Henry's law constant for DCM in [P4444][C5COO] (3.02 Pa·m3·mol−1 at 25 °C) is the lowest among all solvents documented in the literature. The microscopic mechanism was explored by 1H NMR spectra, quantum chemical (QC) calculations and molecular dynamics (MD) simulations. The results suggest that anion plays a dominant role, while weak cation–anion interaction and large free volume of cations are conducive to the absorption of DCM. The proposed IL was considered as a promising alternative absorbent to achieve high absorption capacity, suitable physicochemical properties and excellent recyclability.

Physico-Chemical and Thermodynamic Adsorption Studies of A Few Soils from Delta and Oyo State, Nigeria

Comprehensive study of the physico-chemical properties and interactions of cations with soils is a crucial research need for the development of more sustainable agricultural systems. The analysis of physico-chemical and thermodynamic adsorption studies of various soils from Delta and Oyo State, Nigeria, is the main emphasis of this paper. Two surface soils from the Cocoa Research Institutes of Nigeria (CRIN) and the Isoko North Local Government of Delta State were compared for their physico-chemical properties and heavy metal speciation. The effects of adsorption duration, pH, initial sorbate concentration, and ionic strength were also studied in relation to the adsorption of Cd2+, Pb2+, Cu2+, and Zn2+ ions. On the equilibrium and thermodynamics of the adsorption process, more investigation was conducted. The physico-chemical studies revealed that soil from CRIN had a pH of 6.1 in water and 5.4 in KCl, whereas soil from Isoko North had a pH of 4.3 in water and 3.0 in KCl. The largest percentages of organic matter are found in the soil from Isoko North (3.07%) and CRIN (3.82%). For both soils, the order of exchangeable bases was Ca > K > Mg > Na. The heavy metal concentrations in both soils were in the following order: Zn > Cu > Ni > Pb > Cd = Al; CRIN: 3.82meq/100g for CEC; Isoko North: 2.85meq/100g for CEC. In contrast to CRIN soil, Isoko North soil showed a larger bulk density and a superior hydraulic conductivity. Extractable elements were present in both soils in the following order: Mn > Fe > Zn > Cu. The base saturation in the CRIN soil was higher than the base saturation in the Isoko North soil, which was lower at 60.73%. Zn, Pb, and Cd were the outcomes of the heavy metal speciation for both soils. The equilibrium adsorption data, which were closely related to the Langmuir isotherm model, showed that the maximum capacity of lead for soil from Isoko North was 5.8140 mmol/g and for soil from CRIN was 7.6335 mmol/g. Thermodynamic investigations showed that the adsorption process was spontaneous for simply Cu2+ (for soil from CRIN) and non-spontaneous for other metal ions from both soils. Metal ions from both soils displayed exothermic and endothermic adsorption, respectively, for Cd2+ and Cu2+ (for soil from CRIN).

Complex dielectric response and EDL characteristics of different types of ionic liquid iron oxide nanofluids (ionanofluids)

Ionic liquid based magnetic nanofuids (ILMFs), an important subclass of ‘IoNanofuids’, have promising prospectus in numerous technological fields. Herein, we have investigated on the dielectric response and ac conductance behaviour of 1 wt% iron oxide-based ILMFs synthesized using pyridinium-based ILs viz., 1-Butyl-4-methylpyridinium tetrafuoroborate (A), 1-Butyl-4-methylpyridinium chloride (B), 1-Butyl-4-methylpyridinium bromide (C) and 1-Butylpyridinium bromide (D), and having variable stability. The dielectric permittivity exhibited a strong correlation with temperature and frequency, especially at low frequency ranges. Havriliak-Negami (H-N) function was plotted for all the four ILMFs which demonstrated a complex dielectric behaviour. The complex dielectric responses (in the range between 10−1–107 Hz) of these ILMFs at various frequencies and temperatures showed two relaxation processes following either Debye or non-Debye nature. The ILMF synthesized in B and D were the stablest. In B, two relaxation processes at 104 Hz and 6 × 102 Hz were observed (at 373.15 K), the temperature dependence being much stronger for the second process. Cole-Cole processes are observable in both relaxations. α parameters varied in the range 0.8 – 1.0 and 0.62 – 0.9 for first and second relaxation process respectively and β parameter equal to 1 at all temperature range for both relaxation processes. In ILMF synthesized using D, Debye relaxation with two relaxation processes were observed closer at 9.1 × 103 Hz and 1.1 × 103 Hz. All the α and β parameters were 1 or 0.99 indicating same relaxation time for all molecules. With D having higher anion-cation interaction energy, Debye process could be observed. The alternating current (AC) conductance of these ILMFs tends to increase with increase in temperature as well as frequency of applied field till 105 Hz after which it decreases.

