Macromolecular conformation of the

Within the class of polymer crystals having, ideally, long-range positional order for all the atoms, different crystalline forms (polymorphs) may arise as a result of having different almost isoenergetic macromolecular conformations (of the main chain, in most known cases) or as a result of different, almost isoenergetic modes of packing of macromolecules with identical conformations [1-3]. 

In Figure 7 a comparison is made of the frequency of the CHj antisymmetric stretching vibration as a function of molecular area for DPPC monolayer films at the A/W and A/Ge interfaces. As described above, the frequency of (his vibration is related to the overall macromolecular conformation of the lipid hydrocarbon chains. For the condensed phase monolayer (-40-45 A2 molecule 1), the measured frequency of the transferred monolayer film is virtually the same as that of the in-situ monolayer at the same molecular area, indicating a highly ordered acyl chain, predominately all-trans in character. For LE films as well as films transferred in the LE-LC phase transition region, however, the measured frequency appears independent (within experimental uncertainty) of the surface pressure, or molecular area, at which the film was transferred. The hydrocarbon chains of these films are more disordered than those of the condensed phase transferred films. However, no such easy comparison can be made to the in-situ monolayers at comparable molecular areas. For the LE monolayers (> ca. 70 A2 molecule 1), the transferred monolayers are more ordered than the in-situ film. In the LE-LC phase transition region ( 55-70 A2 molecule 1), the opposite behavior occurs. 

In contrast, however, we have demonstrated that the macromolecular conformation of the zymogen differs markedly from that of the enzyme (17). Thus, if pepsinogen is transferred from an aqueous solution to concentrated urea, the specific rotation, [a]m, decreases from —200° to —320° in the concentration range of 1.5 to 4.0M urea, and the rotatory dispersion constant, Xc, decreases from 236 to 216 m/z. As shown in Figure 2, which also includes the results obtained with pepsin, this change reflects a configurational transition, similar in sharpness to the transition from an a-... 

In order to elucidate the role of conformation of the immunogen, animals were immunized with complexes of polyribonucleotides (double- or triple-stranded) associated with MBS A. The antibodies obtained reacted specifically with double- or triple-stranded complexes and it was concluded that the specificity was determined by the macromolecular conformation of the immunogen (Nahon et al., 1967 Lacour et al., 1968 Michelson et al., 1971). Immunization of rabbits with DNA-MBSA or with double-stranded polynucleotide complexes adsorbed to MBS A ehcits antibodies belonging to the macroglobulin class (Stollar and Sandberg, 1966 Nahon-Merlin et al., 1973). 

The existence of conformational determinants has been clearly demonstrated through the use of synthetic polynucleotides in double-hehcal structures and in triple-stranded complexes. It has also been shown that the specificity of antibodies is determined by the macromolecular conformation of the immunogen. Thus single-stranded polynucleotides induce formation of antibodies specific for the single-strand, while double-stranded hehcal complexes of polynucleotides induce antibodies specific for these structures, and antibodies specific for triple-strand structures are induced by the triple-stranded polynucleotide complexes. 

On the basis of the above data it has been hypothesized that the conductivity of PFCM is due not to the contact between the filler particles but the current passes across the thin (less than 1 -2 microns) polymer interlayers. The conductivity arises when a spontaneous pressure exceeding the threshold value develops in the material. The overstresses apparently arise as a result of PP crystallization in the very narrow gaps between the filler particles [312], Since crystallization must strongly affect the macromolecular conformation whereas the narrowness of the gap and fixed position of molecules on the filler prevent it, the heat released in the process of crystallization must, in part, be spent to overcome this hindrance, whereby a local high pressure may arise in the gap. This effect is possible only where there are gaps of the size comparable with that of macromolecules. The small gap thickness will also hamper pressure relaxation, since the rate of flow from such a narrow clearance should be negligibly small. 

Alzheimer s Disease. Figure 1 A(3 monomers can self-associate to form dimers, trimers and higher oligomers. Globular structures of synthetic A(342 are known as A(3-derived diffusible ligands (ADDLs) (3-12-mers of A(3). These structures are similar to the smallest protofibrils and represent the earliest macromolecular assembly of synthetic A(3. The characteristic amyloid fiber exhibits a high beta-sheet content and is derived in vitro by a nucleation-dependent self-association and an associated conformational transition from random to beta-sheet conformation of the A(3 molecule. Intermediate protofibrils in turn self-associate to form mature fibers. 

The distribution of probabilities of macromolecular conformations in the globular state is well known [30]... 

Figure 17. Schematic lepiesentation of a lamellar polyethylene single ciystal. (a) and (b) show enlaiged features of its stnicture in (o) the zigzag conformation of the macromolecular chain inside the crystal in (b) a hypothetical model for the regular folding, drawn according to the calculation reported in ref. 224a.

Square root of the mean-square end-to-end distance of a linear macromolecular chain averaged over all conformations of the chain. For a freely jointed chain consisting of N segments each of length L, r Y =. ... 

The effects mentioned in the last sub-section are all local ones and do not depend upon the macromolecular nature of the material. A more important group of properties comprises those that are affected by the changes that LCB produces in the space-filling behaviour of polymer molecules under conditions in which they are free or relatively free from conformational constraints, that is in solution or in the melt, or in the amorphous state below 7. ... 

Any discussion of the conformation-dependent properties of macromolecular solutions must start with a consideration of the physical parameters required for quantitative description of the average conformation of the solute molecule in solution. As shown below, three parameters, N, s, and a, are necessary and sufficient for helix-forming homopolypeptides. Here N is the degree of polymerization of the polypeptide molecule, and s and tr have the meanings described in Chapter B. 

Macromolecular conformations describe the positions of the atoms that occur due to rotation about the single bonds in the main chain.2 Polymer chains in solution, melt, or amorphous state exist in what is termed a random coil. The chains may take up a number of different conformations, varying with time. Figure 15.4 shows one possible conformation for a single polymer chain. In order to describe the chain, polymer scientists utilize the root mean square end-to-end distance ((r2)m), which is the average over many conformations. This end-to-end distance is a function of the bond lengths, the number of bonds, and a characteristic ratio, C, for the specific polymer. 

Like the other macromolecular constituents of the cell (membranes, polynucleotides), the proteins of these extreme thermophiles must also be stable enough to resist heat-induced destruction of conformation and covalent structure. Since virtually all proteins (functional as well as structural proteins) exhibit dynamic properties to fulfill the demands of the living cell, their structure must provide a compromise between rigidity and flexibility, allowing not only stability but also conformational freedom for their biological function at the respective temperature. This means they are not only thermoresistant but require the higher temperature for optimal function. 

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