Modified Imidazoles

The simultaneous detection of small cations (ammonium, sodium, potassium, calcium, magnesium, and strontium) and anions (bromide, chloride, nitrite, nitrate, sulfate, perchlorate, thiocyanate, and chlorate) from low explosives in postblast residue using an elaborate electrolyte composed of a cationic chromophore and modifiers (imidazole/HIB A/18-crown-6 ether/ACN), an anionic chromophore (1,3,6-naphthalenesulfonic acid) and flow reversal agent (tetramethylammonium hydroxide) has been presented. " ... 

Edrada, R. A., Stessman, C. C., Crews, P., (2003). Uniquely modified imidazole alkaloids from a calcareous Leucetta sponge. J. Nat. Prod. 66,939-942. 

Imidazoles such as 2-methylimidazole (2-MI) and 2-phenylimidazole (2-PI) contain both a cyclic secondary and a tertiary amine fiinctional groups and are used as catalysts, catalytic curing agents, and accelerators (124,125). They are widely used as catalysts for DICY-cured epoxies in electrical laminates. For powder coatings, 2-MI adducts of LER are often used to facilitate dispersion of the components in powder coating formulations and to enhance shelf-life. Other modified imidazoles are also commercially available. The main advantage of imidazoles is the excellent balance of pot life and fast cure. 2-PI is used to increase Tg and thermal resistance. 

N-Arylation of azoles is achieved either by using arynes, activated halobenzenes (e.g. dinitro) or under Ullmann conditions. Thus benzyne reacts with imidazoles to give N-arylimidazoles (70AHC(12)103), and these compounds have also been prepared under modified Ullmann conditions. 

Several model systems related to metalloenzymes such as carboxypeptidase and carbonic anhydrase have been reviewed. Breslow contributed a great deal to this field. He showed how to design precise geometries of bis- or trisimidazole derivatives as in natural enzymes. He was able to synthesize a modified cyclodextrin having both a catalytic metal ion moiety and a substrate binding cavity (26). Murakami prepared a novel macrocyclic bisimidazole compound which has also a substrate binding cavity and imidazole ligands for metal ion complexation. Yet the catalytic activities of these model systems are by no means enzymic. 

More recently 233) it has been reported that cross-linked polystyrene containing imidazole ligands did not provide a support rigid enough to prevent dimerization, and that the p-oxo dimer was benzene extracted from oxygenated tetraphenyl porphyrin iron(ll), Fe(TPP), which had been attached to the modified polystyrene. A discussion of model synthetic porphyrins, from which definitive structural and other physical data are obtained, is given in section V.C. 

Enzymes modified with N -carbonyldiimidazole (CDI) include horseradish peroxidase 761 /1-lactamase after nitration and reduction,[771 lysozyme, and urease.[781 Ref. [77] describes how the tyrosine side chain of a protein was nitrated, reduced with dithionite to an amino group, and then treated with CDI or A/-(2,2,2-trifluoro-ethoxycarbonyl)imidazole to give the benzoxazolinonyl alanine moiety ... 

Prepare the protein to be modified in a non-amine-containing buffer at a slightly basic pH (i.e., avoid Tris or imidazole). The use of 0.1 M sodium phosphate, 0.15M NaCl, pH 7.2 works well for NHS ester reactions. The concentration of the protein in the reaction buffer may vary from pg/ml to mg/ml, but highly dilute solutions will result in less efficient modification yields. A protein concentration from 1 to 10 mg/ml works well in this reaction. 

Dissolve the amine-dendrimer to be modified in DMF or buffer (50mM sodium borate, pH 8.5) at a concentration of at least lOmg/ml. Avoid the use of amine-containing buffers for an aqueous reaction, such as Tris or imidazole, as these will react with the... 

Dissolve an antibody or protein to be modified at a concentration of l-10mg/ml in 0.1 M sodium phosphate, 0.15M NaCl, pH 1.2-1.5. Lower concentrations of protein may result in decreased reaction yields and require increased quantities of reagent to obtain acceptable levels of biotinylation. Avoid amine-containing buffers or components, such as Tris or imidazole, which will react with the NHS ester and interfere with the biotinylation process. 

Dissolve the antibody to be modified in 0.1 M sodium phosphate, 0.15M NaCl, pFl 7.2, at a concentration of 1-5 mg/ml. Note Phosphate buffers at various pFl values between 7.0 and 7.6 have been used successfully with this protocol. Other mildly alkaline buffers may be substituted for phosphate in this reaction, providing they don t contain extraneous amines (e.g., Tris) or promote hydrolysis of SATA s NHS ester (e.g., imidazole). 

Figure 27.5 Oligonucleotides containing a 5 -phosphate group can be reacted with EDC in the presence of imidazole to form an active phosphorimidazolide intermediate. This derivative is highly reactive with amine nucleophiles, forming a phosphoramidate linkage. Diamines reacted with the phosphorimidazolide result in amine-terminal spacers that can be modified with detectable components.

Modify a purified bait protein by adding an aliquot of crosslinker to achieve a molar excess of 2-10 moles per mole of protein (protect from light). For NHS ester-containing reagents, react in 0.1 M sodium phosphate buffer at pH 7.2-7A. Avoid using any other amine-containing buffer components, such as Tris or imidazole, which will interfere with the reaction. 

---