Quinone Units Research Articles

Redox‐Controlled Fluorescence Modulation in a BODIPY‐Quinone Dyad

AbstractThe synthesis and properties of two closely related boron dipyrromethene (BODIPY) derived dyads, incorporating redox‐active quinone units appended at the meso position, are described. For one dyad, the quinone unit is attached directly to the BODIPY core, whereas a phenylene spacer separates the two units in the second compound. Each of the quinone units is readily converted, by both chemical and electrochemical means, to the corresponding hydroquinone derivative. The strong fluorescence normally associated with the BODIPY unit is efficiently quenched in both dyads in their quinone forms. This is attributed to deactivation of the first excited singlet state by a way of an intramolecular electron‐transfer process. By comparison, moderately intense fluorescence is observed for the hydroquinone derivative containing the phenylene spacer, but not for the analogous directlycoupled dyad. The potential sensing capabilities of the phenylene‐spaced BODIPY quinone and hydroquinone dyads, towards reducing and oxidising species such as ascorbate and peroxide, were tested in a biomembrane mimic. A reversible modulation in fluorescence could be readily detected by eye under standard UV‐light excitation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

New Substituted Tetrathiafulvalene−Quinone Dyads: The Influences of Electron Accepting Abilities of Quinone Units on the Metal Ion-Promoted Electron-Transfer Processes

The metal ion-promoted electron transfer occurs to all new dyads 1, 2, 3, and 4, even one of them, dyad 4, which has a rather weak electron acceptor unit. The results also indicate that the metal ion-promoted electron transfer within the dyads is influenced by the electron accepting abilities of quinone units; dyad 2 with the strongest electron acceptor among the four dyads shows the strongest absorption and ESR signals attributed to TTF.+ in the presence of metal ions.

Synthesis of Singly and Doubly Cage‐Annulated Bicyclo[2.2.2]octenes Derived from Triptycene Skeleton

AbstractTriptycene‐diquinone 5 was synthesized from 1,4‐dimethoxyanthraene (6b) and found to undergo Diels‐Alder reaction with 5,5‐dimethoxy‐1,2,3,4‐tetrachlorocyclopentadiene (DTCp) to afford exclusively the least symmetric (Cs) bis‐adduct 4b. The double Diels‐Alder reaction exhibited π‐facial selectivity, in which the initial cycloaddition occurred preferentially on the π‐face of the benzoquinone moiety of 5 that is syn to the other benzoquinone unit (about 6:1), thereby producing the corresponding mono‐adducts 13b and 13a. Both stereoisomeric 13a and 13b underwent the second cycloaddition via exclusively the π‐face that is opposite to the orientation of previous DTCp addition 5, thus leading to the formation of bis‐adduct 4b as sole product. The structure of 4b was unequivocally established by X‐ray structural determination.

Probing Biocatalytic Transformations with CdSe−ZnS QDs

CdSe/ZnS QDs enable the optical probing of the biocatalytic oxidation of tyrosine derivatives and of the scission of peptides by thrombin. CdSe/ZnS QDs were modified with tyrosine methyl ester or with a tyrosine-containing peptide. The tyrosine units were reacted with tyrosinase/O2 to yield the respective l-DOPA and quinone derivatives. The luminescence of QDs modified by the enzyme-generated quinone units is quenched. The quinone-functionalized peptide associated with the QDs was cleaved by thrombin, a process that restored the luminescence of the QDs.

Synthesis, structure and electrochemical properties of 2,5-bis(alkyl/arylamino)1,4-benzoquinones and 2-arylamino-1,4-naphthoquinones

Various primary amines react with 1,4-benzoquinone to form corresponding 2,5-bis(alkyl/arylamino)1,4-benzoquinone. The crystal structure of three such derivatives namely 2,5-bis(2-propylamino)1,4-benzoquinone, 2,5-bis(cyclohexylamino) 1,4-benzoquinone and 2,5-bis(3-methylanilino)1,4-benzoquinone is determined. The solid-state structure shows absence of intra-molecular hydrogen bonding between the carbonyl of the quinone unit with N–H of the amine group in these molecules. Each of these compounds shows a proton sensitive quasi-reversible redox couple. Analysis on the basis of torsion angle shows that conjugation of the O C–C–N frame has lesser contribution to the quasi-reversible cycle but the couple is effected by variation of the substituents on the nitrogen atom. The reaction of 1,4-naphthoquinone with primary amines also gives corresponding 2-amino-1,4-naphthoquinone derivatives. Two representative crystal structures of 2-amino-1,4-naphthoquinone derivatives are reported.

