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Conformational calculations

Polymers can be crystalline, but may not be easy to crystallize. Computational studies can be used to predict whether a polymer is likely to crystallize readily. One reason polymers fail to crystallize is that there may be many conformers with similar energies and thus little thermodynamic driving force toward an ordered conformation. Calculations of possible conformations of a short oligomer can be used to determine the difference in energy between the most stable conformer and other low-energy conformers. [Pg.311]

Crippen, G. M. Distance Geometry and Conformational Calculations, Research Studies Press, Wiley, New York, 1981. [Pg.303]

Similarly to the fully labelled stars [150], the peak structure in the generalized Kratky plot for core and average contrast conditions is also quite well reproduced by calculating S(Q) on the basis of an ideal (v = 1/2) star conformation. The swollen conformation calculations predict a more diffuse peak in both cases. [Pg.103]

As is well known, the conformational properties of cyclohexane form one of the classical problems of conformational analysis (104) and have been the subject of numerous earlier computational studies (11, 41, 82,105-107). Cyclohexane shows a variety of very interesting conformational properties which make it an ideal candidate for illustrating key features of conformational calculations. [Pg.203]

Crippen, G.M. Distance geometry and conformational calculations. In Chemometrics Research Studies, Vol. 1, Bawden, D. (ed.) John Wiley, Chichester, UK, 1981. [Pg.22]

In terms of the visual clarity of its presentation, biochemistry has still to catch up with anatomy and physiology. In this book, we sometimes use simplified ball-and-stick models instead of the classical chemical formulae. In addition, a number of compounds are represented by space-filling models. In these cases, we have tried to be as realistic as possible. The models of small molecules are based on conformations calculated by computer-based molecular modeling. In illustrating macromolecules, we used structural infor-... [Pg.473]

Isotactic poly(methyl methacrylate), also, is an intricate case, resolved only after a 20-year debate. The repetition period along the chain axis is 10.40 A corresponding to S monomer units the entire cell contains 20 monomer units (four chains). At first, the stmcture was resolved as a 5/1 helix (183) with = 180° and 62 — 108° but no reasonable packing was found using this assumption. Further conformational calculations showed that helices like 10/1 or 12/1 should be more stable than the 5/1 helix. The structure was solved by Tadokoro and co-workers (153b) who proposed the presence of a double helix. Two chains, with the same helical sense and the same direction but displaced by 10.40 A one from the other are wound on each other, each chain having 10 monomer units per turn [i(10/l)] and a 20.80-A repeat period. As a result, the double helix has a 10.40-A translational identity period, identical to that found in the fiber spectmm. The conformational parameters are Of = 179° and 2 = -148°. Energy calculations indicate that the double helix is more stable by 4.4 kcal per-mole of monomer units than two isolated 10/1 helices, a result that is in line with the well-known capacity of this polymer to form complexes in solution (184). [Pg.52]

Recent conformational calculations made on the 2,4-bis(2-naphthyl)-pentanes 1371 gave results similar to the diphenylpentanes. The tt state (EFS) in the 2-naphthyl meso isomer was found to be 2.3 kcal/mole higher than the tg, g+t state, consistent with a larger repulsion between naphthyl rings than for phenyl rings. It is apparent from molecular models, and has been confirmed by Seki et al.138,139), that the... [Pg.57]

Energy diagrams for bond rotation in 2,2,4,4-tetramethylpentane, 2,2,4,4,6,6-hexamethytheptane, and 2,2,4,4,6,6,8,8-octamethylnonane are generated in a completely a priori manner. A relatively simple conformational model gives a good representation of the conformations calculated, and permits a statistical mechanical calculation of the characteristic ratio. [Pg.60]

A semiempirical force field is constructed for the calculation of conformational potential energies of unstrained, acyclic, aliphatic aldehydes and ketones, taking solvent effects into consideration. Detailed conformational calculations for fitting and testing the necessary parameters are done. The results are incorporated into a RIS scheme for polylmethyl vinyl ketonels. [Pg.188]

Conformational calculations are carried out on poly(di-n-hexylsilanes). The most significant finding from the energy calculations is that the a -trans conformation is not the lowest energy structure for the symmetrically alkyl-substituted silane polymers. A helical structure is preferred for the isolated molecule. [Pg.411]

N 031 "Location of Proline Derivatives in Conformetional Space. I. Conformational Calculations, Optical Activity and NMR Experiments ... [Pg.425]

Suppose one double helical turn of a superhelical DNA molecule changes from a B conformation to the Z conformation. Calculate the approximate changes in (1) the linking AL/c, (2) the writhe AWr, and (3) the twist A Tw of the DNA as a result of this transition. Show your calculations and explain your answers. For this problem assume that the B form of DNA has 10.4 bp per turn. Why is the B—> Z transition favored in naturally occurring supercoiled DNA ... [Pg.279]

The computer input for such a conformational calculation consists of (1) the set of atomic coordinates, (2) the bonds about which rotation... [Pg.187]

A trisaccharide fragment of the jV-type oligosaccharides (oc-D-Man-(l-3)-p-D-Man-(l-4)- 3-D-Glc.VAc) including the central P-D-Man has been obtained as single crystals. The dihedral angles of the glycosidic bonds which were obtained from an X-ray analysis are summarized in Fig. 9 [ 137]. This conformation is very closely related to the conformations calculated or determined experimentally in solution by NMR... [Pg.163]

Fig. 15. Stereo plots of the space filling models of the two conformations calculated for the biantennary octasaccharide, (3-D-Gal-(l-4)-P-D-GlcA,Ac-(l-2) (-D-Man-(l-6)-[P- >(- al-(l-4)-[3-D-GlcAA,c-(l-2)-a-D-Man-(l-3)-]-p-D-Man-(l-4)-p-D-GlcAAc, of the A -type oligosaccharides using the GESA program. The reducing end is to the right... Fig. 15. Stereo plots of the space filling models of the two conformations calculated for the biantennary octasaccharide, (3-D-Gal-(l-4)-P-D-GlcA,Ac-(l-2) (-D-Man-(l-6)-[P- >(- al-(l-4)-[3-D-GlcAA,c-(l-2)-a-D-Man-(l-3)-]-p-D-Man-(l-4)-p-D-GlcAAc, of the A -type oligosaccharides using the GESA program. The reducing end is to the right...
The polysaccharides from proteoglycans have been very extensively analyzed by means of X-ray and CD spectroscopy [209, 210]. This section will review only the newer developments based on NMR and conformational calculations. [Pg.196]


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See also in sourсe #XX -- [ Pg.478 ]




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Ab initio calculations on PAHTC conformations

Calculated Conformational Energies

Calculated Conformational Energy Cutoff Values

Calculated conformational

Calculated conformational energies comparison

Calculation of Conformational Parameters

Calculations, and conformations

Chain conformation energy calculations

Conformation calculating energy

Conformation energy calculations

Conformation energy, theoretical calculation

Conformational aspects calculations

Conformational calculations of charged polysaccharides

Conformational energy calculations

Conformational energy calculations isotactic/syndiotactic polymers

Conformational populations, calculated

Gauche conformation calculations

HSEA calculations, conformation

HSEA calculations, conformation oligosaccharides

Helical conformation conformational energy calculations

Linkage conformations, calculated

Minimum energy conformations molecular mechanics calculation

Planar conformation calculations

Poly conformational energy calculations

Polypeptides, calculations of conformations

Solid-state shifts conformational calculations

Trans conformation calculations

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