Hierarchically ordered spherical

Vast tabulations of 13C chemical shift data have been assembled in computer searchable form. These databases form the basis for 13C chemical shift prediction algorithms. For the most part, carbon chemical shifts can be calculated using what is referred to as a Hierarchically Ordered Spherical Environment (HOSE) code approach [28]. To calculate a given carbon s chemical shift, the influence of each successive spherical shell is applied to the starting chemical shift for that carbon to calculate its overall chemical shift. Typically, programs will calculate shifts for 3 or 4 layers, beyond which the effects of most substituents are negligible. The spherical layers surrounding the 23-position of strychnine are shown in Fig. 10.8. 

Consider a conventional encoding of chemical structures in C-NMR spectroscopy as introduced with the so-called HOSE code (hierarchically ordered spherical description of environment). Table 7.4 contains some symbol descriptions of this code. 

Figure 7.3 Spheres around a carbon atom bold face) as the basis for encoding the structure by the hierarchically ordered spherical description of environment (HOSE) code.

HOSE = hierarchically ordered spherical description of environment MCSS = maximal common substructure PEG = pulsed field gradient. 

The HOSE code (hierarchically ordered spherical description of environment) method was introduced by Bremser in 1978 and is widely used in commercially available spectrum prediction programs. The fundamental idea is to convert the connectivity table into a linear notation and to correlate this substructure description with the corresponding chemical shift value. 

The materials which have been mentioned here so far are predominantly shaped in planar films of hierarchical order. However, the synthesis of hierarchically structured particles is also highly desirable, as they might be further processed and used for the preparation of composite porous materials. Wu et al. showed the synthesis of raspberry-like hollow silica spheres with a hierarchically structured, porous shell, using individual PS particles as sacrificial template [134]. In another intriguing approach by Li et al. [135], mesoporous cubes and near-spherical particles (Fig. 10) were formed by controlled disassembly of a hierarchically structured colloidal crystal, which itself was fabricated via PMMA latex and nonionic surfactant templating. The two different particle types concurrently generated by this method derive from the shape of the octahedral and tetrahedral voids, which are present in the template crystal with fee lattice symmetry. 

The phase behaviour of biomimetic polypeptide-based copolymers in solution was described and discussed with respect to the occurrence of secondary structure effects. Evidently, incorporation of crystallisable polypeptide segments inside the core of an aggregate has impact on the curvature of the corecorona interface and promotes the formation of fibrils or vesicles or other flat superstructures. Spherical micelles are usually not observed. Copolymers with soluble polypeptide segments, on the other hand, seem to behave like conventional block copolymers. A pH-induced change of the conformation of coronal polypeptide chains only affects the size of aggregates but not their shape. The lyotropic phases of polypeptide copolymers indicate the existence of hierarchical superstructures with ordering in the length-scale of microns. 

Structural differences, together with differences in the synthesis, result in considerable variations of the physical properties of the PiPAAm structural isomers. Thus, PiPOz is a crystalline polymer [389] and is able to crystallize from water as a fibrous material when its solution is annealed for 24 h above Tip = 65°C [373, 387]. Coagulated PiPOz particles exhibit hierarchical structures with two levels of ordering that are micron-sized spherical particles consisting of fibrils wifh a cross-sectional diameter of about 30-50 nm and a length of several microns [373]. The densely packed microspheres formed in dilute solutions are uniform in size and shape and resemble a ball made of rattan. 

Jenekhe and coworkers showed that solution-cast micellar PPQ-Z -PS films consisted of multilayers with the hexagonally ordered arrays of spherical holes (Jenekhe and Chen, 1998, 1999). The hierarchical self-assembly approach to the microporous solids with a hollow core, a... 

A nanostructure should possess a regular geometric shape, which can be spherical, cylindrical, vesicular, tubular, and so forth. Also, the smallest dimension, such as the diameter of a cylinder, within a nanostructure should be less than 100 nm. A hierarchical stmcture is typically larger than a nanostructure. More importantly, hierarchical structures are formed through the multitier assembly of block copolymers, and have structural order at several length... 

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