Mechanism of release

Being a gas, NO can diffuse freely once produced, and so is not constrained by the usual mechanisms of release and uptake that confine most transmitters to the synapse. Likewise, the fact that it is not stored means that the criteria of presence and storage are... 

Figure 2. Two mechanisms of releasing a protein from its polymeric conjugates.

However, in the foregoing systems, the predominant mechanism allows easy mathematical description. In practice, the dominant mechanism for release will overshadow other processes enough to allow classification as either dissolution rate-limited or diffusion-controlled. Bioerodible devices, however, constitute a group of systems for which mathematical descriptions of release characteristics can be quite complex. Characteristics of this type of system are listed in Table 7. A typical system is shown in Fig. 8. The mechanism of release from simple erodible slabs, cylinders, and spheres has been described [36], A simple expression describing release from all three of these erodible devices is... 

Figure 1 Picture showing the components and mechanism of release for the elementary osmotic pump. (From Ref. 3.)...

In order to design a particular release mechanism, experimental data of statistical significance are compared to a solution of the theoretical model. It is therefore clear that only a combination of accurate and precise data with models accurately depicting the physical situation will provide an insight into the actual mechanism of release. 

A number of conditions must be considered when selecting protective equipment for individuals at the scene of a release. For instances such as "anthrax" letters when the mechanism of release is known and it does not involve an aerosol generating device, then responders can use Level C with high-efficiency particulate air (HEPA) filters. 

Chemical transmission between nerve cells involves multiple steps 167 Neurotransmitter release is a highly specialized form of the secretory process that occurs in virtually all eukaryotic cells 168 A variety of methods have been developed to study exocytosis 169 The neuromuscular junction is a well defined structure that mediates the presynaptic release and postsynaptic effects of acetylcholine 170 Quantal analysis defines the mechanism of release as exocytosis 172 Ca2+ is necessary for transmission at the neuromuscular junction and other synapses and plays a special role in exocytosis 174 Presynaptic events during synaptic transmission are rapid, dynamic and interconnected 175... 

Quantal analysis defines the mechanism of release as exocytosis. Stimulation of the motor neuron causes a large depolarization of the motor end plate. In 1952, Fatt and Katz [11] observed that spontaneous potentials of approximately 1 mV occur at the motor endplate. Each individual potential change has a time course similar to the much larger evoked response of the muscle membrane that results from electrical stimulation of the motor nerve. These small spontaneous potentials were therefore called... 

In this case, the mineralogical studies on the mechanism of sulfide alteration and on the genesis and evolution of secondary oxidation products are of paramount environmental relevance because they allow a better understanding of the source and the mechanisms of release of the ecotoxic elements and the effective... 

Metals Scale of changes Diagnostic media Mechanism of release Ways to living organisms... 

Drug release from soluble polymers is accompanied by the gradual erosion-type dissolution of the polymer. Therefore, polymer dissolution and drug diffusion may be the overall hybrid mechanism of release. Drug release from nonsoluble hydrogels generally follows Fickian or non-Fickian diffusion kinetics [51]. The mechanism of... 

The release of a flammable gas or liquid can lead to different types of fire scenarios. These are dependent on the material released, the mechanism of release, the temperature and pressure of the material, ambient conditions, and the point of ignition. Types of fires include ... 

Corrie et al. studied the photorelease of a caged sulfate from 102 and demonstrated that the mechanism of release of sulfate is, in principle, similar to that observed for 96 (Scheme... 

Pinck L.A., D.A. Soulides, and E.E. Allison (1961b). Antibiotics in soils 2. Extent and mechanism of release. Soil Science 91 94-99. 

Because the forces of attraction prevail when molecules are brought into sufficiently dose proximity under normal conditions, release is best effected if both the strength of the interaction and the degree of contact are minimized. Aliphatic hydrocarbons and fluorocarbons achieve the former effect, finely divided solids the latter. Materials such as microcrystalline wax [64742 42-3] and hydrophobic silica [7631-86-9] combine both effects. Some authors refer to this combined effect as the ball bearing mechanism. A perfluoroalkylated fullerene nanosphere would perhaps be the ultimate example of this combined effect (17). These very general mechanistic remarks can be supplemented by publications on the mechanism of specific classes of release agents such as metallic stearates (18), fatty acids and fluorinated compounds (19), and silicone-coated rdease papers (20,21). The mechanism of release of certain problem adherents, eg, polyurethanes, has also been addressed (22,23). 

