PLAYING IN THE FRONTIERS OF THE WOODWARD-HOFFMANN RULES

2021 ◽  
Author(s):  
Carlos Silva López ◽  
Keyword(s):  
Organic Synthesis ◽  
Microscopic Level ◽  
Pericyclic Reactions ◽  
Computational Tools ◽  
New Era ◽  
Eye Opening ◽  
Degree Of Control ◽  
Chiral Centers ◽  
High Degree

Pericyclic reactions are known for their exquisite selectivity and, in many cases, the formation of multiple chiral centers with a high degree of control. With the advent of accurate computational tools, this control was translated into predictability, and the design and exploitation of this set of reactions opened a new era in organic synthesis. Suddenly, highly complex and profusely decorated polycyclic structures were accessible in relatively short reaction sequences. Out interest in exploring the limits of application of the rules that govern these reactions with ironfist led us to discover a range of eye opening post-transitional effects that are key to ultimately understand reactivity at a microscopic level.

Self-Assembly of a Chiral Cubic Three-Connected Net from the High Symmetry Molecules C60 and SnI4

2020 ◽  
Author(s):  
Daniel B. Straus ◽  
Robert J. Cava
Keyword(s):  
Organic Synthesis ◽  
Self Assembly ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
High Symmetry ◽  
Molecular Chirality ◽  
Chiral Materials ◽  
Self Assembled ◽  
Chiral Centers

The design of new chiral materials usually requires stereoselective organic synthesis to create molecules with chiral centers. Less commonly, achiral molecules can self-assemble into chiral materials, despite the absence of intrinsic molecular chirality. Here, we demonstrate the assembly of high-symmetry molecules into a chiral van der Waals structure by synthesizing crystals of C<sub>60</sub>(SnI<sub>4</sub>)<sub>2</sub> from icosahedral buckminsterfullerene (C<sub>60</sub>) and tetrahedral SnI4 molecules through spontaneous self-assembly. The SnI<sub>4</sub> tetrahedra template the Sn atoms into a chiral cubic three-connected net of the SrSi<sub>2</sub> type that is held together by van der Waals forces. Our results represent the remarkable emergence of a self-assembled chiral material from two of the most highly symmetric molecules, demonstrating that almost any molecular, nanocrystalline, or engineered precursor can be considered when designing chiral assemblies.

Carbohydrates as chiral intermediates in organic synthesis. Two functionalized chemical precursors comprising eight of the ten chiral centers of erythronolide A

1977 ◽  
Vol 55 (6) ◽  
pp. 1111-1113 ◽  
Author(s):  
Stephen Hanessian ◽  
Georges Rancourt
Keyword(s):  
Organic Synthesis ◽  
Chiral Intermediates ◽  
Chiral Centers ◽  
Branched Chain

Two appropriately functionalized branched-chain sugars have been synthesized as potentially useful chemical precursors to erythronolide A, encompassing its C-1–C-6 and C-9–C-15 segments respectively.

Displacements of Simulium damnosum and strategy of control against onchocerciasis

1979 ◽  
Vol 287 (1022) ◽  
pp. 277-288 ◽  
Keyword(s):  
Sensu Stricto ◽  
Control Programme ◽  
West African ◽  
Simulium Damnosum ◽  
Logistic Problem ◽  
Degree Of Control ◽  
High Degree ◽  
Onchocerciasis Control ◽  
Upper Volta ◽  
West African Savannah

Regular aerial treatment of 14000 km of watercourses has achieved and maintained, over an area of 700000 km 2 of West African savannah, a very high degree of control of the larvae of Simulium damnosum sensu stricto and S. sibanum , the vectors of onchocerciasis in this area. However, particular and relatively restricted parts of this area, mainly in northern Ivory Coast and neighbouring parts of Upper Volta, experience regular and prolonged reinvasions by parous female vectors, which have already taken bloodmeals (and many of them carrying the parasites) and arrive from unknown sources probably hundreds of kilometres away, from directions probably between southwest and north. This reinvasion, now experienced in three successive years, represents the outstanding scientific, epidemiological and logistic problem still facing the WHO Onchocerciasis Control Programme. An outline is presented of the multidisciplinary investigations being undertaken to find a solution.

Rethinking Incentives

2020 ◽  
pp. 154-166
Author(s):  
Lea Shaver
Keyword(s):  
Writing Process ◽  
For Profit ◽  
Degree Of Control ◽  
High Degree

This chapter begins by describing an experience of Iceland that casts Samuel Johnson's claim that “No man but a blockhead ever wrote, except for money” into serious doubt. With only 350,000 speakers, the potential readership for Icelandic books is truly small; yet Iceland's publishing scene is thriving. It discusses the counterproductive effect of financial rewards as the strongest for activities that people find psychologically rewarding because they are fun, culturally valued, or otherwise meaningful. An author can experience the writing process as play, in which the creator enjoys a high degree of control over the outcome and may also feel gratified for having made a contribution to society, advancing knowledge in an area that one cares about, or the pure satisfaction of self-expression. The chapter further clarifies that people internalize the notion that doing something for profit makes it less praiseworthy and being financially rewarded may undermine the sense of pride or virtue associated with it.

