Academic literature on the topic 'Chiralité plane'

This chapter argues that control of magnetic domains and domain wall structures is one of the most important issues from the viewpoint of both applied and basic research in magnetism. Its discussion is however limited to static and dynamic properties of magnetic vortex structures. It has been revealed both theoretically and experimentally that for particular ranges of dimensions of cylindrical and other magnetic elements, a curling in-plane spin configuration is energetically favored, with a small region of the out-of-plane magnetization appearing at the core of the vortex. Such a system, whic

Functioning in the Earth gravity field imposes on living organisms a necessity to read directions. The characteristic feature of their bodies, regardless unicellular or multicellular, is axial symmetry. The development of body plan orchestrated by spatiotemporal changes in gene expression patterns is based on formation of the vertical and radial axes. Especially for immobile plants, anchored to the substrate, vertical axis is primary and most important. But also in animals the primary is the axis, which defines the anterior and posterior pole of the embryo. There are many little known chiral processes and structures that are left- or right oriented with respect to this axis. Recent developments indicate the role of intrinsic cell chirality that determines the direction of developmental chiral processes in living organisms. The still enigmatic events in cambia of trees and handedness of phyllotaxis as well as plant living crystals are in focus of the chapter.

Alkaloids are distributed in plant kingdom and play important role in protection, germination as well as plant growth stimulants. Most of them are chiral compounds and are clinically administered as the racemic mixture, even though its enantiomers have been known to exert different pharmacological activity. Liquid chromatography using chiral stationary phases (CSP) proved to be an essential tool with a wide range of applications, including analysis of the stereochemistry of natural compounds. This review gives an overview of chiral separation alkaloids that were used in theoretical studies and/or applications in recent years. It shows the possibilities of polysaccharide CSPs have now also been established as the first-choice of chiral phases for enantiomer separation.

After the first report of deep eutectic mixtures by the team of Abbott in 2003, the advent of green synthesis has been progressively changing the way synthetic chemistry is thought and also taught. Since then, a plethora of efforts worldwide have been taken to stretch the ideas of sustainable as well as environmentally benign approaches to do the crucial synthetic organic transformations under operationally simple yet effective conditions. Although, till date, several green synthetic strategies for examples ultrasound, microwaves, flow as well as grindstone chemistry etc., and green reaction media (e.g. ionic liquid, water, scCO2, and so forth) have successfully been invented. But a low melting mixture of L-(+)-tartaric acid (TA) and N,N′-dimethylurea (DMU), usually plays a double and/or triple role (solvent, catalyst, and/or reagent), though still infancy but enjoys several eye-catching properties like biodegradability, recyclability, non-toxicity, good thermal stability, tunable physiochemical properties, low vapor pressure as well as reasonable prices in addition to the easy preparation with wide functional groups tolerance. To this context, keeping the importance of this novel low melting mixture in mind, we intended to reveal the advancements taken place in this wonderful area of research since its first report by the Köenig’s group in 2011 to till date. In this particular chapter, firstly we would disclose the importance of the green synthesis followed by a brief description of deep-eutectic solvents (DESs) particularly emphasizing on the role of L-(+)-TA and DMU from modern synthetic chemistry perspective.

