Chiral fields

According to this argument, diacetylenic lipids do not have an unusually high value of the chiral field h compared with other lipids. Rather, diacetylenic lipids have an unusual negative value of the coefficient t, which gives a free... 

Preferential helical screw sense polysilanes with main-chain chirality are essentially of two types those in which PSS chirality is induced by an internal chiral field, for example, incorporation of enantiopure chiral (unichiral) side chains or end groups, and those which are inherently achiral, in which PSS chirality is induced by an external chiral field, such as a unichiral additive or solvent. 

The twist angles between the terminal rungs of 141, 142 and 143 are 44.0, 63.0, and 80.3°, respectively. The double helix structures crystallize with equal amounts of left- and right-handed screw sense forms, as expected in the absence of any chiral field. Some ladder polysilanes crystallize with both helical forms in the same centrosymmetric unit cell for others, the two forms can crystallize separately. It will be interesting to carry out the crystallization in a chiral field. 

The Wess-Zumino term in Eq. (11) guarantees the correct quantization of the soliton as a spin 1/2 object. Here we neglect the breaking of Lorentz symmetries, irrelevant to our discussion. The Euler-Lagrangian equations of motion for the classical, time independent, chiral field Uo(r) are highly non-linear partial differential equations. To simplify these equations Skyrme adopted the hedgehog ansatz which, suitably generalized for the three flavor case, reads [40] ... 

Photochemically Triggered Induced Circular Dichroism in Liposomes When an optically inactive chromophore is subject to the effect of optically active environment, optical activity may be induced at the absorption wavelength of the optically inactive chromophore. This phenomenon of induced circular dichroism(ICD) is often observed in polypeptides bearing various achiral chromophores on the side chain( ). The strong chiral environment caused by the peptide helix structure is responsible for this. Distance from, and orientation to, the chiral field decide the degree of ICD appearing on the achiral chromophore. 

An overview of the principles of chiral separations in CE and HPLC is given in the first part of this chapter. The second part is dedicated to an overview of chiral separation with CE. The popularity of electrophoretic techniques has grown spectacularly in recent years, mainly due to their exceptional performances in the chiral field. Various selectors can easily... 

The 0 3 connection has a chiral component that seems to imply that Ti v has a chiral component, or is mixed with the chiral component of the other SU(2) chiral field of the electroweak theory. This is what happens to SU(2) electromagnetism at very high energies. It becomes very similar in formal structure to the theory of weak interactions and has implications for the theory of leptons. The electromagnetic interaction acts on a doublet that can be treated as an element of a Fermi doublet of charged leptons and their neutrinos in the SU(2) theory of the weak interaction. 

Therefore the electroweak theory is chiral at high energies, but is vector and chiral in separate sectors on the physical vacuum of low energies. The high-energy chiral field combines with the other chiral field in the twisted bundle to produce a vector field plus a broken chiral field at low energy. There are independent fields that are decoupled on the physical vacuum at low energies. 

One purpose here is to examine the co3 connection which will have a chiral component. This at first implies that the B 3 field is partly chiral, or that it is mixed with the chiral component of the other SU(2) chiral field in some manner to remove its chirality. 

For these reasons there are reasons to consider this model, or a similar variant, as a reasonable model for the unification of gauge fields outside of gravitation. The extension of the gauge symmetries for electromagnetism at high energy, even if the field is 17(1) on the physical vacuum, leads to a standard model with a nice symmetry between chiral fields, and this symmetry is further contained in GUT. 

Abstract It is well known that spontaneous deracemization or spontaneous chiral resolution occasionally occurs when racemic molecules are crystallized. However, it is not easy to believe such phenomenon will occur when forming liquid crystal phases. Spontaneous chiral domain formation is introduced, when molecules form particular liquid crystal phases. Such molecules possess no chiral carbon but may have axial chirality. However, the potential barrier between two chiral states is low enough to allow mutual transformation even at room temperature. Therefore the systems are essentially not racemic but nonchiral or achiral. First, enhanced chirality by doping chiral nematic liquid crystals with nonchiral molecules is described. Emphasis is made on ester molecules for their anomalous behavior. Second, spontaneous chiral resolution is discussed. Three examples with rod-, bent-, and diskshaped molecules are shown to give such phenomena. Particular attention will be paid to controlling enantiomeric excess (ee). Actually, almost 100% ee was obtained by applying some external chiral stimuli. This is very noteworthy in the sense that we can create chiral molecules (chiral field) without using any chiral species. 

On the lowest level the carbonyl chromophore is viewed as the prototype of an inherently symmetric, but chirally perturbed chromophore This means that in a chiral ketone the particular carbonyl chromophore retains (largely) its (achiral) symmetry and optical activity will be induced by the chiral environment (i.e. the chiral arrangement of other groups in the whole molecule). In terms of perturbation theory this can be expressed by the statement that in zeroth order the chromophore is achiral and chirality is induced by perturbations in first (or higher) order. On the other hand, if, for a given electronic excitation, optical activity exists in zeroth order (without perturbation by the chiral field of the remaining groups of the molecule not directly involved in the electronic transition) the chromophore is termed inherently chiral ... 

Poly(alkyl isocyanate) with isotopic chirality (the uniform chiral field concept) (Green)... 

To close this brief introduction, we hope this book will be useful to readers not currently working in chirality, as well as informative to those who are more familiar with this subject. We would also expect to stimulate fiuther interest and experiments in order to push the horizon of the chirality field further since Pasteur s and Werner s first discoveries up to the present day and beyond. 

Baba et al. (1980b) attempted an asymmetric reduction by 1,4-di-hydropydidine covalently bound to a cyclic peptide, bacitracin, which is an antibiotics and has large affinity to the zinc ion. They intended to enhance the reactivity of 1,4-dihydropyridine by the coordination of a cyclic peptide moiety to a metal ion as well as to achieve the asymmetric reduction by an effect of the chiral field provided by the peptide. However, neither the activity nor the ability for asymmetric induction were so high. The optical yield of ethyl i -mandelate in the reduction of ethyl benzoylformate in the presence of magnesium perchlorate was 5.4 % (7 ) in dry methanol only 1.9 % (i ) in acetonitrile. 

Chirality field h =Ki2qo=Ki2iio (Vxii ) Magnetic Field H... 

Figure 10.6. Phase diagrams of (a), (b) superconductors and (c), (d) liquid crystals, according to de Gennes [14]. The analog of the external magnetic field is the chirality field h = Kiigo-...

Most isotactic vinyl polymers assume helical conformations in the crystalline state [4], but ovnng to the substantial achirality of the macromolecules both screw senses are found in the lattice ceils in equal amounts. This is even more true in a melt or in solution, where left-handed and right-handed helical sections alternate even within the same macromolecular chain. Certainly, an appreciable optical rotation would be observed in the crystalline state provided that crystallization occurred under a chiral field inducing a single screw sense helidty in all chains. Such an optical rotation would promptly be lost on melting or dissolution, as an immediate equilibration between the two opposite helical senses would occur. 

---