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Helical Tubuland Diols: A Synthetic and Crystal Engineering Quest

admin — Tue, 12 May 2009 06:24:49 +0000

Despite many advances in recent years, crystal engineering remains a risky venture. A successful outcome requires manipulation of the noncovalent bonding and properties such as size, shape, repulsion, attraction, polarity, and chirality. In this Account, we describe the interplay of crystal engineering and synthetic organic chemistry required to develop the family of helical tubuland diol hosts, the members of which exhibit a wide range of tube dimensions and inclusion properties. Certain alicyclic dialcohols crystallize with a hydrogen-bonded network structure, termed the helical tubuland lattice, in space group P3121 (or its enantiomorph P3221). Double helices of diol molecules surround parallel tubes that contain guest molecules, which are included on the basis of size and shape rather than functional group. The crystal structure of (diol)3�(chloroacetic acid)1.2 is illustrative. These chiral helical tubulate lattice inclusion compounds are formed when the racemic host diol is allowed to crystallize from solution. Complete enantiomer separation occurs during this process, producing a 1:1 mixture of pure (+)- and pure (?)-crystals (a conglomerate). The challenge of creating this family of compounds required the development of much synthetic chemistry, in particular new pathways to alicyclic ring systems with specific substitution patterns. It was also necessary to understand and control the supramolecular properties of the diol molecules. What makes the original compound tick, and why did it behave in this remarkable manner, when most of its structural neighbors crystallize totally differently? The synthesis of new helical tubuland diols requires not just preparation of a new molecular structure but also a transplant of the original unchanged hydrogen-bonding supramolecular synthon. Synthesis of the specific crystal space group is necessary. This was achieved by defining structural characteristics, termed molecular determinants, which are essential for the helical tubuland structure to occur. If these requirements were met, then the target molecule had a high probability of success. This investigation has close conceptual parallels with the search for pharmacophore properties of bioactive molecules. In both situations, parts of a molecule with little or no chemical reactivity may actually play vital supramolecular roles. The review illustrates how crystal engineering is based on specific supramolecular properties that can be uncovered and then exploited by synthetic chemists.

Roger Bishop
School of Chemistry, The University of New South Wales, UNSW Sydney, NSW 2052, Australia

Heat; mass transfer scale-up issues during freeze-drying, III: Control; characterization of dryer differences via operational qualification tests

admin — Mon, 02 Feb 2009 13:01:02 +0000

The objective of this research was to estimate differences in heat; mass transfer between freeze dryers due to inherent design characteristics using data obtained from sublimation tests. This study also aimed to provide guidelines for convenient scale-up of the freeze-drying process. Data obtained from sublimation tests performed on laboratory-scale, pilot,; production freeze dryers were used to evaluate various heat; mass transfer parameters: nonuniformity in shelf surface temperatures, resistance of pipe, refrigeration system,; condenser. Emissivity measurements of relevant surfaces such as the chamber wall; the freeze dryer door were taken to evaluate the impact of atypical radiation heat transfer during scale-up. �Hot�; �cold� spots were identified on the shelf surface of different freeze dryers,; the impact of variation in shelf surface temperatures on the primary drying time; the product temperature during primary drying was studied. Calculations performed using emissivity measurements on different freeze dryers suggest that a front vial in the laboratory lyophilizer received 1.8 times more heat than a front vial in a manufacturing freeze dryer operating at a shelf temperature of 25�C; a chamber pressure of 150 mTorr during primary drying. Therefore, front vials in the laboratory are much more atypical than front vials in manufacturing. Steady-state heat; mass transfer equations were used to study a combination of different scaleup issues pertinent during lyophilization cycles commonly used for the freeze-drying of pharmaceuticals.

S. Rambhatla1?S. Tchessalov1?Michael J. Pikal1Email:pikal@uconnvm.uconn.edu
[1] School of Pharmacy, University of Connecticut, 06269 Storrs, CT ;[2] Present address: Talecris Biotherapeutic, Inc., Clayton, NC ;[3] Present address: Wyeth BioPharma, Drug Products Development, Andover, MA

admin — Wed, 17 Sep 2008 06:18:04 +0000

The high-temperature strength and deformation behavior of ?/?? two-phase Co�Al�W-base alloys have been studied with polycrystalline and single-crystal materials. The ternary, quaternary and higher-order alloys containing Ta, Cr and/or Re exhibit flow stress anomalies above 873 K due to slip of pairs of 1/21 1 0 superpartial dislocations on {0 0 1} planes, in addition to {1 1 1} planes, in the ?? precipitates. Compression tests on the single-crystal specimens reveal a true anomalous peak temperature of 1073 K for both ternary and Ta-containing quaternary alloys. Above the peak, the ternary alloy exhibits a rapid decrease in strength with temperature, as 1/21 1 0 dislocations bypass the ?? precipitates without significant shearing. Conversely, the Ta-containing quaternary alloy sustains strength to higher temperatures due to the activation of 1/31 1 2 partial dislocation slip that introduces a high density of stacking faults in the ?? precipitates.

