Double-circular states

In order to obtain more information about the interactions between AmB and lipids at the molecular level, we chose to use spectroscopic measurements electronic absorption and circular dichroism (19). The particular structure of the AmB molecule, with several conjugated double bonds in the hydrophobic stretch, means that these techniques can be used to study its aggregation state under different conditions. Of the two, circular dichroism spectroscopy is the more sensitive way of detecting the aggregated forms of AmB. 

Schippers and Dekkers reported on the CD and circularly polarized fluorescence of 4,4-dideuterio-adamantan-2-one (85)193. The CD of 85 originates in transitions to a totally symmetric n -+ n excited state with double minimum potential in the C=0 out-of-plane bending mode. 

Equation [8] is the equation of an elliptic double cone (i.e., with different axes) with vertex at the origin (it will be a circular cone only for the case k = /). Thus, such crossing points are called conical intersections. Indeed, if we plot the energies of the two intersecting states against the two internal coordinates xx and x2 [whose values at the origin satisfy the two conditions and H1 j = H22 and H12 (= H21) = 0], we obtain a typical double-cone shape (see Figure 5). 

The structure of Te4 has been determined (102) from the crystal structures of Te4(AlCl4)a and Te4(AlaCl7)2. In both cases the Te4 ion lies on a center of symmetry and is almost exactly square planar. The tellurium-tellurium distance of 2.66 A is significantly shorter than the tellurium-tellurium distance of 2.864 A within the spiral chain in elemental tellurium (105). This is consistent with a structure exactly analogous to that for 804 + in which each bond has 25% double bond character. The Raman spectra of Te4 in solution and the solid state are analogous to those of 804 and 84 but shifted to lower frequency (Table VIII). The magnetic circular dichroism (75) and visible and... 

An 84 bp segment of a circular DNA in the relaxed state would contain eight double-helical turns, or one for every 10.5 bp. If one of these turns were removed, there would be (84 bp)/7 = 12.0 bp per turn, rather than the 10.5 found in B-DNA (Fig. 24-14b). This is a deviation from the most stable DNA form, and the molecule is thermodynamically strained as a result. Generally, much of this strain would be accommodated by coiling the axis of the DNA on itself to form a supercoil (Fig. 24-14c some of the strain in this 84 bp segment would simply become dispersed in the untwisted struc-... 

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