Esters containing Negative Groups

Cationic polyelectrolytes containing imidazole groups have been investigated by some researchers. Morawetz et alU4 first found that a cationic polymer, poly (l-vinyl-3-ethylimidazolium iodide), 65 (PQMelm), enhanced the hydrolyses of the negatively charged esters, i. e. NABA and 4-acetoxy-3-nitrobenzenesulfonate 66 (NABS). At intermediate pH, a large catalytic effect was observed and this was... 

Figure 9.61 QDs containing carboxylate groups can be coupled to amine-containing proteins or other molecules using the EDC/sulfo-NHS reaction to form amide bond linkages. The intermediate sulfo-NHS ester is negatively charged and will help maintain particle stability due to like charge repulsion between particles.

Disulfosuccinimidyl tartarate (sulfo-DST) is an analog of DST that contains sulfo-NHS esters. The negatively charged sulfonate groups contribute enough hydro-... 

Aldehydes unite, with the elimination of water, with compounds containing the group CH2 between two negative radicals (acetacetic ester, malonic ester, acetylacetone, and others), in two ways. 1. Equal molecules unite in accordance with the following equation ... 

RCH(OH)=CHCOR or -keto esters RCH(OH)=CHCOOR ) dissolve in dilute sodium hydroxide solution, i.e., contain an acidic group of sufficient strength to react with the alkah. Carboxyhc acids and sulphonic acids are soluble in dilute solutions of sodium bicarbonate some negatively-substituted phenols, for example, picric acid, 2 4 6-tribromo-phenol and 2 4-dinitrophenol, are strongly acidic and also dissolve in dilute sodium bicarbonate solution. 

Figure 2.1 Three types of fluorophenyl esters have been used for coupling to amine-containing molecules. The PFP and TFP esters are relatively hydrophobic and typically have better stability toward hydrolysis in aqueous solution than NHS esters. The STP ester is water-soluble due to the negatively charged sulfonate group, and it provides better solubility to associated crosslinkers or bioconjugation reagents similar to that of a sulfo-NHS ester group.

A water-soluble analog of NHS-biotin containing a negatively charged sulfonate group on its NHS ring structure also is available. Sulfo-NHS-biotin may be added directly to aqueous reactions without the need for organic solvent dissolution. A concentrated stock solution may be prepared in water to facilitate the addition of a small quantity to a reaction, but hydrolysis of the NHS ester will occur at a rapid rate, so the solution must be used immediately. 

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