Weak Electrostatic Interactions Research Articles

The Effect of Deoxyfluorination on Intermolecular Interactions in the Crystal Structures of 1,6-Anhydro-2,3-epimino-hexopyranoses.

The effect of substitution on intermolecular interactions was investigated in a series of 1,6-anhydro-2,3-epimino-hexopyranoses. The study focused on the qualitative evaluation of intermolecular interactions using DFT calculations and the comparison of molecular arrangements in the crystal lattice. Altogether, ten crystal structures were compared, including two structures of C4-deoxygenated, four C4-deoxyfluorinated and four parent epimino pyranoses. It was found that the substitution of the original hydroxy group by hydrogen or fluorine leads to a weakening of the intermolecular interaction by approximately 4 kcal/mol. The strength of the intermolecular interactions was found to be in the following descending order: hydrogen bonding of hydroxy groups, hydrogen bonding of the amino group, interactions with fluorine and weak electrostatic interactions. The intermolecular interactions that involved fluorine atom were rather weak; however, they were often supported by other weak interactions. The fluorine atom was not able to substitute the role of the hydroxy group in molecular packing and the fluorine atoms interacted only weakly with the hydrogen atoms located at electropositive regions of the carbohydrate molecules. However, the fluorine interaction was not restricted to a single molecule but was spread over at least three other molecules. This feature is a base for similar molecule arrangements in the structures of related compounds, as we found for the C4-Fax and C4-Feq epimines presented here.

Microwave spectra, molecular geometries, and internal rotation of CH3 in N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O Complexes.

Broadband microwave spectra have been recorded between 7.0 and 18.5 GHz for N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O complexes. Each complex was generated by co-expansion of low concentrations of methylimidazole and H2O in argon buffer gas. The rotational spectra of five isotopologues of each complex have been assigned and analysed to determine rotational constants (A0, B0, C0), centrifugal distortion constants (DJ, DJK) and parameters that describe the internal rotation of the CH3 group. The results allow the determination of parameters in the (r0) molecular geometry of each complex. H2O is the hydrogen bond donor and the pyridinic nitrogen of imidazole is the hydrogen bond acceptor in each case. The ∠(O–Hb⋯N3) angles are 177(5)° and 166.3(28)° for N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O respectively. These results are consistent with the presence of a weak electrostatic interaction between the oxygen atom of H2O and the hydrogen atom (or CH3 group) attached to the C2 carbon atom of imidazole, and with the results of density functional theory calculations. The (V3) barrier to internal rotation of the CH3 group within N-methylimidazole⋯H2O is essentially unchanged from the value of this parameter for the N-methylimidazole monomer. The same parameter is significantly higher for the 2-methylimidazole⋯H2O complex than for the 2-methylimidazole monomer as a consequence of the weak electrostatic interaction between the O atom and the CH3 group of 2-methylimidazole.

Underlying mechanism governing the influence of peanut oil addition on wheat dough viscoelasticity and Chinese steamed bread quality

In this work, how the added Peanut oil (PO) influenced dough characteristics was in depth revealed by dynamic oscillatory test, bread quality determination, gluten properties evaluation, lipids distribution, size exclusion chromatography, matrix-assisted laser desorption ionization-time of flight mass spectrometry, free sulfhydryl and disulfide bonds analysis, electrophoresis, and Fourier transform infrared spectroscopy, which showed the PO addition from 2.0% to 4.0% (Flour weight base) facilitated dough viscoelasticity and steamed bread quality, especially with 3.0% PO displaying the most improved effects. The trapped PO in gluten preferentially interacted with SDS-soluble gluten through hydrophobic and hydrogen bonds and weak electrostatic interactions, resulting in medium glutenin aggregation via dityrosine and disulfide bonds. The extra PO interacted with non-gluten proteins and made globulin retain in gluten network. The retained globulin was then cross-linked with SDS-soluble gluten through non-covalent interactions, weakening disulfide bonds and causing depolymerization of the formed medium glutenin polymers in some degree. This behavior conferred related dough with a moderate protein aggregation which combined with the retained globulin itself contributed to ameliorated dough qualities.

