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Addition of p-substituted styrenes, XSty (X = H, Me, MeO, or Cl) to the solutions of o-chloranil, oCA, in dichloromethane resulted in the transient formation of the charge-transfer complexes, [XSty, oCA], followed by the Diels-Alder reaction. At low temperatures, these reactions led to formation of essentially pure endocycloadducts. As expected for the inverse-electron-demand Diels-Alder reaction, the rate constants of the cycloaddition rose with the increase of the donor strength. However, while facile cycloaddition took place in the neat mixtures of the o-chloranil with p-methyl, p-chloro-, or unsubstituted styrenes at low temperatures, a similar system involving the strongest MeOSty donor was surprisingly persistent. X-ray structural measurements and quantum-mechanical computations indicated that this anomaly is related to the fact that the diene/dienophile orientation in the charge-transfer [MeOSty, oCA] complex is opposite to that in the endocycloadduct and in the lowest-energy transition state leading to this isomer. Thus, the proceeding of the cycloaddition requires dissociation of the (dead-end) complex. For the systems involving the oCA diene and either the HSty, ClSty, or MeSty dienophile, the donor/acceptor arrangements in the charge-transfer complexes apparently are consistent with that in the corresponding products, and the formation of these complexes does not hinder the Diels-Alder reaction. [ABSTRACT FROM AUTHOR]

A simple and selective method for the determination of urea based on the paptode technique is described. The sensor was constructed by immobilizing an ionophore on a TLC strip. The procedure is based on the nucleophilic displacement of urea with tetrachloro- p-benzoquinone (chloranil) as an ionophore, and the formed violet-color product was detected using a flatbed scanner. The color of each spot was analyzed to red ( R), green ( G) and blue ( B) values from 0 to 255 using a program written in visual basic (VB) programming language. The calibration graph obtained with the proposed sensor was linear over the range of 0.05-10.00 mg L with a detection limit of 0.01 mg L for urea. Parameters such as pH and concentration of chloranil were optimized. The proposed sensor was successfully applied for the determination of urea in bovine serum, urine and tap water samples. [ABSTRACT FROM AUTHOR]

Several strains of Sphingobium chlorophenolicum have been isolated from soil that was heavily contaminated with pentachlorophenol (PCP), a toxic pesticide introduced in the 1930s. S. chlorophenolicum appears to have assembled a poorly functioning pathway for degradation of PCP by patching enzymes recruited via two independent horizontal gene transfer events into an existing metabolic pathway. Flux through the pathway is limited by PCP hydroxylase. PCP hydroxylase is a dimeric protein that belongs to the family of flavin-dependent phenol hydroxylases. In the presence of NADPH, PCP hydroxylase converts PCP to tetrachlorobenzoquinone (TCBQ). The kcat for PCP (0.024 s-1) is very low, suggesting that the enzyme is not well evolved for turnover of this substrate. Structure-activity studies reveal that substrate binding and activity are enhanced by a low pKa for the phenolic proton, increased hydrophobicity, and the presence of a substituent ortho to the hydroxyl group of the phenol. PCP hydroxylase exhibits substantial uncoupling; the C4a-hydroxyflavin intermediate, instead of hydroxylating the substrate, can decompose to produce H2O2 in a futile cycle that consumes NADPH. The extent of uncoupling varies from 0 to 100% with different substrates. The extent of uncoupling is increased by the presence of bulky substituents at position 3, 4, or 5 and decreased by the presence of a chlorine in the ortho position. The effectiveness of PCP hydroxylase is additionally hindered by its promiscuous activity with tetrachlorohydroquinonc (TCHQ), a downstream metabolite in the degradation pathway. The conversion of TCHQ to TCBQ reverses flux through the pathway. Substantial uncoupling also occurs during the reaction with TCHQ. Photo used with permission from Johannes Rudolph. [ABSTRACT FROM AUTHOR]

The new series of N-, S-, O-substituted 1,4-naphthoquinone and S-, O-substituted 1,4-benzoquinone compounds were synthesized via vinylic substitution. Compounds 3 and 4 were synthesized from the reaction of 1 with 2. Compounds 6, 7 and 8 were synthesized from reaction of 1 with 5. Compounds 10 and 11 were obtained from the reaction of 1 with 9. Compounds 13 and 14 were synthesized from the reaction of 1 with 12. Compounds 16 and 17 were obtained from the reaction of 15 with 2. Photochemical and electrochemical properties of N-, S-, O-substituted quninone compounds were determined by using fluorescence spectroscopy and cyclic voltammetry. Crystal structure of 2-(7-sulphanyl-4-methyl-coumarinyl)-3-(1-ethoxy)-1,4-naphthoquinone 13 was determined by X-ray diffraction method. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The absorption and fluorescence spectra of Cu(II)-phthalocyanine were recorded in different solvents of varying types. The data fitted well to Lippert–Mataga equation thus confirming the dependence of orientation polarizability on the absorbance and emission values. The spectroscopic data also fitted well to the Kamlet–Abboud–Taft model. Density functional calculations were used to assign the absorption in the visible region to a π–π* transition between the HOMO-1 and LUMO of the complex. The visible region transition occurs between orbitals largely based on the phthalocyanine ligand, with no significant Cu character. The fluorescence emission of the molecule was effectively quenched in the presence of tetrachlorobenzoquinone (TCQ). The fluorescence quenching data shows that both static and dynamic quenching are operative in the present system. This may be due to the aggregation of the phthalocyanine complex in solution which arises from π–π stacking of its wide planar aromatic structure. The fluorescence quantum yields suggest that in the excited state the molecule interacts more with an aprotic solvent, while the ground state is preferentially stabilized in the presence of a protic solvent. [Copyright &y& Elsevier]

