Double encapsulation

The easiest combination of two chiral guests in the cylindrical capsule comes by the double encapsulation of racemic species with adequate size, shape and polarity to be accommodated in pairs, giving two diastereoisomeric complexes, the homochiral couple (R) - (R)/(S) - (S) and the heterochiral (R) -(S) combination. ( )-trans-1,2-Cyclohcxancdiol has all the above requisites and showed a 1.2 ratio between the two complexes in favor of the heterochiral combination [60]. This observation may be related to the preference in nature for centrosymmetric crystals or, alternatively stated, the higher melting points of racemates vs. enantiopure compounds where the resolution is driven by the less soluble pair [61,62], In the cylindrical capsule a single couple of chiral molecules is extrapolated from the bulk and the interactions between the two is governed by the shape of the cavity and their goodness of fit within the cavity. 

Density and Moisture Tester (MC-l). A 50 mCi mixture of Americium-241 and Beryllium is located within the base of the MC-l (about 200 times more than is used in the M43A1 Chemical Agent Detector). Neutron emission occurs when an alpha particle emitter such as Americium-241 is mixed with Beryllium (Be) powder in a tightly compressed pellet. The MC-l also has a 10 mCi Cesium-137 source located in a probe tip used to determine the density of the soil at a construction site. This source is classified as a special form source and is double-encapsulated in stainless steel. TACOM is the NRC license holder for the MC-l and is responsible for item management. 

Instron Universal Testing Machine 4200 Lactose Sucrose Modified cornstarch Butter-oil single and double encapsulated in lactose, sucrose, and modified cornstarch... 

Particle size was also evaluated in encapsulated materials by comparing single- and double-encapsulated butter oil powders in sucrose (<500 pm and 1000 pm, respectively) by Onwulata et al. (1998). Compressibility as a measure of cohesion and mechanical strength at various loads increased for both single-encapsulated powders and double-encapsulated powders. However, larger powders were more impeded in flow than single-encapsulated ones. 

Onwulata, C.L, Smith, P.W., and Holsinger, V.H. 1998. Properties of single- and double-encapsulated butteroil powders. J. Food Sci. 63, 100-103. 

This process may be used for a double encapsulation of spray-dried particles. 

A double-encapsulated flavor powder (spray-dried) is prepared by secondary fat coating process, with better resistance to moisture and oxygen than single encapsulated powder (Cho and Park, 2002). 

Cho Y.H. and Park J., 2002. Characteristics of double-encapsulated Fflavor powder prepared by secondary fat coating process. Food Chemistry and Toxicology, 67, 968-972. 

Microcapsules with desired release rate and patterns can be obtained by carrying out either chemical or physical modifications to the microcapsules. In the case of chemical modifications, the polymeric wall material is modified or, along with active agent, another additive is added. This allows the release of active agent to occur in response to physical/chemical changes in the additive, due in turn to change(s) in the microcapsule environment. Physical modifications involve controlling porosity of the capsule wall, or double encapsulation. The adsorption of an... 

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

MXH (X = Cl, Br)(Sc, Y, Gd, Lu and probably other Ln) Double metal layers of edge-sharing metal octahedra, M Xg-type environment but with encapsulated H atoms... 

Similar methods of encapsulation are also observed in pillared clays, which were also introduced as catalysts as long ago as the early 1980s. The field has been thoroughly reviewed up to 2000 [65], Layered double hydroxide structures have also been used for the entrapment of metal coordination compounds [66],... 

Liposomal contrast agents have also been proposed in recent years. Liposomes are vesicles built from a double layer of lipids encapsulating an aqueous cavity. Their ability to transport substances, either in the lipid bilayer or in the internal aqueous phase, makes them a versatile delivery... 

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