Optimization of the electropolymerization of 1-amino-9,10-anthraquinone conducting films from aqueous media

The optimum conditions for the electrochemical preparation of poly(1-amino-9,10-anthraquinone), PAAQ, films in environmentally safe aqueous solutions were investigated. The conducting polymer films were prepared by electrochemical oxidation of 1-amino-9,10-anthraquinone, AAQ, in sulfuric acid solutions in the potential range from 0.0 to +1.3 V. The influence of scan repetition, scan rate, and monomer concentration on the formation process and the properties of the polymer film were studied. The electrochemical response of the formed polymer film was investigated in both aqueous and non-aqueous media. The polymer films were found to be stable in aqueous acidic media. In non-aqueous solutions, like acetonitrile, dimethyl sulfoxide and dioxin, the polymer films showed remarkable degradation. The best electrochemical response of the PAAQ films was found to be in the potential range between +0.3 and +0.9 V. The presence of quinone units in the polymer film chain suggests promising applications of these conducting polymers in lightweight (rechargeable) batteries, electrochromic display devices, and biosensor and corrosion protection.

A bis-quinone-functionalized Au-electrode subjected to hydrophobic magnetic nanoparticles acts as a three-state “Write-Read-Erase” information storage system

A monolayer consisting of two quinone units Q A and Q B is assembled on a Au electrode and interacted with an aqueous electrolyte/toluene biphase system, where hydrophobic magnetic nanoparticles are dispersed in the toluene phase. The bis-quinone monolayer exposed to the aqueous electrolyte solution reveals two reversible 2e −/2H +-waves at E 1° = −0.36 V and E 2° = −0.16 V (vs. SCE) for the Q A and Q B units in the cyclic voltammogram, respectively. The electrochemical features of the monolayer allow electrochemical encoding of information in the monolayer by applying three different potentials, −0.05 V, −0.3 V or −0.6 V, generating the Q A–Q B, Q A–Q BH 2 or Q AH 2–Q BH 2 states, respectively. The encoded states of the monolayer are read out by the magnetic attraction of the hydrophobic magnetic nanoparticles to the electrode surface, and by analyzing the electrochemical properties of the different monolayer states in the hydrophobic environment provided by the nanoparticles. The oxidized quinone units in the hydrophobic environment reveal a stepwise one-electron reduction process, while the hydroquinone units are electrochemically mute in the same potential range. The encoded information is erased, in the presence of the hydrophobic magnetic nanoparticles, by sweeping the potential to a positive value of 0.4 V that results in the oxidation of the Q AH 2 and Q BH 2 states. The magnetic removal of the hydrophobic nanoparticles from the electrode surface and the exposure of the modified surface to the aqueous electrolyte solution reset the Q A and Q B units for a further cycle of the information storage.

Magneto-controlled Quantized Electron Transfer to Surface-confined Redox Units and Metal Nanoparticles

Hydrophobic magnetic nanoparticles (NPs) consisting of undecanoate-cappedmagnetite (Fe3O4, average diameter ca. 5 nm) are used to control quantized electron transferto surface-confined redox units and metal NPs. A two-phase system consisting of anaqueous electrolyte solution and a toluene phase that includes the suspended undecanoate-capped magnetic NPs is used to control the interfacial properties of the electrode surface.The attracted magnetic NPs form a hydrophobic layer on the electrode surface resulting inthe change of the mechanisms of the surface-confined electrochemical processes. Aquinone-monolayer modified Au electrode demonstrates an aqueous-type of theelectrochemical process (2e- 2H+ redox mechanism) for the quinone units in the absence ofthe hydrophobic magnetic NPs, while the attraction of the magnetic NPs to the surfaceresults in the stepwise single-electron transfer mechanism characteristic of a dry non-aqueous medium. Also, the attraction of the hydrophobic magnetic NPs to the Au electrodesurface modified with Au NPs (ca. 1.4 nm) yields a microenvironment with a low dielectricconstant that results in the single-electron quantum charging of the Au NPs.

