Accelerating the Crystallization of Zeolite SSZ-13 with Polyamines

Tailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ-13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in selected cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ-13 formation, leading to a 4-fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light-scattering techniques demonstrate these conditions lead to polymer-induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from the growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ-13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis.

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. Here, we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

Travelling waves in two-dimensional smectic-C domains

Continued irradiation of smectic-C-like domains of photosensitive Langmuir monolayers from azobenzene derivatives induces the nucleation and propagation of orientational travelling waves as observed with Brewster angle microscopy (BAM). BAM image analysis has allowed to identify different dynamical behaviors involving the generation and propagation of such waves. A model based on the coupling between an orientational and a composition field proposes a scenario for dynamic self-assembly that accounts for most of the observed phenomena, and allows to pinpoint the relevance of boundary defects in wave-emitting structures.-1.

Orientational structures in confined smectic-C domains in Langmuir monolayers

Droplet smectic-C domains in films of surfactant molecules exhibit different orientational textures. For these systems we formulate a kinetic model based on a free energy functional containing bulk (elastic) and surface interactions. Numerical simulations for the corresponding relaxational equation show the existence of two different equilibrium configurations with a centered defect. In particular, when the elastic terms dominate, bend-shaped textures appear, whereas for strong boundary effects mixed bend/splay conformations are displayed. A variational analysis for the free energy functional confirms the validity of the above numerical results. The stability of textures with centered defects with respect to the formation of periferic defects (boojums) is also discussed qualitatively. The above theoretical predictions are compared with experimental results from Brewster angle microscopy imaging of azobenzene Langmuir monolayers.

Chiral sign induction by vortices during the formation of mesophases in stirred solutions

Achiral diprotonated porphyrins, forming homoassociates in aqueous solution, lead to spontaneous chiral symmetry breaking. The unexpected result is that the chirality sign of these homoassociates can be selected by vortex motion during the aggregation process. This result is confirmed by means of circular dichroism spectra. These experimental findings are rationalized in terms of the asymmetric influence of macroscopic forces on bifurcation scenarios and by considering the specific binding characteristics of the porphyrin units to form the homoassociates.

Electrochemical reduction of the biliverdin-serum albumin complex as monitored by absorption and circular dichroism spectroscopy

The cathodic reduction at the mercury electrode of a biliverdin IX alpha-serum albumin complex at physiological pH in an aqueous buffer containing percentages of DMSO ranging from 4% to 20% is studied by cyclic voltametry and controlled potential coulometry. The progression of pigment disappearance and the (stereochemical) nature of the product are monitored by chromatography, UV-visible absorption and circular dichroism spectroscopy. Upon reduction, albumin-bound biliverdin IX alpha, with a slight preference for the P-helicity, affords the corresponding bound bilirubin IX alpha -with an M-chirality conformation. The complex is reduced at -0.64 V (vs. SCE; 8% DMSO), only a little shifted compared to reduction of free biliverdin IX alpha under the same conditions. In contrast, an analogous bilirubin IX alpha-serum albumin complex is essentially inert towards cathodic reduction under conditions where free bilirubin IX alpha is reduced, indicating a better shielding by the protein of the bilirubin IX alpha molecule from the electrode surface. The presence of relative position (as in the biliverdins IX alpha and XIII alpha) or absence (as in mesobiliverdin IX alpha) of vinyl groups in the pigment does not have a significant effect upon its electroreduction behaviour, indicating that the process is not sensitive to the subtle differences imposed by vinyl groups upon the structure of the corresponding biliverdin-albumin complexes.

Proton-induced dismutation of superoxide in aprotic media by bile pigments

Cyclic voltammetry of molecular oxygen in aprotic media (dimethylformamide) and in the presence of bilirubin and other bile pigments shows that superoxide anion (O2-.) undergoes proton-induced dismutation. Lactam hydrogens of bile pigments are sufficiently acid to induce (O2-.) disproportionation to O2 and H2O2. Because of its characteristic lipophilic behavior, a biological role for natural bilirubin similar to that of other non-enzymatic lipophilic scavengers of (O2-.) is suggested.

Biosynthesis and inactivation of ecdysone during the pupal-adult development of the cabbage butterfly, Pieris brassicae L

Injection of labelled ecdysone and 2-hydroxyecdysone into Pieris pupae showed that their catabolism proceeds through 26-hydroxylation followed by conversion into acidic steroids assumed to be 26-oic compounds. This biological system is characterized by the lack of conjugation reactions and by rather long-lived hormones. In vivo biosynthesis of ecdysteroids was investigated by 24 hr [3H]cholesterol labelling, followed by HPLC analysis of the resulting [3H]ecdysone and 20-hydroxyecdysone. Active conversion (up to 0.07% in 24 hours) was observed between 48 hr and 120 hr following pupal ecdysis, a result in good agreement with the variations observed in hormone content. Long-term [3H]cholesterol incorporation experiments made it possible to monitor ecdysteroid dynamics during pupal development. Three periods were observed, corresponding to successive accumulation of ecdysone, 20-hydroxyecdysone and an acidic metabolite. Comparison of these results with those of the experiments involving labelled ecdysone injection shows that the catabolism of injected hormones is not the same as that of endogenous hormones.