Structures saddle-like

Crystal structures have been obtained for Ae C-terminal domain of free TBP from three different species (P.woesei [IS], Ajhaliana [19,20], and S.cerevisiae [21]), revealing a saddle-like structure with stirrups formed by a 10-stranded P-sheet and four a-helices, reflecting the imperfect repeats found in the sequence. All these structures crystallized as dimers, and the dimerization... 

For K < 0 discrete aggregates are preferred and for > 0 saddle-like structures are preferred. It has been found that xrand k are on the order of a few k T [123] and that k is negative. Others have obtained k and k on the order of unity and -0.5 in units of k T [60, 70, 71], respectively. There are also models where k is positive [124] due to how the enthalpy has been taken into account. Small differences in droplet size result in big variations of the derived values for k and k. Since they are often obtained from experimental results as the combination 2k + k)... 

As we continue to larger rings, the results are not so clearcut. There is a tendency for the saddle points to alternate in and out somewhat, but the interaction energy appears to be a maximum at the ring of six atoms. These last more-or-less qualitative comments have been based upon just the two simple Kekule-like structures of the rings, and may not be able to show the proper behavior. The actual surface calculations of ( 2)2 and (H2)3 included many more structures and show strikingly different qualitative behavior. 

In summary, we maintain that while the free volume concept is an intuitively natural concept for liquids confined in a host matrix, it is not an obvious model for ionic/covalent crystals. Saddle-like relaxation is not a universal feature of all crystals. Hence, v/, the free volume necessary for the relaxation to occur, cannot be attributed to the presence of any defect that causes an irregularity in the crystal structure. In the special case of... 

Fig. 5.9. Bifurcation diagram in the (cr, t/) plane. Thick and hatched lines mark the transition from stationary to moving fronts via a Hopf or a saddle-node bifurcation on a limit cycle, respectively. The inset shows a blow-up of a small part of the hatched line revealing its saw-tooth-like structure. Dark and white correspond to stationary and moving fronts, respectively, where the numbers denote the positions of the stationary accumulation front in the superlattice. Upper inset shows the frequency / of the limit cycle which is born above the critical point (marked by a cross in the lower inset) as function of U. [57]...

The solid state structures of CD9, CDio, CDh and CD26 have been reported. The structure of CDg exhibits a distorted elliptical boat-like shape, but it retains a similar structure to regular CDs. CDio and CDh also exhibit a more elliptical macrocyclic ring folded in a saddle-like shape. The structure of CD26 has channellike cavities composed of two short V-amylose helices in anti-parallel orientation, and its structure is very different from the regular CDs [1,7] (Fig. 1.3). 

Fig. 5.0. The structure of the La-sponge phase is built up from one single infinite surfactant bilayer, bent everywhere in a saddle like manner so to be multiconnected to itself over macroscopic distances in the three directions of space. This structure is indeed intriguing and provides a beautiful illustration of the capability of amphiphilic molecules to self assemble spontaneously into various morphologies and structures at thermodynamic equilibrium. (by courtesy of Jean-Pierre Fluxench)...

Condensation reactions on nickel(II) matrices are sensitive to steric effects. X-Ray structm analysis showed [310, 320-328] that H2L263 and its metal complexes are saddle-like, rather than planar. The sources of structural nonplanarity are steric repulsions between methyl groups R, 4 and orr/K>-aromatic protons of the Schiff bases. The increase in the bulk of the groups in these positions hinders macrocyclisation. For example, 3,5-heptanedione, 4,6-nonanedione and 1-phenyl-2,4-pentanedione form cyclic products [Ni(L274)]-[Ni(L276)J, whereas dibenzoyl-methane, 2,6-dimethyl-3,5-heptanedione and 2,2,6,6-tetramethyl-2,5-heptanedione do not give macrocyclic compounds in the presence of nickel(II) and o-phda [300, 320]. In the case of dibenzoylmethane, the nickel(II) )ff-diketonate bis-diamine adduct is isolated (Eq. 2.164) [319]. 

Going in the opposite direction, i.e. when we consider the membrane stability with increasing ionic strength, we notice the approach of k towards zero. Going towards this value, the tendency of the bilayers to form saddle-shaped connections (also called stalks ) between bilayers increases. Saddle-shaped membrane structures also occur in processes like vesicle fusion, endo and exocytosis. The SCF predictions thus indicate that these events will occur with more ease at high ionic strength than at very low ionic strength. 

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