Molecular Mechanical Devices Based on Quinone−Pyrrole and Quinone−Indole Dyads: A Computational Study

A set of intramolecularly connected dyads consisting of a quinone unit and a pyrrole or indole moiety have been designed and evaluated in quantum-chemical calculations. It is shown computationally for several systems, depending on the length and attachment points of the interconnecting chains, that a reduction of the quinone to the semiquinone radical anion or quinolate dianion state leads to a reversible intramolecular reorientation from a pi-stacked to a T-stacked arrangement. In the rearranged structures, a hydrogen bond from the pyrrole or indole N-H function to the semiquinone or quinolate pi-system is created upon reduction. In some systems, hydrogen bonds to the semiquinone or quinolate oxygen atoms are partly feasible and will be preferred over T-stacking. The choice of systems has been based on recent computational observations related to photosystem I. Systems with pyrrole or indole units should provide a better basis for the envisioned molecular motor than recently proposed quinone-benzene dyads. The intramolecular interactions modify the quinone redox potentials. Electronic g-tensors have been computed for the semiquinone states. These reflect characteristically the presence and nature of hydrogen bonds to the semiquinone and represent suitable electron paramagnetic resonance spectroscopic probes for the preferred structures. Intramolecular proton transfer is possible in the dianionic state.

Oxidative Coupling Polymerization of 2,6-Dihydroxynaphthalene in Basic Water

The oxidative coupling polymerization of 2,6-dihydroxynaphthalene was found to take place in basic water. Alkaline metal bases such as NaOH and K2CO3 with the catalyst of copper(II) disodium ethylenediaminetetraacetate tetrahydrate resulted in promoting the over-oxidation to form the quinone unit and the C–O coupling to form the ether unit. When amines were employed as the base, their structures affected the polymerization results. HOCH2CH2NH2, and (HOCH2)3CNH2 produced poly(2,6-dihydroxy-1,5-naphthylene) without the quinone and the ether units, however, which were formed in the presence of Me2NH, Me3N, and BnNH2. Surprisingly, it was found that the catalyst was dispensable for amines to promote this polymerization.

Synthesis and characterization of an electroactive surface that releases γ-aminobutyric acid (GABA)

We report the synthesis and characterization of a new electroactive surface capable of releasing the neurotransmitter γ-aminobutyric acid (GABA) upon reduction. The GABA was anchored to an alkanethiol via electrochemically active quinone (abbreviation, TM-GABA). The quinone unit, upon reduction to the hydroquinone, cyclizes to release GABA into solution. The half-life is 99 s. The self-assembled monolayer (SAM) of TM-GABA on gold was prepared and characterized with several surface sensitive techniques. X-ray photoelectron spectroscopy (XPS) explored the SAM formation of TM-GABA on Au surfaces. Cyclic voltammograms showed the ability to electrochemically control the quinone unit at the distal end of the chain. GABA was selectively released upon electrochemical reduction at a potential of −700 mV. The functional GABA terminal group was detected by surface plasmon resonance measurements of anti-GABA antibody binding.

TTF derivatives containing fused-pyrazine rings for novel donor- acceptor systems

In this work, novel TTF derivatives fused with electron-accepting pyrazine rings are described. We have succeeded in preparing two kinds of TTF derivatives containing two pyrazine rings. Furthermore, we have prepared asymmetrical TTF derivatives containing one pyrazine ring to increase the electron-donating properties. In some cases, hydroxyl groups were introduced to induce intcrmolecular hydrogen bonds. Oxidation of hydroquinone derivatives afforded a new type of donor-acceptor compounds with quinone units, which showed both oxidation and reduction potentials. The electrical conductivity of the D-A compound was about 10 −8 S/cm as single component. We have also prepared several CT complexes based on the new TTF derivatives and investigated the structures and properties.

