Amphi-form

In the case of dioximes bearing different substituents (R Ri) the furoxan isomer obtained can depend on the configuration of the starting dioxime. The classic example is the oxidation of p-methoxybenzil dioxime with ferricyanide (Scheme 6.5) this reaction affords the 4-phenyl furoxan isomer 18 in a regiospecific manner if the dioxime amphi-form 19 is used, the 3-phenyl isomer 20 is produced if the amphi-... 

The ring closure can be achieved stereospecifically, thus allowing the individual isomers of asymmetrically substituted furoxans to be prepared. For example, the two amphi forms (100) and (101) of p-methoxybenzil dioxime are specifically oxidized by ferricyanide to (102) and (103), whereas the syn and anti isomers (104) and (105) give mixtures of the two furoxans. With some oxidants the process is non-stereospecific, either due to a change of mechanism, or as a result of isomerization of the dioxime prior to cyclization. 

Anti. Cryst. from hot HgO. M.p. 161° decOmp. Sol. EtOH, EtgOi Dil. alkalis—> amphi form. 

Bcnzil forms three dioximes which are distinguished by the names syn, anti, and amphi. ... 

That vesicles and liposomes form at all is a consequence of the amphi-pathic nature of the phospholipid molecule. Ionic interactions between the... 

Possible secondary structures of pardaxin (6) were predicted by the Delphi program (12) using decision constants (DHA = -75, DHE = 50) that favor a helices over extended segments and by the Amphi program that identified possible amphipathic a helices and p strands (Guy, unpublish data). Delphi predicted that pardaxin segments 1-8 and 16-25 were a helices and the remainder may be coils or turns. Amphi predicted that segments 1-12 and 13-28 could form amphipathic a helices. 

Several workers have introduced polymerizable groups into twin-tailed amphiphiles and formed vesicles by sonication. They then link the amphi-philes by initiating polymerization, either chemically or photochemically. The polymerized vesicles which are so generated show little tendency to fuse, and are much more stable than the vesicles formed by sonication or vaporization. They therefore have considerable potential for compartmentalizing reagents, although as with normal vesicles there is always the... 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

The structural variety of the compounds that form fibers is as diverse as their chemistries. From glasses (fiberglass), and partially crystalline materials (carbon), to special three-dimensional arrays, including polymers, the small, elongate solids may have aspect ratios up to 5000. From our research and compilation (Appendices 1, 2) we noted many mineral and synthetic compounds that have structures characterized by basic linear units. Amphi-boles, the major mineral group mined as asbestos, are characterized as doublechain structures. Many of the minerals in Appendix 1 are polymorphic (di-or trimorphs), and where one member of a mineral series has been described as fibrous the others in the same series are likely to be able to grow as fibers as well. Probably all compounds with similar structures and compositions, mineral or synthetic, can form fibers, even though they are not presently listed. It is also clear that fibrous formation is not confined to compounds with linear structural units indeed the variety of crystalline structure patterns is remarkably diverse. 

The threshold concentration above which a free amphi-phile will self-assemble and spontaneously form micelles. Below this concentration, no micelles are detectable. Note that micelle formation is not equivalent to a phase separation For most systems, the concentration range associated with the monomer-to-micelle transition is fairly narrow, and c.m.c. values can be obtained from graphical procedures. The symbol for c.m.c. is Cm. Whenever c.m.c. values are reported, the method for the determination should be clearly stated, because different physical techniques may be more or less sensitive to changes in the amphiphile s aggregation state. See Micelle Formation... 

This explanation for the entropy-dominated association of surfactant molecules is called the hydrophobic effect or, less precisely, hydrophobic bonding. Note that relatively little is said of any direct affinity between the associating species. It is more accurate to say that they are expelled from the water and —as far as the water is concerned —the effect is primarily entropic. The same hydrophobic effect is responsible for the adsorption behavior of amphi-pathic molecules and plays an important role in stabilizing a variety of other structures formed by surfactants in aqueous solutions. 

Figure 11.16 Relationship between sorbed and dissolved amphi-phile concentrations (upper isotherm plot). These different parts of the isotherm reflect changes in the solid surface as sorption proceeds, possibly explainable by the following in portion (I) with low dissolved concentrations, sorption occurs via ion exchange and related mechanisms. At some point, sufficient near-surface concentration enhancement occurs that micelles form there (Ha) and rapid coagulation between oppositely charged micelles and the surface follows (lib). When the surface becomes fLilly coated with such micelles, additional sorption is stopped (III). In portion III, the solid surface charge is converted from one sign to the other, implying sorbates must become physically associated with the particle surface, as opposed to simply being present in the diffuse double layer or the vicinal water layer.

