Vicinal fluorine-fluorine coupling constants: Fourier analysis

Stereochemical dependences of vicinal fluorine-fluorine nuclear magnetic resonance coupling constants (3JFF) have been studied with the multiconfigurational self-consistent field in the restricted active space approach, with the second-order polarization propagator approximation (SOPPA), and with density functional theory. The SOPPA results show the best overall agreement with experimental couplings. The relationship with the dihedral angle between the coupled fluorines has been studied by Fourier analysis, the result is very different from that of proton-proton couplings. The Fourier coefficients do not resemble those of a typical Karplus equation. The four nonrelativistic contributions to the coupling constants of 1,2-difluoroethane configurations have been studied separately showing that up to six Fourier coefficients are required to reproduce the calculated values satisfactorily. Comparison with Fourier coefficients for matching hydrogen fluoride dimer configurations suggests that the higher order Fourier coefficients (Cn> or =3) originate mainly from through-space Fermi contact interaction. The through-space interaction is the main reason 3JFF do not follow the Karplus equation.     

Ion adsorption at the rutile-water interface: linking molecular and macroscopic properties

A comprehensive picture of the interface between aqueous solutions and the (110) surface of rutile (alpha-TiO2) is being developed by combining molecular-scale and macroscopic approaches, including experimental measurements, quantum calculations, molecular simulations, and Gouy-Chapman-Stern models. In situ X-ray reflectivity and X-ray standing-wave measurements are used to define the atomic arrangement of adsorbed ions, the coordination of interfacial water molecules, and substrate surface termination and structure. Ab initio calculations and molecular dynamics simulations, validated through direct comparison with the X-ray results, are used to predict ion distributions not measured experimentally. Potentiometric titration and ion adsorption results for rutile powders having predominant (110) surface expression provide macroscopic constraints of electrical double layer (EDL) properties (e.g., proton release) which are evaluated by comparison with a three-layer EDL model including surface oxygen proton affinities calculated using ab initio bond lengths and partial charges. These results allow a direct correlation of the three-dimensional, crystallographically controlled arrangements of various species (H2O, Na+, Rb+, Ca2+, Sr2+, Zn2+, Y3+, Nd3+) with macroscopic observables (H+ release, metal uptake, zeta potential) and thermodynamic/electrostatic constraints. All cations are found to be adsorbed as "inner sphere" species bonded directly to surface oxygen atoms, while the specific binding geometries and reaction stoichiometries are dependent on ionic radius. Ternary surface complexes of sorbed cations with electrolyte anions are not observed. Finally, surface oxygen proton affinities computed using the MUSIC model are improved by incorporation of ab initio bond lengths and hydrogen bonding information derived from MD simulations. This multitechnique and multiscale approach demonstrates the compatibility of bond-valence models of surface oxygen proton affinities and Stern-based models of the EDL structure, with the actual molecular interfacial distributions observed experimentally, revealing new insight into EDL properties including specific binding sites and hydration states of sorbed ions, interfacial solvent properties (structure, diffusivity, dielectric constant), surface protonation and hydrolysis, and the effect of solution ionic strength.     

A versatile method for the synthesis of substituted 1-aminohydantoin derivatives

An efficient and versatile method has been developed for the synthesis of 1-aminohydantoin derivatives which can be substituted at all the possible positions of the hydantoin ring. The starting materials are aldehydes, ketones, carboxylic acids and hydrazides as well as isocyanates readily available from commercial sources. The semicarbazide-type reaction product of an N-acyl-N′-(1-cyanoalkyl)hydrazine, obtained from the above materials by methods known from the literature, and an isocyanate is cyclized in the presence of a basic catalyst to yield 1-acylamino-4-imino-2-oxoimidazolidine derivatives whose acid catalyzed hydrolysis leads to 1-aminohydantoin derivatives in good to excellent yields. The last two steps are carried out in a single reaction medium.     

Electrospray ionisation and ion-trap fragmentation of substituted 3,4-dihydro-2(1H)-pyridin-2-ones

A variety of 5-alkoxycarbonyl-4-aryl-6-methyl-3,4-dihydro-2(1H)-pyridones and hexahydrofuro[3,4-b]-2(1H)-pyridones have been investigated by electron impact (EI) and electrospray ionisation (ESI) techniques. Sequential product ion fragmentation (MS(n)) was performed to elucidate the degradation pathways for these compounds. Comparisons are made between positive and negative even-electron ions from ESI spectra and the molecular radical cations obtained under EI conditions. The data collected in this paper provide information on the strong impact that different substituents have on the ion fragmentation process.     

