Elongated structures

A simple explanation of the existence of deformed nuclei in these ranges is provided by the close-packed-spheron theory (J4) it is that the inner core (of two or five spherons) in these ranges has an elongated structure, and that this elongation is imposed by the inner core on the two surrounding layers. 

The nematic phase of all the compounds CBn is characterized by a coherence length of about 1.4 times the elongated structure of the molecule. Based on this behaviour local associations in form of dimers with cyano-phenyl interactions were postulated. For the smectic A phase a partial bilayer arrangement of the molecules (SAd) is most likely. But there are also example for the smectic A phase with a monolayer (Sai) or a bilayer (Sa2) arrangement of the molecules as well as a commensurate structure A large number of X-ray measurements were carried out in the liquid crystalline state to clear up the structural richness and variability (see Chap. 2, this Vol. [52]). 

The latter type of compounds should preferably carry either one type I unit or at most two units (positioned as far apart as possible), and have an elongated structure (which does not fold as verapamil, for example) with a small cross-sectional area, Ad- The first type of compounds is expected to be transported slowly, whereas the second type may not be transported. Table 20.2 summarizes the drug properties relevant for transporter binding and lipid partitioning of a substrate (modulator or inhibitor) of P-gp. Inspection of the information contained in Table 20.2 shows that the synthesis and membrane incorporation of inhibitors with a low number of H-bond acceptor patterns should be simpler and more efficient than that of inhibitors with a large number of patterns. 

Figure 5. Sorbic acid molecules on HOPG as reported by Smith et. al. (10). This surface was prepared by spin-coating a dilute sorbic acid-benzene solution onto a freshly cleaved HOPG substrate. Images of the surface were obtained in liquid helium. The elongated structure shown was representative of those present on surfaces prepared with this procedure.

With Increased proton character, the H has a tendency to hydrogen bond. Below pH 7.5, the appearance of the cationic form has a marked condensing effect In association with unionized amine oxide and results In the production of elongated structures replacing progressively the small and spherical micelles of LDAO In the nonlonlc form. Below pH 4.5, the elongated structures are progressively converted Into low viscosity, small spherical micelles made of LDAOH. 

In a previous publication ( ), results were presented on the micellar properties of binary mixtures of surfactant solutions consisting of alkyldimethylamine oxide (C12 to Cig alkyl chains) and sodium dodecyl sulfate. It was reported that upon mixing, striking alteration in physical properties was observed, most notably in the viscosity, surface tension, and bulk pH values. These changes were attributed to 1) formation of elongated structures, 2) protonation of amine oxide molecules, and 3) adsorption of hydronium ions on the mixed micelle surface. In addition, possible solubilisation of a less soluble 1 1 complex, form between the protonated amine oxide and the long chain sulfate was also considered. 

The hydrogenosomes of the anaerobic fungus Neocallimastix are round or elongated structures, always enveloped by two distinct but tightly apposed membranes (Figs. 4a,b, 5b) (van der Giezen et al. 1997 Benchimol et al. 1997). 

Yet, Okubo s law and the physical model on which it is based disregard two important properties of measured tracer distributions. The first one concerns the shape of tracer clouds. As indicated in Fig. 22.9, clouds usually develop into elongated structures which can be approximated by ellipses with major and minor principal axes, cma and cmi. The major axis points in the direction of the mean flow. When Okubo... 

Liquid Crystals Liquid-crystal phases may occur between the solid and the liquid phase. Cholesteryl myristate, for example, exists in a liquid-crystal phase between 71 and 85°C [6]. The appearance of liquid-crystal phases depends on the molecular structure. Compounds with elongated structures that are fairly rigid in the central part of the molecule are likely candidates for liquid crystals. The homologous series of p-alkoxybenzylidene-p-n-butylanilines is just one example for compounds with liquid-crystal phases. An excellent introduction to liquid crystals and their properties has been written by Collings [6]. 

Fibrous protein sequences are often characterized by the presence of simple repetitive motifs. Some are exact in length and/or sequence, but others are only approximate and display considerable variation. Some motifs contain residues that are absolutely conserved in some positions, whereas in others it is only the sequence character that is maintained over the repeat length. In many fibrous proteins the repeats occur contiguously, whereas in others they are found widely separated in the sequence. The varieties of sequence repeat that have been observed are typed and catalogued here by Parry (Chapter 2). Each motif forms a discrete element of structure in many instances, these are arranged helically with respect to one another. In many cases an elongate structure is formed, and this can lead naturally to molecular aggregation and the formation of functional filaments. 

Let us discuss a few more consequences of the fact that repulsive adsorbate-adsorbate interactions add up. The formation of superlattices may be hampered by adding up interactions since this may favor attachment to the ends of elongated structures compared to their sides. In the... 

Besides gold nanocrystals of spherical shape, elongated structures such as nanorods are the second most studied ones. Their first synthesis was reported in 2001233 and since then this synthetic procedure has been widely studied and improved. Nonetheless, the influence of various parameters such as the presence of seeds, the nature of the solvent, and the presence of surfactants on the reaction yield and the control of shape make the reproducibility of this synthesis still a challenging task.234-237... 

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