Fenton Degradation of Organic Compounds Promoted by Dyes under Visible Irradiation

The influence of dyes on the Fenton reaction of organic compounds under visible irradiation (lambda > 450 nm) was examined. It was found that the presence of dyes could accelerate greatly the Fenton reaction of organic compounds such as salicylic acid, sodium benzenesulfonate, benzyltrimethylammonium chloride, and trichloroacetic acid under visible irradiation and that a complete mineralization of those compounds could also be achieved. The dyes such as Alizarin Violet 3B which has an anthraquinone structure unit showed much more significant effect on the reaction than the dyes such as malachite green without the quinone unit. A reaction mechanism of dye AV as a cocatalyst in the photo-Fenton reaction of organic compounds under visible irradiation is proposed based on the cycle of Fe(3+)/Fe(2+) catalyzed by quinone species and an electron transfer from the excited dye molecule to Fe3+.

Conformational instability of a proximally-difunctionalized calix[4]-diquinone

We have recently described the electrochemical oxidation of 5,11,17,23-tetra- tert-butyl-25, 26-bis(diphenylphosphinoylmethoxy)-27,28-dihydroxycalix[4]arene into the corresponding diquinone 1. The solid state structure of 1 has now been determined by a single crystal X-ray diffraction study. Diquinone 1 crystallizes in the monoclinic space group with a=10.3507(12), b=25.219(4), c=20.2315(14) Å, β=101.166(8)°, V=5181.1(10) Å 3, Z=4, and D x =1.273 g cm −3. The calixarene skeleton adopts a partial cone conformation in which one quinone ring is anti-oriented with respect to the other three rings of the calixarene core. A variable temperature NMR study shows that 1 is dynamic in solution, each quinone unit undergoing fast oscillation about the axis that passes through the two meta carbon atoms bonded to the adjacent methylene groups. The motion of the quinone rings was confirmed by 2D NMR experiments.

Cyclic voltammetry and theoretical calculations of silyl-substituted 1,4-benzoquinones

Cyclic voltammograms of 2,3,5,6-tetrakis(trimethylsilyl)-1,4-benzoquinone ( 1a), 2,3,5,6-tetrakis(dimethylvinylsilyl)-1,4-benzoquinone ( 1b), 2,3,5,6-tetrakis(dimethylsilyl)-1,4-benzoquinone ( 1c), 4,4,6,6,10,10,12,12-octamethyl-4,6,10,12-tetrasilatricyclo[7.3.0.0 3,7]dodeca-1(9),3(7)-diene-2,8-dione ( 1d), and 5- t-butyl-2-(pentamethyldisilanyl)-1,4-benzoquinone ( 5h) showed that the first reduction step was reversible and that the second step was irreversible. The first half-wave reduction potentials ( E 1 / 2 I s ) of 1a, 1b, 1c, and 1d shifted negatively relative to 1,4-benzoquinone by −0.31, −0.24, −0.03, and −0.18 V, respectively. These results demonstrated that the electron-accepting ability of the chair-form quinones 1a and 1b was lower than that of the planar quinones 1c and 1d. The E 1 / 2 I of 5h (−0.93 V vs. Ag/Ag +) was quite similar to that of 5- t-butyl-2-trimethylsilyl-1,4-benzoquinone ( 5a, −0.94 V). A cyclic voltammogram of dimethylsilylene-bridged 1,4-benzoquinone dimer 7 showed two kinds of E 1 / 2 I (−0.76 and −0.94 V). The electrochemical behavior of 7 would be interpreted in terms of near-neighbor interactions between reduced and non-reduced quinone units. Theoretical calculations of the silyl-1,4-benzoquinones reproduced well the solid state structures of the compounds. Also, the computed vibrational frequencies of the silyl-1,4-benzoquinones were in good agreement with the IR absorption frequencies of the C O units in the compounds. The LUMO energy levels of the silyl-1,4-benzoquinones were quantitatively proportional to the E 1 / 2 I s .

