Electrocatalysis by foreign metal monolayers: Oxidation of formic acid on palladium

Catalytic effects of foreign metal monolayers deposited at underpotentials have been found for the oxidation of formic acid on palladium electrode. Palladium is known to form no poisoning species in oxidation of HCOOH. However, the auto-inhibition of the reaction is found, caused most probably by a species _xC_x(OH)₂. Submonolayer amounts of Pb, Bi, Cd, Tl, Ag and Cu electrosorbed at underpotentials exhibited significant catalytic effects which could be explained by the so-called “third-body” effect in terms of a previously published semiquattitative model. The results have bearing on the understanding of the catalytic effects observed under comparable conditions on platinum and rhodium. Since these effects are orders of magnitude larger than those on palladium, the “third-body” effect probably plays only a minor role at the other two noble metals.     

Effect of plasticization by amines on the physical properties of an acidic styrene copolymer

The dynamic mechanical properties of partly sulfonated (8.1 mole%) polystyrene were investigated at a frequency of ca. 1 Hz, following neutralization with various low molecular weight flexible and rigid amines. IR spectroscopic evidence suggested that the protonated amine units were possibly H-bonded to the sulfonate anion. Neutralization with flexible amines was found to result in a decrease in the glass transition temperature T_g by an amount proportional to the number of carbon atoms in the amine, while neutralization with rigid amines was found to result in an increase in T_g. It was also observed that the amines were more miscible with the sulfonated material than with polystyrene. It was concluded that the changes in properties observed upon neutralization are similar to those expected from a graft.     

Far-infrared studies of ion clustering in ionomers

The far-infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion-site concentration to obtain spectroscopic evidence of domain formation. A far-infrared band, due to the vibration of a higher-order cluster, is found at 170 cm^?1in Na⁺-form PSMA. This band, which is observed in addition to the known cation-motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggregation models.     

A simple insurance model: optimal coverage and deductible

An insurance model, with realistic assumptions about coverage, deductible and premium, is studied. Insurance is shown to decrease the variance of the cost to the insured, but increase the expected cost, a tradeoff that places our model in the Markowitz mean-variance model.     

Alkylated styrene ionomers with variable length spacers. I. Synthesis

Two analogous series of ionomer precursors based on 4-substituted styrene copolymers were prepared with substituents R = -(CH_2)nCO₂Me (n = 1, 5, 10), or R = -O(CH₂)_nCO₂Me (n = 1, 4, 10), and degrees of substitution from 10 to 15 mol%. The synthesis of the alkyl series compounds involved either chloromethylation of polystyrene or bromoalkylation via lithiation of a styrene-4-bromostyrene copolymer, followed by conversion to the nitriles. Methyl esters were then produced by reaction of the nitriles with methanol/HCl gas. The ether series compounds were obtained directly by reacting a styrene-4-hydroxystyrene copolymer with the methyl esters of the corresponding ω-bromoaliphatic carboxylic acids in a Williamson ether-type synthesis.     

Deubiquitinating enzymes are IN/(trinsic to proteasome function)

Covalent conjugation of the ubiquitin tag to cellular proteins plays a central role in a number of processes, the most notable among them being degradation by the 26S proteasome. A fundamental property of this process is that ubiquitination, in contrast to subsequent degradation, is reversible due to a number of deubiquitinating enzymes that mediate the disassembly of ubiquitin-protein conjugates. The uniqueness of ubiquitin as a reversible tag necessitates mechanisms to guarantee its efficiency. Interestingly, some deubiquitinating enzymes are associated with the 26S proteasome itself. We include a brief overview of the key proteasome-associated deubiquitinating enzymes such as Rpn11/POH1, UCH37/Uch2, Ubp6/Usp14 and Doa4/Ubp4. We go on to discuss how these enzymes may contribute to, or possibly counteract, proteolysis by the proteasome. For example, cumulative evidence points to a partitioning of proteasome action between proteolysis and deubiquitination. On the one hand, inhibition of proteolysis promotes deubiquitination, while on the other hand, inhibition of deubiquitination can promote proteolysis. The plethora of deubiquitinating enzymes may serve as proof reading devices altering the equilibrium between these two processes and allowing for reversal of fortune at various stages of the process. To promote degradation over deubiquitination, certain polyubiquitin conformations could be stabilized or protected from deubiquitinating enzymes in order that they can serve as efficient targeting signals leading to the proteasome. We hypothesize that polvubiquitin chains could also serve as "timers": by slowing down chain disassembly, longer chains allow ample time for unfolding and proteolysis of the substrate.     

