Hydrophilic core

FIGURE 10.24 A helical wheel model of halorhodopsin. The amino acids facing the polar, hydrophilic core of the protein are shown. Of these 60 residues, 36 are conserved between halorhodopsin and bacteriorhodopsin. (Adapted from OesterMt, D., and Tittor, f, 1989. Treads ia Biochemical Scieaces 14 57—61.)... 

Figure 11. Size- and shape-control of nanoparticles via salt reduction in (a) the hydrophobic core of a surfactant oil in water micelle and (b) the hydrophilic core of a water-in-oil reverse micelle.

Wooley and coworkers have cross-linked the micellar corona and obtained the so-called shell cross-linked knedellike micelles [83,84]. This strategy was further applied to a wide variety of block copolymer micelles. Armes and coworkers have used a similar approach for the preparation of shell cross-linked micelles with hydrophilic core and shell [85]. Many other related examples can be found in the literature. 

As far as micelles in organic media are concerned, two types of block copolymers can be considered—those with two hydrophobic blocks and those with one hydrophilic and one hydrophobic block. The latter form the so-called reverse micelles, which contain a hydrophilic core surrounded by a soluble hydrophobic corona. 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

Recently, Mecking et al. reported the synthesis of inverse micelles based on a hy-perbranched polyglycerol polymer. Terminal -OH groups were modified with palmi-toyl chloride and gave a polymeric catalyst soluble in organic solvents with hydrophilic core to immobilize water-soluble guest molecules such as PdCl2 or Pd(OAc)2. 

This generalized structure was mimicked by a very simplified artificial molecule 1. The hydrophilic core part 2 was substituted simply by an oligoether carboxylate anion. The carboxylate may act as the polar ionic head group outside the membrane and the ether part of the molecule may be located in the interior part of the membrane to make an ion-conducting pathway. The molecular lengths were adjusted to fit the lipid monolayer in an extended or a helical conformation, with n being 2 or 3 in 1. The hydrophobic exterior was substituted by dioctadecyldimethyl-ammonium cation, which was ion-paired with the carboxylate. 

An inverse (or reverse) micelle, which forms in a non-polar solvent, will have the hydrophilic head groups oriented toward the inside of the sphere, where a water pool is formed and a hydrophilic probe can become associated [10]. Some surfactants commonly employed to stabilize reverse micelles include sodium diisooctylsulfosuccinate (AOT), benzylhexadecyldimethylammonium chloride (BHDC), and dodecylammonium propionate (DAP). Ionic surfactants induce formation of a larger water pool than non-ionic surfactants, but the size of the hydrophilic core also depends on temperature and on the ratio of water to surfactant. 

Nonetheless, sensitization by dyes held within the cores of microemulsions can be easily accomplished [69]. Such sensitization is an important component of photogalvanic effects, the magnitude of which are significantly enhanced in the non-homogeneous environment of a microemulsion [70], The hydrophilic core of an water-in-oil microemulsion can concentrate cation radicals formed via interfacial electron transfer and hence increase the yield of subsequent dimerization the dimethylnaphthalene cation radical exhibits a dimerization equilibrium constant of nearly 500 in a microemulsion [71]. For similar reasons, hexylviologen acts as a much more efficient relay than methyl viologen in a CTAB/hexanol microemulsion [72]. 

For chemotherapeutics to be effective against Gram-negative bacteria requires a balance between hydrophilic and hydrophobic properties. The reason for this is the characteristic construction of the bacterial cell wall, with an outer hydrophilic core, rich in polysaccharides, and a hydrophobic phospholipid bilayer. Only very small and hydrophilic drug molecules up to 600 Da can diffuse through membrane pores [63, 64],... 

Reverse ethylene oxide/propylene oxide block copolymers (in which a hydrophilic core of PEO is terminated at both ends with hydrophobic PO moieties) are used in industrial applications. This is because of the different and unique performance properties compared to the conventional block copolymers, where a hydrophobic PO core is block copolymerized with EO. Dufour and Guyot [30] have built on this observation and synthesized Surfmers in which a PEG core (about 37 EO units) was tipped with about 10 PO units to further react with a chlorine-carrying polymerizable group or with maleic anhydride to produce reactive Surfmers. 

