Inclusion by a fluorenyl diol host with substituted pyridines

The structures of the inclusion compounds formed by the host 9,9’-(ethyne-1,2-diyl)bis(fluoren-9-01) with pyridine and picolines are similar and display tubular topology. The host discriminates poorly between these guests. The kinetics of desorption of the pyridine compound is governed by the Avrami-Erofe’ev equation A2, with an activation energy of 111(7) kJ mol⁻¹.     

Synthesis of novel poly(ethylene glycol) supported benzazepines: the crucial role of PEG on the selectivity of an intramolecular Heck reaction

Poly(ethylene glycol) (PEG 3400) was used as a soluble polymeric support for the synthesis of a series of novel benzazepines. The key step for the preparation of these heterocycles was a phosphine-free palladium-catalyzed Heck reaction. Palladium nanoparticles formed during the course of the reaction were characterized. The presence of PEG 3400 influenced the outcome of the reaction in terms of selectivity.     

Selective synthesis of di(propen-1-yl)sulfone and di(propen-1-yl)sulfoxide

Convenient selective methods of synthesis of the title compounds, based on oxidation of di(propen-1-yl)sulfide with 30% H₂O₂, have been developed.Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 675–679, March, 1992.     

Unique solvent effects on selective electrochemical fluorination of organic compounds

Recent studies on solvent effects on electrochemical partial fluorination are reviewed. At first, the historical background and some problems of electrochemical fluorination in organic solvents like acetonitrile (MeCN) are briefly mentioned. Ethereal solvents like dimethoxyethane (DME) and a mixture of DME and MeCN were found to improve both the yield and current efficiency for electrochemical fluorination since these solvent systems effectively suppress anode passivation and overoxidation of fluorinated products once formed during the electrolysis. It was also found that DME stabilizes radical cationic intermediates of 4-arylthio-1,3-dioxolan-2-ones and 3-phenylthiophthalide leading to α-fluorination while dichloromethane (CH₂Cl₂) destabilizes them leading to fluorodesulfurization. On the other hand, imidazolium ionic liquids and liquid fluoride salts like Et₄NF·4HF and Et₃N·5HF exhibited similar effects to CH₂Cl₂. Selective fluorination of hardly oxidizable phthalide was also achieved using a combination of two kinds of ionic liquids (imidazolium triflate and liquid fluoride salts).     

Separation of chlamydosporol epimers by reversed-phase HPLC using commercial solvent optimisation software

Summary Two epimers of the mycotoxin chlamydosporol were separated by HPLC on an RP-18 column using a quaternary mobile phase consisting of water (79.1%), methanol (10.0%), acetonitrile (10.4%) and tetrahydrofuran (0.5%), with a flow rate of 1 ml min^–1. This optimal composition of mobile phase, with which the resolution value for the two epimers (1 and2) was 2.73 with retention times of 5.88 and 7.12 min, respectively, was achieved by the application of Philips Solvent Optimisation Software PU 6100. The presence of free silanols on the stationary phase was shown to be an essential requirement for the separation of the chlamydosporol epimers.     

Polarisabilites moléculaires et effet diélectrique de milieu à l'état liquide. Étude théorique de la molécule d'eau et de ses diméres

The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p]

     

The effectiveness of solvents as hydrogen bond donors

Taft and Kamlet's -scale of solvent hydrogen bond donation ability is reexamined with regard to its correlations with three widely used polarity scales: Dimroth and Reichardt's E _T (30), Kosower's Z and Mayer's A _N , as well as with the _m values of the solvents when present as monomeric solutes. The correlation with E _T serves to extend the solvent -scale according to the expression:

Asp746 to Glycine Change May have a Greater Influence than Cys751 to Serine Change in Accounting for Ligand Selectivity between EGFR and HER-2 at the ATP Site

Summary We have carried out up to 8.0 ns molecular dynamics simulation on the ATP-bound complexes of EGFR and HER-2 (homology model) receptor kinase domains to explore the possible consequences of amino acid residue changes in or close to the ATP site that might provide insights for selectivity of these kinases towards ATP site inhibitors. The simulation results show the formation of a channel under Thr766 following the movement of the side chain of Gln767 away from the hinge in EGFR. In HER-2, a similar movement of Gln799 occurs, but a simultaneous movement of Arg784 towards the hinge region occurs that tends to close the channel. The movement of Arg784 in HER-2 appears to result from the absence of an anchoring residue like Asp746 in EGFR, which has been changed to Gly778 in HER-2. In EGFR, this Arg784 is held away from the hinge region by interaction with Asp746, thereby leaving the channel open. This might be an important contributory factor to differences in selectivity of the ligands between the two kinases, probably more so than the conservative change of Cys751 of EGFR to serine in HER-2 at the ATP site.     

Determination of partition behavior of organic surrogates between paperboard packaging materials and air

The suitability of recycled paperboard packaging materials for direct food contact applications is a major area of investigation. Chemical contaminants (surrogates) partitioning between recycled paper packaging and foods may affect the safety and health of the consumer. The partition behavior of all possible organic compounds between cardboards and individual foodstuffs is difficult and too time consuming for being fully investigated. Therefore it may be more efficient to determine these partition coefficients indirectly through experimental determination of the partitioning behavior between cardboard samples and air. In this work, the behavior of organic pollutants present in a set of two paper and board samples intended to be in contact with foods was studied. Adsorption isotherms have been plotted and partition coefficients between paper and air have been calculated as a basis for the estimation of their migration potential into food. Values of partition coefficients (Kpaper/air) from 47 to 1207 were obtained at different temperatures. For the less volatile surrogates such as dibutyl phthalate and methyl stearate higher Kpaper/air values were obtained. The adsorption curves showed that the more volatile substances are partitioning mainly in air phase and increasing the temperature from 70 to 100 degrees C their concentrations in air (Cair) have almost doubled. The analysis of surrogates was performed with a method based on solvent extraction and gas chromatographic-flame ionization detection (GC-FID) quantification.     

Solvent-assisted catalysis mechanism on Keto–enol tautomerism of cyameluric acid

The keto–enol tautomerism of cyameluric acid, both in gas phase and in water and methanol solution, has been studied at the B3LYP/6-31++g(d,P) level of theory in this paper. The harmonic frequencies of all the structures are calculated. The results show that the transition states of the tautomerism are 4-membered ring conformations in gas phase, whereas 6-membered ring conformations in solution. In the first proton transfer, activation energy ΔE^# is 56.4 and 50.9 kJ/mol for water and methanol solution, respectively, which is much lower than that in gas phase (163.2 kJ/mol). Solvent molecules (water and methanol) produce an important catalytic effect in the tautomerism, especially for methanol-solvated system. NBO analysis shows that there is a strong interaction between cyameluric acid and solvent molecules in transition states. AIM charge analysis indicates that the keto–enol tautomerism shows a certain degree of proton transfer character. From the reaction enthalpy and reaction rate point of view, keto–enol tautomerism in water-solvated and methanol-solvated system is easier than that in gas phase. The keto–enol tautomerisms are endothermic both in gas phase and in solution, so the enol forms are less stable than the keto ones.