Binding of radionuclides and surrogate to 18-crown-6 ether by density functional theory

We use density functional theory to investigate the interactions of cerium, americium, and curium cations with crown ethers. Our calculations reveal that the modeled structure of cerium integrated within the crown ether is in good agreement with experimental data, with the negative binding energy indicating that capturing the cerium nitrates is thermodynamically favorable. Our results demonstrate that crown ethers can also bind americium and curium, providing insights into the potential applications of crown ether in radionuclide sequestration. Finally, we explore the impact of the skeleton modification of different crown ethers through by substitution of nitrogen atoms in the core of the crown ether for oxygen atoms and find that this structural modification significantly increases the radionuclide binding energies. These findings provide insights on the potential for the use of organic linkers such as crown ethers to address the urgent needs in radionuclide sequestration, separation and sensing.

Electrochemical Characterization of Salt-in-Water and Water-in-Salt Zinc Sulfate and Zinc Acetate Electrolytes

The electrochemical properties of Zn(OAc)2 or ZnSO4 with water at different concentrations are investigated. The electrochemical stability window follows Pt < Au < glassy carbon electrodes, and expands with increasing concentration of electrolytes. The change in salt concentration does not significantly change the double layer capacitance, and the potential of zero charge of Pt, Au and glassy carbon electrodes are estimated to be 0.25–0.35 VSCE, 0.05 VSCE, and –0.20 VSCE, respectively. With hydroquinone as the redox probe, the redox electrochemistry, ion transport and electron transport kinetics in these electrolytes are studied. The apparent redox potential of hydroquinone increases with the electrolyte concentration, and the diffusion coefficients of hydroquinone in Zn(OAc)2 and ZnSO4 electrolytes decrease with the increase of electrolyte concentration. The electron transfer rate constants (k) between the electrode and hydroquinone in Zn(OAc)2 and ZnSO4 electrolytes range in 1.28–1.46 cm s−1 and 0.29–0.81 cm s−1, respectively. The lower k in ZnSO4 electrolytes is related to the lower solvent reorganization energy, the interaction of electroactive ions with water, and the interaction of electrolyte cations.

Two UV organic-inorganic hybrid antimony-based materials with superior optical performance derived from cation-anion synergetic interactions

Finding suitable strategies to effectively enhance the optical properties of materials are the goal being pursued by researchers. Herein, cation-anion synergetic interactions strategy was proposed to develop two novel organic-inorganic hybrid antimony-based optical materials, (C3H5N2)SbF2SO4 (I) and (C5H6N)SbF2SO4 (II), which were obtained by introducing Sb3+cation containing stereochemically active lone-pair (SCALP) and organic π-conjugated cations into sulphate system. The synergistic interactions of the organic π-conjugated cations, the inorganic [SbO2F2]3− seesaw anions and the [SO4]2− distorted tetrahedra anions make their ultraviolet (UV) absorption edges approach 297 and 283 nm, respectively, and raise their birefringence up to 0.193@546 nm and 0.179@546 nm, respectively. Interestingly, although the two compounds have the same stoichiometric ratio and similar one-dimensional (1D) chain structure, they show opposite macroscopic symmetry, where the NCS compound (II) exhibits a large second-harmonic generation (SHG) response (1.6 times that of KH2PO4). The two reported compounds are found to be promising UV optical materials in the experimental tests.

Pressure-dependent cationic associations of ionic liquids with bentonite nanoclay

Pressure-dependent IR spectroscopy is used to investigate the possibility of stabilizing ionic liquid (IL)–hydrophilic bentonite (Bent) composites with the application of high pressures. Ambient-pressure experiments suggest IL hydrophilicity/hydrophobicity impacts cation and anion interactions with Bent. For example, both the cation and anion of hydrophilic 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) experience composition-dependent vibrational mode wavenumber shifts. However, anion–Bent interactions are suppressed at ambient pressure when the nanoclay is paired with hydrophobic 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf2]). Compression to high pressures triggers significant blue shifts for ring-bound C–H stretching bands. The rates of these changes upon pressurization indicate the two ILs experience different interaction motifs with the Bent surface. Large wavenumber shifts for C4–H and C5–H stretching modes of [BMIM][NTf2] imply preferential coordination to Bent surface sites through these groups. This presumably leaves the C2–H group available for hydrogen bonding with the NTf2 anion. The situation is different for [BMIM][DCA], where all three C–H groups on the imidazolium ring appear to interact with Bent surface sites. Depressurization reveals further differences between the two systems. Spectroscopic features are reversible for [BMIM][NTf2], whereas the C–H stretching mode blue shifts for [BMIM][DCA] are either irreversible or the relaxation is kinetically hindered upon return to ambient pressure. Taken together, the spectroscopic data strongly suggests that IL–Bent interactions are pressure sensitive, and IL assemblages along the interface may be manipulated through the application of high pressure.

