One Carbon Ring Expansion of Bipyrrole to Bipyridine Enables Access to a π-Extended, Non-innocent, Corrole-like Ligand.

A π-extended, diaza-triphenylene embedded, mono-anionic corrole analogue and its NiII complex were synthesized from a diaza-triphenylene precursor, which was obtained from a double one-carbon insertion into a naphthobipyrrole diester. Following conversion to the corresponding activated diol and acid-catalyzed condensation with pyrrole, subsequent reaction with pentafluorobenzaldehyde afforded mono-anionic, π-extended bipyricorrole-like macrocycle. Attempted NiII insertion with Ni(OAc)2 ⋅ 4H2 O resulted an ESR active, NiII bipyricorrole radical complex, which was converted to a stable cationic NiII complex upon treatment with [(Et3 O)+ (SbCl6 )- ]. Both complexes were characterized by 1 H and 13 C NMR, UV/Vis spectroscopy and single crystal X-ray diffraction analysis. The NiII bipyricorrole radical complex is converted to a cationic NiII complex by single-electron reduction using cobaltocene. Both the cationic NiII complex and the radical NiII complex exhibited ligand-centered redox behavior, whereas the NiII remains in the +2 oxidation state.

Grignard Reagent-Catalyzed Hydroboration of Esters, Nitriles, and Imines.

The reduction in esters, nitriles, and imines requires harsh conditions (highly reactive reagents, high temperatures, and pressures) or complex metal-ligand catalytic systems. Catalysts comprising earth-abundant and less toxic elements are desirable from the perspective of green chemistry. In this study, we developed a green hydroboration protocol for the reduction in esters, nitriles, and imines at room temperature (25 °C) using pinacolborane as the reducing agent and a commercially available Grignard reagent as the catalyst. Screening of various alkyl magnesium halides revealed MeMgCl as the optimal catalyst for the reduction. The hydroboration and subsequent hydrolysis of various esters yielded corresponding alcohols over a short reaction time (~0.5 h). The hydroboration of nitriles and imines produced various primary and secondary amines in excellent yields. Chemoselective reduction and density functional theory calculations are also performed. The proposed green hydroboration protocol eliminates the requirements for complex ligand systems and elevated temperatures, providing an effective method for the reduction in esters, nitriles, and imines at room temperature.

Influence of Electronic Environment on the Radiative Efficiency of 9-Phenyl-9H-carbazole-Based ortho-Carboranyl Luminophores.

The photophysical properties of closo-ortho-carboranyl-based donor-acceptor dyads are known to be affected by the electronic environment of the carborane cage but the influence of the electronic environment of the donor moiety remains unclear. Herein, four 9-phenyl-9H-carbazole-based closo-ortho-carboranyl compounds (1F, 2P, 3M, and 4T), in which an o-carborane cage was appended at the C3-position of a 9-phenyl-9H-carbazole moiety bearing various functional groups, were synthesized and fully characterized using multinuclear nuclear magnetic resonance spectroscopy and elemental analysis. Furthermore, the solid-state molecular structures of 1F and 4T were determined by X-ray diffraction crystallography. For all the compounds, the lowest-energy absorption band exhibited a tail extending to 350 nm, attributable to the spin-allowed π-π* transition of the 9-phenyl-9H-carbazole moiety and weak intramolecular charge transfer (ICT) between the o-carborane and the carbazole group. These compounds showed intense yellowish emission (λem = ~540 nm) in rigid states (in tetrahydrofuran (THF) at 77 K and in films), whereas considerably weak emission was observed in THF at 298 K. Theoretical calculations on the first excited states (S1) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the o-carborane. Furthermore, photoluminescence experiments in THF‒water mixtures demonstrated that aggregation-induced emission was responsible for the emission in rigid states. Intriguingly, the quantum yields and radiative decay constants in the film state were gradually enhanced with the increasing electron-donating ability of the substituent on the 9-phenyl group (‒F for 1F < ‒H for 2P < ‒CH3 for 3M < ‒C(CH3)3 for 4T). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9H-carbazole group. Consequently, the efficient ICT-based radiative decay of o-carboranyl compounds can be achieved by appending the o-carborane cage with electron-rich aromatic systems.

