Search

It is well known that copper ions play a critical role in various physiological processes. However, a variety of human diseases are tightly correlated with copper overload. Although there are numerous fluorescent probes capable of detecting copper ions, most of them are "turn-off" probes owing to copper (II) ions fluorescence quenching effect, resulting in poor sensitivity. Herein, a novel "turn-on" near-infrared (NIR) fluorescent probe PZ-N based on phenoxazine was designed and synthesized for the selective detection of copper (II) ions (Cu2+ ). Upon the addition of Cu2+ , the probe could quickly react with Cu2+ and emit strong fluorescence, along with colour change from colourless to obvious blue. Moreover, the probe PZ-N showed good water solubility, high selectivity, and excellent sensitivity with low limit of detection (1.93 nM) towards copper (II) ions. More importantly, PZ-N was capable of effectively detecting Cu2+ in living cells.

Structurally robust tetradentate gold(III)-emitters have potent material applications but are rare and unprecedented for those displaying thermally activated delayed fluorescence (TADF). Herein, a novel synthetic route leading to the preparation of highly emissive, charge-neutral tetradentate [C^C^N^C] gold(III) complexes with 5-5-6-membered chelate rings has been developed through microwave-assisted C-H bond activation. These complexes show high thermal stability and with emission origin (3 IL, 3 ILCT, and TADF) tuned by varying the substituents of the C^C^N^C ligand. With phenoxazine/diphenylamine substituent, we prepared the first tetradentate gold(III) complexes that are TADF emitters with emission quantum yields of up to 94 % and emission lifetimes of down to 0.62 μs in deoxygenated toluene. These tetradentate AuIII TADF emitters showed good performance in vacuum-deposited OLEDs with maximum EQEs of up to 25 % and LT95 of up to 5280 h at 100 cd m-2 .

Herein, the synthesis of the novel acceptor-donor-acceptor (A-D-A)-structured small molecule Si-PO-2CN based on dithienosilole (DTS) as building block flanked by electron-rich phenoxazine (POZ) units, which are terminated with dicyanovinylene, is presented. Si-PO-2CN showed unique electrochemical and photophysical properties and has been successfully employed in perovskite solar cells (PSCs) as well as in bulk heterojunction organic solar cells (OSCs). The PSCs fabricated with dopant-free Si-PO-2CN as hole-transport material (HTM) exhibited a power conversion efficiency (PCE) of 14.1 % (active area=1.02 cm2 ). Additionally, a PCE of 5.6 % has been achieved for OSCs, which employed Si-PO-2CN as p-type donor material when blended with a [6,6]-phenyl C71 butyric acid methyl ester (PC71 BM) acceptor. The versatile application of Si-PO-2CN provides a pathway for further implementation of DTS-based building blocks in solar cells for designing new molecules.

In 1982, Buckley et al. reported on the hydroxy-functionalized derivative of 6,13-diazapentacene (DAP), namely 5,12-dihydroxo-6,13-diazapentacene. In an attempt to reproduce the synthetic procedure, ¹H NMR and ¹³C{¹H} NMR spectroscopic data revealed the formation of a constitutional isomer of the supposed compound. A single crystal X-ray structure determination elucidated the actual structure of the dark violet product, namely 6-amino-5H-dibenzo[a,h]phenoxazin-5-one (2), a benzo[a]phenoxazine derivative. These kinds of compounds are, along with a wide range of pharmacological applications, known for their specific fluorescent properties, which were analyzed for compound 2. Furthermore, it was shown, that 2 can be utilized as reagent for the synthesis of other benzo[a]phenoxazine derivatives, herein 6-(dimethylamino)-5H-dibenzo[a,h]phenoxazin-5-one (3)

Photoredox catalysis is a versatile approach for the construction of challenging covalent bonds under mild reaction conditions, commonly using photoredox catalysts (PCs) derived from precious metals. As such, there is need to develop organic analogues as sustainable replacements. Although several organic PCs have been introduced, there remains a lack of strongly reducing, visible-light organic PCs. Herein, we establish the critical photophysical and electrochemical characteristics of both a dihydrophenazine and a phenoxazine system that enables their success as strongly reducing, visible-light PCs for trifluoromethylation reactions and dual photoredox/nickel-catalyzed C-N and C-S cross-coupling reactions, both of which have been historically exclusive to precious metal PCs.

