Phenolate Anion Research Articles

Iron and copper based catalysts containing anionic phenolate ligands for atom transfer radical polymerization

Iron and copper complexes with anionic phenolate-bis(pyridyl)amine ligands were synthesized and examined as catalysts for atom transfer radical polymerization (ATRP) of methyl (meth)acrylate and styrene. With copper complexes, polymers with narrow molecular weight distributions, M w /M n ~1.2, were prepared. The catalytic performance of copper catalysts was affected by nature of halogen species and by the steric and electronic effects. In iron-mediated ATRP procedures, the number-average molecular weights of the polymers increased with monomer conversion, however, the molecular weight distributions of the resulting polymers were relatively broad M w /M n ~1.7, due to slow deactivation processes.

Sensitivity of Photoelectron Angular Distributions to Molecular Conformations of Anions.

An anion photoelectron imaging study probing the sensitivity of the photoelectron angular distribution (PAD) to conformational changes is presented. The PADs of a series of para-substituted phenolate anions is compared with those calculated using the Dyson orbital formalization. Good agreement was attained for the two observed direct detachment channels of all anions, except for the lowest-energy detachment channel of para-ethyl phenolate for which two conformations exist that yield very different PADs. The conformational freedom leads to an observed PAD that is the incoherent sum of the PADs from all conformers populated under experimental conditions. In contrast, a second detachment channel shows no sensitivity to the conformational flexibility of para-ethyl phenolate. Our results show that PADs can provide detailed information about the electronic structure of the anion and its conformations.

Photo absorption of p-coumaric acid in aqueous solution: RISM-SCF-SEDD theory approach.

Photo absorption properties of p-coumaric acid, the chromophore of photoactive yellow protein, in aqueous solution were investigated by means of reference interaction site model self-consistent field with spatial electron density distribution (RISM-SCF-SEDD) method. RISM-SCF-SEDD is a combination methodology of electronic structure theory and statistical mechanics for molecular liquids. Here, time-dependent density functional theory was coupled with RISM equation to study the electronic structure of p-coumaric acid in aqueous system. Excitation energies of the chromophore in its neutral, two monoanionic and dianionic forms were computed to elucidate the effect of the deprotonation and solvation on the spectroscopic properties. We found that solvation strongly affects the excitation character of the chromophore, especially for phenolate anion and dianion. The free energy difference among the four protonation states is also discussed. © 2017 Wiley Periodicals, Inc.

Synergistic dielectric and semiconducting properties in fluorescein monopotassium salt random copolymers

The low dielectric constant (εr ∼ 3–4) for semiconducting polymers has been a major cause for their poor performance compared with the inorganic semiconductors, which possess high dielectric constants above 10. This study aimed to increase the electronic/atomic dielectric constant at high frequencies (i.e., εr∞) for semiconducting polymers. A new design strategy was proposed based on the electric field-induced tautomeric structures in conjugated fluorescein. To achieve this goal, fluorescein monopotassium salt-containing random copolymers were synthesized with 50 and 75 mol.% functionality. To reduce the strong electrostatic attraction between the K+ cation and the phenolate anion, 18-crown-6 ether was complexed with K+ in the fluorescein copolymers. A relatively high εr∞ of ∼5.5 and high electron mobility of 0.153 cm2/(V·s) were achieved for the 75 mol.% fluorescein K+/18C6 copolymer. The high electron mobility could be attributed to the relatively high static dielectric constant (εrs ∼ 9 at 1 Hz) of the sample. The fluorescein monopotassium salt copolymers behaved as n-type semiconductors with an optical band gap around 2.26 eV.

Substrate Specificity and Leaving Group Effect in Ester Cleavage by Metal Complexes of an Oximate Nucleophile.

Deprotonated zinc(II) and cadmium(II) complexes of a tridentate oxime nucleophile (1, OxH) show a very high reactivity, breaking by 2-3 orders of magnitude the previously established limiting reactivity of oximate nucleophiles in the cleavage of substituted phenyl acetates and phosphate triesters, but are unreactive with p-nitrophenyl phosphate di- and monoesters. With reactive substrates, these complexes operate as true catalysts through an acylation-deacylation mechanism. Detailed speciation and kinetic studies in a wide pH interval allowed us to establish as catalytically active forms [Cd(Ox)]+, [Zn(Ox)(OH)], and [Zn(Ox)(OH)2]- complexes. The formation of an unusual and most reactive zinc(II) oximatodihydroxo complex was confirmed by electrospray ionization mass spectrometry data and supported by density functional theory calculations, which also supported the previously noticed fact that the coordinated water in [Zn(OxH)(H2O)2]2+ deprotonates before the oxime. Analysis of the leaving group effect on the cleavage of phenyl acetates shows that the rate-determining step in the reaction with the free oximate anion is the nucleophilic attack, while with both zinc(II) and cadmium(II) oximate complexes, it changes to the expulsion of the leaving phenolate anion. The major new features of these complexes are (1) a very high esterolytic activity surpassing that of enzyme hydrolysis of aryl acetate esters and (2) an increased reactivity of coordinated oxime compared to free oxime in phosphate triester cleavage, contrary to the previously observed inhibitory effect of oxime coordination with these substrates.

