Metal-independent production of hydroxyl radicals by halogenated quinones and hydrogen peroxide: an ESR spin trapping study

The metal-independent production of hydroxyl radicals (*OH) from H(2)O(2) and tetrachloro-1,4-benzoquinone (TCBQ), a carcinogenic metabolite of the widely used wood-preservative pentachlorophenol, was studied by electron spin resonance methods. When incubated with the spin trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO), TCBQ and H(2)O(2) produced the DMPO/*OH adduct. The formation of DMPO/*OH was markedly inhibited by the *OH scavenging agents dimethyl sulfoxide (DMSO), ethanol, formate, and azide, with the concomitant formation of the characteristic DMPO spin trapping adducts with *CH(3), *CH(CH(3))OH, *COO(-), and *N(3), respectively. The formation of DMPO/*OH and DMPO/*CH(3) from TCBQ and H(2)O(2) in the absence and presence, respectively, of DMSO was inhibited by the trihydroxamate compound desferrioxamine, accompanied by the formation of the desferrioxamine-nitroxide radical. In contrast, DMPO/*OH and DMPO/*CH(3) formation from TCBQ and H(2)O(2) was not affected by the nonhydroxamate iron chelators bathophenanthroline disulfonate, ferrozine, and ferene, as well as the copper-specific chelator bathocuproine disulfonate. A comparative study with ferrous iron and H(2)O(2), the classic Fenton system, strongly supports our conclusion that *OH is produced by TCBQ and H(2)O(2) through a metal-independent mechanism. Metal-independent production of *OH from H(2)O(2) was also observed with several other halogenated quinones.

Sodium borohydride/chloranil-based assay for quantifying total flavonoids

A novel sodium borohydride/chloranil-based (SBC) assay for quantifying total flavonoids, including flavones, flavonols, flavonones, flavononols, isoflavonoids, flavanols, and anthocyanins, has been developed. Flavonoids with a 4-carbonyl group were reduced to flavanols using sodium borohydride catalyzed with aluminum chloride. Then the flavan-4-ols were oxidized to anthocyanins by chloranil in an acetic acid solution. The anthocyanins were reacted with vanillin in concentrated hydrochloric acid and then quantified spectrophotometrically at 490 nm. A representative of each common flavonoid class including flavones (baicalein), flavonols (quercetin), flavonones (hesperetin), flavononols (silibinin), isoflavonoids (biochanin A), and flavanols (catechin) showed excellent linear dose-responses in the general range of 0.1-10.0 mM. For most flavonoids, the detection limit was about 0.1 mM in this assay. The recoveries of quercetin from spiked samples of apples and red peppers were 96.5 +/- 1.4% (CV = 1.4%, n = 4) and 99.0 +/- 4.2% (CV = 4.2%, n = 4), respectively. The recovery of catechin from spiked samples of cranberry extracts was 97.9 +/- 2.0% (CV = 2.0%, n = 4). The total flavonoids of selected common fruits and vegetables were measured using this assay. Among the samples tested, blueberry had the highest total flavonoid content (689.5 +/- 10.7 mg of catechin equiv per 100 g of sample), followed by cranberry, apple, broccoli, and red pepper. This novel SBC total flavonoid assay can be widely used to measure the total flavonoid content of fruits, vegetables, whole grains, herbal products, dietary supplements, and nutraceutical products.

Catalytic, Enantioselective [4 + 2]-Cycloadditions of Ketene Enolates and o-Quinones: Efficient Entry to Chiral, α-Oxygenated Carboxylic Acid Derivatives

We report catalytic, enantioselective [4 + 2]-cycloadditions of o-quinones with ketene enolates (derived from readily available acid chlorides) using cinchona alkaloid derivatives as catalysts to produce products in high enantiomeric excess (ee) and good to excellent yields. The thermodynamic driving force for these reactions is due in part to the restoration of aromaticity to the products. The resulting chiral, bicycloadducts can be synthetically manipulated in a variety of useful ways, for example to provide a flexible synthesis of alpha-oxygenated carboxylic acid derivatives.

