Anthraquinone Groups Research Articles

Development of New Electrodes Based on Activated Carbon Functionalized with Anthraquinone Groups for Application in Electrochemical Capacitors

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Complexation Studies of Nucleotides by Tetrandrine Derivatives Bearing Anthraquinone and Acridine Groups

Water soluble dicationic cyclophane-type macrocycles bearing two anthraquinone (1) or two acridine groups (2) have been prepared by chemical modification of S,S-(+)-tetrandrine. Complexation of nucleotide anions (mono- di- and triphosphates) and D/L phenylalanine by tetrandrine derivatives has been studied by UV-Visible and fluorescence titrations in water. Association of nucleotides to semi-synthetic hosts 1 and 2 increases with increasing guest charge in the series AMP2 − < ADP3 − < ATP4 − . It was demonstrated for the 1- ATP and ADP complexes that association strength is increased in the absence of salt (NaCl). Besides, receptor 1 shows a slight preference for the complexation of UMP over nucleotides containing A (adenine), G (guanine), C (cytosine) or T (thymine) as bases. The major forces stabilizing the complexes result from ion pairing between the charged groups of host and guest and from stacking or hydrophobic interactions. Receptor 1 displayed chiral recognition towards D/L phenylalanine.

In situ generation of diazonium cations in organic electrolyte for electrochemical modification of electrode surface

The modification of glassy carbon electrode was achieved by electrochemical reduction of in situ generated diazonium cations in acetonitrile. The in situ generation of 4-nitrophenyl diazonium cations in acetonitrile was investigated by spectroscopic methods. UV–visible spectroscopy revealed slow kinetics for the reaction of 4-nitroaniline with tert-butylnitrite in acetonitrile to form the corresponding diazonium cation. As a result, a coupling reaction, which implies a consumption of the amine and loss of the already formed diazonium cations, was evidenced by 1H NMR spectroscopy. This spectroscopic study allowed the optimization of the in situ diazonium cations generation prior to the modification step. The electrochemical modification of the carbon electrodes with 4-nitrophenyl, 4-bromophenyl and anthraquinone groups was characterized by cyclic voltammetry and the resulting grafted layer were characterized by electrochemical techniques. The cyclic voltammetric behaviour during the electrochemical grafting was very similar to the one observed for an isolated diazonium salt dissolved in acetonitrile. In the case of the anthraquinone-modified electrode, the use of acetonitrile, into which the corresponding amine is soluble but not in aqueous media, allowed for its grafting by the in situ approach. The barrier properties of these grafted layers are similar to those obtained from isolated diazonium salts. Finally, the chemical composition of the grafted layers was determined by X-ray photoelectron spectroscopy and surface coverage in the range 5–7 × 10 −10 mol cm −2 was estimated for films grown in our experimental conditions.

2′-Anthraquinone-Conjugated Oligonucleotide as an Electrochemical Probe for DNA Mismatch

We previously prepared the oligonucleotides (ODNs) conjugated to an anthraquinone (AQ) group via one carbon linker at the 2'-sugar position. When these modified ODNs bind to cDNA sequences, the AQ moiety can be intercalated into the predetermined base-pair pocket of a duplex DNA. In this paper, 2'-AQ-modified ODNs are shown to be an excellent electrochemical probe to clarify the effect of a mismatch base on the charge transfer (CT) though DNA. Two types of DNA-modified electrodes were constructed by assembly of disulfide-terminated 2'-AQ-ODN duplexes onto gold electrodes. One type of electrodes (system I) contains fully matched base pairs or a single-base mismatch in duplex DNA between the redox center and the electrode. The other (system II) consists of the mismatch but at the outside of the redox center. The modified electrodes were analyzed by cyclic voltammetry to estimate the CT rate through duplex DNA. In system I, the CT rate was found to be approximately 50 s (-1) for the fully matched AQ-ODN duplexes, while the CT rates of the mismatched DNA were considerably slower than that of the fully matched DNA. In system II, the AQ-ODN duplexes showed almost similar CT rates ( approximately 50 s (-1)) for the fully matched DNA and for the mismatched DNAs. The detection of a single-base mismatch was then performed by chronocoulometry (CC). All the DNA duplexes containing a mismatch base in system I gave the reduced electrochemical responses when compared to the fully matched DNA. In particular, the mismatched DNAs including G--A mismatch can be differentiated from fully matched DNA without using any electrochemical catalyst. We further tested the usefulness of single-stranded (ss) AQ-ODN immobilized on a gold electrode in the electrochemical detection of a single-base mismatch through hybridization assay. The ss-AQ-ODN electrodes were immersed in target-containing buffer at room temperature, and the CC measurements were carried out to see the changes in the integrated charge. Within 60 min, the mismatched DNA was clearly distinguishable by the CC differences from the fully matched target. Thus, the electrochemical hybridization assay provides an easy and convenient detection for DNA mutation that does not require any extra reagents, catalyst, target labeling, and washing steps.

