Reactive processes, compartmentalized

The maintenance of cellular homeostasis implies the dynamic coordination of cellular processes to finely compensate for subtle variations of the external and internal environments (e.g., pH, osmolarity, nutrients, and oxygen supply) but also to monitor and regulate intracellular signalling and compartmentalization. Cellular stress occurs when a threat to homeostasis is detected by highly reactive and efficient protective mechanisms. Depending on the intensity (dose) and duration (exposure) of the stress, these defenses can either cope without any observable change in cellular homeostasis or be overcome, resulting in a detectable shift from basal metabolic or cellular functions. 

Although there is no commonly accepted definition of a membrane reactor (MR), the term is usually applied to operations where the unique abilities of membranes to organize, compartmentalize, and/or separate are exploited to perform a (bio)chemical conversion under conditions that are not feasible in the absence of a membrane. In every MR, the membrane separation and the (bio)catalytic conversion are thus combined in such a way that the synergies in the integrated setup entail enhanced processing and improved economics in terms of separation, selectivity, or yield, compared to a traditional configuration with reactor and separation separated in time and space. When the membrane itself carries the catalytic functions, it is mostly referred to as a reactive membrane. ... 

The existence of a physical structure has several important consequences. It determines a number of physical properties, notably mechanical ones viscosity, elasticity, consistency, fracture properties. Because of the physical inhomogeneity, some kinds of physical instability can occur, often manifest as a kind of segregation, and these are generally undesired. Chemical components are to some extent compartmentalized, which may affect their mutual reactivity, hence the chemical stability of a food. The compartmentalization also tends to affect flavor. The result of some process operations can greatly depend on the physical structure of the system, and several processes are intended to produce or to alter structure. 

Metals, which enter aquatic organisms directly from the surrounding water, are compartmentalized within tissues in membrane-limited vacuoles and bound to ligands to reduce the toxic reactivity (Roesijadi 1992, Viarengo and Nott 1993). Amiard (1988) suggested that phytoplankton fixes metals and makes them unavailable to oysters. Compartmentalization processes remove metals from tissue fluids, and diffusion gradients inwards from surrounding water are maintained (Nott 1998). 

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