Spectroscopic and thermodynamic study of charge transfer complexes of cloxacillin sodium in aqueous ethanol medium

Cloxacillin sodium has been shown to form charge transfer (CT) complexes of 1:1 stoichiometry with a number of electron acceptors in 50% (v/v) aqueous ethanol medium. From the trends in the CT absorption bands, the vertical ionization potential of the drug molecule (cloxacillin sodium) has been estimated to be 7.89 eV. The enthalpies and entropies of formation of two such complexes have been determined by estimating the formation constants spectrophotometrically at five different temperatures. The oscillator strengths and transition dipole moments of these complexes have been determined. It has further been noted that the reduction of o-chloranil by aqueous ethanol is completely inhibited by cloxacillin sodium, a phenomenon that makes the present study of formation equilibrium possible.

New modes of action of desferrioxamine: scavenging of semiquinone radical and stimulation of hydrolysis of tetrachlorohydroquinone

Desferrioxamine (DFO) is a common drug used in the treatment of iron overload. In addition to its iron-chelation, other properties have been identified. Alas, DFO has demonstrable effects which cannot be explained by its classically established properties; i.e., DFO protects against DNA single strand breaks induced by tetrachlorohydroquinone (TCHQ), while other iron chelators such as DTPA (diethylenetriaminepentaacetic acid) do not. The autooxidation process of TCHQ yielding the tetrachlorosemiquinone radical (TCSQ.) intermediate, was studied here in the presence of chelators. DFO led to a marked reduction in both concentration and life span of TCSQ. via formation of DFO-nitroxide radical (DFO.). In contrast, DTPA had no detectable effect on TCHQ autooxidation. Present studies indicate that the protective effects of DFO on TCHQ-induced DNA damage were not due to the binding of iron, but rather to scavenging of the reactive TCSQ. and the formation of the less reactive DFO.. An additional mode of action of DFO was identified, via stimulation of the hydrolysis (dechlorination) of tetrachloro-1,4-benzoquinone (chloranil), which is the oxidation product of TCHQ, to form 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid). The results of this study demonstrate two new modes of action for DFO: the scavenging of deleterious semiquinone radical, and the stimulation of the hydrolysis of halogenated substituents on the quinone structure. Both modes might prove highly relevant to the biological activities of DFO.

Quinone-induced inhibition of urease: Elucidation of its mechanisms by probing thiol groups of the enzyme

In this work we studied the reaction of four quinones, 1,4-benzoquinone (1,4-BQ), 2,5-dimethyl-1,4-benzoquinone (2,5-DM-1,4-BQ), tetrachloro-1,4-benzoquinone (TC-1,4-BQ) and 1,4-naphthoquinone (1,4-NQ) with jack bean urease in phosphate buffer, pH 7.8. The enzyme was allowed to react with different concentrations of the quinones during different incubation times in aerobic conditions. Upon incubation the samples had their residual activities assayed and their thiol content titrated. The titration carried out with use of 5,5'-di-thiobis(2-nitrobenzoic) acid was done to examine the involvement of urease thiol groups in the quinone-induced inhibition. The quinones under investigation showed two distinct patterns of behaviour, one by 1,4-BQ, 2,5-DM-1,4-BQ and TC-1,4-BQ, and the other by 1,4-NQ. The former consisted of a concentration-dependent inactivation of urease where the enzyme-inhibitor equilibrium was achieved in no longer than 10min, and of the residual activity of the enzyme being linearly correlated with the number of modified thiols in urease. We concluded that arylation of the thiols in urease by these quinones resulting in conformational changes in the enzyme molecule is responsible for the inhibition. The other pattern of behaviour observed for 1,4-NQ consisted of time- and concentration-dependent inactivation of urease with a nonlinear residual activity-modified thiols dependence. This suggests that in 1,4-NQ inhibition, in addition to the arylation of thiols, operative are other reactions, most likely oxidations of thiols provoked by 1,4-NQ-catalyzed redox cycling. In terms of the inhibitory strength, the quinones studied formed a series: 1,4-NQ approximately 2,5-DM-1,4-BQ<1,4-BQ<TC-1,4-BQ.

