Kinetically trapped

These systematic studies not only demonstrated that the relative populations of different Rg XY conformers are not kinetically trapped within the... 

The ability to detect discrete rovibronic spectral features attributed to transitions of two distinct conformers of the ground-state Rg XY complexes and to monitor changing populations as the expansion conditions are manipulated offered an opportunity to evaluate the concept of a thermodynamic equilibrium between the conformers within a supersonic expansion. Since continued changes in the relative intensities of the T-shaped and linear features was observed up to at least Z = 41 [41], the populations of the conformers of the He - lCl and He Br2 complexes are not kinetically trapped within a narrow region close to the nozzle orifice. We implemented a simple thermodynamic model that uses the ratios of the peak intensities of the conformer bands with changing temperature in the expansion to obtain experimental estimates of the relative binding energies of these complexes [39, 41]. 

The phase diagram in Fig. 56 reveals an irreversible temperature-induced OOT between C and G, with the former being the low-temperature phase, which differs from previous studies on PS-fr-PI/PS or PI blends [10]. The irreversibility of the OOT was attributed to a kinetic effect. At temperatures between ODT and OOT the system assembles in a G morphology. This structure is kinetically trapped and persists at temperatures below OOT, where cylinders are expected to be formed. 

After extensive experimentation, it was discovered that exposure of silyl ether (+)-97 to potassium trithiocarbonate and trifluoroacetic acid in dichloromethane affords a 25 7 1 mixture of endolendo endo/exo exo/exo bisdithiepanethione products, reflecting a ca. 5 1 preference for nucleophilic approach from the endo-face of each diketopiperazine moiety. Resubjection of the isolated bisdithiepanethione diastereomers to the original reaction conditions did not result in their equilibration, indicating that the products were a result of kinetic trapping. 

Scheme 15. Kinetic trapping model for the enrichment of isoprenylated proteins with a free acylation site in specific membranes...

Slipping. The slipping method exploits the kinetic stability of the rotaxane. Provided the end groups of the dumbbell are of appropriate size, they are able to reversibly thread through the macrocycle at higher temperatures, but by lowering the temperature the dynamic complex becomes kinetically trapped as a rotaxane. 

Tao P. and Sosnick T. R. Intermediates and kinetic traps in the folding of a large ribo-zyme revealed by circular dichroism and UV absorbance spectroscopies and catalytic activity. Nat Struct. Biol. (1997) 4(11) 931-938. 

The first phase of our efforts was the unambiguous synthesis of each model substrate. PN and PX were already well characterized materials (1) While direct synthesis of the phenyl and carbomethoxy compounds from PN and/or PX was attempted, this approach was unsuccessful due to the sluggish reactivity of the norbornenyl double bonds in these molecules (2). A successful approach to CBN and (fiBN based on N-phenyl maleimide (NPMI) trapping of the respective thermodynamically favored 1-substituted cyclopentadienes is shown in Equation 1. Similarly, kinetic trapping of 2-phenyl cyclopentadiene, from the in situ dehydration of 3-hydroxy, 3-phenyl cyclopentene, gives a clean yield of (f)VN (Equation 2). The remaining phenyl isomer (VX) and the three other carbomethoxy isomers (CBX, CVN, CVX) were all obtained by the thermal isomerization chemistry described in the next section of this paper. They were each isolated in pure form by liquid chromatography We were unable to obtain any (f)BX or any of the 7-substituted isomers by any means. 

Whitelam, S., Geissler, P.L. Avoiding unphysical kinetic traps in Monte Carlo simulations of strongly attractive particles. J. Chem. Phys. 2007, 127, 154101. 

The process opposite to vesicle division is that of fusion, when two or more vesicles come together and merge with each other, yielding a larger vesicle. As outlined in the previous chapter, vesicle fusion is generally not a spontaneous process. If two populations of POPC liposomes with different average dimensions are mixed with each other, they do not fuse to produce a most stable intermediate structure - they stay in the same solution as stable, distinct species. This is connected to the notion of kinetic traps, as discussed previously, and is supported by theoretical and experimental data from the literature (for example, Hubbard etal, 1998 Olsson and Wennerstrom, 2002 Silin et al, 2002). 

Efforts have been made to eliminate diffusion-control of solid-solid reactions by using superlattices of nanometric dimensions as reactants. Formation of Cu MOgSeg from the superlattices of Cu, Mo and Se is one such example (Fister et al., 1994). The results reveal that superlattice reactant geometry could be used to kinetically trap the ternary phases which are thermodynamically unstable with respect to the binary phases. 

In the structure of the apo-form of HIV PR, the flaps from both monomers are related by crystallographic two-fold symmetry and can be considered as being in an open conformation. In the structures of related proteases from Rous Sarcoma Virus and HIV-2, the flaps are either crystallographically disordered or in a partly closed conformation [18]. This suggests that, in solution, in the absence of ligands, the flaps are rather flexible and that the stable conformation of the flaps observed in the crystal structure of the apo-enzyme of HIV PR could be considered to result from kinetic trapping during the crystallization process. 

As a general principle, it is established that the gelation of one (or both) of the biopolymer components retards the process of phase separation and so leads to kinetically trapped microstructures (Bourriot et al., 1999 Butler and Butler-Heppenstall, 2003 Loren and Hermans son, 2000). 

---