Radical Salts Research Articles

TTF–fluorene dyads and their M(CN)2−(M = Ag, Au) salts designed for photoresponsive conducting materials

To explore photoresponsive conducting materials, we developed new tetrathiafulvalene (TTF)–fluorene D–A dyads with a σ-bonded thiomethylene spacer (1a–d) or a π-conjugated ethylene spacer (2a–b) and reported their synthesis, electrochemical and optical properties. Fluorescence studies suggested that the fluorescence from an excited fluorene part is quenched by an intramolecular electron transfer process from the electron-donating TTF part to the fluorene part, and the intramolecular interaction through the π-conjugated ethylene spacer is stronger and shows more suppression than the non-planar σ-bonded thiomethylene spacer. We also investigated photoelectric conversion functionality by a photoelectrochemical method using the thin films of dyads 1–2 spin-coated on ITO-coated glass substrates. We observed electric current generation that depends on the absorption spectra of thin films, suggesting that absorbed photons are converted to electric currents on the thin film/ITO electrode. Crystal structure analysis and measurement of photoconductivity of a single crystalline sample of molecule 1d having 4,5-bis(methylthio)-substituents suggest generation of photocurrents along the stacking direction of the TTF parts by the photoinduced intramolecular electron transfer and the resultant charge-separated state. Furthermore, we also reported the crystal structure analyses, photoconductivity and magnetic properties of the cation radical salts, 2b2M(CN)2 (M = Ag, Au), where 2b contains a 4,5-ethylenedithio-substituent. The Ag(CN)2 salt showed a semiconducting behaviour with a room temperature conductivity of 0.088 S cm−1 due to a half-filled Mott insulating band structure of this crystal that originates from a strongly dimerized intermolecular interaction. Upon photoirradiation, this salt showed a slight enhancement of conductivities of ca. 14%.

Antioxidant capacity of maillard reaction products formed by a porcine plasma protein hydrolysate-sugar model system as related to chemical characteristics

This study investigated the chemical characteristics and antioxidant properties of Maillard reaction products (MRPs) prepared by porcine plasma protein hydrolysate (PPH) with three monosaccharides (glucose, fructose, and galactose) at 95°C for different lengths of time (0–6 h). The results revealed that the pH value and free amino group content decreased (p<0.05), whereas the color (redness and yellowness), browning intensity, and intermediate products increased as the reaction time increased (p<0.05). There was an obvious increase in the reducing power, 2,2′-aminodi(2-ethyl-benzothiazoline sulfonic acid-6)ammonium salt (ABTS) radical and hydroxide radical scavenging activities of the MRPs with increasing heating time (p<0.05). The PPH-galactose combination rendered a higher browning intensity, intermediate products and antioxidant activities than the PPH-glucose or PPH-fructose combination. The reducing power, ABTS and hydroxyl scavenging activities were significantly correlated with the color, the UV absorbance and the browning intensity in each model system. The results indicate that the Maillard reaction could improve the antioxidant capacity of PPH.

Nonelectrochemical Synthesis, Crystal Structure, and Physical Properties of the Radical Salt [ET]2[CuCl4] (ET = Bis(ethylenedithio)tetrathiafulvalene)

The radical salt [ET]2[CuCl4] was obtained by chemical oxidation of bis(ethylenedithio)tetrathiafulvalene (ET) with the tetranuclear copper(II) halide cluster [Cu4OCl10](4-). Although a complex mixture of anions forms in solution during the redox reaction, only this product is obtained as large (>3 mm) single crystals. X-ray diffraction analysis determined that the ET molecules stack in the solid state forming dimerized 1D chains along the a axis, interleaved by [CuCl4](2-) anions. The ET dimers show very short S···S contacts (<3.41 Å). The physical properties are dominated by these intradimer ET interactions. The magnetic behavior shows antiferromagnetic coupling with a singlet-triplet gap >620 K (430 cm(-1)). The Cu(2+) (S = 1/2) centers are magnetically isolated and yield a narrow EPR line in the X-band at g = 2.01. The ET moieties are EPR silent.