Tapia C, Buckton G, Newton JM. Eactors influencing the mechanism of release from sustained release matrix pellets, produced by extrusion/spheronization. Int J Pharm 1993 92 211-218. 

In order to investigate the mechanism of release, the following semi-empirical equation was used [8]. 

The anomalous behaviour for potassium chloride matrices with a value <0.5 emphasizes the complex release of this drug. Peppas [8] did not interpret values of <0.5 but stated that such occurrences were an indication of statistical analysis problems or were due to diffusion through a polymeric network where diffusion occurred partially through a swollen matrix and partly through water-filled pores. In this case, in order to investigate the mechanism of release, the percentage release v. time profile was evaluated for goodness of fit. The details of the use of this statistical... 

The release from microcap systems is more complicated. First the drug has to dissolve in dissolution fluid which has diffused into the tablets via pores and then between the plates of poly (DL-lactic acid) forming the walls of the microcapsules. This drug solution then has to diffuse out of the tablet via the same route. The effect of compression on the release has more significance in the simple matrix tablets than the microcap systems, because of the above mechanism of release. Higher compressions reduce the size of the pores between the poly(DL-lactic acid) plates, which extends the release. 

The classification of polymers for oral drug delivery can be done by using various means. To make this discipline readily accessible to the novice reader, the hydro-phobic-hydrophilic nature of the polymer was chosen to group polymers since the mechanism of biomacromolecule release from most hydrophobic polymeric devices is similar the mechanism of release from most hydrophilic polymeric devices also have similar mechanisms. Hydrophobic polymers are described first, followed by hydrophilic polymers. 

The term aqueous phase separation is often more simply described as oil-in-water microencapsulation. The two encapsulation processes described above are examples of this oil-in-water encapsulation. In this process the core material is the oil and it should be immisible in the continuous phase, namely water. A commercial example of aqueous phase separation would be the microencapsulation of an oily flavor such as sour cream with a gelatin wall. These microcapsules would then be dispersed in a dry cake mix. The mechanism of release would be during the moist baking cycle of the cake, moist-heat causing the capsule walls to first swell and then rupture. 

Most important are the mechanisms of release, the release position relative to the surroundings, and atm conditions. These determine how the fuel mixes with air and its movement in the atm once a fuel/air cloud is formed. The conditions under which the fuel had been contained and its pressure-temp characteristics frequently determine if the cloud is predominantly a mist and whether it is dense or light compared to the atm... 

The retention of fission product iodine and xenon by unirradiated and irradiated pyrolytic-carbon-coated (Th,U)C2 fuel particles has been studied in annealing experiments and has been compared with similar studies of the release (or retention) of barium and strontium. The objective was to study the effects of irradiation on the retention of the two types of fission products and to determine the mechanism of release which could account for the observed behaviors. In both unirradiated and irradiated particles, iodine and xenon were found to be retained highly by the impervious isotropic pyrolytic coating which was unaffected by the irradiation. In contrast, the fuel kernel which controls the release of the metallic species is damaged severely by the irradiation, resulting in a marked decrease in its ability to retain the metals. 

A great deal of work has been carried out on model compounds with phenolate and catecholate ligands,1186,1187 and to some extent with modified siderophores.1188 The important question of the mechanism of release of iron(III) from the siderophore has also been a central issue in these model studies. 

Particular discussion has centred around the mechanism of release of the iron, in view of its high affinity for the siderophore. A very attractive proposal is that this simply involves the reduction of the FeIn-siderophore complex. Iron(II) has much lower affinity for the siderophore, and so can be released values of log It for Fe11 are about 8. Good evidence has been found for siderophore reductase activity in bacteria and fungi.1198 Reduction of Feni-hydroxamate siderophores can occur readily under physiological conditions. 

Dressman, J. Mechanism of release from coated pellets, in Ghebre-Sellassie, I. (ed.), Multiparticulate Oral Drug Delivery. New York Marcel Dekker, 1994, pp. 285-306. 

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