Highly efficient magnesium initiators for lactide polymerization

Two monomeric, six-coordinated magnesium complexes with bulky aminophenolate ligands [(Htbpoa)2Mg] (1) and [(Htbpca)2Mg(THF)2] (2), where Htbpoa =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-dioxolaneamine and Htbpca =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine have been prepared, characterized and employed as initiators for lactide polymerization. The crystal structure of the homoleptic compound 1 has been determined and shows that the six-coordinate magnesium atom in 1 is surrounded by two tridendate tbpoa ligands. In the solution, however, complex 1 exists in equilibrium with a five-coordinate species 1a having one oxolane fragment dangling. The tbpoa and tbpca ligands in 1 and 2 play a dual role, as the ancillary ligand stabilizing the monomeric magnesium species and as the initiating polymerization group.     

Infrared,Raman, and cndo studies of the effect of ions on the electron density distribution in formamide

Infrared and Raman spectra of electrolyte solutions in formamide have been investigated for amide I and CH stretching regions. The effects of the cation-molecule and anion-molecule interactions on the frequency shift and IR intensity are discussed in terms of CNDO/2 calculations performed for the model formamide complexes with Li⁺ and F^? ions. It is suggested that the considerable CH frequency shift upon cornplexing with cation is due to the trans lone pair effect.     

Influence of heavy metals, especially lead, on lipid metabolism, serum alpha-tocopherol level, total antioxidant status, and erythrocyte redox status of copper smelter workers

An assessment of influence of the occupational exposure to heavy metals, especially lead, on serum lipids (including lipid peroxides), total antioxidant status, erythrocyte redox status, and serum alpha-tocopherol level was performed in a group of 141 healthy male copper smelter workers. The following parameters were measured: blood lead and cadmium levels, serum manganese, copper, zinc, calcium and magnesium levels, free erythrocyte protoporphyrins (FEP), total cholesterol, HDL₂-, HDL₃-cholesterol, triglycerides and lipid peroxides in serum, erythrocyte superoxide dismutase (SOD_E), catalase (Cat_E) and glutathion peroxidase (PxGSH_E) activities, erythrocyte reduced glutathione level (GSH_E), serum alpha-tocopherol level, and serum total antioxidant status (TAS). Mean Pb_B was within the norm range (328.2 ± 141.7 μg/L), but mean Mn_S concentration slightly exceeded 10 μg/L (11.04 ± 3.79 μg/L). Mean cholesterol and triglycerides concentrations were near the highest borderline values. We found a significantly negative correlation between lead levels and HDL₃-cholesterol (r = 0.253, P < 0.05). Erythocyte catalase activity and TAS were lowered. TAS showed significant negative correlation with Pb_B. A group of workers with Pb_B≥ 400 μg/L had significantly lower Cat_E, lower TAS, and lower HDL₃-cholesterol, compared to the workers with Pb < 400 μg/L. We have also found positive correlation between alpha-tocopherol and total cholesterol (r = 0.267, P < 0.05) and between alpha-tocopherol and LDL-cholesterol (r = 0.207, P < 0.05).     

Synthesis of a Bifunctional 1,1′-Diphenyl-1,2,3,4-tetrahydroquinoline Derivative: 1,1′-Diphenyl-1,2,3,4,1′,2′,3′,4′-octahydro-6,6′-biquinolinyl-3,3′-diol

Summary. Intramolecular cyclization of N,N′-di(3-chloro-2-hydroxy)propyl-N,N′-diphenylbenzidine occurs to give bis-1,2,3,4-tetrahydroquinoline derivative 1,1′-diphenyl-1,2,3,4,1′,2′,3′,4′-octahydro-6,6′-biquinolinyl-3,3′-diol.     

Electronic structure of compound I in human isoforms of cytochrome P450 from QM/MM modeling

Human cytochromes P450 play a vital role in drug metabolism. The key step in substrate oxidation involves hydrogen atom abstraction or C=C bond addition by the oxygen atom of the Compound I intermediate. The latter has three unpaired electrons, two on the Fe-O center and one shared between the porphyrin ring and the proximal cysteinyl sulfur atom. Changes in its electronic structure have been suggested to affect reactivity. The electronic and geometric structure of Compound I in three important human subfamilies of cytochrome P450 (P450, 2C, 2B, and 3A) that are major contributors to drug metabolism is characterized here using combined quantum mechanical/molecular mechanical (QM/MM) calculations at the B3LYP:CHARMM27 level. Compound I is remarkably similar in all isoforms, with the third unpaired electron located mainly on the porphyrin ring, and this prediction is not very sensitive to details of the QM/MM methodology, such as the DFT functional, the basis set, or the size of the QM region. The presence of substrate also has no effect. The main source of variability in spin density on the cysteinyl sulfur (from 26 to 50%) is the details of the system setup, such as the starting protein geometry used for QM/MM minimization. This conformational effect is larger than the differences between human isoforms, which are therefore not distinguishable on electronic grounds, so it is unlikely that observed large differences in substrate selectivity can be explained to a large extent in these terms.     

