Problems in the IR measuring the acidity of zeolite bridging hydroxyls by low-temperature CO adsorption

Two infrared OH stretching bands are produced after interaction of CO with H-ZSM-5 bridging hydroxyls. These two bands are not due to heterogeneity of the acid sites but arise from Fermi-resonance.     

Formation of monodisperse charged vesicles in mixtures of cationic gemini surfactants and anionic SDS

The aggregation behavior of catanionics formed by the mixture of cationic geminis derived from dodecyltrimethylammonium chloride (DTAC) and anionic sodium dodecylsulfate (SDS) was studied by means of phase studies and comprehensive small-angle neutron scattering (SANS) experiments at 25 °C and 50 mM overall concentration. The results are compared to those for the previously studied SDS + DTAC system. Various gemini spacers of different natures and geometries were used, but all of them had similar lengths: an ethoxy bridge, a double bond, and an aromatic ring binding the two DTACs in three different substitutions (ortho, meta, and para). SANS and SAXS data analysis indicates that the spacer has no large effect on the spheroidal micelles of pure surfactants formed at low concentration in water; however, specific effects appear with the addition of electrolytes. Microstructures formed in the catanionic mixtures are rather strongly dependent on the nature of the spacer. The most important finding is that for the hydrophilic, flexible ethoxy bridge, monodisperse vesicles with a fixed anionic/cationic charge ratio (depending only on the surfactant in excess) are formed. Furthermore, the composition of these vesicles shows that strongly charged aggregates are formed. This study therefore provides new opportunities for developing tailor-made gemini surfactants that allow for the fine tuning of catanionic structures.     

Aqueous laponite clay dispersions in the presence of poly(ethylene oxide) or poly(propylene oxide) oligomers and their triblock copolymers

The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low M w whereas the opposite occurs for larger Mw. This behavior is explained on the basis that an effective R G is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of noninteracting polydisperse core+shell disks, where the thickness of the polymer layer increases with the Mw. The adsorbed polymer is in a more compact conformation compared to a random coil distribution while the fraction of the polymer in the shell formed around the laponite RD particles is nearly independent of Mw. For increasing laponite RD amounts, at a given polymer composition, the thickness of the polymer slightly changes. In some cases, where also gelation is sped up, a structure factor with attractive interaction was employed which allowed to evaluate the attractive forces between the laponite RD particles. The gelation time was determined for mixtures at fixed copolymer and laponite RD concentrations. Surprisingly, it is observed that gels are formed despite the fact that the binding sites of the laponite RD particles are almost covered but the polymer size is too small to prevent aggregation. The gelation rate is correlated to structure and thermodynamics of these systems. Namely, when the balance between the steric forces and the depletion attractive forces undergoes an abrupt change the gelation time also undergoes a sharp variation. For lower and comparable Mw, PPO speeds up the gelation more efficiently than PEO while for higher Mw the gelation kinetics is slowed down again. Interestingly, copolymers of PEO and PPO blocks do not induce gelation in the time-window where the homopolymers do.     

Synthesis, chemical properties, and antimicrobial activity of 2- and 2,3-substituted [(tetrahydro-2,4-dioxopyrimidin-1(2H)-yl)phenoxy]naphthalene-1,4-diones

Abstract  

Mono- and disubstituted [(tetrahydro-2,4-dioxopyrimidin-1(2H)-yl)phenoxy]naphthalene-1,4-diones were synthesized by the reaction of dihydro-1-(3-hydroxy- and 4-hydroxyphenyl)pyrimidine-2,4(1H,3H)-diones and their 5- and 6-methyl derivatives with 2,3-dichloro-1,4-naphthoquinone. Their stability in alkaline and acidic media was investigated. Four of the compounds exhibited good antimicrobial activity against Staphylococcus aureus, Mycobacterium luteum, Candida tenuis, and Aspergillus niger.     

