Interactions between inorganic salts and polyacrylamide in aqueous solutions and gels

The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous solutions were predominantly affected by anion type and increased according to the lyotropic series ranking of sodium halide anions: F^? < (H₂O) < Cl^? < Br^? < I^?. The osmotic pressure of PAAm in all examined salt solutions followed the scaling theory, with an exponent of 2.3 ± 0.1. In solutions of a sodium halide series, the value of the pre‐exponential factor seemed to depend on salt concentration, anion radius, and the apparent “anionic‐portion radius” of the water molecule. This radius, extracted from the literature data, marks a transition point of the anion radius effect. Larger anions increase the osmotic pressure of PAAm more significantly as their concentration increases and vice versa. The effects of the anions on the osmotic pressure of PAAm are related to their preferential interactions with the polymer. Iodide, which increased the osmotic pressure of PAAm with respect to its value in pure water, seemed to preferentially adsorb onto the polymer with a binding constant of K_b = 9.7 ± 2.0 M^?1 determined by isothermal titration microcalorimetry. However, fluoride, which decreased the osmotic pressure, was preferentially repulsed. The mechanisms of attraction and repulsion were attributed to ion‐water‐polymer interactions and the solvent quality of the hydrated ions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 508–519, 2003     

SL(2,C) Gauge Theory of Gravitation and the Quantization of the Gravitational Field

A new approach to quantize the gavitationalfield is presented. It is based on the observation thatthe quantum character of matter becomes more significantas one gets closer to the big bang. As the metric loses its meaning, it makes sense to considerSchrodinger's three generic types of manifolds —unconnected differentiable, affinely connected, andmetrically connected — as a temporal sequencefollowing the big bang. Hence one should quantize thegravitational field on general differentiable manifoldsor on affinely connected manifolds. The SL(2,C) gaugetheory of gravitation is employed to explore thispossibility. Within this framework, the quantization itselfmay well be canonical.     

Anomaly constraints on nonlinear sigma models

Anomalies in nonlinear sigma models can sometimes be cancelled by local counterterms. We show that these counterterms have a simple topological interpretation, and that the requirements for anomaly cancellation can be easily understood in terms of 't Hooft's anomaly matching conditions. We exhibit the anomaly cancellation on homogeneous spaces $\text{G}\text{H}$ and on general riemannian manifolds $\text{M}$. We include external gauge fields on the manifolds and derive the generalized anomaly-cancellation conditions. Finally, we discuss the implications of this work for superstring theories.     

On relative stability of linear stationary feedback control systems with time delay

A method is presented whereby the absolute and relative stabilityof linear control systems containing transport lag can be determined.As a result feedback systems with variable time delay and loopgain, may be investigated in straightforward manner.     

Acid soap formation of oleic acid and catanionic complex formation in the alkyldimethylamine oxide/sodium oleate equimolar mixtures

The influence of adding alkyldimethylamine oxide (CnDMAO) with varying alkyl chain lengths (n_c) on the acid soap formation of oleic acid was investigated. The solutions of equimolar mixtures of CnDMAO and sodium oleate (Na⁺Ol^–), each 25 mmol kg^–1, became turbid at a certain critical pH (pH_c) on decreasing pH. Values of the pH_c depended on n_c and showed the minimum at C10DMAO/NaOl mixture. The presence of the minimum was interpreted in terms of two different kinds of the complex formed in the micelles depending on n_c: the catanionic complex (CnDMAOH⁺/Ol^–) in the mixed micelles of n_c=16, 14, 12 and 10, and the acid soap of oleic acid for C6DMAO/NaOl and C8DMAO/NaOl mixtures. At pH_c where the amounts of these complexes of double-chain nature reached certain critical values in the mixed micelles, a phase separation (most probably lamella formation) took place. It was expected that the critical amount of the catanionic complex was smaller for the mixtures of higher n_c values and hence pH_c increased with n_c for the mixtures n_c10. For the mixtures of n_c<10, it was expected that the amount of the acid soap in the mixed micelles increased with decreasing n_c at a given pH and the pH_c increased with decreasing n_c. Micelle compositions at cmc were evaluated on the basis of the regular solution theory coupled with the pseudo phase approximation. The micelle compositions at 100 mmol kg^–1 were examined with ¹³C-NMR. The results showed the mixed micelle formation for n_c=16–10, while the micelles mostly consisting of oleic acid for the mixtures of n_c=8 and 6. The assumption of two different complexes for the two groups of the mixture was thus supported. The cmc range of mixed micelles was evaluated and it was well correlated with the observed concentration range of pyrene fluorescence change.     

