Rigid compact structure

Bovine serum albumin (BSA) is a globular protein with a rigid compact structure, but it is also known to have good emulsifying and oil-binding prop-... 

Because of the compact structure of the cycloaliphatic resins the intensity of cross-linking occurring after cure is greater than with the standard diglycidyl ethers. The lack of flexibility of the molecules also leads to more rigid segments between the cross-links. 

Relationships between stereocenters vary between two extremes. On the one hand, stereocenters may interact strongly in a spatial sense if they are directly joined, proximate to one another, or part of a compact rigid-ring structure. On the other hand, two stereocenters which are remote from one another and/or flexibly connected may be so independent that one cannot be used to provide substrate spatial control for the other. Nonetheless, this latter type of stereorelationship may still be clearable if the target molecule can be disconnected to divide the two stereocenters between two precursors or if an appropriate enantioselective transform is available. 

As previously recognized (e.g., Table 4.52), this corresponds to the ideal pattern of three cu bonds, three lone pairs, and sd2 (90°) hybridization, locking in a rigid octahedral structure. On the basis of the formally duodectet-rule-consistent parent species FeH3, the overall co-bonding is compactly described by the two resonance structures... 

Paracyclophane also has a compact structure in solution, as is readily seen on comparing its partition coefficient with that of p-xylene for the system octanol/water 32>. Rigid superposition of the benzene rings leads to an intramolecular delocalization of the hydrophobic -electron clouds and hence to an increased affinity for the aqueous phase. Accordingly, the logarithm of the partition coefficient is found to be smaller than the value observed for p-xylene, and not twice as large, as would be expected for completely hydrophobic surfaces. 

The most spectacular effect resulting from the highly rigid and compact structure of Cu2(K-84)p+ is undoubtedly its extraordinary kinetic inertness in the cyanide demetalation process. Measurement of the absorbance decay of its MLCT band in the visible region (A = 524 nm) could be performed by classical absorption spectrophotometry (whereas stopped-flow techniques were required for the methylene-bridged knots) and allowed to demonstrate that its demetalation implies two rate-limiting steps, well resolved in time, as schematically represented in Figure 27. 

Diffusion requires cooperative motions of both the polymer and the diffusant [27] and is therefore only low below T , and severely restricted below Tg. The diffusion of various stabilizers was elucidated in amorphous and semicrystalline polymers and in multiphase systems. In semicrystalline polymers, diffusion takes place almost exclusively in the amorphous phase and the value of D is sensitive to the total crystallinity and the morphology. It is difficult to predict D within a homologuous series of stabilizers. For a given molecular weight, long and flexible molecules diffuse more rapidly than more rigid and compact structures. For a given stabilizer, the value of D is usually lower in PP and HDPE than in LDPE. It was demonstrated that typical AO molecules have a very restricted mobility in polymers. They are, however, insufficient experimental data to correlate the AO mobility and the AO efficiency. 

The denaturation of 3-lactoglobulin by nonpolar agents and the conformational effects of disulfide cleavage upon serum albumin and ribonu-clease demonstrate that sources of stability in addition to helical segments may be required for the rigid compact shape of globular proteins. A number of further studies upon the respective contributions of secondary and tertiary structure to this stability may be selected to illustrate the role that optical rotation, used as a method solely for determining secondary structure, can play in conjunction with other methods of structural assessment. 

While the modeling of polymers as rigid particles is somewhat questionable, the modeling of proteins which have a compact structure as rigid particles is common (9, 14, 16) especially for globular proteins. 

Knowing that we needed to develop a CNS drug, we then reduced the number of rotatable bonds of compound 11 and designed the rigid, compact 5,5 -diphenyl iminohydantoin core structure (compound 12) which, despite being only weakly active, now showed excellent lead-like properties with good LE, much better LLE, and an overall favorable profile with respect to cellular potency, selectivity, rat PK, and brain penetration (Fig. 4e). Thus, compound 12 was the superior choice for lead optimization. 

Low-spin Fe(II) or Fe(III) is more compact than high-spin iron. Consequently if the geometry of the ligands is fixed e.g. as in porphyrin system or by a rigid protein structure the binding energy and coordination geometry of the metal may be different in its two spin states. 

Proteins adopt their native conformation under physiological conditions. This conformation is usually very rigid and compact due to the many intra- and intercatenary, intra- and intermolecular bonds (secondary, tertiary, and quaternary structures). Therefore the detailed conformation of native proteins can be evaluated by X-ray diffraction measurements on protein crystals. Hydrodynamic measurements, on the other hand, only yield information about the external shape (sphere, rod, ellipsoid) of these compact structures. 

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