Spirobifluorene-Based o-Carboranyl Compounds: Insights into the Rotational Effect of Carborane Cages on Photoluminescence.

9,9'-Spirobifluorene-based closo-o-carboranyl (SFC1 and SFC2) compounds and their nido-derivatives (nido-SFC1 and nido-SFC2) were prepared and characterized. The two closo-compounds displayed major absorption bands assignable to π-π* transitions involving the spirobifluorene group, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene moieties. The nido-compounds exhibited slightly blueshifted absorption bands resulting from the absence of the ICT transitions corresponding to the o-carborane moieties due to the anionic character of the nido-o-carboranes. While SFC1 exhibited only high-energy emissions in THF at 298 K (only from locally excited (LE) states assignable to π-π* transitions on the spirobifluorene group), remarkable emissions in the low-energy region were observed in the rigid state such as in THF at 77 K and in the film state. SFC2 displayed intense emissions in the low-energy region in all states. The fact that neither of the nido-derivatives of SFC1 and SFC2 exhibited low-energy emissions and the TD-DFT calculation results of each closo-compound clearly verified that the low-energy emission was based on ICT-based radiative decay. The conformational barriers from each relative energy calculation upon changing the dihedral angles around the o-carborane cages for both compounds confirmed that the rotation of the o-carborane cages and terminal phenyl rings for SFC1 is freer than that for SFC2.

Deboronation-Induced Ratiometric Emission Variations of Terphenyl-Based Closo-o-Carboranyl Compounds: Applications to Fluoride-Sensing.

Closo-o-carboranyl compounds bearing the ortho-type perfectly distorted or planar terphenyl rings (closo-DT and closo-PT, respectively) and their nido-derivatives (nido-DT and nido-PT, respectively) were synthesized and fully characterized using multinuclear NMR spectroscopy and elemental analysis. Although the emission spectra of both closo-compounds exhibited intriguing emission patterns in solution at 298 and 77 K, in the film state, closo-DT mainly exhibited a π-π* local excitation (LE)-based emission in the high-energy region, whereas closo-PT produced an intense emission in the low-energy region corresponding to an intramolecular charge transfer (ICT) transition. In particular, the positive solvatochromic effect of closo-PT and theoretical calculation results at the first excited (S1) optimized structure of both closo-compounds strongly suggest that these dual-emissive bands at the high- and low-energy can be assigned to each π-π* LE and ICT transition. Interestingly, both the nido-compounds, nido-DT and nido-PT, exhibited the only LE-based emission in solution at 298 K due to the anionic character of the nido-o-carborane cages, which cannot cause the ICT transitions. The specific emissive features of nido-compounds indicate that the emissive color of closo-PT in solution at 298 K is completely different from that of nido-PT. As a result, the deboronation of closo-PT upon exposure to increasing concentrations of fluoride anion exhibits a dramatic ratiometric color change from orange to deep blue via turn-off of the ICT-based emission. Consequently, the color change response of the luminescence by the alternation of the intrinsic electronic transitions via deboronation as well as the structural feature of terphenyl rings indicates the potential of the developed closo-o-carboranyl compounds that exhibit the intense ICT-based emission, as naked-eye-detectable chemodosimeters for fluoride ion sensing.

Pyrazinoindole-Based Lewis-Acid/Base Assembly: Intriguing Intramolecular Charge-Transfer Switching through the Dual-Sensing of Fluoride and Acid.

