A Novel and Expedient Approach to New Thiazoles, Thiazolo[3,2-a]pyridines, Dihydrothiophenes, and Hydrazones Incorporating Thieno[2,3-b]thiophene Moiety

This paper reports details about the synthesis of a series of novel functionalized symmetrical bis-heterocyclic compounds containing a thieno[2,3-b]thiophene motif. Bis-thiazole derivatives 2, 3a-c and thiazolo[3,2-a]pyridine derivatives 4a-c are achieved. The hitherto unknown dihydrothiophene derivatives 6a-dvia bis-pyridimium salt 5 are obtained. Additionally, the novel hydrazonothieno[2,3-b]thiophene derivatives 10a-c are obtained via bis-tosylacetylthieno[2,3-b]thiophene derivative 9. All compounds are characterized by (1)H-, (13)C-NMR, GCMS, IR, and UV-vis spectrometry. These compounds represent a new class of sulfur and nitrogen containing heterocycles that should also be of interest as new materials.     

Synthesis and Antimicrobial Studies of Some Novel Bis-[,,]thiadiazole and Bis-thiazole Pendant to Thieno[2,3-b]thiophene Moiety

The synthetic utility of 3,3'-(3,4-dimethylthieno[2,3-b]thiophene-2,5-diyl)bis (3-oxopropanenitrile) (1) in the synthesis of some novel bis-[1,3,4-thiadiazole] 6a-g and bis-thiazole 10 and 13 derivatives with thieno[2,3-b]thiophene moiety is reported. Antimicrobial evaluation of some selected examples from the synthesized products was carried out and showed promising results.     

Comprehensive and Facile Synthesis of Some Functionalized Bis-Heterocyclic Compounds Containing a Thieno[2,3-b]thiophene Motif

A comprehensive and facile method for the synthesis of new functionalized bis-heterocyclic compounds containing a thieno[2,3-b]thiophene motif is described. The hitherto unknown bis-pyrazolothieno[2,3-b]thiophene derivatives 2a-c, bis-pyridazin othieno[2,3-b]thiophene derivatives 4, bis-pyridinothieno[2,3-b]thiophene derivatives 6a,b, and to an analogous bis-pyridinothieno[2,3-b]thiophene nitrile derivatives 7 are obtained. Additionally, the novel bis-pyradazinonothieno[2,3-b]thiophene derivatives 9, and nicotinic acid derivatives 10, 11 are obtained via bis-dienamide 8. The structures of all newly synthesized compounds have been elucidated by (1)H, (13)C NMR, GCMS, and IR spectrometry. These compounds represent a new class of sulfur and Nitrogen containing heterocycles that should also be of interest as new materials.     

Kinetic study of 3,6-dimethylthieno[3,2-b]thiophene electropolymerisation

A systematic investigation was carried out by means of cyclic voltammetry, chronoamperometry and chronopotentiometry on 3,6-dimethylthieno[3,2-b]thiophene (DMTT) electropolymerisation on vitreous carbon in acetonitrile (ACN) containing 0.1 M LiClO₄. The electrochemical doping–undoping process was reversible and the coulombic efficiency over a charge–discharge cycle was ca. 100%. The electropolymerisation mechanism was unchanged by the presence of methyl groups. When an aluminium electrode was used, poly(DMTT) deposition could only be performed in the potentiostatic mode. In this case, electropolymerisation hindered the pitting process on Al, which was initiated in the early stages of anodisation.     

Electrochemical detection of dopamine and cytochrome c at a nanostructured gold electrode

A nanostructured gold surface consisting of closely packed outwardly growing spikes is investigated for the electrochemical detection of dopamine and cytochrome c. A significant electrocatalytic effect for the electrooxidation of both dopamine and ascorbic acid at the nanostructured electrode was found due to the presence of surface active sites which allowed the detection of dopamine in the presence of excess ascorbic acid to be achieved by differential pulse voltammetry. By simple modification with a layer of Nafion, the enhanced electrocatalytic properties of the nanostructured surface was maintained while increasing the selectivity of dopamine detection in the presence of interfering species such as excess ascorbic and uric acids. Also, upon modification of the nanostructured surface with a monolayer of cysteine, the electrochemical response of immobilised cytochrome c in two distinct conformations was observed. This opens up the possibility of using such a nanostructured surface for the characterisation of other biomolecules and in bio-electroanalytical applications.     

