Anionic States Research Articles

Unusual reactivity of a flavin in a bifurcating electron-transferring flavoprotein leads to flavin modification and a charge-transfer complex

From the outset, canonical electron transferring flavoproteins (ETFs) earned a reputation for containing modified flavin. We now show that modification occurs in the recently recognized bifurcating (Bf) ETFs as well. In Bf ETFs, the 'electron transfer' (ET) flavin mediates single electron transfer via a stable anionic semiquinone state, akin to the FAD of canonical ETFs, whereas a second flavin mediates bifurcation (the Bf FAD). We demonstrate that the ET FAD undergoes transformation to two different modified flavins by a sequence of protein-catalyzed reactions that occurs specifically in the ET site, when the enzyme is maintained at pH 9 in an amine-based buffer. Our optical and mass spectrometric characterizations identify 8-formyl flavin early in the process and 8-amino flavins (8AFs) at later times. The latter have not previously been documented in an ETF to our knowledge. Mass spectrometry of flavin products formed in Tris or bis-tris-aminopropane solutions demonstrates that the source of the amine adduct is the buffer. Stepwise reduction of the 8AF demonstrates that it can explain a charge transfer band observed near 726nm in Bf ETF, as a complex involving the hydroquinone state of the 8AF in the ET site with the oxidized state of unmodified flavin in the Bf site. This supports the possibility that Bf ETF can populate a conformation enabling direct electron transfer between its two flavins, as has been proposed for cofactors brought together in complexes between ETF and its partner proteins.

State-Specific Chemical Dynamics of the Nonvalence Bound State of the Molecular Anions.

Nonvalence bound states (NBS) are anionic states where the excess electron is extremely loosely bound to the neutral core through long-range potentials. In contrast to the valence orbitals of which the electron occupancy determines the molecular structure, as well as the chemical reactivity, the nonvalence orbital is quite diffuse and located far from the neutral core. The NBS can be classified into the dipole-bound state (DBS), quadruple-bound state (QBS), or correlation-bound state (CBS) according to the nature of the electron-neutral interaction, although their interaction potentials may cooperatively contribute. The NBS is ubiquitous in nature and has the strong implications in atmospheric, interstellar, or biological chemistry. Accordingly, NBS has long been conceived to play the role of the doorway into the formation of a stable anion or dissociative electron attachment (DEA). Despite intensive and extensive studies, however, the quantum-mechanical nature of NBS is still far from being thorough understanding. Herein, we describe a new aspect of state-specific NBS-mediated chemical dynamics, which has been revealed through a series of recent studies by our group. We have employed picosecond time-resolved pump-probe spectroscopy combined with cryogenically cooled ion trap and velocity-map imaging techniques to study closed-shell anions generated by electrospray ionization. DBS vibrational Feshbach resonances are prepared by the optical excitation of phenoxide, for instance, and their individual lifetimes have been precisely measured in a state-specific manner to reveal the strong mode-dependency of the autodetachment rate. Fermi's golden rule turns out to be extremely useful for a rational explanation of the experiment, although the more sophisticated theoretical model is desirable for the more quantitative analysis. For the DBS of para-chlorophenoxide or para-bromophenoxide where the polarizability of neutral core is substantial, the Fermi's golden rule based on the charge-dipole potential needs to be significantly modified to include the correlation effects to explain the exceptionally slow autodetachment rates. For the QBS of 4-cyanophenoxide, the mode-specific behavior of the quadrupole ellipsoid tensor explains the strong mode-dependent autodetachment rate. Meanwhile, the nonadiabatic transition of the excess electron into the valence orbital can result in stable anion formation or immediate chemical bond rupture. In the DBS of ortho-, meta-, or para-iodophenoxide, the transformation of the loosely bound excess electron into the πσ* antibonding orbital occurs to give I- as a final fragment. The fragmentation mediated by DBS occurs competitively with the concomitant autodetachment, paving a new way of the reaction control by tuning the quantum-mechanical nature of the DBS Feshbach resonance. This experimental observation provides the foremost evidence for the dynamic role of the DBS as a doorway into anion chemistry, such as DEA. The ponderomotive force on the electron in the nonvalence orbital has been demonstrated for the first time in a strong optical field, giving great promise for the manipulation of polyatomic molecules in terms of the spatial location, as well as the AC-Stark control of the chemical reaction.