Spectrophotometric determination of fluoxetine and sertraline using chloranil, 2, 3 dichloro-5, 6 dicyano benzoquinone and iodine

Spectrophotometric procedures are presented for the determination of two commonly used antidepressant drugs, fluoxetine (I) and sertraline hydrochloride (II). The methods are based mainly on charge transfer complexation reaction of these drugs with either pi acceptors chloranil and 2, 3 dichloro-5, 6-dicyanoquinone (DDQ) or sigma acceptor iodine. The colored products are quantified spectrophotometrically at 550, 450 and 263 nm for fluoxetine and at 450, 455 and 290 nm for sertraline in chloranil, DDQ and iodine methods, respectively. The molar combining ratio and the optimum assay conditions were studied. The methods determine the cited drugs in concentration ranges of 8-640, 16-112 and 7.5-60 microg/ml with mean percentage recoveries of 99.83, 99.76 and 100.00% and R.S.D. of 1.24, 0.95 and 1.13% in fluoxetine and ranges of 16-160, 15-105 and 6-48 microg/ml with mean percentage recoveries of 100.39, 99.78 and 99.69% and R.S.D. of 1.02, 0.81 and 0.57% in sertraline for chloranil, DDQ and iodine methods, respectively. A more detailed investigation of the complex formed was made with respect to its composition, association constant K(AD)c, molar absorptivity xiAD(A) and free energy change deltaG. The proposed methods were applied successfully to the determination of the cited drugs either in pure or dosage forms with good accuracy and precision. The results were compared statistically with those given by the reported methods.

A surprising mechanistic "switch" in Lewis acid activation: a bifunctional, asymmetric approach to alpha-hydroxy acid derivatives

We report a detailed synthetic and mechanistic study of an unusual bifunctional, sequential hetero-Diels-Alder/ring-opening reaction in which chiral, metal complexed ketene enolates react with o-quinones to afford highly enantioenriched, alpha-hydroxylated carbonyl derivatives in excellent yield. A number of Lewis acids were screened in tandem with cinchona alkaloid derivatives; surprisingly, trans-(Ph(3)P)(2)PdCl(2) was found to afford the most dramatic increase in yield and rate of reaction. A series of Lewis acid binding motifs were explored through molecular modeling, as well as IR, UV, and NMR spectroscopy. Our observations document a fundamental mechanistic "switch", namely the formation of a tandem Lewis base/Lewis acid activated metal enolate in preference to a metal-coordinated quinone species (as observed in other reactions of o-quinone derivatives). This new method was applied to the syntheses of several pharmaceutical targets, each of which was obtained in high yield and enantioselectivity.

Sequestration of a highly reactive intermediate in an evolving pathway for degradation of pentachlorophenol

Microbes in contaminated environments often evolve new metabolic pathways for detoxification or degradation of pollutants. In some cases, intermediates in newly evolved pathways are more toxic than the initial compound. The initial step in the degradation of pentachlorophenol by Sphingobium chlorophenolicum generates a particularly reactive intermediate; tetrachlorobenzoquinone (TCBQ) is a potent alkylating agent that reacts with cellular thiols at a diffusion-controlled rate. TCBQ reductase (PcpD), an FMN- and NADH-dependent reductase, catalyzes the reduction of TCBQ to tetrachlorohydroquinone. In the presence of PcpD, TCBQ formed by pentachlorophenol hydroxylase (PcpB) is sequestered until it is reduced to the less toxic tetrachlorohydroquinone, protecting the bacterium from the toxic effects of TCBQ and maintaining flux through the pathway. The toxicity of TCBQ may have exerted selective pressure to maintain slow turnover of PcpB (0.02 s(-1)) so that a transient interaction between PcpB and PcpD can occur before TCBQ is released from the active site of PcpB.

Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors

Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, (1)H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

Potent methyl oxidation of 5-methyl-2'-deoxycytidine by halogenated quinoid carcinogens and hydrogen peroxide via a metal-independent mechanism

Halogenated quinones are a class of carcinogenic intermediates and are newly identified chlorination disinfection by-products in drinking water. We found recently that the highly reactive and biologically important hydroxyl radical ((•)OH) can be produced by halogenated quinones and H2O2 independent of transition metal ions. However, it is not clear whether these quinoid carcinogens and H2O2 can oxidize the nucleoside 5-methyl-2'-deoxycytidine (5mdC) to its methyl oxidation products and, if so, what the underlying molecular mechanism is. Here we show that three methyl oxidation products, 5-(hydroperoxymethyl)-, 5-(hydroxymethyl)-, and 5-formyl-2'-deoxycytidine, could be produced when 5mdC was treated with tetrachloro-1,4-benzoquinone (TCBQ) and H2O2. The formation of the oxidation products was markedly inhibited by typical (•)OH scavengers and under anaerobic conditions. Analogous effects were observed with other halogenated quinones and the classic Fenton system. Based on these data, we propose that the oxidation of 5mdC by TCBQ/H2O2 might be through the following mechanism: (•)OH produced by TCBQ/H2O2 may first abstract hydrogen from the methyl group of 5mdC, leading to the formation of 5-(2'-deoxycytidylyl)methyl radical, which may combine with O2 to form the peroxyl radical. The unstable peroxyl radical transforms into the corresponding hydroperoxide 5-(hydroperoxymethyl)-2'-deoxycytidine, which reacts with TCBQ and results in the formation of 5-(hydroxymethyl)-2'-deoxycytidine and 5-formyl-2'-deoxycytidine. This is the first report that halogenated quinoid carcinogens and H2O2 can induce potent methyl oxidation of 5mdC via a metal-independent mechanism, which may partly explain their potential carcinogenicity.

Microwave-Assisted Syntheses of Regioisomerically Pure Bromorhodamine Derivatives

[structure: see text] Regioisomerically pure bromo-substituted rhodamine derivatives (bromorosamines) were prepared via microwave-accelerated condensation reactions followed by oxidation with chloranil. Reaction optimization was conveniently performed by monitoring UV absorptions attributed to the product.

Nucleobase-Dependent Reactivity of a Quinone Metabolite of Pentachlorophenol

Pentachlorophenol (PCP) is a possible human carcinogen detected widely in the environment. A quinone metabolite of PCP, tetrachloro-1,4-benzoquinone (Cl4BQ), is a reactive electrophile with the capacity to damage DNA by forming bulky covalent DNA adducts. These quinone adducts may contribute to chlorophenol carcinogenesis, but their structures, occurrence, and biological consequences are not known. Previous studies have indicated that several DNA adducts are formed in vivo in rats exposed to Cl4BQ, but these adducts were not identified structurally. In the present study, we have elucidated the structure of new agent-specific DNA adducts resulting from the reaction of dGuo, dCyd, and Thd with Cl4BQ. These have been characterized chemically by liquid chromatography-electrospray ionization mass spectrometry, HPLC, UV, and NMR analysis. Two dGuo adducts and one dCyd adduct resulting from the reaction of double-stranded DNA with Cl4BQ have been identified. The results indicate that, in the structural context of DNA, Cl4BQ reacts most readily with dGuo compared to the other DNA bases and that the mode of Cl4BQ reactivity is dependent on the base structure; i.e., multiple types of adducts are formed. Finally, DNA adducts consistent with Cl4BQ reactions are observed when DNA or dGuo is treated with PCP and a peroxidase-based bioactivating system.

Chemical, Pulse Radiolysis and Density Functional Studies of a New, Labile 5,6-Indolequinone and Its Semiquinone

