Cone-like structure

JHC129>. In the solid state the cyclic peptide based on dipeptidyl imidazole 26 organizes to a rigid molecule in which all lone pairs of the imidazole nitrogens and the hydrogens of the secondary amides point toward the center of the macrocycle. The valine side-chains all lie on the same face of the molecule and adopt axial positions. The imidazole moieties form a cone-like structure <2002TL6335>. 

It is important to note that diffusion parameters can also depend critically on the dimensions of small particles. A recent model accounts for the formation of hollow filaments, based upon the precipitation of carbon on the catalytic particle. As a result, graphite planes grow parallel to the exterior fibre planes and a hollow core is formed [100]. However, other studies by Boellard et al. [101] on the filament tips where the metal particle is located suggested that the basal planes were positioned at an angle to the filament axis. In this case, the Ni particles were aligned with respect to its [112] axis, parallel to the filament axis (cone-like structures). 

These drops loose solvent molecules by evaporation, and at the Raleigh hmit (electrostatic repulsion of the surface charges > surface tension) much smaller droplets (so-called microdroplets) are emitted. This occurs due to elastic surface vibrations of the drops, which lead to the formation of Taylor cone-like structures. 

General packing schemes of cyclodextrin molecules in crystalline lattices. Cyclodextrins are seen from the side, the cone-like structure is indicated by wider (02,03 hydroxyls) and narrower (06 hydroxyls) dimensions cavities are marked by hatched areas. (A) Fishbone-type cage, (B) brick-type cage, (C) channel-type arrangement (a head-to-head packing of cyclodextrin molecules is shown). 

In Fig. 7.2, we show a general cartoon of a conical intersection. In addition to the energy, the double cone like structure is defined by two geometrical coordinates Xi and X2 (first introduced in Fig. 7.1). Thus, as one moves away from the apex of the cone, the degeneracy is lifted. In Fig. 7.3 we show another important effect. 

Fig. 8. The lip of PCNTs with continuous hollow core (a) and the cone-like shape (b) (T indicates the toroidal structure shown in detail in Fig. 11).

CVD graphite can have several structural forms columnar, laminar, or isotropic. The columnar form is shown in Fig. 7.2. The crystallites are deposited with the basal planes (ab directions) essentially parallel to the deposition surface. Their structure tends to be columnar (cone-like) as a result of uninterrupted grain growth toward the reactant source. 

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

How exactly the molecules are oriented inside the channels depends on their specific shape and on the adsorption interaction between the dyes and the channel walls or charge compensating cations. Because of the dye s oblongness, a double-cone-like distribution in the channels is a reasonable model. This distribution is illustrated in Fig. 19a. The arrows represent the transition moments of the dyes and a describes the half-opening angle of the double cone. The hexagonal structure of the zeolite L crystal hence allows six equivalent positions of the transition moments on this double cone with respect to the channel axis. 

The white pine, like most of its allies among the Coniferse, bears cones. These structures are of two kinds, viz. staminate and car-pellate. Both kinds are produced on the same tree. 

Fig. 7.14 (A) The chemical structure of a-, (1, and y-cyclodextrin. (B) Schematic representation of the cone-like conformation of cyclodextrins, with the upper rim presenting the secondary 2,3-hydroxy and the lower rim the primary 6-hydroxy groups.

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