Hydrophilic linkers

Acosta E, Uchiyama H, Sabatini D, Harwell JH (2002) The Role of Hydrophilic Linker. J Surfact Deterg 5 151-157... 

Gly-Gly-Gly-Ser-Gly-Gly-Gly-Ser a noncleavable, flexible, hydrophilic linker that is highly resistant to in vivo proteolysis... 

DNA that was covalently bound to a polymer. The hybridized P-1 and P-2 DNA chains functioned as hydrophilic linkers in addition, they increased the negative electric charge density on the surface. For these reasons, our DNA-conjugated polymer-coated substrate showed better prevention of nonspecific hybridization of SNP sequences and was selective exclusively for fully matched DNA. 

In this method, peptides or small molecules are prepared by the split-mix synthesis method and cleaved from the resin to form an encoded solution-phase library such that each library compound is tethered to a PNA code via a hydrophilic linker (11). The library then is mixed with the target protein and later exposed to planar oligonucleotide microarrays of predetermined sequences. Alternatively, the encoded soluble library can be hybridized to the oligonucleotide microarrays before incubation with the target protein. 

Second, several types of asymmetric supported bilayer structures, in which the composition of the two monolayers is different, have been created as alternatives to symmetric PSLBs. One example is the HBM [45,46], The inner monolayer in an HBM is an alkyl SAM, typically an alkanethiol on gold, upon which an outer lipid monolayer is deposited by either LBS or vesicle fusion methods. A more sophisticated type of asymmetric supported bilayer is the tethered bilayer lipid membrane (tBLM) in which the SAM is replaced with an inner lipid monolayer. Some or all of the molecules in the inner monolayer are covalently tethered to the underlying support, usually through a hydrophilic linker that creates a water-swollen spacer layer between the tBLM and the substrate surface [47-51],... 

Lipophilic linkers (Salager, 1998) and hydrophilic linkers (Uchiyama, 2000 Acosta, 2002) are used to increase the value of SP and decrease y. Lipophilic linkers are long-chained alcohols (above C8) and their low oxyethylenation products that increase the surfactant-oil interaction. The most effective ones have hydrophobic chain lengths that are an average of the hydrophobic chain length of the surfactant and the chain length of the alkane oil. Hydrophilic linkers increase the surfactant-water interaction. Examples are mono- and dimethylnaphthalene sulfonates and sodium octanoate... 

The same concept was transferred to the water side and the respective molecules were called hydrophilic linker [47, 48]. However, since the shape of the water molecules and their interactions are quite different from those of oils, hydrophilic linkers are no elongated molecules like the lipophilic linkers. Up to now the hydrophilic linker concept has been tested with alkyl naphtalene sulphonates only. Non-alkylated naphtalene sulphonate is a... 

Supersolubilisation of NAPL can be achieved by adding lipophilic linkers to the system. Best results for chlorinated hydrocarbons were obtained with both hydrophilic and lipophilic linkers [71]. Lipophilic linkers increase the interaction between surfactant and oil [72], and hydrophilic linkers the interaction between surfactant and water. Systems with Aerosol MA as surfactant, sodium mono- and dimethyl naphthalate as hydrophilic linker, and dodecanol as lipophilic linker display the best performance regarding efficiency, economy and environmental aspects [65]. 

Hydrophilic linkers act on the water-rich side of the interface by segregating or coadsorbing with the surfactant while avoiding a strong interaction with the oil phase. Because of a limited number of potential segregation sites the concentration range where linker molecules are able to enhance the solubilisation capacity is also limited. The behaviour of co-added lipophilic and hydrophilic linkers can be interpreted in terms of an assembled surfactant resulting in a very smooth and continuous variation of the polarity from bulk water to bulk oil. Assembled surfactants have already been applied to formulate biocompatible micro emulsions [51]. 

Fig. 2 Supramolecular natural polymeric hydrogels discussed in this chapter, (a) Chemical structure of the most-repeated sequence in collagen, forming the a-chain that folds in a three-stranded superhelix [135]. These superhelices bundle to fram the collagen fiber, (b) Representative chemical structure of fibroin and the antiparallel p-sheet formation connected by hydrophilic linkers, (c) Chemical structure of alginic acid, cross-linked by calcium ions (highlighted), (d) Left Top view of two a-helixes of keratin forming a coiled coll by hydrophobic interactions. Right Overview of subsequent formation of the fibril. The left part is adapted from [57] with permission of The Royal Society of Chemistry...

Fig. 13 Hexyl glucoside used as a hydrophilic linker to formulate bio-compatible microemulsions, illustration reproduced from Ref. 104,...

Early attempts to use calixarenes as new stationary phases in the HPLC of biomolecules focussed on silica gel materials with a short hydrophilic linker between the silanol groups and the phenolic OH groups at the lower rim (Fig. 24.30). However, the new materials behaved more or less like reversed phases, and separated nucleobases according to their polarity increase [93]. 

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