Molecular dynamics in aqueous solutions of β-cyclodextrin

Water molecule mobility in ion-containing and nonionic aqueous solutions of β-cyclodextrin was studied by quasielastic neutron scattering (QENS). The total self-diffusion coefficients and their components corresponding to the contributions from collective (Lagrange type) and single-particle (jump diffusion) parts of molecular motions were determined. From the data obtained, one can conclude that the molecular mobility of free water in nonionic aqueous solutions of β-cyclodextrin with guest molecules (2-aminopyridine) proceeds by a single-particle mechanism. The addition of Pb²⁺ ions into the solution leads to increase in self-diffusion coefficients and growth of a bound water fraction.     

Effect of the pH of the medium on the electronic absorption spectra and structure of 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone

On the basis of the electronic absorption spectra it was found that 3-methyl-1-phenyl-4-phenylazo-5-pyrazolone exists in acidic solutions in mono- and diprotonated forms. It was established by means of calculations by the Pariser—Parr—Pople (PPP) method that in the neutral and protonated forms the quinone hydrazone tautomer of the phenylazopyrazolone is more stable than the azo tautomer, and it was determined that the protonation center is the N₍₂₎ atom of the pyrazolone ring. The diprotonated form is most likely the quinone hydrazone tautomer protonated at the heteroring N₍₂₎ atom and the -nitrogen atom of the azo group. In an alkaline medium the phenylazopyrazolone exists in the form of an anion with predominance of the azo form. The effect of substituents ion the diazo component of the phenylazopyrazolone on the long-wave bands of the electronic absorption spectra in various media was explained on the basis of calculation of the distribution of the -electron density during electron transitions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1331–1336, October, 1991.     

Synthesis and Structure of Metal Complexes of 1-(1-R-3-Methylpyrazole-5-onilidene-4)-1,2,3,4-tetrahydroisoquinoline Derivatives

Twenty new complexes were synthesized by reacting Co(II), Cu(II), Zn, Cr(III), Fe(III), Cd and Ag salts with 3,3-dimethyl-1-(3-methylpyrazole-5-onilidene-4)-1,2,3,4-tetrahydroisoquinoline (L¹), spiro{cyclohexane-1,3"-[1-(1-phenyl-3-methylpyrazole-5-onilidene-4)-1,2,3,4-tetrahydroisoquinoline]} (L²), and 3,3-dimethyl-1-(1-phenyl-3-methylpyrazole-5-onilidene-4)-1,2,3,4-tetrahydroisoquinoline (L³). These compounds were studied by IR and electronic absorption spectroscopy. The type of coordination of their ligands was discussed on the basis of the results obtained and X-ray diffraction data for L³ and [CuL₂ ² Cl₂] · 2L² obtained previously.     

Tautomerism in Athraquinones: II. α-Hydroxy-substituted Anthraquinones

The fine structure of experimental π_l,π*-absorption bands of the α hydroxyanthraquinones originates from the prototropic anthraquinoid tautomerism. The tautomeric transformations occur both in the ground and excited states of the molecules; therewith the excited states are more sensitive to the tautomerization than the ground ones. The wavelength and intensity of the π_l,π*-bands, the values of all quantum-chemical characteristics studied for the tautomers of α hydroxyanthraquinones are linearly related to the number of hydroxy groups. The effect of the isomerism of di- and trihydroxyanthraquinones on this relationship was considered.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 722–729.Original Russian Text Copyright © 2005 by Fain, Zaitsev, Ryabov.     

Relaxation dynamics in glycerol-water mixtures: I. Glycerol-rich mixtures

We discuss the relaxation dynamics of glycerol-water mixtures, as studied by dielectric spectroscopy in the frequency range from 1 Hz to 250 MHz and at temperatures between 173 and 323 K. The experimental results obtained for the glycerol-rich mixtures suggest that the main dielectric relaxation process, as well as the so-called high-frequency "excess wing" (EW) and dc conductivity, follow the same temperature dependence. This result indicates that all of these processes are induced by the same molecular origin. A new phenomenological function is proposed to describe the whole dielectric spectrum in the covered frequency range, and some possible mechanisms of dielectric behaviors through the dc conductivity, the main relaxation process, and the EW are discussed.     

Structural and mechanistic look at the orthoplatination of aryl oximes by dichlorobis(sulfoxide or sulfide)platinum(II) complexes

Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes [PtCl(2)L(2)] (2, L = SOMe(2) (a), rac-SOMePh (b), R-SOMe(C(6)H(4)Me-4) (c), and SMe(2) (d)) to afford the corresponding platinacycles cis-(C,S)-[Pt(II)(C(6)H(3)-2-CR'=NOH-5-R)Cl(L)] (3, R, R' = H, Me) have been investigated. The reaction of acetophenone oxime with sulfoxide complex 2a in methanol solvent occurs noticeably faster than with sulfide complex 2d due to the fact that the sulfoxide is a much better platinum(II) leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formation of unreactive dichlorobis(N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenone oxime and suggests the importance of pseudocoordinatively unsaturated species for the C-H bond activation by Pt(II). A comparative X-ray structural study of dimethyl sulfoxide platinacycle 3b (R = R' = Me) and its sulfide analogue 3e (R = H, R' = Me), as well as of SOMePh complex 3c (R = H, R' = Me), indicated that they are structurally similar and a sulfur ligand is coordinated in the cis position with respect to the sigma-bound phenyl carbon. The differences concern the Pt-S bond distance, which is notably longer in the sulfide complex 3e (2.2677(11) A) as compared to that in sulfoxide complexes 3b (2.201(2)-2.215(2) A) and 3c (2.2196(12) A). Whereas the metal plane is practically a plane of symmetry in 3b due to the H-bonding between the sulfoxide oxygen and the proton at carbon ortho to the Pt-C bond, an S-bonded methyl of SOMePh and SMe(2) is basically in the platinum(II) plane in complexes 3c and 3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex 3b. An interesting structural feature of complex 3c is that the two independent molecules in the asymmetric unit of the crystal reveal an extremely short Pt-Pt contact of 3.337 A.     

Tautomerism of anthraquinones: V. 1,5-Dihydroxy-9,10-anthraquinone and its substituted derivatives

1,5-Dihydroxyanthraquinone and its substituted derivatives are capable of existence in the states structurally described as 9,10-, 1,10-, and 1,5-quinoid tautomerism, and as rotational isomerism involving a cleavage of intramolecular hydrogen bond. 1,5-Quinoid tautomers are characteristic only of substituted derivatives, and also appear in some metal complexes. The considerable color changes on introducing into the 1,5-dihydroxy-anthraquinone methyl, methoxy, and sulfo groups are caused by the shift in tautomeric and conformer equilibria.     

Synthesis, Crystalline Structure, and Spectra of 3,3-Dimethyl-1-(3-methyl-1-phenylpyrazol-5-onylidene-4)-1,2,3,4-tetrahydroisoquinoline

3,3-Dimethyl-1-(3-methyl-1-phenylpyrazol-5-onylidene-4)-1,2,3,4-tetrahydroisoquinoline has been synthesized and its crystalline and molecular structures determined. It was found by IR and electronic absorption spectroscopic methods that the structure of this compound is not changed in solutions.