Evaluation of the chiral recognition properties as well as the column performance of four chiral stationary phases based on cellulose (3,5-dimethylphenylcarbamate) by parallel HPLC and SFC

The performance of four commercially available cellulose tris(3,5-dimethylphenylcarbamate) based chiral stationary phases (CSPs) was evaluated with parallel high performance liquid chromatography (HPLC) and super critical fluid chromatography (SFC). Retention, enantioselectivity, resolution and efficiency were compared for a set of neutral, basic and acidic compounds having different physico-chemical properties by using different mobile phase conditions. Although the chiral selector is the same in all the four CSPs, a large difference in the ability to retain and resolve enantiomers was observed under the same chromatographic conditions. We believe that this is mainly due to differences in the silica matrix and immobilization techniques used by the different vendors. An extended study of metoprolol and structure analogues gave a deeper understanding of the accessibility of the chiral discriminating interactions and its impact on the resolution of the racemic compounds on the four CSPs studied. Also, a clear difference in enantioselectivity is observed between SFC and LC mode, hydrogen bonding was found to play an important role in the differential binding of the enantiomers to the CSPs.     

Structural portrait of filamin interaction mechanisms

We review the most recent findings on human filamin structure, with particular emphasis on the relationships between structure, function, and interaction. Filamin is a cytoskeletal actin-binding protein and it is therefore crucial in providing cells with the necessary mechanical and dynamical properties. Filamentous actin cross-linking by filamin is regulated by a number of other proteins and the molecular mechanisms of this complex interaction network can be understood by highlighting the structural features of isolated filamin moieties and of their complexes with several partners. Here we describe first the structure-function relationships of the isolated filamin, its flexibility, and its dimerization mechanism. Secondly, we illustrate the structural mechanism with which filamin can recognize its partners, both the actin filaments and the regulatory proteins.     

Polypeptide hybrid copolymers as selective micellar nanocarriers in nonaqueous media

The self-assembly of polystyrene-block-poly(l-lysine) (PS-PLLys·HCl) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles exhibit size variations upon addition of acids or bases, as indicated by light and neutron scattering studies. It is shown that pyridine induces a shrinking of the polystyrene chains in the corona region of the micelles, decreasing the aggregate solvent interface. The addition of benzoic acid, on the other hand, leads to a swelling of the copolymer micelles proportional to the molar fraction of polypeptide. This behavior suggests a selective permeability of the PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature.     

Quantitative assessment of hysteresis in voltammetric curves of electrochemical capacitors

A family of coefficients for quantitative assessment of hysteresis in cyclic voltammetric (CV) curves of electrochemical capacitors and of electrodes for electrochemical capacitors has been defined. Hysteresis index 1 (HI1) is based on the maximum in the difference in current measured at the same potential in ascending and descending branch of CV curve, and HI2 is based on the average difference in current measured at the same potential in ascending and descending branch of CV curve. The values of HI1 and HI2 range from 0 (no hysteresis) to 1 for an ideal capacitor. CV curves of two commercially available electrochemical capacitors over a potential range 0–1500 mV at scan rate of 5 mV/s showed HI1 of 0.94 and 0.97 and HI2 of 0.77 and 0.83, respectively. At the same experimental conditions, a series of 52 home made electrochemical capacitors showed HI1 up to 0.7 and HI2 up to 0.55. HI1 and HI2 measured at constant scan rate (5, 20 or 50 mV/s) in that series of capacitors showed a correlation coefficient >0.98 while HI1 and HI2 measured at different scan rates showed limited correlation. 98 CV curves of electrochemical capacitors and of electrodes for electrochemical capacitors from literature, obtained at various conditions show HI1 from 0.42 to 1, HI2 from 0.27 to 0.97, and a correlation coefficient of 0.90 between HI1 and HI2.     

Bringing brain imaging to the school to assess arithmetic problem solving: chances and limitations in combining educational and neuroscientific research

Scientific collaboration between neuroscience and mathematics education has mostly focused on brain imaging trying to inform education. This study aims at meeting expectations of both research fields, thus enhancing the ecological validity. We investigated the influence of age, mathematical competency, and task characteristics (format, complexity) on students’ arithmetic performance. Based on behavioral data from a pilot study (n = 73), arithmetic tasks were chosen for a subsequent investigation (n = 90), in which parietal brain activation was measured with near-infrared spectroscopy. Substantial group differences in calculation time were observed. While task characteristics influenced arithmetic performance in both age groups, this influence was much smaller for grade 8 students. However, parietal brain activation during calculation was not affected by age, mathematical competency, or task characteristics. Limitations of the experimental design and general problems of applying imaging methods to the school context are discussed.