PEG Reagents

Coupling of affinity molecules to surfaces also can be enhanced by the use of discrete PEG linkers. Nishimura et al. (2005) modified an amino surface with a NHS-PEG -maleimide crosslinker to create a hydrophilic self-assembled monolayer (SAM) surface that was thiol reactive for the conjugation of sulfhydryl-modified RNAs. This array then was used to investigate the binding specificity of synthetic kanamycins with selected RNA sequences to prove the specific interaction of ribosomal RNA with this molecule. The PEG linkers on surfaces provide lower nonspecific binding character than alkyl linkers, when preparing SAM surfaces for affinity interactions. 

The low nonspecificity of PEG layers also was used to eliminate biomolecule binding to certain areas of an array. Kidambi et al. (2004) patterned an mPEG-carboxylate molecule onto polyelectrolyte multilayers to mask portions of the surface. The extremely low binding character of PEG provides advantages for creating patterned surfaces that other modifiers using aliphatic alkyl linkers do not provide. 

In another application involving a study of biotin compounds for potential use in vivo, it was found that the preferred structures included molecules that contained PEG spacers to 

Organic solvents that can be used with discrete PEG compounds include DMSO, DMF, DMAC (i 7,N -dimcthylacetamide), and methylene chloride. The compounds also are very soluble in many other commonly used organic solvents, which provide flexibility for doing reactions. DMAC is particularly convenient, because it is easily dried of contaminating water (using molecular sieves), it doesn t decompose like DMF (producing amines), and it doesn t have the odors of some of the other solvents. Methylene chloride can be used for water-insoluble molecules that are to be reacted with the PEG compounds, but don t require subsequent water miscibility. 

Compounds having the same functionality on both ends are homobifunctional in nature and can be conjugated with the same target functionality on biomolecules, surfaces, or other molecules. Chapter 4 describes traditional homobifunctional compounds in detail, but the discrete PEG-based reagents are described here, because of their unique hydrophilic properties. 

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Fella C, Walker GF, Ogris M, Wagner E (2008) Amine-reactive pyridylhydrazone-based PEG reagents for pH-reversible PEI polyplex shielding. Eur J Pharm Sci 34 309-320... 

Large polymer PEG reagents having molecular weights >2,000 Da have been used for over 20 years as modification agents for biological molecules (Chapter 25). These compounds often are... 

These interesting properties can be utilized to an advantage in the preparation and purification of PEG derivatives, particularly PEG reagents and PEG smaU-mole-cule drugs. Eor example, one can conduct a reaction in methylene chloride and purify the product by precipitation in ether. 

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