Effect of Disorder and Doping on Electronic Structure and Diffusion Properties of Li3V2O5

V2O5 in its ω phase (Li3V2O5) with excess lithium is a potential alternative to the graphite anode for lithium-ion batteries at low temperature and fast charging conditions owing to its safer voltage (0.6 V vs Li+/Li(s)) and high lithium transport rate. In-operando cationic disorder, as observed in most ordered materials, can produce significant changes in charge compensation mechanisms, anionic activity, lithium diffusion, and operational voltages. In this work, we report the variation in structural distortion, electronic structure, and migration barrier accompanied by disorder using first-principles calculations. Owing to the segregation of lithium atoms in the disordered state, we observe greater distortion, emergence of metallic behavior, and potential anionic activity from nonbonding oxygen states near the Fermi level. Redox capacity can be tuned by doping with 3d metals, which can adjust the participating cationic states, and by fluorine substitution, which can stabilize or suppress anionic states. Moreover, the suppression of anionic activity is found to decrease structural distortion, which is crucial for mitigating voltage fade and hysteresis. Diffusion barrier calculations in the presence of disorder indicate the activation of the remaining 3D paths for lithium hopping which are unavailable in the ordered configuration, explaining its fast-charging ability observed in experiments.

The Mechanisms and Kinetics of Radical Scavenging Activity of Edaravone: A Computational Insight

Edaravone (EDV, 3-methyl-1-phenyl-2-pyrazolin-5-one) is a neuroprotective drug that has been used to treat acute stroke caused by cerebral thrombosis and embolism. Studies showed that EDV could be used to treat diseases related to oxidizing agents; however, the activity has not been fully studied yet. In this study, the free radical scavenging activity of EDV was investigated by thermodynamic and kinetic calculations. The results showed that EDV exhibited good HOO• radical scavenging activity in an aqueous medium at pH = 7.40 (koverall(HOO) = 8.58´107 M-1 s-1) through the electron transfer mechanism of the anion state. In contrast, this activity was insignificant in non-polar environments. EDV also exhibited excellent antiradical activity against HO·, CH3O·, CH3OO·, O2·-, NO2, SO4·-, N3· and DPPH radicals in the aqueous solution. Thus, it appears to suggest that EDV is a promising radical scavenger in polar environments.

External fields in conceptual density functional theory.

The necessity of the recent incorporation of new external variables in the context of conceptual DFT (CDFT) is discussed based on the ever-increasing portfolio of experimental reaction conditions in the endeavor of experimentalists to synthesize new molecules with unprecedented properties. Electric and magnetic fields (ε and B), mechanical forces (F), and confinement are proposed as valuable new variables, extending conventional CDFT and its associated response functions. A finite field approach is used to calculate the evolution of both global and local descriptors in a selected series of atomic and molecular applications, and from it derive new response function involving, with one exception, the first derivative to the field considered. The electricfield results, displaying, for example, a case of a field-induced enantioselectivity in the Fukui function, may be instrumental in the recent upsurge of chemistry in oriented external electric fields. The study of atomic electronegativity and hardness in magnetic fields displays a piecewise behavior, associated to configurational jumps upon increasing field strength and reveals an overall compression of their ranges for stronger fields, which may be guiding upon investigating chemistry in extremely high fields like in white dwarfs. The evolution of the electronegativity and hardness of diatomics under mechanical force can elegantly be traced back to differences in their equilibrium distance in the neutral, cationic, and anionic state. The well-known reduction of the polarizability under confinement can be seen as a fore-runner of the increasing hardness of atoms under pressure, presently under investigation. Periodicity showing up in a spontaneous way in the variety of properties is a leitmotiv in this study, as well as the interconnections/analogies between the different response functions.

