THE B.A.S.I.C. (BINO-ANSA-SPIRO-IN-CYCLOPHOSPHAZENES) SYSTEM. PART I: NEW DERIVATIVES OF THE BIS-(TETRACHLORO-CYCLOTRIPHOSPHAZENYL)-SPERMINE

Abstract

The synthesis of new derivatives of bis-(tetrachlorocyclotriphosphazenyl)-spermine was achieved upon reaction of some MONOSPIRO–N₃P₃Cl₄[HN–(CH₂) _n –NH] (n = 2,3,4) derivatives and of the gem–N₃P₃Az₂Cl₄ with spermine. All compounds were obtained in the monomeric state. ³¹P and ¹³C high-resolution NMR were used, together with IR spectroscopy and mass spectrometry, to assign molecular structures and to reveal conformational equilibria, if any.     

Effect of Network Structure on Characterization and Flow Modeling Using X-ray Micro-Tomography Images of Granular and Fibrous Porous Media

Image-based network modeling has become a powerful tool for modeling transport in real materials that have been imaged using X-ray computed micro-tomography (XCT) or other three-dimensional imaging techniques. Network generation is an essential part of image-based network modeling, but little quantitative work has been done to understand the influence of different network structures on modeling. We use XCT images of three different porous materials (disordered packings of spheres, sand, and cylinders) to create a series of four networks for each material. Despite originating from the same data, the networks can be made to vary over two orders of magnitude in pore density, which in turn affects network properties such as pore-size distribution and pore connectivity. Despite the orders-of-magnitude difference in pore density, single-phase permeability predictions remain remarkably consistent for a given material, even for the simplest throat conductance formulas. Detailed explanations for this beneficial attribute are given in the article; in general, it is a consequence of using physically representative network models. The capillary pressure curve generated from quasi-static drainage is more sensitive to network structure than permeability. However, using the capillary pressure curve to extract pore-size distributions gives reasonably consistent results even though the networks vary significantly. These results provide encouraging evidence that robust network modeling algorithms are not overly sensitive to the specific structure of the underlying physically representative network, which is important given the variety image-based network-generation strategies that have been developed in recent years.     

Nucleic acid affinity of clustered-charge anion exchange adsorbents: effects of ionic strength and ligand density

In previous work we demonstrated the improved protein-binding capacity and selectivity of ion-exchange adsorbents displaying a "clustered" rather than random, distribution of surface charges. For example, anion-exchange adsorbents displaying 5 mM of positive charge in the form of 1 mM penta-argininamide show much higher affinity and capacity for alpha-lactalbumin than do adsorbents displaying the same 5 mM total charge in the form of single dispersed argininamide charges. We also found that clustered adsorbents selectively favor proteins with inherent charge clustering. In the present work, "clustered" penta-argininamide adsorbents showed DNA binding capacity comparable to that of conventional dispersed adsorbents with 10-100-fold higher ligand density. We also observed that at moderate ionic strength the DNA affinity of all adsorbents tested increased with salt while RNA affinity decreased, so that selectivity for DNA over RNA was enhanced as salt concentration increased.     

The Effects of Representations,Constructivist Approaches,and Engagement on Middle School Students' Algebraic Procedure and Conceptual Understanding

This study examined the effects of types of representations, constructivist teaching approaches, and student engagement on middle school algebra students' procedural knowledge and conceptual understanding. Data gathered from 16 video lessons and algebra pretest/posttests were used to run three multilevel structural equation models. Symbolic representations (p < .02), shared meanings (p < .05), and meaningful feedback (p < .10) significantly increased procedural and conceptual understanding. Enactive representations significantly increased procedural knowledge (p < .05). There was also a significant relationship between the two types of learning at the within level (p < .01) and between level (p < .05).     

A mathematical model of aging-related and cortisol induced hippocampal dysfunction

Background  

The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated.     

Novel 3-D structures in polymer films by coupling external and internal fields

A route to produce novel three-dimensional structures in thin films is demonstrated. Such structures are most difficult to produce in a simple manner without the use of multiple fabrication steps. Here, we show the generation of 3-D cage-type structures using a combination of electrohydrodynamic instabilities and dewetting in a polymer/polymer/air trilayer. Removal of one of the components by use of a selective solvent or by degradation of one of the components reveals the formation of a three-dimensional structure, where one polymer is encased in the other. Thus, by coupling an external field with a surface field inherent to the polymers, a novel fabrication strategy is shown that has clear applications in microfluidics and microelectromechanical systems with extensions to patterned surfaces and structured fluids, like block copolymers.     

On convergence of configurations

The transition rule F of a cellular automaton may sometimes be regarded as a “rule of growth” of a crystal from a “seed” ω. A study is made of the iterates ω, Fω, F²ω,…. For certain growth rules F it is proved that when ω is “sufficiently large” the sequence F^pω “converges” to a rational polytope W. The limiting shape W depends only on F.     

Further studies on the synthesis of 24(S),25-epoxycholesterol. A new, efficient preparation of desmosterol

Efforts to improve the synthesis of 24(S),25-epoxycholesterol (1) from stigmasterol (3) have included identification of 6 alpha-hydroxy-i-steroid 11 as a byproduct from the ozonolysis of 9 and an attempt to effect conversion of sulfone 14 to diol 18 via Payne rearrangement and nucleophilic trapping of epoxide 25, which led instead to 27 and 28 (97% yield). A more efficient synthesis of 1 was achieved via coupling of cuprate 21 with allylic acetate 31 to give 73% of 16, in the most efficient conversion yet of a C22 intermediate to desmosterol (5) or its acetate 6.