Spectrophotometric determination of some benzothiadiazine diuretics with 7,7,8,8-tetracyanoquinodimethane

A new spectrophotometric method for the determination of some benzothiadiazine drugs is presented, based on reaction with 7,7,8,8-tetracyanoquinodimethane in sodium acetate medium and measurement at 578 nm. Beer's law is obeyed in the concentration range 0.7-6.0 mug/ml for all eight drugs tested.     

High pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and CuTCNQ

The high-pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) single crystals and polycrystalline CuTCNQ are presented in this paper. TCNQ shows a phase transition at 22 kbar, a pressure higher than reported earlier. CuTCNQ undergoes a first order phase transition at 30 kbar, which is characterized by the abrupt disappearance of all the Raman bands.     

Reactions of hexamethyldilead with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE)

Hexamethyldilead reacts with TCNQ to give Pb(TCNQ)₂ and tetramethyllead and with TCNE to give Pb(TCNE).     

A re-examination of the use of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in determining the critical micelle concentrations

Summary A detailed re-examination of the use of TCNQ in ] determining the critical micelle concentration (c. m. c.'s) of aqueous and reversed micelles was carried out. The mechanism of the interaction of TCNQ with ionic and non-ionic detergents was investigated in order to delineate the origin of the production of the dye anion-radical. In several cases, the formation of the latter species can be eliminated, or kept to a minimum, if highly purified detergents and solvents were used. Under these conditions, the neutral TCNQ visible absorption band should be used in the c.m.c. determination. The origin of the formation of the TCNQ anion-radical has been traced to the presence of difficulty removable impurities in the anionic and/or non-ionic surfactants, and to the reaction of the dye with the counter-ion of the positive micelles.     

Spectrophotometric determination of some phenothiazine drugs using chloramine-T-iodine-starch

A simple, accurate, and sensitive spectrophotometric method for the determination of promethazine hydrochloride (PMH), prochlorperazine maleate (PCPM), trifluoperazine hydrochloride (TFPH), trimeperazine tartrate (TMT), fluphenazine dihydrochloride (FH), and trifluopromazine hydrochloride (TPH) is described. The method is based on the oxidation of the studied drugs by a known excess of chloramine-T in a hydrochloric acid medium and subsequent determination of the unreacted oxidant by interacting it with iodide in the same acid medium. Liberated iodine subsequently reacts with starch to form a stable starch-iodine complex. The reacted oxidant corresponds to the drug content. The colored complex exhibits a maximum absorption at 590 nm. The apparent molar absorptivity and Sandell sensitivity values are in the range 4.07 × 10⁴ − 1.18 × 10⁵ L/mol cm and 45.00−95.00 ng/cm², respectively. The proposed method has been applied to the assay of phenothiazine drugs in pure and dosage forms. The reliability of the analysis was established using parallel determination by the reference method. The text was submitted by the authors in English.     

Utility of iodine and 7,7,8,8-tetracyanoquinodimethane for determination of terfenadine

Simple and sensitive spectrophotometric methods for the assay of terfenadine are described. The first is based on the reaction of terfenadine with iodine to give a molecular charge-transfer complex, the terfenadine acting as an n-electron donor and iodine as a sigma-electron acceptor. The second depends on the formation of a highly coloured stable radical anion between terfenadine and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor. Beer's law is obeyed over the terfenadine concentration range 0.2-1.2 mg/100 ml. The proposed methods have been successfully applied to the analysis of commercial terfenadine tablets.     