Effect of Solid Substrates on the Molecular Structure of Ionic Liquid Nanofilms.

Fundamental understandings of the interfacial molecular structure of solid-confined ionic liquids (ILs) have significant impacts on the development of many cutting-edge applications. Among the extensive studies on the molecular structure at the IL/solid interface, direct observation of a double-layering quantized growth of [Cnmim][FAP] on mica was recently reported. In the current work, the atomic force microscopy (AFM) results directly show that the growths of [Bmim][FAP] nanofilms on silica and amorphous carbon are different from the double-layering growth on mica. The growth of [Bmim][FAP] nanofilms on silica is dominated by the aggregation of the IL molecules, which can be attributed to the inadequate negative charging of the silica surface resulting in a weak electrostatic interaction between silica and the IL cation. [Bmim][FAP] on amorphous carbon shows a fairly smooth film for the thinner nanofilms, which can be attributed to the π-π+ parallel stacking between the cation imidazolium ring and the randomly distributed sp2 carbon on the amorphous carbon surface. Our findings highlight the effect of different IL/solid interactions, among the several competing interactions at the interface, on the resulting molecular arrangements of various IL.

First-principles study on methane storage properties of porous graphene modified with Mn

Porous graphene (PG) has a promising future for gas storage owing to its unique pore characteristics and large specific surface area. The adsorption properties of PG and Mn atoms decorated PG (Mn-PG) for methane (CH4) molecules have been studied based on the first-principles density functional theory. It is discovered that the optimum adsorption position of CH4 on PG is the carbon ring pore, and the adsorption energy is − 0.174 eV. The optimal position of the PG system decorated by single Mn atom is the central hole of the carbon ring, and the optimal position of the two Mn atoms is that Mn atoms are, respectively, located at different carbon ring holes on the opposite side of PG, with an average binding energy of − 4.101 eV. The modification of the Mn atom enhances the electronegativity of the PG substrate and forms a negative electrical center at the carbon ring, which facilitates the enhancement of the adsorption performance of the CH4 molecules that are positively charged with the surface. The CH4 molecule, close to Mn atom shows negative charge, and its strong electrostatic interaction with positively charged Mn atom is dominant, resulting in higher adsorption energy. The surface of CH4 molecule far away from the Mn atom is positively charged, the weak electrostatic interaction with the negatively charged PG substrate and the Van der Waals interaction between CH4 molecules are dominant, and the adsorption energy is low. The CH4 molecules are adsorbed on the PG surface through the electrostatic interaction with Mn atoms and PG substrate as well as the intermolecular force of CH4 molecules. The Mn-PG system is single-sided adsorption 6 CH4 molecules, and the average adsorption energy is − 0.345 eV. When two Mn atom modification PG, 12 CH4 molecules can be adsorbed on both sides, and the average adsorption energy is − 0.338 eV, the adsorption capacity is up to 38.43 wt.%.

Stereoisomeric selection upon adsorption: A structural and optical study of curcuminoid derivatives on ultrathin films of KCl on Au(111) and on bulk KCl(001)

