Of oriented samples

In spite of the presence of ECC, the sample exhibiting a domain structure remains unoriented on the macroscopic level. Figure 3 c shows a great difference in the structures obtained, if molecular orientation exists and if hydrostatic compression is applied. Although the method of hydrostatic compression of the melt is of paramount importance from the scientific view point just for samples crystallized under pressure it was possible to prove unequivocally the existence of ECC), it does not allow a direct preparation of oriented samples of high strength (they are brittle and readily crumble to powder under minimum strain). However, the material obtained in this way can probably serve as a semi-finished product for further technological treatment that would improve its mechanical properties. 

FIG. 33 X-Ray Diffraction Patterns of Ammonium Dodecane 1-Sulfonate. 2-D (a) and 3-D plots (b) of oriented samples. Both pictures show the presence of a nonordered smectic phase, since the diffuse, weak, wide-angle diffraction indicates only an average distance between the molecules and the sharp, intense small angle reflections a very well defined layer distance. The reflections are perpendicular to each other, so the structure should correspond to an orthogonal smectic A type. The pictures were obtained using an x-1000 area detector from Siemens. 

The applications of polarized x-ray absorption spectroscopy (PXAS) for structure determination in inorganic and bioinorganic systems are discussed. PXAS studies of oriented samples add angular detail to the information obtained from x-ray absorption edges and from EXAFS. In some cases, PXAS can be used to determine molecular orientation. In other cases, PXAS can be used to infer the details of electronic structure or of chemical bonding. Some of the potential future applications of PXAS are discussed. 

X-ray studies of oriented samples of LC polymers are therefore the main method for the structural study of smectic mesophase, as well as for any other structural type of LC polymers. 

Up to now we have considered the CP film as an amorphous, homogeneous and isotropic medium. However, CPs are intrinsically anisotropic since the 7r-electrons are delocalized along the macromolecule backbone. An anisotropic optical response, typical of oriented samples, is extremely important both for fundamental science (e.g., comparison with theoretical predictions) and for technological reasons (polarized emission is recommended in displays [55,56]). The orientation process for conjugated polymers is very difficult and several approaches have been used to remove the typical random-coil conformation of CP and to induce the extended aligned conformation. It is not the aim of this article to review all orientational techniques used with CPs. However, it should be mentioned that very high degrees of orientation have been achieved... 

The CD and IR spectra of oriented samples also agree with the view that the reaction center contains considerable a-helical structure, and that the helices are oriented (on the average) approximately normal to the chromatophore membrane [114], The observation that the amino-terminal end of the L subunit can be labeled from the cytoplasmic side of the membrane [115] identifies the bottom of Fig. 3 with this side of the membrane, and the top of the figure with the periplasmic side. 

Sandos, C. R., and Landis, G. C. (1994) Facile Acquisition and Assignment of Oriented Sample NMR Spectra for Bilayer Surface-Associated Proteins. J. Am. Chem. Soc. 116, 6470-6471. 

Another way to obtain information about molecular structure is by means of polarized IR radiation (see Section 3.3.10). This method has the potential advantage of providing the direction of the vibrating dipole. There are also disadvantages some kind of oriented sample is... 

In this section, solid-state NMR of fibrous proteins is reviewed. For solid-state NMR studies of oriented samples, orientation-dependent nuclear spin interaction tensors serve as probes with which the relative orientations of specific bond vectors can be determined as described in Chapter 8. 

The location of the binding site can yield distance constraints to filter possible solutions and this is implemented in our procedure. An intermolecu-lar residue-residue interaction is defined if any pair of atoms is closer than a 4.5 A cut off. This cut off considers the probable error in conformation of any predicted complex. One feature of the Fourier correlation method implemented in FTDOCK, is that biological constraints on one molecule cannot be used to reduced the initial search. For any orientation of the movable molecule, it is placed at every translational position with respect to the static molecule. However, if constraints were available for both molecules, the range of orientations sampled by the movable molecule could be restricted. 

In addition to swelling chlorite (vermiculite) there is also in association with mixed-layer minerals of the ilUte-montmorillonite type (sometimes Fe-bearing) a chlorite that is unstable on thermal treatment. The diffractogram of oriented samples is char-... 

Trioctahedral lllite. This is observed in all argillaceous fractions. The characteristic feature of this mineral in the terrigenous-halitic complex is its heterogeneity. In diffractograms of oriented samples the peak occurs in the range 10-10.3 A. Based on spectral analyses the hydromicas may be classed as Fe-illites. 

Although NMR-based applications on dipolar coupling have been mainly associated with solid-state NMR or NMR of oriented samples, they have been recently applied to solution NMR for studying macromolecular structure and function in an aqueous solution [20,21]. The dipolar coupling describes a through-space interaction that arises between any two magnetically active nuclei. It depends upon the distance between two atoms, which is constant for the nuclei connected by covalent bonds such as or and the orientation of the connecting vector with respect... 

The principle behind these techniques is that certain modes of vibration can occur only for either the syndiotactic or the isotactic version of a particular polymer. Figure 4.3 shows the IR spectra of isotactic and two forms of syndiotactic polypropylene which illustrate this. The spectra are of oriented samples and the reason for the differences between the spectra for the two directions of polarisation is explained in chapter 11. They are shown here merely to illustrate how different the spectra for the different tacticities can be. 

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