The first uranyl complexes with valerate ions

FT–IR spectroscopy and single‐crystal X‐ray structure analysis were used to characterize the discrete neutral compound diaquadioxidobis(n‐valerato‐κ²O,O′)uranium(VI), [UO₂(C₄H₉COO)₂(H₂O)₂], (I), and the ionic compound potassium dioxidotris(n‐valerato‐κ²O,O′)uranium(VI), K[UO₂(C₄H₉COO)₃], (II). The U^VI cation in neutral (I) is at a site of 2/m symmetry. Potassium salt (II) has two U centres and two K⁺ cations residing on twofold axes, while a third independent formula unit is on a general position. The ligands in both compounds were found to suffer severe disorder. The FT–IR spectroscopic results agree with the X‐ray data. The composition and structure of the ionic potassium uranyl valerate are similar to those of previously reported potassium uranyl complexes with acetate, propionate and butyrate ligands. Progressive lengthening of the alkyl groups in these otherwise similar compounds was found to have an impact on their structures, including on the number of independent U and K⁺ sites, on the coordination modes of some of the K⁺ centres and on the minimum distances between U atoms. The evolution of the KUO₆ frameworks in the four homologous compounds is analysed in detail, revealing a new example of three‐dimensional topological isomerism in coordination compounds of U^VI.     

The Influence of the Chain Length of Polycations on their Complexation with Anionic Liposomes

A series of strong polycations is synthesized through the anionic polymerization of 2‐vinylpyridine, followed by subsequent quaternization of the resulting polymer. Polycations based on quaternized 2‐vinylpyridine (PVPQs) with degrees of polymerization (DP) from 20 to 440 are adsorbed on the surface of small anionic liposomes. Liposome/PVPQ complexes are characterized by using a number of physicochemical methods. All PVPQs are totally adsorbed onto the liposome surface up to a certain concentration at which saturation is reached (which is specific for each PVPQ). The integrity of the adsorbed liposomes remains intact. Short PVPQs interact with anionic lipids localized on the outer membrane leaflet, whereas long PVPQs extract anionic lipids from the inner to outer leaflet. Complexes tend to aggregate, and the largest aggregates are formed when the initial charge of the liposomes is fully neutralized by the charge of the PVPQ. PVPQs with intermediate DPs demonstrate behavioral features of both short and long PVPQs. These results are important for the interpretation of the biological effects of cationic polymers and the selection of cationic polymers for biomedical applications.     

Monitoring and Understanding the Paraelectric–Ferroelectric Phase Transition in the Metal–Organic Framework [NH4][M(HCOO)3] by Solid‐State NMR Spectroscopy

The paraelectric–ferroelectric phase transition in two isostructural metal–organic frameworks (MOFs) [NH₄][M(HCOO)₃] (M=Mg, Zn) was investigated by in situ variable‐temperature ²⁵Mg, ⁶⁷Zn, ¹⁴N, and ¹³C solid‐state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder–order transition of NH₄⁺ cations causes a change in dielectric properties. It is thought that [NH₄][Mg(HCOO)₃] exhibits a higher transition temperature than [NH₄][Zn(HCOO)₃] due to stronger hydrogen‐bonding interactions between NH₄⁺ ions and framework oxygen atoms. ²⁵Mg and ⁶⁷Zn NMR parameters are very sensitive to temperature‐induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric–ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although ²⁵Mg and ⁶⁷Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal‐atom environments in [NH₄][M(HCOO)₃] give rise to relatively narrow spectra that can be acquired in 30–60 min at a low magnetic field of 9.4 T. Complementary ¹⁴N and ¹³C SSNMR experiments were performed to probe the role of NH₄⁺–framework hydrogen bonding in the paraelectric–ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH₄][M(HCOO)₃] system and shows great potential for molecular‐level studies on electric phenomena in a wide variety of MOFs.     

Kinetics and mechanism of the reaction of alkoxymethylidene malonate and malononitrile with hydrazines and anilines

The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R¹–NH₂ (R¹: (CH₃)₂N, CH₃NH, NH₂, C₆H₅NH, CH₃CONH, 4‐CH₃C₆H₄SO₂NH, 3‐ and 4‐X‐C₆H₄; X: H, 4‐Br, 4‐CH₃, 4‐CH₃O, 3‐Cl) were studied at 25 °C in methanol. It was found that the reactions with all hydrazines (the only exception was the reaction of (ethoxymethylidene)malononitrile with N,N‐dimethylhydrazine) showed overall second‐order kinetics and k_obs were linearly dependent on the hydrazine concentration which is consistent with the rate‐limiting attack of the hydrazine on the double bond of the substrate. Corresponding Brønsted plots are linear (without deviating N‐methyl and N,N‐dimethylhydrazine), and their slopes (β_Nuc) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the C–N bond formed in the transition state. The deviation of both methylated hydrazines is probably caused by the different site of nucleophilicity/basicity in these compounds (tertiary/secondary vs. primary nitrogen). A somewhat different situation was observed with the anilines (and once with N,N‐dimethylhydrazine) where parabolic dependences of the kinetics gradually changing to linear dependences as the concentration of nucleophile/base increases. The second‐order term in the nucleophile indicates the presence of a steady‐state intermediate ‐ most probably T^±. Brønsted and Hammett plots gave β_Nuc = 1.08 and ρ = ?3.7 which is consistent with a late transition state whose structure resembles T^±. Copyright © 2013 John Wiley & Sons, Ltd.     

Herd behaviour experimental testing in laboratory artificial stock market settings. Behavioural foundations of stylised facts of financial returns

Many scholars express concerns that herding behaviour causes excess volatility, destabilises financial markets, and increases the likelihood of systemic risk. We use a special form of the Strongly Typed Genetic Programming (STGP) technique to evolve a stock market divided into two groups—a small subset of artificial agents called ‘Best Agents’ and a main cohort of agents named ‘All Agents’. The ‘Best Agents’ perform best in term of the trailing return of a wealth moving average. We then investigate whether herding behaviour can arise when agents trade Dow Jones, General Electric, and IBM financial instruments in four different artificial stock markets. This paper uses real historical quotes of the three financial instruments to analyse the behavioural foundations of stylised facts such as leptokurtosis, non-IIDness, and volatility clustering. We found evidence of more herding in a group of stocks than in individual stocks, but the magnitude of herding does not contribute to the mispricing of assets in the long run. Our findings suggest that the price formation process caused by the collective behaviour of the entire market exhibit less herding and is more efficient than the segmented market populated by a small subset of agents. Hence, greater genetic diversity leads to greater consistency with fundamental values and market efficiency.     

Products of Hyperbolic Metric Spaces

Let (X _i d _i ), i=1,2, be proper geodesic hyperbolic metric spaces. We give a general construction for a 'hyperbolic product' X ₁× _h X ₂ which is itself a proper geodesic hyperbolic metric space and examine its boundary at infinity.