Pressure-induced core packing and interfacial dehydration in nonionic C12E6 micelle in aqueous solution

A spherical micelle of C12E6 is simulated at different pressures, from 0.001 to 3 kbar, by molecular dynamics. On increasing the pressure the alkyl tails of the surfactants pack tightly and stretch. At 3 kbar we observe dynamical slowing down of the oil core of the micelle. At that pressure the core is characterized by a high oil density, rho oil approximately 0.85 g/cm(3), regular density oscillation, and low chain entropy. Pressure affects the interfacial region as well. Dehydration, induced by the collapse of the hydrophilic head groups, is observed in the inner part of the interface. Such dehydration resembles temperature dehydration but differs in details. Our results support the interpretation of recent experiments on micellar solutions at high pressure.     

Synthesis and characterization of epoxy-modified cement slurries--kinetic data at hardened slurries/HCl interfaces

In this study, two new epoxy-modified oilwell cement slurries were synthesized. All characterization measurements were performed and compared in relation to a standard cement slurry, which was synthesized using only cement and water. The XRD patterns, as well as TG/DTG and DSC analyses have suggested that portlandite (Ca(OH)2) and carbonate phases were not present in detectable amounts in the new cement slurries. The isothermal kinetic data of the interaction of HCl with the epoxy-modified cement were obtained using the batch mode from 25 to 55 degrees C. The kinetic data were best fitted to the second-order and the Avrami kinetic models, since differences between experimental and calculated values were lower for these models. The intraparticle diffusion model has pointed out that the new slurries present positive values for the parameter "C," which is related to higher boundary layer resistance to HCl diffusion into the internal parts of the slurries, in relation to the standard slurry. The characterization and the HCl interaction kinetic studies have suggested that the new cement slurries present good potential, from the chemical viewpoint, to be used in oilwell operations.     

Electrokinetics in nanochannels: part II. Mobility dependence on ion density and ionic current measurements

In the first of this two-paper series, a new model was developed for calculating the electric potential field in a long, thin nanochannel with overlapped electric double layers. The model takes into account the dependence of ion mobility on local ion densities and pH. This model is used here to study and demonstrate the effect of ion density and pH on ionic current measurements. A comparison is shown of predictions based on each of three boundary conditions, as studied in Part I. The model developed in Part I is validated by comparing simulations with measurements of ionic current as a function of sodium borate concentration. Results show that predictions based on extended Debye-Hückel theory for ion mobility significantly improve the accuracy of simulations, but that these do not predict exact scaling behavior. A simple bulk conductivity measurement used as input parameter for the simulations, in place of the predicted bulk conductivity (K(0)), guarantees agreement with data in the thin EDL region. Results also indicate that the charge regulation boundary condition, complemented with an adequate bulk electrolyte model, provides better agreement with experimental trends than the specified zeta potential or specified surface net charge boundary conditions. Further, it is shown that currents due to advection (by electroosmotic flow) are in all cases studied less than 25% of the total current in the system.     

Electrokinetics in nanochannels: part I. Electric double layer overlap and channel-to-well equilibrium

In this paper a new model is described for calculating the electric potential field in a long, thin nanochannel with overlapped electric double layers. Electrolyte concentration in the nanochannel is predicted self-consistently via equilibrium between ionic solution in the wells and within the nanochannel. Differently than published models that require detailed iterative numerical solutions of coupled differential equations, the framework presented here is self-consistent and predictions are obtained solving a simple one-dimensional integral. The derivation clearly shows that the electric potential field depends on three new parameters: the ratio of ion density in the channel to ion density in the wells; the ratio of free-charge density to bulk ion density within the channel; and a modified Debye-Hückel thickness, which is the relevant scale for shielding of surface net charge. For completeness, three wall-surface boundary conditions are analyzed: specified zeta-potential; specified surface net charge density; and charge regulation. Predictions of experimentally observable quantities based on the model proposed here, such as depth-averaged electroosmotic flow and net ionic current, are significantly different than results from previous overlapped electric double layer models. In this first paper of a series of two, predictions are presented where channel depth is varied at constant well concentration. Results show that under conditions of electric double layer overlap, electroosmosis contributes only a small fraction of the net ionic current, and that most of the measurable current is due to ionic conduction in conditions of increased counterion density in the nanochannel. In the second of this two-paper series, predictions are presented where well-concentration is varied and the channel depth is held constant, and the model described here is employed to study the dependence of ion mobility on ionic strength, and compare predictions to measurements of ionic current as a function of channel depth and ion density.     