Abstract: This Letter explores the potential utility of the constrained self-consistent field (CSCF) method as an efficient methodology for estimating the external fields that reproduce desired physical quantities. Using the fact that a Lagrange multiplier introduced in CSCF corresponds to an external field (perturbation), numerical assessments of CSCF were carried out on the benzene molecule. The activation energies and critical electric fields that reverse the polarizations of the ferroelectric material tetrathiafulvalene-p-chloranil (TTF-CA) were efficiently estimated. The numerical assessments demonstrate the potential applicability of CSCF for the practical designs of materials possessing certain desired physical quantities induced by external fields. [Copyright &y& Elsevier]

Charge-transfer interactions of perhydroisoquinoline (PHIQ) with 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (DDQ), p-chloranil (CHL), and 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) in chloroform as a solvent have resulted in stable complexes with a general formula [(PHIQ)(acceptor)] with a molar ratio of 1:1 (donor:acceptor). Elemental (C, H, N) and thermogravimetric (TGA/DTG) analyses, photometric titration, and electronic, infrared, and H NMR spectra were used to give an idea of the charge-transfer interaction between donating and accepting sites. The Benesi-Hildebrand method and its modification were used to determine an association constant (K) and a molar extinction coefficient (ε). [ABSTRACT FROM AUTHOR]

Many bee species are adapted to just a few specific plants in order to collect pollen (oligolecty). To reproduce successfully, it is important for oligolectic bees to find and recognise the specific host flowers. In this study, we investigated the role of floral volatiles used by an oligolectic bee to recognise its host plants. We compared the attractiveness of natural and synthetic scent samples of host flowers to foraging-naïve and -experienced Hoplitis adunca (Megachilidae) bees that are specialised on Echium and Pontechium (Boraginaceae) plants. The investigations showed that naïve H. adunca females are attracted to 1,4-benzoquinone. During their lifetime, bees learn additional floral cues while foraging on host flowers. In contrast to naïve ones, experienced H. adunca females use, in addition to 1,4-benzoquinone, other compounds to recognise their host plants. 1,4-Benzoquinone is an uncommon floral compound only known from the host plants of H. adunca, and is therefore ideally suited to be used as a plant-specific recognition cue. Several arthropods use this compound to deter insect predators. Therefore, 1,4-benzoquinone as an attractant in Echium flowers may have evolved from a primary function as a defensive compound against insect herbivores. [ABSTRACT FROM AUTHOR]

In this work, we describe an electrochemical method using p-chloranil as a mediator and multi-wall carbon nanotube and TiO as sensors for sensitive determination of epinephrine (EP) in aqueous solution at pH = 10.0. It has been found that under optimum condition (pH 10.0) in cyclic voltammetry, the oxidation of EP occurred at a potential about 171 mV less positive than that unmodified carbon nanotube paste electrode. The diffusion coefficient ( D) and the kinetic parameters, such as electron transfer coefficient, ( α) and heterogeneous rate constant ( k) for EP were also determined using electrochemical approaches. The electrocatalytic currents increase linearly with the EP concentration over the range 0.6-135 μM. The detection limits for EP will be equal to 0.25 μM. The relative standard deviation percentage values for 10.0 and 15.0 μM EP were 1.7% and 1.9%, respectively. Finally, this modified electrode was also examined as a selective, simple, and precise new electrochemical sensor for the determination of EP in real sample such as urine and epinephrine injection solution. [ABSTRACT FROM AUTHOR]

A quantitative structure-property relationship (QSPR) study was conducted to develop models to relate the structure of 46 donor compounds to their charge-transfer complex formation constants with chloranil for the first time. Donors were a diverse set of organic compounds having different functional groups. QSPR models were calculated using multiple linear regressions (MLR) and partial least squares regression (PLSR) to predict charge-transfer complex formation constants. Some important descriptors in charge-transfer complex formation were calculated and added to the descriptors taken from DRAGON software. After a reduction step using variable importance in projection, stepwise regression was employed to select the most relevant descriptors and develop the QSPR models. Results of the PLSR and MLR modeling by the selected descriptors were markedly similar. The results showed that descriptors related to nitrogen, carbonyl group, and polarizability strengthen the charge-transfer interactions. [ABSTRACT FROM AUTHOR]

