Phenol Cation Research Articles

Ultra‐Broadband Organic THz Generators: Influence of Substituents on THz Phonon Vibrations in Phenolic Parallel‐Type Cation–Anion Assembly

AbstractOrganic terahertz (THz) crystals consist of polar molecules with various functional substituents, resulting in numerous molecular phonon vibrations in the THz frequency range. However, the effect of incorporating substituents into organic THz crystals on the resulting THz absorption is rather an unexplored area. In this work, by choosing an appropriate model system consisting of two benchmark organic nonlinear optical crystals, exhibiting an identical type of phenolic cation–anion assembly but different substituents, their ultra‐broadband THz wave generation characteristics are demonstrated and investigated. Compared to the unsubstituted crystals, the substituted crystals possess one more methoxy substituent on highly polar cationic chromophores. Their vibrational modes and THz absorption characteristics are investigated theoretically by periodic density functional theory and experimentally by ultra‐broadband THz spectroscopy up to 12 THz. In phenolic parallel‐type cation–anion assembled organic THz crystals, the existence of a methoxy substituent differently influences the molecular vibrations in low and high THz frequency ranges. In the lower THz frequency range, the unsubstituted crystals exhibit additional strong entire molecular vibrations, the so‐called cation‐on‐cation slipping vibrations, which do not exist in the substituted crystals. In contrast, the methoxy substituent leads to additional strong intramolecular vibrations in the higher THz frequency range.

Electrochemical and Spectroscopic Characterization of Oxidized Intermediate Forms of Vitamin E.

Vitamin E, a collection of lipophilic phenolic compounds based on chroman-6-ol, has a rich and fascinating oxidative chemistry involving a range of intermediate forms, some of which are proposed to be important in its biological functions. In this review, the available electrochemical and spectroscopic data on these oxidized intermediates are summarized, along with a discussion on how their lifetimes and chemical stability are either typical of similar phenolic and chroman-6-ol derived compounds, or atypical and unique to the specific oxidized isomeric form of vitamin E. The overall electrochemical oxidation mechanism for vitamin E can be summarized as involving the loss of two-electrons and one-proton, although the electron transfer and chemical steps can be controlled to progress along different pathways to prolong the lifetimes of discreet intermediates by modifying the experimental conditions (applied electrochemical potential, aqueous or non-aqueous solvent, and pH). Depending on the environment, the electrochemical reactions can involve single electron transfer (SET), proton-coupled electron transfer (PCET), as well as homogeneous disproportionation and comproportionation steps. The intermediate species produced via chemical or electrochemical oxidation include phenolates, phenol cation radicals, phenoxyl neutral radicals, dications, diamagnetic cations (phenoxeniums) and para–quinone methides. The cation radicals of all the tocopherols are atypically long-lived compared to the cation radicals of other phenols, due to their relatively weak acidity. The diamagnetic cation derived from α–tocopherol is exceptionally long-lived compared to the diamagnetic cations from the other β–, γ– and δ–isomers of vitamin E and compared with other phenoxenium cations derived from phenolic compounds. In contrast, the lifetime of the phenoxyl radical derived from α–tocopherol, which is considered to be critical in biological reactions, is typical for what is expected for a compound with its structural features. Over longer times via hydrolysis reactions, hydroxy para–quinone hemiketals and quinones can be formed from the oxidized intermediates, which can themselves undergo reduction processes to form intermediate anion radicals and dianions. Methods for generating the oxidized intermediates by chemical, photochemical and electrochemical methods are discussed, along with a summary of how the final products vary depending on the method used for oxidation. Since the intermediates mainly only survive in solution, they are most often monitored using UV-vis spectroscopy, FTIR or Raman spectroscopies, and EPR spectroscopy, with the spectroscopic techniques sometimes combined with fast photoinitiated excitation and time-resolved spectroscopy for detection of short-lived species.

