Ionic Environments Research Articles

Bayesian unsupervised learning reveals hidden structure in concentrated electrolytes.

Electrolytes play an important role in a plethora of applications ranging from energy storage to biomaterials. Notwithstanding this, the structure of concentrated electrolytes remains enigmatic. Many theoretical approaches attempt to model the concentrated electrolyte by introducing the idea of ion pairs, with ions either being tightly "paired" with a counter-ion or "free" to screen charge. In this study, we reframe the problem into the language of computational statistics and test the null hypothesis that all ions share the same local environment. Applying the framework to molecular dynamics simulations, we find that this null hypothesis is not supported by data. Our statistical technique suggests the presence of two distinct local ionic environments at intermediate concentrations, whose differences surprisingly originate in like charge correlations rather than unlike charge attraction. Through considering the effect of these "aggregated" and "non-aggregated" states on bulk properties including effective ion concentration and dielectric constant, we identify a scaling relation between the effective screening length and theoretical Debye length, which applies across different dielectric constants and ion concentrations.

Cryo-Electron Microscopy and Mass Analysis of Oligolysine-Coated DNA Nanostructures.

Cationic coatings can enhance the stability of synthetic DNA objects in low ionic strength environments such as physiological fluids. Here, we used single-particle cryo-electron microscopy (cryo-EM), pseudoatomic model fitting, and single-molecule mass photometry to study oligolysine and polyethylene glycol (PEG)-oligolysine-coated multilayer DNA origami objects. The coatings preserve coarse structural features well on a resolution of multiple nanometers but can also induce deformations such as twisting and bending. Higher-density coatings also led to internal structural deformations in the DNA origami test objects, in which a designed honeycomb-type helical lattice was deformed into a more square-lattice-like pattern. Under physiological ionic strength, where the uncoated objects disassembled, the coated objects remained intact but they shrunk in the helical direction and expanded in the direction perpendicular to the helical axis. Helical details like major/minor grooves and crossover locations were not discernible in cryo-EM maps that we determined of DNA origami coated with oligolysine and PEG-oligolysine, whereas these features were visible in cryo-EM maps determined from the uncoated reference objects. Blunt-ended double-helical interfaces remained accessible underneath the coating and may be used for the formation of multimeric DNA origami assemblies that rely on stacking interactions between blunt-ended helices. The ionic strength requirements for forming multimers from coated DNA origami differed from those needed for uncoated objects. Using single-molecule mass photometry, we found that the mass of coated DNA origami objects prior to and after incubation in low ionic strength physiological conditions remained unchanged. This finding indicated that the coating effectively prevented strand dissociation but also that the coating itself remained stable in place. Our results validate oligolysine coatings as a powerful stabilization method for DNA origami but also reveal several potential points of failure that experimenters should watch to avoid working with false premises.

Performance of ionic liquid as a lubricant in turning inconel 825 via minimum quantity lubrication method

Nickel-based super alloys have low thermal conductivity, thus a large amount of heat is generated during machining, which reduces the superiority of the machined component and life of the cutting tool. Existing work is focused on the usage of ionic liquids as lubricants in turning Inconel 825. Taguchi’s L27 orthogonal array was used to detect the results of turning process factors, such as cutting speed, feed, depth of cut and environmental conditions, in three different machining environments: dry, oil under minimum quantity lubrication and ionic liquids with minimum quantity lubrication (IL). The output parameters considered were surface roughness, cutting temperature, tool wear and chip thickness. A multicriteria decision making (MCDM) method executed through the combination of an analytical hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) was used for optimization. The results showed that ionic liquids with the minimum quantity lubrication (MQL) method minimized the surface roughness by 88 %, reduced the cutting temperature by 74 %, reduced the chip thickness by 89 % and minimized tool wear. Furthermore, the SEM study revealed the wear on a tool in turning Inconel 825 in dry, oil and ionic liquid environments. The outcomes obtained through analysis clearly prove the importance of employing ionic liquids with minimum quantity lubrication to reduce surface roughness, cutting temperature, tool wear and chip thickness.

