A novel family of ordered,mesoporous inorganic/organic hybrid polymers containing covalently and multiply bound microporous organic hosts

We have prepared a new family of periodic hybrid polymers containing microporous cavities provided by covalently bound organic hosts. Cyclodextrin (CD) or calixarene (CX) hosts are attached to four or more trialkoxysilyl groups, which are polymerized to form a polysilsesquioxane matrix. Structural integrity is provided by copolymerization with tetraethoxysilane, which produces a polysilicate co-matrix. Periodic order is created by carrying out the polymerization in the presence of a surfactant, cetyltrimethylammonium bromide. The resulting as-synthesized polymers from these three starting materials were characterized by solid-state nuclear magnetic resonance spectroscopy. The (13)C and (29)Si spectra provided evidence for intact polysilsesquioxane, polysilicate, organic host, and surfactant. Removal of the surfactant by washing produced a polymer containing cavities of mesoporous dimensions, in addition to the microporous host cavities. The purpose of introducing mesoporosity is to allow enhanced access of guests to the microporous hosts. Transmission electron microscopy demonstrated that both as-synthesized and solvent-extracted polymers have a periodic structure. All polymers are completely insoluble in water. The as-synthesized CD-containing polymers extracted up to >99% of 4-nitrophenol from aqueous solution, and the solvent-extracted CX-containing polymers extracted up to 67% of Fe(3+) and lesser amounts of other metal cations from aqueous solution, with interesting selectivity patterns. Simple filtration then removes the polymer containing the extracted organic molecule or metal cation. These extraction abilities are superior to previous materials.     

Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.     

Optically and thermally induced electron transfer pathways in hexakis[4-(N,N-diarylamino)phenyl]benzene derivatives

The optically and thermally induced electron transfer pathways of highly symmetrical (D(3)) hexaarylbenzene systems with six triarylamine redox sites have been investigated. Owing to slightly different local redox potentials, the radical trication could be selectively generated by electrochemical methods. This trication shows a strong intervalence charge-transfer band in the near infrared (NIR) that was measured by spectroelectrochemistry and analysed using multi-dimensional Mulliken-Hush theory. Quantum chemical AM1 CI calculations indicate that there is no optically induced concerted three-electron transfer that transforms the ground state into a state in which all three positively charged triarylamine moieties change place with their neutral neighbours. The potential energy surface of the ground state was constructed by using quadratic potentials. From this potential surface it is apparent that there is also no thermally allowed concerted three-electron transfer pathway. Instead, three consecutive one-electron transfer steps are necessary for this process.     

Synthetic studies towards the penicisulfuranols: Synthesis of an advanced spirocyclic diketopiperazine intermediate

The 2,5-diketopiperazine (DKP) moiety is a core feature of many natural products and medicinally relevant scaffolds. As part of our efforts directed towards a total synthesis of penicisulfuranol B, we have developed and report herein: (1) the preparation of an N-hydroxy diketopiperazine intermediate accessible via a molybdenum-mediated oxidation of a parent diketopiperazine, and (2) further synthetic studies leading to a novel spirocyclic dihydrobenzofuran-containing diketopiperazine.     

The ICP-MS approach to environmental studies

The certification of marine materials for trace metals is a process which challenges every technique involved, especially if a technique is as recent as inductively coupled plasma mass spectrometry (ICP-MS), Developmental work was required for several materials (natural waters, biological materials, marine sediments). It is reviewed here, in an attempt to show how one can take full advantage of ICP-MS. This includes a review of the digestion procedures developed for the multielement analysis of biological materials and marine sediments in order to minimize spectroscopic interferences. The multielement analysis of natural waters is also reviewed, in particular that of saline waters which requires a separation of the analytes from the alkali and alkaline earths elements and a preconcentration of the analytes on a column of silicaimmobilized 8-hydroxyquinoline. The potential of performing this separation/preconcentration procedure on-line is showed using both published and original results. Finally, the application of ICP-MS to speciation is illustrated by the determination of methylmercury in biological materials after extraction, and by the determination of arsenic species by high performance liquid chromatography coupled to ICP-MS.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, AustriaThe work described was carried out while the author was a Research Associate at the Analytical Chemistry Section, Chemistry Division, National Research Council of Canada, Ottawa, K1A OR9, Canada     