Several benzo[a]phenoxazine dyes containing a maleimide moiety have been synthesised and characterised by proton nuclear magnetic resonance spectroscopy and mass spectrometry. The spectroscopic properties, such as absorption and emission spectra, of these dyes – 9-maleimido-5H-benzo[a]phenoxazin-5-one (7a), 6-chloro-9-maleimido-5H-benzo[a]phenoxazin-5-one (7b), and 6-bromo-9-maleimido-5H-benzo[a]phenoxazin-5-one (7c) – were examined. These compounds were evaluated as potential fluorescent and colorimetric probes for the detection of biothiols. Results show that the studied compounds exhibit colorimetric and fluorescent responses to l-cysteine at pH 7.4. In the presence of l-cysteine, the fluorescence intensity of synthesised dyes is greatly enhanced. The addition of l-cysteine to solutions of dyes 7a to 7c also results in red shifts of their absorption bands. The cytotoxic effect of tested dyes 7a to 7c against human neuroblastoma cells (SH-SY5Y) was determined by MTT assay. The fluorescent response of these compounds to thiols SH-SY5Y was examined. The results show that the tested compounds exhibit fluorescent response in this cell line, and the benzo[a]phenoxazine dyes substituted in the 6-position with a halogen (7b and 7c) are less toxic against cells under experimental conditions than their unsubstituted analogue (7a).

A newly designed electron donor-acceptor conjugate consisting of an endohedral dimetallofullerene (La2 @Ih -C80 ) and phenoxazine (POZ) was successfully synthesized under Prato conditions. Our results document that the 1,3-dipolar cycloaddition took place across the [5,6] junction to afford exclusively the corresponding [5,6] cycloadduct. The structure of the conjugate was characterized by means of NMR spectroscopy, absorption spectroscopy, and electrochemical studies. Computational calculations suggest that the electron density of the highest occupied molecular orbital (HOMO) is distributed on the POZ moiety, whereas that of the lowest unoccupied molecular orbital (LUMO) is located at the endohedral La atoms, leading to efficient separation of the HOMO and LUMO in the conjugate. Time-resolved absorption spectroscopic investigations and spectroelectrochemical measurements corroborate the formation of the energetically low-lying (La2 @Ih -C80 ).- -(POZ).+ radical-ion-pair state by means of ultrafast through-space electron transfer.

Considering different solar dyes configuration, four novel metal-free organic dyes based on phenoxazine as electron donor, thiophene and cyanovinylene linkers as the π-conjugation bridge and cyanoacrylic acid as electron acceptor were designed to optimize open circuit voltage and short circuit current parameters and theoretically inspected. Density functional theory and time-dependent density functional theory calculations were used to study frontier molecular orbital energy states of the dyes and their optical absorption spectra. The results indicated that D2-4 dyes can be suitable candidates as sensitizers for application in dye sensitized solar cells and among these three dyes, D3 showed a broader and more bathochromically shifted absorption band compared to the others. The dye also showed the highest molar extinction coefficient. This work suggests optimizing the configuration of metal-free organic dyes based on simple D- π-A configuration containing alkyl chain as substitution, starburst conformation, and symmetric double D- π-A chains would produce good photovoltaic properties.

As pseudo-capacitive materials, conducting polymers are generally attractive as they have high charge density and low cost. In this work, two novel conjugated ladder polymers based on phenoxazine were synthesized and applied as electrode materials in aqueous symmetric supercapacitors. Their electrochemical properties were investigated in two-electrode configuration. Owing to the good hydrophilicity and perfect backbone conjugation, the acid-doped polymer greatly outperformed the intrinsic ones, and achieved a specific capacitance of 311 F g-1 with an energy density of 10.1 Wh kg-1 at a current density of 1 A g-1 in an aqueous sulfuric acid electrolyte, which performance capacitated the material to be a potential competitor to the classical polymer electrode materials for powerful supercapacitors. In addition, a type of sheet-like supercapacitor was also developed to verify the practicability of the material, which was easy to be used as a tandem capacitor.

Nile red and Nile blue are highly fluorescent and photostable organic dyes from the benzo[a]phenoxazine family. They have been used as histological stains for imaging lysosomes and lipids in vitro. The dyes' high quantum yields and solvent-dependent optical properties make them ideal scaffolds for the development of pH probes and local polarity indicators. Reviews of the literature in this area are scarce with only one review ever published in 2006. It has been 10 years since and the field has evolved. This review aims to expand upon topics covered by the previous reviewers and to report on recent advances in the literature. As authors, we hope to convey a sense of scope and to spark renewed interest in this useful niche of dye chemistry.