Photocatalytic Hedgehog Particles for High Ionic Strength Environments.

High ionic strength environments can profoundly influence catalytic reactions involving charged species. However, control of selectivity and yield of heterogeneous catalytic reactions involving nano- and microscale colloids remains hypothetical because high ionic strength leads to aggregation of particle dispersions. Here we show that microscale hedgehog particles (HPs) with semiconductor nanoscale spikes display enhanced stability in solutions of monovalent/divalent salts in both aqueous and hydrophobic media. HPs enable tuning of photocatalytic reactions toward high-value products by adding concentrated inert salts to amplify local electrical fields in agreement with Derjaguin, Landau, Verwey, and Overbeek theory. After optimization of HP geometry for a model photocatalytic reaction, we show that high salt conditions increase the yield of HP-facilitated photooxidation of 2-phenoxy-1-phenylethanol to benzaldehyde and 2-phenoxyacetophenone by 6 and 35 times, respectively. Depending on salinity, electrical fields at the HP-media interface increase from 1.7 × 104 V/m to 8.5 × 107 V/m, with high fields favoring products generated via intermediate cation radicals rather than neutral species. Electron transfer rates were modulated by varying the ionic strength, which affords a convenient and hardly used reaction pathway for engineering a multitude of redox reactions including those involved in the environmental remediation of briny and salty water.

Uranyl oxalate species in high ionic strength environments: stability constants for aqueous and solid uranyl oxalate complexes

Abstract Uranyl ion, UO2 2+, and its aqueous complexes with organic and inorganic ligands can be the dominant species for uranium transport on the Earth surface or in a nuclear waste disposal system if an oxidizing condition is present. As an important biodegradation product, oxalate, C2O4 2−, is ubiquitous in natural environments and is known for its ability to complex with the uranyl ion. Oxalate can also form solid phases with uranyl ion in certain environments thus limiting uranium migration. Therefore, the determination of stability constants for aqueous and solid uranyl oxalate complexes is important not only to the understanding of uranium mobility in natural environments, but also to the performance assessment of nuclear waste disposal. Here we developed a thermodynamic model for the UO2 2+–Na+–H+–Cl––ClO4 ––C2O4 2––NO3 ––H2O system to ionic strength up to ∼11 mol•kg−1. We constrained the stability constants for UO2C2O4(aq) and UO2(C2O4)2 2− at infinite dilution based on our evaluation of the literature data over a wide range of ionic strengths up to ∼11 mol•kg−1. We also obtained the solubility constants at infinite dilution for solid uranyl oxalates, UO2C2O4•3H2O, based on the solubility data over a wide range of ionic strengths. The developed model will enable for the accurate stability assessment of oxalate complexes affecting uranium mobility under a wide range of conditions including those in deep geological repositories.

Divalent Cation Dependence Enhances Dopamine Aptamer Biosensing.

Oligonucleotide receptors (aptamers), which change conformation upon target recognition, enable electronic biosensing under high ionic-strength conditions when coupled to field-effect transistors (FETs). Because highly negatively charged aptamer backbones are influenced by ion content and concentration, biosensor performance and target sensitivities were evaluated under application conditions. For a recently identified dopamine aptamer, physiological concentrations of Mg2+ and Ca2+ in artificial cerebrospinal fluid produced marked potentiation of dopamine FET-sensor responses. By comparison, divalent cation-associated signal amplification was not observed for FET sensors functionalized with a recently identified serotonin aptamer or a previously reported dopamine aptamer. Circular dichroism spectroscopy revealed Mg2+- and Ca2+-induced changes in target-associated secondary structure for the new dopamine aptamer, but not the serotonin aptamer nor the old dopamine aptamer. Thioflavin T displacement corroborated the Mg2+ dependence of the new dopamine aptamer for target detection. These findings imply allosteric binding interactions between divalent cations and dopamine for the new dopamine aptamer. Developing and testing sensors in ionic environments that reflect intended applications are best practices for identifying aptamer candidates with favorable attributes and elucidating sensing mechanisms.