Polypyrrole complexation on biomass-derived powdered carbon for adsorptive elimination of emerging pharmaceutical contaminant Sulfamethoxazole: A comprehensive insight

Carbon-based adsorbents are a preferred class of adsorbents for eliminating an array of pollutants owing to their rigid porous morphology. However, the limitation of nitrogen-containing functional groups limits their applicability in targeting organic pollutants like antibiotic species. Such groups offer positively charged surfaces for the efficient adsorption of anionic antibiotic species. The current study aims to enrich the surface of the prepared biomass-derived powdered carbon (PC) with nitrogen-rich polymer viz. Polypyrrole (PPy) via in-situ oxidative polymerisation to prepare an N-enriched adsorbent (PPy-PC) for the adsorptive elimination of emerging antibiotic contaminant Sulfamethoxazole (SMX) from aqueous setups. Efficient adsorptive interactions between PPy-PC and SMX were reported at pH 6.0, owing to strong electrostatic interactions between anionic SMX species (pKa = 5.7) and cationic polypyrrole states viz. Polaron (PPy+.) and bi-polaron (PPy++) state. Other interactions, viz. π-π electron donor-acceptor (EDA) interaction, hydrogen bonding, Lewis acid-base interaction, charge-assisted hydrogen bonding (CAHB) etc., also contributed to the adsorptive interactions. Isotherm model studies verified good fitting of both Freundlich and Langmuir isotherm models with the experimental data, verifying the possibility of multilayer and monolayer fashion of SMX's adsorption on PPy-PC. Elevating ionic strength of the SMX medium showed a slight decline in its adsorption capacity. Co-existing heavy metals had little effect on SMX's adsorption, whereas co-existing antibiotics significantly affected SMX's adsorption over the PPy-AC surface. Desorption and re-adsorption analysis verified the recyclability potential of the adsorbent for multiple cycles. Seed toxicity studies using Vigna mungo seeds verified the adsorbent's efficacy in remediating SMX solution. Continuous column studies verified lower column bed heights (cm), higher inlet feed concentrations (mg/L), and higher initial feed flow rates (mL/min) resorted to quick saturation of the packed bed column.

Electrochemical and computational estimations of cephalosporin drugs as eco-friendly and efficient corrosion inhibitors for aluminum in alkaline solution

In this study, the anionic state of Ceftriaxone sodium (Cefx) and Ceftazidime (Cefz) medication corrosion inhibition capabilities for Al in 0.1 M NaOH solution are explored using various electrochemical analyses. Furthermore, the morphological structure and surface chemical composition of the impact of these drugs on the Al substrate in NaOH are investigated. For the prediction and analysis of interactions between molecule structure and inhibition efficiency, quantum chemical calculations (QC), Monte Carlo simulations (MC), and molecular dynamics (MD) simulations (MD) are performed. The electrochemical findings reveal that the inhibitory effectiveness increases with increasing drug concentrations and declines with rising temperature, reaching a maximum value of 78.4% for 300 ppm Cefx while 59.5% for 300 ppm Cefz at 293 K, implying that Cefx outperforms for Cefz. In addition, the studied drugs act as cathodic inhibitors, and their adsorption is spontaneous and mixed type adsorption in its nature that obeys Freundlich isotherm for Cefz while Temkin isotherm is the best-fitted one for Cefx. Surface analysis and wettability measurements imply that Cefx and Cefz shield the Al against corrosion by surface adsorption and generating a protective hydrophobic film. Thermodynamic activation parameters in the absence and presence of 300 ppm of the studied drugs are calculated and discussed. The energies of the border molecular orbitals and computed molecular parameters for the investigated drugs revealed that anionic Cefx is more readily adsorbed on the Al surface than Cefz. This finding is validated further using MC and MD simulations. Overall, the proposed cephalosporin drugs delivered a cost-effective and facile approach for boosting the efficiency of corrosion inhibitors for Al under aggressive conditions.