The chemical and spectroscopic characterization of 5,6-indolequinones and their semiquinones, key transient intermediates in the oxidative conversion of 5,6-dihydroxyindoles to eumelanin biopolymers, is a most challenging task. In the present paper, we report the characterization of a novel, relatively long-lived 5,6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach. The quinone was obtained by oxidation of 5,6-dihydroxy-3-iodoindole (1a) with o-chloranil in cold ethyl acetate or aqueous buffer: it displayed electronic absorption bands around 400 and 600 nm, was reduced to 1a with Na2S2O4, and reacted with o-phenylenediamine to give small amounts of 3-iodo-1H-pyrrolo[2,3-b]phenazine (2). The semiquinone exhibited absorption maxima at 380 nm (sh) and 520 nm and was detected as the initial species produced by pulse radiolytic oxidation of 1a at pH 7.0. DFT investigations indicated the 6-phenoxyl radical and the N-protonated radical anion as the most stable tautomers for the neutral and anion forms of the semiquinone, respectively. Calculated absorption spectra in water gave bands at 350 (sh) and 500 nm for the neutral form and at 310 and 360 (sh) nm for the anion. Disproportionation of the semiquinone with fast second-order kinetics (2k = 1.1 x 1010 M-1 s-1) gave a chromophore with absorption bands resembling those of chemically generated 1a quinone. Computational analysis predicted 1a quinone to exist in vacuo as the quinone-methide tautomer, displaying low energy transitions at 380 and 710 nm, and in water as the o-quinone, with calculated absorption bands around 400 and 820 nm. A strong participation of a p orbital on the iodine atom in the 360-380 nm electronic transitions of the o-quinone and quinone-methide was highlighted. The satisfactory agreement between computational and experimental electronic absorption data would suggest partitioning of 1a quinone between the o-quinone and quinone-methide tautomers depending on the medium.

The effect of pressure on hydrogen transfer reactions with quinones

The effect of pressure on the oxidation of hydroarenes 3-9 with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ; 1 a) or o-chloranil (10), leading to the corresponding arenes, has been investigated. The activation volumes were determined from the pressure dependence of the rate constants of these reactions monitored by on-line UV/Vis spectroscopic measurements in an optical high-pressure cell (up to 3500 bar). The finding that they are highly negative and only moderately dependent on the solvent polarity (DeltaV( not equal ) = -13 to -25 in MTBE and -15 to -29 cm(3) mol(-1) in MeCN/AcOEt, 1:1) rules out the formation of ionic species in the rate-determining step and is good evidence for a hydrogen atom transfer mechanism leading to a pair of radicals in the rate-determining step, as was also suggested by kinetic measurements, studies of kinetic isotope effects, and spin-trapping experiments. The strong pressure dependence of the kinetic deuterium isotope effect for the reaction of 9,10-dihydroanthracene 5/5-9,9,10,10-D(4) with DDQ (1 a) can be attributed to a tunneling component in the hydrogen transfer. In the case of formal 1,3-dienes and enes possessing two vicinal C--H bonds, which have to be cleaved during the dehydrogenation, a pericyclic hydrogen transfer has to considered as one mechanistic alternative. The comparison of the kinetic deuterium isotope effects determined for the oxidation of tetralin 9/9-1,1,4,4-D(4)/9-2,2,3,3-D(4)/9-D(12) either with DDQ (1 a) or with thymoquinone 1 c indicates that the reaction with DDQ (1 a) proceeds in a stepwise manner through hydrogen atom transfer, analogously to the oxidations of 1,4-dihydroarenes, whereas the reaction with thymoquinone 1 c is concerted, following the course of a pericyclic hydrogen transfer. The difference in the mechanistic courses of these two reactions may be explained by the effect of the CN and Cl substituents in 1 a, which stabilize a radical intermediate better than the alkyl groups in 1 c. The mechanistic conclusions are substantiated by DFT calculations.

Spectrophotometric, Fourier transform infrared spectroscopic and theoretical studies of the charge-transfer complexes between methyldopa [(S)-2 amino-3-(3,4-dihydroxyphenyl)-2-methyl propanoic acid] and the acceptors (chloranilic acid, o-chloranil and dichlorodicyanobenzoquinone) in acetonitrile and their thermodynamic properties