Texture classification and in situ cation measurements by SEM-EDX provide detailed quantitative insights into cell wall cation interaction changes during ageing, soaking, and cooking of red kidney beans

Hard-to-cook (HTC) is a textural defect that delays the softening of common bean seeds during cooking. While this defect is commonly associated with conventionally stored beans, soaking/cooking of beans in CaCl2 solutions or sodium acetate buffer can also prolong the cooking time of beans due to formation of Ca2+ crosslinked pectin retarding bean softening during cooking. In this study, the role of the cell wall-bound Mg2+/Ca2+ content and the degree of pectin methyl esterification (DM) was quantified, as important factors for bean texture-related changes stipulated in the pectin-cation-phytate hypothesis, the most plausible hypothesis of HTC development. Evaluation of texture changes during cooking of conventionally aged beans (35 °C and 83% RH for up to 20 weeks), beans soaked/cooked in CaCl2 solutions (0.01 to 0.1 M) or soaked in 0.1 M sodium acetate buffer (pH 4.4) revealed large bean-to-bean variations. Therefore a texture-based classification approach was used to better capture the relation between texture characteristics and cell wall polymer, in particular pectin, related changes. While cell wall-bound Ca2+ and pectin DM did not change/were not related to the texture variation during cooking of fresh beans, increased cell wall-bound Ca2+ and decreased pectin DM were associated with prolonged conventional storage of beans and their texture changes during subsequent cooking (due to pectin cross linking, retarding its solubilization during cooking). Exogenously added Ca2+ from pre-treating beans in CaCl2 solutions promoted to a great extent the cell wall-bound Ca2+ during soaking but even more so during cooking, complementing the harder texture associated with these beans during cooking (compared to conventionally stored and fresh beans). Similarly, free Ca2+ endogenously generated by phytase-catalysed phytate hydrolysis (beans treated by acetate buffer) promoted crosslinking of pectin by Ca2+ (cell wall-bound Ca2+), delaying softening of beans during cooking.

Preparation of soluble colorless poly(amide‐imide) films with high glass transition temperature and low coefficient of thermal expansion by coordination interaction of Li cations

AbstractTo meet the needs of high heat‐resistant and colorless polyimide (CPI) films, a series of poly(amide‐imide) (PAI) films were synthesized by copolymerization of 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CBDA), terephthaloyl chloride (TPC), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2′‐bis(trifluoromethyl)benzidine (TFDB) with the addition of lithium chloride (LiCl) for ionic coordination. The coordination of Li cations with carbonyl groups significantly reduced the coefficient of thermal expansion (CTE) and improved the mechanical properties. Moreover, by adjusting the ratio of CBDA and TPC, all PAI films exhibited high glass transition temperature (Tg), low CTE and high transparency. Among these PAI films, PAI‐6‐2Li exhibited excellent comprehensive performance with a high Tg of 363 °C, low CTE of 6.4 ppm/K, high transmittance of 84% at 400 nm and tensile modulus of 7.2 GPa, which was expected to be used in the field of flexible displays.

Understanding the Behavior of Sodium Polyacrylate in Suspensions of Silica and Monovalent Salts.

This study investigated the interaction of monovalent cations with different sizes on quartz surfaces and the rheological impact that this causes in concentrated suspensions when subjected to the action of a rheological modifier, in this case, sodium polyacrylate (NaPA). Yield stress was determined using a rheometer with a vane-in-cup configuration to establish the relationship between shear stress and strain. Experiments were carried out in LiCl, NaCl, KCl, and CsCl solutions. The results show that the yield stress increases following the order Li < Na < K < Cs in the absence of PAA. However, the addition of NaPA significantly reduced the yield stress in all cases. This reduction was more noticeable in the LiCl and NaCl solutions than in the KCl and CsCl solutions, suggesting a more pronounced effect of PA in maker salts. We conducted molecular dynamics simulations to understand how PA interacts with dissolved salts on the quartz surface. Our results showed that Li had the highest adsorption, followed by Na, K, and Cs. As the salt concentration increased, so did the adsorption. We validated these simulation results with rheological experiments, which helped us understand the observed differences. The molecular interactions indicate that, in the lithium system, cationic bridges and the synergy between hydrogen bridges and hydrophobic bridges predominate mainly. This tendency decreases as the type of cation is changed due to the decrease in the electrical density of the cation in the following order: Li < Na < K < Cs. This reduces bridging with the quartz surface and, therefore, directly impacts the system's rheological properties.