A Potent Antioxidant Sesquiterpene, Abelsaginol, from Abelmoschus sagittifolius: Experimental and Theoretical Insights.

The sesquiterpenoid compound abelsaginol (AS) was successfully isolated from Abelmoschus sagittifolius for the first time. The compound was identified using NMR and MS data. The antioxidant activity of AS was also evaluated both theoretically and experimentally. AS was found to be a weak HOO• radical scavenger in organic solvents such as pentyl ethanoate and dimethyl sulfoxide (koverall = ∼ 102 M–1 s–1), in a good agreement with the results of the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assay. However, AS exhibited good HOO• antiradical activity in water at pH 7.40 (koverall = 9.00 × 106 M–1 s–1) through the single-electron transfer mechanism of the anion state. Further calculations also demonstrated that AS could exert good to moderate activity against CH3O•, CH3OO•, CCl3OO•, NO2, and SO4•– radicals, with kf values from 4.00 × 103 to 1.52 × 107 M–1 s–1. However, AS exerted much lower activity against HO•, CCl3O•, NO, O2•–, and N3• radicals under the studied conditions. In general, the activity of AS in water at pH 7.40 is higher than that of Trolox or butylated hydroxytoluene, which are common reference antioxidants. Thus, in an aqueous physiological milieu, AS is a promising natural antioxidant.

Electron-impact high-lying N2− resonant states

Quasibound states of the nitrogen molecular anion are studied by electron scattering from ${\mathrm{N}}_{2}$ using ab initio $R$-matrix theory and a close-coupling model. Scattering calculations are performed using both cc-pVTZ and cc-pVQZ target basis sets involving up to 26 low-lying target states in a complete active space configuration-interaction representation. Complex resonance potential energy curves are characterized as a function of internuclear separation for all eight ${{\mathrm{N}}_{2}}^{\ensuremath{-}}$ states identified, including the well-known $X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{g}$ shape resonance, one $1{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ Feshbach resonance, as well as six core-excited resonances involving 1 ${}^{2}{\mathrm{\ensuremath{\Delta}}}_{g}$, 1 ${}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}$, 2 ${}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}$, 3 ${}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}$, 1 ${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}$, and 1 ${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{\ensuremath{-}}$. The ${}^{2}{\mathrm{\ensuremath{\Delta}}}_{g}$ and ${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{\ensuremath{-}}$ resonant states are identified and characterized. Comparisons are made with the very different resonance structure in the isoelectronic ${\mathrm{CO}}^{\ensuremath{-}}$ anion. The present resonance analysis provides a starting point for studies of the vibrational excitation, electron-impact dissociation, and other resonance-driven phenomena in ${\mathrm{N}}_{2}$.

L-Histidine with nitric acid: A comparison of crystal structures and Hirshfeld surfaces analysis

L-histidine crystallizes in three different crystal structure with nitric acid, i.e. L-histidinium nitrate, L-histidinium nitrate monohydrate and L-Histidinium dinitrate. Also there is DL-histidinium dinitrate. Though the structural aspects of histidinium nitrate monohydrate, L-Histidinium dinitrate and DL-histidinium nitrate are well studied, the structural studies on L-histidinium nitrate is not dealt in detail. Here we have tried to discuss in detail the crystal structure of L-histidinium nitrate using both single crystal X-ray and neutron diffraction. The crystal structure consists one L-histidine molecule which has the amino and imino groups protonated, but the carboxylic acid group is deprotonated. The nitrate ion is in anionic state ie NO3−. The conformation of histidine (N1-C2-C3-C4=64.99°) is gauche (-). Also a comparison of the structure of L-histidinium nitrate with other three available crystal structures retrieved using CSD have been carried out. It was found that L-histidine in L-histidinium nitrate monohydrate adopts gauche (+) conformation and in other three structure it is gauche (-), and L-histidinium nitrate has the lowest volume. Hirshfeld surface and interaction energies analysis of all the above structures were carried out using the x-ray data. L-histidinium nitrate monohydrate shows maximum globuarity. Interaction energy obtained from energy framework showed that L-histidinium nitrate monohydrate has maximum total energy of -41.5(kJ/Mole). The asphericity of our structure L-histidinium nitrate is 0.252 indicating prolate nature unlike the other three complexes. The percentage of H…H contacts is maximum in L-histidinium nitrate which is 27.3%. A comparison of various contacts of histidine between the x-ray and neutron structure of ours shows that the maximum change is reflected in the C…H and H…H contacts with C…H having a higher percentage and H…H having a lower percentage in the neutron structure indicating that the neutron diffraction maps shows the hydrogen bond interaction more accurately.The three complexes, except DL Histidinium dinitrate crystallizes in a non-centrosymmetric space group and hence could exhibit second-order optical non-linear properties, attempts were made to calculate heats of formation, dipole moments (D), polarizabilities (α) and first hyperpolarizabilities (β) using the semi empirical method at the PM6 level using MOPAC2009 and the packing energy as implemented in MERCURY. It was found that the average β of L-histidinium nitrate monohydrate was the highest amongst the three showing that it is more suitable for NLO material.

