Structure-stability relationship of Immobiline chemicals for isoelectric focusing as monitored by capillary zone electrophoresis

Hydrolytically stable, diaminocarboxylic acid-based membranes buffering in the pH range from 6 to 8.5 for isoelectric trapping separations

Diaminocarboxylic acid carrier ampholytes, such as L-histidine, 2,3-diaminopropionic acid, L-ornithine, and L-lysine, were reacted with glycerol-1,3-diglycidyl ether (GDGE) and poly(vinyl alcohol) (PVA) in the presence of sodium hydroxide to produce hydrolytically and mechanically stable hydrogels, supported on a PVA substrate, for use as buffering membranes in isoelectric trapping (IET) separations. The pH values of the DACAPVA membranes were determined with the help of small-molecule pI markers and proteins and were found to be in the 6 < pH < 8.5 range. The membranes were successfully used to isoelectrically trap small ampholytes, desalt ampholyte solutions in IET mode, and effect the binary separation of chicken egg white proteins.

Towards new formulations for polyacrylamide matrices: N-acryloylaminoethoxyethanol, a novel monomer combining high hydrophilicity with extreme hydrolytic stability

Matrices for electrokinetic separations, based on a unique class of mono- and disubstituted (on the amido nitrogen) acrylamides such as e.g., N-acryloylaminoethoxyethanol (AAEE) and acrylamido-N,N-diethoxyethanol, offer the following advantages: (i) strong resistance to alkaline hydrolysis (most zone separations occurring at basic pH values), (ii) high hydrophilicity and (iii) greater porosity, due to the higher molecular weight of the monomers. When compared with conventional poly(acrylamide), a poly(AAEE) matrix, when subjected to mild alkaline hydrolysis (0.1 N NaOH, 70 degrees C) appears to be 500 times more stable. Such stability is also confirmed under strong alkaline hydrolysis (1 N NaOH, 100 degrees C) as well as under mild and strong acidic hydrolysis. Mildly hydrolyzed poly(AAEE) matrices still perform extremely well in both conventional isoelectric focusing and immobilized pH gradients, techniques which are quite sensitive to traces of acrylate in the polymer coil. Conversely, mildly hydrolyzed poly(acrylamide) matrices, when used in isoelectric focusing, generate pH gradients between pH 4 and 5, having an inflection point (pH 4.6) equivalent to the pK value of acrylic acid. This novel class of monomers shows great promise for future applications in all electrokinetic methodologies.

The Immobiline family: from "vacuum" to "plenum" chemistry

We list here a total of 17 acrylamido acids and bases as potential buffers and titrants for isoelectric focusing separations in immobilized pH gradients. The chemistry of these compounds is reviewed and general guidelines are given for their proper use. In particular, it is shown that the most delicate compounds are the basic species, since they can undergo several degradation pathways, including: (i) spontaneous hydrolysis to acrylic acid and a diamine; (ii) spontaneous autopolymerization to oligomers and n-mers; (iii) oxidation to N-oxides during the persulfate polymerization step. A hydrophobicity scale has been constructed, by partitioning the deprotonated species in water/1-octanol phases. A scale of resistance to alkaline hydrolysis for the basic acrylamido buffers is also given, followed by general consideration on the structure/stability relationship of these chemicals.