Antioxidant properties of processed cheese spread after freeze-dried and oven-dried grape skin powder addition

Processed cheese spread (PCS) is a popular product with high nutritional value and containing protein, fat and minerals. Grape skin is waste from winery processing plants that still has phenolic substances with significant antioxidant activity that could be used for valorisation of processed cheese and increasing the content of nutrients, phenolics and overall antioxidant properties. Both oven-dried (OD) and freeze-dried (FD) grape skin (GS) powder was characterised by the principal ingredients, the content of phenolic compounds and antioxidant capacity. Similarly, the influence of the addition of OD-GS and FD-GS powders on processed cheese spread (PCS) at 1% and 2% (w/w) levels were examined. The OD-GS and FD-GS powders were characterised by protein content, fat content, moisture and dietary fibre, thus showing that drying technique did not affect those parameters. The OD-GS powder exhibited higher content of rutin, (+)-catechin, (-)-epicatechin and total flavonoid content (TFC), while higher total phenolic content (TPC) and ABTS radical cation were observed for freeze-dried GS powder. Fortification of PCS with 1% and 2% (w/w) of GS powder increased protein content. An ANOVA procedure revealed that addition of FD-GS powder to processed cheese spread was superior to TPC values together with rutin, (+)-catechin, and (-)-epicatechin contents. The higher phenolic contents reflected the higher antioxidant capacity of PCS samples fortified with FD-GS powder. Freeze-dried gape skin powder was the better choice for valorisation of processed cheese spread.

Low-Cost Biochar Adsorbents for Water Purification Including Microplastics Removal

The applicability of steam activated pine and spruce bark biochar for storm water and wastewater purification has been investigated. Biochar samples produced from the bark of scots pine (Pinus sylvestrus) and spruce (Picea spp.) by conventional slow pyrolysis at 475 °C were steam activated at 800 °C. Steam activation was selected as a relatively inexpensive method for creating porous biochar adsorbents from the bark-containing sidestreams of the wood refining industry. A suite of standard analytical procedures were carried out to quantify the performance of the activated biochar in removing both cations and residual organics from aqueous media. Phenol and microplastics retention and cation exchange capacity were employed as key test parameters. Despite relatively low surface areas (200–600 m2/g), the steam-activated biochars were highly suitable adsorbents for the chemical species tested as well as for microplastics removal. The results indicate that ultra-high porosities are not necessary for satisfactory water purification, supporting the economic feasibility of bio-based adsorbent production.

Oxidative Cross‐Coupling of Substituted Phenols with Unactivated Aromatics

A regioselective C–H arylation of substituted phenols or naphthols with substituted aromatics in the presence of K2S2O8 and Bu4N+·HSO4– in CF3COOH at ambient temperature providing unsymmetrical biaryls is described. The cross‐coupling reaction is compatible with various substituted phenols and aromatics. Based on oxidation potential studies, it was observed that phenols with oxidation potentials up to 0.68 V and naphthols up to 0.88 V were compatible with the reaction. The cross‐coupling reaction proceeds through the reaction of K2S2O8 with substituted phenol, providing a cationic phenol radical intermediate that was further converted into the phenoxy radical intermediate by the dissociation of H+. Subsequent radical‐anion coupling of the phenoxy radical intermediate with a substituted aromatic affords the cross‐coupling product. The formation of a cationic phenol radical intermediate and phenoxy radical intermediate were confirmed by UV/Vis and EPR studies.

Investigation of IRGANOX®1076 as a dosimeter for clinical X-ray, electron and proton beams and its EPR angular response