Isolation of p-tricyanovinylphenyldicyanomethide ion via a [2+2] cycloaddition of 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules

In the presence of CoCl₂·6H₂O and dppm (bis(diphenylphosphino) methane), the reaction of TCNQ (7,7,8,8-tetracyanoquinodimethane) molecules by [2+2] cycloaddition forms a p-tricyanovinylphenyldicyanomethide ion (PCQ⁻), which has been obtained as one anion unit in one new compound [Co(dppmdo)₃][PCQ⁻]₂·H₂O 1 (dppmdo = bis(diphylphospine oxide) methane). Its structure was determined by X-ray crystallography: 1 crystallizes in with a = 14.174(3) Å, b = 19.553(4) Å, c = 19.776(4) Å, α = 112.72(3)°, β = 95.43(3)°, γ = 110.79(3)°, and Z = 2. It was characterized by IR spectra, UV–Vis spectra, and cyclic voltammogram. Magnetic properties indicate that no magnetic coupling between PCQ⁻ and [Co(dppmdo)₃]²⁺ unit.     

A novel reaction of 7,7,8,8-tetracyanoquinodimethane (TCNQ): charge-transfer chromophores by [2 + 2] cycloaddition with alkynes

A series of donor-acceptor molecules, featuring intense low-energy intramolecular charge-transfer bands, was prepared by regioselective [2 + 2] cycloaddition between 7,7,8,8-tetracyanoquinodimethane (TCNQ) and N,N-dialkylanilino-substituted (DAA-substituted) alkynes, followed by ring opening of the initially formed cyclobutenes.     

The Photovoltage-gas Sensitive Properties of 7,7,8,8-Tetracyanoquinodimethane(TCNQ)

In this paper, surface photovoltage technique (SPV) was applied to the study of photovoltaic and gas sensitive properties of TCNQ polycrystal. It was found that SPV shows two peaks at 390 nm(P1) and 480 nm (P2) in the ultraviolet-visible range. And they are opposite in phase. The results of gaseous adsorption confirm that P, shows the acceptor characteristics, while PI shows that of donor. During adsorption, donor gas interacts with conjugated II * orbital, acceptor gas with the terminal group C=N .     

Photoinduced electron transfer ring opening of α-epoxyketones using 7,7,8,8-tetracyano-p-quinodimethane (TCNQ)

Photoinduced electron transfer ring opening of α-epoxyketones using 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) in methanol and acetic acid solutions resulted in the formation of diastereomeric products, hydroxy ethers and hydroxy esters, respectively. However, the formation of cis-1,3-dioxolanes and cis-spirodioxolanes has been observed on reaction in acetone and cyclohexanone solutions, respectively. The effect of the electron donating character of the substituent influenced the rate of the ring opening. Quantum computational studies explain the mechanism of the addition.     

Spectrophotometric determination of some drugs for osteoporosis

Three simple, accurate and sensitive spectrophotometric methods are developed for the determination of some new drugs for the treatment of osteoporosis: risedronate sodium (I), alendronate sodium (II) and etidronate disodium (III). The first method is based on the measurement of difference in absorbance (Delta A) of risedronate sodium in 0.01 mol l(-1) hydrochloric and 0.1 mol l(-1) sodium hydroxide at 262 nm. Beer's law is obeyed over a concentration range of 15-150 microg ml(-1) with mean recovery 99.75+/-1.22 and molar absorptivity (epsilon) 1.891 x 10(3). The second method is based on the reaction of the primary amino group of (II) with ninhydrin reagent in methanolic medium in the presence of 0.05 mol l(-1) sodium bicarbonate. The colored product is measured at 568 nm, and the linearity range is found to be 3.75-45 microg ml(-1) with mean recovery 99.77+/-0.73 and epsilon 9.425 x 10(3). The third method is based on oxidation of the three mentioned drugs with ceric (IV) sulphate in 0.5 mol l(-1) sulphuric acid at room temperature and subsequent measurement of the excess unreacted cerium (IV) sulphate at 320 nm. The method obeyed Beer's law over a concentration range of 2-24 microg ml(-1) for the three drugs with mean recovery 99.79+/-1.16, 99.73+/-1.38 and 99.86+/-1.13 and epsilon 14.427 x 10(3), 13.813 x 10(3) and 14.000 x 10(3) for drugs I, II, III respectively. The proposed methods were successfully applied for the determination of the studied drugs in bulk powder and in pharmaceutical formulations. The results were found to agree statistically with those obtained the reported methods. Furthermore, the methods were validated according to USP regulations and also assessed by applying the standard addition technique.     