We present a combined scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and differential reflectance spectroscopy (DRS) study aiming at the characterization of the relationship between structural and optical properties of a supramolecular assembly of a curcuminoid derivative adsorbed on two kinds of substrates: bilayers of KCl on Au(111) [2 ML KCl/Au(111)] and KCl(001) bulk. The molecule features a difluoroboron (${\mathrm{BF}}_{2}$) complex as well as cyano (CN) end groups, which induces an internal dipole moment of a few Debyes. The comparative study of the structural properties of the molecules adsorbed on 2 ML KCl/Au(111), which allows for STM characterization, and KCl bulk, which allows for nc-AFM and DRS characterization, shows that the molecular adsorption is similar on both substrates. STM and nc-AFM give evidence that the on-surface condensation of the molecules into supramolecular assemblies is steered by two main interactions: the molecule-substrate interaction between the CN end groups of the molecule and the cationic ${\mathrm{K}}^{+}$ species, as well as an in-plane intermolecular interaction involving ${\mathrm{BF}}_{2}$ and phenyl groups. Based on density functional theory calculations, we propose an epitaxial molecular structure described by a two-molecule unit cell forming an $8\ifmmode\times\else\texttimes\fi{}2$ supercell on the KCl surface that grows in form of ribbons along the $\ensuremath{\langle}100\ensuremath{\rangle}$ or $\ensuremath{\langle}010\ensuremath{\rangle}$ directions of the substrate, which are polar. Among several possible stereoisomers for the molecule, it is found that the balance between vertical and in-plane interactions selects the one whose size matches the distance between ${\mathrm{K}}^{+}$ species to condense on the substrate and not the most stable one stemming from the gas phase. Finally, optical spectroscopy in solvent and DRS measurements performed on the supramolecular assembly exhibit similar features identified as three absorption peaks tracing a $\ensuremath{\pi}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{*}$ electronic transition followed by a vibronic progression, plus a broader band featuring a set of higher-energy transitions. Due to both the weak electrostatic interactions and a lack of $\ensuremath{\pi}\text{\ensuremath{-}}\ensuremath{\pi}$ interactions in the condensed molecular phase, DR spectra exhibit no major excitonic effect, but a nonrigid redshift of the molecular absorption band compared to the situation in solvent. This observation is found to be consistent with the isomer selection due to the transition from the gas phase to the on-surface condensed phase.

Rapid polymerization of polyhedral oligomeric siloxane-based zwitterionic sulfoalkylbetaine monolithic column in ionic liquid for hydrophilic interaction capillary electrochromatography

A novel polyhedral oligomeric siloxane (POSS)-based zwitterionic monolithic capillary column was prepared via one-pot polymerization in ionic liquid porogen, using N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine (DMMSA) and methacrylic ethyl trimethylammonium chloride (META) as binary functional monomers, and methacryl substituted POSS as cross-linker. The pore structure, permeability and homogeneity were well tuned by optimizing the polymerization conditions. The resultant monolith was characterized by scanning electron microscopy, nitrogen adsorption/desorption isotherm and Fourier transform infrared spectroscopy. The incorporation of zwitterionic ligand (DMMSA), quaternary amine group (META) and rigid POSS skeleton endows the hybrid organic-silica monolith with high hydrophilicity, electrostatic interaction and good mechanical stability, as well as a tunable electroosmotic flow over wide pH range. A close investigation of capillary electrochromatographic separations of different types of polar compounds such as bases, nucleosides and benzoic acids on such stationary phase exhibited a retention independent column efficiency up to 118,000 plates/m (thiourea), as well as a mixed-mode hydrophilic interaction chromatography (HILIC) retention mechanism including weak electrostatic interaction, hydrophobic interaction and anion exchange.

A highly compressible hydrogel electrolyte for flexible Zn-MnO2 battery

Compressibility of zinc-manganese oxide (Zn-MnO2) batteries is an essential element of modern flexible electronics. Hydrogel electrolytes with superior elasticity and compressibility are highly demand to guarantee a stable energy output of the flexible Zn-MnO2 battery. Herein, a highly compressible hydrogel electrolyte was developed by introducing soybean protein isolate nanoparticles (SPI) into covalently cross-linked polyacrylamide (PAAM) polymer networks. The SPI/PAAM hydrogel electrolyte for Zn-MnO2 battery possessed outstanding reversible compressibility due to the aggregation of SPI nanoparticles on the PAAM chains through the weak electrostatic interaction, which could dissipate energy effectively. Consequently, the Zn-MnO2 battery based on the compressible hydrogel electrolyte displayed a decent specific capacity (299.3 mA h g−1) and desirable capacity retention rate (78.2%) after 500 charge/discharge cycles. Notably, the device could maintain stable power output under 96% compress strain and light the bulb even under severe mechanical stimulation like being-bent and hammered. It’s believed that the compressible Zn-MnO2 batteries hold enormous potential as the energy storage devices in the field of flexible wearable electronics.