Autoregulatory mission impossible: when afferent arterioles lose contractility

The myogenic response of afferent arterioles is a key autoregulatory mechanism that protects the glomeruli from barotrauma. Afferent arteriolar smooth muscle cells contract to increased intraluminal pressure through mechanosensitive cation channels and interactions between integrin and extracellular matrix that trigger calcium-dependent actomyosin contraction. The study by Feng etal. provides evidence supporting the concept that increased matrix metalloproteinase 9 in kidney microvessels of Dahl salt-sensitive rats interferes with integrin-matrix binding and promotes phenotypic transformation of afferent arterioles, causing loss of myogenic constriction and hypertensive nephropathy.

Self-Assembly of an Anionic [Cu5I8]3- Supramolecular Cluster Driven by Ion-Pair Interaction and Catalytic Properties.

The rational design and controlling synthesis of an anionic cuprous iodide supramolecular cluster with high nuclearity through noncovalent interactions remains a significant challenge. Herein, a cationic organic ligand (L1)3+ was driven by anion-cation ion-pair electrostatic interaction to induce free cuprous iodide to aggregate into an anionic supramolecular cluster, [(Cu5I8)3-(L1)3+] (C1). Moreover, five copper(I) atoms bind with eight iodides through multiply bridged Cu-I bonds associated with intramolecular cuprophilic interactions in this butterfly-shaped cluster core. Supramolecular cluster C1 exhibited a solid-state emission at 380 nm and an emission at 405 nm in acetonitrile at room temperature, respectively. Interestingly, this unprecedented cuprous iodide cluster demonstrated a good catalytic performance for azide-alkyne cycloaddition reaction (CuAAC) and the catalytic yield can be up to 80% for eight different substrates at 80 °C. Furthermore, the density functional theory (DFT) calculation revealed that the thermodynamic-dependent cycloaddition reaction underwent a four-step pathway with an overall energy barrier of -43.6 kcal mol-1 on the basis of intermediates monitored by mass spectrum.

Electrical Effects of Ionic Deficient Cubic Ferrite Spinels: A Case Study on MgFe2O4

AbstractElectron transport via indirect exchange interactions between octahedral sites in spinels is affected by cationic or anionic vacancies. Thus, the deviation of the electron hopping mechanism is investigated, from a constant energy barrier toward a variable range energy barrier in iron‐deficient and oxygen‐deficient cubic magnesium ferrite spinels. Variable range electron hopping activation energy at high temperatures is consistent with the modified cation–anion interactions in the distorted structure of an ionic deficient cubic magnesium ferrite spinel. For these observations, an instrumental method is developed to evaluate the electron exchange interactions and general redox kinetics on surfaces, managed by exposure to the flow of a wide variety of desired gases. The applications of this instrument are far beyond the example studies reported here.

Supramolecular assembly of coumarin 7 with sulfobutylether-β-cyclodextrin for biomolecular applications.

Coumarins, in general, exhibit a wide range of photophysical characteristics and are highly sensitive to their microenvironment, and, therefore, their fluorescence characteristics have attracted immense attention as sensors in chemical and biological systems. In the present study, the supramolecular interaction of a bichromophoric coumarin dye, namely, Coumarin 7 (C7) with sulfobutylether-β-cyclodextrin (SBE7βCD) macrocyclic host at different pH conditions has been investigated by using optical spectroscopic techniques such as absorption, steady-state and time-resolved emissions, and circular dichroism measurements and compared with that of βCD. Considerable enhancement in the fluorescence intensity and lifetime of C7 on complexation with SBE7βCD proposes that non-radiative processes like TICT behavior are strictly hindered due to the confinement in the host cavity experienced by the C7 dye. The increase in the rotational correlation time evaluated from the fluorescence anisotropy decay kinetics further confirms the formation of tightly bound inclusion complexes. The binding constant values reveal that the monocationic form of dye at pH 3 shows ∼3 times stronger interaction with SBE7βCD than the neutral form of dye at pH 7 due to strong electrostatic cation-anion interaction. SBE7βCD:C7 exhibits an improved photostability and an upward pK a shift of 0.4 unit compared to the contrasting downward pK a shift of 0.5 with the βCD. The enhanced fluorescence yield and increased photostability have been exploited for bioimaging applications, and better images were captured by staining the Drosophila fly gut with the SBE7βCD:C7 complex. The enhancement in the binding interaction and the emission intensity were found to be responsive to external stimuli such as small competitive binders or metal ions and nearly quantitative dissociation of the complex was demonstrated to release the dye and would find stimuli-responsive applications.

