Handedness, determining

We thank Dr. D. M. Belnap (LSBR) for help with the procapsid handedness determination experiment Dr. E. Kocsis (OD-NIH) for help with the ROTASTAT program Drs. J.-M. Valpuesta and J. L. Carrascosa (Centro de Biotecnologia Molecular, Madrid) for kindly providing the images for Fig. 2g, j, and k and Dr. R. Wade (IBS) for providing computational facilities. 

In ellipsometry only quantities 1 and 2 (and sometimes 3) are determined. The absolute intensity or phase of the light doesn t need to be measured, which simplifies the instrumentation enormously. The handedness information is normally not critical. 

Like helical gears, worms and worm gears have handedness, which is determined by the direction of the angle of the teeth. The worm and worm gear must be the same hand in order to mesh correctly. 

Accurate experimental determinations require that not only the handedness of the produced light, but its exact degree of polarization, are known. The theoretical performance of an undulator may be in practice be degraded by magnetic defects, and the optical beam can be further depolarized by reflections along the beamline. Again, the dephasing on optical elements can in principle be... 

Before attempting to develop any theory correlating molecular to cholesteric handedness, one must be completely sure of the experimental data. A cholesteric phase is fully described by its handedness and pitch, and often also knowledge of the pitch variations with temperature is fundamental. In particular, the determination of the handedness is quite a delicate matter. Before discussing the methods currently used to determine handedness and pitch, the principal textures of the cholesteric phase must be briefly reviewed The planar or Grandjean textures are obtained in thin cells by rubbing the cell walls (with... 

As mentioned in the introduction, the first empirical correlation between the absolute configuration of dopants and the handedness of induced cholesterics was proposed in 1975.20 The first attempt to find a general correlation was a few years later Krabbe et al.58 related the sense of the cholesteric to a stereochemical descriptor of the dopant based on the effective volume of the substituents and listed many compounds following this rule. However, exceptions were described at that time,59 and, furthermore, this approach neglects the role of the structure of the nematic solvent in determining the sense of the cholesteric. It is well known that chiral compounds may induce cholesterics of opposite handedness in different nematics.60,61... 

The main factor in determining the handedness of the cholesterics induced by bridged 1,1 -binaphtliyls is the helicity (P or M) of the solute, and this observation is the basis of many configurational studies of chiral binaphthyls. All the homochiral (aP)-binaphthyls 15-19 have an M helicity of the core, and all induce, in biphenyl nematics, M cholesterics.65,75 By systematic structural variations of the covalent bridge, it is possible to obtain I J -binaphthalenes with dihedral angles ranging from 60° to 96° (see series 20-24) the handedness of the cholesteric phase always matches the helicity... 

In a recent paper, Krasnow and co-workers (120) applied a Rec A protein coating to DNA knots and catenanes to enhance visualization of the helical DNA segments and, in particular, to determine the absolute handedness of the knots. The Rec A protein is known to bind cooperatively to duplex DNA, forming a stiffened complex about 100 A in diameter in the presence of ATPase (121). 

Successful examples of the sort of correlations postulated above would add additional independent pieces of information for use in a combined strategy of noncrystallographic protein structure determination. Empirical regularities such as the handedness of crossover... 

This hydrogen-bond-driven large-scale structural organization has parallels in abiotic systems as well. For example, 1 1 mixtures of ra -l,2-diaminocyclohexane and C2 symmetric 1,2-diols self-assemble into well-defined supramolecular structures which have been characterized by X-ray diffraction analysis. The structures, some of which are stable to sublimation, are helical, the handedness of the helices being determined by the handedness of the 1,2-diamine [222]. 

A clear description of the RS system for naming stereoisomers, with practical suggestions for determining and remembering the handedness of isomers. 

Specific applications of FRET and FRET include observation of myosin movement (Fig. 19-14),157 measurement of distances between binding sites on tubulin,161 determining stoichiometry of subunit assembly in a y-aminobutyrate receptor of brain,162 association of proteins in peroxisomes,160 study of hydridization of deoxyribonucleotides,163 verifying the handedness of various forms of DNA,164 and other studies of DNA and RNA.164a b... 

However, it is possible to introduce two new factors into the problem of multilayer structure, either of which can influence structure in an interesting way. It is possible to replace the ordinary hydrocarbon chain by a perfluorinated chain and it is possible to dip over a subphase containing a trivalent cation. The perfluorinated carbon chain has a helical structure which produces a chain which appears to be approximately cylindrical. The handedness of a chain is determined randomly so that an equal number of right handed and left handed molecules exist in a given batch. 

Helices, like threads on screws, have a handedness or chirality. The handedness can be determined by curving the fingers of the right hand so as to follow the chain in its rotation around the axis of a drawing or model of the proposed helix. If the thumb points in the direction of the translation, then the helix is right handed, as is illustrated in Figure 2.29. If, instead, the left hand has to be used to achieve this relationship between rotation and translation, then the helix is left handed. 

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