Direct palladium-catalyzed C-3 arylation of free (NH)-indoles with aryl bromides under ligandless conditions

A new method for the efficient, practical, and highly regioselective direct palladium-catalyzed C-3 arylation of free (NH)-indole and its electron-rich 1-unsubstituted derivatives under ligandless conditions is described. The reactions, which are run outside a glovebox without purification of solvent and reagents, involve treatment of free (NH)-indoles with activated, unactivated, and deactivated aryl bromides in refluxing toluene in the presence of K2CO3 as the base and a catalyst system consisting of a combination of Pd(OAc)2 and benzyl(tributyl)ammonium chloride. The experimental results are consistent with a catalytic cycle based on an electrophilic palladation pathway at the 3-position of 1-indolyl potassium salts.     

Reactivity of niobium and tantalum pentahalides with cyclic ethers and the isolation and characterization of intermediates in the polymerization of tetrahydrofuran

The complexes MX5(THF) (M = Nb, X = Cl, 2a; M = Ta, X = F, 2c, X = Cl, 2d) and [MX4(THF){O(CH2)4O(CH2)3CH2)}][MX6] (M = Nb, X = Cl, 3a; M = Ta, X = Cl, 3d, X = Br, 3e, X = I, 3f) result from reactions of MX5 with 0.5 and 1.5 equiv of THF, respectively. Compounds 3 contain the unprecedented 4-(tetrahydrofuran-1-ium)-butan-1-oxo ligand and are likely to play a role in the course of THF polymerization catalyzed by MX5. The addition of L (L = 2,5-dimethyltetrahydrofuran, tetrahydropyran, 1,4-dioxane) to MX5 results in the formation of the hexacoordinated complexes MX5(L). The molecular structures of 2d, 3d, and NbCl5(dioxane), 6a, have been ascertained by X-ray diffraction studies.     

Development and validation of an HPLC method to quantify camptothecin in polymeric nanocapsule suspensions

A simple, rapid, and sensitive reversed-phase column high-performance liquid chromatographic method was developed and validated to quantify camptothecin (CPT) in polymeric nanocapsule suspensions. The chromatographic separation was performed on a Supelcosil LC-18 column (15 cm x 4.6 mm id, 5 microm) using a mobile phase consisting of methanol-10 mM KH2PO4 (60 + 40, v/v; pH 2.8) at a flow rate of 1.0 mL/min and ultraviolet detection at 254 nm. The calibration graph was linear from 0.5 to 3.0 microg/mL with a correlation coefficient of 0.9979, and the limit of quantitation was 0.35 microg/mL. The assay recovery ranged from 97.3 to 105.0%. The intraday and interday relative standard deviation values were < 5.0%. The validation results confirmed that the developed method is specific, linear, accurate, and precise for its intended use. The current method was successfully applied to the evaluation of CPT entrapment efficiency and drug content in polymeric nanocapsule suspensions during the early stage of formulation development.     

Efficient synthesis and environmentally friendly reactions of PEG-supported 1,2-diaza-1,3-butadiene

[reaction: see text] Here, we report the protocol for the preparation of new poly(ethylene glycol)-supported 1,2-diaza-1,3-butadiene. In addition, we discuss an application of this supported reagent in an efficient and environmentally friendly one-pot synthesis of 2-thiazol-4-one derivatives by reaction with thioamides.     

Using ring strain to inhibit a decomposition path: first synthesis of an Alkyl-BIAN ligand (Alkyl-BIAN = bis(alkyl)acenaphthenequinonediimine)

N-Alkyl imines of acenaphthenequinone are not stable because an isomerization occurs that releases part of the ring strain of the initially formed imine by changing the hybridization of one of the ring carbon atoms from sp(2) to sp(3); however, if an even more strained ring is present in the alkyl group, the isomerization becomes unfavorable and the compound is stable.