Structure crystallographic

The amount of computation necessary to try many conformers can be greatly reduced if a portion of the structure is known. One way to determine a portion of the structure experimentally is to obtain some of the internuclear distances from two-dimensional NMR experiments, as predicted by the nuclear Over-hauser effect (NOE). Once a set of distances are determined, they can be used as constraints within a conformation search. This has been particularly effective for predicting protein structure since it is very difficult to obtain crystallographic structures of proteins. It is also possible to define distance constraints based on the average bond lengths and angles, if we assume these are fairly rigid while all conformations are accessible. 

Although experimental studies of DNA and RNA structure have revealed the significant structural diversity of oligonucleotides, there are limitations to these approaches. X-ray crystallographic structures are limited to relatively small DNA duplexes, and the crystal lattice can impact the three-dimensional conformation [4]. NMR-based structural studies allow for the determination of structures in solution however, the limited amount of nuclear overhauser effect (NOE) data between nonadjacent stacked basepairs makes the determination of the overall structure of DNA difficult [5]. In addition, nanotechnology-based experiments, such as the use of optical tweezers and atomic force microscopy [6], have revealed that the forces required to distort DNA are relatively small, consistent with the structural heterogeneity observed in both DNA and RNA. 

Huber, R., et al. Crystallographic structure studies of an IgG molecule and an Fc fragment. Nature 264 ... 

Hogle, J.M., Maeda, A., Harrison, S.C. Structure and assembly of turnip crinkle virus. I. X-ray crystallographic structure analysis at 3.2 A resolution. /. Mol. Biol. 

The simplest situation is one in which a planar substrate lacks any crystallographic structure. Then the confined fluid is homogeneous and isotropic in transverse (x,y) directions. All off-diagonal elements of T vanish, Txx = Tyy = T, and Eq. (5) simplifies to... 

While the smooth substrate considered in the preceding section is sufficiently reahstic for many applications, the crystallographic structure of the substrate needs to be taken into account for more realistic models. The essential complications due to lack of transverse symmetry can be dehneated by the following two-dimensional structured-wall model an ideal gas confined in a periodic square-well potential field (see Fig. 3). The two-dimensional lamella remains rectangular with variable dimensions Sy. and Sy and is therefore not subject to shear stresses. The boundaries of the lamella coinciding with the x and y axes are anchored. From Eqs. (2) and (10) one has... 

X-Ray crystallographic structure of a Ti2(dibenzyltartamide)2(OiPr)4 species has been obtained. 

Aquaporins. Figure 1 (a) The hour-glass model. The scheme depicts the six transmembrane helices (H1-H6), the connecting loops A-E, including the helical parts of loops B ((H)B) and E (E(H)), and the conserved NPA (Asn-Pro-Ala) motif of canonical aquaporins. (b) Structure of the conserved NPA motif region, flanked by the indicated helices, (c) Crystallographic structure of AQP1 tetramer. The four water pores in atetramer are indicated [1]. 

It should be stressed that in the case of pc-Pt electrodes the crystallographic structure of the surface probably exerts a very pronounced influence, so that the experimental pzc and pztc values do not correspond to the condition ffpc = 0. 

Almost all that is known about the crystal face specificity of double-layer parameters has been obtained from studies with metal single-crystal faces in aqueous solutions. Studies in nonaqueous solvents would be welcome to obtain a better understanding of the influence of the crystallographic structure of metal surfaces on the orientation of solvent molecules at the interface in relation to their molecular properties. 

Our laboratory has planned the theoretical approach to those systems and their technological applications from the point of view that as electrochemical systems they have to follow electrochemical theories, but as polymeric materials they have to respond to the models of polymer science. The solution has been to integrate electrochemistry and polymer science.178 This task required the inclusion of the electrode structure inside electrochemical models. Apparently the task would be easier if regular and crystallographic structures were involved, but most of the electrogenerated conducting polymers have an amorphous and cross-linked structure. 

An interesting mass spectral study of 17 mono- and dflialogenoquinoxahnes, some bearing methyl groups, has been reported the X-ray crystallographic structure of hexachloroquinoxaline has been measured. ... 

Carbocations are intermediates in several kinds of reactions. The more stable ones have been prepared in solution and in some cases even as solid salts, and X-ray crystallographic structures have been obtained in some cases. An isolable dioxa-stabilized pentadienylium ion was isolated and its structure was determined by h, C NMR, mass spectrometry (MS), and IR. A P-fluoro substituted 4-methoxy-phenethyl cation has been observed directly by laser flash photolysis. In solution, the carbocation may be free (this is more likely in polar solvents, in which it is solvated) or it may exist as an ion pair, which means that it is closely associated with a negative ion, called a counterion or gegenion. Ion pairs are more likely in nonpolar solvents. 

The positions of the oxygen atoms have been tentatively assumed but they are in agreement with the structure of the precursor molecule S7O and with the Raman spectrum of S7O2. No crystallographic structure determination has been published for S7O2 yet. However, Jones [68] investigated 14 cyclic... 

The crystallographic structure of the D. vulgaris protein has been reported by Lindley and collaborators (132). The structure was solved to a resolution of 1.7 A. The major findings are consistent with most of the conclusions derived from the Mossbauer work done in the D. desulfuricans protein. The protein was found to contain two distinct clusters of the same nuclearity. Also, one cluster has a mixed N, O, S ligand environment, while the other has a regular iron-sulfur core... 

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