Extraction behavior of ion-pairs of azo-dye cations and their analytical applications

The extraction of ion-pairs of monovalent organic acid anions and inorganic anions with 4-(4-diethylaminophenylazo)-N-alkylpyridinium cation (azo-dye cation) is described. The alkyl groups studied were methyl, ethyl, propyl, butyl and benzyl groups. The ion association, distribution and extraction constants for the ion-pairs were determined from partition equilibrium studies. These azo-dye cations can extract chelate anions containing sulfonic acid groups into chloroform. The cobalt complex of 2-nitroso-1-naphthol-4-sulfonic acid is extracted quantitatively into chloroform with the propyl derivative as a 1:3 Co: dye complex; measurement of the absorbance of the extracted ion-pair provides a very sensitive determination of cobalt, the apparent molar absorptivity in chloroform being 1.66 × 10⁵ l mol^-1 cm^-1 at 566 nm. The methyl derivative is suitable for cation extraction of monovalent anions such as the complex nickel anion of 4-chloro-2-nitroso-1-naphthol, and anionic surfactants. The possibilities for application of these azo-dye cations in extraction-spectrophotometric determinations are very large.     

A convenient synthesis of 3-aryl-1,2,4-triazolo[4,3-c]quinazolines

The synthesis and characterization of several 3-aryl-1,2,4-triazolo[4,3-c]quinazolines is described. The first step comprises the condensation of aromatic aldehydes with 2-(H or Cl)-4-hydrazinoquinazolines 2 to afford the corresponding hydrazones 3 . The second step involves the cyclization to the title compounds 4 in bromine/acetic acid. Reaction of 4 (X = Cl) with cyclic amines gave the corresponding 5-cyclicamino 5 or 5-alkoxy derivatives 6 .     

Charge-transfer complexes as polymerization inhibitors. I. Amine–chloranil complexes as inhibitors for the radical polymerization of methyl methacrylate

Charge-transfer complexes of N,N-dimethylaniline (DMA) and triethylamine (TEA) with chloranil have been investigated as inhibitors for the sensitized polymerization of methyl methacrylate (MMA) in bulk and in solution. Complete inhibition is achieved by the complexes of both amines followed by retardation only in case of DMA. The higher inhibiting efficiency of the TEA complexes is attributed to their greater stability. The polymers formed in the presence of chloranil alone or its complexes with both amines are quinonoid and contain no combined nitrogen. The results support the idea that inhibition reaction involve electron transfer from the growing chains to the quinone, with formation of molecular complexes of polymeric cations and semiquinone anions. The latter are the actual inhibiting species, so that the efficiency of inhibiting depends on their concentration, which is determined by the stability of the molecular complexes formed. The inhibition reactions should accordingly be considered as oxidation–reduction processes in which the growing chains are the electron donors. The suggested mechanism affords an explanation for the great differences in the inhibiting power of a particular quinone for the polymerization of different monomers.     

Analysis of serotonin in brain microdialysates using capillary electrophoresis and native laser-induced fluorescence detection

Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples.     

Molecular tectonics. Selective exchange of cations in porous anionic hydrogen-bonded networks built from derivatives of tetraphenylborate

Tetraphenylmethanes with multiple hydrogen-bonding sites are known to associate to form robust porous supramolecular networks. Analogous anionic networks can be built from the corresponding tetraphenylborates. Crystallization of the tetraphenylphosphonium salt of tetraphenylborate 2 produces an anionic network in which 74% of the volume is available for including cations and neutral guests. Other salts of anion 2 with diverse cations crystallize consistently to form the same network, whereas a neutral analogue of anion 2, tetraphenylmethane 1, produces an uncharged network that is far less open. Cations can be exchanged in single crystals of salts of tetraphenylborate 2 with retention of crystallinity and with selectivities similar to those observed in typical zeolites. Together, these observations provide new strategies for making ordered molecular materials by design, and they reveal that constructing such materials from charged subunits offers special advantages.     

2,5‐Dicarboxy­anilinium chloride monohydrate

The title compound, C₈H₈NO₄⁺·Cl⁻·H₂O, is the chloro­hydrated form of 2‐amino­benzene‐1,4‐dicarboxylic acid, the basic crystal structure of which is still not known. Mol­ecules are linked by classical N—H⋯O, O—H⋯O, N—H⋯Cl and O—H⋯Cl hydrogen bonds, mainly along the mol­ecular plane, into sheets built by unusual R₆⁴(26), R₆⁴(22) and R₄³(22) rings. The stacking between layers is stabilized by another N—H⋯Cl hydrogen bond and by π–π inter­actions between aromatic rings facing each other.     

Tandem use of carboxypeptidase Y reactor and displacement chromatograph for peptide synthesis

A packed-bed enzyme reactor with immobilized carboxypeptidase Y was used in tandem with a displacement chromatograph for the preparation of N-benzoyl-L-arginyl-L-methioninamide, from N-benzoyl-L-arginine and L-methioninamide. The pumps and valves of the coupled enzyme reactor and displacement chromatograph were controlled by a microprocessor. The enzyme was immobilized on microparticulate amino-silica by glutaraldehyde and packed into a 60 X 4.6 mm I.D. column. The packed-bed reactor was used in the recirculating mode and components of the reaction mixture were subsequently separated by displacement chromatography on a 250 X 4.6 mm octadecyl-silica column using butoxyethoxyethanol as the displacer. Unreacted L-methioninamide was returned to the reaction mixture. Both the progress of the reaction and the extent of separation by displacement chromatography were monitored by high-performance liquid chromatographic analysis. The system was designed so that enzymatic peptide synthesis, separation by displacement chromatography, and column regeneration were carried out simultaneously by using two identical columns in parallel. An amount of 460 mg of N-benzoyl-L-arginyl-L-methioninamide having purity greater than 99% could be obtained in 24 h with this system. The tandem operation of the enzyme reactor and liquid chromatograph operated in the displacement mode offers a means for the synthesis and purification of peptides.     

Dissociation constants of some Schiff bases and stability constants of their copper,cobalt, nickel and zinc complexes

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (H₂L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt (H₂L¹) were studied by potentiometric titration. The stability constants of H₂L and H₂L¹ Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 °C and 0.1 m KCl ionic strength. The dissociation constants for H₂L were obtained as 3.007, 7.620 and 9.564 and for H₂L¹, 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L)₂] for M = Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II) < Ni(II). The high stability of H₂L¹ towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest. Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry, deprotonation and stability constants via the SUPERQUAD computer program.     

Chelate Compounds of a Selected Non-Transition and Transition Metal Ions with Some Salicylic Acid Derivatives

A series of binary complexes of Zn(II), Hg(II), Pb(II), La(III), Ce(III), Th(IV) and UO₂(II) with 3,5-dinitrosalicylic acid and 5-sulphosalicylic acid have been isolated and characterized. The solution equilibria of these complexes have been studied pH-metrically. The formation constants (log K) at 25±1°C and ionic strength of 0.2M NaClC₄ have been calculated. Stability of the complexes formed in relation to ligand molecular structure and nature of the metal ion has been examined and discussed.