The difference in the nucleophilic reactivities of the and groups can be satisfactorily explained on the basis of Pearson's acid‐base concept[21]. The thiophosphoryl sulfur is a typical “soft base”, and reacts preferentially with sub‐group B metals, halogens, and sp3 hybridized carbon, whereas it is largely inert to “hard acids” such as protons, carbonyl carbon, and tetrahedral phosphorus. Since a nucleophilic attack by the thiophosphoryl sulfur leads to a decrease in the charge density of the phosphorus atom, the latter (or the α‐carbon atom in O‐alkyl esters) becomes more open to nucleophilic attack. This reaction principle forms the basis of sulfur exchange, dealkylation, isomerization, and the Pistschimuka and Michalski reactions.

An immunoregulatory circuit is described in which B cell blasts activate syngeneic Ly-1+2-3- T cells to (a) start a reaction which is indistinguishable from a graft-vs.-host reaction (syngeneic GvH) and (b) induce suppressor cell activity which abrogates the syngeneic GvH. Since capping the surface immunoglobulin (Ig) on B cell blasts blocks their ability to activate the circuit, it is likely that the relevant cell surface structure "seen" on the B cell by the Ly-1 T cell is either Ig itself or another molecule in association with Ig.

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Thiophosphate and phosphate esters have been synthesized in great variety since about 1945, and are being produced in increasing quantities, mainly for plant protection. An important property of alkyl phosphates and thiophosphates is their alkylating power, which is comparable with that of dialkyl sulfates and alkyl p‐toluenesulfonates. The chemistry of thiophosphates is largely determined by their alkylating properties, since the sulfur, both in the alkyl thiophosphate and in the thiophosphate anion formed on dealkylation, can act as a point of attack for self‐alkylation.

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