Three isomeric phenanthroline compounds, namely o-PXZP, m-PXZP, and p-PXZP, are constructed by incorporating electron-donor phenoxazine unit into ortho-, meta-, or para-positions of a rigid electron-acceptor phenanthroline core. This approach functionalizes these compounds to exhibit thermally activated delayed fluorescence (TADF) characteristics with microsecond-scale photoluminescence (PL) lifetimes. Their thermal, electrochemical properties, emissive characteristics, and energy levels can be finely tailored through isomer engineering. The meta- and para-linking compounds (m-PXZP and p-PXZP) possess higher decomposition temperatures, deeper lowest unoccupied molecular orbital levels, higher PL quantum efficiencies, smaller singlet–triplet energy splitting, and reduced DF lifetimes relative to their ortho-disposition isomer (o-PXZP). Consequently, a green fluorescence organic light-emitting diode (OLED) based on m-PXZP achieves a maximum external quantum efficiency of 18.9%, and has a slow efficiency roll-off of 28% at the luminance of 1000 cd m−2. Notably, m-PXZP-based device exhibits a nearly 100% utilization efficiency of electro-generated singlet and triplet excitons. These results demonstrate for the first time that phenanthroline derivatives can be employed as TADF emitters for high-efficiency OLEDs. The isomer engineering for TADF emitters provides a simple method to extend structure diversity of TADF emitters, and moreover it provides a flexible method to optimize optoelectronic properties and thereby manipulate electroluminescence performance.

The synthesis of a set of tetrazine-bearing fluorogenic dyes suitable for intracellular labeling of proteins in live cells is presented. The red excitability and emission properties ensure minimal autofluorescence, while through-bond energy-transfer-based fluorogenicity reduces nonspecific background fluorescence of unreacted dyes. The tetrazine motif efficiently quenches fluorescence of the phenoxazine core, which can be selectively turned on chemically upon bioorthogonal inverse-electron-demand Diels-Alder reaction with proteins modified genetically with strained trans-cyclooctenes.

A number of anthraquinone imines (1–3, 5–8) and an anthrone diamine (4) have been synthesized by the condensation of 9,9-dimethoxy-10-anthrone derivatives (13, 18, and 23) with different primary aromatic amines and, in the case of benzoacridinone 7, by a subsequent photoinduced 6 electrocyclization. All the compounds were fully characterized by UV/Vis spectroscopy, cyclic voltammetry, and X-ray diffraction. The XRD analyses proved that the preferred tautomers of 1, 3, and 5 have the 9-amino-1,10-anthraquinone or 1-hydroxy-9,10-anthraquinone imine core. Furthermore, aminoanthraquinone 9 and phenoxazine 10 were synthesized by the reaction of 1-amino-9,10-anthraquinone with 3,5-di-tert-butylphenyl-o-benzoquinone, which led to dyes with high molar extinction coefficients of up to 101600 L mol–1 cm–1. In addition, the absorption maxima of the 1-hydroxy-9,10-anthraquinone imines appear in the range of 246 and 591 nm, at variance with the absorption maxima of the parent 1-hydroxy-9,10-anthraquinone. The cyclic voltammograms of all the compounds show multiple redox processes. In addition, the optical absorption and photoluminescence spectra of 3 show suppressed segregation on mesoporous TiO2 and an almost pure molecule photoluminescence spectrum containing two main transitions. A new excitonic transition was found in the crystal form.

The synthesis of some new thiophenyl-derivatized and furanyl-derivatized phenothiazine and phenoxazine dyestuffs is described. This was achieved by two methods after the synthesis of 6-chloro-5H-benzo[a]phenothiazin-5-one, 6-chloro-5H-benzo[a]phenoxazin-5-one, and 6-chloro-5H-naphtho[2,1-b]pyrido[2,3-e][1,4]oxazin-5-one intermediates via anhydrous base condensation reaction of 2,3-dichloro-1,4-naphthoquinone with 2-aminothiophenol, 2-aminophenol, and 2-aminopyridinol, respectively. The first method involved treatment of tributyl(thien-2-yl) or tributyl(furan-2-yl) stannane with chlorophenothiazine/chlorophenoxazine under mild basic chemical formula (CsF) and 1,4-dioxane or toluene solvent at 80°C to supply dazzling yellow solid in high yields. In the second method, the catalytic system was pre-activated in acetonitrile, followed by addition of coupling partners and K3PO4 to obtain high melting and variety of highly colored products in moderate to high yields. The reaction conditions were compatible with unprotected N–H and carbonyl functional groups. The intense colors of these dyes and their ease of re-oxidation of Na2S2O4-reduced derivatives make them suitable as vat dyes. Also, they were found to be good colorants for textiles, papers, paint, ink, soap, polish, candle, and plastic materials.