Pyrazinoindole-based Lewis-acid/base assemblies are prepared through the use of regioselective formal [3 + 3] cycloaddition reactions, and their intriguing photophysical properties are described. The assemblies exhibit strong emissions in THF solution, which are attributed to through-space intramolecular charge-transfer (ICT) transitions between the branched Lewis-acid/base moieties. Furthermore, these show ratiometric color-change responses in PL titration experiments, which give rise to new colors through turn-on emissions ascribable to ICT transitions that alternate between the pyrazinoindole units and each triarylboryl or amino moiety, a consequence of the binding of the fluoride or acid. Pieces of filter paper covered by these assemblies exhibited blue-shifted color changes when immersed in aqueous acidic solutions, suggesting that these are promising candidate indicators that detect acid through emissive color. Computational data for these assemblies and their corresponding adducts verify the existence of ICT transitions that alternate through fluoride or acid binding.

Carbazole-Appended Salen-Indium Conjugate Systems: Synthesis and Enhanced Luminescence Efficiency.

Novel carbazole-conjugated salen-In complexes (Cz1 and Cz2) were prepared and fully characterized by 1H and 13C NMR spectroscopy, elemental analysis, and high-resolution mass spectrometry. The major low-energy absorption bands at λabs = 342 nm for Cz1 and 391 nm for Cz2, respectively, are assigned to typical intramolecular charge transfer (ICT) transitions between the carbazole unit and the salen-In center. The solvatochromism effects in various organic solvents and their large Stokes shift distinctly supported the ICT nature. The photoluminescent spectra of Cz1 and Cz2 showed broad emission bands are centered at 459 nm (blue, λex = 354 nm) and 507 nm (green, λex = 396 nm) in THF, respectively, which are typical feature of CT transitions. In particular, Cz1 showed 8-fold enhanced quantum efficiency relative to that of Cz2, at least 10-fold higher than those of the carbazole-free salen-In complexes. Such enhanced luminescence efficiency of Cz1 originated from efficient radiative decay based on the ICT transition between the salen-In moieties and carbazole parts, as well as its structural rigidity in conversion process between the ground (S0) and excited (S1) states. In other words, Cz2 exhibited low quantum yield due to its structural fluctuation, which is free rotation of both the appended carbazole moieties and bridged phenylene rings in conversion between the S0 and S1 structures. Theoretical calculations clearly supported these intriguing results. In addition, these salen-In complexes exhibited high thermal stability (Td5 = 367 °C for Cz1 and 406 °C for Cz2) and electrochemical stability.

Systematic Control of the Overlapping Energy Region for an Efficient Intramolecular Energy Transfer: Functionalized Salen-Al/Triphenylamine Guest-Host Assemblies.

A series of triphenylamine (TPA)-containing salen-Al assembly dyads, [salen(3- tBu-5-R)2Al(OC6H4- p-N(C6H5)2)] [salen = N, N'-bis(salicylidene)ethylenediamine; R = H (D1), tBu (D2), Ph (D3), OMe (D4), and NMe2 (D5)], were prepared in good yield (50-80%) and fully characterized by NMR spectroscopy and elemental analysis. Both the UV/vis absorption and photoluminescence (PL) spectra of D1-D4, except for D5, in a tetrahydrofuran solution exhibited dual patterns, which are assignable to the salen-Al-centered π-π* transition (low-energy region) and the TPA-centered π-π* transition (high-energy region). In particular, the emission spectra of the dyads displayed interesting dual-emissive patterns via a significant intramolecular energy transfer (IET) process between the salen-Al moiety and TPA group. Notably, this IET process was systematically tuned by varying the substituents and dominantly observed in the rigid state. More interestingly, compared to the salen-Al complexes (A1-A4) without the TPA group, D1-D4 exhibited enhanced quantum efficiencies. Time-dependent density functional theory calculations on the S1-optimized structures of D1-D5 further supported these experimental results by indicating the existence of independent transition states between the salen-Al moiety and TPA group in the assembly dyads. The present study reports the first example of salen-Al complexes bearing electron-rich TPA moieties.

A Series of Quinolinol-Based Indium Luminophores: A Rational Design Approach for Manipulating Photophysical Properties.