Degradation of poly(terphenylenephthalide) at high temperatures

The thermal and thermooxidative degradation of poly(terphenylenephthalide) has been studied by thermal analysis, IR and UV spectroscopy, and mass spectrometry. On the basis of the spectral data and the chemical composition of degradation products, it has been shown that both the thermal and thermooxidative degradations of poly(terphenylenephthalide) are characterized by intramolecular cyclization reactions. Depending on the mode of closure of intermediates generated in the course of thermal decomposition of neighboring phthalide groups (head-to-head or head-to-tail), either phenyl-substituted anthraquinones, fluorenones, and fluorenes or symmetric and nonsymmetric dicyclic compounds containing end anthraquinone, fluorenone, and fluorene groups may be formed. The oxidation of poly(terphenylenephthalide) likewise gives rise to cyclic products—the compounds of xanthone and dibenzofuran series.

New soluble, thermally stable poly(amide–imide)s containing cardo anthraquinone unit

Preparation of new types of polyimides with high thermal stability and improved solubility was considered. In this way, two new amide diamines containing bulky pendant units were prepared in two steps: nucleophilic substitution reactions of 1- and 2-aminoanthraquinone with 3,5-dinitrobenzoyl chloride to form amide containing dinitro compounds, and then reduction of resulted dinitro compounds with hydrazine monohydrate in the presence of palladium/activated carbon. Two series of new poly(amide–imide)s were prepared from the reactions of these two diamines with various dianhydrides by one step polyimidation process. All poly(amide–imide)s were characterized by FTIR and 1H-NMR spectroscopies and elemental analysis. The polymers were obtained in high yields with inherent viscosities of 0.54–0.69 dl g −1. X-ray diffraction patterns (XRD) showed that all the polymers were amorphous and therefore this factor in addition to the introduction of bulky anthraquinone group led to good solubility of the polymers in most common organic solvents especially in N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), and dimethylsulfoxide (DMSO). Thermal analysis showed glass transition temperature between 204 and 226 °C. Decomposition temperatures were more than 293 °C, also 10% weight loss were in the range of 387–419 °C in air.

Emergent Functionality of Nucleobase Radical Cations in Duplex DNA: Prediction of Reactivity Using Qualitative Potential Energy Landscapes

The one-electron oxidation of a series of DNA oligonucleotides was examined. Each oligomer contains a covalently linked anthraquinone (AQ) group. Irradiation of the AQ group with near-UV light results in a one-electron oxidation of the DNA that generates a radical cation (electron "hole"). The radical cation migrates through the DNA by a hopping mechanism and is trapped by reaction with water or molecular oxygen, which results in chemical reaction at particular nucleobases. This reaction is revealed as strand cleavage when the irradiated oligonucleotide is treated with piperidine. The specific oligomers examined reveal the existence of three categories of nucleobase sequences: charge shuttles, charge traps, and barriers to charge migration. The characterization of a sequence is not independent of the identity of other sequences in the oligonucleotide, and for this reason, the function of a particular sequence emerges from an analysis of the entire structure. Qualitative potential energy landscapes are introduced as a tool to assist in the rationalization and prediction of the reactions of nucleobases in oxidized DNA.