Abstract: The interactions of FeIIPc and FeIIIPc with π-acceptor 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, p-CHL) have been investigated spectroscopically (UV/vis and FT-IR) and spectrofluorimetrically at three different temperatures. The stoichiometry of the complexes was found to be 1:1. The results of electronic spectral studies indicated that the formation constant for FeIIPc-p-CHL system is found to be higher than that for FeIIIPc-p-CHL system. This observation is well supported by the results of fluorescence quenching studies and the association constants calculated for FeIIPc-p-CHL system is 4.2×103 molL−1 and that for FeIIIPc-p-CHL system is 2.2×103 molL−1. The data are discussed in terms of physico-chemical parameters viz. molar extinction coefficient, oscillator strength, dipole moment, ionization potential, dissociation energy and thermodynamic parameters. The results indicated that the formation of π–π CT complex is spontaneous and endothermic. Preliminary studies indicated that the CT complex can effectively be used as a colorimetric agent for sensing amino acids and amines. [Copyright &y& Elsevier]

Abstract: The production of chloranil is regarded as a potentially significant source of unintentional POPs. This research aimed to identify the contamination levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HxCBz), pentachlorobenzene (PeCBz) and polychlorophenols in chloranil samples and identify the formation pathways. The toxicity equivalent (TEQ) values for PCDD/Fs in the chloranil samples ranged from 163 to 1540200pg I-TEQg−1, while the PCB TEQ values ranged from 1.9 to 3.3pg WHO–TEQg−1. High levels of HxCBz, PeCBz and polychlorophenols were also detected in the chloranil samples. The average emission factors were 522.2mg I-TEQt−1 (PCDD/Fs), 0.0026mg WHO–TEQt−1 (PCBs), 32.6mgt−1 (HxCBz), and 136.6mgt−1 (PeCBz). The PCDD/Fs and PCBs are thought to be formed from the polychlorophenols and polychlorobenzenes generated during the chloranil production process. Purification of the chloranil products can reduce the unintentional POPs releases and protect the environment. [Copyright &y& Elsevier]

In this article, we report the structure of a 1:1 charge transfer complex between pyridine (PYR) and chloranil (CHL) in solution (CHCl3) from the measurement of hyperpolarizability (βHRS) and linear and circular depolarization ratios, Dand D′, respectively, by the hyper-Rayleigh scattering technique and state-of-the-art quantum chemical calculations. Using linearly (electric field vector along X) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D= IX,X2ω/IX,Z2ωand D′ = IX,C2ω/IZ,C2ωin the laboratory fixed XYZframe by detecting the second harmonic (SH) scattered light in a polarization resolved fashion. The stabilization energy and the optical gap calculated through the MP2/cc-pVDZ method using Gaussian09 were not significantly different to distinguish between the cofacial and T-shape structures. Only when the experimentally obtained βHRSand the depolarization ratios, Dand D′, were matched with the theoretically computed values from single and double configuration interaction (SDCI) calculations performed using the ZINDO-SCRF technique, we concluded that the room temperature equilibrium structure of the complex is cofacial. This is in sharp contrast to an earlier theoretical prediction of the T-shape structure of the complex. [ABSTRACT FROM AUTHOR]

Cyclometalated Ru(II) complexes having a 3-phenylbenzo[b][1,6]naphthyridine (phbn) ligand have been synthesized and characterized by spectroscopic methods. The photo- and electrochemical redox behavior of the complexes are demonstrated. Complex [Ru(phbn)(bpy)2]PF6 ([1]PF6) readily undergoes proton coupled two electron reduction by chemical, electrochemical, and photochemical methods to generate [Ru(phbnHH)(bpy)2]PF6 ([1HH]PF6). The photochemical oxidation of [1HH]PF6 was also observed in presence of p-chloranil. [ABSTRACT FROM AUTHOR]

Eight new para-quinones and one known analogue have been synthesized from p-chloranil. Five have been structurally characterized by single crystal diffraction, and a range of ligand folding is observed. All nine have been tested for their potency towards Gram(+) S. aureus and Gram(−) E. coli. Quinones 3, 6, 7 and 8 have shown activity towards S. aureus and quinones 3 and 8 also show good activity towards E. coli. [ABSTRACT FROM AUTHOR]

6-Hydroxy-2-methyl(aryl)-1,3-benzoxazoles were synthesized by bromination of N-acetyl(aroyl)-1,4-benzoquinone monoimines. [ABSTRACT FROM AUTHOR]

