Conformation solid state

Fig. 3. The solid-state conformations of 3- uoro-chloramphenicol (6, R = NO2) showing the corresponding rotamers and schematics of the stabilising...

The solid state conformations of macromolecular phosphazene chains can be successfully modeled using short chain oligomers. 

Fig. 8. —Proposed Solid-state Conformation of l2s-ANs as Segments in Regular Regions of Heparin.348...

The oxepane and oxepanone derivatives 51 and 52 respectively, were made by allylindation of, or allylmagnesium bromide addition to, acyclic tetrakis(tetrahydrofuranyl) dialdehydes. The solid state conformation of 52 was determined by X-ray diffraction analysis <00JOC4303>. 

In order to obtain more information about the receptor-active conformation of muscimol, X-ray structure analysis, and ab initio quantum chemical studies have been applied to this compound (14). The flexibility of muscimol exclusively resides in the side chain (O-C-C-N bond) and a calculated potential energy curve for the rotation about this bond of muscimol in its zwitterionic form is shown in Fig. 3. These studies have demonstrated that in order for muscimol to obtain the conformation displayed by THIP, a conformational energy of 8.9 kcal/mol is required, which makes it less likely that the receptor-active conformation of muscimol corresponds to that of THIP. On the contrary, the conformation of THIP seems to mimic a high-energy conformation of muscimol as shown on the energy curve in Fig. 3, where the dihedral angles corresponding to the solid-state conformations of the muscimol zwitterion and the THIP cation are denoted. 

Fig. 3. Calculated potential energy curve for the rotation about the O-C-C-N bond in the muscimol zwitterion using HF/6-31+G ab initio quantum chemical calculations. Dihedral angles corresponding to the global energy minimum of muscimol and the solid-state conformations of the muscimol zwitterion and the THIP cation are denoted by arrows.

Methyl substituents at position 6 caused a change in the solid-state conformations of 4-phenyltetrahydro-l,3-oxazin-2-ones 80 and 81. In the 6-unsubstituted heterocycle 80, the 4-phenyl group was situated in an axial position, whereas 1,3-interactions arising from the presence of geminal methyl groups at position 6 of 81 led to an equatorial orientation for the 4-phenyl substituent <2006OBC2753>. 

Wawer, I. and Zielinska, A., C CP-MAS NMR studies of flavonoids. I. Solid-state conformation of quercetin, quercetin 5 -sulphonic acid and some simple polyphenols, Solid State Nucl. Mag., 10, 33, 1997. 

L. patella from Fiji contained patellins 1-5 (50-54) [82] and earlier, solution- and solid-state conformational studies were carried out on patellin 2 (51), and the structure was determined by X-ray analysis [83]. A Lissoclinum sp. from the Great Barrier Reef yielded patellins 3 (52), 5 (54) and 6 (55) and the heptapeptide trunkamide A (56) [82]. Compounds 50-56 were all identified by interpretation of spectral data and through use of Marfey s method to determine the absolute stereochemistry of the constituent amino acids [82]. A total synthesis of the proposed structure of trunkamide A (56) revealed that the structure... 

Solution- and solid-state conformations of tawicyclamides A (57) and B (58), proline-containing cyclic peptides from a Philippines specimen of L. patella, were determined by spectroscopic and X-ray analyses respectively [87]. Patellins 1-6 (50-55), trunkamide A (56) and the tawicyclamides A-B (57-58) all lack the oxazoline ring present in most other cyclic peptides isolated from the Lissoclinum genus [22]. 

Methods used to obtain conformational information and establish secondary, tertiary, and quaternary structures involve electron microscopy, x-ray diffraction, refractive index, nuclear magnetic resonance, infrared radiation, optical rotation, and anisotropy, as well as a variety of rheological procedures and molecular weight measurements. Extrapolation of solid state conformations to likely solution conformations has also helped. The general principles of macromolecules in solution has been reviewed by Morawetz (17), and investigative methods are discussed by Bovey (18). Several workers have recently reexamined the conformations of the backbone chain of xylans (19, 20, 21). Evidence seems to favor a left-handed chain chirality with the chains entwined perhaps in a two fold screw axis. Solution conformations are more disordered than those in crystallites (22). However, even with the disorder-... 

Figure 1.4. Space-filling models of cyclosporin A. (a) Solid-state conformation (X-ray analysis) (b) computer-generated conformation in apolar solvents (NMR measurements).

The situation for 172 was quite similar, but trends between conformers were reversed the solid-state conformer (chair-chair-boat) corresponded to the minor solution isomer of 184, whereas the minor solution isomer of 172 corresponded to the major all-chair conformer of 184. Imakura s desethano artemisinin 171 was found to exist in the all-chair arrangement by X-ray and exhibited a nontempera-ture-dependent proton NMR spectrum. MM2 studies of 171 showed that the all-chair conformer was 4-5 kcal/M more stable than the next lowest energy conformer, a chair-chair-boat, and were thus consistent with experimental observations. Studies to correlate conformer populations and energetics with antimalarial activities have not provided clear answers.141... 

The thermal decomposition of 7, 8 and 9 into fullerenic substructures is a milestone in fullerene formation and represents the first example of a macroscopic preparation of closed-shell carbon particles from acetylenic precursors. However, molecular allotropes of carbon, such as Cgo or higher fullerenes were not found among the decomposition products. It is interesting to note in this context that 10 [24], a structural isomer of 7 with a saddle-shaped solid state conformation, also shows thermal transformations, but in this case they occur at temperatures ca. 50 °C lower than those of 7 and are accompanied by a release of 50 kj mol-1 more energy. Although an insoluble carbonaceous material is formed during this process, further details of its nature are currently not known. 

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