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PubMed2002

Insertion of a strongly pi-pi stacked chloranilate pair into an M4 arrangement preorganized within a large macrocyclic ligand (M = Zn2+ and Cu2+).

Four Zn(II) ions arranged within a pyridine-modified large phenolate-containing macrocyle Lpy2- encapsulate two chloranilate ions in a double bis-didentate bridging fashion; the ligands are strongly pi-pi stacked with each other with a short distance of 3.27 A and are electrochemically reduced at the same potential of -1.00 V to produce a reasonably stable biradical species with T1/2 = 60 min at 25 degrees C.

Journal Article↗
PubMed2006

Large dielectric susceptibility associated with proton transfer in a supramolecular structure of chloranilic acid and 5,5'-dimethyl-2,2'-bipyridine.

A 1:1 adduct of chloranilic acid with 5,5'-dimethyl-2,2'-bipyridine, in which two kinds of molecules are connected by infinite hydrogen bond chains, exhibits a distinct dielectric phase transition when cooled. Below T(c)(=318 K) the hydrogen atoms participating in hydrogen bonding undergo long-range ordering and form an antiferroelectric-like state, taking a single minimum potential in the high-temperature phase (T>T(c)) due to the bifurcate hydrogen bond system. The proton-transfer phenomenon was clearly observed by electron density distribution analysis using a maximum entropy method of synchrotron x-ray diffraction data.

Journal Article↗
PubMed2006

X-ray diffraction and inelastic neutron scattering study of 1:1 tetramethylpyrazine chloranilic acid complex: temperature, isotope, and pressure effects.

The x-ray diffraction studies of the title complex were carried out at room temperature and 14 K for H/D (in hydrogen bridge) isotopomers. At 82 K a phase transition takes place leading to a doubling of unit cells and alternation of the hydrogen bond lengths linking tetramethylpyrazine (TMP) and chloranilic acid molecules. A marked H/D isotope effect on these lengths was found at room temperature. The elongation is much smaller at 14 K. The infrared isotopic ratio for O-H(D)...N bands equals to 1.33. The four tunnel splittings of methyl librational ground states of the protonated complex required by the structure are determined at a temperature T=4.2 K up to pressures P=4.7 kbars by high resolution neutron spectroscopy. The tunnel mode at 20.6 microeV at ambient pressure shifts smoothly to 12.2 microeV at P=3.4 kbars. This is attributed to an increase of the strength of the rotational potential proportional to r(-5.6). The three other tunnel peaks show no or weak shifts only. The increasing interaction with diminishing intermolecular distances is assumed to be compensated by a charge transfer between the constituents of deltae/e approximately 0.02 kbar(-1). The phase transition observed between 3.4 and 4.7 kbars leads to increased symmetry with only two more intense tunneling bands. In the isotopomer with deuterated hydrogen bonds and P=1 bar all tunnel intensities become equal in consistency with the low temperature crystal structure. The effect of charge transfer is confirmed by a weakening of rotational potentials for those methyl groups whose tunnel splittings were independent of pressure. Density functional theory calculations for the model TMP.(HF)2 complex and fully ionized molecule TMP+ point out that the intramolecular rotational potential of methyl groups is weaker in the charged species. They do not allow for the unequivocal conclusions about the role of the intermolecular charge transfer effect on the torsional frequencies.

Journal Article↗
PubMed2001

1:2 Complexes of chloranilic acid with pyrazole and imidazole, and the acetonitrile solvate of a 1:1 complex with imidazole.

2,5-Dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) forms X-H.Y (X, Y = N or O) and C-H.Cl hydrogen bonds with pyrazole and imidazole to afford bis(pyrazolium) dichloroanilate and bis(imidazolium) dichloroanilate, (I) and (II), both 2C(3)H(5)N(2)(+).C(6)Cl(2)O(4)(2-), and imidazolium chloroanilate acetonitrile solvate, C(3)H(5)N(2)(+).C(6)HCl(2)O(4)(-).C(2)H(3)N, (III). Their crystal structures demonstrate three novel supramolecular architectures based on supramolecular synthons to build a ladder, (I), a two-dimensional network, (II), and a flat ribbon, (III).