We describe the novel synthesis of a bis(hydrazone)iron(II) complex in protonated [Fe(Hpbph)2]Cl2 (1) and deprotonated [Fe(pbph)2] (2) forms and several hydrogen-bonded proton-transfer (HBPT) assemblies having different dimensionalities of hydrogen-bonded network structures, [Fe(Hpbph)2](CA)·2CH3OH (3), [Fe(Hpbph)2](HCA)2·2THF (4), and [Fe(Hpbph)2](CA)(H2CA)2·2CH3CN (5) (Hpbph = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone), consisting of a deprotonated Fe(II)-hydrazone complex (2) as a proton acceptor (A) and chloranilic acid (H2CA) as a proton donor (D). The deprotonated complex 2 exhibited two-step reversible protonation reactions to form the double-protonated form 1, and the acid-dissociation constants were determined to be 7.6 and 10.3 in methanol solution. Utilizing this proton-accepting ability of 2, we succeeded in synthesizing HBPT assemblies 3, 4, and 5 from the reactions in CH3OH, THF, and CH3CN, respectively, with the same D/A ratio of H2CA/[Fe(pbph)2] = 10:1. These assemblies were found to have one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) hydrogen-bonded networks with D/A ratios of 1:1, 2:1, and 3:1 for 3, 4, and 5, respectively. In 3, a 1-D hydrogen-bonded chain composed of the alternate arrangement of [Fe(Hpbph)2]2+ and CA2-, {···[Fe(Hpbph)2]2+···CA2-···}∞, was surrounded by solvated methanol molecules to form isolated 1-D hydrogen-bonded chains. In the HBPT assembly 4, a 2-D hydrogen-bonded sheet was formed from two types of hydrogen-bonded chains, {···[Fe(Hpbph)2]2+···HCA-···HCA-···}∞ and {···HCA-···HCA-···}∞, and solvated THF molecules did not form any hydrogen bonds. In 5, two orthogonal hydrogen-bonded chains constructed from the neutral chloranilic acid molecules, {···CA2-···2(H2CA)···}∞, were formed in addition to the 1-D hydrogen-bonded chain similar to that in 3, resulting in the formation of a rigid 3-D hydrogen-bonded network structure. By controlling the dimensionality of the hydrogen bond network, we found that the 2-D HBPT assembly 4 is sufficiently flexible to exhibit interesting vapochromic behavior in response to various organic vapors. [ABSTRACT FROM AUTHOR]

Abstract: The molecular complexes of the donors ketaconazole (KTZ) and oxatomide (OXA) drugs with 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, p-CHL) have been investigated spectroscopically (UV–vis, FT-IR and 1H NMR) and spectrofluorimetrically in different solvents and temperatures. The stoichiometry of the complexes was found to be 1:1. The data are discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, ionization potential, dissociation energy and thermodynamic parameters. The results indicated that the formation of molecular complex is spontaneous and endothermic. The fluorescence quenching studies indicated that the interaction of the donors is spontaneous and the fluorescence quenching increased with an increase in the intensity of complexation with the acceptor. [Copyright &y& Elsevier]

Abstract: Series of 1,n-dicarbazolylalkanes and 1,n-di(3-methylcarbazolyl)alkanes (where n =1–5) were synthesized and the molar extinction coefficients, equilibrium constants, enthalpies, and entropies of their charge-transfer (CT) complexes with the π-acceptors p-chloranil, tetracyanoethylene, and tetracyanoquinodimethane were investigated. 1,n-Di(3-methylcarbazolyl)alkanes formed CT complexes with higher equilibrium constants, more negative enthalpies and entropies than 1,n-dicarbazolylalkanes. Vibrational spectra of CT complexes of one of the donor molecules (1,4-dicarbazolylbutane) with all three acceptors were compared. [Copyright &y& Elsevier]

Abstract: Ultrasonic investigation has been carried out on six ternary systems to establish the complex formation between p-chloranil (acceptor) and six aromatic hydrocarbons (donors), namely, benzene, toluene, o-xylene, m-xylene, p-xylene and mesitylene in DMSO medium at 303.15K and at atmospheric pressure. Studies were carried out in the concentration range of 0.002 to 0.02M of acceptor and donor with equimolar concentration of the two components in solution. The trend in the acoustical parameters and magnitude of excess thermo acoustical parameters has been used to identify the existence of strong intermolecular interaction through charge transfer complex formation. The formation of 1:1 complex was also confirmed by UV–Visible spectroscopic method at 303.15K in these systems. It may be pointed out that the formation constants of the charge transfer complexes determined by Benesi–Hildebrand (spectroscopic) and Kannappan (ultrasonic) methods show similar trend and well establish the influence of structural aspect of the donor aromatic compounds on the stability of charge transfer complexes. [Copyright &y& Elsevier]

Abstract: Electron donor acceptor complexes (EDA) of the 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) as a rich donor were spectrophotometrically discussed and synthesized in solid form according the interactions with different nine of usual π-acceptors like 2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione (p-chloranil; p-CHL), tetrachloro-1,2-benzoquinone (o-chloranil; o-CHL), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), 2,6-dichloroquinone-4-chloroimide (DCQ), 2,6-dibromoquinone-4-chloroimide (DBQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid; CLA), N-bromosuccinimide (NBS), 2,4,6-trinitrophenol (picric acid; PA). Spectroscopic and physical data such as formation constant (K CT), molar extinction coefficient (ɛ CT), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ), resonance energy (R N) and ionization potential (I p) were estimated in chloroform or methanol at 25°C. Based on the elemental analysis and photometric titrations the CT-complexes were formed indicated the formation of 1:1 charge-transfer complexes for the o-CHL, TCNQ, DCQ, DBQ and NBS acceptors but 1:3 ratio for p-CHL, DDQ, CLA and PA, respectively. The charge-transfer interactions were interpretative according to the formation of dative ion pairs [18C6 +, A −], where A is acceptor. All of the resulting charge transfer complexes were isolated in amorphous form and the complexes formations on IR and 1H NMR spectra were discussed. [Copyright &y& Elsevier]

