Intermolecular hydrogen bonds: Comparison of associates in crystals and liquids

The density and sound velocity were measured within wide ranges of temperature for a number of liquids (water, formamide, diols, aliphatic alcohols, cellosolves, ketones), in which various types of H-associate can exist. The temperature dependences of the adiabatic and molar adiabatic compressibility, density, and molar volume are analyzed. The values of the molar adiabatic compressibility permit one to evaluate the dimensionality of H-associates existing in liquids; the values of adiabatic compressibility do not offer this possibility. The terms responsible for the similarity and difference between H-associates in crystals and liquids are discussed.     

Aggregation of amphiphilic aminomethylated calix[4]resorcinarenes and the nonionic surfactant Triton-X-100 in organic solvents

Aggregation and intermolecular interactions of amphiphilic calix[4]resorcinarene (1), aminomethylated calix[4]resorcinarenes (AMC 2—7) with different structures of the upper rim (including the oxazine structure in 6 and 7) and hydrophobic substituents on the lower (2—5), upper (6), or both rims (7) in the absence and in the presence of the nonionic surfactant Triton-X-100 (8) and p-nitrophenol (9) in chloroform and 1,4-dioxane were studied by permittivity measurements and 2D ROESY ¹H NMR technique. The tendency of amphiphilic derivatives 1—7 toward self-aggregation and mixed aggregation with surfactant 8 primarily depends on the nature of both the solvent and the polar groups on the upper rim of calixarenes. In chloroform, AMC—8 aggregates show interactions of the methyl and methylene groups of the hydrophobic substituents of AMC with the ethyleneoxy fragments of surfactant 8, while in stable intermolecular complexes of 5 and 6 with compound 9, the methylene groups of the long-chain radicals of the AMC strongly interact with the aromatic protons ortho to the hydroxy group of 9. In 1,4-dioxane, calix[4]resorcinarenes 1 and 5 are bound in stable solvates, which prevents them from forming aggregates and mixed micelles.     

Formation of ternary ion associates using diprotic acid dyes and its application to determination of cationic surfactants

A sensitive and selective method is described for the determination of cationic surfactants, such as benzethonium, benzalkonium, cetylpyridinium and trimethylstearylammonium, based on the formation and extraction of ternary ion associates with an acid dye (bromophenol blue or bromochlorophenol blue) and quinidine. Quinidine reacts with divalent anionic dyestuffs to form a bulky 11 complex anion, which is extractable into 1,2-dichloroethane as ternary ion associates with cationic surfactants in nearly neutral media. The ternary ion associate gives a blue product. Linearity of the calibration curve is improved and the extractability of the cationic surfactants is enhanced in the presence of quinidine. In addition, many other amines do not interfere with the determination. The blue ion associates can be used for the selective and sensitive spectrophotometric determination of cationic surfactants.     

Double proton migrations in the associates of formic acid with nitrous,nitric, orthophosphoric,and sulfuric acids

Mechanisms of the proton transfer in dimeric associates of formic acid with nitrous, nitric, orthophosphoric, and sulfuric acids were studied by theab initio (HF/6-31G^**) method. The mechanism of the cooperative (concerted or one-step) proton transfer was shown to occur in all cases. The calculated activation barriers of the proton transfer reactions for the associates investigated are equal to 19.9, 14.2, 13.3, and 10.7 kcal mol^–1, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2184–2189, September, 1996.     

Spectral-Luminescent Properties of Deposited Rhodamine 6G Films

We have investigated the absorption and fluorescence spectra of Rhodamine 6G thin (20–100 nm) films vacuum-deposited on solid dielectric substrates: quartz and borosilicate glasses and polymer films. By the absorption spectra several molecular absorption centers — monomers, dimers, and complex associates — have been revealed. For the first time luminescence of vacuum-deposited Rhodamine 6G films has been obtained and investigated. We classified it as fluorescence of plane dimers and dimers of the house-of-cards type and also as luminescence of complex associates. The dependence of the spectral composition of the films on the excitation wavelength in the 293–353 K temperature range has been studied. It has been proposed that amorphous Rhodamine 6G films obtained by the vacuum deposition method contain crystalline zones and microclusters of adsorbed water molecules.     