Design of weakly cationic alco-cryogels consisting of poly(alkylmethacrylates)-based sulfonated terpolymer network with tunable multiresponsive assembly

Cryogels with ion-, and solvent-responsiveness have been designed by cryogelation of 2-(diethylamino)ethyl methacrylate (DEAEMA) as weakly cationic monomer, hydroxyethyl methacrylate as neutral comonomer and 2-acrylamido-2-methyl-1-propanesulfonic acid as anionic termonomer in ethanol-water mixture (50:50 v/v), which had been proved to offer a good miscibility of monomers. Influence of composition of terpolymer and polymerization temperature on the properties of terpolymer cryogels (Cgels) and hydrogels (Hgels) were evaluated by swelling kinetics, and response against rapid ionic strength change. Degree of swelling was extremely sensitive to salt concentration, cation/counterion type as well as the solvent type; acetone and monohydric alcohols with various hydrophobic alkyl groups; methanol, ethanol, and 2-propanol. Swelling of terpolymer networks in the form of Cgel and Hgel decreased with increase in the size of ions present in swelling medium and followed the order of swelling behavior Cl− > Br− > I−. Terpolymer alcogels exhibited salting-out behavior in the presence of Cl− and Br− ions, while “salting-in” behavior was observed in KI solutions of high concentrations. Sensitivity sequence of terpolymer alcogels to mono- and di-valent cations with a common anion (SO42−) on swelling was Na⁺ > K⁺ > Mg2⁺> Zn2+. Variation of elastic moduli with swelling in salt solutions was investigated and for terpolymer hydrogels, possible contribution of ionic crosslinks to effective crosslinking density νe was discussed. Increasing Na2SO4 concentration up to 0.1 M induced a 2-fold increase in the elastic modulus of terpolymer alcogels. With attention to the polarity of solvent, terpolymer gels exhibited an irregular swelling profile with a change in composition of solvent, showing the so called cosolvency phenomena. After two successive cycles of swelling and shrinking promoted by the change of ionic strength of KCl solution, the terpolymer gels were stable and dynamic swelling process was reversible. Swelling data agree well with second-order kinetic model and with increasing amount of DEAEMA in terpolymer feed, diffusion mechanism changed from non-Fickian type to Fickian diffusion. In ionic environments, the salt-sensitivity and excellent water absorption/retention capability give this intelligentized terpolymer gels wide potential applications.

Scanning Ion Conductance Microscopy Reveals Differences in the Ionic Environments of Gram-Positive and Negative Bacteria.

This paper reports on the use of scanning ion conductance microscopy (SICM) to locally map the ionic properties and charge environment of two live bacterial strains: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis. SICM results find heterogeneities across the bacterial surface and significant differences among the Gram-positive and Gram-negative bacteria. The bioelectrical environment of the B. subtilis was found to be considerably more negatively charged compared to E. coli. SICM measurements, fitted to a simplified finite element method (FEM) model, revealed surface charge values of -80 to -140 mC m-2 for the Gram-negative E. coli. The Gram-positive B. subtilis show a much higher conductivity around the cell wall, and surface charge values between -350 and -450 mC m-2 were found using the same simplified model. SICM was also able to detect regions of high negative charge near B. subtilis, not detected in the topographical SICM response and attributed to the extracellular polymeric substance. To further explore how the B. subtilis cell wall structure can influence the SICM current response, a more comprehensive FEM model, accounting for the physical properties of the Gram-positive cell wall, was developed. The new model provides a more realistic description of the cell wall and allows investigation of the relation between its key properties and SICM currents, building foundations to further investigate and improve understanding of the Gram-positive cellular microenvironment.