Real-World Contexts

2015 ◽  
Author(s):  
Diana C. Mutz
Keyword(s):  
Real World ◽  
Production Quality ◽  
Political Conflict ◽  
The Political ◽  
Causal Inferences ◽  
Camera Perspective ◽  
Degree Of Control ◽  
Experimental Treatments ◽  
High Degree ◽  
The Impact

This chapter looks at the characteristics of the experimental treatments that are used to manipulate incivility, as well as the kinds of people used in the experiments. Because of the high degree of control over the political content of the broadcasts, the participants involved in the conflicts, and the way in which the cameras covered the dispute, it is possible to draw strong causal inferences about the impact that incivility and camera perspective have on viewers' experiences of political conflict. Although the professional production quality meant that none of the subjects voiced suspicions about the programs themselves, it is still plausible that other, unidentified differences between the real world and this exchange may have altered the outcomes.

A New Era in Cross-strait Relations? A Post-sovereign Enquiry in Taiwan’s Investment Treaty System

2019 ◽  
pp. 290-310
Author(s):  
Horia Ciurtin
Keyword(s):  
International Law ◽  
Main Trend ◽  
The European Union ◽  
New Era ◽  
Investment Treaty ◽  
System P ◽  
International Economic Law ◽  
Starting Point ◽  
Eye Opening ◽  
Litmus Test

The author provides a post-sovereign enquiry in Taiwan’s investment treaty system. Going beyond the traditional legal divisions, Taiwan showed that it can bypass such limitations, being a main trend-setter in innovating the area of international economic law. Specifically, a close look at Taiwan’s nexus of investment treaty is eye-opening; Taiwan concluded twenty-nine BITs and six ample economic cooperation agreements with related investment provisions. The number and the importance of these agreements reveal that the concept of international recognition does not directly influence the behaviour of states which are willing to interact legally and economically. In this regard, non-diplomatic relations might be used as a step forward, as Taiwan is closer to conclude an agreement with another post-sovereign entity, the European Union. This global actor may open up the scene for a multi-tier dynamic where some of its component member states are in principle against any liaison with Taiwan, but will be bound to it because of their membership to the EU. To solve such legal contradiction, the established instruments of international law cannot be applied, and a new theoretical framework shall be developed. To this end, the starting point must be to discuss sovereignty thoroughly. The chapter assesses the polity’s effort for the development of diplomatic structures by means of investment agreements, in this way avoiding the problems related to recognition. This kind of agreement can be considered as a litmus test, showing Taiwan’s capacity to shift traditional categories of Westphalian international law and emerge as a self-standing actor.

Template-Directed Syntheses of Catenanes

1997 ◽  
Vol 62 (4) ◽  
pp. 527-557 ◽  
Author(s):  
Martin Bělohradský ◽  
Françisco M. Raymo ◽  
J. Fraser Stoddart
Keyword(s):  
Self Assembly ◽  
Molecular Level ◽  
Covalent Bonds ◽  
Topological Features ◽  
Multistep Synthesis ◽  
Chance Event ◽  
Degree Of Control ◽  
High Degree ◽  
Acyclic Precursor ◽  
Molecular Compounds

The art and science of introducing mechanical-interlocking at the molecular level in order to generate catenanes - molecules composed of two or more macrocyclic components - offers the opportunity of constructing a new range of molecular compounds possessing intriguing properties. However, the topological features displayed by catenanes has rendered the syntheses of such molecular compounds an extremely challenging task for synthetic chemists to address. Their early syntheses were based upon either statistical approaches - the threading of a small amount of a macrocycle on to an acyclic precursor as a chance event - or directed approaches, relying upon the temporary introduction of covalent bonds in the multistep synthesis of a so-called precatenane, followed by its conversion ultimately into a catenane. These approaches afforded catenanes in very low yields overall and only after following tedious and laborious synthetic procedures. Fortunately, however, with the advent of supramolecular chemistry, template-directed methods that allow us to self-assemble [n]catenanes much more efficiently have become available. Numerous successful template-directed syntheses have now emerged - some by chance and others by design. These methods have been based upon (i) metal coordinating, (ii) hydrogen bonding, (iii) solvophobic, and/or (iv) π-π stacking interactions which have been found to govern self-assembly processes to catenated compounds from appropriate precursors. Their relative simplicity, the high degree of control with which they can be employed, and the remarkable efficiency with which they proceed has already provided the opportunity to synthetic chemists to self-assemble a series of [n]catenanes, incorporating from two up to five mechanically-interlocked macrocyclic components.

