Daniel Koshland is a Biochemist, has a laboratory on the UCB Campus.
Koshland's Reagent is a four membered ring, 1,2 di sulfur substituted cyclo butane.
Disulfide linkages abound in biological systems. Cysteine amino acid residues cross link in an oxidative process. Koshland's reagent is a mild reagent for the reaction to oxidize two cysteine amino acid residues by taking their hydrogens. After having done so the two sulfurs are linked by a disulfide bond and the hydrogens go with the now opened ring, ring strain being relieved and the entropy change for the reaction is part of the driving force.