Chemical equilibria of Eosin Y and its synthetic ester derivatives in non-ionic and ionic micellar environments

Eosin (EOS) and its synthetic ester derivatives have adequate properties to be employed as histological markers for and as drugs for photodynamic therapy. However, they present a very complex protolytic and tautomeric equilibrium that reflects on their photophysical properties. Hence their biomedical applications are strongly affected by the medium's pH, charge and hydrophobicity. In this study, we evaluated the effects of two neutral (Pluronic® F-127 and P-123) and two ionic (anionic SDS and cationic CTAB) surfactant micelles as a simple membrane model on the protolytic/tautomeric equilibrium of EOS and its ester derivative dyes. Multivariate analysis based on Q-Imbrie's factor and the K-matrix method on the electronic absorption spectroscopy data in different pH conditions allowed for the understanding of the complex protolytic/tautomeric equilibrium, and the influence of medium microenvironment on the EOS dyes at each pH. Our results demonstrated that, when close to physiological pH (~7.4), and electrostatic attraction towards cationic surfaces favor dyes locating close to the micelle's (biomembrane model) interface, where their biomedical applications are favored. Therefore, the analysis in different environments shows that the interactions of EOS and its derivatives with biomembranes can be modulated based on the hydrophobicity of the xanthene derivative and the cell membrane charge.

Euryhaline Hydrogel with Constant Swelling and Salinity‐Enhanced Mechanical Strength in a Wide Salinity Range

AbstractIn nature, many biological organisms possess a unique osmoregulation feature that enables them to survive in environments of different salinity, which is called euryhaline characteristics (e.g., salmon that can survive in freshwater and seawater). Drawing inspiration from these salinity‐tolerant organisms, here a strategy that integrates two polymer chain segments with different salinity tolerances is reported to produce a euryhaline hydrogel with stable water retention, constant swelling properties, superoleophobicity, and low‐adhesion to oil in aqueous environments over a wide range of salinity. The formation of internal dynamic complementary crosslinks is a key structural factor of the euryhaline attributes. The euryhaline hydrogel‐coated meshes can be successfully utilized in various oil/aqueous phase separation in a wide range of salinity. Furthermore, by creating a double network with dynamic bonds, superior euryhaline hydrogel with unique salinity‐enhanced mechanical strength can be obtained. It is anticipated that the euryhaline hydrogel will have broad application prospects in complex and variable ionic environments.

The effect of different morphology of fluoride-mediated TiO2 based on Ostwald ripening on photocatalytic activity

The morphology of the catalyst is one of the important factors affecting the photocatalytic activity. In this work, fluoride-mediated TiO2 with different morphologies was successfully prepared based on Ostwald ripening. In particular, the morphology and structure of the TiO2 sample can be adjusted according to different ionic environments. Combining experiments and characterization, the regulation mechanism of different fluorides on the morphology and structure of TiO2 was proposed, and the transport behavior of photogenerated carriers was evaluated. The results show that the morphology and structure have a greater impact on the photocatalytic activity of TiO2. The hollow structure can promote the separation and transfer of carrier and enhance the light collection ability. The surface fluoride as an electron trap can reduce the carrier recombination rate, which is beneficial to the photocatalytic activity of the as-prepared sample. The hollow structure sample shows a good photocatalytic efficiency in the photocatalytic removal of Hg0 in the gas phase, reaching about twice the commercial P25. Finally, the photocatalytic mechanism of the catalyst and the electron-hole migration path are proposed. This research provides new ideas for the design of hollow TiO2 microspheres, which can be widely used in the field of catalysis.

Production routes to tailor the performance of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are bio-based, high aspect ratio nanoparticles that are industrially produced in tonne-per-day quantities across the globe. CNCs can be used to improve the performance of a large range of materials such as emulsions and foams, biomedical devices, electronics and sensors, high-viscosity fluids and polymer composites. Their ability to do so, however, is highly dependent on the way they are produced. In this Review, we assess the properties of CNCs from more than 30 production routes and 40 biomass sources to help CNC users select the right material for their desired application. CNCs produced by various methods are evaluated against three target properties: colloidal stability, size and crystallinity index. Alternative production routes and/or starting materials are suggested to overcome challenges associated with CNC use, including increasing compatibility with hydrophobic materials, resistance to thermal degradation and colloidal stability in high ionic strength environments. Additionally, we discuss industrial production of CNCs, as well as considerations for increasing the yield and reducing the environmental impact of these processes. Overall, this Review guides researchers and CNC users towards a deeper understanding of how production processes can be modified to control CNC properties and subsequently tailor their performance. Cellulose nanocrystals are rigid rod-shaped nanoparticles that show promise as additives in composites, emulsions, foams and biomedical devices and as rheological modifiers. In this Review, the authors guide end users towards selecting cellulose sources and production routes that optimize the performance of cellulose nanocrystals in their intended application.