Characterization of Anthocyanins in Fruit of Kadsura coccinea (Lem.) A.C. Smith by UPLC/Q-TOF-MS Analysis and Evaluation of Stability of the Major Anthocyanins

Anthocyanins in fruit of Kadsura coccinea (Lem.) A.C. Smith were identified by ultra-performance liquid chromatography–quadrupole–time of flight mass spectrometry analysis. Contents of anthocyanins in K. coccinea fruit were determined by HPLC analysis. Colour stability, thermal degradation and antioxidant activity of purified cyanidin-3-xylosylrutinoside were further analysed. As a result, four anthocyanins were identified as delphinidin-3-xylosylrutinoside (1), cyanidin-3-glucosylrutinoside (2), cyanidin-3-xylosylrutinoside (3), and cyanidin-3-rutinoside (4). The individual content of anthocyanins identified was 4.36 ± 0.06, 3.01 ± 0.03, 49.92 ± 0.76 and 2.33 ± 0.04 mg/500 g deseeded K. coccinea fruit, respectively. Cyanidin-3-xylosylrutinoside was stable at pH around 1. Moreover, cyanidin-3-xylosylrutinoside was very sensitive to temperature change and it was even unstable at room temperature. Cyanidin-3-xylosylrutinoside tended to degrade into cyanidin-3-rutinoside, cyanidin-sambubioside and cyanidin at high temperatures. Cyanidin-3-xylosylrutinoside exhibited much better 1,1-diphenyl-2-picrylhydrazyl and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical scavenging activities than those of butylated hydroxytoluene. However, cyanidin-3-xylosylrutinoside and other three anthocyanin components contributed little to the antioxidant activity of K. coccinea fruit.

Infrared and Raman spectroscopic studies of the charge localization in one-dimensional organic metals (DMtTTF)2 X (X = ReO4 , ClO4 ) with regular organic stacks

A novel selective synthesis of the unsymmetrically substituted tetrathiafulvalene dimethyltrimethylene-tetrathiafulvalene (DMtTTF) is described together with its electrocrystallization to the known conducting mixed-valence ClO4– and ReO4– salts. Infrared (IR) and Raman spectra of the two isostructural quasi-one-dimensional cation radical salts (DMtTTF)2X (X = ReO4–, ClO4–) are investigated as a function of temperature (T = 5–300 K). At ambient temperature, these salts show metallic-like properties and below Tρ = 100–150 K, they undergo a smeared transition to semiconducting state. To study this charge localization, we measured temperature dependence of polarized IR reflectance spectra (700–16 000 cm–1) and Raman spectra (150–3500 cm–1, excitation λ = 632.8 nm) of single crystals. For both compounds, the Raman data and especially the bands related to the C=C stretching vibration of the DMtTTF molecule show that the charge distribution on molecules is uniform down to the lowest temperatures. Similarly, IR data confirm that down to the lowest temperatures, there is neither charge ordering nor important modification of the electronic structure. However, the temperature dependence of Raman spectra of both salts reveals a regime change at about 150 K. Additionally, using Density Functional Theory (DFT) methods, the normal vibrational modes of the neutral DMtTTF0 and cationic DMtTTF+ species and also their theoretical IR and Raman spectra were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral DMtTTF0 molecule. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis, Electronic Properties, Thermoelectric Power, and Crystal and Band Structures of Unsymmetrical EDOB-EDT-TTF Salts Composed of PF6 −, AsF6 −, and SbF6 − at Various Temperatures

The synthesis and crystal structure of EDOB-EDT-TTF donor were described. Novel EDOB-EDT-TTF radical salts with different octahedral AsF6 − and SbF6 − were prepared. Based on the electrical conductivity measurements, the newly prepared conductive AsF6 salt underwent a metal-to-semiconductor (MS) transition similar to the previously reported isostructural PF6 salt. The X-ray analyses of the AsF6 and SbF6 salts at various temperatures elucidated their structural characteristics. The AsF6 salt formed a dimer below 330 K with the formation of an O⋅⋅⋅H short contact in the intermolecular intradimer along the stacking column. Simultaneous measurements of the thermoelectric power and the resistivity on a single sample were performed for the PF6, AsF6, and SbF6 salts. The MS transition temperatures of these PF6 and AsF6 salts were also determined from thermoelectric power data. The band structures and Fermi surfaces for the AsF6 salts at 293 and 350 K were calculated.