Probing the structures and bonding of Ag/H end-capping acetylene and polyyne, AgC2nH− (n = 1, 2), a combined photoelectron imaging and quantum chemical calculation study

The electronic structures of AgC2nH− (n = 1, 2) are reported by using photoelectron imaging and ab initio calculations. The results indicate that all the ground states of anion and neutral AgC2nH have a linear geometry. The electron affinities (EAs) are measured to be 1.123 and 1.379 eV for AgC2H and AgC4H, respectively. The NRT analysis shows that ionic character dominates the Ag–C chemical bond in these neutral species. The calculated static dipole polarizability (α) and second hyperpolarizability (γ) of the molecules indicate that the cap of Ag could enhance the nonlinear optical responses.

Complex energies and transition dipoles for shape-type resonances of uracil anion from stabilization curves via Padé.

Absorption of slow moving electrons by neutral ground state nucleobases has been known to produce resonance metastable states. There are indications that such metastable states may play a key role in DNA/RNA damage. Therefore, herein, we present an ab initio non-Hermitian investigation of the resonance positions and decay rates for the low lying shape-type states of the uracil anion. In addition, we calculate the complex transition dipoles between these resonance states. We employ the resonance via Padé (RVP) method to calculate these complex properties from real stabilization curves by analytical dilation into the complex plane. This method has already been successfully applied to many small molecular systems, and herein, we present the first application of RVP to a medium-sized system. The presented resonance energies are optimized with respect to the size of the basis set and compared with previous theoretical studies and experimental findings. Complex transition dipoles between the shape-type resonances are computed using the optimal basis set. The ability to calculate ab initio energies and lifetimes of biologically relevant systems paves the way for studying reactions of such systems in which autoionization takes place, while the ability to also calculate their complex transition dipoles opens the door for studying photo-induced dynamics of such biological molecules.

Phenalenyl Radical: Smallest Polycyclic Odd Alternant Hydrocarbon Present in the Graphene Sheet.

Phenalenyl, a zigzag-edged odd alternant hydrocarbon unit can be found in the graphene nanosheet. Hückel molecular orbital calculations indicate the presence of a nonbonding molecular orbital (NBMO), which originates from the linear combination of atomic orbitals (LCAO) arising from 13 carbon atoms of the phenalenyl molecule. Three redox states (cationic, neutral radical, and anionic) of the phenalenyl-based molecules were attributed to the presence of this NBMO. The cationic state can undergo two consecutive reductions to result in neutral radical and anionic states, stepwise, respectively. The phenalenyl-based radicals were found as crucial building blocks and attracted the attention of various research fields such as organic synthesis, material science, computation, and device physics. From 2012 onward, a strategy was devised using the cationic state of phenalenyl-based molecules and in situ generated phenalenyl radicals, which created a new domain of catalysis. The in situ generated phenalenyl radicals were utilized for the single electron transfer (SET) process resulting in redox catalysis. This emerging range of applications rejuvenates the more than six decades-old phenalenyl chemistry. This review captures such developments ranging from fundamental understanding to multidirectional applications of phenalenyl-based radicals.