In Situ-Grown Cdot-Wrapped Boehmite Nanoparticles for Cr(VI) Sensing in Wastewater and a Theoretical Probe for Chromium-Induced Carcinogen Detection.

In modern society, massive industrialization escalates environmental degradation by liberating various contaminants into the environment. Hexavalent chromium is a heavy metal that is being discharged from tannery and other industries, resulting in various carcinogenic diseases. This study reports a carbon dot (cdot)-based fluorometric probe for detecting hexavalent chromium in water. This is the very first time that cdots are tailored over the boehmite nanoparticle's surface using an in situ approach. Validation of formation of the nanocomposite has been discussed in detail employing the Rietveld refinement-based X-ray crystallography method. Vibrational spectroscopy and electron microscopy of the sample authenticate the nucleation process and the growth mechanism. The Stern-Volmer approach and time-resolved fluorescence measurements justify the sensitivity of the sensor (∼58 nM), and selectivity is analyzed by exposing the material to different ionic environments. Density functional theory (DFT) is applied herein to analyze the origin of fluorescence and the sensing mechanism of the probe, which shows that photoinduced electron transfer is responsible for the turn-off-based sensing of Cr(VI). The molecular docking simulation is carried out to ensure the binding of cdots to the binding pocket of the glutathione enzyme, which is responsible for treating reactive oxygen species-mediated DNA damage due to elements such as hexavalent chromium. Time-dependent density functional calculations show that the fluorometric probe is capable of detecting Cr(VI) in living cells making it an early stage chromium-mediated carcinogen detector.

Spectroscopic characterisation of Grubbs 2nd generation catalyst and its p-cresol derivatives

p-Cresol derivatives of the Grubbs 2nd generation catalyst were prepared with either hydrogen bonds between p-cresol and the Cl-ligands or ligand exchange between the Grubbs 2nd generation catalyst and thallium p-cresolate to form Ru-O coordination bonds and TlCl. ATR FTIR and UV–Vis spectroscopic studies revealed a blue shift in certain bands, indicating that coordination occurred. X-ray Photoelectron Spectroscopy was recorded for each of the three Ru-complexes. The binding energy of the Ru 3d5/2, Ru 3p3/2 photoelectron line (found at ca. 281 and 462 eV, respectively) of the different complexes showed the influence of the inductive electronic effects of the p-cresol interaction with the complexes. The Cl 2p photoelectron lines indicated ionic and covalent environments, representing the TlCl and the Ru-Cl bonds, respectively. The atomic ratio between Ru:P:Cl:N:Tl confirmed the binding modes of p-cresol to the Grubbs 2nd generation catalyst.

Marine Structural Protein Stability Induced by Hofmeister Salt Annealing and Enzymatic Cross-Linking.

The Humboldt squid is one of the fiercest marine predators thanks in part to its sucker ring teeth that are biopolymer blends of a protein isoform family called suckerin with compression strength that rivals silkworm silk. Here, we focus on the popular suckerin-12 isoform to understand what makes the secondary structure of this biopolymer different in water and the potential role of diverse physical and chemical cross-linkings. By choosing a salt post-treatment, in accordance with the Hofmeister series, we achieved film stability with salt annealing that is comparable to chemical cross-links. By correlating the film morphology with the protein secondary structure changes, suckerin-12 films were shown to contract upon treatment with kosmotropic salts and exhibited increased stability in water. These changes are related to the rearrangement of suckerin-12 secondary structure from random coils and helices to β-sheets. Overall, understanding secondary structure changes caused by aqueous and ionic environments can be instructive for the tuning of the suckerin film sclerotization, its conversion to a tough biological material, and to ultimately produce the natural squid sucker ring teeth.