Oxygen electroreduction on chemically modified glassy carbon electrodes in alkaline solution

Abstract The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with aryl groups has been studied using the rotating disk electrode (RDE) technique. The GC electrodes were grafted by electrochemical reduction of diazonium salts. The diazonium derivatives of benzene, naphthalene and anthracene were used in surface modification. The blocking behaviour of aryl layers towards oxygen reduction was investigated. An unexpected order of blocking efficiency of the aryl moieties was observed for O2 reduction in 0.1 M KOH. The phenyl-modified GC electrode was less active than those electrografted with naphthalene and anthracene. Comparative measurements were carried out in 1 mM K3Fe(CN)6. A much larger extent of blocking was evident for the Fe ( CN ) 6 3 - / 4 - couple. This effect was explained by a significant difference in size between the Fe ( CN ) 6 3 - / 4 - ions and O2 molecule. A mixed film of anthraquinone (AQ) and phenyl groups was formed by diazonium reduction and its relevance in the kinetics investigations was discussed. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model for quinone-modified electrodes.

Long-distance radical cation transport in DNA: horizontal charge hopping in a dimeric quadruplex

A series of DNA hairpins were synthesized and shown to associate to form quadruplexes formed by stacking five G-quartets in an antiparallel orientation. One of the hairpins in the quadruplex was linked covalently at the 5'-end to an anthraquinone (AQ) group and a 32P label was incorporated either at the 3'-terminus of the AQ-containing hairpin or on its partner hairpin in the quadruplex. Irradiation of the AQ group with UV light leads to the one-electron oxidation of the DNA and concomitant introduction of a radical cation into the DNA. Analysis by PAGE and autoradiography shows that the radical cation reacts at guanines both on the AQ-containing strand and with its partner hairpin in the quadruplex. This observation demonstrates that charge migration in DNA occurs vertically along a DNA chain and horizontally within a G-quartet.

Synthesis and in Vitro Antileukemic Activity of Some New 1,3-(Oxytetraethylenoxy)cyclotriphosphazene Derivatives

A new series of 1,3-(oxytetraethylenoxy)cyclotriphosphazene derivatives bearing 2-chloroethylamine or salicylaldehyde (2-hydroxybenzaldehyde) or its Schiff base (after condensation with 2-chloroethylamine) units and having also 2-naphthyl or anthraquinone groups as cosubstituents has been synthesized. The in vitro cytotoxic activity of these compounds against a panel of four cancer cell lines has been studied. Most of the compounds exhibited antiproliferative activity in the range of the international criterion for synthetic agents (4 microg/mL) against the MOLT4, L 1210, HL-60, and P388 cell lines chosen for testing.

3‘-Immobilized Probes with 2‘-Caps: Synthesis of Oligonucleotides with 2‘-N-Methyl-2‘-(anthraquinone carboxamido)uridine Residues

[reaction: see text] A synthesis for oligodeoxynucleotides with a 3'-terminal 2'-N-methyl-2'-acylamido-2'-deoxyuridine residue was developed. Unlike their unmethylated counterparts, these oligodeoxynucleotides can be stably immobilized on aldehyde-displaying glass surfaces to provide DNA microarrays. An anthraquinone carboxamido group as a 2'-substituent doubled the capture efficiency of an immobilized tetradecamer.

Porphyrin-anthraquinone dyads: Synthesis, spectroscopy and photochemistry

Free-base (H2L2), copper(II) (CuL2) and zinc(II) (ZnL2) derivatives of a porphyrin-anthraquinone conjugate with an azomethine group separating the two photoactive subunits have been synthesized and characterized by mass (FAB), IR, UV-visible, 1H NMR and ESR spectroscopic techniques and also by cyclic and differential pulse voltammetric methods. Analysis of the data reveals that the spectral and electrochemical properties of the individual chromophoric entities are retained and that there is no specific π-π interaction between the porphyrin and anthraquinone subunits. H2L2 and ZnL2 are shown to exhibit substantial quenching (88–97%) of the porphyrin fluorescence compared to their corresponding monomeric analogues. An intramolecular electron-transfer mechanism is proposed for the substantial decrease in fluorescence in both derivatives. The fluorescence decays of porphyrin-anthraquinone conjugates are fit to 2/3 exponentials and indicate that multiple orientations of the porphyrin and anthraquinone groups contribute to the electron-transfer event. These results are in good agreement with steady-state fluorescence results. From the time-resolved fluorescence data, the electron-transfer rate constants are calculated, indicating kET values in the range of 1·1 × 109 to 9·9 × 1010 s−1 that are dependent upon the solvent.