Polystyrene-b-poly(acrylic acid) vesicle size control using solution properties and hydrophilic block length

Polymeric vesicles have attracted considerable attention in recent years, since they are a model for biological membranes and have versatile structures with several practical applications. In this study, we prepare vesicles from polystyrene-b-poly(acrylic acid) block copolymer in dioxane/water and dioxane/THF/water mixtures. We then examine the ability of additives (such as NaCl, HCl, or NaOH), solvent composition, and hydrophilic block length to control vesicle size. Using turbidity measurements and transmission electron microscopy (TEM) we show that larger vesicles can be prepared from a given copolymer by adding NaCl or HCl, while adding NaOH yields smaller vesicles. The solvent composition (ratio of dioxane to THF, as well as the water content) can also determine the vesicle size. From a given copolymer, smaller vesicles can be prepared by increasing the THF content in the THF/dioxane solvent mixture. In a given solvent mixture, vesicle size increases with water content, but such an increase is most pronounced when dioxane is used as the solvent. In THF-rich solutions, on the other hand, vesicle size changes only slightly with the water concentration. As to the effect of the acrylic acid block length, the results show that block copolymers with shorter hydrophilic blocks assemble into larger vesicles. The effect of additives and solvent composition on vesicle size is related to their influence on chain repulsion and aggregation number, whereas the effect of acrylic acid block length occurs because of the relationship among the block length, the width of the molecular weight distribution, and the stabilization of the vesicle curvature.     

Stable room-temperature molecular negative differential resistance based on molecule-electrode interface chemistry

We show reproducible, stable negative differential resistance (NDR) at room temperature in molecule-controlled, solvent-free devices, based on reversible changes in molecule-electrode interface properties. The active component is the cyclic disulfide end of a series of molecules adsorbed onto mercury. As this active component is reduced, the Hg-molecule contact is broken, and an insulating barrier at the molecule-electrode interface is formed. Therefore, the alignment of the molecular energy levels, relative to the Fermi levels of the electrodes, is changed. This effect results in a decrease in the current with voltage increase as the reduction process progresses, leading to the so-called NDR behavior. The effect is reproducible and repeatable over more than 50 scans without any reduction in the current. The stability of the system, which is in the "solid state" except for the Hg, is due to the molecular design where long alkyl chains keep the molecules aligned with respect to the Hg electrode, even when they are not bound to it any longer.     

Influence of metalation on the morphologies of poly(ethylene oxide)-block-poly(4-vinylpyridine) block copolymer micelles

Micellization of a poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO45-b-P4VP28) copolymer in water during metalation (incorporation of gold compounds and gold nanoparticle formation) with three types of gold compounds, NaAuCl4, HAuCl4, and AuCl3, was studied using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The transformations of the PEO45-b-P4VP28 block copolymer micelles in water were found to depend on a number of parameters including the thermal history of the as-prepared block copolymer, the type of the metal compound, and the metal loading. For the HAuCl4-filled PE045-b-P4VP28 micelles, the subsequent reduction with hydrazine hydrate results in a significant fraction of rodlike micelles, suggesting that slow nucleation (confirmed by the formation of the large gold nanoparticles) and facilitated migration of gold ions yields the ideal conditions for sphere-to-rod micellar transition.     

Chiral enhancement in diethyl malonate addition by morphosynthesized L-proline mesoporous silica

l-Proline was immobilized onto mesoporous silica through direct synthesis method via morphosynthesis possessing short channels and plugs in the pore structure which provided chiral enhancement in the diethyl malonate addition reaction.