Electric Fields at Breast Cancer and Cancer Cell Collective Galvanotaxis

Cancer growth interferes with local ionic environments, membrane potentials, and transepithelial potentials, resulting in small electrical changes in the tumor microenvironment. Electrical fields (EFs) have significant effects on cancer cell migration (galvanotaxis/electrotaxis), however, their role as a regulator of cancer progression and metastasis is poorly understood. Here, we employed unique probe systems to characterize the electrical properties of cancer cells and their migratory ability under an EF. Subcutaneous tumors were established from a triple-negative murine breast cancer cell line (4T1), electric currents and potentials of tumors were measured using vibrating probe and glass microelectrodes, respectively. Steady outward and inward currents could be detected at different positions on the tumor surface and magnitudes of the electric currents on the tumor surface strongly correlated with tumor weights. Potential measurements also showed the non-homogeneous intratumor electric potentials. Cancer cell migration was then surveyed in the presence of EFs in vitro. Parental 4T1 cells and metastatic sublines in isolation showed random migration in EFs of physiological strength, whereas cells in monolayer migrated collectively to the anode. Our data contribute to an improved understanding of breast cancer metastasis, providing new evidence in support of an electrical mechanism that promotes this phenomenon.

Comparing Computational Predictions and Experimental Results for Aluminum Triflate in Tetrahydrofuran.

Exploring reliable electrolytes for aluminum ion batteries requires an in-depth understanding of the behavior of aluminum ions in ethereal-organic solvents. Electrolytes comprised of aluminum trifluoromethanesulfonate (Al-triflate) in tetrahydrofuran (THF) were investigated computationally and experimentally. Optimized geometries, redox potentials, and vibrational frequencies of species likely to be present in the electrolyte were calculated by density functional theory and then measured spectroscopically and electrochemically. Aluminum appears to be electrochemically active in THF with a reduction onset near 0 V versus Al/Al3+. Spectroscopic measurements reveal explicit evidence for the presence of two concentration-dependent ionic environments for the triflate anions, namely, outer-shell ligands and Al-bound triflates. Additionally, ionic conductivities of ∼2.5 mS/cm were measured for these electrolytes ∼0.8M.

Self-Assembled Monolayers for Anti-Fouling and Highly Selective Electrode Interfaces

The detection, collection and/or conversion of biological-based molecules has applications to sensing, wearables, and biofuels. Flexible, wearable electronics for real-time detection of, for example, Neuropeptide Y in human sweat [1], or flagella protein in biofuels, enables deviation from bulky laboratory benchtop analyses such as ELISA. Challenges include required limits of detection, as biological materials can be present in small amounts (nM to pM concentrations) in complex high ionic strength environments[2], the need for a highly selective sensor interface that avoids non-specific binding, and a quick response to account for degradation of analytes.This work will discuss the implementation of a mixed self-assembled monolayer (SAM) interface with highly selective bio-recognition elements (BREs) on gold disk electrodes, focusing on target application for aqueous sensing in biofuels, with room for expansion to sensing in other biological fluids. The SAM composition was systematically varied to assess functionality towards preventing fouling/non-specific binding and increase the selectivity of the interface for the analyte of interest. Briefly, mixed monolayer combinations included pseudo-zwitter surfaces to prevent fouling, blocking groups similarly employed in the literature[3] to help rectify BREs, and dithiobis(succinimidyl propionate) (DSP) cross-linking chemistry[4] to attach various BREs to the gold electrode. BREs include concanavilin A, streptavidin, nanobodies, and synthetic lectins. Streptavidin and it’s interaction with biotin was chosen as a control, due to their known strong interaction. Electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) were used to estimate changes in the resistance to charge transfer to redox mediators either immobilized or in solution. EIS is one of the most common modern techniques used in biosensing, but as a time-intensive measurement it can be undesirable for accurate sensing in analyte-degrading environments. Therefore, SWV was employed as a substitute which reduces times of measurements by an order of magnitude, and is shown to provide the same information as EIS. To corroborate these electrochemical effects with a definite surface coverage/binding event, ellipsometric experiments of functionalized electrodes are underway.Our SAM interface produces nM level detection for yeast through the employment of gold immobilized charge transfer mediators and concanavalin A with selective binding to the yeast cell wall. Specifically, a decrease in charge transfer resistance (or increase in peak current as measured in SWV) occurs upon binding of yeast cells to concanavalin A. The streptavidin-biotin interaction also manipulated the charge transfer resistance similarly, confirming our method effectiveness. Nanobodies (binding fragment of antibodies) were also shown to have some success in detecting flagella protein with redox mediators in solution.These proof-of-concept results demonstrate feasibility and indicate forward paths towards highly selective sensor electrodes with simultaneous anti-fouling properties that prevents non-specific binding. Ongoing efforts include modifying electronic device interfaces with SAMs for combined signaling and amplification, such as modification of gate electrodes in printable electrochemical transistors.