A Dinuclear Cobalt Complex Featuring Unprecedented Anodic and Cathodic Redox Switches for Single-Molecule Magnet Activity

One-electron oxidation or reduction of the paramagnetic dinuclear Co(II) complex dmp2Nin{Co[N(SiMe3)2]}2 (1; dmp2Nin(2-) = bis(2,6-dimethylphenyl)nindigo), by fully reversible chemical or electrochemical methods, generates the radical salts [1(OEt2)](+) and [1](-), respectively. Full structural and magnetic analyses reveal the locus of the redox changes to be nindigo-based, thus giving rise to ligand-centered radicals sandwiched between two paramagnetic and low-coordinate Co(II) centers. The presence of these sandwiched radicals mediates magnetic coupling between the high-spin (S = 3/2) cobalt ions, which gives rise to single-molecule magnet (SMM) activity in both the oxidized ([1(OEt2)](+)) and reduced ([1](-)) states. This feature represents the first example of a SMM exhibiting fully reversible, dual "ON/OFF" switchability in both the cathodic and anodic states.

In Vitro Antioxidant Activity and Effect of Parkia biglobosa Bark Extract on Mitochondrial Redox Status

Aqueous-methanolic extract of Parkia biglobosa bark (PBB) was screened for its polyphenolic constituents, in vitro antioxidant activity, and effect on mitochondria redox status. The in vitro antioxidant activity was assessed by using the scavenging abilities and the reducing powers of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) diammonium salt radical cation against Fe3+. Subsequently, the ability of PBB to inhibit lipid peroxidation induced by FeSO4 (10 μm) and its metal-chelating potential were investigated. The effects of the extract on basal reactive oxygen species (ROS) generation and on the mitochondrial membrane potential (ΔΨm) in isolated mitochondria were determined by using 2′, 7′-dichlorodihydrofluorescin (DCFH) oxidation and safranin fluorescence, respectively. PBB mitigated the Fe(II)-induced lipid peroxidation in rat tissues and showed dose-dependent scavenging of DPPH (IC50: 98.33 ± 10.0 μg/mL) and ABTS. (trolox equivalent antioxidant concentration, TEAC value = 0.05), with considerable ferric-reducing and moderate metal-chelating abilities. PBB caused slight decreases in both the liver and the brain mitochondria potentials and resulted in a significant decrease (p < 0.001) in DCFH oxidation. Screening for polyphenolics using high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD) revealed the presence of caffeic acid, gallic acid, catechin, epigalocatechin, rutin, and quercetin. These results demonstrate for the first time the considerable in vitro antioxidant activity and favorable effect of PBB on mitochondria redox status and provide justification for the use of the plant in ethnomedicine.

Utilization of σ-Holes on Sulfur and Halogen Atoms for Supramolecular Cation···Anion Interactions in Bilayer Ni(dmit)2 Anion Radical Salts

We prepared novel Ni(dmit)2 anion radical salts with ethyl-4-halothiazolium cations (Et-4XT, with X denoting the halogen: I, Br, or Cl), (Et-4IT)[Ni(dmit)2]2 (1), (Et-4BrT)[Ni(dmit)2]2 (2), and (Et-4ClT)2[Ni(dmit)2]5 (3). Single-crystal X-ray diffraction analysis of 1–3 indicates that, unlike the halogen atoms that have only one σ-hole each, the cations’ sulfur atoms each have two σ-holes that lie approximately along the extensions of the C–S bonds. The presence of the σ-holes is supported by electrostatic potential of the cations calculated based on the density functional theory method. In the crystals of 1–3, these σ-holes interact with lone pairs on the terminal thioketone moieties in the Ni(dmit)2 anion radicals to form electrostatic σ-hole bonds (halogen bonds and chalcogen bonds). This results in supramolecular cation···anion networks. Crystal and electronic structure analyses, and electrical and magnetic measurements reveal that the salts 1 and 2 are isostructural bilayer Mott systems, in which two...

