Paracrystallinity

One of the insufficiently explored aspects of cellulose structure is the problem of paracrystallinity. Based on yearly structural investigations it was concluded that cellulose is a paraciystalline potymer because its lattice has a poor three-dimensional order (Kitaygorodslty et al., 1959). Howsman s model of cellulose structure included an expanded paracrystalline phase and gradual transition between fully amorphous and fully ciystalline phases along the 

Recent studies have shown that for the study of cellulose paracrystallinity, the combination of WAXS and deuteration methods is required (loelovich et al., 2010). Using these methods, it was found that the accessibility (A) of cellulose samples to deuteration exceeds the content of non-crystalline domains (H (Fig. 7.11). 

This means that part of crystallites, and namely their paracrystalline fraction, is also accessible to deuterium exchange. As was discovered, the paracrystalline fraction is located on the surface of crystallites as thin monomolecular layers having an average thickness of h = 0.4 nm. 

the cellulose is not paracrystalline pol5mier. Moreover, the paracrystallinity is not the separate phase of cellulose, but only thin surface layer of crystallites. 

The distorted paracrystalline layers are characterized by a specific volume Rp = 0.664 cm g and specific gravitypp = 1.51 g/cm. The degree of paracrystallinity, Xp, in the sample, as well as the paracrystallinity fraction of crystallites, p, can be calculated as follows  

Mixed oxides have the ability to form paracrystalline phases that represent an intermediate phase between the crystalline and the amorphous phase. Because of the disordered structure paracrystallinity causes defects that occur due to the inhibition of recrystallization and are initiated by the introduction of additional anions or molecules into the lattice structure. The formation of these deformed crystalline structures depends on the used synthesis method as well as the nature of the cation precursor. Thermal decomposition of the LDHs leads to the formation of the metastable phase that contains divalent and trivalent cations with densely packed configuration [2,32]. After the reduction, tri-valent ions are trapped inside the crystallites of divalent ions causing the formation of active centers. The centers that exhibit higher reactivity are believed to be formed on the surface of the paracrystalline crystals. After deactivation, the grain size of these mixed oxides increases due to the gradual removal of the defects in the crystal lattice [2]. 

---

The word particle has become so widely used ia the technical mbber and carbon black Hterature that it is convenient to retain the term when ia fact nodule is meant. The layer planes are curved, distorted, and of varyiag size. They also iatersect and interconnect one particle or nodule with its neighbors. This type of stmcture has been termed paracrystalline. It is obvious that iadividual particles do not exist ia carbon blacks, with the exception of thermal... 

Brosse et al. [41] modified isotactic polypropylene and other polyolefins by a cold plasma. In isotactic polypropylene, plasma treatment results in a polypropylene crystallization of paracrystalline or smectic form into a a-crystalline form. Further, the active films are susceptible to react with monomers in a postgrafting reaction. 

In this review, phenomena connected with the paracrystallinity as well as ordered liquids are not considered. 

Vincristine and vinblastine (vinca alkaloids) comprise another class of drugs that inhibit the polymerization of microtubules but do so by binding to the tubulin molecule at a site different from the colchicine site. Cultured cells exposed to high concentrations of vinca alkaloids develop intracytoplasmic paracrystalline aggregates of tubulin. These drugs are employed clinically in cancer chemotherapy to inhibit the growth of tumors composed of rapidly dividing cells. 

Nelson, D.G.A., Featherstone, J.D.B., Duncan, J.E and Cuttress, T.W. 1982 Paracrystalline disorder of biologieal and synthetic carbonate-substituted apatites. Journal of Denial Research 61 1274-1281. 

Wheeler, E. J. and Lewis, D. 1977 An X-ray study of the paracrystalline nature of bone apatite. 

RGB Murray. In TJ Beveridge, SF Koval, eds. Advances in Bacterial Paracrystalline Surface Layers. New York Plenum Press, 1993. pp 3-9. 

What is the difference between paracrystalline regions and crystalline regions ... 

It is worth to be noted that these definitions of first- and second-order distortions according to Warren-Averbach are model-free. From a linear or a quadratic increase of peak breadths it can neither be concluded in reverse that strain broadening, nor that paracrystalline disorder were detected. 

Distortions of the Second Kind and Linear Paracrystallinity. The idea of lattice distortions of the second kind goes back to the famous work of Zernike... 