Chloro-substituted phenothiazines and phenoxazines were successfully derivatized with phenylboronic and styrylboronic acids using Suzuki–Miyaura cross-coupling reaction catalyzed by Pd(0)/XPhos for the first time in good yields. The protocol employed 4 mol% Pd and 7 mol% XPhos with K3PO4 in acetonitrile at 80°C. The reaction condition is compatible with carbonyl and unprotected N–H groups in substrates. Structural assignments were established by combined spectroscopic (UV, IR, 1H, and 13C NMR), MS, and elemental analytical data.

Novel phenoxazine dyes are successfully introduced as sensitizers into dye-sensitized solar cells (DSCs) with cobalt-based electrolyte. In sensitizers with triphenylamine (TPA) groups recombination from electrons in the TiO2 conduction band to the cobalt(III) species is suppressed. The effect of the steric properties of the phenoxazine sensitizers on the overall device performance and on recombination and regeneration processes is compared. Optimized DSCs sensitized with IB2 having two TPA groups in combination with tris(2,2′-bipyridyl) cobalt-(II/III) yield efficiencies of 6.3%, similar to that of IB3, which is equipped with mutiple alkoxy groups. TH310 with only one TPA group gives lower efficiency and open circuit voltage, while IB1 without TPA groups performs even worse. These results demonstrate that both TPA groups on the IB2 are needed for an efficient blocking effect. These results reveal a possible new role for TPA units in DSC sensitizer design. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multi-branched multi-anchoring metal-free dyes as photosensitizers for dye-sensitized solar cells (DSSCs) are reviewed. The article outlines design strategies, main synthetic routes and optical and photovoltaic properties of two families of multi-branched sensitizers: (a) D–(π–A)n (D = donor, π = π-spacer, A = acceptor/anchoring functionality) structures containing arylamine, carbazole, phenothiazine or phenoxazine derivatives as D groups, and (b) multi-donor multi-anchoring architectures from interconnected mono-branched D–π–A arms, together with X- and Y-shaped dyes. Although this class has been reported only in the last five years, a variety of molecular architectures, donors, and π-spacers have been used and combined in multi-branched molecules. The multi-branched geometry induces distinctive features including enhanced qualitative and quantitative optical properties, increased currents and quantum efficiencies, and control of molecular aggregation.

A series of novel (1H-benzo[d]imidazole-2-yl)-6-(diethylamino)-3H-one-xanthene, phenoxazine, and oxazine derivatives have been synthesized from 2-(2′,4′-dihydroxyphenyl) benzimidazole intermediate. Synthesized compounds 8a, 8b, 8c, 8d are fluorescent in solution, photophysical properties of compounds were studied and results revealed that compounds absorb and emit in UV–visible region with good fluorescence quantum yield. Synthesized compounds are thermally stable up to 300°C. The antibacterial activities of the synthesized compounds were studied by the well-diffusion method. Escherichia coli (ATTC-25922), Staphylococcus aureus (ATCC-25923), Micrococcus (ATCC-4698), and Bacillus subtilis (ATCC-55422) were used to investigate the antibacterial activities.

Palladium-catalyzed aminations of bulky aryl halides such as meso-bromoporphyrins and 9-haloanthracenes with diarylamines provided efficient syntheses of meso-aminoporphyrins and 9-aminoanthracenes. Commercially available and air-stable Pd-PEPPSI complexes that have N-heterocyclic carbene (NHC) as ligands have the highest catalytic activities. The scope of diarylamines is wide enough to use diphenylamine, phenoxazine, phenothiazine, 9,10-dihydroacrydine, and carbazole.

A novel reductive N-methylation protocol under acidic conditions with the TTT (1,3,5-trioxane–triethylsilane–trifluoroacetic acid) system is disclosed. This method is highly specific for aromatic amines and several N-heterocycles (indoles and annulated analogues, phenoxazine, phenothiazine), insensitive to steric hindrance, and compatible with a wide range of functional groups. Further the N-methylation step can be combined with an in situ N-Boc deprotection. Compounds in which the nucleophilicity of the NH group is eliminated by protonation under the reaction conditions (aliphatic amines, azaarenes of noteworthy basicity) are inert. In several examples, it was demonstrated that the TTT system is complementary to other N-methylation protocols.