Journal Article↗
PubMed1998

Thermodynamic studies of the charge-transfer interactions of chloranilic acid with moclobemide and promethazine hydrochloride.

Spectrophotometric absorption studies gave evidence for the formation of strongly bonded charge-transfer complexes between moclobemide and promethazine hydrochloride with chloranilic acid in non-aqueous media comprising chloroform and 1,4-dioxane. The transitions involved were detected at wavelengths longer than those of the single pure substances in the visible region. Equilibrium constants from the Scott equation could be measured together with other thermodynamic parameters and molar absorptivities at different temperatures. Theoretical arguments are presented as to the spontaneity of these interactions.

Benzamides↗
PubMed2003

Spectroscopic analytical study for the charge-transfer complexation of certain cephalosporins with chloranilic acid.

Studies were carried out to develop a simple, rapid and accurate spectrophotometric method for the analysis of fifteen cephalosporins. The method depends on the charge-transfer complexation reaction between any of these drugs as an n-electron donor and p-chloranilic acid (p-CA) as a pi-acceptor to form a violet chromogen measured at 520 nm. Different variables affecting the reaction were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9986-0.9996) were found between the absorbances and the concentrations of the studied drugs in the range of 4-1,200 microg ml(-1). The limits of assay detection ranged from 2.54 to 42.83 microg ml(-1). The accuracy and precision of the method were satisfactory. The method was successfully applied to an analysis of the studied drugs in their pharmaceutical formulations; the recovery percentages ranged from 96.76 +/- 0.87% to 100.50 +/- 1.30%. The interaction sites were confirmed by UV/VIS, IR, 1H-NMR techniques. Molecular modeling for the interaction was used for deriving an equation for calculating the epsilon value for a particular drug. This equation gave a perfect prediction for the degree of interaction of the investigated drugs with the p-CA reagent.

Benzoquinones↗
PubMed2004

Validated spectrophotometric methods for the determination of amiodarone hydrochloride in commercial dosage forms using p-chloranilic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

Two simple, sensitive and economical spectrophotometric methods have been developed for the determination of amiodarone hydrochloride in pure form and commercial dosage form. These methods (A and B) are based on the reaction of amiodarone base as n-electron donor with p-chloranilic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as pi-acceptors to give highly colored complex species which absorb maximally at 535 and 570 nm, respectively. Beer's law is obeyed in the concentration ranges 10.0 - 360.0 and 2.0 - 65.0 microg ml(-1) for methods A and B, respectively. Application of the proposed methods to commercial pharmaceutical tablets are presented.

Amiodarone↗
PubMedDate not supplied

Chromatographic detection of cimetidine and famotidine using chloranilic acid as a spray reagent.

Qualitative determination of cimetidine and famotidine by TLC using chloranilic acid as the detecting spray reagent was carried out in different elution systems. On spraying, coloured spots corresponding to the drugs were formed which were stable for over three hours. In a particular solvent system, a commercial sample gave the same Rf value as its corresponding pure reference sample without any interference from the excipient.

Anti-Ulcer Agents↗
PubMedDate not supplied

Spectrophotometric and some thermodynamic parameters of the charge transfer complexation between chloranilic acid and chlorpheniramine.

The principle of charge transfer complexation involving a pi-acceptor (chloranilic acid) and an n-donor (chlorpheniramine) was utilized in the assay of the later in its pure form and in its tablet dosage forms. Some thermodynamic parameters of the complex such as association constant (Kc), molar absorptivity (epsilon c), free energy change (delta G degree), enthalpy (delta H degree) and entropy (delta S degree) changes were determined to establish the stability of the complex and the optimum conditions for the complex formation. The values obtained for these thermodynamic parameters indicated that the complex formed between this two chemical entities is highly stable. Assay of chlorpheniramine in its pure form and in its tablet dosage forms gave high percentage recoveries. The principle of charge transfer complexation could therefore be employed in the colorimetric assay of chlorpheniramine in its tablet dosage forms.

