Chemical Reactivity Chemicals in Action

Thiothionyl Fluoride and Difluorodisulfane. Thiothionyl fluoride [1686-09-9] S=SF2, and difluorodisulfane [13709-35-8] FSSF, are isomeric compounds which may be prepared as a mixture by the action of various metal fluorides on sulfur vapor or S2CI2 vapor. Chemically, the two isomers are very similar and extremely reactive. However, in the absence of catalytic agents and other reactive species, FSSF is stable for days at ordinary temperatures and S=SF2 may be heated to 250°C without significant decomposition (127). Physical properties of the two isomers are given in Table 6. The microwave spectmm of S=SF2 has been reported (130). 

Goldenberg and Safrin suggested that the sensory effects of topical irritants may be neutralized by antiirritants. 51 They proposed three possible mechanisms of action of antiirritants complexing of the irritant, blocking the reactive sites in the skin, and preventing physical contact with the skin. The main antiirritant cosmetic chemicals are imidazole, hydroxy, and carboxyl compounds. Studies of the safety and efficacy of these antiirritants in cosmetics are ongoing.11... 

A number of chemicals with demonstrable suppression of immune function produce this action via indirect effects. By and large, the approach that has been most frequently used to support an indirect mechanism of action is to show immune suppression after in vivo exposure but no immune suppression after in vitro exposure to relevant concentrations. One of the most often cited mechanisms for an indirect action is centered around the limited metabolic capabilities of immunocompetent cells and tissues. A number of chemicals have caused immune suppression when administered to animals but were essentially devoid of any potency when added directly to suspensions of lymphocytes and macrophages. Many of these chemicals are capable of being metabolized to reactive metabolites, including dime-thylnitrosamine, aflatoxin Bi, and carbon tetrachloride. Interestingly, a similar profile of activity (i.e., suppression after in vivo exposure but no activity after in vitro exposure) has been demonstrated with the potent immunosuppressive drug cyclophosphamide. With the exception of the PAHs, few chemicals have been demonstrated to be metabolized when added directly to immunocompetent cells in culture. A primary role for a reactive intermediate in the immune suppression by dimethylnitrosamine, aflatoxin Bi, carbon tetrachloride, and cyclophosphamide has been confirmed in studies in which these xenobiotics were incubated with suspensions of immunocompetent cells in the presence of metabolic activation systems (MASs). Examples of MASs include primary hepatocytes, liver microsomes, and liver homogenates. In most cases, confirmation of a primary role for a reactive metabolite has been provided by in vivo studies in which the metabolic capability was either enhanced or suppressed by the administration of an enzyme inducer or a metabolic inhibitor, respectively. 

Because of the severity of the rubbing conditions and the complexity of the rubbing phenomena, there are no demonstrations of the performance of interaction films that are as elegant as the best demonstrations of the existence and functioning of oriented adsorbed films. Instead, much of the work on the mechanism of additive action by interaction films involves conjecture. Part of the conjecture requires knowledge of the reactive elements in the additive and the chemical structures in which they occur. The three most common reactive elements in the additives of commerce are sulfur, chlorine and phosphorus. Table 10-14 lists the most significant structural combinations in which these elements occur, as well as some other elements that have been found to participate in the formation of interaction films. 

The part that relative chemical reactivity plays in additive action can be explored in still another way. Let us take a value of 0.000433 second as the time required for the full circumference of the track on the disk to pass under the contact area of the rider this corresponds to a circumference of 10.16 cm rotating at 65 cm per second. In that time... 

Fig. 6 Capsules in action examples of stabilization unfavored isomers and controlling chemical reactivity through encapsulation.

---