Effect of Solvent (Plasticizers) on PVC Degradation

Both plasticized (semi-rigid and flexible) PVC materials as well as PVC in solutions, the rate of their thermal degradation and effective stabilization are caused by essentially different fundamental phenomena in comparison to aging of PVC in absence of the solvent. Both structure and macromolecular dynamics render the significant influence on its stability, i.e. chemical nature of the solvent (plasticizer), its basicity, specific and non-specific solvation, degree of PVC in a solution (solubility), segmental mobility of macromolecules, thermodynamic properties of the solvent (plasticizer), formation of associates, aggregates, etc. The chemical stabilization of PVC plays a less significant role. The effect of above factors on stability (behavior) of semi-rigid and flexible PVC will be done on quantitative level. It will be described effect of “echo”-type of stabilization on the stability of PVC in the presence of plasticizers. If we would like to have stable material from PVC we should make stabilization of plasticizers as more reactive chemical compounds.     

Extraction and Spectrophotometric Determination of Diclofenac in Pharmaceuticals

A new simple, rapid and sensitive spectrophotometric method has been developed for the determination of diclofenac sodium (Dicl) in pharmaceutical preparations. This method is based on the reaction of diclofenac sodium with an analytical reagent 1,3,3‐trimethyl‐5‐thiocyanato‐2‐[3‐(1′,3′,3′‐trimethyl‐3′‐H‐indol‐2′‐ylidene)‐propenyl]‐indolium cloride (TIC) at pH 8.0‐11.0 and the extraction of ion associate colored complex. Optimal conditions for the complex formation between Dicl and TIC were studied. This ion associate complex (1:1) was detected and extracted with toluene and an absorption maximum at 566.2 nm against a blank reagent. The calibration graph was linear from 0.9‐11.0 μg/mL of diclofenac and the detection limit was 0.86 μg/mL.     

Molecular characteristics of water-soluble fullerene derivatives of amino acids and peptides

The diffusion of fullerene derivatives of amino acids and peptides in dilute aqueous solutions has been studied. These derivatives can exist in solution both as separate molecules and as associates. The degree of association depends both on the nature of the amino acid or peptide residue and on the concentration of the solution.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 879–882, April, 1996.     

Mixed ternary ion associate formation between xanthene dye, cinchona-alkaloid and quaternary ammonium ion and its application to the determination of trace amounts of quaternary ammonium salts in pharmaceuticals

Xanthene dyes such as eosin and tetraiodofluorescein form 1:2 ion associates with quaternary ammonium ions at pH 7-9; however, the development of color in the organic solvent is poor. When a quaternary ammonium salt is added in the extractable 1:2 associate formed between a xanthene dye and a cinchona-alkaloid in the neutral media, a mixed ternary ion associate (xanthene dye:cinchona-alkaloid:quaternary ammonium ion=1:1:1) is formed. Its extractability is enhanced due to the more bulky associate formation. The ion association caused by addition of cinchona-alkaloids is unique. Of the cinchona-alkaloids, quinidine and cinchonidine with tetraiodofluorescein show excellent effects on sensitivity and extractability. Eosin and tetraiodofluorescein are useful as ion association reagents in the ion associate formation. The apparent molar absorptivities are about 1×10⁵ l mol⁻¹ cm⁻¹ and the calibration range for quaternary ammonium salt is from 2.5×10⁻⁷ to 1.5×10⁻⁶ M. The proposed method is applicable to the selective and sensitive determination of cetylpyridinium chloride, berberine chloride and benzethonium chloride in pharmaceuticals.     

Interaction of chromophores in dissimilar associates of cationic and anionic polymethine dyes in water

A strong interaction between chromophores of cationic and anionic components was found based on the analysis of electronic absorption spectra of aqueous solutions of mixtures of cationic indopolycarbocyanines with anionic cyanines. Strong dissimilar 1∶1 associates are formed. Association constants were estimated spectrophotometrically. The main factors determining the degree of interaction of chromophores were revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 950–955, May, 1997.