Abstract: A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA)2] and [(o-TOL)(CA)2] have been prepared. The 13C NMR, 1H NMR, 1H-Cosy, and IR show that the charge-transfer chelation occurs via the formation of chain structures O–H⋯N intermolecular hydrogen bond between 2NH2 groups of o-TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning the two reactions in methanol were performed and the measurements show that the donor–acceptor molar ratio was found to be 1:2 using the modified Benesi–Hildebrand equation. The spectroscopic data were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer complexes showed that the complexes were more stable than their parents. The thermodynamic parameters were estimated from the differential thermogravimetric curves. The results indicated that the formation of molecular charge transfer complexes is spontaneous and endothermic. [Copyright &y& Elsevier]

Crystal structures of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates and their solvent-free salts are determined. p-Semiquinone anion radical reveals enhanced aromaticity of the ring compared to the quinone. A pair of π-stacked radical anion (p-semiquinone) rings occurs in crystal structures of potassium and rubidium salts of tetrachlorosemiquinone anion acetone solvates and their potassium tetrabromo analogue. The ring centroid separation distances are about 3.2 Å and carbon–carbon contacts between the contiguous rings are 0.3 Å shorter than the sum of van der Waals radii. The spin-coupling of the two unpaired electrons between the two anion radical rings (forming a stacked dimer) correlates with the diamagnetic property of the crystals. Magnetic properties of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates were examined by electron paramagnetic resonance spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic and spectrofluorimetric techniques have been employed to investigate the structure of the charge transfer (CT) complexes of Trimethoprim (TMP) and Cimitidine (CTD) drugs with 2,3,5,6-tetrachloro-1,4-benzoquinone (p-chloranil, p-CHL). The stoichiometry of the complexes was found to be 1:2 for TMP-p-CHL system and 1:1 for CTD-p-CHL system. The thermodynamic results indicated that the formation of molecular complex between the donors and the acceptor is spontaneous and endothermic. The results of electronic spectral studies indicated that the formation constant for CTD-p-CHL system is found to be higher than that for TMP-p-CHL system. The observation is well supported by the results of fluorescence quenching studies and the association constants calculated for CTD-p-CHL system is 36.2×103 molL−1 and that for TMP-p-CHL system is 2.6×103 molL−1. The kinetic results, in both the cases, indicated that the interaction is first order each with respect to the concentration of the donor and the acceptor. The physico-chemical parameters viz. oscillator strength, dipole moment, ionization potential and dissociation energy of the complexes were also determined and discussed. Structural characterization of the complexes were done using FT-IR and 1H NMR spectral techniques and the results indicated that, in TMP, the free NH2 group while in CTD the pyrazole Ninvolves in complexation with the acceptor, p-CHL. [Copyright &y& Elsevier]

Abstract: This work describes the synthesis of the green and black polymorphic forms of the tetrathiafulvalene–chloranil (TTF–CA) charge transfer salt as pure phases, by solvent-assisted mechanochemistry. Both materials were characterized using laboratory and high-resolution X-ray powder diffraction (XRPD), elemental analysis and scanning electron microscopy (SEM). The high-resolution XRPD pattern of the TTF–CA black polymorph was indexed with a triclinic lattice a =10.756(5)Å, b =11.057(4)Å, c =6.614(2)Å, α =101.36(2)°, β =93.69(3)°, γ =89.37(3)°, V =769.6(5)Å3. The chemical stability of these phases upon heating was investigated using thermogravimetric analysis (TGA), elemental analysis and X-ray powder diffraction (XRPD), indicating that both polymorphs undergo chemical decomposition, and ruling out the transition to an air-stable high temperature polymorph. [Copyright &y& Elsevier]

Abstract: The present work reports vibrational spectra and density functional theory calculations for chloranil, imidazole and their complexes. The experimentally observed infrared and Raman bands have been assigned with the help of calculated vibrational frequencies and potential energy distribution analysis. Some bands of chloranil and imidazole have been found to shift on the complex formation due to partial electronic charge transfer from imidazole to chloranil. The charge transfer between these molecules is also corroborated by the electronic absorption spectroscopy and calculations. The theoretical values of the interaction energy of various possible chloranil–imidazole interactions suggest that the two molecules interact preferably via N and H atoms of imidazole and Cf chloranil with their molecular planes almost perpendicular to each other. [Copyright &y& Elsevier]

Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10 l mol s. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate constant of 0.005 s. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical method is described for the voltammetric determination of isoproterenol in the presence of uric acid using p-chloranil-carbon nanotubes paste electrode. Cyclic voltammetric, chronoamperometric, and electrochemical impedance spectroscopic methods have used to investigate the suitability of p-chloranil as a mediator for the electrocatalytic oxidation of isoproterenol at pH=10.5. Using differential pulse voltammetry, isoproterenol (ISPT) and uric acid (UA) in a mixture can be measured simultaneously and individually with a potential difference of 360mV. The electrocatalytic currents increase linearly with ISPT and UA concentrations over the concentration ranges of 0.015–100μmolL−1 ISPT and 3.0–310μmolL−1 UA. The detection limits for ISPT and UA were equal to 0.009 and 2.3μmolL−1, respectively. The diffusion coefficient and the kinetic parameters such as electron transfer coefficient and heterogeneous rate constant were determined for ISPT, using the electrochemical approaches. The proposed method was successfully applied to the determination of isoproterenol in both ampoule and urine samples. [Copyright &y& Elsevier]

