Raft formation

Sphingolipid Regulation of Signaling via Control of Raft Formation and Stability... 

Waarts BL, Bittman R, WUschut J. SphingoUpid and cholesterol dependence of alphavirus membrane fusion. Lack of correlation with lipid raft formation in target liposomes. J. Biol. Chem. 2002 277 38141-38147. 

Obviously, these two enhancements are closely related through the well-known impact of cholesterol on both raft formation and functioning of raft-containing TM domains, such as GPCR proteins. Thus, with the intended modifications, the model should be able to elucidate the role of cholesterol and... 

Microdomain (Raft) Format in the Cell Membranes , Maku, 2003,28,102 R 698 H. Akutsu, Protein Analytical Method Development of NMR , Gendai Kagaku, 2003, 387,12... 

Rizis G, vande Ven TGM, Eisenberg A (2014) Raft formation by two-dimensional self-assembly of block copolymer rod micelles in aqueous solution. Angew Chem Int Ed 53 9000-9003... 

RAFT polymerizations under very high pressure (5 kbar) have been reported.509-512-513 At high pressures, radical-radical termination is slowed and this allows the formation of much higher molecular weight polymers and higher rates of polymerization than are achievable at ambient pressure. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

With appropriate choice of reaction conditions, hyperbranched polymers can be formed by sclf-condcnsing vinyl polymerization of monomers that additionally contain the appropriate initiator (NMP, ATRP), when the compounds are called inimers, or RAFT agent functionality. Monomers used in this process include 340,716 341717 and 34204 (for NMP), 108714,714 and 344 and related monomers720 723 (for ATRP) and 343408 (for RAFT). Careful control of reaction conditions is required to avoid network formation. 

The very small number of growing polymer chains, when compared to the monomer concentration results in a very low overall concentration of free control agent and leads to inefficient capping of chain ends. One solution to this problem is the addition of a free or unbound control agent to the polymerization medium. This can take the form of a low molecular weight alkoxyamine, ATRP initiator, RAFT agent or, alternatively, free deactivator such as nitroxide or Cu(II). This species is often called a sacrificial agent. This solution also leads to the formation of free polymer that must ultimately be removed from the brush. 

GPC distributions 553 mechanisms 551 4 precursors 549, 551 microgcl formation 554-5 seif-condensing v iuyl polymerization 555-6 shell-erossjinking of micelles 555 dendritic cores 556-7 thiocarbonvltbio RAFT agents 464, 501-2, 505-14... 

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Jolly C, Sattentau QJ. Human immunodeficiency virus type 1 virological synapse formation in T cells requires lipid raft integrity. J Virol 2005 79(18) 12088-12094. 

While in most of the reports on SIP free radical polymerization is utihzed, the restricted synthetic possibihties and lack of control of the polymerization in terms of the achievable variation of the polymer brush architecture limited its use. The alternatives for the preparation of weU-defined brush systems were hving ionic polymerizations. Recently, controlled radical polymerization techniques has been developed and almost immediately apphed in SIP to prepare stracturally weU-de-fined brush systems. This includes living radical polymerization using nitroxide species such as 2,2,6,6-tetramethyl-4-piperidin-l-oxyl (TEMPO) [285], reversible addition fragmentation chain transfer (RAFT) polymerization mainly utilizing dithio-carbamates as iniferters (iniferter describes a molecule that functions as an initiator, chain transfer agent and terminator during polymerization) [286], as well as atom transfer radical polymerization (ATRP) were the free radical is formed by a reversible reduction-oxidation process of added metal complexes [287]. All techniques rely on the principle to drastically reduce the number of free radicals by the formation of a dormant species in equilibrium to an active free radical. By this the characteristic side reactions of free radicals are effectively suppressed. 

To make further use of the azo-initiator, tethered diblock copolymers were prepared using reversible addition fragmentation transfer (RAFT) polymerization. Baum and co-workers [51] were able to make PS diblock copolymer brushes with either PMMA or poly(dimethylacrylamide) (PDMA) from a surface immobihzed azo-initiator in the presence of 2-phenylprop-2-yl dithiobenzoate as a chain transfer agent (Scheme 3). The properties of the diblock copolymer brushes produced can be seen in Table 1. The addition of a free initiator, 2,2 -azobisisobutyronitrile (AIBN), was required in order to obtain a controlled polymerization and resulted in the formation of free polymer chains in solution. 

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