Improving the Chinese Medicine Culture Self-Confidence of Students in Chinese Medicine Universities

2020 ◽  
Vol 9 (4) ◽  
pp. 156
Author(s):  
Yu Wang ◽  
Xue Yu ◽  
Afei Tang ◽  
Jin Zhu ◽  
Ce Cao
Keyword(s):  
College Students ◽  
Chinese Medicine ◽  
The Self ◽  
Quality Development ◽  
New Era ◽  
Chinese Nation ◽  
Self Confidence ◽  
The World ◽  
Challenges And Opportunities ◽  
High Degree

As one of the most important creations of Chinese civilization, Chinese medicine culture is a treasure of our country and even the world, and it is also a precious treasure passed down from generation to generation of the Chinese nation. "Pharmaceutical business" reflects the importance of Chinese medicine culture in the new era. The self-confidence of Chinese medicine culture is the cornerstone of the revitalization of Chinese medicine culture. Facing the challenges and opportunities of the development of Chinese medicine culture in the future, college students of TCM schools can only advance the Chinese medicine industry to a higher level if they have a high degree of self-confidence in Chinese medicine culture. Higher quality development.

Laser Forming of ERW Steel Square Tubes within Metallurgical Constraints

2013 ◽  
Vol 549 ◽  
pp. 68-75 ◽  
Author(s):  
Ghazal Sheikholeslami ◽  
Jonathan Griffiths ◽  
Stuart P. Edwardson ◽  
Ken Watkins ◽  
Geoff Dearden
Keyword(s):  
Laser Forming ◽  
Contact Method ◽  
Fem Model ◽  
Minimal Impact ◽  
Beam Laser ◽  
Out Of Plane ◽  
Degree Of Control ◽  
Metallurgical Study ◽  
High Degree ◽  
Shape Data

Laser forming (LF) is a non-contact method to shape metallic sheets and tubes by induced thermal stress without melting using a de-focused laser beam. Laser forming offers the industrial promise of controlled shaping of metallic and non-metallic components for prototyping, correction of design shape or distortion and precision adjustment applications. In order to fulfil this promise in a manufacturing environment the process must have a high degree of control, be repeatable and have a minimal impact on the material and mechanical properties of the part to be formed. In order to demonstrate the capability of the LF process a study is presented in this paper on the 3D Laser Forming of ERW steel square tubes SHS EN10305-5 E220 +CR2 (1.5x25x25mm and 1.5x50x50mm 300mm long tube) using a 1.5kW CO2laser and industrial 5 axis gantry. Strategies have been developed for out of plane bending with specific emphasis on process throughput balanced with minimising adverse localised changes to material properties that could lead to stress concentration features in a component in service. Presented in this paper is empirical 3D LF shape data verified by a scanning laser profiler, a metallurgical study, hardness testing and a FEM model developed in Comsol Multi-Physics. The results of these studies were employed to develop optimised scan strategies for the controlled laser forming of the ERW steel square tubes within strict metallurgical constraints.

scholarly journals Soil water regulates the control of photosynthesis on diel hysteresis between soil respiration and temperature in a desert shrubland

2017 ◽  
Vol 14 (17) ◽  
pp. 3899-3908 ◽  
Author(s):  
Ben Wang ◽  
Tian Shan Zha ◽  
Xin Jia ◽  
Jin Nan Gong ◽  
Charles Bourque ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Soil Respiration ◽  
Soil Water ◽  
Soil Surface ◽  
Volumetric Soil Water Content ◽  
Desert Shrub ◽  
Physical Mechanisms ◽  
Diel Variations ◽  
Degree Of Control ◽  
High Degree

Abstract. Explanations for the occurrence of hysteresis (asynchronicity) between diel soil respiration (Rs) and soil temperature (Ts) have evoked both biological and physical mechanisms. The specifics of these explanations, however, tend to vary with the particular ecosystem or biome being investigated. So far, the relative degree of control of biological and physical processes on hysteresis is not clear for drylands. This study examined the seasonal variation in diel hysteresis and its biological control in a desert-shrub ecosystem in northwest (NW) China. The study was based on continuous measurements of Rs, air temperature (Ta), temperature at the soil surface and below (Tsurf and Ts), volumetric soil water content (SWC), and photosynthesis in a dominant desert shrub (i.e., Artemisia ordosica) over an entire year in 2013. Trends in diel Rs were observed to vary with SWC over the growing season (April to October). Diel variations in Rs were more closely associated with variations in Tsurf than with photosynthesis as SWC increased, leading to Rs being in phase with Tsurf, particularly when SWC > 0.08 m3 m−3 (ratio of SWC to soil porosity  =  0.26). However, as SWC decreased below 0.08 m3 m−3, diel variations in Rs were more closely related to variations in photosynthesis, leading to pronounced hysteresis between Rs and Tsurf. Incorporating photosynthesis into a Q10-function eliminated 84.2 % of the observed hysteresis, increasing the overall descriptive capability of the function. Our findings highlight a high degree of control by photosynthesis and SWC in regulating seasonal variation in diel hysteresis between Rs and temperature.

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