Simple, rapid and highly sensitive spectrofluorimetric methods were developed for the determination of venlafaxine in pure and pharmaceutical preparations. The proposed methods were based on the reaction of venlafaxine as n-electron donor with π-acceptors namely, p-bromanil and p-chloranil. The method for the determination of venlafaxine over a concentration range of 5-100 and 5-150 ng/mL, for p-bromanil and p-chloranil methods, respectively. The intra- and inter-day precisions were satisfactory, the relative standard deviations did not exceed 1.69%. The proposed method was successfully applied to the determination of venlafaxine in its pharmaceutical preparations with good accuracy; the mean recovery percentages were 99.80%. The results were compared favorably with those of the reference method. [ABSTRACT FROM AUTHOR]

A new, simple, selective and more reproducible spectrophotometric method for the determination of trimetazidine (TMZ), a piperizinyl antianginal has been developed and validated. This method was based on the formation of a blue colored chromogen between trimetazidine and chloranil acetaldehyde reagent in DMSO. The chromogen exhibit maximum absorbance at 627 nm with molar absorptivity of 5.205 x 104 lit mol-1 cm-1 in methanol. Beer's law was found to be obeyed in the concentration range of 30 - 65 µg mL-1 with linear regression of 0.9984, while the percentage recovery and the limit of detection 98.81-99.91%, 5.5 µg mL-1 respectively. From the percentage recovery and placebo studies it was concluded that there was no interference of additives during the estimation. This shows the suitability of this method for the routine analysis of the trimetazidine in tablet formulation. [ABSTRACT FROM AUTHOR]

Abstract: A study has been conducted on the effect of specific adsorption of o-chloranil, OCA, at an activated glassy carbon electrode, AGCE, surface on its electrochemical behavior in an aqueous solution. The voltammetric responses of OCA at an AGCE show an anodic prepeak and a cathodic postpeak other than the diffusion main couple in weak acidic and neutral pHs. The anodic prepeak and the cathodic postpeak are ascribed to specific adsorption of OCA. The pK a value of the adsorbed redox couple of OCA at an AGCE is at least by 4 and 2 pK a units higher than those of the free redox couple in solution at bare and activated glassy carbon electrodes, respectively. The slop of (I p)ads/(I p)diff ratio versus ν 1/2 for the cathodic and anodic peaks indicates a stronger adsorption of OCA at AGCE in comparison with OCAH2. The effects of OCA concentration on its adsorption behavior and applied potential on anodic adsorption of OCA at AGCE have been studied and the surface coverage of OCA (Γ OCA) has been calculated. [Copyright &y& Elsevier]

The organic oxidizing agents l.4-benzoquinone and its nontoxic derivative 2,3,5,6-tetrachloro-1,4-benzoquinone have been shown to be alternatives to the toxic and carcinogenic hexavalent chromium which is routinely used in most etching solutions. The newly developed etching solutions delineate both grown-in and process-induced defects in silicon-on-insulator substrates fabricated by the Smart-Cut technology and show a good correlation to the defect densities obtained with a dilute Secco (0.04 M) etching solution serving as a reference. In combination with an aqueous solution of the nontoxic fluorinating agent tetrafluoroboric acid, which has been introduced as an alternative to the very toxic solution of hydrofluoric acid (49%), a completely nontoxic etching solution is presented. An etching mechanism will be discussed, explaining the generation of elemental hydrogen which is formed during the etching process. [ABSTRACT FROM AUTHOR]

A spectrophotometric study of chlorpropamide is described. The method is based on the charge-transfer complexation between chlorpropamide (the π-electron donor) with chloranilic acid (the π-acceptor) to form a violet coloured complex having absorption maxima at 530 nm. Beer's law is obeyed for up to 5-25 μg/ml of chlorpropamide. Results of the analysis of this method were validated statistically by recovery studies. The proposed method is simple, accurate and precise for the quantitative determination of chlorpropamide in bulk and tablet formulations. [ABSTRACT FROM AUTHOR]

With the aid of laser-flash photolysis, the one-electron oxidation of conformationally mobile tetramethoxydibenzobicyclo[4.4.1]undecane (1), using photoexcited chloranil as an oxidant, allows us to show that extended 1•undergoes a conformational transformation to π-stacked folded 1•on a microsecond time scale (τ ≈ 1 μs), which is at least six times longer than that found for the conformationally locked model compound. [ABSTRACT FROM AUTHOR]