The suitability of IRGANOX®1076 in paraffin wax as a near-tissue equivalent radiation dosimeter was investigated for various radiotherapy beam types; kV and MV X-rays, electrons and protons over clinically-relevant doses (2 −20Gy). The radical formed upon exposure to ionising radiations was measured by Electron Paramagnetic Resonance (EPR) spectroscopy, and the single peak signal obtained for solid solutions of IRGANOX®1076 in wax is attributed to the phenoxyl radical obtained by net loss of H•. Irradiation of solid IRGANOX®1076 gives a doublet consistent with the formation of the phenol cation radical, obtained by electron loss. Solid solutions of IRGANOX®1076 in paraffin wax give a linear dose response for all types of radiations examined, which was energy independent for MV, electron and proton beams, and energy-dependent for kV X-ray irradiation. Reliable dose measurements were obtained with exposures as low as 2Gy, and comparisons with alanine wax-pellets containing the same amount of dosimeter material (w/w) gave similar responses for all beam types investigated. Post-irradiation measurements (up to 77 days for proton irradiation for samples stored in the dark and at room temperature) indicate good signal stability with minimal signal fading (between 1.6 to 3.8%). Relative to alanine dosimeters, solid solutions of IRGANOX®1076 in wax give EPR signals with better sensitivity at low dose and do not significantly change with the orientation of the sample. Solid solutions of IRGANOX®1076 are ideal for applications in radiotherapy dosimetry for X-rays and charged particles, as IRGANOX®1076 is relatively cheap, can easily and reproducibly prepared in wax and be moulded to different shapes.

Quantitative Temperature Dependence of the Microscopic Hydration Structures Investigated by Ultraviolet Photodissociation Spectroscopy of Hydrated Phenol Cations.

To discuss the temperature effect on microscopic hydration structures in clusters, relative populations of the isomers having different hydration structures at well-defined temperatures are quite important. In the present study, we measured ultraviolet photodissociation spectra of the temperature-controlled hydrated phenol cation [PhOH(H2O)5]+ trapped in the 22-pole ion trap. Two isomers having a distinct hydration motif with each other are identified in the spectra, and a clear change in the relative populations is observed in the temperature range from 30 to 150 K. This behavior is quantitatively interpreted by statistical mechanical estimation based on density functional theory calculations. A ring with tail-type hydration motif is dominant in cold conditions, whereas a chain-like motif is dominant in hot conditions. The present study provides very quantitative information about the temperature effect on the microscopic hydration structures.

Biorefining of blackcurrant pomace into high value functional ingredients using supercritical CO2, pressurized liquid and enzyme assisted extractions

This study reports valorisation of blackcurrant pomace using multistep processes for its biorefining into valuable food-grade ingredients. Firstly, supercritical carbon dioxide extraction (SFE-CO2) was optimized for effective isolation of lipophilic fraction using response surface methodology based on central composite design. Afterwards pressurized liquid (PLE) and enzyme assisted (EAE) extractions were applied for the isolation of higher polarity substances. The yield of SFE-CO2 at optimal parameters (60°C, 45MPa, 120min) were up to 14.6%, while PLE and EAE with acetone, ethanol or water enabled additionally obtain 12.3–39.9% of extracts from SFE-CO2 residues. Lipophilic extracts were rich in polyunsaturated fatty acids (linoleic 46.89%, γ-linolenic 14.02%) and tocopherols (in total 2468μg/g oil), while polar fractions demonstrated strong antioxidant capacity as it was evaluated by the total phenolic content, DPPH radical and ABTS cation radical scavenging, ferric reducing antioxidant power and oxygen radical scavenging capacity assays.

Effect of ionic charge on O[formula omitted]H⋯Se hydrogen bond: A computational study

Complexes between para-substituted cationic phenol and SeH2 have been investigated in electronic ground state at the B3LYP, B3PW91, and ωB97xD levels of theory using 6-311++G(3df,3pd) basis set. Various electron-donating and withdrawing substituents (NH2, OH, CH3, H, F, Cl, CN, and NO2) are used to characterize electronic substituent effect on intermolecular +OH⋯Se hydrogen bond. Electron withdrawing substituent increases hydrogen bond stabilization energy and red shift in OH stretching frequency. Introduction of a positive charge transforms weak hydrogen bond of neutral OH⋯Se type into a strong hydrogen bond. Complexation induced changes on various hydrogen bond parameters, such as, stabilization energy, change in OH bond length, change in OH stretching frequency, extent of charge transfer from hydrogen bond acceptor to donor, hydrogen bond orders, electron density at the hydrogen bond critical point exhibit conventional electronic substitution effect. Stabilization energy of +OH⋯Y hydrogen bond are similar in the complexes between cationic phenol and SH2/SeH2, whereas it is almost twice with OH2 in case of +OH⋯Y hydrogen bond.