IN VITRO ANTIOXIDATIVE PROFILING OF DIFFERENT EXTRACTS OF FAGONIA SCHWEINFURTHII (HADIDI) HADIDI

The present study was aimed to evaluate in vitro antioxidant activity of Fagonia schweinfurthii (Hadidi) Hadidi. F. schweinfurthii was successively extracted with different solvents such as petroleum ether, chloroform, ethyl acetate and methanol. The antioxidant activity of F. schweinfurthii extracts was investigated using different assays like 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging activity, 2,2’-azino-bis(3ethylbenzthiazoline-6-sulfonic acid) (ABTS) diammonium salt radical scavenging activity, hydrogen peroxide (H2O2) scavenging activity, nitric oxide (NO) scavenging activity, ferric reducing power and β-carotene bleaching assay. Total phenolic and flavonoid contents of the extracts were determined by using Folin-Ciocalteu method and aluminium chloride method, respectively in order to evaluate a relationship between the antioxidant activity and the phytochemical constituents. The F. schweinfurthii methanolic extract (FSME) exhibited significantly (p < 0.05) higher ABTS radical, NO radical and H2O2 scavenging activity, reducing power ability and inhibition of β-carotene bleaching. Total phenol and flavonoid contents were highest in the FSME (94.61 ± 1.51 mg GAE/g and 21.52 ± 0.17 mg QE/g) respectively. The present study showed that FSME had more antioxidant power than other extracts. Further studies are necessary to isolate active principles responsible for the overall antioxidant activity of the extracts.

Breathing Some New Life into an Old Topic: Chalcogen-Nitrogen π-Heterocycles as Electron Acceptors

Recent progress in the design, synthesis and characterization of chalcogen-nitrogen π-heterocycles, mostly 1,2,5-chalcogenadiazoles (chalcogen: S, Se and Te) and their fused derivatives, possessing positive electron affinity is discussed together with their use in preparation of charge-transfer complexes and radical-anion salts—candidate building blocks of molecule-based electrical and magnetic functional materials.

Multidimensional Network Structures and Versatile Magnetic Properties of Intermolecular Compounds of a Radical–Anion Ligand, [1,2,5]Thiadiazolo[3,4-f][1,10]phenanthroline 1,1-Dioxide

The crystal structures and magnetic properties of seven kinds of [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 1,1-dioxide (tdapO2) radical-anion salts, namely, K·tdapO2, K·tdapO2·0.5MeCN, K·(tdapO2)2, Rb·(tdapO2)2, Cs7·(tdapO2)6·ClO4, (NH4)2·tdapO2·I, and Hppda·tdapO2·MeCN, were investigated. Single-crystal X-ray analyses of these radical-anion salts revealed formation of π-stacking columns and the presence of intercolumnar coordination bonding or hydrogen bonding. The intermolecular magnetic coupling constants in these salts range from strong antiferromagnetic (J/kB = -310 K) to ferromagnetic (J/kB = 24 K). Ab initio calculations performed on the nearest-neighbor radical pairs in the π-stacking columns suggested that the magnetic interactions are strongly governed by the overlap between the two anionic radical species and well explain the observed ferromagnetic and antiferromagnetic interactions. In addition, calculations of a hypothetical oxygen-less tdap analogue suggested that the presence of oxygen in tdapO2 significantly reduces the hopping integral and enhances the probability of ferromagnetic interaction.

Interplay between crystal and magnetic structure of the anion-radical salt (N-Me-2,6-di-Me–Py)(TCNQ)2 (Py is pyridine)

Genuine organic anion-radical salt (N-Me-2,6-di-Me–Py)(TCNQ)2 with pyridine-based cation was synthesized and its crystal structure was resolved. The DC magnetic susceptibility was measured in temperature range from 2 K to 300 K in magnetic fields 10 mT, 100 mT and 1 T. Zero field cooling (ZFC) and field cooling (FC) modes were used. The results were studied in terms of one-dimensional magnetic models and we have found that the most suitable of them is an antiferromagnetic linear Heisenberg S = 1/2 system with small amount of free spins. An additional peak observed at low temperatures can be explained by an interchain coupling between free chain-end spins.