On the other hand, lattice distortions of the second kind are considered. Assuming [127] that ID paracrystalline lattice distortions are described by a Gaussian normal distribution go (standard deviation ay, its Fourier transform Gd (.S ) = exp (—2n2ols2) describes the line broadening in reciprocal space. Utilizing the analytical mathematical relation for the scattering intensity of a ID paracrys-tal (cf. Sect. 8.7.3 and [127,128]), a relation for the integral breadth as a function of the peak position s can be derived [127,129]... 

Figure 8.21. Features of a ID correlation function, yi (x/L) for perfect and disordered topologies. L is the number-average distance of the domains from each other (i.e., long period). Dotted Perfect lattice. Dashed and solid lines Paracrystalline stacks with increasing disorder. a = — v/j / (1 — v/j) with 0 < v/j < 0.5 is a measure of the linear volume crystallinity in the material, which is either or 1 —...

If the statistical model of a paracrystalline stack is assumed, it turns out that the renormalization attenuates the influence of polydispersity on the position of the first zero. In general, the first-zero method is more reliable than the valley-depth method, although it is not perfect. Even the first-zero method is overestimating the value of V . The deviation is smaller than 0.05, if the found crystallinity is smaller than 0.35. If bigger crystallinities are found, the significance of the determination is... 

Figure 8.22. Testing the first-zero method for the determination of the linear crystallinity, V[, from the linear correlation function, yi (x/Lapp) with Lapp being the position of the first maximum in yi (x) (not shown here - but cf. Fig. 8.21). Model tested Paracrystalline stacking statistics with Gaussian thickness distributions. The interval of forbidden zeroes is shown. An additional horizontal non-linear axis permits to determine the linear crystallinity directly. A corresponding vertical axis shows the variation of the classical valley-depth method ... 

If other statistical models of polydispersity should prove more appropriate than the paracrystalline stack, validations of the first-zero method may be carried out in analogy to the one presented here. 

Figure 8.42. ID structural models with inherent loss of long-range order, (a) Paracrystalline lattice after HOSEMANN. The lattice constants (white rods) are decorated by centered placement of crystalline domains (black rods), (b) Lattice model with left-justified decoration, (c) Stacking model with formal equivalence of both phases (no decoration principle)... 

Figure 8.44. Effect of paracrystalline distortions on a series of reflections in a scattering diagram after compensation of the decay according to POROD s law (lattice factor (1 /N) Z 2). The quadratic increase of integral breadths of the reflections is indicated by boxes of equal area and increasing integral breadth. L is the average long period...

Analytical Expressions for Lattice Models. Concerning the aforementioned paracrystalline lattice, an analytical equation has first been deduced by Hermans [128], His equation is valid for infinite extension. Ruland [84] has generalized the result for several cases of finite structural entities. He shows that a master equation... 

FIGURE 1-7 A lipofiiscin granule from a cortical neuron shows membrane-bound lipid (dense) and a soluble component (gray). The denser component is lamellated. The lamellae appear as paracrystalline arrays of tubular profiles when sectioned transversely (arrow). The granule is surrounded by a single-unit membrane. Free ribosomes also can be seen. X96,000. 

It is worth noting that in polymer structures the various kinds of long-range positional order of the equilibrium positions of the structural elements may be lost after not too big numbers of repetitions owing to the presence of lattice distortions (different from the thermal one), which have been called distortions of the second kind. According to Hosemann and Bagchi,171 these forms are called paracrystalline modifications. 

Harris JR. The production of paracrystalline two-dimensional monolayers of purified protein molecules. Micron 1982 13 147-168. 

Paracrystallinity, Cu/ZnO/AIjOj, 31 295 2"-Paracyclophanes, 32 453 Paracyclophanes, macrocycles, 29 206-208 Paraffin, see also Alkanes alkylation, 10 165, 27 98 carbon selectivity, bed residence time effects, 39 249-250 cracking, 39 283 cyclization, 28 295 rates, 28 301, 302 double cyclization, 28 312-314 in exhaust gases, 24 66, 67 hydrogenolysis, 30 43-44 hydroisomerization, 39 183 oxidation, 32 118-121 solubility enhanced hydrogeolysis, 39 285 Parahydrogen conversion rate correlations, 27 48-50... 

Fig. 6.29 S(Q,t)/S(Q) measured at the IN15 on a 156 mg/mL apoferritin solution with 0.01 mM salt. Despite the paracrystalline order no permanent restriction of motion is present as indicated by the virtually full decay of the relaxation curve (Q=0.09 A ). (Reprinted with permission from [333]. Copyright 2003 Elsevier)...

---