A highly colored impurity formed at low levels during the preparation of 3-amino N,N-dimethyl salicylamide was isolated and identified as 2-amino-N,N,N′,N′-tetramethyl-3-oxo-3H-phenoxazin-4,6-dicarboxamide using mass spectrometry and two-dimensional NMR methods that included long-range 1H-15N heteronuclear chemical shift correlation data to assemble the proton-deficient “right-half” of the 2-aminophenoxazin-3-one nucleus. The structure was independently confirmed using computer-assisted structure elucidation methods and by synthesis.

A series of metal-free organic dyes with a core phenoxazine chromophore have been synthesized and tested as sensitizers in dye-sensitized solar cells. Overall conversion efficiencies of 6.03-7.40% were reached under standard AM 1.5G illumination at a light intensity of 100 mW cm(-2) . A clear trend in electron lifetime could be seen; a dye with a furan-conjugated linker showed a shorter lifetime relative to dyes with the acceptor group directly attached to the phenoxazine. The addition of an extra donor unit, which bore insulating alkoxyl chains, in the 7-position of the phenoxazine could increase the lifetime even further and, together with additives in the electrolyte to raise the conduction band, an open circuit voltage of 800 mV could be achieved. From photoelectron spectroscopy and X-ray absorption spectroscopy of the dyes adsorbed on TiO(2) particles, it can be concluded that the excitation is mainly of cyano character (i.e., on average, the dye molecules are standing on, and pointing out, from the surface of TiO(2) particles).

The rate constants of hydrodesulfurization of phenothiazine, phenoxathiine thianthrene and thioxanthene on sulfided NiO-MoO3/γ-Al2O3 catalyst, at 340°C under 70 bar H2, are similar to one another and about 10-fold higher than that of dibenzothiophene. From comparison with HDS of dibenzothiophene, the presence of a second heteroatom, N,S,O or of a methylene group has no or little effect on the HDS rates of the title compounds. The observed rate enhancement could result from differences in the strength of adsorption between the adsorbed state and the transition state (anchor effect) which depends on whether the molecules are planar or folded. The comparison of the rate constants of hydrodeoxygenation of homologous oxygenated compounds, xanthene and phenoxazine, with that of dibenzofurane leads to the same conclusion.

Carbon paste electrodes modified with a phenoxazine derivative, Meldola blue, and a phenothiazine derivative, methylene green, both strongly adsorbed on a synthetic zeolite were investigated using either glassy carbon powder (Sigradur K, SK) or single-walled carbon nanotubes (SWCNT) as conductive electrode material. In the case of SWCNT based electrodes, the formal potential of both mediators was pH dependent, as expected for a redox process involving proton transfer. In contrast, the formal potential of both mediators of SK based modified electrodes was practically insensitive to pH. This behavior is discussed in terms of interactions existing in the heterogeneous system mediator-zeolite-electrode material.

Bioelectrodes employing the conversion of N-substituted phenothiazine/hexacyanoferrate(II) and N-substituted phenoxazine/hexacyanoferrate(II) that act as synergistic substrates were built using graphite electrode and recombinant laccase. The response of the bioelectrodes to low reactive substrate (hexacyanoferrate(II)) increases 2.9–97 times in presence of high reactive phenothiazine or phenoxazine mediator. The sensitivity of the bioelectrodes reaches 0.5–14.3 A/M⋅cm2. To background a scheme of bioelectrodes action the kinetics of laccase-catalyzed synergistic substrates oxidation was investigated in homogenous solution. A satisfactory agreement of experimentally determined rate constants and calculated using parameters of bioelectrocatalytical system confirms the scheme of bioelectrodes action.