The Solution Structure of 1:2 Phenol/N-Methylpyridinium bis{(trifluoromethyl)sulfonyl}imide Liquid Mixtures

Neutron diffraction has been used to investigate the liquid structure of a 1:2 solution of phenol in the ionic liquid N-methylpyridinium bis{(trifluoromethyl)sulfonyl}imide at 60\(\,^{\circ }\)C, using the empirical potential structure refinement process to model the data obtained from the SANDALS diffractometer at ISIS. Addition of phenol results in suppression of the melting point of the pyridinium salt and formation of a room temperature solution with aromatic phenol–cation and phenol-OH to anion hydrogen-bonding interactions.

Infrared spectroscopy of phenol-triethylsilane dihydrogen-bonded cluster and its cationic analogues: intrinsic strength of the Si-H···H-O dihydrogen bond.

Spectroscopic and theoretical investigations have been carried out for neutral phenol-triethylsilane clusters to reveal an intrinsic nature of the Si-H···H-O type dihydrogen bond. On the basis of the laser-induced fluorescence and infrared spectra, four isomers are identified. Three of them have a structure in which the dihydrogen bond and the dispersion interaction are competing in the stabilization of the cluster. However, the other isomer is found to have a distinct structure in which the dihydrogen bond is much stronger than the other isomers. In addition to the neutral clusters, cationic phenol(+)-diethylmethylsilane and phenol(+)-triethylsilane clusters are investigated by infrared photodissociation spectroscopy. It is found that the dihydrogen bond is the dominant intermolecular interaction in these clusters. On the basis of the red shifts of the OH stretching bands, it is revealed that the strength of the Si-H···H-O dihydrogen bond is stronger than that of the π-type hydrogen bond. The proton affinities of triethylsilane and diethylmethylsilane estimated by the theoretical calculation are larger than those of benzene and ethylene. These results are consistent with our experimental observations.

Stability of resorcinol-formaldehyde resins in alkaline solutions

Physicochemical relationships of the 137Cs recovery from alkaline solutions using resorcinol-formaldehyde resins were studied. The instability of resorcinol-formaldehyde resins in alkaline solutions is due to oxidative degradation of the polymer. Oxidation of resorcinol-formaldehyde cation exchanger in alkaline solutions is accompanied by the loss of the selectivity to cesium, without changes in the capacity. An NMR study showed that oxidation in alkaline solutions is accompanied by cleavage of the bridging -CH2-bonds of the polymer. Intense depolymerization of the phenolic cation exchanger is concluded to be responsible for the decrease in the resin selectivity.

Removal of phenol from saline water by polyamine chelating resin

Removal of phenol from saline water was carried out with chelating resin. A polyamine chelating resin, Diaion CR-20, removed phenol compounds selectively from industrial wastewater containing 2% salt. From saline water containing 20 mg/L phenol, 70% of the phenol was removed. After treatment, phenol was eluted from the resin by aqueous NaOH, and the resin could also be regenerated by heating in air. Diaion CR-20 adsorbed phenol even in the presence of FeCl3, indicating that treatment with this resin of wastewater containing metal can remove phenol and metal cations in a single step.