Abstract: The charge-transfer complexes of the donor sulfamethoxazole (SZ) with iodine (I2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL) and picric acid (PA) have been studied spectrophotometrically in chloroform or methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CT-complexes in case of four acceptors. The stoichiometry of the complexes was found to be 1:1 ratio by molar ratio method between donor and acceptor with maximum absorption bands (CT band). The data are discussed in terms of formation constant (K CT), molar extinction coefficient (ε CT), standard free energy (ΔG°), oscillator strength (ƒ), transition dipole moment (μ), resonance energy (R N) and ionization potential (I D). The results indicate that the formation constant (K CT) for the complexes were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used. IR, 1H NMR, mass spectra, UV–Vis techniques, elemental analyses (CHN) and TG–DTG investigation were used to characterize the four sulfamethoxazole charge-transfer complexes. [ABSTRACT FROM AUTHOR]

Abstract: Unique nucleophilic substitution and addition reactions of nitrogen and sulfur nucleophiles with 1,4-quinones in aqueous suspension with amines and thiols have recently been demonstrated by us. However, the reactivity of oxygen nucleophiles toward nucleophilic substitution compared to nitrogen and sulfur nucleophiles ‘on water’ is not facile. An unprecedented economical, green methodology approach using ordinary laundry detergent (LD; washing powder, 0.5mol%, reusable)/SDS as surfactant ‘in water’ for nucleophilic substitution by oxygen nucleophiles in 1,4-quinones in excellent yields has been demonstrated. [Copyright &y& Elsevier]

Abstract: Simple, rapid and sensitive spectrophotometric procedures are developed for the analysis of gabapentin in pure form as well as in their pharmaceutical formulations. The methods are based on the reaction of gabapentin as n-electron donor with ninhydrin and pi-acceptors namely, 2,3,5,6-tetrachloro-1,4-benzoquinone, chloranilic acid, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane. The obtained complexes were measured at 568, 230, 314, 304, 335 and 439 nm for ninhydrin, chloranil, Chloranilic acid, DDQ, TCNE and TCNQ respectively. The proposed procedures could be successfully applied to the determination of gabepentin with good recovery; percent ranged from 99.3 to 100.7 The association constants and free energy changes using Benesi–Hildebrand plots are also studied. [Copyright &y& Elsevier]

A new spectrophotometric method was developed for the determination of two important nitroimidazoles; metronidazole (MZ) and tinidazole (TZ). The method was based on the charge-transfer (CT) complexation reaction of reduced forms of metronidazole and tinidazole as π-electron donors and chloranilic acid (CAA) as π-electron acceptor to form a purple-colored complex with a new absorption band at 520 nm which was adopted as the analytical wavelength. Molar absorptivities of 2.741 x 102 L M-1 cm-1 and 2.681 x 102 L M-1 cm-1 were obtained for MZ and TZ, respectively. Optimization of reducing agent and time of reduction revealed the superiority of metal hydrides over reducing metals. Reduction of MZ and TZ was completed at 30°C within 10 min. Optimizations of temperature and time for the complexation reaction revealed that the reaction was completed at 30 °C within 5 min. A 60:40 mixture of 1,4-dioxane:acetonitrile was found to be the best diluting solvent for optimal detector response. The complexes were stable at room temperatures for weeks. Beer's law was observed in the concentration of 5-40 μg ml (MZ) and 4.8-79.2 μg ml-1 (TZ) with low limits of detection of 1.88 and 0.74 μg ml-1, respectively. Overall recoveries of MZ and TZ from quality control samples were 103.19± 2.05 (%RSD = 1.99, n = 12) and 101.63 ±1.41 (%RSD = 1.39) over three days. There was no interference from commonly utilized tablet excipients. No significant difference existed between the results of the new method and the BP titrimetric procedures (p > 0.05). The new CT procedure described in this paper is simple, fast, convenient, accurate and precise and has the novelty of carrying out the reactions at room temperature compared to previously described procedures. The new method could be adopted as an alternative procedure for the quality assessment of MZ and TZ in bulk and dosage forms. [ABSTRACT FROM AUTHOR]

The reaction of 2,6-difluorobenzaldehyde, 2-chloro-6-fluorobenzaldehyde, or 2,6-dichlorobenzaldehyde and ethyl cyanoacetate and thiourea, in the presence of potassium carbonate, yielded a mixture of the cis- and trans-5,6-dihydro-2-thiouracil derivatives 4a-c. Compounds 4a-c, which were found to be resistant to atmospheric oxidation even at high temperatures, were successfully dehydrogenated to 5a-c via prolonged heating with chloranil in toluene. Meanwhile, oxidation of the dihydro derivative 4b by heating in dimethylsufphoxide for 10 min yielded the corresponding 2-thiouracil 5b in 73% yield, in addition to the disulfide derivative 7 as a minor product. [ABSTRACT FROM AUTHOR]