The concept of the carbon atom with four bonds extending in a tetrahedral fashion was put forward by van’t Hoff and Le Bel in 1874. It coincided with the realization that such an arrangement could be asymmetric if the four substituents were different, as shown in Figure 10.1a (van’t Hoff, 1874; Le Bel, 1874). Thus, for any compound containing one such asymmetric carbon atom, there are two isomers of opposite chirality (individually called enantiomers), for which threedimensional representations of their structural formulas are related by a mirror plane. Aqueous solutions of these enantiomers rotate the plane of polarized light in opposite directions. As discussed in Chapter 7, Pasteur showed that crystals of sodium ammonium tartrate had small asymmetrically located faces and that crystals with these so-called “hemihedral faces” rotated the plane of polarization of light clockwise, while crystals with similar faces in mirror-image positions rotated this plane of polarization counterclockwise. Thus the external form (that is, the morphology) of the crystals illustrated in Figure 10.1b was used to separate enantiomers (see Patterson and Buchanan, 1945). Pure enantiomers can only crystallize in noncentrosymmetric space groups unless both isomers are present. But even if the chemical formula and the three-dimensional structure of a molecule such as tartaric acid have been determined by standard X-ray diffraction methods, there is an ambiguity about the absolute configuration. Information about the absolute configuration is not contained in the diffraction pattern of the crystal as it is normally measured. Thus, although the substituents on the asymmetric carbon atoms have been identified, and even the detailed three-dimensional geometry of the molecule has been determined, it is not known which of the two enantiomers (mirror-image forms, analogous to those shown in Figure 10.1a) represents the three-dimensional structure of a particular individual molecule that has some distinguishing chiral property, such as the ability to rotate the plane of polarized light to the right. In other words, what is the absolute structure of the dextrorotatory form of the compound under study? A means of determining the absolute configurations of molecules was, however, provided by X-ray crystallographic studies.

It was Otto Wallach (1847– 1931) who first coined the term “terpene” and made the observation that many plant-derived essential oils had chemical structures whose composition was based on multiples of a basic five-carbon unit. His work with turpentine and the organic products derived from it was consistent with earlier studies of natural rubber which had shown that its thermal decomposition released “isoprene” (2-methyl-1,3-butadiene) as the principal product. This led eventually to the formulation of the so-called biogenetic isoprene rule of Leopold Ruzicka (1887–1976) in 1953 which stated that “the carbon skeleton of the terpenes is composed of isoprene units linked in regular or irregular arrangement.” As it turns out, biosynthetic pathways to terpenes are found in nearly all organisms, producing a remarkable variety of different structural types, as we will soon see. In fact, something in excess of over 25,000 different terpenes with a wide variety of biological functions have been isolated from the plant kingdom over the years. Interestingly, while many terpenes are simple achiral compounds, others are chiral as can be seen in the case of α-pinene in Fig. 4.1. But unlike the naturally occurring L-amino acids and D-carbohydrates, different organisms may produce the same terpene product but in different enantiomeric forms. For example, limonene is formed by more than 300 plants, with the (+)-(R) enantiomer being the most widespread form as the major constituent of citrus peel essential oils (orange oil). As the most abundant of all terpenes, its pleasant citrus fragrance and flavor have led to its worldwide use in the food and fragrance industries and also as a botanical insecticide. A number of plants produce both enantiomers of limonene, while others produce only the (−)-(S)-enantiomer which possesses a strong pine smell reminiscent of turpentine. This obviously speaks to the chirality and enantioselectivity of our own olfactory receptor sites which can readily distinguish between the two enantiomers, thus signaling a different odor response in each case.

There is significant amount of research to analyze the thermal, electrical and other physical properties of carbon nanotubes (CNTs). However, the energy transport mechanism at the contact of two tubes is still not well understood. This study investigates the interfacial thermal interaction between two carbon nanotubes using molecular dynamics simulation and wavelet methods. We place the tubes in a crossed configuration and pass a high temperature pulse along one of the CNTs while keeping other ends fixed, and analyze the interaction of this pulse with other nanotube. We apply this technique fo

This paper presents the design of a bio-inspired crawling robot comprised of bi-stable origami building blocks. This origami structure, which is based on Kresling origami pattern, expands and contracts through coupled longitudinal and rotational motion similar to a screw. Controlled snapping, facilitated by buckling instability, allows for rapid actuation as seen in the mechanism of the hummingbird beaks or the Venus flytrap plant, which enables them to capture insects by fast closing actions. On a much smaller scale, a similar buckling instability actuates the fast turning motion of uni-flage