Effect of Microhydration on the Temporary Anion States of Pyrene.

The influence of incremental hydration (≤4) on the electronic resonances of the pyrene anion is studied using two-dimensional photoelectron spectroscopy. The photoexcitation energies of the resonances do not change; therefore, from the anion’s perspective, the resonances remain the same, but from the neutral’s perspective of the electron–molecule reaction, the resonances decrease in energy by the binding energy of the water molecules. The autodetachment of the resonances shows that hydration has very little effect, showing that even the dynamics of most of the resonances are not impacted by hydration. Two specific resonances do show changes that are explained by the closing of specific autodetachment channels. The lowest-energy resonance leads to efficient electron capture as observed through thermionic emission and evaporation of water molecules (dissociative electron attachment). The implications of low-energy electron capture in dense molecular interstellar clouds are discussed.

Redox‐Addressable Single‐Molecule Junctions Incorporating a Persistent Organic Radical**

AbstractIntegrating radical (open‐shell) species into non‐cryogenic nanodevices is key to unlocking the potential of molecular electronics. While many efforts have been devoted to this issue, in the absence of a chemical/electrochemical potential the open‐shell character is generally lost in contact with the metallic electrodes. Herein, single‐molecule devices incorporating a 6‐oxo‐verdazyl persistent radical have been fabricated using break‐junction techniques. The open‐shell character is retained at room temperature, and electrochemical gating permits in situ reduction to a closed‐shell anionic state in a single‐molecule transistor configuration. Furthermore, electronically driven rectification arises from bias‐dependent alignment of the open‐shell resonances. The integration of radical character, transistor‐like switching, and rectification in a single molecular component paves the way to further studies of the electronic, magnetic, and thermoelectric properties of open‐shell species.

Redox-Addressable Single-Molecule Junctions Incorporating a Persistent Organic Radical.

Integrating radical (open‐shell) species into non‐cryogenic nanodevices is key to unlocking the potential of molecular electronics. While many efforts have been devoted to this issue, in the absence of a chemical/electrochemical potential the open‐shell character is generally lost in contact with the metallic electrodes. Herein, single‐molecule devices incorporating a 6‐oxo‐verdazyl persistent radical have been fabricated using break‐junction techniques. The open‐shell character is retained at room temperature, and electrochemical gating permits in situ reduction to a closed‐shell anionic state in a single‐molecule transistor configuration. Furthermore, electronically driven rectification arises from bias‐dependent alignment of the open‐shell resonances. The integration of radical character, transistor‐like switching, and rectification in a single molecular component paves the way to further studies of the electronic, magnetic, and thermoelectric properties of open‐shell species.

On the free radical scavenging and metallic ion chelating activities of pyridoxal - Could the pro-oxidant risk be competitive?

Primary and secondary antioxidant activities of pyridoxal have been investigated by using density functional theory (DFT) at the M05–2X level combined with 6–311++G(d,p) basis set for non-metallic atoms and LanL2DZ for metallic ions. The former has been examined by its free radical scavenging activity towards HOO●, HO●, and NO2●via different mechanisms including formal hydrogen transfer (FHT), proton transfer (PT), single electron transfer (SET), and radical adduct formation (RAF). The latter has been accomplished through its transition metal-chelating ability with Fe(III)/Fe(II) and Cu(II)/Cu(I) ions. The results show that pyridoxal illustrates as an efficient radical scavenger, especially, for HO● and NO2● in water. The overall rate constants (koverall) for the reactions with HOO●, HO●, and NO2● radicals are 1.30 × 104, 5.76 × 109, and 1.43 × 109 M−1s−1, respectively. The SET from the anionic state is the most dominant for the HOO● and NO2● scavenging reactions, while both RAF and SET contribute largely to the reaction with highly reactive HO● radicals. Moreover, the anionic form of pyridoxal demonstrates a better role as a metal chelator than the neutral. However, the pro-oxidant risks of the formed complexes could be observed if there are superoxide radical anion (O2●–) and ascorbate (Asc–) in aqueous media.