An approach to the design of a series of quinolinol-based indium complexes that can exhibit different optical properties is proposed. Mono-incorporated (Inq1 and InMeq1), bis-incorporated (InMeq2), and tris-incorporated (Inq3 and InMeq3) indium quinolinate complexes have been prepared. These complexes have also been characterized by X-ray crystallography. The photophysical properties of these complexes have also been examined by a combination of experimental and theoretical techniques. The indium complexes with a single quinolinol ligand (Inq1 and InMeq1) showed higher quantum efficiency than those with two or three quinolinate ligands; in particular, InMeq1 exhibited the highest quantum yield [ΦPL = 59% in poly(methyl methacrylate) film]. The insights into the nature of these findings were obtained by the sequential synthesis of the quinolinol-based indium luminophores and a detailed investigation of their structural stability.

Photophysical Properties of Spirobifluorene-Based o-Carboranyl Compounds Altered by Structurally Rotating the Carborane Cages.

9,9'-Spirobifluorene-based o-carboranyl compounds C1 and C2 were prepared and fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The solid-state structure of C1 was also determined by single-crystal X-ray diffractometry. The two carboranyl compounds display major absorption bands that are assigned to π-π* transitions involving their spirobifluorene groups, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene groups. While C1 only exhibited high-energy emissions (λem = ca. 350 nm) in THF at 298 K due to locally excited (LE) states assignable to π-π* transitions involving the spirobifluorene group alone, a remarkable emission in the low-energy region was observed in the rigid state, such as in THF at 77 K or the film state. Furthermore, C2 displays intense dual emissive patterns in both high- and low-energy regions in all states. Electronic transitions that were calculated by time-dependent-DFT (TD-DFT) for each compound based on ground (S0) and first-excited (S1) state optimized structures clearly verify that the low-energy emissions are due to ICT-based radiative decays. Calculated energy barriers that are based on the relative energies associated with changes in the dihedral angle around the o-carborane cages in C1 and C2 clearly reveal that the o-carborane cage in C1 rotates more freely than that in C2. All of the molecular features indicate that ICT-based radiative decay is only available to the rigid state in the absence of structural fluctuations, in particular the free-rotation of the o-carborane cage.

Effect of Planarity of Aromatic Rings Appended to o-Carborane on Photophysical Properties: A Series of o-Carboranyl Compounds Based on 2-Phenylpyridine- and 2-(Benzo[b]thiophen-2-yl)pyridine.

Herein, we investigated the effect of ring planarity by fully characterizing four pyridine-based o-carboranyl compounds. o-Carborane was introduced to the C4 position of the pyridine rings of 2-phenylpyridine and 2-(benzo[b]thiophen-2-yl)pyridine (CB1 and CB2, respectively), and the compounds were subsequently borylated to obtain the corresponding CN-chelated compounds CB1B and CB2B. Single-crystal X-ray diffraction analysis of the molecular structures of CB2 and CB2B confirmed that o-carborane is appended to the aryl moiety. In photoluminescence experiments, CB2, but not CB1, showed an intense emission, assignable to intramolecular charge transfer (ICT) transition between the aryl and o-carborane moieties, in both solution and film states. On the other hand, in both solution and film states, CB1B and CB2B demonstrated a strong emission, originating from π-π * transition in the aryl groups, that tailed off to 650 nm owing to the ICT transition. All intramolecular electronic transitions in these o-carboranyl compounds were verified by theoretical calculations. These results distinctly suggest that the planarity of the aryl groups have a decisive effect on the efficiency of the radiative decay due to the ICT transition.

Synthesis and Dual-Emission Feature of Salen-Al/Triarylborane Dyads.

Novel salen-Al/triarylborane dyad complexes were prepared and characterized with their corresponding mononuclear compounds. The UV-vis and photoluminescence experiments for dyads exhibited photoinduced energy transfer from borane to the salen-Al moiety in an intramolecular manner. Theoretical calculation and fluoride titration results further supported these intramolecular energy-transfer features.

Intriguing Indium-salen Complexes as Multicolor Luminophores.

The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N'-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7; OTf = CF3SO3-) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1-7 are highly stable in air and even aqueous solutions. The solid-state structures for 3-5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1-7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455-622 nm).

Understanding the structural differences between spherical and rod-shaped human insulin nanoparticles produced by supercritical fluids precipitation.