Membrane optode for uranium(vi) preconcentration and colorimetric determination in real samples

A membrane optode formed by physical inclusion of a chromophore 2-(2-benzothiazolylazo)phenol (BTAP) and uranium(vi) anions into a plasticized cellulose triacetate (CTA) matrix was illustrated for preconcentration and colorimetric determination of U(vi) from aqueous samples.

Chromophores of chromophores: a bottom-up Hückel picture of the excited states of photoactive proteins

Many photoactive proteins contain chromophores based on para-substituted phenolate anions which are an essential component of their electronic structure. Here, we present a reductionist approach to gain fundamental insight into the evolution of electronic structure as the chromophore increases in complexity from phenolate to that in GFP. Using frequency- and angle-resolved photoelectron spectroscopy, in combination with electronic structure theory, the onset of excited states that are responsible for the characteristic spectroscopic features in biochromophores are determined. A comprehensive, yet intuitive picture of the effect of phenolate functionalisation is developed based on simple Hückel theory. Specifically, the first two bright excited states can be constructed from a linear combination of molecular orbitals localised on the phenolate and para-substituent groups. This essential interaction is first observed for p-vinyl-phenolate. This bottom-up approach offers a readily accessible framework for the design of photoactive chromophores.

Anion Dependent Dynamics and Water Solubility Explained by Hydrogen Bonding Interactions in Mixtures of Water and Aprotic Heterocyclic Anion Ionic Liquids.

Molecular dynamics simulations were used to compare water solubilities and the effects of water on the structure and dynamics of ionic liquids (ILs) composed of phosphonium cations paired with azolide and phenolate anions. The addition of water decreases ordering of the ions compared to the dry ILs with the exception of anion-anion ordering in the phenolate IL. The result is that the dynamics of the azolide ionic liquids increase significantly upon addition of water, whereas the phenolate IL dynamics show little change. The relative water solubilities were compared through calculation of Henry's law constants. Water is much more soluble in the phenolate IL due to strong hydrogen bonding interactions between water and the phenolate oxygen atom. Anions can therefore be selected to control IL-water hydrogen bonding for optimal performance in applications such as CO2 separation.

Acid-base dissociation and tautomerism of two aminofluorescein dyes in solution

The four-step dissociation of two fluorescein dyes bearing the amino group in 4′- and 5′-positions of the phthalic moiety was studied in water. The constants describing the equilibria H4R2+⇄H3R+⇄H2R⇄HR−⇄R2− were determined using the spectrophotometric method, at 25°C. In water, four steps of aminofluoresceins dissociation occur within pH range of 0–9. On going to 50mass% aqueous ethanol, the increase in the pKa1, pKa2 and decrease in the pKa0, pKa(−1) values take place. The visible absorption spectra, referring to all the ionic (molecular) forms, were singled out. On the whole, the behavior of 4′-aminofluorescein is closer to that of the mother compound. The shift of the equilibria on introducing 50mass% ethanol into the aqueous solution allowed better understanding the detailed scheme of prototropic equilibrium. The tautomeric equilibrium of the molecules shifts toward the colorless lactone. This effect is expressed stronger for the 5′-aminofluorescein. For this dye, even signs of such tautomers of the single-charged anion as anion-lactone and phenolate anion are observed in aqueous ethanol, which are atypical for fluorescein in water-based solvents.

Complexes of α-, β-, and γ-cyclodextrins with nitrophenols: A theoretical study of the structure and energy

Detailed quantum mechanical calculations of the interaction of cyclodextrin (α-, β-, and γ-CD) with 4-nitrophenol (I), 4-nitro-2,6-dimethylphenol (II), 4-nitro-3,5-dimethylphenol (III), and their anions (IVVI) with the formation of intercalation complexes are carried out for the first time. The calculations of the compounds are performed within the density functional theory by the hybrid Becke–Lee–Yang–Parr (B3LYP) method with LanL2DZ basis sets. For the α-CD+III and α-CD+VI complexes it is shown that a nitrophenol molecule of III and a nitrophenolate anion of VI are not contained in the α-CD torus, which agrees with the experimental equilibrium constants. It is found that the calculated equilibrium constants of the formation of guest–host complexes with phenolate anions are much larger than those of neutral molecules. The most stable CD complexes with nitrophenols and their anions should be expected for γ-CD. The β-CD complexes when the guest enters into the host cavity are formed only with compounds I, V, and VI.