Direct electrochemistry and electrocatalysis of cytochrome c based on chitosan-room temperature ionic liquid-carbon nanotubes composite

A robust and effective composite film combined the benefits of room temperature ionic liquid (RTIL), chitosan (Chi) and multi-wall carbon nanotubes (MWNTs) was prepared. Cytochrome c (Cyt c) was successfully immobilized on glassy carbon electrode (GCE) surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Cyt c were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Cyt c was obtained in 0.1 mol L⁻¹ pH 7.0 phosphate buffer solution (PBS), indicating the Chi-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0 × 10⁻⁶ to 2.6 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ (S/N = 3). The apparent Michaelis-Menten constant (K_m) was calculated to be 0.45 ± 0.02 mmol L⁻¹. Moreover, the modified electrode displayed a rapid response (5 s) to H₂O₂, and possessed good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

A self-assembled cytochrome c/xanthine oxidase multilayer arrangement on gold

A polyelectrolyte multilayer combining cytochrome c (cyt.c) and xanthine oxidase (XOD) is assembled on a gold electrode and investigated with respect to a signal chain formation from a xanthine oxidase substrate in solution. The multilayer assembly is prepared by means of an electrostatic self-assembly technique and consists of two parts each comprising one type of protein, which is responsible for a specific function. The outer part of the film contains XOD immobilized within poly(ethylenimin) layers and is responsible for selectivity towards hypoxanthine (HX) by its enzymatic conversion to uric acid. The inner layers contain cyt.c molecules embedded into a sulfonated polyaniline (PASA) matrix. The signal transfer mechanism within the assembly is proposed to be a mediated one. Thus, cyt.c plays a role of an internal transducer translating a HX concentration into an amperometric electrode response. Formation of the multilayer structure is confirmed by surface plasmon resonance (SPR), electrochemical experiments and UV-vis spectrophotometry. Influence of the multilayer composition on sensor performance is discussed.     

Investigations on the electrochemical properties of new conjugated polymers containing benzo[c]cinnoline and oxadiazole moieties

A four-step route was designed to synthesize 3,8-benzo[c]cinnoline dicarboxylic acid (4). New conjugated polymers, POXD (I) and POXD (T), containing benzo[c]cinnoline and oxadiazole moieties, were obtained by thermal cyclodehydration of their soluble polyhydrazide precursors PHA (I) and PHA (T), respectively. Two reduction peaks were observed for these new conjugated polymers during CV cathodic scan. From the CV voltammograms combined with the results from molecular simulation, we concluded that the first reduction occurred at oxadiazole moiety and benzo[c]cinnoline moiety was responsible for the second reduction. It indicates that oxadiazole has stronger electron affinity than benzo[c]cinnoline. We proposed a mechanism to explain this two-stage reduction process. Due to the planar and electron-accepting ability of benzo[c]cinnoline and oxadiazole moieties, POXD (I) and POXD (T) exhibited very low LUMO (−3.42 and −3.45 eV) and HOMO (−6.23 and −6.27 eV) energy levels. They can be used as hole-blocking or electron-injection layers for OLED applications.     

Development of new dyeing photoinitiators based on 6H-indolo[2,3-b]quinoxaline skeleton

The series of new dyes, which structures are based on 6H-indolo[2,3-b]quinoxaline skeleton that possess characteristic electronic absorption band at a boundary of UV and visible light were tested as potential light absorbing chromophores for photoinitiated polymerization.The studied dyes can be classified into two different groups. The first is the group, so called ‘the branched dyes’, which structures possess the part of molecule that can rotate without restraints and are characterized by low photoinitiation ability. The second, planar and rigid group of molecules provides another chromophores, which possess quite different properties in comparison to that observed for the branched dyes. Their photoinitiation ability is comparable to that observed for many commercially available photoinitiating systems.The location of electronic absorption spectra at a boundary of UV and visible light makes the tested dyes the good candidates for the photoinitiating system applied in dental restorative materials. Their high molar absorption coefficient allows to decrease the dyes concentration in dental formulation in comparison to commonly used camphorquinone.     

