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.     

Two-point versus multipartite entanglement in quantum phase transitions

We analyze correlations between subsystems for an extended Hubbard model exactly solvable in one dimension, which exhibits a rich structure of quantum phase transitions (QPTs). The T = 0 phase diagram is exactly reproduced by studying singularities of single-site entanglement. It is shown how comparison of the latter quantity and quantum mutual information allows one to recognize whether two-point or shared quantum correlations are responsible for each of the occurring QPTs. The method works in principle for any number D of degrees of freedom per site. As a by-product, we are providing a benchmark for direct measures of bipartite entanglement; in particular, here we discuss the role of negativity at the transition.     

1-Aminopyrazolin-5-ones. Synthesis and reactivity

A synthesis of 1-aminopyrazolin-5-ones (I) by chloramine attack on the 2-benzylpyrazolones (IVd-e) has been accomplished. Nucleophilic substitution reactions of aminopyrazolones (I) are investigated; with 1,4-diketones, N,N'-pyrrolylpyrazolones (XVIIa-c) are obtained. Chlorination of acetylaminopyrazolones (VII) led to the corresponding 1-amino-5-chloropyrazoles (XXI) via the isolable pyrazolo[3,2-b]oxadiazoles (XIX).