ChemInform Abstract: Reactions of Polycyano‐Alkenes with Alkynyl‐ and Poly‐ynyl‐Group 8 Metal Complexes

AbstractReview: 80 refs.

Electrochromic and spectroelectrochemical properties of novel 4,4′-bipyridilium–TCNQ anion radical complexes

Three novel electrochromic materials 7,7,8,8-tetracyanoquinodimethane (TCNQ) anion radical salts with substituted 4,4′-bipyridilium derivatives (monosubstituent-4,4′-bipyridilium) were prepared. The structure of the complexes was characterized by Elemental analyses, Solid IR spectra and UV–vis spectroscopy. The electrochromic behaviors and electrooptical properties of the complexes were investigated by cyclic voltammetry and UV–vis absorption spectra. Electrochromic devices based on monosubstituent 4,4′-bipyridilium–TCNQ anion radical salts (abbreviated as MBTS) were fabricated which exhibited green–magenta color change. Their color reversibility was excellent with high color-change efficiency after 1000 cycles of the transmittance and transmittance change.

Time-Resolved Infrared Vibrational Spectroscopy of the Photoinduced Phase Transition of Pd(dmit)2 Salts Having Different Orders of Phase Transition

To clarify the mechanism of the later process of photoinduced phase transition (PIPT) in organic charge-transfer complexes, we examined by time-resolved infrared vibrational spectroscopy two dimeric anion radical salts, Et2Me2Sb[Pd(dmit)2]2 (Et2Me2Sb salt) and Cs[Pd(dmit)2]2 (Cs salt) (Et, Me, and dmit are C2H5, CH3, and 1,3-dithiol-2-thione-4,5-dithiolate, respectively), having similar characteristics except for the order of their phase transitions at thermal equilibrium. The phase transition is first order for the Et2Me2Sb salt and second order for the Cs salt at thermal equilibrium. Although both salts exhibit a high-temperature phase at later delay times (>100 ps) after the photoexcitation of the low-temperature phase, the time required for the emergence of the high-temperature phase was significantly different: 70 ps for the Et2Me2Sb salt and <0.1 ps for the Cs salt. The slow emergence of the high-temperature phase in the PIPT of the Et2Me2Sb salt presumably has an origin similar to that recognized for the first-order thermal phase transition, that is, steric effects of the Et2Me2Sb cation when the phase transitions occur.

Exploration of Charge-Transfer Solids Utilizing Nucleobases: Nanoarchitectures by Hydrogen-Bonds in the Ionic Assemblies of Guanine and TCNQ Derivatives

We studied formation and structural characteristics of charge-transfer solids of 9-n-butylguanine (BuG) with fluorinated tetracyanoquinodimethane derivatives (FnTCNQ, n = 4, 2, and 1). Complex formation in a methanol (MeOH)-containing solvent generated two types of salts composed of either a methoxy-substituted anion or a fully ionic anion radical of FnTCNQ. In all anion radical salts, BuG existed as a protonated or a hemiprotonated species, BuGH+ or (BuG)(BuGH+), respectively, and formed hydrogen-bonded (H-bonded) assemblies. In these BuGH+ assemblies, FnTCNQ•– molecules were fixed and aligned periodically, providing H-bonded polycationic templates. In (BuGH+)(F4TCNQ•–), BuGH+ dimers by complementary H-bonds formed a two-dimensional (2D) polycationic sheet. The F4TCNQ•– face-to-face dimers formed a one-dimensional (1D) segregated column aided by formation of H-bonds with BuGH+. In (BuGH+)(F2TCNQ•–)(MeOH), BuGH+ dimers by complementary double H-bonds formed a 1D polycationic ribbon supported by MeOH-media...