Efficient Electronic Modulation of g-C 3 N 4 Photocatalyst by Implanting Atomically Dispersed Ag 1 -N 3 for Extremely High Hydrogen Evolution Rates

Efficient Electronic Modulation of g-C ₃ N ₄ Photocatalyst by Implanting Atomically Dispersed Ag ₁ -N ₃ for Extremely High Hydrogen Evolution Rates

Deficiency and surface engineering boosting electronic and ionic kinetics in NH4V4O10 for high-performance aqueous zinc-ion battery

Aqueous zinc-ion batteries present their unique advantages, such as cost-efficient and non-flammability for large-scale energy storage. However, their widespread application is hindered by the development of cathode materials, sluggish intrinsic ion/electron kinetics, and unsatisfied structural stability. Herein, we report a high-performance NH4V4O10 cathode with oxygen vacancy (denoted as NH4V4O10-x) and reduced graphene oxide (rGO) surface modification. The oxygen vacancies enhance the Zn2+ diffusion ability and stabilize the NH4V4O10 structure. Meanwhile, the density functional theory calculations further confirm the deficiency engineering leads to high electronic conductivity, weak electrostatic interaction, and low Zn2+ diffusion barrier. In addition, the rGO surface modification provides fast electron transfer. The NH4V4O10-x@rGO delivers high capacity (391 mAh g−1 at 1 A g−1), impressive rate ability (211 mAh g−1 at the 15 A g−1), and stable cycle performance with 90.5% capacity retention after 2000 cycles. This work provides a reasonable strategy to design cathode materials with deficiency and surface engineering to improve the electrochemical performance of zinc-ion batteries.

Facile fabrication of N-doped hierarchical porous carbons derived from soft-templated ZIF-8 for enhanced adsorptive removal of tetracycline hydrochloride from water

N-doped hierarchical porous carbons (NHPCs) were successfully prepared from soft-templated zeolitic imidazolate framework-8 (ZIF-8) precursors using sodium dodecylbenzene sulfonate (SDBS) as a template through facile one-step carbonization and applied in tetracycline hydrochloride (TCH) adsorption. The NHPC synthesized at 1000 °C with an SDBS/Zn2+ molar ratio of 0.075 exhibited the highest TCH adsorption (qm = 80.92 mg g−1) owing to its relatively large BET surface area (1067.41 m2 g−1) and pore volume (1.22 cm3 g−1) and the stronger surface interaction between TCH and NHPCs (HC1000–0.075). Compared with surfactant-free ZIF-8-derived carbon (HC), introduction of SDBS in the ZIF-8 precursor not only improved the pore structure of the carbon materials but also increased the nitrogen content and the number of surface functional groups. Adsorption kinetics and isotherms showed that the pseudo-second-order model and Sips model fit the TCH adsorption behavior on HC and HC1000–0.075 well. Adsorption experiments and characterizations revealed that the adsorption mechanism involved in TCH adsorption on HC1000–0.075 mainly depended on the synergistic effect of pore filling, H-bonding, π-π interactions, and weak electrostatic interactions. This study provides an effective and simple strategy for fabricating MOF-derived NHPCs as a promising adsorbent for the removal of antibiotics from water.

Mechanics and strain engineering of bulk and monolayer Bi2O2Se

High-mobility semiconductive ultrathin films of bismuth oxyselenide (Bi2O2Se) have attracted great interest due to their potential applications in advanced electronic and photoelectronic devices. Enthusiasm aside, future success of such applications hinges upon the fundamental understanding of two dimensional (2D) Bi2O2Se, which is far from mature. In particular, unlike many other 2D materials with a van der Waals gap, 2D Bi2O2Se features a weak electrostatic stacking interaction, which gives rise to a significantly different mechanical response. The unique mechanical response of 2D Bi2O2Se has a strong influence on its band gap, a critical property toward its device applications. Here, using ab initio calculations, we investigate the mechanical and electronic responses of both bulk and monolayer Bi2O2Se under uniaxial and biaxial tension as well as those of monolayer Bi2O2Se under in-plane shearing. The distinct mechanical responses of bulk and monolayer Bi2O2Se under different mechanical deformation are explained by the associated study of the evolution of electron localization function and charge density analysis. We reveal that the band gap of both bulk and monolayer Bi2O2Se decreases as the applied tensile strain increases. The critical uniaxial and biaxial tensile strains, above which bulk and monolayer Bi2O2Se transform from being semiconductive to being metallic, are determined. These findings suggest fertile yet largely unexplored opportunities of strain engineering of 2D Bi2O2Se toward new device applications.