Análise voltamétrica do corante têxtil do tipo antraquinona empregando eletrodos de carbono impresso

O corante reativo Reactive Blue (RB4), que possui como grupo cromóforo uma antraquinona e um grupo diclorotriazina como grupo reativo, foi determinado em níveis de micromol utilizando eletrodos de carbono impresso empregando a técnica de voltametria de pulso diferencial. Foram obtidas respostas lineares entre a corrente de pico e a concentração do corante entre 3,4 x 10-6 e 3,0 x 10-4 mol L-1 em solução de KCl pH 1,0. Empregando as condições otimizadas para a analise do corante, foi estudada a influência da temperatura de aquecimento na hidrólise do grupo reativo, monitorando um pico de redução em -1,1 V (vs. carbono impresso).

Decolourization of anthraquinone reactive dye by electrochemical reduction on reticulated glassy carbon electrode

The electrochemistry reduction for the removal of Reactive Blue 4 (RB4) dye from aqueous solution using reticulated glassy carbon electrode is investigated. At pH < 8.0 the anthraquinone group of the RB4 dye are reduced in one cathodic step to hidroquinone after a reversible two-electron process involving a precedent two protons reaction. A stable semiquinone is detected by spectrophotometric technique. At pH > 8.0 the reduction process involves two reversible 2-electron steps, whose species are generated by a protonation equilibrium of anthraquinone group. The results shows that 60% of color removal was obtained after 3 hours of RB4 dye electrolysis at acidic and neutral conditions and only 37% at alkaline conditions. Simultaneously 64% of total organic carbon was removed after electrolysis at pH 2.0.

Transport and reactions of radical cations in DNA: steric and energetic control of reactivity

A series of DNA oligomers was prepared that contain an anthraquinone group (AQ) linked to a 5′-terminus and have 8-methylguanine ( M G) or 8-bromoguainine ( B G) substituted for G at various positions. Irradiation of the AQ injects a radical cation into the oligonucleotide, which migrates through the DNA and reacts primarily at G n sites where n = 2 or 3. Substitution with M G, which has an oxidation potential ( E OX ) slightly below G, traps the migrating radical cation, substitution with B G, which has an E OX above G, does not. However, both M G and B G affect the relative reactivity of the guanines in G n steps. Moreover, a (G) 3 sequence has a much smaller effect on the efficiency of radical cation migration than does M G, which demonstrates that the E OX of G in the (G) 3 sequence is above that of M G. These findings show that the E OX of the base controls the efficiency of radical cation transport and that steric effects influence the relative reactivity of G in G n sequences.

One-electron oxidation of DNA: the effect of replacement of cytosine with 5-methylcytosine on long-distance radical cation transport and reaction.

One-electron oxidation of duplex DNA generates a radical cation that migrates through the nucleobases until it is trapped by an irreversible reaction with water or oxygen. The trapping site is often a GG step, because this site has a relatively low ionization potential and this causes the radical cation to pause there momentarily. Modifications to guanine that lower its ionization potential convert it to a better trap for the radical cation. One such modification is the formation of the Watson-Crick base pair with cytosine, which is reported to very significantly decrease its ionization potential. Methylation of cytosine to form 5-methylcytosine (5-MeC) is a naturally occurring reaction in genomic DNA that may be associated with regions of enhanced oxidative damage. The G.5-MeC base pair is reported to be more rapidly oxidized than normal G.C base pairs. We examined the oxidation of DNA oligomers that were substituted in part with 5-MeC. Irradiation of a covalently linked anthraquinone group injects a radical cation into the DNA and results in strand cleavage after piperidine treatment. For the sequences examined, substitution of 5-MeC for C has no measurable effect on the reactions. Cytosine methylation is not a general cause of enhanced oxidative damage in DNA.

Toward efficient Zn(II)-based artificial nucleases.