In this study, the thermal denaturation mechanism and secondary structures of two types of human insulin nanoparticles produced by a process of solution-enhanced dispersion by supercritical fluids using dimethyl sulfoxide (DMSO) and ethanol (EtOH) solutions of insulin are investigated using spectroscopic approaches and molecular dynamics calculations. First, the temperature-dependent IR spectra of spherical and rod-shaped insulin nanoparticles prepared from DMSO and EtOH solution, respectively, are analyzed using principal component analysis (PCA) and 2D correlation spectroscopy to obtain a deeper understanding of the molecular structures and thermal behavior of the two insulin particle shapes. All-atom molecular dynamics (AAMD) calculations are performed to investigate the influence of the solvent molecules on the production of the insulin nanoparticles and to elucidate the geometric differences between the two types of nanoparticles. The results of the PCA, the 2D correlation spectroscopic analysis, and the AAMD calculations clearly reveal that the thermal denaturation mechanisms and the degrees of hydrogen bonding in the spherical and rod-shaped insulin nanoparticles are different. The polarity of the solvent might not alter the structure or function of the insulin produced, but the solvent polarity does influence the synthesis of different shapes of insulin nanoparticles.

Determination of precise pyrimidine cationic structure by vacuum ultraviolet mass-analyzed threshold ionization spectroscopy.

The vibrational spectrum of a pyrimidine cation in the ground electronic state was obtained using vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. Accurate ionization energy of pyrimidine was determined from the 0-0 band position in the VUV-MATI spectrum and was measured by varying the PFI field to the zero field limit, which is 75,258 ± 7 cm(-1) (9.3308 eV). The spectrum displayed a large number of vibrational peaks, which could be nearly completely assigned through Franck-Condon analysis performed with variations of geometrical parameters at the B3LYP/cc-pVTZ level. Based on the excellent agreement between experimental and calculated results, the definite geometry of the pyrimidine cation in the ground electronic state was determined to be a planar structure with C2v symmetry with a decreased N-N distance in the ring.

Transport Dynamics of Water Molecules Confined between Lipid Membranes.

Water molecules confined between biological membranes exhibit a distinctive non-Gaussian displacement distribution, far different from that of bulk water. Here, we introduce a new transport equation for water molecules in the intermembrane space, quantitatively explaining molecular dynamics simulation results. We find that the unique transport dynamics of water molecules stems from the lateral diffusion coefficient fluctuation caused by their longitudinal motion in the direction perpendicular to the membranes. We also identify an interfacial region where water possesses distinct physical properties, which is unaffected by changes in the intermembrane separation.

Molecular Dynamics Simulation Study of the Protonation State Dependence of Glutamic Acid Transport through a Cyclic Peptide Nanotube.

The effect of the protonation state of glutamic acid on its translocation through cyclic peptide nanotubes (CPNs) was assessed by using molecular dynamics (MD) simulations. Anionic (GLU-), neutral zwitterionic (GLU0), and cationic (GLU+) forms of glutamic acid were selected as three different protonation states for an analysis of energetics and diffusivity for acid transport across a cyclic decapeptide nanotube. Based on the solubility-diffusion model, permeability coefficients for the three protonation states of the acid were calculated and compared with experimental results for CPN-mediated glutamate transport through CPNs. Potential of mean force (PMF) calculations reveal that, due to the cation-selective nature of the lumen of CPNs, GLU-, so-called glutamate, shows significantly high free energy barriers, while GLU+ displays deep energy wells and GLU0 has mild free energy barriers and wells inside the CPN. The considerable energy barriers for GLU- inside CPNs are mainly attributed to unfavorable interactions with DMPC bilayers and CPNs and are reduced by favorable interactions with channel water molecules through attractive electrostatic interactions and hydrogen bonding. Unlike the distinct PMF curves, position-dependent diffusion coefficient profiles exhibit comparable frictional behaviors regardless of the charge status of three protonation states due to similar confined environments imposed by the lumen of the CPN. The calculated permeability coefficients for the three protonation states clearly demonstrate that glutamic acid has a strong protonation state dependence for its transport through CPNs, as determined by the energetics rather than the diffusivity of the protonation state. In addition, the permeability coefficients also imply that GLU- is unlikely to pass through a CPN due to the high energy barriers inside the CPN, which is in disagreement with experimental measurements, where a considerable amount of glutamate permeating through the CPN was detected. To resolve the discrepancy between this work and the experimental observations, several possibilities are proposed, including a large concentration gradient of glutamate between the inside and outside of lipid vesicles and bilayers in the experiments, the glutamate activity difference between our MD simulations and experiments, an overestimation of energy barriers due to the artifacts imposed in MD simulations, and/or finally a transformation of the protonation state from GLU- to GLU0 to reduce the energy barriers. Overall, our study demonstrates that the protonation state of glutamic acid has a strong effect on the transport of the acid and suggests a possible protonation state change for glutamate permeating through CPNs.