Aggregation State Reactivity Activation of Intramolecular Charge Transfer Type Fluorescent Probe and Application in Trace Vapor Detection of Sarin Mimics

The reactivity of most Intramolecular Charge Transfer (ICT) based probes in the film state is much poorer than that in solution, due to the serious solid state aggregation of the large polarity molecules. In this contribution, an efficient method for activating the aggregation state reactivity of ICT based probes has been developed. Multiple hydrogen bonds formed by the oxime group, together with the phenol anion, could activate the aggregation state reactivity of the oxime group. By enhancing frontier orbital energy level, and constructing porous film structure, the probe becomes more compatible for highly efficient vapor phase reaction. In application, the TOP-I film can distinguish different organic phosphates with significant fluorescence change. The detection limit for diethyl chloro phosphate (DCP) is 1.2 ppb, lower than the Immediately Dangerous to Life and Health (IDLH) level of Sarin. Such a reactivity activating strategy can be extended to detect other harmful vapors by inducing suitable functio...

Crystal structure of {(E)-2-[(phenyl-imino)-meth-yl]phenolato-κ(2) N,O}bis-[2-(pyridin-2-yl)phenyl-κ(2) C (1),N]iridium(III) di-chloro-methane monosolvate.

In the title compound, [Ir(C11H8N)2(C13H10NO)]·CH2Cl2, the Ir(III) ion is six-coordinated by two C,N-bidentate 2-(pyridin-2-yl)phenyl ligands and one N,O-bidentate 2-[(phenyl-imino)-meth-yl]phenolate anion, giving rise to a distorted octa-hedral environment. The C,N-bidentate ligands, in which the C and N atoms are statistically disordered over two sites and therefore both pairs of C and N atoms are trans and cis relative to each other, are almost perpendicular to each other [the dihedral angle between the least-square planes is 87.00 (4)°]. An intra-molecular C-H⋯O hydrogen bond, as well as inter-molecular C-H⋯π inter-actions and π-π inter-actions, contribute to the stabilization of the mol-ecular and crystal structure.

Mesolysis Processes with Benzylic Carbon–Oxygen Bond Cleavage in Radical Anions of Aryl Benzyl Ethers Studied by Electron Pulse Radiolysis in DMF

Abstract Based on transient absorption measurements obtained upon electron-pulse radiolysis of aromatic ethers in N,N-dimethylformamide (DMF), mesolysis processes of the radical anions were investigated. We observed transient absorption spectral change due to the formation of the radical anions in the temperature range (220–295 K). The transient absorption of the radical anions decreased with first-order kinetics along with the growth of the absorption spectrum of the corresponding benzylic radical. Arrhenius analysis of the decay rates of the radical anions provided the activation energies and the frequency factors for the mesolysis. These observations indicated that the mesolysis of the radical anions occurs via a stepwise mechanism, resulting in the formation of benzylic radical and phenolate anion due to the C–O bond cleavage.

Thermodynamic modelling of liquid-liquid extraction of naphthenic acid from dodecane using imidazolium based phenolate ionic liquids

In this work, N-alkyl imidazolium based ionic liquids with phenolate anions have been used for the separation of naphthenic acid from model oil. The liquid-liquid equilibrium (LLE) data for the ternary mixture of [Cnmim][Phe], dodecane and naphthenic acid were experimentally obtained at a constant temperature of 303.15K and atmospheric pressure. The effect of chain length on the extraction capability was observed by calculating the distribution coefficient. The experimental tie line data was correlated using the non-random two liquid model (NRTL) and Universal Quasi Chemical (UNIQUAC) model and new interaction parameters for the ternary systems are reported. The experimental data provides a good correlation with the modelling data and a very low root mean square deviation (RMSD) value was observed for all the systems.

Electrochemical study of 4-chloro-3-methylphenol on anodically pretreated boron-doped diamond electrode in the absence and presence of a cationic surfactant

Electrochemical behavior as a basis for voltammetric detection of the priority environmental pollutant 4-chloro-3-methylphenol (PCMC) on a bare boron-doped diamond electrode using DC voltammetry, differential pulse voltammetry, and square-wave voltammetry is presented. PCMC provides a well-defined and highly reproducible oxidation peak in the region from +1000mV to +1200mV (vs. Ag|AgCl, 3molL−1 KCl) in aqueous media in pH range 2.0–10.0. Boron-doped diamond electrodes with metallic type of conductivity (B/C ratio in gaseous phase during deposition procedure 2000ppm–8000ppm) and anodic pretreatment of the electrode surface exhibit a better electrochemical response and sensitivity in comparison with cathodic pretreatment and detection using semiconductive electrodes (500ppm and 1000ppm B/C ratio). Further, voltammograms are narrowed and visibly amplified in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) at pH values higher than 9.0 due to its electrostatic interaction with the phenolate anion of PCMC (pKa=9.55). Under optimized experimental conditions the developed electroanalytical methods exhibit detection limits in the 10−7molL−1 concentration range in alkaline media (0.01molL−1 NaOH) in the presence of CTAB or in acidic media (0.1molL−1 phosphate buffer, pH2.0) in its absence.

