Stress-induced chemical reactivity

Paracetamol is a widely used analgesic, which causes liver necrosis and sometimes renal failure after overdoses in many species. The half-life is increased after overdoses because of impaired conjugation of the drug. Toxicity is due to metabolic activation and is increased in patients or animals exposed to microsomal enzyme inducers. The reactive metabolite (NAPQI) reacts with GSH, but depletes it after an excessive dose and then binds to liver protein. Cellular target proteins for the reactive metabolite of paracetamol have been detected, some of which are enzymes that are inhibited. Therefore, a number of events occur during which ATP is depleted, Ca levels are deranged, and massive chemical stress switches on the stress response. 

In conclusion, closed-packed (111) surfaces tend to retain the (1x1) normal surface structure, while the less dense (110) faces tend to reconstruct or to relax, at least partly, the surface stress or to form ordered phases if they are favoured. The closed packed (111) faces have modified chemical reactivities associated to stress effects and/or ligand effects. In the case of more open (110) faces, stressed surfaces tend to relax and generate original structures with peculiar sites of new and specific catalytic properties. The tendency for ordering induces a possible isolation of the surface Pd atoms this will decrease the number of active sites for a given reaction or produce specific arrangements of interest for specific reactions. 

We stress that all the approaches presented in this subsection, leading to normal and anomalous diffusion, are intended to model dispersion. As clearly seen in (2.28) and their equivalents for anomalous diffusion these equations damp the higher Fourier modes so that there is a relative increase of variance at larger scales. But in situations such as in modelling dispersion induced by turbulent flows the dispersion is a consequence of the stretching of fluid elements that is associated with compression along the complementary directions. This produces a direct cascade of variance towards small scales that is not captured by the diffusion equation (2.9). Thus the small scale distribution and phenomena strongly dependent on this, like chemical reactivity, may not be adequately modelled in the framework of diffusion equations alone. 

Gibson JD, Pumford NR, Samokyszyn VM, Hinson JA (1996) Mechanism of acetaminophen-induced hepatotoxicity covalent binding versus oxidative stress. Chem Res Toxicol 9 580-585 Gillette JR, Nelson SD, Mulder GJ, Jollow DJ, Mitchell JR, Pohl LR, Hinson JA (1981) Formation of chemically reactive metabolites of phenacetin and acetaminopheiL Adv Exp Med Biol 136 (Pt B) 931-950... 

Pressure tends to increase the chemical reactivity of nitromethane as well as the rate of thermal decomposition. It was observed, quite accidentally, that a pressure-induced spontaneous explosion of single crystals of nitromethane at room temperature can occur. Further study revealed that single crystals grown from the liquid with the (111) and either the (001) or the (100) crystal faces perpendicular to the applied load direction in the DAG, if pressed rapidly to over 3 GPa, explode instantaneously accompanied by an audible snapping sound. The normally transparent sample becomes opaque instantly. Visual examination of the residue revealed a dark brown solid which was stable when heated to over 300 C. Subsequent x-ray analysis showed the material to be amorphous. Mass spectral analysis of the residue was inconclusive because no well defined spectra were observed. Because most of the sample is recovered as solid residue after the explosion and is stable to over 300°C, the material may be amorphous carbon. This stress-induced explosion occurs only in protonated nitromethane because similar attempts on the deuterated form did not result in explosion. Shock experiments on oriented pentaerythritol (PETN) crystals have shown similar type behavior [25]. In this case it was suggested that the sensitivity of shock pressures to crystal orientation is the result of the availability of slip planes or system of planes in the crystal to absorb the shock, thereby increasing the threshold to explosion. A similar explanation may be applicable to the nitromethane crystals as well. The deuteration effect must play a role in the initiation chemistry. An isotope effect has been observed previously in the sensitivity of HMX and RDX to shock and thermal conditions [23]. 

Recall that increasing the tensile or shear stress will (1) first stretch the chains in an amorphous region of a polymer sample, (2) then order the polymer chains, and (3) then induce crystallinity in regions of the polymer. These changes will affect chemical reactivity because molecular diffusion is slower in ordered and cystalline phases compared to amorphous phases consequently, intermolecular reaction rates, such as those in the autooxidation cycle, will be slower in ordered polymers. 

---