The hydroperoxyl antiradical activity of Trolox in water: The effects of pH values on rate constants

Abstract Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid) is a highly hydrophilic α-tocopherol analog that is widely used as a standard against which the antioxidant ability of other chemicals is measured and represented in Trolox equivalents. However, the effect of pH values on the hydroxyl radical scavenging activity has not been fully studied yet. In this study, the HOO• antiradical activity of Trolox in water was studied. It was found that the H-abstraction of the O1-H bond determined the activity of the neutral and monoanion states, whereas the electron transfer reaction of the hydroxyl anion state determined the activity of the dianion state. Although the total rate constant increased following the increase in pH levels, the overall rate constant of the Trolox + HOO• reaction in water changed when pH levels rose due to the decrease in HOO• molar fraction. The results also revealed that at pH < 2, the O1-radical was the main intermediate of the Trolox + HOO• reaction in water, whereas, at pH ---gt--- 5, the anion-radical was the significant intermediate. Thus the rate constants and the reaction intermediates vary with the pH values.

Origin of Selective Nitrate Removal by Ni2+–Al3+ Layered Double Hydroxides in Aqueous Media and Its Application Potential in Seawater Purification

Abstract To understand the origin of the nitrate anion selectivity in layered double hydroxide (LDH; [Ni1−xAlx(OH)2]Clx) materials (i.e., Cl−-NiAl(x)LDH; x = 1/3 and 1/5) comprising Ni2+, Al3+, and exchangeable chloride anions, the equilibrium and kinetic properties of the chloride-to-nitrate anion exchange reaction were investigated in aqueous media. The anion exchange isotherms of the studied systems showed that the nitrate anion selectivity was significantly higher at x = 1/5 than at x = 1/3. The fine crystal structures of the LDH materials and the hydration states of the nitrate anions in their interlayer spaces were identified by synchrotron-radiation X-ray diffraction (SXRD) and Raman spectroscopy, respectively. The nitrate anion selectivities of Cl−-NiAl(x)LDH (x = 1/3 and 1/5) were determined by the relationship between the magnitudes of the thermal vibration parameters of the chloride and nitrate anions; the anion exchange reaction primarily gave NiAl(x)LDH containing anions with smaller thermal vibration parameters. Time-resolved SXRD measurements of the anion exchange reaction revealed that the exchange pathway differed depending on the nitrate anion selectivity. The nitrate anion removal ability and selectivity of Cl−-NiAl(x)LDH (x = 1/3 and 1/5) in artificial seawater were maintained, suggesting that Cl−-NiAl(1/5)LDH could be used for nitrate removal from contaminated seawater.

Pushing the Length Limit of Dihydrodiboraacenes: Synthesis and Characterizations of Boron-Embedded Heptacene and Nonacene.

Boron-embedded heteroacenes (boraacenes) have attracted enormous interest in organic chemistry and materials science. However, extending the skeleton of boraacenes to higher acenes (N≥6) is synthetically challenging because of their limited stability under ambient conditions. Herein, we report the synthesis of boron-embedded heptacene (DBH) and nonacene (DBN) as the hitherto longest boraacenes. The former is highly stable (even after 240 h in tetrahydrofuran), while the latter is air-sensitive with the half-life (t1/2 ) of 11.8 min. The structures of both compounds are verified by single-crystal X-ray diffraction, revealing a linear backbone with an antiaromatic C4 B2 core. Photophysical characterizations associated with theoretical calculations indicate that both compounds exhibit highly efficient anti-Kasha emissions. Remarkably, the air-stable DBH manifests an ultrahigh photoluminescence quantum yield (PLQY) of 98±2 % and can be chemically reduced to its radical anion and dianion states, implying the value of boron-doped higher acenes as novel functional materials.