Abbreviations for biosynthetic types are composed from abbreviations of nucleoside residues of activated forms of the monosaccharide components. 6 See footnote a to Table VI lin. and br. mean linear and branched polysaccharides. c Including other bacterial amphi-philes of Gram-negative, outer membranes. d Including amphiphiles of Gram-positive cell-membranes. 

These examples emphasize that not only the macromolecular architecture plays an important role in the determination of the aggregate morphology, but that also interactions between block copolymer segments can strongly influence the final structure of the assemblies formed by these types of amphiphiles as seen for the smaller molecular amphi-philes. 

They designated these forms ayn, amphi and anti. The writers are aware of only one occasion on which an acetal of a polyhydric alcohol has actually been isolated in isomeric forms of the type under discussion, namely that on which Ness, Hann and Hudson71 obtained two of the four theoretically possible diastereomers of 1,3 5,7-dibenzylidene-D-perseitol. One isomer, having m. p. 153-155° and [a]J° — 58.2° (in pyridine), resulted from the treatment of D-perseitol with benzaldehyde in ethanol at 25°, 50% sulfuric acid being employed as the catalyst. The other, having m. p. 280 2° and [a] ° — 58.1° (in pyridine), was produced when the condensation was carried out at 0° in aqueous ethanol saturated with hydrogen chloride. The former was converted into the latter by recrystallization from a pyridine-alcohol mixture. The corresponding labile and stable forms of l,3 5,7-dibenzylidene-L-perseitol also have been prepared.71 The facility with which the labile form could be converted into its stable isomer in the presence of basic substances may well explain why other workers have failed to isolate isomers of this type. 

Metamorphosis has also been extensively studied in amphibians, a class of vertebrates which includes frogs, toads, and salamanders. Amphibian means dual (amphi ) life form (-bian) and refers to the typical life history of these animals, in which an aquatic larva metamorphoses into a terrestrial adult. The reptiles, such as turtles, lizards, and snakes, is another class of vertebrates whose species superficially resemble adult amphibians, but do not undergo metamorphosis. 

Amphiphilic compounds with surface-active properties, such as surfactants or ten-sides, assemble in water to form spherical aggregates. The size and shape of these aggregates depends on the structure of the amphiphile. As a general rule amphi-philes with one polar head group and one nonpolar alkyl chain form micelles. 

Consider a ternary (three-component) system of amphi-phile, hydrocarbon, and water. What structure do you expect to form if small amounts of the first two components are mixed with a large amount of water ... 

Garnet morphology. Garnets in calcic pelite 462536 are similar in form in both the amphi-bole-rich and biotite-rich bands. Grains are up to 5 mm in diameter and are characterized by a broad inclusion-rich core and an inclusion-poor rim, with euhedral facets. The inclusions in the core are principally quartz and ilmenite and vary in size from a few micrometres to >100 pm. Smaller (c. 2 mm) euhedral garnets preserve only a small zone of inclusions in their core. The garnet depicted in Figure 7a is from the biotite-rich domain in calcic pelite 462536. 

Later, more sophisticated supramolecular complexes capable of improved molecular recognition started to be studied. New supramolecular approaches to constmct synthetic biohybrid catalysts were developed [190]. An example is the giant amphi-philes, formed by a (hydrophilic) enzyme headgroup and a synthetic apolar tail. These biohybrid amphiphilic compounds self-assemble in water to yield enzyme fibers and enzyme reaction vessels (nanoreactors [202]). 

Initial investigations from the early 1990s onwards have provided [53] a reliable means by which the tetracationic cyclophane CBPQT4+ and a number of [2]- and [3]catenanes can be self-organized at the air-water interface. Although an amphiphilic character is usually required to obtain a Langmuir monolayer, it is obvious that the catenane 174+ - when associated with four hexafluorophosphate counterions - possesses few bipolar properties. This realization is reflected in the fact that the hexafluorophosphate (PF ) salt of 174+ forms brittle monolayers that are difficult to reproduce. The amphi-... 

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