A series of cis-cis-triaminocyclohexane Zn(II) complex-anthraquinone intercalator conjugates, designed in such a way to allow their easy synthesis and modification, have been investigated as hydrolytic cleaving agents for plasmid DNA. The ligand structure comprises a triaminocyclohexane platform linked by means of alkyl spacers of different length (from C(4) to C(8)) to the anthraquinone group which may intercalate the DNA. At a concentration of 5 microM, the complex of the derivative with a C(8) alkyl spacer induces the hydrolytic stand scission of supercoiled DNA with a rate of 4.6 x 10(-6) s(-1) at pH 7 and 37 degrees C. The conjugation of the metal complex with the anthraquinone group leads to a 15-fold increase of the cleavage efficiency when compared with the anthraquinone lacking Zn-triaminocyclohexane complex. The straightforward synthetic procedure employed, allowing a systematic change of the spacer length, made possible to gain more insight on the role of the intercalating group in determining the reactivity of the systems. Comparison of the reactivity of the different complexes shows a remarkable increase of the DNA cleaving efficiency with the length of the spacer. In the case of too-short spacers, the advantages due to the increased DNA affinity are canceled due to the incorrect positioning of the reactive group, thus leading to cleavage inhibition.

Mechanism for radical cation transport in duplex DNA oligonucleotides.

We investigated the photoinduced one-electron oxidation of a series of DNA oligomers having a covalently linked anthraquinone group (AQ) and containing [(A)(n)GG](m) or [(T)(n)GG](m) segments. These oligomers have m GG steps, where m = 4 or 6, separated by (A)(n) or (T)(n) segments, where n = 1-7 for the (A)(n) set and 1-5 for the (T)(n) set. Irradiation with UV light that is absorbed by the AQ causes injection of a radical cation into the DNA. The radical cation migrates through the DNA, causing chemical reaction, primarily at GG steps, that leads to strand cleavage after piperidine treatment. The uniform, systematic structure of the DNA oligonucleotides investigated permits the numerical solution of a kinetic scheme that models these reactions. This analysis yields two rate constants, k(hop), for hopping of the radical cation from one site to adjacent sites, and k(trap), for irreversible reaction of the radical cation with H(2)O or O(2). Analysis of these findings indicates that radical cation hopping in these duplex DNA oligomers is a process that occurs on a microsecond time scale. The value of k(hop) depends on the number of base pairs in the (A)(n) and (T)(n) segments in a systematic way. We interpret these results in terms of a thermally activated adiabatic mechanism for radical cation hopping that we identify as phonon-assisted polaron hopping.

Long-distance radical cation migration in duplex DNA: the effect of contiguous A.A and T.T mismatches on efficiency and mechanism.

A series of DNA oligomers was prepared. Each oligomer contained an anthraquinone group (AQ, sensitizer) covalently linked at a 5'-end and two GG steps that surrounded a variable region. The variable region was composed of A.T base pairs or A.A or T.T mismatches. Irradiation of the AQ injected a radical cation (hole) into the DNA that migrated through the duplex, being trapped by reaction with H2O of O2 at the GG steps. The effect of substituting A.A or T.T mismatches for Watson-Crick base pairs was examined. For A.A mispairs, charge transfer through the mismatch region was as efficient as through normal DNA. For the T.T mismatches, radical cation transport was strongly distance-dependent. These findings suggest that A.A mismatches form a zipper-like motif, and charge transport proceeds by a hopping mechanism. In contrast, charge transport through the T.T mismatches (where there are no purines) may proceed by quantum mechanical tunneling.

Long-distance radical cation reactions in DNA three-way junctions: inter-arm interaction and migration through the junction.

DNA three-way junctions (TWJ) are branched molecules having three 'arms'. We studied long-distance radical cation migration in these assemblies by incorporating anthraquinone (AQ) groups linked by a covalent tether to one strand of one arm of the TWJ. Excitation of the AQ at 350 nm results in one-electron oxidation of the DNA, which generates a base radical cation. This leads to relatively inefficient (compared with duplex DNA) strand cleavage at guanines following piperidine treatment of the irradiated samples. When the AQ is linked to the 5'-terminus of arm III by a flexible tether, gel electrophoretic analysis shows that strand cleavage occurs at the guanines in all three arms. We also investigated a TWJ in which the anthraquinone is specifically intercalated in arm III. In this case, a different pattern of strand cleavage is detected. We conclude that there are at least two mechanisms for long-distance radical cation migration in TWJs: (i) by inefficient charge hopping through the junction; (ii) by a through-space, cross-arm interaction when the AQ is on a flexible tether.