A concept for bifocal contact‐ or intraocular lenses: liquid single crystal hydrogels (“LSCH”)

The synthesis of liquid single crystal hydrogels (“LSCH”) in suitable molds offers an innovative concept to realize bifocal contact‐ or intraocular‐lenses. LSCH combine the properties required for applications as bifocal ophthalmic lenses: the soft and water‐containing hydrogel enables oxygen permeation and exhibits high birefringence due to the liquid crystalline phase structure built up by rigid rod‐like amphiphiles. Via a photo‐initiated crosslinking reaction of aqueous solutions of monomeric lyotropic liquid crystalline amphiphiles in the macroscopically ordered liquid crystalline state, we obtain optically uniaxially ordered and transparent LSCH. The orientation process and the phase structure of the anisotropic hydrogel is analyzed by deuterium NMR‐spectroscopy. Copyright © 2002 John Wiley & Sons, Ltd.     

Supramolecular stabilization of the phosphite-based polyoxomolybdate [Mo6(PO3)(HPO3)3O18]

A novel phosphite-based hetero-polyoxomolybdate, [Mo₆(PO₃)(HPO₃)₃O₁₈]⁹⁻, has been isolated and structurally characterized. The most striking feature of this polyanion is the presence of peripheral phosphite groups linked to the MoO₆ octahedra. In the solid state, this cluster shows strong hydrogen bonding interactions that apparently play a key role in its stabilization and isolation from solution.     

Ternary complexes of cimetidine and phenobarbital with Cu(II) in methanolic solution

The formation constants of the binary complexes Cu(CM)²⁺ and Cu(CM) ₂ ²⁺ as well as those of the ternary complexes Cu(CM)L ⁺ and Cu(CM)₂ L ⁺ (CM=Cimetidine=N-Cyano-N-methyl-N[(5-methyl-1H-imidazol-4-yl)methyltioethyl]-guanidine; HL=Phenobarbital=5-ethyl-5-phenyl-barbituric acid) have been determined in 0.1 and 1.0 mol dm^–3 NaClO₄ methanol solutions at 25±0.2°C. The values of logX, log _stat.., and logK confirm the stability of the ternary complexes.

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Ternäre Komplexe von Cimetidin und Phenobarbital mit Cu(II) in methanolischer Lösung

Zusammenfassung Die Stabilitätskonstanten der binären Komplexe Cu(CM)²⁺ und Cu(CM) ₂ ²⁺ sowie die der ternären Komplexe Cu(CM)L ⁺ und Cu(CM)₂ L ⁺ (CM=Cimetidin=N-Cyan-N-methyl-N-[(5-methyl-1H-imidazol-4-yl)methylthioethyl]-guanidin; HL=Phenobarbitalum=5-Ethyl-5-phenyl-barbitursäure) wurden in 0.1 und 1.0M Lösungen von NaClO₄ in Methanol bei 25±0.2°C bestimmt. Die Werte von logX, log _stat. und logK bestätigen die Stabilität der ternären Komplexe.

     

Leitfähigkeitsmessungen an Tetraethylammoniumhexacyanoferrat(III) und Tetrabutylammoniumhexacyanoferrat(III) in verschiedenen Lösungsmitteln

Based on conductivity measurements, the dissociation of tetraalkylam-moniumhexacyanoferrates(III) in water, ethanol, formamide,N-methylformamide,N,N-dimethylformamide, propylenecarbonate and acetonitrile is discussed. Interactions of the solvent as donor and as acceptor, the latter interaction being dominant, with (et ₄N)₃Fe(CN)₆ and (bu ₄N)₃Fe(CN) were found to be important factors in the formation of solvated ions.

     

Computer-assisted optimization of selectivity by tuning temperature and carrier gas pressure drop in two GC capillary columns coupled in series

The paper shows a computer-assisted procedure for the optimization of selectivity of two columns coupled in series by tuning the working temperature (using the isothermal mode) and columns coupling-point pressure at constant inlet and outlet carrier gas pressures. The optimization procedure validation was tested by the separation of 32 hydrocarbons in a column series with the aim to resolve the maximum number of components in the shortest possible analysis time.Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday     

On the unperturbed dimensions of polyisoprene chains

The characteristic ratio C_∞ = 〈r²〉 _o/nl² and its temperature coefficient dlnC_∞/dT for synthetic polyisoprenes with high cis 1,4 and trans 1,4 contents have been determined by various experimental methods, involving viscometric determinations. The θ-solvent dioxane at 31.2°C and benzene at temperatures in the range 25–45°C have been used with the cis isomer. Thermodynamic quantities required for the analysis in benzene, such as the reduced residual chemical potential χ and its temperature coefficient d_χ/dT, have been taken from the rigorous work of Eichinger and Flory, in which the equation-of-state theory was introduced. A large error has been found in the determination of the temperature coefficient in benzene, arising from the small values for ($\text{1}\text{2}\text{?}{}_{\mathrm{\chi }}$) and d_χ/dT. Selected θ-mixtures, toluene/n-propanol at various temperatures, have been employed with trans polyisoprene. Experimental values have been compared with those obtained from theoretical calculations carried out by authors since Mark in 1964. Reasonable agreement was found, especially for the trans isomer.