EPR characteristics of heat treated complexes of metals with demineralised humic brown coal in air and ammonia atmospheres

Investigations were carried out on complexes of metal ions with solvent pre-extracted and demineralised Lubstow humic brown coal (HC) ( Eocene, Midlands Poland; content of humic acids above 80%). Metal–humic brown coal complexes (HC–M) were obtained at pH 5.1 by ion exchange of solid HC with the following metal ions: Mg 2+, Ca 2+, Ba 2+, Ti 3+, Cr 3+, Mn 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Ag +1, Zn 2+, Cd 2+, Al 3+, Ga 3+, Tl 3+, Sn 2+, Pb 2+, and Bi 3+. Metal uptake by the HC is dependent on the radius of the metal ion and its susceptibility to complexation in polyfunctionalised humic matrix. The complexes were heat treated to different final temperatures in a range up to 650 °C. Raw HC–M complexes and resultant chars were characterised by elemental composition, IR, and quantitative electron paramagnetic resonance spectroscopy (QEPR). The binding sites of the metal cations are oxygen functional groups (mainly –COOH, –OH phenolic). EPR parameters (i.e., concentration of stable free radicals and g-value) were determined in air and gaseous ammonia atmosphere. The nature of the observed free radicals in raw HC–M complexes is mainly of semiquinone type ( g=2.0036 in air and 2.0045 in gaseous ammonia atmosphere). Heat treatment of the complexes causes gradual defunctionalisation, resulting in elimination of quinone and hydroquinone structural units and generation of polyaromatic sheets containing aromatic type free radicals. Practically complete disappearance of semiquinone radicals occurs at 400 °C heat treatment, and intensive development of aromatic type free radicals occurs above that temperature. Paramagnetic metal ions cause strong decrease of the observed free radical concentration in HC–M complexes due to antiferromagnetic interaction with electrons of semiquinone type radicals (Cu 2+>Fe 3+>Mn 2+>Cr 3+>Ti 3+). The observed concentration of free radicals in the HC–M complexes with alkaline metal ions of s and p block metals as well as d 10 metal ions is higher compared to the value of uncomplexed HC. Gaseous ammonia strongly shifts hydroquinone–semiquinone–quinone equilibria towards generation of semiquinone anion radicals, which is manifested by elevated concentrations of free radicals and increases of g-value in chars of heat treated samples in the region below 400 °C. The control of free radical types and concentrations in environment allows to: (i) predict the state of temporal alkalinity (due to use of ammonia and urea based fertilisers), (ii) binding of heavy metal cations, and (iii) degree of humic matter maturation.

Heteroaromatic and aromatic conjugated polymers synthesized by organometallic coupling — preparation and selected electrochemical properties

Various electrochemically active π-conjugated polymers were synthesized by organometallic polycondensations. p-Dopable polymers such as polypyrrole, polythiophene, and polyselenophene exhibited a linear correlation between the ionization potential of the corresponding monomeric compound and the oxidation potential of the π-conjugated polymer with a slope of about 1.5. On the other hand, n-dopable polymers containing imine nitrogen or quinone unit showed linear correlation with a slope of about 0.75 between the electron affinity of the corresponding monomeric compound and the reduction potential of the polymer. Cyclic voltammetric analysis in solutions indicated that the oxidation peak current ( i pa) is proportional to a square root of the sweep rate ( v 1 / 2 ) in many cases. For poly(3-hexylthiophene-2,5-diyl), the diffusion coefficient ( D) calculated with the Matsuda's equation was 10 −7 cm 2 s −1 at a molecular weight of about 3000, and it decreased steeply with increase in the molecular weight.