Proposed mechanism for post-translational self-modification of Co-NHase based on Co2+ diffusion limitation.

Nitrile hydratase (NHase), was an excellent biocatalyst for the synthesis of amide compounds. NHase was typical heterodimeric metalloprotein, required of the assistance of activator for active expressions. In this work, we found a special Co-NHase HBA from Caldalkalibacillus thermarum, which had the ability of post-translational self-modification and could incorporate Co2+ into the catalytic center in the absence of activator. We simulated the movement of Co2+ in silico and established a hypothetical model to predict the Co2+ incorporation efficiency (XCo ) of NHases. According to the simulation results, NHase mutants with different positive charge distribution were constructed. Compared with wild-type, the Co2+ incorporation efficiency of K1 (M10K) was increased by 2.1-fold from 0.36 to 0.76, and the specific activity was increased by 3.2-fold from 136.3 to 432.0 U mg-1 , while mutant K1H1 (M10K, D11H) and K2H2 (M10K, D11H, E20K, N21H) lost the ability of post-translation self-modification. The interactions of positively charged residues near the catalytic center, such as lysine with strong electrostatic repulsive interaction, arginine with weak electrostatic repulsive interaction and histidine with metal affinity, could limit the free diffusion of Co2+ in NHase and affect the efficiency of post-translational self-modification. This work also provided an effective strategy for protein engineering of NHases and other metalloenzymes.

Hybrid inorganic-organic fluorescent silica nanoparticles—influence of dye binding modes on dye leaching

Silica nanoparticles with embedded fluorescent dyes represent an important class of markers for example in biological imaging. We systematically studied the various incorporation mechanisms of fluorescent xanthene dyes in 30–40 nm silica nanoparticles. An important parameter was the interaction of the dye with the matrix material, either by weak electrostatic or strong covalent interactions, which also has implications on the stability of fluorescence and brightness of the dyes. Factors that can influence leaching of dyes such as the position of the dyes in particles and the intensity of the particle-dye interaction were investigated by using the solvatochromic effect of xanthene dyes and by stationary fluorescence anisotropy measurements. We compared uranine and rhodamine B, which were physically embedded, with modified fluorescein isothiocyanate and rhodamine B isothiocyanate, which were covalently bound to the silica matrix within a usual Stöber synthesis. Systematic leaching studies of time spans up to 4 days revealed that covalent bonding of dyes like fluorescein isothiocyanate or rhodamine B isothiocyanate is necessary for fluorescence stability, since dyes bound by physical interaction tend to leach out of porous silica networks. Coverage of silica particles with hydrophobic protection layers of alkyltrialkoxysilanes or hydrophilic polyethylene glycol (PEG) groups resulted in a better retention of physisorbed dyes and provides the possibility to adapt the particles to the polarity of the medium. Best results were archived with PEG groups, but even small trimethylsilyl (TMS) groups already reduce leaching.

Solution-Processable Conductive Composite Hydrogels with Multiple Synergetic Networks toward Wearable Pressure/Strain Sensors.