A novel conjugated polymer based on cyclopenta[def]phenanthrene backbone with spiro group

Poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[def]phenanthrene)) (PCPP) is a stable blue light emitting conjugated polymer even after annealing at 150 °C or operation of the device in air. The spiro form of PCPP, poly(2,6-(3′,6′-bis(2-ethylhexyloxy)-4,4′-spirobi(4H-cyclopenta[def]phenanthrene))) (spiro-PCPP), has been synthesized by Yamamoto polymerization. The PL emission spectrum of the polymer in THF solution shows a maximum peak at 398 nm, nearly identical with that of PCPP. The PL spectrum of the polymer in the solid state exhibits a maximum peak at 451 nm, which is red-shifted over 50 nm from that of the solution, due to the inter-chain interaction of the polymers. The PL spectra of spiro-PCPP in the mixture of THF and MeOH from 9:1 to 3:7 ratios showed increasing peaks at 458 and 484 nm. With an increased ratio of the hydrophilic solvent (MeOH), the inter-chain interaction of the hydrophobic polymers was enhanced to show peaks at 458 and 484 nm. This phenomenon has the same tendency as compared to the PL spectrum in solid thin film state. The polymer LED with the configuration of ITO/PEDOT/spiro-PCPP/Ca:Al emitted light with maximum peaks at around 463 nm. The emission color of the spiro-PCPP device is sky blue with the CIE coordinates of (0.14, 0.15), which are close to those of the standard blue (0.14, 0.08).     

Nickel complexes bearing 2-(1H-benzo[d]imidazol-2-yl)-N-benzylidenequinolin-8-amines: Synthesis,structure and catalytic ethylene oligomerization

A series of 2-(1H-benzo[d]imidazol-2-yl)-N-benzylidenequinolin-8-amines was synthesized and characterized. They are stable as solids while displaying a tendency to decompose in solution. On reaction with NiCl₂, different coordination pattern sets of L·NiCl₂ or [L₂Ni]²⁺·2Cl⁻ are obtainable in THF or ethanol. When activated by Et₂AlCl, the complexes L·NiCl₂ exhibit good to high catalytic activities and selectivities for 1-C₄ in ethylene oligomerization, while the complexes [L2Ni]²⁺·2Cl⁻ hardly showed any activity, which is attributable to nickel coordination by two ligands barring interaction of ethylene with the metal center.     

Two Diterpenoids and a Cyclopenta[c]pyridine Derivative from Roots of Salvia digitaloids

Two new glucosides, salviadigitoside A (1) and salviatalin A-19-O-β-glucoside (2), belonging to the salviatalin type diterpenoids, and a new cyclopenta[c]pyridine, salviadiginine A (3), were isolated from the roots of Salvia digitaloids. Structures of these compounds were determined on the basis of spectroscopic analysis. In addition, compounds 1–3 were evaluated for their anti-inflammatory activity, but the results showed a weak anti-inflammatory activity.     

Computer simulation and SERR detection of cytochrome c dynamics at SAM-coated electrodes

In this paper we present a combined experimental and theoretical study of the heterogeneous electron transfer reaction of cytochrome c electrostatically adsorbed on metal electrodes coated with monolayers of 6-mercaptohexanoic acid. Molecular dynamics simulations and pathways calculations show that adsorption of the protein leads to a broad distribution of orientations and, thus, to a correspondingly broad distribution of electron transfer rate constants due to the orientation-dependence of the electronic coupling parameter. The adsorbed protein exhibits significant mobility and, therefore, the measured reaction rate is predicted to be a convolution of protein dynamics and tunnelling probabilities for each orientation. This prediction is confirmed by time-resolved surface enhanced resonance Raman which allows for the direct monitoring of protein (re-)orientation and electron transfer of the immobilised cytochrome c. The results provide a consistent explanation for the non-exponential distance-independence of electron transfer rates usually observed for proteins immobilized on electrodes.     

A novel DNA biosensor based on ssDNA/Cyt c/l-Cys/GNPs/Chits/GCE

A novel DNA biosensor was fabricated by modified multilayer of ssDNA, cytochrome c, l-cysteine, metal gold nanoparticles and Chitosan (denoted as ssDNA/Cyt c/l-Cys/GNPs/Chits/GCE). The behavior of the DNA biosensor was then investigated by voltammetry, impedance spectrum and atomic force microscope (AFM), and the morphologic differences among each layer of the DNA biosensor were also observed. Results revealed that two well-defined redox peaks exhibited at 0.120 V and 0.362 V, and the amount of adsorbed DNA was 1.672 × 10⁻¹⁰ mol cm⁻². We concluded that the modified electrode could be used to detect DNA with the indicator daunomycin.     

Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V (versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20-200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10⁻⁷ to 8.0 × 10⁻⁶ M and the detection limit was 1.0 × 10⁻⁷ M (three times the ratio of signal to noise, S/N = 3).     

Synthesis of light-emitting π-conjugated poly(pyrimido[5,4-d]-pyrimidine-2,6-diyl) with bulky side chains and high molecular weight

New poly(pyrimido[5,4-d]pyrimidine-2,6-diyl) (PPympym) with bulky dialkylamino substituents (-NR₂, R=hexyl, decyl) was prepared by organometallic dehalogenative polycondensation using a zerovalent Ni complex. The obtained PPympym was soluble in common organic solvents such as CHCl₃ and THF, and GPC analysis (in CHCl₃; vs. polystyrene standards) indicated that new Ppympyms had high number-average molecular weights M_n of 19,100-34,000; they also gave a high [η] value of about 2.1 dl g⁻¹. PPympym showed strong photoluminescence both in CHCl₃ and in film, and greenish-blue electroluminescence from PPympym-based double-layer light-emitting devices (ITO/PEDOTh/PPympym/Ca-Al; PEDOTh, poly(ethylenedioxythiophene)) was observed.     

Synthesis, X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, ¹H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a-f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a-f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a-f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421-444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.     

Direct electrochemistry of Cytochrome c on natural nano-attapulgite clay modified electrode and its electrocatalytic reduction for H2O2

Natural nano-structural attapulgite clay was purified by mechanical stirring with the aid of ultrasonic wave and its structure and morphology was investigated by XRD and transmission electron microscopy (TEM). Cytochrome c was immobilized on attapulgite modified glassy carbon electrode. The interaction between Cytochrome c and attapulgite clay was examined by using UV-vis spectroscopy and electrochemical methods. The direct electron transfer of the immobilized Cytochrome c exhibited a pair of redox peaks with formal potential (E0′) of about 17 mV (versus SCE) in 0.1 mol/L, pH 7.0, PBS. The electrode reaction showed a surface-controlled process with the apparent heterogeneous electron transfer rate constant (k_s) of 7.05 s⁻¹ and charge-transfer coefficient (α) of 0.49. Cytochrome c immobilized on the attapulgite modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide (H₂O₂). The calculated apparent Michaelis-Menten constant was 470 μmol/L, indicating a high catalytic activity of Cytochrome c immobilized on attapulgite modified electrode to the reduction of H₂O₂. Based on these, a third generation of reagentless biosensor can be constructed for the determination of H₂O₂.     

Colloidal silver nanoparticles modified electrode and its application to the electroanalysis of Cytochrome c

A colloidal silver nanoparticles (CSNs) chemically modified electrode was prepared and its application to the electroanalysis of Cytochrome c (Cyt. c) was studied. The CSNs were prepared by reduction of AgNO₃ with NaBH₄, and were stabilized by oleate. They could be efficiently immobilized on the surface of a silver electrode. The result showed that the CSNs could clearly enhance the electron transfer process between Cyt. c and the electrode compared with bulk silver electrode. Linear sweep voltammetric measurement of Cyt. c at the chemical modified electrode indicated that the oxidative peak current of Cyt. c was linear to its concentration ranging from 8.0 nmol L⁻¹ to 3.0 μmol L⁻¹ with the calculated detection limit was about 2.6 nmol L⁻¹. The direct electrochemistry of Cyt. c was also studied by cyclic voltammetry.     

Synthesis of highly fluorescent coumarinyl chalcones derived from 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and their spectral characteristics

A series of novel coumarin based chalcones were synthesized by the classical crossed aldol condensation reaction of 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and various substituted benzaldehydes. These novel ketocoumarin derivatives having a 1,4-diethyl-1,2,3,4-tetrahydroquinoxaline framework exhibited brilliant fluorescence. The novel chalcones absorbed in the range of 458-523 nm in various solvents. The wavelength of maximum absorption of these chalcones was found to be significantly longer than their simple acyl derivative known in the literature. The dyes displayed longer wavelength of absorption in the high polarity solvents compared to non-polar solvents. Thermogravimetric analysis of the chalcones revealed that the chalcones possess good thermal stability.