Methyldopa is a much used antihypertensive drug. It is the subject matter of study mostly for the determination and estimation of methyldopa in pharmaceutical properties. These considerations led us to study the charge-transfer interactions between methyldopa, a centrally acting antihypertensive agent of limited use with the known acceptors like o-chloranil (o-ClN), chloranilic acid (ClA) and dichlorodicyanobenzoquinone (DDQ). Methyldopa (MDP) formed beautifully colored complexes (having absorption maxima at 581 nm and 368 nm; 519 nm; 583.5 nm, 547 nm and 346 nm, respectively) with the acceptors mentioned before. The physico-chemical properties of the complexes were studied using UV-visible spectrophotometry and FTIR measurements. The composition, the accurate association constants and thermodynamics of the complexes were determined spectrophotometrically. Attempts were made to interpret the thermodynamics of complexes in terms of I(D)(V), E(A)(V) and hν(CT). Solid CT complexes between MDP+o-ClN, MDP+ClA and MDP+DDQ were prepared and FTIR spectra of the complexes were studied. The energies hν(CT) of the charge-transfer complexes and vertical ionization potential I(D)(V) of methyldopa were compared with the theoretical values of hν(CT) obtained from HOMO and LUMO of the donors and acceptors calculated using Density Function Theory utilizing different basis sets. The agreement between the results can be regarded to be reasonable. Oscillator strengths and dipole strengths of the complexes were determined theoretically and experimentally and the limitations of the calculations were outlined.

Charge-transfer complex formation between o-chloranil and a series of polynuclear aromatic hydrocarbons

The equilibrium constants, enthalpies and entropies of formation of molecular electron donor-acceptor (EDA) complexes of o-chloranil with a series of aromatic hydrocarbons have been determined spectrophotometrically. Spectroscopic and thermodynamic aspects of these complexes have been analysed.

Utility of certain pi-acceptors for the spectrophotometric determination of perindopril

Simple, rapid, accurate and sensitive spectrophotometric methods are described for the determination of perindopril. The methods are based on the reaction of this drug as n-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoquinone(DDQ)-7,7,8,8- tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), chloranil (CL) and p-chloranilic acid (p-CA) as pi-acceptors to give highly coloured complex species. The coloured products are measured spectrophotometrically at 588, 843, 419, 550 and 520 nm for DDQ, TCNQ, TCNE, CL and p-CA, respectively, optimization of different experimental conditions is described. Beer's law is obeyed in the range of 20-200 micrograms ml-1 and colours were produced in non-aqueous media and were stable for at least 1 h. Application of the suggested methods to perindopril tablets are presented.

Room temperature solution studies of complexation between o-chloranil and a series of anilines by spectrophotometric method

Electron donor-acceptor (EDA) complex formation between o-chloranil and a series of anilines has been studied in CCl4 medium. In all the cases, EDA complexes are formed instantaneously on mixing the donor and acceptor solutions. N,N-dimethylaniline and N,N-dimethyl-p-toluidine form stable EDA complexes with o-chloranil while the other complexes decay slowly into secondary products. The kinetics of all these reactions has been studied by UV-VIS absorption spectrophotometric method and the rate constants of the reactions and formation constants of the EDA complexes have been determined. The charge transfer (CT) transition energies of the complexes are found to change systematically with change in the number and position of the methyl groups in the donor molecules (methylanilines). From an analysis of this variation, the electron affinity of o-chloranil has been found to be 2.54 eV. A perturbational inductive effect Hückel parameter hMe has been found from this trend and the value obtained (-0.27) is very close to that (-0.3) obtained by Lepley (J. Am. Chem. Soc., 86 (1964) 2545) from a study of tetracyano ethylene (TCNE)-methylbenzene complexes.

Synthesis, spectroscopic and thermal investigations of solid charge-transfer complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane and the acceptors iodine, TCNE, TCNQ and chloranil

The solid charge-transfer complexes formed in the reaction of the electron donor 1,4,7-trimethyl-1,4,7-triazacyclononane (TMTACN) with the acceptors iodine, tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been isolated. These were characterized through electronic and infrared spectra as well as thermal and elemental analysis. The results show that the formed solid CT-complexes have the formulas [(TMTACN)I]I3, [(TMTACN)(TCNE)5] and [(TMTACN)(TCNQ)3] in full agreement with the known reaction stoichiometries in solution. The chloranil CT-solid complex cannot be isolated in pure form.