Photophysics and Inverted Solvatochromism of 7,7,8,8-Tetracyanoquinodimethane (TCNQ)

We report absorption, fluorescence, and Raman spectroscopy of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a variety of solvents. The fluorescence quantum yields (QYs) of linear alkane solutions are similar to one another, but QY is shown to acutely decrease in other solvents with increasing polarities. The slope of the solvatochromic plot of absorption maxima is inverted from negative to positive with an increase in solvent polarity. A significant change in the frequency of carbon-carbon double bond stretching modes is not observed in Raman spectra of TCNQ in different solvents. The molar absorption coefficient is determined to calculate the oscillator strength of the absorption band. The radiative decay rate constant calculated from the oscillator strength is approximately ten times larger than that elucidated from the fluorescence lifetime and QY. These spectroscopic parameters reveal that the relaxation occurs from a Franck-Condon excited state to a distinct fluorescence emissive state with a smaller transition dipole moment.     

Ion-radical salt of 2-tert-butyltetrathiatetracene with 7,7,8,8-tetracyanoquinodimethane (2∶1)

Conclusions We synthesized 2-tert-butyltetrathiatetracene and its 2:1 complex with 7,7,8,8-tetra-cyanoquinodimethane, which has an ion-radical nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 696–697, March, 1977.The authors express their gratitude to L. I. Buravov for measuring the electrical conductivity.     

Complexes of arenechromium compounds with 7,7,8,8-tetracyanoquinodimethane

Conclusions For the first time complexes of arenechromium compounds with 7,7,8,8-tetracyanoquinodimethane were obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2124–2125, September, 1968.     

Spectrophotometric determination of some antiamoebic and anthelmintic drugs with metol and chromium(VI)

A sensitive spectrophotometric method is reported for the determination of tinidazole (TZ), metronidazole (MZ), benzoyl metronidazole (BMZ) or niclosamide (NS) either in pure form or in formulations. This method is based on reduction with zinc dust and hydrochloric acid followed by reaction with metol and potassium dichromate at pH 3.0 +/- 0.2 to give a coloured product having maximum absorbance at 720 nm (for TZ, MZ and BMZ) or 530 nm (for NS).     

Vanadium 7,7,8,8-tetracyano-p-quinodimethane (V[TCNQ]2)-based magnets

A new family of molecule-based magnets of general formula V[TCNQR(2)](2).zCH(2)Cl(2) has been synthesized and characterized (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane; R = H, Br, Me, Et, i-Pr, OMe, OEt, and OPh). In addition, solid solutions of V[TCNQ](x)()[TCNQ(OEt)(2)](2)(-)(x)().zCH(2)Cl(2) composition have been prepared. Except R = Br, magnetic ordering was observed for all materials, with T(c) values between 7.5 K (R = Me) and 106 K (R = OEt), with R = H at 52 K. The substitution of electron-donating OMe and OEt groups for H in TCNQ increased T(c), whereas the substitution of less electron-donating alkyl groups (with respect to alkoxy groups) decreased T(c). The results of MO calculations indicate that neither the spin nor charge densities of the disubstituted TCNQs are sufficiently different to explain the wide range of critical temperatures. Although the structures of the amorphous materials are not known, it is proposed that the oxygen atom of the [TCNQR(2)](*)(-) acceptor (R = OMe and OEt) and the V(II) interact to form a seven-membered ring. This interaction could stabilize the structure and enhance the magnetic coupling, leading to an increased T(c). The magnetic properties of V[TCNQ](x)()[TCNQ(OEt)(2)](2)(-)(x)().zCH(2)Cl(2) deviated from the expected linear relationship with respect to x, exhibiting magnetic behavior more characteristic of a step function in a plot of T(c) versus x.