A biocompatible, flexible, yet robust conductive composite hydrogel (CCH) for wearable pressure/strain sensors has been achieved by an all-solution-based approach. The CCH is rationally constructed by in situ polymerization of aniline (An) monomers in the polyvinyl alcohol (PVA) matrix, followed by the cross-linking of PVA with glutaraldehyde (GA) as the cross-linker. The unique multiple synergetic networks in the CCH including strong chemical covalent bonds and abundance of weak physical cross-links, i.e., hydrogen bondings and electrostatic interactions, impart excellent mechanical strength (a fracture tensile strength of 1200 kPa), superior compressibility (ε = 80%@400 kPa), outstanding stretchability (a fracture strain of 670%), high sensitivity (0.62 kPa-1 at a pressure range of 0-1.0 kPa for pressure sensing and a gauge factor of 3.4 at a strain range of 0-300% for strain sensing, respectively), and prominent fatigue resistance (1500 cycling). As the flexible wearable sensor, the CCH is able to monitor different types of human motion and diagnostically distinguish speaking. As a proof of concept, a sensing device has been designed for the real-time detection of 2D distribution of weight or pressure, suggesting its promising potentials for electronic skin, human-machine interaction, and soft robot applications.

Mechanochemical disproportionation reaction of sulfur on Bi2O3 to synthesize Bi2O2S for simultaneous removals of Cu2+ and Cl- from waste solution

As to chemical precipitation for heavy metal removals, sulfide formations will give much lower concentrations of remaining heavy metals and the accompanying salts in the solutions than alkaline neutralization due to much smaller constants of solubility products of the precipitates. However, the preparation of sulfide precipitant such as Na2S by reducing the sulfate with carbon at high temperature is very environmentally risky and bad in cost performance. In this regard, a new approach is proposed just by co-grinding sulfur with bismuth oxide (Bi2O3) with an aid of NaOH to induce a disproportionation reaction of sulfur to prepare Bi2O2S, which can precipitate both Cu2+ and Cl- in case of CuCl2 in the solution at the same time. Under the optimized experimental conditions, removal efficiencies of Cu2+ and Cl- as high as 99.83% and 98.17%, respectively have been achieved at one step. Bi2O2S has a layered structure composed of [Bi2O2]2+ and S2- layers by weak electrostatic interaction. Through the exchange of Cl- to S2-, two kinds of precipitates as BiOCl and copper sulfide can be obtained, offering a new concept to remove both cations and anions simultaneously for the treatment of wastewater, besides the environment-friendliness of the synthesis process itself.

‘Plug and play’ microelectrode assisted with Y-motif-mediated primer-free cyclic signal amplification for sensitive quantitation of DNA methyltransferase activity

DNA methyltransferase (MTase), modulating the level of genomic DNA methylation, harbors both a pharmacological target for clinical therapy and a potential biomarker for genetic disorders and tumorigenesis. Typical homogeneous electrochemical approaches, employing solution phase probes, have been considered simple, efficient, and economical method, yet these architectures usually require electroactive molecules labeling, rely on weak electrostatic adsorption interaction, and possess low sensitivity. For circumventing the above drawbacks, herein, we devise a ‘plug and play’ microelectrode featuring microminiaturization, rapid response time and enhanced mass transport to quantify MTase activity through monitoring the variation of diffusion current of methylene blue (MB) induced by the less-mobile G-quadruplex framework. By coupling the unique signal-transduction approach with Y-motif-mediated primer-free cyclic signal amplification (YPCSA), the miniaturized biosensor possesses low detection limit (down to 2.5 × 10−4 U mL−1), high specificity, good stability and satisfying reusability, and has been successfully applied to the screening of MTase inhibitors, holding great potential in clinical diagnosis and pharmacological research.

Retention of Iodide and Chloride by Formation of a Green Rust Solid Solution GR-Cl1-xIx: A Multiscale Approach.

