Encapsulated dynamics

The resolution of racemic ethyl 2-chloropropionate with aliphatic and aromatic amines using Candida cylindracea lipase (CCL) [28] was one of the first examples that showed the possibilities of this kind of processes for the resolution of racemic esters or the preparation of chiral amides in benign conditions. Normally, in these enzymatic aminolysis reactions the enzyme is selective toward the (S)-isomer of the ester. Recently, the resolution ofthis ester has been carried out through a dynamic kinetic resolution (DKR) via aminolysis catalyzed by encapsulated CCL in the presence of triphenylphosphonium chloride immobilized on Merrifield resin (Scheme 7.13). This process has allowed the preparation of (S)-amides with high isolated yields and good enantiomeric excesses [29]. 

Dynamic light-scattering experiments or the analysis of some physicochemical properties have shown that finite amounts of formamide, A-methylformamide, AA-dimethyl-formamide, ethylene glycol, glycerol, acetonitrile, methanol, and 1,2 propanediol can be entrapped within the micellar core of AOT-reversed micelles [33-36], The encapsulation of formamide and A-methylformamide nanoclusters in AOT-reversed micelles involves a significant breakage of the H-bond network characterizing their structure in the pure state. Moreover, from solvation dynamics measurements it was deduced that the intramicellar formamide is nearly completely immobilized [34,35],... 

Water-in-oil microemulsions (w/o-MEs), also known as reverse micelles, provide what appears to be a very unique and well-suited medium for solubilizing proteins, amino acids, and other biological molecules in a nonpolar medium. The medium consists of small aqueous-polar nanodroplets dispersed in an apolar bulk phase by surfactants (Fig. 1). Moreover, the droplet size is on the same order of magnitude as the encapsulated enzyme molecules. Typically, the medium is quite dynamic, with droplets spontaneously coalescing, exchanging materials, and reforming on the order of microseconds. Such small droplets yield a large amount of interfacial area. For many surfactants, the size of the dispersed aqueous nanodroplets is directly proportional to the water-surfactant mole ratio, also known as w. Several reviews have been written which provide more detailed discussion of the physical properties of microemulsions [1-3]. 

This study has shown that typical coating biocides can be encapsulated within modified silica frameworks. These porous frameworks offer a means to inhibit the aqueous extraction of the biocide. In such combinations the biocides retain their anti-microbial properties, while controlled delivery facilitates a dynamic equilibrium to maintain a minimum inhibitory concentration at the coating interface, over an extended time period. There is evidence that biocide housed in such frameworks has a longer effective activity for a given initial concentration, since it is to some extent protected from the usual environmental degradation processes. 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

Several enzymes have been immobilized in sol-gel matrices effectively and employed in diverse applications. Urease, catalase, and adenylic acid deaminase were first encapsulated in sol-gel matrices [72], The encapsulated urease and catalase retained partial activity but adenylic acid deaminase completely lost its activity. After three decades considerable attention has been paid again towards the bioencapsulation using sol-gel glasses. Braun et al. [73] successfully encapsulated alkaline phosphatase in silica gel, which retained its activity up to 2 months (30% of initial) with improved thermal stability. Further Shtelzer et al. [58] sequestered trypsin within a binary sol-gel-derived composite using TEOS and PEG. Ellerby et al. [74] entrapped other proteins such as cytochrome c and Mb in TEOS sol-gel. Later several proteins such as Mb [8], hemoglobin (Hb) [56], cyt c [55, 75], bacteriorhodopsin (bR) [76], lactate oxidase [77], alkaline phosphatase (AP) [78], GOD [51], HRP [79], urease [80], superoxide dismutase [8], tyrosinase [81], acetylcholinesterase [82], etc. have been immobilized into different sol-gel matrices. Hitherto some reports have described the various aspects of sol-gel entrapped biomolecules such as conformation [50, 60], dynamics [12, 83], accessibility [46], reaction kinetics [50, 54], activity [7, 84], and stability [1, 80],... 

The 02 center of the encapsulated Li20 is only square-planar coordinated because of the lower lithium content. However, the four Li centers of the Li40 core are disordered. This disordering of the metal-coordinated 02 center has also been seen in the case of the first dode-cameric disodium arsandiide-Na20 complex (Fig. 10) (25). Whereas the positions of the outer Na centers have been precisely located, the six inner Na centers can adopt 20 equivalent sites. This is probably due to the larger void of the Asi2Na2o double shells. However, the origin of this disorder (static and/or dynamic) is not yet known. 

Scheme 1 summarizes four different approaches used to characterize dendrimer structures by photophysical and photochemical probes 1. Non-covalent, inter-molecularly bound interior probes - to study the internal cavities and the encapsulation abilities of dendrimers. 2. Non-covalent, intermolecularly bound surface probes - to study surface characteristics of dendrimers. 3. Covalently linked probes on dendrimer surfaces - to study the molecular dynamics of dendrimers. 4. Covalently linked probes at the dendrimer central core - to study the site isolation of the core moiety and define the hydrodynamic volume of dendrimers by the concentric dendrimer shells. Critical literature in these four categories will be described using representative examples. 

In the preceding section, we reviewed the non-covalent dynamic encapsulation of guest probe molecules within dendrimer interiors. The second case, Scheme 2, involves the physical encapsulation of guest molecules wherein, guest molecules are locked inside dendritic containers (so-called dendritic boxes). This concept was originally proposed by Tomalia et al and referred to as unimolecular encapsulation [2]. More recent and well characterized examples have now been demonstrated by Meijer and co-workers [11-15]. 

CNTs can also be encapsulated with DNA molecules. As shown in Fig. 9.1, a DNA molecule could be spontaneously inserted into a SWNT in a water solution via molecular dynamics simulation (Gao et al., 2003). The van der Waals and hydrophobic forces were very key factors for the insertion process, with the former playing a more dominant role in the course of DNA entering into the hole of CNT. Experiment also confirmed that Pt-labeled DNA molecules can be encapsulated into multi-walled carbon nanotubes in water solution at 400 K and 3 Bar as shown in Fig. 9.2 (Cui et al., 2004). The CNTs filled with DNA molecules have potential in applications such as gene delivery system, and electronic sequencing, nanomotor, etc. 

Equation 5.11 is important. It relates the experimentally observed vapor pressure ratio to the theoretically important isotope effects on the free energy differences and/or partition function ratios. This equation encapsulates the essential physics of the vapor pressure isotope effect and, as we shall see, provides a path for its theoretical interpretation in terms of molecular structure and dynamics via the partition function ratios. 

This confidence stems from a unique capability to co-evolve with the fluid IT environment within which Infosys operates. Continuity and change are inherent in Infosys s operations as it uses the very resources and capabilities it has built in the past as platforms to explore and exploit emerging opportunities. Scalability lies in Infosys s ability to encapsulate its past experiences such that the accumulated stock and associated flows result not in core rigidities - the perpetuation of Infosys as it once was - but in dynamic capabilities that fuel its continual transformation. That is, Infosys represents a continually upgradable platform, a firm that is always in the making. 

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