Antioxidant effects of phenothiazine (PtzNH), phenoxazine (PozNH), and iminostilbene (IsbNH) on the oxidation of linoleic acid (LH) and DNA induced by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) were investigated in this work. LH was suspended in the liposome of dipalmitoyl phosphatidylcholine (DPPC) to mimic a biomembrane. In the course of AAPH-induced oxidation of LH, the inhibition period (tinh) generated by PtzNH, PozNH, and IsbNH was proportional to the concentrations of PtzNH, PozNH, and IsbNH employed. The abilities of PtzNH, PozNH, and IsbNH to protect LH were similar to that of trolox (6-hydroxyl-2,5,7,8-tetramethylchroman-2-carboxylic acid). Quantum chemical calculations elucidated that the nonplanar configurations of PtzNH, PozNH, and IsbNH transformed to planar ones when they were converted into radicals. In addition, spin-densities (SDs) on the N atom in the radicals derived from PtzNH, PozNH, and IsbNH were calculated. The N atom in the radical of PtzNH possessed the lowest SD, indicating that the radical of PtzNH was the most stable one. Moreover, PtzNH, PozNH, and IsbNH were applied to protect the DNA against AAPH-induced oxidation, in which PozNH and IsbNH were able to generate tinh. The tinh generated from PozNH and IsbNH was also proportional to their concentrations. The antioxidant effect of PozNH on the oxidation of DNA was higher than that of IsbNH. Copyright © 2009 John Wiley & Sons, Ltd.

Various phenoxazine, phenothiazine, phenazine, indophenol and bipyridilium derivatives were tested for their effectiveness as redox mediators in microbial fuel cells containing Alcaligenes eutrophus, Bacillus subtilis, Escherichia coli, or Proteus vulgaris as the active biological agent, and glucose or succinate as the oxidisable substrate. A ferricyanide-Pt cathode was used. The open-circuit cell e.m.f.′s increased in the order of increasing negative formal redox potentials at pH 7(E7m) of the redox compounds. Several of the redox agents worked well as mediators, maintaining steady currents over several hours, and thionine was found to be particularly effective in maintaining relatively high cell voltages when current was drawn from the cell. A number of the compounds tested did not function well, either because they were incompletely or slowly reduced by the microorganisms or because of their instability. P. vulgaris, with thionine as mediator and glucose as substrate, showed the best performance in a fuel cell. This system was examined in some detail under various conditions of external load to establish the effects of organism concentration, mediator concentration, and substrate addition. Coulombic outputs from these cells were calculated by integration of the current-time plots. Coulombic yields of 30–60% were obtained, on the basis of (theoretical) complete oxidation of added substrate to CO2 and water.

An investigation of the photosensitization of triarylsulfonium salts at wavelengths greater than 400 nm was carried out with phenothiazine and phenoxazine compounds possessing extended benzenoid conjugation. Accordingly, three isomeric benzophenothiazines and 12H-benzo[b]phenoxazine were prepared and employed for the photosensitization of several different types of triarylsulfonium salts. These compounds display a tail absorption that extends at least to 450 nm, making them useful for conducting photopolymerizations using long wavelength emission sources. The photosensitized vinyl and ring-opening polymerizations of a number of monomers were conducted and the results are reported in this communication.

The major objective was to measure the trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) equivalent antioxidant capacity (TEAC) of carbazole derivatives (Ar2NHs) by means of scavenging 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS+·). The Ar2NHs included phenoxazine (PozNH), phenothiazine (PtzNH), iminostilbene (IsbNH) and diphenylamine (DpaNH), and the TEAC of trolox, α-tocopherol (TocH), l-ascorbic acid (VC) and l-ascorbyl-6-laurate (VC-12) were measured as well. The TEAC results revealed that the ability to scavenge DPPH (PozNH > IsbNH ~PtzNH ~TroH ~TocH ~VC ~VC12), differed from the ability to scavenge ABTS+ (PtzNH > IsbNH > PozNH > DpaNH ~TroH ~TocH ~VC ~VC12). CazNH did not react with DPPH and ABTS+·. Furthermore, the addition of acetic acid accelerated the reaction rate of Ar2NH to scavenge DPPH, suggesting that a sequential proton loss electron transfer (SPLET) mechanism occurred with amine-type antioxidants during the trapping of DPPH. In contrast, the addition of acetic acid or pyridine reduced the reaction rate of Ar2NH to scavenge ABTS+., suggesting that the hydrogen atom transfer (HAT) mechanism is the basis for the reaction that is occurring.

Reductive acetylation of 3-aminophenoxaz-2-one (II) gave 3-acetylamino-2-acetoxy-phenoxazine (IV). Thermolysis of (IV) gave 2-methyl-5H-oxazolo(4,5-b)phenoxazine (V). The styryl derivatives (VIII) were synthesised by condensation of (V) with aromatic aldehydes. Quaternisation of (V) was carried out giving (VII). Oxidation of (V) using SeO2 gave 2-formyl-5H-oxazolo(4,5-b)phenoxazine (VI). Fragmentation patterns of certain of the products under electron impact are suggested.