Highly emissive 4-carbazole-appended salen-indium complex: the effect of strong donor-acceptor interaction.

Herein, we report our findings on 4-carbazole (CBZ)-appended salen-based indium complexes, CBZIn1 and CBZIn2, which feature diimine bridges exhibiting different electron-accepting properties. Notably, CBZIn2 exhibited a significantly higher photoluminescence quantum efficiency (PLQY, ΦPL) in toluene than CBZIn1, with a value over 15 times greater (ΦPL = 57.7% for CBZIn2; ΦPL = 3.7% for CBZIn1). In particular, in the rigid state of THF at 77 K, CBZIn2 exhibited a near-unity PLQY of 98.2%. Even in the PMMA film, CBZIn2 maintained a high level of PLQY (ΦPL = 70.2%). These results can be attributed to the highly efficient radiative decay process based on intramolecular charge-transfer (ICT) transition between the moderately twisted CBZ, characterized by its conformational rigidity and the 1,2-dicyanoethylene-bridged salen, which exhibits a strong electron-accepting ability. Furthermore, these findings are supported by theoretical calculations.

Preparation of ethyl 2-aryl 2,3-alkadienoates via palladium-catalyzed selective cross-coupling reactions.

Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield.

Alteration of intramolecular electronic transition via deboronation of carbazole-based o-carboranyl compound and intriguing 'turn-on' emissive variation.

The conversion of closo-o-carborane-containing compounds to the nido-o-species via deboronation causes photophysical changes that could be used for sensing applications. 9-Methyl-9H-carbazole-based closo- (closo-Cz) and nido-o-carboranyl (nido-Cz) compounds were prepared and fully characterised by multinuclear NMR spectroscopy and elemental analysis, and the solid-state molecular structure of closo-Cz was analysed by X-ray crystallography. Although the closo-compound exhibited an emissive pattern centred at λ em = ca. 530 nm in the rigid state only (in THF at 77 K and as a film), nido-Cz demonstrated intense emission in the near-UV region (λ em = ca. 380 nm) in both solution and film states at 298 K. The positive solvatochromic effect of nido-Cz and the results of theoretical calculations for both the o-carboranyl compounds supported that these emissive features originate from intramolecular charge transfer (ICT) corresponding to the o-carborane. Furthermore, the calculations verified that the electronic role of the o-carboranyl unit changed from acceptor to donor upon deboronation from closo-Cz to nido-Cz. Investigations of the radiative decay mechanisms of closo-Cz and nido-Cz according to their quantum efficiencies (Φ em) and decay lifetimes (τ obs) suggested that the ICT-based radiative decays of closo-Cz and nido-Cz readily occur in the film (solid) and solution state, respectively. These observations implied that the emission of closo-Cz in the solution state could be drastically enhanced by deboronation to nido-Cz upon exposure to an increasing concentration of fluoride anions. Indeed, turn-on emissive features in an aqueous solution were observed upon deboronation, strongly suggesting the potential of closo-Cz as a turn-on and visually detectable chemodosimeter for fluoride ion sensing.