Branched versus linear oligo(dimethylsiloxane): Differences in their thermodynamic interaction with solvents

The thermodynamic behavior of linear and of branched oligo(dimethylsiloxane) (O‐DMS) solutions was studied by means of vapor pressure measurements and vapor pressure osmometry at different temperatures for the thermodynamically favorable solvent THF. The branched material required for that purpose was synthesized and afterwards fractionated by means of the single solvent acetone to eliminate components of low degrees of branching. The Flory‐Huggins interaction parameters, χ, for the systems THF/O‐DMS as a function of composition pass a minimum at all temperatures (25, 40, and 60 °C) in the case of the branched material. For the unbranched oligomer such a minimum is only observed at 60 °C. At 40 °C the results are ambigous whereas the dependence is definitely linear at 25 °C. This exceptional behavior of the linear product at the latter temperature is tentatively attributed to the formation of favorable orientational order in the pure state under these conditions. At high oligomer concentrations THF interacts more favorably with the branched material, however, this preference is reversed upon dilution. All measured composition dependencies of χ can be modeled quantitatively by an approach accounting for chain connectivity and for the ability of the oligomers to change their conformation upon dilution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1309–1318, 2010     

Total synthesis and determination of the absolute configuration of coscinosulfate. A new selective inhibitor of Cdc25 protein phosphatase.

The first total synthesis of coscinosulfate 1, a metabolite isolated from a sea sponge, starting from (+)-sclareolide 3 is described. The convergent synthesis strategy relies on the coupling of sulfone 21 with the bromide 26. The sulfone fragment 21 was obtained by successive asymmetric aldol reaction with aldehyde 2 to introduce the stereocenters at C-12 and C-13, followed by one-carbon homologation via Horner-Wadsworth-Emmons olefination. The selective sulfatation at C-12 was accomplished through the quinone intermediate 31 obtained by selective oxidation of hydroquinone 30; this, when followed by reduction, furnished the desired coscinosulfate 1. X-ray analysis of the intermediate aldehyde 18 confirmed the proposed structure.     

Designing chiral amido-oxazolines as new chelating ligands devoted to direct Cu-catalyzed oxidation of allylic CH bonds in cyclic olefins

A new type of amido-oxazoline ligands was conveniently synthesized from inexpensive and commercially available materials in high yields and enantiomeric excesses. The corresponding chiral copper complexes with this class of ligands [C₂ symmetric S,S-bis(amido-oxazoline-Cu(II) complex] were synthesized accordingly. The ORTEP diagram of ligand 6a and complex 6a-copper were compared and characterization of the complex confirmed the involvement of both dentate parts of the ligands, the oxygen and nitrogen atoms, in complexation with copper. The utilization of this amido-oxazoline ligands in the copper-catalyzed enantioselective esterification of allylic CH bonds of cyclic olefins with tert-butyl-4-nitrobenzoperoxoate resulted in the highest activities, yields (up to 95%) and enantioselectivities (up to 96%) in the presence of HZSM-5 zeolite. These new findings highlight the protocol as one of the most attractive and useful methods for the oxidation of the asymmetric allylic CH bond of cycloalkenes compared to other methodologies reported in the literature.     

A reinvestigation of the acid-promoted heterocyclization of 2-(2-oxo-2-arylethyl)malononitriles in the presence of amines

The reinvestigation of the acid-promoted cyclization of 2-(2-oxo-2-arylethyl)malononitriles, in the presence of benzylamine or aniline, in ethanol or acetonitrile, has confirmed that this is a long-time reaction process for a low-yielding synthesis of 2-amino-5-arylfuran-3-carbonitriles (2), or 2-amino-5-aryl-1-phenyl-1H-pyrrole-3-carbonitriles (4), depending on the base used. However, the microwave-assisted synthesis of 2-amino-5-(4′-methoxyphenyl)furan-3(4)-(di)carbonitriles (2c and 3c) proceeds in shorter reaction times and higher yields than does the classical thermal heating protocol. In these reactions we have observed for the first time, and characterized by their spectroscopic data and X-ray analysis, the unexpected formation of 2-amino-5-aryl-3 (4)-(di)carbonitriles (3), whose formation has been rationalized by density functional theory (DFT) analysis of the proposed reaction mechanism.     

Temperature Sensitive Superabsorbent Hydrogels from Poly(N-t-butyl acrylamide-co-acrylamide) Grafted on Sodium Alginate

Temperature-sensitive hydrogels based on N-t-butylacrylamide (TBA), acrylamide (AAm), and sodium alginate were prepared by free radical polymerization method. Methylenebisacrylamide (MBA) and amonium persulfate (APS) were applied as water soluble crosslinker and initiator, respectively. The chemical structure of the hydrogels was confirmed by FT-IR spectroscopy and thermogravimetric analysis (TGA) methods. Morphology of the samples was examined by scanning electron microscopy (SEM). By changing the initial TBA/AAm mole ratios, hydrogels with different swelling properties were obtained. The rate parameters were found to be 2.0, 2.4, and 3.5 min for the superabsorbents with AAm/TBA weight ratio of 1.0, 1.3 and 2.0 respectively. The swelling behavior in distilled water and different pH solutions was investigated. A preliminary swelling kinetics and the absorbency under load (AUL) were also studied. At the applied pressure (2.07 kPa), maximum swelling was found to be 17, 19, and 21 (g/g) for the superabsorbent hydrogels with AAm/TBA weight ratios of 1.0, 1.5 and 2.0, respectively.     