Brilliant cresyl blue (BCB), one of the phenoxazine dyes, was electropolymerized on the glassy carbon (GC) electrode. The resulting electroactive polymer film could provide more active sites for anodic oxidation of nitrite, based on which a novel nitrite sensor was developed. The optimized fabrication and sensing conditions were investigated. This sensor exhibited high sensitivity, low detection limit and simple operation toward the electrochemical oxidation of nitrite. It was successfully applied to the determination of nitrite in some food samples and the results were consistent with those obtained with the standard spectrophotometric procedure.

In order to investigate an effective method for carrier injection into the phosphor of organic electroluminescent (EL)devices, we synthesized fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] derivatives containing hole-trapping moieties, such as diphenylamine, carbazole, and phenoxazine. Their photoluminescent maxima were observed around the maximum of Ir(ppy)3. These values were slightly shifted depending on the hole-trapping moieties: redshifted due to diphenylamine and blueshifted due to carbazole and phenoxazine. Further, these moieties affected the oxidation potentials of Ir complexes in cyclic voltammetry. EL devices using an Ir complex with diphenylamine exhibited high EL performance because 1,1-bis[4-(di-p-tolylamino)phenyl]cyclohexane (TAPC) was employed as a hole-transporting layer. The maximum external quantum efficiency (ηext) was recorded as 12.2 %. This value is comparable to that observed in a device using Ir(ppy)3. These results indicate that the diphenylamino substituent is favorable to serve as a hole-trapping moiety of Ir(ppy)3. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The electrochemical conversion of N-substituted phenoxazines (NSP's) bearing a CH2CH2X substitute (where XOH, COOH, CH2NH2, CH2SO3H, CH2NHCOR) was investigated using cyclic voltammetry on a bulk gold electrode and a thin-layer spectroelectrochemical cell. The electrochemical oxidation of NSP's on the gold electrode was quasi-reversible and proceeded in a diffusion-controlled regime. The formal redox potential of NSP's covered the range from 0.39 to 0.45 V vs. SCE. The electrochemical oxidation of NSP's in the thin-layer spectroelectrochemical cell produced radical cations that showed absorbance at 385, 410 and 530 nm. Electrochemical conversion fitted the general voltammetric current-potential equation of a reversible wave, whereas electrolysis at constant potential showed a typical Cottrell behavior. Combining of NSP's with a biologically-relevant theophylline molecule did not change electrochemical and spectral properties of the phenoxazine core. Theophylline enlarged with NSP's demonstrated electrochemical and biocatalytic behavior similar to that of NSP's. The investigated NSP's possess electrochemical and spectral properties that are useful as biomolecular labels for electroanalysis.

Reagentless biosensors sensitive to hydrogen peroxide have been developed and compared. These biosensors are comprised of a carbon paste electrode modified with horseradish peroxidase (HRP) and one phenothiazine (methylene blue), one phenoxazine (meldola's blue) or one phenazine (phenazine methosulfate) dye adsorbed on silica gel modified with niobium oxide (SN). The enzyme was immobilized onto the graphite powder by cross-linking with glutaraldehyde and mixing with one of the electron transfer mediators (dyes) adsorbed on SN. The amperometric response was based on the electrocatalytic properties of the dye to mediate electrons, which were generated in the enzymatic reaction of hydrogen peroxide under catalysis of HRP. The dependence on the biosensor response in terms of pH, buffer, HRP amounts and applied potential was investigated. The best results were found with a biosensor containing methylene blue dye showing an excellent operational stability (around 92% of the activity was maintained after 300 determinations). The proposed biosensor also presented good sensitivity (32.87 nA cm−2 μmol−1 L) allowing hydrogen peroxide quantification at levels down to 0.52×10−6 mol L−1 an optimum response at pH 6.8 and at a potential of −50 mV (vs. SCE) and showing a wide linear response range (from 1 to 700 μmol L−1 for hydrogen peroxide).

Several highly colored by-products were observed chromatographically during the synthesis of 3-amino-N,N-dimethylsalicylamide. One of these, an oxidative dimerization products, bis-(N,N-dimethylcarboxamido)-aminophenoxazinone, was previously isolated and characterized. A tris-(N,N-dimethylcarboxamido)-benzoxazino[3,2-b]phenoxazine, presumably a higher oxidation or further reaction product of the previously isolated and characterized 2-amino-3H-phenoxazin-3-one, has also been isolated and characterized by mass spectrometry and multinuclear NMR methods. We now wish to communicate the results of that structure characterization effort.