The uptake of iodide and chloride during the synthesis of green rust (GR), the Fe endmember of the layered double hydroxide (LDH) group, was investigated. GR compounds were prepared by aerial oxidation of Fe(OH)2 in suspension, considering various I/Cl ratios at constant ionic strength. Only GR compounds formed in all experiments, and the associated I/Cl ratio increased with that of the starting suspension. No preferential uptake of any halide could be detected, and all compounds had comparable morphology. Furthermore, the height of the interlayer gallery increased with the I/Cl ratio from ∼7.7 Å for the chloride endmember to ∼8.3 Å for the iodide endmember, and the observed linear increase was attributed to increasing interlayer iodide content. In all compounds, Fe K-edge X-ray absorption spectroscopy evidenced the presence of sixfold coordinated iron with a Fe2+/Fe3+ ratio of 3, homogeneously distributed within flattened octahedral sites, with six Fe as next-nearest neighbors. The Fe short-range environment was not affected by the interlayer composition, and no halide from the interlayer could be detected. Furthermore, iodide and chloride anions are located in a water-like environment, being loosely bound by weak electrostatic interactions to the octahedral sheet likely above ferric iron. Results consistently hint at the formation of a solid solution between chloride and iodide GR endmembers, certainly facilitated by the crystallization of both compounds in the same space group. This study provides further insights into the ability of LDH to simultaneously accommodate several anionic species of various sizes. The formation of such LDH compounds in a deep geological repository for nuclear waste thus represents a possible retention barrier to the migration to the far field of anionic species like 36Cl- and 129I- mobilized from the waste matrix. The extent of retention in disposal sites will depend, among others, on the availability of GR and on the concentration of competing anions.

Attoampere Nanoelectrochemistry.

Electrochemical microscopy techniques have extended the understanding of surface chemistry to the micrometer and even sub-micrometer level. However, fundamental questions related to charge transport at the solid-electrolyte interface, such as catalytic reactions or operation of individual ion channels, require improved spatial resolutions down to the nanoscale. A prerequisite for single-molecule electrochemical sensitivity is the reliable detection of a few electrons per second, that is, currents in the atto-Ampere (10-18 A) range, 1000 times below today's electrochemical microscopes. This work reports local cyclic voltammetry (CV) measurements at the solid-liquid interface on ferrocene self-assembled monolayer (SAM) with sub-atto-Ampere sensitivity and simultaneous spatial resolution < 80nm. Such sensitivity is obtained through measurements of the charging of the local faradaic interface capacitance at GHz frequencies. Nanometer-scale details of different molecular organizations with a 19% packing density difference are resolved, with an extremely small dispersion of the molecular electrical properties. This is predicted previously based on weak electrostatic interactions between neighboring redox molecules in a SAM configuration. These results open new perspectives for nano-electrochemistry like the study of quantum mechanical resonance in complex molecules and a wide range of applications from electrochemical catalysis to biophysics.

Impacts of solvent electric dipole and ion valency on energy storage in ultrananoporous supercapacitor: An ising model study

A four-state BEG model is constructed to investigate effects of electric dipole of solvent molecule and ion valency on differential capacitance Cd and energy storage Eof the supercapacitor based on electrical double layer inside an ultranano-cylindrical pore about the size of the ions and solvent. In the model, existence of voids is permitted, solvent molecule is modelled as neutral hard sphere with an electrical dipole moment and ions are described by the primitive model; all electrostatic interactions between cation, anion, and polarized charges on the solvent molecule are limited to the nearest neighbor interactions. The present investigation is limited to weak solvent-solvent electrostatic interaction in comparison to that of the solvent-ion and ion-ion. New effects are found and summarized as follows. (i) There appears a zero Cd and zero E platform around the zero surface potential, which widens with the increase of the solvent transfer energy w0 and moves to positive surface potential side with replacement of the monovalent cation by bivalent cation. (ii) The saturated surface potential |Usat|, beyond which Cd reduces to zero and E reaches its saturation value Esat, is positively correlated with the w0 value. The correlation strength reduces with the counter-ion valence. (iii) For appropriate positive w0 value, both |Usat| and Esat always increase with the solvent polarized charge valence b and dipole length l whether the electrolyte type is +1: 1 or +2: 1; whereas for negative w0 value, the value and l value effects are very small and graphically unobservable. (iv) Presence of bivalent counter-ions causes an increase of the Cd peak strength and Esat value, whereas the presence of bivalent co-ion almost does not bring graphically observed effect. (v) Within the ranges of the b and l values considered, the energy storage is raised by increasing the solvent electrical dipole moment (whether by increasing b valueb or l value) without paying for the cost of high surface potential applied.