Optimization of dispersive liquid-liquid microextraction coupled with inductively coupled plasma-optical emission spectrometry with the aid of experimental design for simultaneous determination of heavy metals in natural waters

In this study, dispersive liquid-liquid microextraction (DLLME) combined with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed for simultaneous preconcentration and trace determination of chromium, copper, nickel and zinc in water samples. Sodium diethyldithiocarbamate (Na-DDTC), carbon tetrachloride and methanol were used as chelating agent, extraction solvent and disperser solvent, respectively. The effective parameters of DLLME such as volume of extraction and disperser solvents, pH, concentration of salt and concentration of the chelating agent were studied by a (2^f−1) fractional factorial design to identify the most important parameters and their interactions. The results showed that concentration of salt and volume of disperser solvent had no effect on the extraction efficiency. In the next step, central composite design was used to obtain optimum levels of effective parameters. The optimal conditions were: volume of extraction solvent, 113 μL; concentration of the chelating agent, 540 mg L⁻¹; and pH, 6.70. The linear dynamic range for Cu, Ni and Zn was 1-1000 μg L⁻¹ and for Cr was 1-750 μg L⁻¹. The correlation coefficient (R²) was higher than 0.993. The limits of detection were 0.23-0.55 μg L⁻¹. The relative standard deviations (RSDs, C = 200 μg L⁻¹, n = 7) were in the range of 2.1-3.8%. The method was successfully applied to determination of Cr, Cu, Ni and Zn in the real water samples and satisfactory relative recoveries (90-99%) were achieved.     

Optimized ultrasonic assisted extraction-dispersive liquid-liquid microextraction coupled with gas chromatography for determination of essential oil of Oliveria decumbens Vent

Ultrasonic assisted extraction-dispersive liquid-liquid microextraction (UAE-DLLME) coupled with gas chromatography (GC) was applied for extraction and determination of essential oil constituents of the plant Oliveria decumbens Vent. Scanning electron microscopy (SEM) was used to see the effect of ultrasonic radiation on the extraction efficiency. By comparison with hydrodistillation, UAE-DLLME is fast, low cost, simple, efficient and consuming small amount of plant materials (～1.0 g). The effects of various parameters such as temperature, ultrasonication time, volume of disperser and extraction solvents were investigated by a full factorial design to identify significant variables and their interactions. The results demonstrated that temperature and ultrasonication time had no considerable effect on the results. In the next step, a central composite design (CCD) was performed to obtain the optimum levels of significant parameters. The obtained optimal conditions were: 0.45 mL for disperser solvent (acetonitrile) and 94.84 μL for extraction solvent (chlorobenzene). The limits of detection (LODs), linear dynamic range and determination coefficients (R(2)) were 0.2-29 ng mL(-1), 1-2100 ng mL(-1) and 0.995-0.998, respectively. The main components of the essential oil were: thymol (47.06%), carvacrol (23.31%), gamma-terpinene (18.94%), p-cymene (8.71%), limonene (0.76%) and myristicin (0.63%).     

Synthesis and Application of Co‐Poly(2‐hydroxyethyl methacrylate‐ethylene dimethacrylate) Coupled with Alizarin Yellow for Preconcentration and Determination of Lead in Water Samples by Flame Atomic Absorption Spectrometry

Poly(2‐hydroxyethyl methacrylate‐ethylene dimethacrylate) (PHEMA‐EDMA) beads were produced by free radical co‐polymerization of 2‐hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA). Then, metal complexing ligand alizarin yellow was covalently attached onto PHEMA‐EDMA beads. The resulting resin has been characterized by FT‐IR and studied for the preconcentration and determination of trace Pb(II) ion from solution samples. The optimum pH value for sorption of the metal ion was 5. The sorption capacity of functionalized resin is 100 mg.g^‐1. The chelating resin can be reused for 20 cycles of sorption‐desorption without any significant change in sorption capacity. A recovery of 96% was obtained for the metal ion with 0.1 M nitric acid as eluting agent. The equilibrium adsorption data of Pb(II) on modified resin were analyzed by Langmuir and Freundlich models. Based on equilibrium adsorption data the Langmuir and Freundlich constants were determined 2.571 and 418.7 at pH 5 and 25 °C. The method was applied for lead ions determination from well water sample.