Systematic Modulation of Michael-Type Reactivity of Thiols through the Use of Charged Amino Acids

Abstract

A quantitative structure-reactivity relationship for the Michael-type addition of thiols onto acrylates was determined. Several thiol-containing peptides were investigated by examining the correlation between the second-order rate constant of their addition onto PEG-diacrylate and the pK(a) of the thiols within a peptide. By introducing charged amino acids in close proximity to a cysteine, the pK(a) of the thiol was systematically modulated by electrostatic interactions. Positive charges from the amino acid arginine decreased the pK(a) of the thiol and accelerated the reaction with acrylates while negative charges from aspartic acids showed the opposite effect. A linear correlation between thiolate concentrations and kinetic constants was found, confirming the role of thiolates as the reactive species in this Michael-type reaction. The relevant factors influencing the reactivity were the sign and the number of the neighboring charges, while the position of these charges had little effect on reactivity. These results provide a basis for the rational design of peptides, where the kinetics and thus selectivity of protein/peptide conjugation with polymeric structures via Michael-type addition reactions can be controlled.

Reactivity of zinc finger cysteines: Chemical modifications within labile zinc fingers in estrogen receptor

“…Consequently, the protonated thiol form of cysteine may serve as the preferred nucleophile relative to the thiolate that is the predominant species occurring under basic conditions. This is in contrast to previous reports which indicated that in Michael-type reactions, thiolates (S Ϫ ) rather than thiols (SH) are the generally preferred nucleophiles° [23][24][25].°However,°our°observed°K3°reac-tion kinetics are consistent with an earlier study showing that protonated cysteine thiols are reactive to Michael acceptors having an ␣,␤ unsaturated carbonyl system,°such°as°K3° [26].…”

Manipulation of hydrogel assembly and growth factor delivery via the use of peptide–polysaccharide interactions

“…Given that PEG is highly hydrophilic and generally nonadhesive to proteins or cells, it has found widespread use as a drug carrier [14], and many PEG hydrogels have been produced from aqueous solutions containing linear or branched PEG macromolecules via chemical crosslinking [15][16][17][18]. In addition to hydrogels formed via radical crosslinking reactions, PEG hydrogels have been formed, for example, via Michael-type addition reactions upon mixing with thiol-bearing compounds [19,20] or via the reaction between amino-terminated poly (ethylene glycol) and the herbal iridoid glycoside genipin [21]. In some cases, cell adhesive peptide domains or biodegradable sequences have been introduced into PEG hydrogels to endow them with biological signaling functions [22], including the capacity for growth factor delivery.…”

Michael-Type Addition Reactions for the In Situ Formation of Poly(vinyl alcohol)-Based Hydrogels

“…According to the work of Hubbell and Tirelli, 19 Michael-type addition of thiols to unsaturated esters offers an interesting route for networking functionalized polymer chains without using a photoreticulation process. In this context, we have studied the kinetics of the addition of thiol end-capped PVA chains to grafted PVA-MA.…”

“…19 This effect can be explained by the limited diffusivity of the macromolecular chains involved in the addition reaction. However, a similar rate constant for the addition of , -methylethylcysteine to acrylonitrile, i.e., 0.26 M -1 min -1 has been reported in the literature.…”