Structure flexibility

The thermodynamic stability of a protein in its native state is small and depends on the differences in entropy and enthalpy between the native state and the unfolded state. From the biological point of view it is important that this free energy difference is small because cells must be able to degrade proteins as well as synthesize them, and the functions of many proteins require structural flexibility. 

The [4-1-3] cycloaddition has also been realized in acceptors containing a nitrogen atom. While a,/ -unsaturated aldimines, and structurally flexible ketimine such as (87), generally only undergo [3-1-2] cycloadditions (see Scheme 24), the ketimine (112), which is rigidly held in a cisoid conformation, does give exclusively the [4-1-3] adduct azepine (113). On the other hand, the steroidal imine (114) produces a quantitative yield of a 1 1 mixture of the [4-1-3] and [3-1-2] cycloadducts (115) and (116), respectively (Scheme 2.31) [36]. 

Scheme 2.30 TMM [4+3 cycloadditions with structurally flexible 1,3-dienes...

Figure 4 (curve 1) shows that in the absence of extension the distribution function W(fi) lies in the range 0 < /S < 0.2 for relatively long chains. In other words, in the absence of external forces, crystallization of flexible-chain polymers always proceeds with the formation of FCC since in the unperturbed melt the values of /3 are lower than /3cr. For short chains, the function W(/3) is broader (at the same structural flexibility f) (Fig. 4, curve 2) and the chains are characterized by the values of > /3cr, i.e. they can crystallize with the formation of ECC. Hence, at the same crystallization temperature, a... 

Glos and Reiser [23] introduced aza-bis(oxazolines) as new chiral ligands for copper and palladium catalysts. Because of the structural flexibility of these compounds they also prepared an immobilized ligand by covalent grafting to methoxypoly(ethyleneglycol) (structures 14 and 15 in Scheme 9). 

A schematic cross-section of a p-i-n a-Si H solar cell [11] is shown in Figure 72a. In this so-called superstrate configuration (the light is incident from above), the material onto which the solar cell structure is deposited, usually glass, also serves as a window to the cell. In a substrate configuration the carrier onto which the solar cell structure is deposited forms the back side of the solar cell. The carrier usually is stainless steel, but flexible materials such as metal-coated polymer foil (e.g. polyimid) ora very thin metal make the whole structure flexible [11]. 

To limit the structural flexibility of these two aromatic residues, conformationally restricted analogues of Phe and/or Tyr were substituted [28,30] (Fig. 1). 

The physical origin of this structural flexibility of the FeO overlayer is still unclear, the more so since no clear trend is observable in the sequence of lattice parameters of the coincidence structures. The FeO(l 11) phase forming up to coverages of 2-3 ML is clearly stabilized by the interactions with the Pt substrate since FeO is thermodynamically metastable with respect to the higher iron oxides [106,114], FeO has the rock salt structure and the (111) plane yields a polar surface with a high surface energy [115], which requires stabilization by internal reconstruction or external compensation. The structural relaxation observed in the form of the reduced Fe—O... 

Mizuno H, Mai TR, Walchli M, Rikuchi A, Fukano T, Ando R, Jeyakanthan J, Taka J, Shiro Y, Ikura M, Miyawaki A (2008) Light-dependent regulation of structural flexibility in a photochromic fluorescent protein. Proc Natl Acad Sci USA 105 9227-9232... 

It appears that Te is more flexible in the possible arrangements (Figure 18) 72,73 it should be noted though that the counterions of these Te cations are more basic than the fluorinated anions used for S and Se cations. Thus, it may well be that the structural flexibility of the Te cations is a result of the increased cation-anion interactions in these salts. 

The analysis of the cytochrome crystal structures reveals extensive differences among the mammalian and the human CYPs that may reflect the structural flexibility of these enzymes and therefore the broad substrate specificity observed. In general, the secondary elements and the overall structure of the CYP are conserved. Nevertheless, it seems that in most enzymes, the most flexible regions are located between the F-G helixes and the B-C loop. For example in the CYP2B4 apoprotein (lpo5) the... 

Structural flexibility relative to functional groups and their placement. 

This is probably due to the high electron donating character of the acyclic bis (amino)carbene as compared to the NHCs, and to its structural flexibility which could liberate the reaction site on the metal center. 

In both case (gel and dried gels) the advantage or a scheme based on the protcfilament is the high degree of resultant structural flexibility. Interf ila.ment contacts of the physical reticulation can occur by filament juxtaposition, by a fusion of all protofilaments of the two incoming filaments (say n protofilaments) to form an n-start helical fusion zone of reticulation or by an int erf ilament exchange of just one or iP.ore protofilaments. 

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