Effect of ultrafine grinding on physicochemical and antioxidant properties of dietary fiber from wine grape pomace

Wine grape pomace dietary fiber powders were prepared by superfine grinding, whose effects were investigated on the composition, functional and antioxidant properties of the wine grape pomace dietary fiber products. The results showed that superfine grinding could effectively pulverize the fiber particles to submicron scale. As particle size decrease, the functional properties (water-holding capacity, water-retention capacity, swelling capacity, oil-binding capacity, and nitrite ion absorption capacity) of wine grape pomace dietary fiber were significantly (p < 0.05) decreased and a redistribution of fiber components from insoluble to soluble fractions was observed. The antioxidant activities of wine grape pomace and dietary fiber before and after grinding were in terms of DPPH radical scavenging activity, ABTS diammonium salt radical scavenging activity, ferric reducing antioxidant power, and total phenolic content. Compared with dietary fiber before and after grinding, micronized insoluble dietary fiber showed increased ABTS radical scavenging activity, ferric reducing antioxidant power, and total phenolic content yet decreased DPPH radical scavenging activity. Positive correlations were detected between ABTS radical scavenging activity, ferric reducing antioxidant power, and total phenolic content.

Bis(toluene)chromium(I) [1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl and [1,2,5]Thiadiazolo[3,4-b]pyrazinidyl: New Heterospin (S1 = S2 = 1/2) Radical-Ion Salts

Bis(toluene)chromium(0), Cr(0)(η(6)-C7H8)2 (3), readily reduced [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (1) and [1,2,5]thiadiazolo[3,4-b]pyrazine (2) in a tetrahydrofuran solvent with the formation of heterospin, S1 = S2 = ½, radical-ion salts [3](+)[1](-) (4) and [3](+)[2](-) (5) isolated in high yields. The salts 4 and 5 were characterized by single-crystal X-ray diffraction (XRD), solution and solid-state electron paramagnetic resonance, and magnetic susceptibility measurements in the temperature range 2-300 K. Despite the formal similarity of the salts, their crystal structures were very different and, in contrast to 4, in 5 anions were disordered. For the XRD structures of the salts, parameters of the Heisenberg spin Hamiltonian were calculated using the CASSCF/NEVPT2 and broken-symmetry density functional theory approaches, and the complex magnetic motifs featuring the dominance of antiferromagnetic (AF) interactions were revealed. The experimental χT temperature dependences of the salts were simulated using the Van Vleck formula and a diagonalization of the matrix of the Heisenberg spin Hamiltonian for the clusters of 12 paramagnetic species with periodic boundary conditions. According to the calculations and χT temperature dependence simulation, a simplified magnetic model can be suggested for the salt 4 with AF interactions between the anions ([1](-)···[1](-), J1 = -5.77 cm(-1)) and anions and cations ([1](-)···[3](+), J2 = -0.84 cm(-1)). The magnetic structure of the salt 5 is much more complex and can be characterized by AF interactions between the anions, [2](-)···[2](-), and by both AF and ferromagnetic (FM) interactions between the anions and cations, [2](-)···[3](+). The contribution from FM interactions to the magnetic properties of the salt 5 is in qualitative agreement with the positive value of the Weiss constant Θ (0.4 K), whereas for salt 4, the constant is negative (-7.1 K).

Catechol-appended TTF derivatives

abstract EDT-TTF-CONHCatOH, a catechol-appended TTF derivative, 5 was synthesized through a straightforwardstrategy. The electronic absorption and the electrochemical investigations as well as molecular orbitalcalculations for compounds 4 and 5 have been performed. The electrochemical measurements of 5 indi-cate that it is a suitable candidate for the formation of zwitterionic molecular solids and also two-com-ponent radical cation salts. The crystal structure of compound 5 reveals supramolecular dimersassembled via a set of O–H O hydrogen bonds between the catechol and amide units. 2013 Elsevier Ltd. All rights reserved. Tetrathiafulvalene (TTF) and its many derivatives have been thesubject of numerous studies due to their use as precursors formolecular conductors and superconductors. 1 This is mainly dueto their strong electron donating which results in two sequentialand reversible oxidation processes, affording radical cation (TTF + )and dication (TTF 2+ ) species. 2 It is well known that intermolecularinteractions play a significant role in controlling the electronicstate, molecular arrangements, and solid-state physical propertiesof these crystalline materials. Thus, efforts have been devoted todirect the intermolecular interactions in both the neutral, closed-shell molecules as well as in the corresponding charge transfercomplexes and radical cation salts.