Synthesis and Electrochemical Properties of New Main Chain Type Polyquinones Constituted of Thiophene-Fused Benzoquinone and Transformation of the Polymers to a Dicyanoquinonediimine Type Polymer

New main chain type polyquinones, poly(3,7-dialkylbenzo[1,2-b:4,5-b']dithiophene-4,8-dione-2,6-diyl), P(2,6-Th 2 Bq(diR)) (R = hexyl(Hex); octyl(Oct); dodecyl(Dod)), and poly(benzo[1,2-c:4,5-c']dithiophene-4,8-dione-1,3-diyl), P(1,3-Th 2 Bq), were prepared by organometallic polycondensation. P(2,6-Th 2 Bq(diR)) was soluble in organic solvents such as chloroform and dichloromethane. P(1,3-Th 2 Bq) is soluble in CF 3 COOH, NMP, and DMI (1,3-dimethyl-2-imidazolidione). P(2,6-Th 2 Bq(diHex)) received electrochemical two step reduction with peak reduction potentials (E pc ) of - 1.18 V and -1.84 V vs. Ag + /Ag, respectively. This electrochemical reduction corresponds to Wurster type reduction characteristic of quinones. P(1,3-Th 2 Bq) was also electrochemically active and its reduction took place at E pc = -1.50 V and -1.74 V vs. Ag + /Ag. The film of P(1,3-Th 2 Bq) changed its color from brown to blue (electrochromism) on the electrochemical reduction. Powder XRD patterns of P(2,6-Th 2 Bq(diR))s indicated that they assumed an ordered structure; they showed an XRD peak in a low angle region (2θ (Cu-Kα)< 7°). The d-value of the peak increased linearly with increase in the number of the carbon of the R groups, suggesting that the d-value corresponded to a distance between the polymer main chains separated by the R groups and P(2,6-Th 2 Bq(diR)) took a stacked structure in the solid. The quinone unit of P(2,6-Th 2 Bq(diR))s was transformed to a strong electron withdrawing dicyanoquinonediimine (DC-QNl) unit by reaction with bis(trimethylsilylcarbodiimide) (TMS-N=C=N-TMS); a high degree of transformation was observed by elemental analysis. A cast film of the obtained polymer underwent the electrochemical reduction with the first E pc 1 at a very high potential of -0.56 V vs. Ag + /Ag, reflecting the high electron-withdrawing properties of the DCNQI unit.

Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction.

A unified synthesis of several quinone sesquiterpenes is described herein. Essential to this strategy is a novel radical addition reaction that permits the attachment of a fully substituted bicyclic core 16 to a variably substituted quinone 10. The addition product 15 can be further functionalized, giving access to natural products with a high degree of oxygenation at the quinone unit. The quinone addition reaction is characterized by excellent chemoselectivity, taking place only at conjugated and unsubstituted double bonds, and regioselectivity, being strongly influenced by the resonance effect of heteroatoms located on the quinone ring. These features were successfully applied to the synthesis of avarol (1), avarone (2), methoxyavarones (4, 5), ilimaquinone (6), and smenospongidine (7), thereby demonstating the synthetic value of this new method.

Electrochemical preparation and characterization of poly(1-amino-9,10-anthraquinone) films

Poly(1-amino-9,10-anthraquinone), PAAQ, films were prepared by electrochemical oxidation of the monomer, AAQ, in acetonitrile using LiClO 4 as supporting electrolyte. The influence of scan repetition, scan rate and monomer concentration on the formation of polymer film was studied. The electrochemical behavior of the formed polymer films was investigated in both non-aqueous and aqueous media. The prepared films were found to be more stable in organic solvents than in aqueous solutions. The investigated organic solvents are methanol, ethanol, acetone, carbon tetrachloride, benzene, and chloroform. The polymer film shows electrochemical response in both non-aqueous and aqueous media. In non-aqueous solutions it has a wide potential range of electroactivity (from −1.5 to +1.3 V). In aqueous media the polymer film shows electrochemical response in the potential range between −0.3 and +1.3 V only. The presence of quinone units suggests potential applications in diverse areas such as electrocatalytic processes and lithium ion batteries.