Novel pH microsensor based on a thin film gold electrode modified with lead dioxide nanoparticles

Microchimica Acta - A highly sensitive thin-film pH micro-sensor has been fabricated by deposition of lead dioxide (β-PbO2) nanoparticles (NPs) on a planar gold electrode. The resulting pH...     

A grid redistribution method for singular problems

Many physical phenomena develop singular, or nearly singular behavior in localized regions, e.g. boundary layers or blowup solutions. Using uniform grids for such problems becomes computationally prohibitive as the solution approaches singularity. Ren and Wang developed a semi-static adaptive grid method [W. Ren, X.P. Wang, An iterative grid redistribution method for singular problems in multiple dimensions, J. Comput. Phys. 159 (2000) 246–273] for the solution of these problems, known as the iterative grid redistribution (IGR) method. In this study we develop a theoretical basis for semi-static adaptive grid method for singular problems. Based on this theory, we obtain the key result of this study – a methodology for designing robust weight functionals which ensures grid resolution in the singular region, as well as control of the maximal grid spacing in the outer region. Using this methodology, we introduce a semi-static adaptive grid method, which does not involve an iterative procedure for grid redistribution, as in the IGR method. We demonstrate the efficacy of this method with numerical examples of solutions which localize by more than nine orders of magnitude.     

Lower bounds in communication complexity based on factorization norms

We introduce a new method to derive lower bounds on randomized and quantum communication complexity. Our method is based on factorization norms, a notion from Banach Space theory. This approach gives us access to several powerful tools from this area such as normed spaces duality and Grothendiek's inequality. This extends the arsenal of methods for deriving lower bounds in communication complexity. As we show, our method subsumes most of the previously known general approaches to lower bounds on communication complexity. Moreover, we extend all (but one) of these lower bounds to the realm of quantum communication complexity with entanglement. Our results also shed some light on the question how much communication can be saved by using entanglement. It is known that entanglement can save one of every two qubits, and examples for which this is tight are also known. It follows from our results that this bound on the saving in communication is tight almost always. © 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2009     

The first stereoselective total synthesis of the Z-isomer of cytospolide E

A convergent and highly stereoselective total synthesis of the Z-isomer of cytospolide E has been achieved via Evan’s aldol reaction, Sharpless kinetic resolution and RCM cyclisation.     

A one-round,two-prover,zero-knowledge protocol for NP

The model of zero-knowledge multi-prover interactive proofs was introduced by Ben-Or, Goldwasser, Kilian and Wigderson in [4]. A major open problem associated with this model is whether NP problems can be proven by one-round, two-prover, zero-knowledge protocols with exponentially small error probability (e.g. via parallel executions). A positive answer was claimed by Fortnow, Rompel and Sipser in [12], but its proof was later shown to be flawed by Fortnow who demonstrated that the probability of cheating inn independent parallel rounds can be much higher than the probability of cheating inn independent sequential rounds (with exponential ratio between them). In this paper we solve this problem: We show a new one-round two-prover interactive proof for Graph Hamiltonicity, we prove that it is complete, sound and perfect zeroknowledge, and thus every problem in NP has a one-round two-prover interactive proof which is perfectly zero knowledge under no cryptographic assumptions. The main difficulty is in proving the soundness of our parallel protocol namely, proving that the probability of cheating in this one-round protocol is upper bounded by some exponentially low threshold. We prove that this probability is at most 1/2 ^n/9 (wheren is the number of parallel rounds), by translating the soundness problem into some extremal combinatorial problem, and then solving this new problem.     

Stereospecific hydride transfer under NCI/OH− conditions. 2—Origins of the C2H4O elimination from stereoisomeric alkoxyketal derivatives1

A new stereospecific intramolecular hydride transfer, induced by an alkoxide, has been demonstrated under NCI/OH^? conditions using unimolecular and collision-induced decomposition spectra.     

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

Dendrimers, the aesthetically beautiful macromolecules displaying a variety of potentially useful architecture‐induced properties, are traditionally assembled in solution. However, since 1988, a number of dendritic structures have been assembled on insoluble organic and inorganic polymers, and thus dendronized supports have been formed. One of the major applications of these new materials is in the field of heterogeneous catalysis. Supported dendritic catalytic systems, bearing the catalytic units on the dendron periphery, have been examined in the last 5 years in such reactions as hydroformylation, Heck and other Pd‐catalyzed C? C bond formations, oxidation, and enantioselective addition to aldehydes. In the majority of these studies, substantial dendritic effects on the reactivity, selectivity, or recyclability of the catalysts were observed. Although a number of factors have been suggested as sources of the effects, it is most likely that the phenomenon has a multicomponent origin. Additional research, including a full determination of the effects and their causes, is likely to lead to markedly better heterogeneous catalytic systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 235–262, 2005     

Preparation and pH triggered inversion of vesicles from poly(acrylic acid)-block-polystyrene-block-poly(4-vinyl pyridine)

The aggregate morphologies of the biamphiphilic triblock PAA(26)-b-PS(890)-b-P4VP(40) have been studied by TEM as a function of pH in DMF/THF/H(2)O mixtures. The outside surfaces of the aggregates were characterized by zeta potential measurements. Starting at the apparent pH (pH) of 1, and increasing gradually to pH14, the aggregate morphologies of this triblock change progressively from vesicles (pH1), to solid spherical or ellipsoidal aggregates (pH3 approximately 11), and finally back to vesicles (pH14). Vesicles prepared at pH1 contain P4VP chains on the outside and PAA chains on the inside, while those prepared from the same triblock at pH14 contain PAA outside and P4VP inside. The segregation is based on the difference in repulsive interactions within the PAA or P4VP corona under different pH conditions. At low pH, the curvature is stabilized through increased repulsive interactions between the P4VP chains on the outside relative to the less repulsive interactions between the PAA chains on the inside. At pH14, by contrast, the PAA is preferentially segregated to the outside and the P4VP to the inside because of the increased repulsive interaction between PAA chains and the decreased repulsive interaction between P4VP chains at high pH. Most importantly, vesicles with PAA on the outside can be inverted to P4VP on the outside by changing the pH while the vesicles have swollen cores and are under dynamic conditions. The conversion mechanism is suggested to involve a whole vesicle process because the CMC is far too low for single chain reassembly to be involved.     

Beneficial effect of water as second solvent in ionic liquid biphasic catalytic hydrogenations

When reactions take place in ionic liquids, a solvent is normally used to extract the products after reaction. It is reported here how the presence of the solvent during the reaction already can seriously improve the catalytic performance. Above all, employing water as the added solvent enhanced the catalytic activities significantly, ascribed to the creation of a well mixed ‘emulsion-like’ system. The reductions of methyl 2-acetamidoacrylate with Rh-EtDuPHOS and of 2-cyclohexen-1-one with Wilkinson’s catalyst in bmimPF₆ were thus successfully performed in the presence of water. The complexes were easily recycled and Rh-EtDuPHOS was even no longer air sensitive.