Interface achiral

Unlike electron and scanning tunneling microscopy, the use of fluorescent dyes in monolayers at the air-water interface allows the use of contrast imaging to view the monolayer in situ during compression and expansion of the film. Under ideal circumstances, one may observe the changes in monolayer phase and the formation of specific aggregate domains as the film is compressed. This technique has been used to visualize phase changes in monolayers of chiral phospholipids (McConnell et al, 1984, 1986 Weis and McConnell, 1984 Keller et al., 1986 McConnell and Moy, 1988) and achiral fatty acids (Moore et al., 1986). 

Figure 8.14 Illustration of first achiral antiferroelectric system bilayer tilted smectic with alternating synclinic and anticlinic layer interfaces.

Apparently this switching mode is disfavored since, in fact, the chirality of the layers does not change upon switching to the ferroelectric state rather the layer interface clinicity changes. This occurs when the molecules in alternate layers simply precess about the tilt cone in a manner exactly analogous to antiferroelectric to ferroelectric switching in the chiral SmC phase. As shown in Figure 8.25, the ferroelectric state obtained from the ShiCsPa antiferroelectric phase is a ShiCaPf structure, an achiral macroscopic racemate with anticlinic layer interfaces. 

From this discussion the clear similarity between the SmAPA and SmCsPA structures is easily seen. In addition, the suggestion of Brand et al.29 that a bilayer smectic with all anticlinic layer interfaces (the SmAPF) would produce an achiral ferroelectric smectic follows directly. The unanticipated tilt of the director in the tilt plane, leading to a chiral layer structure, seems to be a general response of the bent-core mesogens to the spontaneous nonpolar symmetry breaking occurring in these rigid dimer structures. 

Abstract To appreciate the technological potential of controlled molecular-level motion one only has to consider that it lies at the heart of virtually every biological process. When we learn how to build synthetic molecular motors and machines that can interface their effects directly with other molecular-level sub-structures and the outside world it will add a new dimension to functional molecule and materials design. In this review we discuss both the influence of chirality on the design of molecular level machines and, in turn, how molecular level machines can control the expression of chirality of a physical response to an inherently achiral stimulus. 

With the chiral center located in a side chain that is bent away from the surface, an achiral lattice is formed by the chiral diacetylene isophthalic acid derivative at the 1-octanol/graphite interface [73]. Because of the relatively weak interaction between the dangling chiral side chains, the achiral part of the molecule interacting with the substrate dominated the pattern formation. 

Figure 2.7 Schematic diagram to represent natural numbers and their conjugates as two spirals that meet at infinity. The mirror image of each spiral represents negative numbers. Real and conjugate number spirals are chiral. In projection on orthogonal axes in the complex plane, together they create an achiral interface...

The persistent correlation that recurs between number patterns and physical structures indicates a similarity between the structure of space-time and number. Like numbers and chiral growth, matter has a symmetry-related conjugate counterpart. The mystery about this antimatter is its whereabouts in the universe. By analogy with numbers, the two chiral forms of fermionic matter may be located on opposite sides of an achiral bosonic interface. In the case of numbers this interface is the complex plane, in the physical world it is the vacuum. An equivalent mapping has classical worlds located in the two surfaces and the quantum world, which requires complex formulation, in the interface. 

Entities that move in the interface are achiral and massless. A virtual photon consists of a virtual particle/anti-particle pair. The vector bosons that mediate the weak interaction are massive and unlike photons, distinct from their anti-particles. The weak interaction therefore has reflection symmetry only across the vacuum interface and hence /3-decay violates parity conservation. 

The adsorption of (7 ,/ )-tartaric acid on a Cu(llO) surface formed the basis of our initial studies and we present it to demonstrate the hierarchical expression of chirality at surfaces. The behaviour of this system reveals the explicit role played by the surface and the adsorption process in introducing additional asymmetry at an interface, and we use this to demonstrate how such surface events can lead to chiral expression in initially achiral systems such as succinic acid on Cu(llO). 

On the subject of spontaneous generation of chirality, it is of interest to know that spontaneous formation of chiral aggregates from nonchiral monomers is known to occur, e.g. the assembly of tetra-alkyl benzimidocyanins 3 as monitored by CD (circular dichroism). Formation of chiral crystals from achiral monomers is also reported, e.g. by photodimerization in the solid state. " In a recent example, chiral crystals of acridine 4 and diphenylacetic acid 5 give excess of the (.S)-product 6 upon a photodecarboxylating condensation reaction. Symmetry breaking is also known to occur for supramolecular complexes of achiral components e.g. glu-tarimide 7 and the diaminopyridine 8, and, as will be discussed below, in monolayers at the air-water interface. ... 

Spiral structures can also arise in monolayers of achiral molecules, as in the study by polarized laser excitation fluorescence microscopy of chiral defects in pentade-canoic acid. Using a rigid achiral molecule with a series of chiral centers (14), separation of chiral domains in the racemate has been observed by atomic force microscopy (AFM) on monolayers transferred from the air-water interface to... 

In anticipation we point out that the four-dimensional Minkowski space of relativity is natmally segmented into time-like and space-like regions, separated by a conical light surface. It could imply two equal massive regions of opposite chirality, separated by an achiral electromagnetic interface. Maybe there is a logical resolution of the chirahty paradox after all. 

The idea that the vacuum represents an achiral interface that separates two space-time segments of opposite chirality developed from the notion that mass-dependent quantum effects arise from a field in the vacuum which affects the smallest of objects most prominently. The original argument (Boeyens, 1992) was that quantum behaviour results from feeble interactions through the interface, which create the impression of random wave-like perturbations imposed on the regular motion of small particles. 

The asymmetric polymerization in crystalline architectures provides an excellent environment to conduct the absolute asymmetric synthesis of polymers, and also provides an effident route for the ampHfication of chirality. Mirror-symmetry breaking might occur either through total asymmetric transformations, either in enantiomorphous crystals that have self-assembled from achiral molecules, or within racemic crystalline architectures which are delineated by chiral rims or surfaces when one of the chiral faces is blocked by an interface. The self-assembly of nonracemic mixtures into a mixture comprising eutectic compositions of a racemic compound and an enantiomorphous assembly, followed by asymmetric transformation, provides a series of thermodynamically controlled, alternative routes for the effident ampHfication of homochirality. 

Yunfeng Qiu, Penglei Chen, Minghua Liu. (2008). Interfacial Assembly of an Achiral Zinc Phthalocyanine at the AirAVater Interface A Surface Pressure Dependent Aggregation and Supramolecular Chirality. Langmuir, 24, 7200-7207. 

As mentioned already, achiral molecules can also be employed to obtain chiral surfaces. Wang et studied the self-assembly of an achiral aldehyde-substituted oligo (p-phenylene vinylene) (OPV3-CHO) at the air/graphite interface (Figure 12a) focusing on the structure and... 

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