Efficient separation of phenolic compounds from model oil by the formation of choline derivative-based deep eutectic solvents

Abstract Phenolic compounds are an important class of compounds for organic chemical industry. In their traditional production processes, strong acid and base have to be used for the separation of phenolic compounds from oils, which often causes serious environmental problems. In this work, choline derivative salts [N 1,1, n C 2 OH]Cl ( n = 1, 4, 6, 8) have been used as new extractants for the separation of 26 kinds of phenolic compounds from model oil (toluene) by forming deep eutectic solvents (DESs). It is found that only 16 kinds of phenolic compounds can be removed from toluene with single-step removal efficiency from 28.1% to 94.7%, strongly depending on the chemical structure of phenolic compounds. The nature, position and number of substituent groups in the phenolic compounds have a great effect on their removal efficiency. Far infrared spectroscopy and density functional theory calculations indicate that hydrogen bonds formed between –OH of the phenolic compounds and anion of the choline derivative salts is the main driving force for such DES-based separation. The correlation observed experimentally between structure of phenolic compounds and their removal efficiencies has been discussed from hydrogen bonding in DESs, electrostatic interaction of cation and anion of the choline salts, and solvation of the phenolic compounds and choline salts in the oil.

CO2 Chemistry of Phenolate-Based Ionic Liquids.

We synthesized ionic liquids (ILs) comprising an alkylphosphonium cation paired with phenolate, 4-nitrophenolate, and 4-methoxyphenolate anions that span a wide range of predicted reaction enthalpies with CO2. Each phenolate-based IL was characterized by spectroscopic techniques, and their physical properties (viscosity, conductivity, and CO2 solubility) were determined. We use the computational quantum chemical approach paired with experimental results to reveal the reaction mechanism of CO2 with phenolate ILs. Model chemistry shows that the oxygen atom of phenolate associates strongly with phosphonium cations and is able to deprotonate the cation to form an ylide with an affordable activation barrier. The ATR-FTIR and (31)P NMR spectra indicate that the phosphonium ylide formation and its reaction with CO2 are predominantly responsible for the observed CO2 uptake rather than direct anion-CO2 interaction.

Extraction of naphthenic acid from highly acidic oil using phenolate based ionic liquids

In this study, N-alkyl imidazolium ionic liquids with highly alkaline phenolate anions were used for the removal of naphthenic acid from model acid oil. The effect of alkyl spacer length on the deacidification process was evaluated by attaching butyl, hexyl, octyl, decyl and dodecyl groups on imidazolium cation. It was found that increase in the alkyl chain length increases the percent naphthenic acid removal. Extremely low amount of ionic liquids were necessary for the complete deacidification of model oil with high TAN. The reusability of the phenolate ionic liquids was also investigated. COSMO-RS calculations were performed on phenolate ionic liquids to study their extraction efficiency, selectivity and solvent capacity.

Facile One-Pot Synthesis of Flavanones Using Tetramethylguanidinum-Based Ionic Liquids as Catalysts

Several tetramethylguanidinum-based ionic liquids (TMGILs) were prepared, characterized and used as catalysts in one-pot synthesis of flavanones. The results indicated that TMGILs composed of phenolate anion was beneficial for one-pot synthesis of flavanones, and [TMG][4-MeO–PhO] induced the good yields of flavanones owing to the electron-donating effect of methoxy substituent on phenolate anion. Furthermore, [TMG][4-MeO–PhO] was found to be used repetitively at least five times without obvious decrease in activity and quantity.

QM/MM study of the S2 to S3 transition reaction in the oxygen-evolving complex of photosystem II

Catalytic reactions of the proton and electron transfers occurring at the oxygen-evolving complex (OEC) of photosystem II during the S2–S3 transition were investigated by the quantum mechanics/molecular mechanics (QM/MM) methodology. Two favorable reaction pathways were elucidated. Both reactions start by moving the Ca-bound water (W3) to the vacant Mn(III) coordination at the left-opened (L) or right-opened (R) form. The former reaction pathway, in which W3 coordinates to the Mn4 at the S2-L form, has lower activation barriers than the latter. Thus, easier proton transfers from W3 to the Tyr161 phenol anion can be performed.