Super-hydrophobic, highly adhesive, polydimethylsiloxane (PDMS) surfaces

Super-hydrophobic surfaces have been fabricated by casting polydimethylsiloxane (PDMS) on a textured substrate of known surface topography, and were characterized using contact angle, atomic force microscopy, surface free energy calculations, and adhesion measurements. The resulting PDMS has a micro-textured surface with a static contact angle of 153.5° and a hysteresis of 27° when using de-ionized water. Unlike many super-hydrophobic materials, the textured PDMS is highly adhesive, allowing water drops as large as 25.0 μL to be inverted. This high adhesion, super-hydrophobic behavior is an illustration of the "petal effect". This rapid, reproducible technique has promising applications in transport and analysis of microvolume samples.     

Bioaccessibility of total arsenic and arsenic species in seafood as determined by a continuous online leaching method

A continuous leaching method coupled online with inductively coupled plasma mass spectrometry (ICP-MS) detection was used to assess the maximum bioaccessibility of arsenic (As) in seafood samples. The method simulates continuous-flow digestion by successively pumping artificial saliva, gastric and intestinal juices through a mini-column of powdered sample directly connected to the nebuliser of an ICP-MS instrument. The method allows the real-time measurement of As being released by a given reagent. Because the analyte is continuously removed from the system, in contrast to batch methods, the dissolution equilibrium is driven to the right, hence quickly providing information about the worst-case scenario. Following consecutive leaching by the digestive reagents, the leachates were subject to speciation analysis by ion-exchange chromatography with ICP-MS detection to determine the arsenic species released. Finally, the remaining residue from the mini-column was fully digested to verify mass balance. The method was used to determine the bioaccessibility of total As and As species in four certified reference materials and in several real seafood samples. The mass balance was verified in each case. Generally speaking, the non-toxic form was easily released whereas the inorganic forms were poorly bioaccessible.     

The optical activity of carvone: a theoretical and experimental investigation

The optical rotatory dispersion (ORD) and circular dichroism of the conformationally flexible carvone molecule has been investigated in 17 solvents and compared with results from calculations for the "free" (gas phase) molecule. The G3 method was used to determine the relative energies of the six conformers. The optical rotation of (R)-(-)-carvone at 589 nm was calculated using coupled cluster and density functional methods, including temperature-dependent vibrational corrections. Vibrational corrections are significant and are primarily associated with normal modes involving the stereogenic carbon atom and the carbonyl group, whose n → π? excitation plays a significant role in the chiroptical response of carvone. Without the inclusion of vibrational corrections the optical rotation calculated with CCSD and DFT has the opposite sign of experimental data. Calculations of optical rotation performed in solution using the polarizable continuum model were also opposite in sign when compared to that of the experiment.     

Charge-transfer interactions in a multichromophoric hexaarylbenzene containing pyrene and triarylamines

Two different hexaarylbenzenes with three pyrene and three triarylamine substituents in different positions (trigonal symmetric and asymmetric arrangement) were synthesized, and their charge-transfer states were investigated by optical spectroscopy. In these multichromophoric systems triarylamine acts as the electron donor and pyrene as the electron acceptor. A reference chromophore with only one donor-acceptor pair was also investigated. All these chromophores form charge-transfer states upon photoexcitation which relax with a moderate fluorescence quantum yield to the ground state. The compounds do not differ significantly concerning most of their fluorescence properties, which shows that the fluorescent charge-transfer state is very similar in all chromophores. This observation indicates symmetry breaking for the symmetric chromophore within fluorescence lifetime of several tens of ns. This interpretation was substantiated by fluorescence excitation anisotropy measurements in a sucrose octaacetate matrix.