Electrochemical properties of beta-(10-phenoxazinyl) propylamine (APPX) and beta-(10-phenoxazinyl) propionic acid (PPX) have been studied in solution, and in immobilized state on gold electrodes modified with monolayers of cystamine and mercaptoundecanoic acid. A reversible diffusion-controlled process of APPX and PPX was observed at a bare gold electrode. The electrochemical conversion of both compounds at modified gold electrodes was a quasireversible diffusion-controlled process. The redox potential of immobilized APPX (443 mV) was similar to the potential in solution, while the value of the immobilized PPX was 131 mV higher than in solution. The immobilized mediators were electrocatalytically active in the fungal peroxidase-catalyzed hydrogen peroxide reduction

Exfoliated graphite (EG) particles covalently functionalized with phenoxazine-based molecules have been used to prepare bulk-modified electrodes. The electrodes are of two types: 1) binder-less covalently modified EG pellets and 2) sol-gel derived composites of silicate and modified EG particles. The covalent modification is confirmed by infrared spectroscopy. The electrochemistry of attached molecules has been carried out to decipher the catalytic activity of immobilized phenoxazines towards NADH oxidation. Fast response time of about 4-6 seconds and a low detection limit of 20 µM have been achieved using these electrodes. The sensor is found to yield a linear range of current response versus concentration between 0.02 and 1 mM of NADH. Biosensing in presence of alcohol dehydrogenase enzyme and NAD + shows a linear response between 1 and 13 mM and the response time for alcohol sensing is found to be 20-30 s. These electrodes are found to be very stable during operation and can be stored without any deterioration over a period of several months.

The photolysis of 1-aryloxy-2-azidoanthraquinones (3) in benzene is described herein which gave 1-hydroxy-2-arylaminoanthraquinones (4) and two types of 5H-naphtho[2,3-c]phenoxazine-8,13-diones (5 and 6). Thermolysis of 3 yielded only one of phenoxazines 5 and small amount of 4. On the other hand thermolysis of 3 in the presence of phenols gave phenoxazine 6 as a major product. The mechanism of the photolysis and thermolysis of 2-azido-1-aryloxyanthraquinones (3) is proposed and supported by the results from semiempirical calculations. A relative contribution of the primary photoreactions-azido group dissociation and aryl group migration was estimated to be 3:1. Photolysis and thermolysis of 4-azido-1-(p-tert-butylphenoxy)-9,10-anthraquinone (8) gave 3-(p-tert-butylphenoxy)-anthra[1,9-cd]-izoxazole-6-one (9) as the only product.

An oligonucleotide analogue containing a novel heterocyclic analogue, the guanidinium G-clamp, was designed to allow formation of five H-bonds to guanosine. The guanidinium group was introduced postsynthetically by treatment of the deprotected oligonucleotide containing a free amino group with a solution of 1H-pyrazole-1-carboxamidine and purified by a combination of size-exclusion chromatography and reversed-phase HPLC. A single incorporation of this modification into an oligodeoxynucleotide sequence was found to increase duplex stability by 13{sup o} and 16{sup o} per modification to RNA and DNA, respectively. Crystals of a self-complementary decamer sequence containing this modification were grown and diffracted to 1-{angstrom} resolution. The structure was solved by molecular replacement and revealed that the modification forms additional H-bonds to O(6) and N(7) of guanosine through the amino and imino N-atoms, respectively. The origins of enhanced duplex stability are also attributed to increased stacking interactions mediated by the phenoxazine moiety of the G-clamp and formation of H-bond networks between the positively charged guanidinium group, H{sub 2}O molecules, and negatively charged O-atoms from phosphates on the adjacent strand.

Currently, Ragaglitazar is being developed as a drug for the treatment of hyperglycaemia and hyperlipidemia in patients with type 2 diabetes. Here, we report the labelling of Ragaglitazar with carbon-14 and tritium for in vivo and in vitro investigations. Two different carbon-14 labelled as well as two different tritium labelled tracers of Ragaglitazar were synthesised. The carbon-14 label was introduced from either ethyl bromo[2-14C]acetate (5 steps/33% overall yield) or [U-14C]phenoxazine (4 steps/48% overall yield). Tritium was incorporated either by catalytic tritiation of an alkene precursor followed by chiral HPLC separation (2 steps/17% overall yield) or by catalytic tritium–halogen exchange of an aryl bromide precursor (2 steps/68% overall yield). Copyright © 2003 John Wiley & Sons, Ltd.