Insight into Tetramolecular DNA G-Quadruplexes Associated with ALS and FTLD: Cation Interactions and Formation of Higher-Ordered Structure.

The G4C2 hexanucleotide repeat expansion in the c9orf72 gene is a major genetic cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), with the formation of G-quadruplexes directly linked to the development of these diseases. Cations play a crucial role in the formation and structure of G-quadruplexes. In this study, we investigated the impact of biologically relevant potassium ions on G-quadruplex structures and utilized 15N-labeled ammonium cations as a substitute for K+ ions to gain further insights into cation binding and exchange dynamics. Through nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we demonstrate that the single d(G4C2) repeat, in the presence of 15NH4+ ions, adopts a tetramolecular G-quadruplex with an all-syn quartet at the 5'-end. The movement of 15NH4+ ions through the central channel of the G-quadruplex, as well as to the bulk solution, is governed by the vacant cation binding site, in addition to the all-syn quartet at the 5'-end. Furthermore, the addition of K+ ions to G-quadruplexes folded in the presence of 15NH4+ ions induces stacking of G-quadruplexes via their 5'-end G-quartets, leading to the formation of stable higher-ordered species.

In-Situ Low-Frequency SERS Observation at Various Electrochemical Interfaces

Surface-selective vibrational spectroscopy, which is a powerful tool to study electrochemical interfaces, is typically operated in the mid-infrared region; chemical information obtained can give deep insights into electrochemical reactions at the molecular level. However, when the vibrational frequency range is extended into far-infrared or terahertz (THz) region, one can expect to obtain additional information about the interfaces because external vibrations such as surface-adsorbate vibrations and intermolecular vibrations appear in this range. Unfortunately, most of vibrational methods using THz radiation are not suitable for surface-selective observation of buried electrochemical interfaces. On the other hand, surface-enhanced Raman scattering (SERS) is potentially capable of detecting low-frequency vibrations at interfaces. Recently, the detectable frequency range of SERS has been extended into the low-frequency region down to 10 cm-1 [1], and then a vibrational analysis procedure for such low-frequency region has also been developed using a density of states format of SERS spectrum [2-4]. Using this method, for example, we have simultaneously observed both chemical information and molecular mass of surface adsorbates at interfaces [5]. In this talk, we focus on intermolecular interactions such as hydrogen bonding and anion-cation interactions at electrochemical interfaces. We present in-situ low-frequency SERS observation at various electrochemical interfaces under potential control [6].To obtain low-frequency SERS spectra, volume Bragg grating filters were used for both monochromatization of He-Ne laser radiation of 632.8 nm and removal of Rayleigh scattered light. SERS-active Au electrodes were prepared by electrochemical surface roughening in 0.1M KCl solution. For SERS-active Pt electrodes, monoatomic Pt overlayers were formed on the roughened Au surfaces. SERS spectra for both aqueous electrolyte solutions and ionic liquid electrolyte solutions were measured on these electrode surfaces under application of electrochemical potentials. The measured spectra were converted to density states of formats by reducing the Purcell factor, Bose-Einstein thermal factor, and frequency factor.Fig. 1 shows measured and reduced SERS spectra for 0.1M H2SO4/Au interface in the low-frequency region covering both Stokes and anti-Stokes branches. In the measured spectrum, vibrational features are not recognized because the huge background continuum dominates in the spectrum. This background continuum, caused by plasmon-enhanced electronic Raman scattering in the conduction band of Au, can be reduced in the density states of format, leading to considerable improvement in analyzability of vibrational features. Indeed, THz vibrational features are clearly unveiled in the reduced spectrum. Incidentally, the symmetry of the response between the Stokes and anti-Stokes branches in the reduced spectrum indicates that the SERS spectrum is properly converted to the reduced form because the Stokes and anti-Stokes Raman processes are connected due to the time reversal symmetry. Potential-dependence of these THz vibrational features will be discussed in the talk.[1] M. Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 4236-4240 (2017).[2] M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807-9717 (2020).[3] M. Inagaki, K. Motobayashi, K. Ikeda, Nanoscale, 12, 22988-22994 (2020).[4] R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 2100589 (2022).[5] T. Kondo, M. Inagaki, K. Motobayashi, K. Ikeda, Catal. Sci. Technol., 12, 2670-2676 (2022).[6] T. Isogai, M. Inagaki, M. Uranagase, K. Motobayashi, S. Ogata, K. Ikeda, submitted. Figure 1