Akane SuzukiaEmail:suzukia@ge.com?Tresa M. Pollockb
[a]GE Global Research, One Research Circle, Niskayuna, NY 12309, USA;[b]Department of Materials Science; Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, MI 48109, USA

Homogeneous nucleation of dislocation loops in nanocrystalline metals and ceramics

admin — Wed, 17 Sep 2008 04:04:11 +0000

A special mechanism of dislocation nucleation in deformed nanocrystalline metals and ceramics is theoretically described. The mechanism represents non-local homogeneous nucleation of a nanoscale loop of �non-crystallographic� partial dislocation whose Burgers vector magnitude continuously grows during the nucleation process. The dislocation loop nucleation is accompanied by nucleation and evolution of a generalized stacking fault bounded by the loop. It is shown that the special mechanism can effectively produce nanoscale loops of lattice dislocations in nanocrystalline metals (Al, Ni) and ceramics (3C�SiC) deformed at high mechanical stresses achieved in shock-wave and indentation load regimes.

M.Yu. Gutkin aEmail:gutkin@def.ipme.ru?I.A. Ovid�koa
[a]Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, Bolshoj 61, Vasilievskii Ostrov, St. Petersburg 199178, Russia

HOW DIFFERENT TEAM DOWNSIZING APPROACHES INFLUENCE TEAM-LEVEL ADAPTATION AND PERFORMANCE.

admin — Tue, 16 Sep 2008 23:50:50 +0000

This study examined the relative effectiveness of three structural approaches to reducing team size. Seventy-one five-person teams engaged in a simulated interactive task in which the approach to downsizing was manipulated. Results suggest that the structural approaches to reducing team size differentially impact team performance, and this relationship is mediated by how and to what degree teams adapt their task-related behaviors. Moreover, results from this study emphasize the importance of team composition in cases of team downsizing. Specifically, emotional stability and extraversion can help mitigate the negative effects associated with reducing team size.

DeRue, D. Scott1 dsderue@umich.edu?Hollenbeck, John R.2 jrh@msu.edu?Johnson, Michael D.3 mdj3@u.washington.edu?Ilgen, Daniel R.4 ilgen@msu.edu?Jundt, Dustin K.5 jundtdus@msu.edu
[1]Associate Professor of Management and Organizations at the Stephen M. Ross School of Business at the University of Michigan;[2]Eli Broad Professor of Management at the Eli Broad Graduate School of Business Administration at Michigan State University;[3]Assistant Professor of Management and Organization at the University of Washington Business School;[4]John A. Hannah Distinguished Professor of Industrial-Organizational Psychology and Management at Michigan State University;[5]Doctoral Candidate in Industrial-Organizational Psychology at Michigan State University

HOW DO MNCS VOTE IN DEVELOPING COUNTRY ELECTIONS?

admin — Tue, 16 Sep 2008 23:46:25 +0000

Research on multinational corporations (MNCs) and host government political risk in developing countries has largely ignored local electoral politics, economic policies, and the MNC investment incentives they may generate. In response, I develop and test a framework for understanding MNC risk and investment behavior based on political business cycle considerations. Analyses of 408 MNC investments worth $199 billion in 18 developing countries holding 35 presidential elections from 1987 through 2000 are consistent with these considerations: MNCs perceive higher (lower) risk and announce fewer (more) investment projects as right-wing (left-wing) incumbents appear more likely to be replaced by left-wing (right-wing) challengers.

Vaaler, Paul M.1 vaa10001@umn.edu
[1]Associate Professor of International Business at the University of Minnesota’s Carlson School of Management

How will HIV/AIDS transform African governance?

admin — Sun, 22 Jun 2008 23:26:44 +0000

The HIV/AIDS pandemic in Africa has far-reaching implications for governance and development. In addition to killing millions of individuals and causing serious economic contractions, the pandemic threatens structural transformations in African economies, institutions and governance. Decreased adult life expectancy has important adverse impacts upon savings, capital accumulation, skills acquisition, and institutional functioning. This article examines how the impacts of the pandemic can be envisaged as running processes of demographic transition, economic development and the growth of a bureaucratic state, in reverse. Meanwhile, expanded HIV/AIDS programming is likely to become a major feature of some African countries. The article examines different models for social and political mobilization against the pandemic and sketches a unified framework for understanding its impact.

Alex de Waal

Histologic findings and comparison with sputum smears in pulmonary aspiration of vegetable particles in syringomyelia:a case report

admin — Wed, 02 Apr 2008 03:18:28 +0000

BACKGROUND: Pulmonary aspiration of vegetable matter may be a serious cause of lung damage, requiring, almost always, the help of a histopathologic examination. CASE: We report the case of a 55-year-old woman with a granulomatous pneumonitis due to repeated pulmonary aspiration of vegetable particles and affected by a syringomyelia. Histologic findings from a lobectomy section are shown and compared with those observed in different cytologic sputum samples. CONCLUSION: The recognition of uncommon morphologic structures, and their comparison with others already known, both in histologic sections and in cellular smears, may be useful when it comes to establishing a sure diagnosis.

Martinez-Giron,R　Ribas-Barcelo,A　Astudillo-Gonzalez,A　Calvo-Temprano,D
INCLINICA Foundation, Oviedo, Spain. rafaelmgiron@terra.es

Cytodiagnosis　 Female　 Foreign Bodies　 Granuloma　 Humans Lung Middle Aged

How to Write an Exercise Prescription for the Airdyne Ergometer

admin — Wed, 12 Mar 2008 01:09:58 +0000

ACSM s health & fitness journal
1091-5397, Volume 4, Issue 5, 2000, Pages 17-19

Lamont, Linda S.

Abstract Combined arm-leg ergometers are popular exercise devices. The Airdyne cycle ergometer promotes cardiovascular fitness by using a unique system for applying mechanical resitance. This article presents step-by-step instructions on how to write a precription for exercise using the airdyne.