The top side of the helix contains only hydrophobic side chains, while the other surfaces are polar or charged this is an amphipathic helix. As an integral membrane protein, it is likely to dip its hydrophobic surface into the lipid bilayer but expose the other surfaces to the aqueous phase. An alternative arrangement might be to cluster, say, 10 helices, one from each of 10 subunits, around a central hydrophilic core, while exposing only the hydrophobic surface to the lipid bilayer. 

The hydrophobic moment gives an orientation of the a-helix with respect to the lipid environment and the aqueous interface of the membrane surface for single a-helices or the hydrophilic core formed from a cluster of transmembrane a-helices (seven and twelve helices are quite common). Other methods, conceptually along similar lines, have produced power spectra which are cleaner, facilitating the identification of the lipophilic moment [12]. 

The result matches very well with the theoretical values based on CPK models and molecular simulation of the various dendrimers in the gas phase [33,34,72]. This similarity implieates that the hydrophilic core of the higher generation dendrimers has a more ellipsoidal conformation. The results obtained from the monolayer experiments also indicate that the higher generation dendrimer has a more flat conformation, because in that case all the attached chains can count for the observed molecular area. 

An interesting topographic feature of Complex I is that although the flavoprotein and FeS protein subcomplexes are soluble in water, each appears to be buried in the intact membrane-bound enzyme. Thus, the three flavoprotein subunits are inaccessible to surface labelling, and some of the proteins in the ISP fraction are probably transmembranous [289,299]. The corollary of this would be that the enzyme may have a hydrophilic core within the membrane, which is surrounded by hydrophobic protein components (Fig. 3.13B). 

Interaction between protein and polymer Preventing adsorption by modifying hydrophilicity of the polymer surface/ pre-entrapment of protein in the hydrophilic core/ including adsorption competitors. ... 

Self assembly using amphiphilic components to trap drug in solution within a hydrophobic or hydrophilic core has been explored for decades for the delivery of drugs. The most notable example is that of the liposome, which, however, suffered from low entrapment efficiency, leakage, and rapid clearance by the reticuloendothelial system of the liver. This rapid clearance was reduced by the use of PEGylated phospholipids to form of the so-called sterically stabilized or stealth liposomes. ... 

Amphiphilic and Double-Hydrophilic Core-Shell Cylindrical Brushes... 

We also prepared double hydrophilic core-shell brushes with PMAA as the core and poly(oligoethyleneglycol methacrylate) (POEGMA) as the shell. Due to the weak polyelectrolyte nature of the PMAA, at low pH the brushes also showed typical pearl-necklace conformations, whereas at high pH the core adopts more extended structures [158], The polychelates of the brush and Fe3+ behave in a similar way to the amphiphilic polychelates. 

Screening of a number of fermentation cultures of microorganisms afforded potent inhibitors of squalene synthase. Squalestatins 1 (25), 2 (26) and 3 (27) were isolated from cultures of Phoma sp. C2932 [50-52]. All of these three compounds possess the hydrophilic core unit, [1S-(1 a,3a,4p,5a,6a,7P)]-4,6,7-trihydroxy-2,8-dioxabicyclo-[3.2.1 ]octane-3,4,5-tricarboxylic acid. These compounds showed potent inhibitory activities against rat liver squalene synthase (IC50 = 15.2,15.1 and 5.9 nM, respectively) [52]. 

Apolipoproteins are structural components of plasma lipoproteins, and they maintain the integrity of the lipoproteins through the interactions with the hydrophilic core and the surrounding aqueous environments. These apolipoproteins act as ligands for specific cell receptors and activators or inhibitors for enzymes involved in lipoprotein metabolism. There are at least 11 apolipoproteins, which differ in molecular mass (from 6.5 to 600 kDa) and amino-acid composition, and they form less than 2 g/L of normal plasma protein. The apolipoprotein classes are designated by letters of the alphabet—A, B, C, D, and E—and numerals for subclasses (e.g., apo C-II). 

Encapsulation of Hydrophilic Core with Interfacial Polymerization.321... 

Ribeiro, M., Morselli, A., Daniel, B., and C.R Grosso. The effect of adding oleic acid in the production of stearic acid lipid microparticles with a hydrophilic core by a spray-cooUng process. Food Res Int, 47 (2012) 38-44. 

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