Significant structures

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. 

Another significant structural effect that inrparts high nucleophilicity is the alpha effect. It is observed that atoms which are directly bonded to an atom with one or rhore unshared pairs of electrons tend to be stronger nucleophiles than would othermse be expected. Examples in Table 5.7 include H02, which is more nucleophilic than HO , and... 

The retrosynthetic operations that we have addressed thus far have not resulted in significant structural simplification. After all, intermediate 6 still possesses a linear fusion of four rings and six contiguous asymmetric carbon atoms. But, nevertheless, intermediate 6 could potentially be derived in one step from intermediate 8, a polyunsaturated monocyclic compound containing only one stereogenic center. Under conditions that would be conducive to a heterolytic cleavage of the C-OH bond in 8, it is conceivable that the resultant tertiary allylic carbonium ion 7 would participate in a... 

The smaller cluster ions 83", 84" and 85 + have been examined by Zakrzewski and von Niessen at the HF/6-3H-G level [82]. The lowest cationic states are predicted to be 82, and A" for 83 (Cyv), 84 (I>4h) and (Cs), respectively. The ionisation processes may result in significant structural relaxation leading to the sequence of states different from that of the vertical states. The calculated lowest adiabatic ionisation energies, using the GI method with a very large ANO basis set, are 9.53, 8.05, and 8.20 eV for 83, 84 and 85 , respectively. 

In this method the liquid of Interest Is sheared between two seml-Inflnlte reservoirs. The reservoirs contain particles Identical with the ones In the main liquid slab and at the same density. The reservoir particles and the particles of the main liquid slab Interact by exerting forces on each other but they do not mix because they are separated by Impenetrable hard walls extending on the yz plane. Therefore, the reservoirs are fluld-llke and confine the main liquid slab In the x direction. Despite appearances, the main liquid slab behaves like a bulk fiuld because the reservoirs Induce no significant structure In the confined liquid. Furthermore, the hard Impenetrable reservoir walls are not to be confused with the fiat 10-4 LJ pore walls mentioned In the previous subsection. 

Corey EJ, Wipke WT, Cramer RD HI, Howe WJ. Techniques for perception by a computer of synthetically significant structural features in complex molecules. J Am Chem Soc 1972 94 431-9. 

Selective oxidation of p-xylene to terephthaldehyde (TPAL) on W-Sb oxide catalysts was studied. While WO3 was active in p-xylene conversion but non-selective for TPAL formation, addition of Sb decreased the activity in p-xylene conversion but increased TPAL selectivity significantly. Structure change was also induced by Sb addition. Evidences from various characterization techniques and theoretical calculation suggest that Sb may exist as various forms, which have different p-xylene adsorption property, reactivity toward p-xylene and TPAL selectivity. Relative population of each species depends on Sb content. 

In the usual chemical formulas written for chain polymers the sue-cessive units are projected as a co-linear sequence on the surface of the sheet of paper. This form of representation fails to convey what is perhaps the most significant structural characteristic of a long polymer chain, namely, its capacity to assume an enormous array of configurations. This configurational versatility is a consequence of the considerable degree of rotational freedom about single bonds of the chain. In the simple polymethylene chain, for example, the conventional formula... 

In order to obtain more structural information about the molybdenum species in Mo/NaY, EXAFS measurements of the cluster 1 and Mo/NaY were carried out. The Fourier transforms of the EXAFS data are shown in Figure 2. Structural parameters (Table 3) showed no change of the Mo-0, Mo-S and Mo-Mo distances, suggesting that there is no significant structural difference between the cluster 1 and the molybdenum compound in the Mo/NaY. From these EXAFS parameters and the UV-visible spectra, it is considered the structure of cluster 1 remained vinually intact after ion exchange. 

The in vivo antihistaminic activity results indicate that all test compounds protected the animals from histamine-induced bronchospasm significantly. Structural activity relationship (SAR) studies indicated that different alkyl substituents on the first position of the triazoloquinazohne ring exerted varied biological activity. 

The organization of chemokine families based on the cysteine sequence has functional significance. Some human chemokines can compete for binding and activation of receptors with other intrafamily chemokines. This raised the possibility that significant structural differences in chemokine-receptor interactions... 

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