Abstract: BLT2, a low-affinity leukotriene B4 (LTB4) receptor, is a member of the G-protein coupled receptor (GPCR) family and is involved in the pathogenesis of inflammatory diseases such as asthma. Despite its clinical implications, however, no pharmacological inhibitors are available. In the present study, we screened for small molecules that interfere with the interaction between the third intracellular loop region of BLT2 (BLT2iL3) and the Gαi3 protein subunit (Gαi3), using a high-throughput screening (HTS) assay with a library of 1040 FDA-approved drugs and bioactive compounds. We identified two small molecules—purpurin [1,2,4-trihydroxy-9,10-anthraquinone; IC50 =1.6μM for BLT2] and chloranil [tetrachloro-1,4-benzoquinone; IC50 =0.42μM for BLT2]—as specific BLT2-blocking agents. We found that blockade of the BLT2iL3-Gαi3 interaction by these small molecules inhibited the BLT2-downstream signaling cascade. For example, BLT2-signaling to phosphoinositide-3 kinase (PI3K)/Akt phosphorylation was completely abolished by these molecules. Furthermore, we observed that these small molecules blocked LTB4-induced chemotaxis by inhibiting the BLT2-PI3K/Akt-downstream, Rac1-reactive oxygen species-dependent pathway. Taken together, our results show that purpurin and chloranil interfere with the interaction between BLT2iL3 and Gαi3 and thus block the biological functions of BLT2 (e.g., chemotaxis). The present findings suggest a potential application of purpurin and chloranil as pharmacological therapeutic agents against BLT2-associated inflammatory human diseases. [Copyright &y& Elsevier]

A new approach to 3-nitro-2-substituted thiophenes has been developed. Exposure of commercially available 1 ,4-dithane-2,5-diol to nitroalkenes in the presence of 20% triethylamine results in a tandem Michael—intramolecular Henry reaction to form the corresponding tetrahydrothiophene. Subsequent microwave irradiation on acidic alumina in the presence of chloranil effects the solvent free dehydration and aromatization to form 3-nitro-2-substituted thiophenes cleanly and rapidly. A simple workup procedure removes the requirement for purification by chromatography in most cases. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors. [Copyright &y& Elsevier]

We have prepared a novel organic molecule, 2-sulfo-3,5,6-trichloro-1,4-benzoquinone (1), that has both an electron acceptor part (chloranil) and an anionic part (sulfonate). The reduction potential of the PPh4salt is −0.34 V (vs.SCE in PhCN) which indicates it is a weaker acceptor than chloranil (−0.18 V). The anionic acceptor provided one TTF (tetrathiafulvalene) and two BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) salts, the structures and physical properties of which are reported. [ABSTRACT FROM AUTHOR]

Abstract: The development of an efficient hydrogenation method of 17α-hydroxy-6-methylen-pregna-4,9(11)-diene-3,20-dione by using wet (10%) Pd on carbon and triethylamine led us to the corresponding 6α-methyl-pregnane in good yield. This chemoselective process allowed us to set up a large-scale procedure for the synthesis of the ophthalmic drug fluorometholone with 45% overall yield. [Copyright &y& Elsevier]

Abstract: The charge-transfer interactions between the electron donor 4,4′-trimethylenedipiperidine (TMDP) and the acceptors 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil), 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) and iodine have been studied spectrophotometrically in CHCI3 solutions. The formed solid charge-transfer complexes were also isolated and characterized through infrared spectra as well as thermal and elemental analysis. The stoichiometry of the complexes was found to be 1:1 in the case of TMDP–chloranil and TMDP–TBCHD systems and 1:2 in the case of TMDP–DDQ and TMDP–TCNQ systems and 1:3 in the case of TMDP–iodine system. Taking this into consideration along with infrared spectra and thermal and elemental analysis, the formed CT-complexes have the formulas [(TMDP)(chloranil)], [(TMDP)(TBCHD)], [(TMDP)(DDQ)2] [(TMDP)(TCNQ)2] and [(TMDP)I]+·I5 −, respectively. [Copyright &y& Elsevier]

Abstract: The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (K CT), charge transfer energy (E CT) and molar extinction coefficients (ɛ CT) of the formed CT-complexes were obtained. [Copyright &y& Elsevier]

Abstract: The development of an efficient dehydration method of steroidal 4-en-3-ones by using chloranil and BSTFA in the presence of triflic acid in refluxing toluene allowed us, starting from testosterone, to set a large-scale procedure for the synthesis of the anti-cancer drug exemestane in 70% overall yield. [Copyright &y& Elsevier]

Abstract: 2-Substituted benzothiazoles were efficiently synthesized by radical cyclization of thioformanilides induced by chloranil under irradiation in 1,2-dichloroethane and toluene at 80°C. Hydrogen atom abstraction from thiobenzamide by triplet chloranil was the key step of the mechanism, as confirmed by LFP experiments. The methodology developed is simple and afforded the easily isolated products from moderate to good yield. [Copyright &y& Elsevier]

Abstract: The cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of vanadium(V) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) with presence of chloranilic acid as a ligand is presented. The calibration graph obtained for V(V) is linear from 0.25nM (12.7ngL−1) to 150nM (7.6μgL−1) for a preconcentration time of 20s, with correlation coefficient of 0.9992. For a Hg(Ag)FE with a surface area of 6.6mm2 the detection limit for a preconcentration time of 90s is as low as 0.5ngL−1. The repeatability of the method at a concentration level of the analyte as low as 1.3μgL−1, expressed as RSD is 2.1% (n =5). The proposed method was successfully applied and validated by studying the certified reference materials TMRAIN-95, SPS-SW1, SPS-SW2 and simultaneously recovery of V(V) from spiked water samples. [Copyright &y& Elsevier]