Pi-accepting-pincer rhodium complexes: an unusual coordination mode of PCP-type systems

The novel pi-accepting, pincer-type ligand, dipyrrolylphoshinoxylene (DPyPX), is introduced. This ligand has the strongest pi-accepting phosphines used so far in the PCP family of ligands and this results in some unusual coordination chemistry. The rhodium(I) complex, [(DPyPX)Rh(CO)(PR3)] (4, R=Ph, Et, pyrrolyl) is prepared by treating the relevant [(DPyPX)Rh(PR3)] (3) complex with CO and is remarkably resistant to loss of either ligand. X-ray crystallographic analysis of complex 4 b (R=Et) reveals an unusual cisoid coordination of the PCP phosphine ligands. These observations are supported by density functional theory (DFT) calculations.     

α-Chlor-nitrone V: Substitutionsreaktionen an Olefin- und Benzolderivaten. Eine Methode zur Darstellung von β,γ-un-gesättigten und β- arylsubstituierten Aldehyden. Stereospezifische Bildung von tetra-alkylsubstituierten Olefindoppelbindungen. Über synthetische Methoden, 9. (vorläufige) Mitteilung

The Ag⁺-induced α-chloro-aldonitrone/olefin reaction in polar solvents can proceed by substitution, thereby providing a method for the preparation of β, γ-unsaturated aldehydes. Positional as well as configurational retention of the olefinic double bond are mechanistically significant and preparatively useful characteristics of this process. Substitution also occurs with great ease at nucleophilic aromatic nuclei; this offers a simple preparative route to certain β-aryl-aldehydes. The results illustrate a general aspect of the chemistry of α-chloro-aldonitrones: the N-alkenyl-N-alkyl-nitrosonium-ions derived from them can serve as preparative equivalents of the elusive corresponding α-acyl-carbonium-ions.     

Rhodium complexes with chiral counterions: achiral catalysts in chiral matrices

The neutral complexes [Rh(I)(NBD)((1S)-10-camphorsulfonate)] (2) and [Rh(I)((R)-N-acetylphenylalanate)] (4) reacted with bis-(diphenylphosphino)ethane (dppe) to form the cationic Rh(I)(NBD)(dppe) complexes, 5 and 6, respectively, accompanied by their corresponding chiral counteranions. Analogously, 4 reacted with 4,4^′-dimethylbipyridine to yield complex 7. Complexes 5 and 6 disproportionated in aprotic solvents to form the corresponding bis-diphosphine complexes 8 and 9, respectively. 8 was characterized by an X-ray crystal structure analysis. In order to form achiral Rh(I) complexes bearing chiral countercations new sulfonated monophosphines 13-16 with chiral ammonium cations were synthesized. Tris-triphenylphosphinosulfonic acid (H₃TPPS, 11) was used to protonate chiral amines to yield chiral ammonium phosphines 14-16. Thallium-tris-triphenylphosphinosulfonate (Tl₃TPPS, 12) underwent metathesis with a chiral quartenary ammonium iodide to yield the proton free chiral ammonium phosphine 13. Phosphines 15 and 16 reacted with [Rh(NBD)₂]BF₄ to afford the highly charged chiral zwitterionic complexes [Rh(NBD)(TPPS)₂][(R)-N,N-dimethyl-1-(naphtyl)ethylammonium]₅ (17) and [Rh(NBD)(TPPS)₂][BF₄][(R)-N,N-dimethyl-phenethylammonium]₆ (18), respectively. Complexes 5, 6, and 18 were tested as precatalysts for the hydrogenation of de-hydro-N-acetylphenylalanine (19) and methyl-(Z)-(α)-acetoamidocinnamate (MAC, 20) under homogeneous and heterogeneous (silica-supported and self-supported) conditions. None of the reactions was enantioselective.     

Competitive C-I versus C-CN reductive elimination from a Rh(III) complex. Selectivity is controlled by the solvent

The RhIII complex [(PNP)Rh(CN)(CH3)][I] 5, obtained by oxidative addition of methyl iodide to [(PNP)Rh(CN)] 2, reacts selectively in two pathways: In aprotic solvents C-I reductive elimination of methyl iodide followed by its electrophilic attack on the cyano ligand takes place, giving the methyl isonitrile RhI complex [(PNP)Rh(CNCH3)][I] 3, while in protic solvents C-C reductive elimination of acetonitrile takes place forming an iodo RhI complex [(PNP)RhI] 9. Reaction of 2 with ethyl iodide in aprotic solvents gave the corresponding isonitrile complex, while in protic solvents no reactivity was observed. The selectivity of this reaction is likely due to a hydrogen bond between the cyano ligand and the protic solvent, as observed by X-ray diffraction, which retards electrophilic attack on this ligand.