Measurement of hemoglobin and albumin adducts of tetrachlorobenzoquinone

Tetrachloro-1,4-benzoquinone (Cl4BQ), a metabolite of pentachlorophenol (PCP), is believed to play a role in the genotoxicity of PCP. We have developed a method to measure the adducts of Cl4BQ with cysteine residues of hemoglobin (Hb) and albumin (Alb). This method employs the use of Raney nickel to selectively cleave the sulfur-bound adducts. Adducts of Hb and Alb with Cl4BQ were measured following modification of rat blood with Cl4BQ (0-90 microM) in vitro. The formation of both Hb and Alb adducts was linear over the entire range with second-order rate constants of 6.89 and 167 L mol-1 h-1, respectively. The proportions of the concentrations of these Hb and Alb adducts to those of all covalently-bound products were estimated to be 0.053 and 0.178, respectively, at initial Cl4BQ concentrations between 3 and 90 microM. The overall rate of reaction of Cl4BQ in rat blood (in vitro) was pseudo-first-order with an estimated half-time of 4.35 h. Hb and Alb adducts of Cl4BQ were also measured in vivo following oral administration of PCP to rats (0-20 mg/kg body wt). Linear production of Hb and Alb adducts was observed over the entire range of dosages, with slopes of 0.09 and 8.22 pmol of adduct (g of protein)-1 [(mg of PCP)/(kg body wt)]-1, respectively. On the basis of production of Hb adducts in vitro and in vivo, it is estimated that 2.7 x 10(-7) mol of Cl4BQ was released to the blood of rats per mole of PCP administered.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectroscopic studies of charge transfer complexes between colchicine and some pi acceptors

Charge transfer complexes between colchicine as donor and pi acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21 degrees C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used.

Synthetic approaches towards the multi target drug spironolactone and its potent analogues/derivatives

Spironolactone is a well-known multi-target drug and is specifically used for the treatment of high blood pressure and heart failure. It is also used for the treatment of edema, cirrhosis of the liver, malignant, pediatric, nephrosis and primary hyperaldosteronism. Spironolactone in association with thiazide diuretics treats hypertension and in association with furosemide treats bronchopulmonary dyspepsia. The therapeutic mechanism of action of spironolactone involves binding to intracellular mineralocorticoids receptors (MRs) in kidney epithelial cells, thereby inhibiting the binding of aldosterone. Since its first synthesis in 1957 there are several synthetic approaches have been reported throughout the years, Synthetic community has devoted efforts to improve the synthesis of spironolactone and to synthesize its analogues and derivatives. This review aims to provide comprehensive insight for the synthetic endeavors devoted towards the synthesis of a versatile drug spironolactone and its analogues/derivatives.

Halogen vs hydrogen bonding in thiazoline-2-thione stabilization with σ- and π-electron acceptors adducts: theoretical and experimental study

Molecular charge-transfer complexes (CT) between thiazoline-2-thione (THZ) and different σ- (I2) and π-acceptors (Tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL)) were investigated. UV-Vis absorption spectroscopy and theoretical calculations using both MP2/aug-cc-pVDZ-PP and B3LYP/6-311++G(d,p) level of theory were corroborated to study the nature of the stabilizing forces for THZ-I2, THZ-DDQ, THZ-TCNE, and THZ-CHL. Halogen bonding (XB) was the stabilizing attractive force in THZ-I2 and THZ-CHL whereas; hydrogen bonding (HB) was dominated in both THZ-TCNE, and THZ-DDQ complexes. Formation constant (K), extinction coefficient (ɛ), thermodynamic parameters such as enthalpy change (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were measured in different solvents.

Photochemical Acetalization of Carbonyl Compounds in Protic Media Using an in Situ Generated Photocatalyst

Carbonyl compounds are conveniently converted into their corresponding dimethyl acetals in good yields and short reaction times by means of a photochemical reaction in methanol with a catalytic amount of chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, CA) as the sensitizer. Using aldehydes gives better results than using ketones, which also tend to form enol ethers as side products. These results are similar to those of simple acid-catalyzed acetalization reactions, suggesting the involvement of a photochemically generated acid. On the basis of steady state and laser flash photolysis data the reaction is proposed to involve the in situ generation of a photocatalyst (2,3,5,6-tetrachloro-1,4-hydroquinone, TCHQ) via reaction of CA with the solvent. The acetalization process is initiated by ionization of TCHQ, followed by loss of a proton to the solvent or the carbonyl, which starts a catalytic reaction. The photocatalyst is regenerated via a disproportionation reaction.