The structure and binding energies of the van der Waals complexes of Ar and N2 with phenol and its cation, studied by high level ab initio and density functional theory calculations

We have investigated, using both ab initio and density functional theory methods, the minimum energy structures and corresponding binding energies of the van der Waals complexes between phenol and argon or the nitrogen molecule, and the corresponding complexes involving the phenol cation. Structures were obtained at the MP2 level using a large basis, and the corresponding energies were corrected for basis set superposition error (BSSE), higher order electron correlation effects, and for basis set size. The structures of the global minima were further refined for the effects of BSSE and the corresponding binding energies were evaluated. For each neutral species, we find only a single true minimum, pi bonded for argon and OH bonded for nitrogen. For both cationic species, we find that the OH-bonded complex is preferred over other minima which we have identified as having Ar or N(2) between exogeneous atoms. The ab initio calculations are generally in excellent agreement with experimental binding energies and rotational constants. We find that the B3LYP functional is particularly poor at describing these complexes, while a density functional theory (DFT) method with an empirical correction for dispersive interactions (DFT-D) is very successful, as are some of the new functionals proposed by Zhao and Truhlar [J. Phys. Chem. A 109, 5656 (2005); J. Chem. Theory Comput. 2, 1009 (2006); Phys. Chem. Chem. Phys. 7, 2701 (2005); J. Phys. Chem. A 108, 6908 (2004)]. Both the ab initio and DFT-D methods accurately predict the intermolecular vibrational modes.

A DFT study on the deprotonation antioxidant mechanistic step of ortho-substituted phenolic cation radicals

The conformers of the 2-, 3- and 4-substituted phenolic cation radicals, 2-X-, 3-X- and 4-X-ArOH + , and the respective phenoxyl radicals, ArO , the intramolecular hydrogen bond strength (Δ H intra) estimate along with the electronic effects of five electron withdrawing (EWG) and eight electron donating groups (EDG) on the gas-phase O–H proton dissociation enthalpies, (PDEs), of the short-lived, 2-X-ArOH + , (involved in the single-electron transfer antioxidant mechanism), are studied at the DFT/B3LYP level of theory. EWG result to smaller PDEs, hence to stronger acidity; EDG to weaker acidity. The deprotonation antioxidant mechanistic step is not a rate-controlling step for 2-X-ArOH to scavenge free radicals. Approximate estimations of the ΔPDEs (hence acidities as well) can be derived from calculated structural and/or vibrational frequency values. Δ H intras correlate reasonably with geometrical parameters for the closed-shell, neutral counterparts, in contrast with previous estimates.

Thermo gravimetric analysis of supramolecular complexes of p-tert-butylcalix[6]arene and ammonium cations: crystal structure of diethylammonium complex

Thermo gravimetric analysis of ammonium- p-tert-butylcalix[6]arene salts were carried out to determine the stoichiometry of the inclusion compounds and the temperature of leaving of the ammonium cation, as amine, from the solid phase by a reverse proton transfer reaction to calixarene. The chain length of the amine molecules and their relative basicity order are the main factors which determine the decomplexation temperatures for the ammonium salts of piperidinium, diethylammonium, ethylenediammonium, morpholinium, s-butylammonium, butylammonium, hexylammonium and triethylammonium salts of p-tert-butylcalix[6]arene anion. The solid state structure of bis-diethylammonium- p-tert-butylcalix[6]arene dianion is reported. The calix moiety adopts a 1,2,3 alternate conformation, with one ammonium as exo-calix and other as endo-calix, with an intricate array of hydrogen bonds between phenol, phenolate and ammonium cations.

Theoretical study of neutral and cationic complexes involving phenol

AbstractGeometry and interaction energy in complexes of the Ph–L type (L = Ar, N2, CO, H2O, NH3, CH4, CH3OH, CH3F) involving neutral or cationic phenol were determined using the density functional theory formalism based on the minimization of the total energy bifunctional and gradient‐dependent approximations for its exchange‐correlation and nonadditive kinetic‐energy parts. For the neutral complexes the calculated interaction energies range from 1 kcal/mol for the Ph–Ar complex to about 10 kcal/mol for Ph–NH3. The interactions are stronger if the cationic phenol is involved (up to 25 kcal/mol). It is found, except for neutral Ph–Ar, that the hydrogen‐bonded structure is more stable than the π‐bound one. Calculated interaction energies (De) correlate well with the experimental dissociation energies (D0). © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Facile, high-yield, regioselective synthesis of ortho-nitro derivatives of hydroxy heterocycles using cerium (IV) ammonium nitrate

