Amphiphile structure, determination

Hess HA, Roper JC, Grill SW, Koelle MR (2004) RGS-7 completes a receptor-independent heterotrimeric G protein cycle to asymmetrically regulate mitotic spindle positioning in C. elegans. Cell 119 209-218 Higashijima T, Burnier J, Ross EM (1990) Regulation of Gi and Go by mastoparan, related amphiphilic peptides, and hydrophobic amines mechanism and structural determinants of activity. J Biol Chem 265 14176-14186... 

Donaldson, S. Radhakrishnan, B. Soltero, R. Structure Determination of a Modified Amphiphilic Recomnbinant Salmon Calcitonin Conjugate and Related Conjuates, presented at the AAPS National Meeting, Toronto, November 2002. 

Xu,Z.T. Kiang, Y.H. Lee, S. Lobkovsky. E.B. Emmott, N. Hydrophilic-to-hydrophobic volume ratios as structural determinant in small-length scale amphiphilic crystalline systems Silver salts of phenylacetylene nitriles with pendant oligo(ethylene oxide) chains. J. Am. Chem. Soc. 2000. 122. 8376-8391. 

The differences between standard thermotropic LCs and macromolecular condis crystals are summarized in Fig. 8. The first three and the last two points make it easy to experimentally identify low molecular mass LCs. For macromolecules, however, the viscosity may be suflBciently large to lose the obvious liquid character the birefringence does not always show the well-known LC texture (55) the small ASj of LCs may be confused with partial crystallinity of the condis crystals and in polymers, some larger main-chain rigid groups are not always easily identifiable as mesogens. This leaves points four and eight for differentiation between the two mesophases. Points five and six are more difficult to establish, and solid state NMR and detailed X-ray structure-determinations may be necessary for full characterization. Furthermore, borderline structures may be possible between thermotropic LCs, amphiphilic LCs, and condis crystals. A few examples and the resolution of their structures are discussed next, to illustrate the resolution of some of these problems. 

Packing parameter and Curvature. An important factor determining the shape of self-assembled amphiphilic structures is the size of the hydrophobic part of the amphiphile relative to the hydrophilic part. The shape can be parameterized in terms of the packing parameter A, which is given by... 

A synthesis of fluorolipopeptides by the modular methodology (Scheme 32) leads to the nonionic amphiphilic structures 38 [86,87]. Because derivatives 38 are poorly soluble in water, their surfactant properties have been determined in formamide [88]. Hemolytic tests carried out with some of these compounds indicate no activity toward red blood cells they show, however, a marked toxicity for hybridoma cells [89]. 

Like proteins, the primary structures of the amphiphilic dendrons determine their tertiary structure. As such, Percec has compared dozens of his AB2- and ABs-derived dendron libraries in an effort to determine trends or nano-periodic self-assembly patterns as proposed by others [137]. Percec s seminal comparison produced the first three Mendeleev-like, predictive nano-periodic tables for the self-assembly of aryl ether dendrons [151]. The first of these nano-periodic tables is shown in Fig. 36. 

TABLE 5.1. Expected Aggregate Characteristics of Amphiphiles as Determined by Their Molecular Structure and Packing Parameter Pc... 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

The same group modified the linker by using different numbers of carbon atoms (1, 5, 10) to afford variations of the local saccharide concentrations at the dendrimer surface.418 This study was aimed to determine the influence of this linker parameter on the glycodendrimer-protein interactions, the relationship between structure and water solubility, and to investigate amphiphilic properties. 

Fig. 4 Representative membrane-active peptides that have been studied by solid-state 19F-NMR. (a) The primary sequences show which positions were substituted (filled green boxes) or which ones could in principle be substituted (dotted green lines), (b) Characteristic conformations of the peptides in the membrane-bound state. The space-filling solvent-accessibility models emphasize the amphiphilicity by colouring hydrophobic residues in yellow and cationic side-chains in blue. (c) Observed structures and alignment states of the peptides as determined by 19F-NMR...

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

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