Theoretical studies of aluminoxane chains, rings, cages, and nanostructures

Alumina nanostructures and three families of aluminoxanes, linear, cyclic, and cagelike structures, have structures that resemble their isovalent electronic hydrocarbon analogues. Specific examples of each family are the counterparts of fullerene, allene, benzene, and cubane, respectively. The aluminoxanes and alumina nanostructures are related to each other; the latter can be regarded as a hydrogen- or alkyl-free form of aluminoxane. By exploiting this relationship, the relative stabilities of the three families of aluminoxanes, alumina nanostructures, and alumina crystal lattices have been estimated. According to ab initio calculations, aluminoxane cages, which take the form of a truncated octahedron and related polyhedra, are favored. The stability of the preferred cage, T-symmetric Al28O28H28, is practically equal to that of the alpha-alumina crystal lattice.     

On potential isomorphism and non-structure

We show in the paper that for any non-classifiable countable theory T there are non-isomorphic models and that can be forced to be isomorphic without adding subsets of small cardinality. By making suitable cardinal arithmetic assumptions we can often preserve stationary sets as well. We also study non-structure theorems relative to the Ehrenfeucht-Fraïssé game. The research of the first and second author was partially supported by Academy of Finland grant 40734 Mathematics Subject Classification (2000): 03C55, 03C45     

Screening the Thermodynamics of Trimethylaluminum‐Hydrolysis Products and Their Co‐Catalytic Performance in Olefin‐Polymerization Catalysis

Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)_n(AlMe₃)_m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe₃ molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co‐catalytic activity in olefin‐polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.     

Fluorescent small molecule probe to modulate and explore α2β1 integrin function

Collagen binding integrins are an important family of cell surface receptors that mediate bidirectionally signals between the interior of the cell and the extracellular matrix. The protein-protein interactions between cells and collagen are necessary for many physiological functions, but also promote diseases. For example, the interaction of α2β1 integrin and collagen has been shown to have an important role in thrombus formation and cancer spread. The fact that the discovery of small molecules that can block such protein-protein interactions is highly challenging has significantly hindered the discovery of pharmaceutical agents to treat these diseases. Here, we present a rationally designed novel fluorescent molecule that can be synthesized in just a few minutes from commercially available starting materials. This molecule blocks the protein-protein interaction between α2β1 integrin and collagen, and due to its fluorescent properties, it can be employed in wide variety of biological applications.     

Lab‐on‐a‐Chip Reactor Imaging with Unprecedented Chemical Resolution by Hadamard‐Encoded Remote Detection NMR

The development of microfluidic processes requires information‐rich detection methods. Here we introduce the concept of remote detection exchange NMR spectroscopy (RD‐EXSY), and show that, along with indirect spatial information extracted from time‐of‐flight data, it provides unique information about the active regions, reaction pathways, and intermediate products in a lab‐on‐a‐chip reactor. Furthermore, we demonstrate that direct spatial resolution can be added to RD‐EXSY efficiently by applying the principles of Hadamard spectroscopy.     

Accessibility of hydroxyl groups in birch kraft pulps quantified by deuterium exchange in D2O vapor

Deuterium exchange in a deuterium oxide (D₂O) atmosphere (95 % relative humidity), quantified by a dynamic vapor sorption (DVS) apparatus, was applied for assessing the accessibility of hydroxyl groups in birch kraft pulps. Achieving the maximum deuteration level exhibited slower kinetics than was earlier reported for experiments with ground wood and bacterial cellulose. The deuterium exchange process followed two parallel phenomena. Applying multiple drying and rewetting cycles gave kinetic information also on the hornification phenomenon occurring during these cycles. Dry birch pulps treated with sodium hydroxide solution of varying alkalinities at elevated temperatures were assessed for their accessible hydroxyl groups by DVS with deuterium exchange. This method was evaluated against deuteration combined with Fourier transform infra-red spectroscopy and water retention value (WRV). DVS measurements were in correlation with WRV and both the methods indicated that an alkaline treatment of dry birch pulp improves cellulose accessibility. The level of irreversible deuteration also decreased as the alkalinity was increased. DVS was shown to provide quantitative information on the accessibility but to be a time-consuming method for the pulp samples. A potential means to decrease the duration of the measurement is increased D₂O exposure by excluding the drying phases.     

Intra-Channel Nonlinear Effect on Optical PPM Pulse Transmission

PPM encoded Gaussian pulse sequence shows more immunity than non-PPM schemes on optical fiber intra-channel nonlinearity and demonstrated by a numerical study of IXPM and IFWM effects deploying on 100Gb/s single channel system.