Benzoquinones↗
PubMedDate not supplied

Spectrophotometric determination of nikethamide by charge--transfer complexation with chloranilic acid.

A Spectrophotometric method is described for assay of nikethamide which was based on charge transfer complexation between it and chloranilic acid. They form a complex with stoichiometric ratio of 1:1 and showed l-max at 535 nm. Maximum complexation occurred 30 min after mixing the reactants and was stable for 12 hr. The molar absorptivity, association constant and free energy for the complex were 1.05 x 1.0(2), 4.40 x 10(-2) litre mole-1 and 1819.02 kcal respectively. Conformity to Beer's Law was within the concentration range of 1-2.5 x 10(-4), which enabled the assay of dosage forms of the drug at microquantities.

Benzoquinones↗
PubMed2004

[Fluorescence spectroscopy determination of lomefloxacin by charge transfer complex formation with chloranilic acid].

Charge-transfer complex was formed between LMX as the donor and Chloranilic Acid (CL) as the acceptor has been studied by fluorimetry. It was shown that the n-pi complex can be formed at ambient temperature, which can emit, which strong fluorescence. Different variables and parameters affecting the reactions were studied and optimized. Based on this, a simple and reliable fluorescence spectroscopy method for the determination of Lomefloxacin (LMX) has been developed. Interference from some co-formulated drugs was also studied. No interference was observed due to additives commonly present in the pharmaceutical preparations. The proposed methods could be applied successfully to the investigated pure compounds and pharmaceutical dosage forms with good accuracy and precision. The linear range is 0.04-0.8 mg x L(-1), the detection limit is 0.04 mg x L(-1), the recoveries of LMX are 97.4%-99.3%, and RSD is 1.3%-2.6%. Finally, the charge-transfer reaction mechanism was discussed. The composition of the change-transfer complex was found to be 1:1 by Bent-French and curved intersection methods. This ratio may be due to the presence of the fluorine atom acting as an electron drawing group in the molecule of lomefloxacin. The benzene ring has lower electron density, but nitrogen atom in 4' of piperazingl has higher electron density and is less sterically hindered. So n-pi charge transfer complexes were formed.

Antitubercular Agents↗
PubMedDate not supplied

Spectrophotometric analysis of selective serotonin reuptake inhibitors based on formation of charge-transfer complexes with tetracyanoquinodimethane and chloranilic acid.

A simple, accurate, and sensitive spectrophotometric method for analysis of selective serotonin reuptake inhibitors (SSRIs) has been developed and validated. The analysis was based on the formation of colored charge-transfer complexes between the intact molecule of SSRI drug as an n-electron donor and each of tetracyanoquinodimethane (TCNQ) or p-chloranilic acid (pCA) as electron acceptors. The formed complexes were measured spectrophotometrically at 842 and 520 nm for TCNQ and pCA, respectively. Different variables and parameters affecting the reactions were studied and optimized. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9975-0.9996) were found between the absorbances and the concentrations of the investigated drugs in the concentration ranges of 4-50 and 20-400 microg/mL with TCNQ and pCA, respectively. With all the investigated drugs, TCNQ gave more sensitive assays than pCA; the limits of assay detection were 2.5-4.8 and 20-40 microg/mL with TCNQ and pCA, respectively. The intra- and interassay precisions were satisfactory; the relative standard deviations did not exceed 2%. The proposed procedures were successfully applied to the analysis of the studied drugs in pure form and pharmaceutical formulations with good accuracy; the recovery values were 98.4-102.8 +/- 1.24-1.81%. The results obtained from the proposed method were statistically comparable with those obtained from the previously reported methods.

Benzoquinones↗