4-(Chloroacetyl)pyridinium Salt: A New Chromophoric and Solvatochromic Reagent of the Thiol Group
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- 作者：Michel Holler ; Alain Burger ; and Jean-Franç ; ois Biellmann
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：March 6, 1996
- 年：1996
- 卷：118
- 期：9
- 页码：2153 - 2159
- 全文大小：318K
- 年卷期：v.118,no.9(March 6, 1996)
- ISSN：1520-5126
文摘
N-(4'-chlorobenzyl)-4-(chloroacetyl)pyridiniumchloride was prepared from theN-(4'-chlorobenzyl)-4-acetylpyridinium chloride by chlorination with sulfuryl chloride.This chloro ketone had a half life of 150 min atpH 7.3 and reacted specifically with thiols. The reaction productwith pentanethiol crystallized as an enol whosestructure was determined by X-ray diffraction. The structureindicated conjugation of the sulfur with the pyridiniumring. In solution this enol was in equilibrium with thecorresponding ketone and with the hydrate or the hemiketalaccording to the solvent. The enol was the major species in DMSOwhile in water the ketone and the hydrate weremajor. This solvent dependent equilibrium was reflected in thevariation of the absorption coefficient at the maximumwavelength at around 400 nm according to the solvent. Theabsorption maximum wavelength of the thioether, anegative solvatochrome, depended on the solvent and showed a close tolinear relationship with the polarity indexof Snyder. The enolic hydroxyl group has apKa of 7.4 and the 
thioether ketone apKa of 7.9. The chloro ketoneis a useful reagent to explore the environment of reactive cysteineresidue in proteins, giving information on thepolarity of the environment by the position of the absorption maximumwavelength and the pKa of the enolichydroxylgroup.
thioether ketone apKa of 7.9. The chloro ketoneis a useful reagent to explore the environment of reactive cysteineresidue in proteins, giving information on thepolarity of the environment by the position of the absorption maximumwavelength and the pKa of the enolichydroxylgroup.