Crystal structures of molecules

Disordered O-H 0 intramolecular hydrogen bonds are not uncommon in crystal structures of molecules having cis-enol configurations, but without evidence for an order-disorder transition, they do not necessarily imply that proton transfer takes place in the crystalline state. 

A derivative that stands apart in this analysis is NDI 7, in which the carboxylic acids (or esters) have been replaced by amide groups, thus allowing the possibility of a new type of hydrogen bonding interaction. The crystal structure of molecule 7 was obtained by slow evaporation of an acetone solution and the analysis showed a complex network of molecules connected via a large number of hydrogen bonds. 

Fig. 10 (a) Crystal structure of molecule 7 and its hydrogen bonding interactions with four adjacent NDI molecules in the solid state, (b) Top view of the crystal packing of 7 indicating a complex network of hydrogen bonding interactions between amide units of 7... 

Molecule XI was included as an additional category 1 target midway through the 2004 blind test, after it was found that some information on the crystal structure of molecule VIII had been reported. Although most participants continued their predictions without using this experimental information, this molecule might not be considered a true blind test. 

The improvement in results with more accurate electrostatic models can also be seen by studying the blind test results in more detail. For example, the observed crystal structure of molecule VIII contains molecular tapes based on / (8) hydrogen bond dimers... 

Four crystal structures of molecules with aliphatic spacers (13b-e) and two crystal structures of molecules with the aromatic spacer -(CeUi)-, having 1,4- (13f-l) and 1,3-(13f-2) substitution, have been reported [25]. In the cases of 13b, 13c and 13f-2, amide-to-amide hydrogen bonds are not observed as the amide N-H is involved in N-H... N hydrogen bonds with pyridine-nitrogen to form a corrugated 2-D layer which has similar connectivity to the N-H...O 2-D layer (Scheme 7.4, Figure 7.16). The amide-carbonyl is involved in C-H... O contacts with neighbouring layers. 

The crystal structures of molecules 13d and 13e were found to form an isostructural hydrogen bonding pattern which resembles a /3-sheet. However, the conventional fi-sheet contains all N-H... O hydrogen bonds, whereas in the structures observed here. 

As the computational methods develop into reliable tools for predicting the most likely crystal structures of molecules, possible applications extend beyond the problem of structure solution. Even when a crystal structure of... 

Another way to learn of the likely molecular shapes for cellulose depends on extrapolation of the shapes that are found in crystal structures of molecules such as cellobiose (Chu and Jeffrey 1968), a-cellobiose complexed with Nal and HjO (Peralta-Inga et al. 2002), cellobiose octaacetate (Leung et al. 1976) and related compounds (French and Johnson 2004a). Similar, although less accurate. 

Molecule IX was not considered in the re-evaluation study with the DFT(d) method because its van der Waals correction was originally not parameterised for iodine. This parameterisation has now been carried out and the crystal structures of molecule IX have been optimised using the DFT(d) method. The experimental structure is found to be the lowest energy crystal packing alternative among all the predicted structures submitted by the 2004 blind test participants. 

Figure 1. The unit cell of crystal structure of molecule I (monoclinic space group = P21/n a = 9.435A b = 18.105A c = 14.373A gt= 90.00° 103.62° 3 90.00°).

Crystal structure of solids. The a-crystal form of TiCla is an excellent catalyst and has been investigated extensively. In this particular crystal form of TiCla, the titanium ions are located in an octahedral environment of chloride ions. It is believed that the stereoactive titanium ions in this crystal are located at the edges of the crystal, where chloride ion vacancies in the coordination sphere allow coordination with the monomer molecules. 

Fig. 18. Crystal structures of recent clathrate design (a) coordinatoclathrate between host (39) (Fig. 17) and / -butanol (host—guest hydrogen bonding in the shaded area) (b) perspective view of the hehcal inclusion channel formed by diol host (43) (Fig. 17 all except one host molecule are represented...

Many biochemical and biophysical studies of CAP-DNA complexes in solution have demonstrated that CAP induces a sharp bend in DNA upon binding. This was confirmed when the group of Thomas Steitz at Yale University determined the crystal structure of cyclic AMP-DNA complex to 3 A resolution. The CAP molecule comprises two identical polypeptide chains of 209 amino acid residues (Figure 8.24). Each chain is folded into two domains that have separate functions (Figure 8.24b). The larger N-terminal domain binds the allosteric effector molecule, cyclic AMP, and provides all the subunit interactions that form the dimer. The C-terminal domain contains the helix-tum-helix motif that binds DNA. 

Figure 13.15 Schematic diagram of the heterotrimeric Gap complex based on the crystal structure of the transducin molecule. The a suhunit is hlue with some of the a helices and (5 strands outlined. The switch regions of the catalytic domain of Gq are violet. The (5 suhunit is light red and the seven WD repeats are represented as seven orange propeller blades. The 7 subunit is yellow. The switch regions of Gq interact with the p subunit, thereby locking them into an inactive conformation that binds GDP but not GTP.

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