The Effect of Phenyl Substitutions on Microstructures and Dynamics of Tetraalkylphosphonium Bis(trifluoro- methylsulfonyl)imide Ionic Liquids.

Extensive atomistic simulations demonstrated that a gradual substitution of hexyl chains with phenyl groups in tetraalkylphosphonium cations results in remarkable changes in hydrogen bonding interactions, liquid structures and scattering structural functions, and rotational dynamics of hexyl chains and phenyl groups in tetraalkylphosphonium bis(trifluoromethylsulfonyl)imide ionic liquids. Hydrogen donor sites in hexyl chains present competitive characteristics with those in phenyl groups in coordinating anions, as well as their continuous and intermittent hydrogen bonding dynamics. Cation-cation and anion-anion spatial correlations show concomitant shift to short distances with decreased peak intensities with variations of cation structures, whereas cation-anion correlations have a distinct shift to large radial distances due to decreased associations of anions with neighboring cations. These microstructural changes are qualitatively manifested in shifts of prominent peaks for prevalent charge alternations and adjacency correlations between ion species in scattering structural functions. Meanwhile, rotational dynamics of hexyl chains speed up, which, in turn, slow down rotations of phenyl groups, whereas anions exhibit imperceptible changes in their rotational dynamics. These computational results are intrinsically correlated with conformational flexibilities, molecular sizes, and steric hindrance effects of phenyl groups in comparison with hexyl chains, and constrained distributions of anions around cations in heterogeneous ionic environments.

A miniaturized, self-sustaining, and integrable bio-solar power system

Abstract We demonstrate a practical and sustainable bacterial power source for low-power electronic applications. Self-sustainable electricity is produced from revolutionarily structured microliter-scale bio-solar cells using a co-culture of heterotrophic and autotrophic bacteria. Two bio-solar cells are integrated on a single chip and connected in series, continuously generating light-responsive electricity from heterotrophic bacterial respiration with the organic substrates produced by photosynthetic autotrophs. Agar-based anolyte, catholyte, and salt-bridge provided solid-state ionic environments for more efficient syntrophic interactions between co-cultures without bacterial competition, further enhancing the device performance and lifespan. The solid-phase platform allows versatile device configuration in a small footprint without a cumbersome fluidic feeding system and permits easy integration and operation with solid-state applications. The device is sealed with a gas-permeable polydimethylsiloxane (PDMS) membrane to facilitate gas exchange to the bacteria and cathodic reactions, even ideally allowing for replenishing bacterial gasses from environments for self-sustainable energy harvesting. A DC-DC booster circuit is integrated with the stacked bio-solar cells to increase the operational voltage (~500 mV) to a maximum output of >3 V for self-powering an on-chip, light-emitting diode (LED). This is the first demonstration of the microliter-scale bio-solar cell as a practical power source.