Atmospheric and electrochemical oxidation of ascorbic acid in anionic,nonionic and cationic surfactant systems

It is well known that the antioxidant activity of some species in homogenous solutions may not be the same as that in heterogeneous media. This environment dependence is the reason for investigating ascorbic acid antioxidant activity in surfactant solutions. In our study we have investigated the kinetics of atmospheric oxidation and electrochemical oxidation of ascorbic acid in aqueous solutions of the four surfactants: SDS, AOT (anionic), TRITON-100 (nonionic), and CTAB (cationic). For each surfactant the concentrations below and above CMC were investigated. As expected, a general trend in the atmospheric oxidation rate changes in the following manner: the micellar solution of nonionic surfactant shows a faster oxidation rate than that of the anionic surfactant, and the cationic surfactant an even higher one. The more subtle effects were observed with each surfactant concentration change. The influence of the surfactants on the electrochemical behavior of ascorbic acid was also studied. A general conclusion emerging from our investigation is that surfactants shift the ascorbic acid oxidation potential and change the peak current value. This phenomenon is due mainly to the surfactant film formed at the electrode/solution interface.     

Poly(phenylene oxide) films modified with allylamine plasma as a support for invertase immobilization

The paper describes a method for preparation of polymer support suitable for covalent invertase immobilization. Modification of poly(phenylene oxide) films by plasma polymerization of allylamine has been applied to introduce amine functionality on the polymer surface. It has been observed that the polymer surface became covered in plasma by a loosely fixed, moderately hydrophilic layer that should be removed before the immobilization process. The chemical character of the stable sub-layer has been related to several modification parameters: geometry of reactor, mode of plasma action and composition of gaseous mixture. Methods for determination of surface concentration of amine groups have also been presented and discussed from the immobilization point of view.     

Singlet excitation energies of thiophene derivatives of fluorene: TD‐DFT study

Fluorene‐thiophene (FT)‐based oligomers and polymers and their derivatives are good candidates for organic blue light‐emitting diodes. In this work, the intrinsic properties of the ground and excited states of FT monomer and its derivatives are studied. The ground‐state optimized structures and energies are obtained using molecular orbital theory and density functional theory (DFT). The ground‐state potential energy curves or surfaces of FT and its derivatives are also obtained. All derivatives are nonplanar in their electronic ground states. The character and energy of the first 20 singlet–singlet electronic transitions are investigated by applying the time‐dependent density functional theory (TD‐DFT) approximations to the correspondingly optimized ground‐state geometries. The lowest singlet state is studied with the configuration interaction (singles) approach (CIS). Excitation energies are red shifted when the FT unit or its derivatives are extended longitudinally. CIS results suggest geometry relaxation in the first singlet excited state. When available, a comparison is made with experimental results. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Sodium dithionite initiated reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane with enol ethers of cyclic ketones

Sodium dithionite initiated reactions of 1-bromo-1-chloro-2,2,2-trifluoroethane (1) with methyl and trimethylsilyl ethers of cyclopentanone and cyclohexanone enols (2a-d) in a MeCN/H₂O system were investigated. 2-(2,2,2-Trifluoroethylidene)cyclopentanone (4a) and 2-(2,2,2-trifluoroethylidene)-cyclohexanone (4b), respectively, were obtained as the main products and isolated in reasonable yields. The reaction with a 1:1 mixture of 5- and 3-methyl substituted 1-methoxycyclohexenes, 2e and 2f, revealed strong influence of steric hindrance on the reaction rate; a mixture of 2-(2,2,2-trifluoroethylidene)-5-methylcyclohexanone (6) and 2-(2,2,2-trifluoroethylidene)-3-methylcyclohexanone (7) in a 9:1 ratio was formed. Ketones 4a and 4b were reduced to the corresponding alcohols 8 and 9 and the reaction of 4b with hydrazine gave an indazole derivative 10.     

The analysis of the electrical properties of BLT ceramics fabricated from sol-gel derived powders

The (Ba_xLa_1?x)Ti_1?x/4O₃ (BLT,0.001 ≤ x ≤ 0.005) amorphous gel was prepared by sol-gel process. The electricalproperties of obtained materials has been investigated by impedance spectroscopy. Detailedanalysis of impedance spectra allowed to propose an adequate equivalent circuit, whichdescribed the electric properties of discussed materials very well. Basing on the obtainedcircuits and the fitting procedure the grain and grain boundary resistivity was determinedas a function of temperature and La concentration. With increase of La admixture thecontribution of grain and grains impedance to the bulk impedance changes. It was foundthat the small amount of La additive decreases the blocking factor of the grain boundaryin the temperature range 600–850 K, whereas the amount of La on the level of 0.4–0.5 mol.%causes the sharp increase of the mentioned factor. The fact may be attributed to adecrease of grain activation energy and increase of the grain boundary one.