Phasmids

To date, the crystal structures of more than 200 mesogenic compounds are known. In this review, we wish to present a general overview of the crystal structures of mesogenic compounds up to the end of 1997. Unfortunately, it is not possible to consider the crystal structure determinations of carbohydrate liquid crystals [13, 14], metallomesogens [15-18], phasmid and biforked mesogens [19-22], perfluorinated mesogenic compounds [23-27], benzoic acids [6, 28-31], cinnamic acids [7, 32, 33], dicarboxylic acids [34, 35], cinnamate compounds [8, 36-40], and discotic liquid crystals [41-43] due to the lack of space. 

Fig, 18a,b, The polymorphic behaviour of the phasmidic-like mesogens a molecular model with six terminal chains b phase diagram for the binary mixture of double swallow-tailed compound (I) with conventional rod-like mesogen (II) (adapted from Letko et al. [123])... 

On the other hand, the defensive secretions of Sipyloidea sipylus and of Megacrania tsudai, two phasmid insects originating from Asia, contain volatile compounds, and, in both cases, the whole secretion has a repellent activity [180,181]. 

Note 3 In some cases the discotic nematic mesophase is formed by compounds that do not have molecules of discotic shape (for example, phasmidic compounds, salt-like materials and oligosaccharides). 

Thus far no sex pheromone has been described in the Phasmida. Some phasmids produce toxic monoterpenes in typical Class III integumentary glands located behind the head (e.g. Happ et al., 1966). The glands exhibit lipid reserves, carboxylic esterases, phosphatases, alcohol dehydrogenase, and a mevalonate kinase, all of which are suggested to be involved in the production of the toxic compounds (Happ et al., 1966). 

Happ G. M., Strandberg J. D. and Happ C. M. (1966) The terpene-producing glands of a phasmid insect cell morphology and histochemistry. J. Morphol. 119, 143-160. 

Mameli M., Tuccini A., Mazza M., Petacchi R. and Pelosi P. (1996) Soluble proteins in chemosensory organs of Phasmids. Insect Biochem. Mol. Biol. 26, 875-882. 

Z11-16 0H and Zll-18 Ac, although with lower specificity than that observed for MbraPBPl and MbraGOBP2 (Bohbot et al., 1998). N-terminal sequencing of these bands revealed the sequence EDKYT which is highly similar to proteins of the CSP family found in insects as diverse as Drosophila, phasmid, and cockroach which are proposed to have diverse functions depending on the specific protein. As mentioned earlier, the first member of this protein family was independently identified in Drosophila and named OS-D (McKenna et al., 1994) or A10 (Pikielny et al., 1994). Related proteins were subsequently referred to as either OS-D like, CSPs or SAPs. 

In the phasmid Eurycantha calcarata, a CSP has been isolated from the cellular layer underlying the cuticle (Marchese el ah, 2000). In the cockroach Periplaneta americana, the CSP plO is expressed in legs and antennae (Nomura et al., 1992 Kitabayashi et al., 1998 Picimbon et al., 2001), and other CSPs have been detected in tissues including legs, brain and cerci (Picimbon and Leal, 1999 unpublished). 

In the section on calamitic materials, we discussed how, by appropriate consideration of the molecular shape of bis( -diketonato)copper(II) complexes, either nematic and lamellar, or columnar mesophases could be realized. Furthermore, increasing the number of chains on the periphery of calamitic mesogens can lead to molecules which demonstrate both types of mesomorphism, e.g. the phasmids of Malthete... 

Phasmids are lambda phages that have an inserted plasmid. They have the same basic features as lambda phage vectors, but inserted DNA fragment can be separated from the phage arms DNA and converted into a plasmid form. There are two main ways for such conversion biological and enzymatic. In the first case, the... 

In some cases, it is more convenient to work with a genomic library in plasmid than in lambda phage form. The construction of representative genomic library directly in a plasmid vector has several drawbacks and difficulties. However, these problems can be easily solved with the help of phasmid and diphasmid vectors. In this case, a genomic library is constructed in lambda phage (e.g., SK40), and then the whole library is converted to plasmid form. 

The same type of columnar structure is also proposed for other polycatenar materials, such as tetrone derivatives [51], phasmidic macrocyclic liquid crystals [52], silver (I) complexes [53], or 2,2 -bipyridine derivatives [54]. 

Molecules which combine the features of the rod and the disc may be expected to form new types of mesophases. An example is the biaxial nematic phase reported in thermotropic systems (see 6.6). Malthete et a/. have prepared an interesting series of mesogens shaped like stick insects called phasmids (fig. 6.1.5(n)). Some of them form columnar mesophases the structure proposed for the hexagonal phase is shown schematically in fig. 6.1.5( >). 

Fig. 6.1.5. (a) Hexa-n-alkoxy terepthal-fe -(4-benzoyloxyaniline) and (Jb) the structure of the hexagonal columnar mesophase formed by this compound. The mesophase has been described as phasmidic . (Malthete, Levelut and Tinh. )... 

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