A series of hydroxy heterocycles with two different unsubstituted ortho sites undergo exclusive regioselective nitration with the CAN/NaHCO3 reagent at the less hindered ortho site. Neither dinitro nor oxidized products were observed. The hydroxy heterocycles studied include: some derivatives of 7-hydroxycoumarins, sesamol, 2,3-dihydrobenzo[b]furan-3-one, 6-hydroxy-1,3benzoxathiol, 5-hydroxybenzothiazol, 5-hydroxyindole, 7-benzofuranol, and (5isoxazolyl)phenols. A mechanism is proposed in which an initial oxidation of the phenol to a radical cation by CAN occurs. Another molecule of CAN subsequently reacts with the phenolic radical cation to give an radical adduct from which an NO2 radical is transferred to the less hindered carbon via a tight ion-radical pair yielding the Wheland complex that furnishes the nitrophenol after proton loss.

Classical trajectory calculations of intramolecular vibrational energy redistribution. II. Phenol-water complex.

Ab initio classical trajectory calculations have been applied to the intramolecular vibrational energy redistribution process of an O-H stretching vibration for phenol cation, [phenol]+, and its hydrogen-bonded water complex, [phenol-water]+. In phenol cation, a single narrow peak in the power spectrum, obtained by Fourier transformation of the autocorrelation function of its total momentum, indicates that the initial energy given to the O-H stretching oscillator of the phenol moiety is conserved and no energy flow occurs. On the other hand, for phenol-water cation, the calculated broadened power spectrum implies that the initial energy is not conserved and the energy flow causes an energy redistribution among various vibrational modes.

Ionization-induced switch in aromatic molecule–nonpolar ligand recognition: Acidity of 1-naphthol+(1-Np+) rotamers probed by IR spectra of 1-Np+–Lncomplexes (L = Ar/N2, n ≤ 5)

The interaction of the trans (t) and cis (c) rotamers of the 1-naphthol cation (1-C10H8O+ = 1-Np+ = 1-hydroxynaphthalene+) with nonpolar ligands in the ground electronic state is characterized by IR photodissociation spectra of isolated 1-Np+–Ln complexes (L = Ar/N2) and density functional calculations at the UB3LYP/6-311G(2df,2pd) level. Size-dependent frequency shifts of the O–H stretch vibration (Δν1) and photofragmentation branching ratios provide information about the stepwise microsolvation of both 1-Np+ rotamers in a nonpolar hydrophobic environment, including the formation of structural isomers, the competition between H-bonding and π-bonding, the estimation of ligand binding energies, and the acidity of t/c-1-Np+. t-1-Np+ is predicted to be more stable than c-1-Np+ by 9 kJ mol−1, with an isomerization barrier of 38 kJ mol−1. The OH group in t-1-Np+ is slightly more acidic than in c-1-Np+ leading to stronger intermolecular H-bonds. Both 1-Np+ rotamers are considerably less acidic than the phenol cation because of enhanced charge delocalization. The 1-Np+−Ar spectrum displays ν1 bands of the more stable H-bound and the less stable π-bound t-1-Np+–Ar isomers. Only the more stable H-bound dimers are identified for t/c-1-Np+–L2. Analysis of the Δν1 shifts of the H-bound dimers yields a first experimental estimate for the proton affinity of the t-1-naphthoxy radical (∼908 ± 30 kJ mol−1). The Δν1 shifts of 1-Np+–Ln (n ≤ 2 for Ar, n ≤ 5 for N2) suggest that the preferred microsolvation path begins with the formation of H-bound 1-Np+–L, which is further solvated by (n−1) π-bound ligands. Ionization of 1-Np−Ln drastically changes the topology of the intermolecular interaction potential and thus the preferred aromatic substrate–nonpolar ligand recognition pattern.