Dimers magnetic circular dichroism

Similarly, the analog 54 also forms a self-assembled dimer [54]2 in non-polar solvents. In the presence of pyridine, the dimer dissociates into the monomeric species 54 Py [53,54], Further addition of AgPF6 leads to the formation of a novel Ag-linked phthalocyanine dimer [54]2Ag PF6 (Scheme 5) [55]. On the basis of its electronic absorption and magnetic circular dichroism properties, it has been suggested that this dimer adopts a planar and nms-con formation. Addition of NH4C1, which can remove the silver ions as AgCl, regenerates the monomeric 54 Py. 

A novel tribenzotetraazachlorin fused with a Cgo unit and three 15-crown-5 moieties (compound 114) has recently been prepared by Kobayashi et al. [96], As expected, the C6o unit and the macrocyclic core show strong electronic interactions. As shown by UV-Vis, magnetic circular dichroism, and mass spectroscopic methods, this compound undergoes edge-to-edge dimerization in the presence of K+ ions, while for Na+ ions, they are simply trapped inside the crown ether voids of 114. 

Magnetic Circular Dichroism of Metal Atoms and Dimers Copper and Lead... 

The effects of the role of matrix birefringence, photoselection, and rotational diffusion on measuring the circular dichroism of chiral excited triplets embedded in a rigid matrix have been examined. The techniques described in this paper are applied to chiral dimer-like molecules in the binaphthyl and spirobifluorene series. Natural and magnetic circular dichroism spectra of selenofenchone provide evidence for a singlet-triplet component of the n - IT transition. ... 

A crystal structure of the all-tram isomer of [Cr2(gly)4(OH)2] has been reported.1162 Its low temperature magnetic susceptibility has been fitted to both the Van Vleck and modified Van Vleck models. The uncorrected model leads to, uef = 3.80BM with 2/= 8.4 cm-1 1162,1163,1164 with the inclusion of quadratic exchange 2/=7.4 cm-1.1162 Related studies of alanine,1153,1163 valine, phenylalanine, leucine,1163,1149 proline1166,1167 and histidine1168 complexes have appeared. The proline complex is unusual in that it is soluble in methanol and DMSO. Circular dichroism spectra have been measured the X-ray structure shows the complex to be the L-bms(N), L-tram(0) isomer.1166 More complicated dimers of unusual stoichiometry have been reported.1169... 

Peptoid stmcture has been smdied extensively in solution, primarily using circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopies, as weU as through computational modeling. The first report of peptoids already employed molecular mechanics simulations of peptoid monomers to generate preUminary Ramachandran plots. Additional early efforts by Hoflman and coworkers examining sarcosine dimers... 

A combination of circular dichroism, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, chemical crosslinking, and analytical ultracentrifugation studies showed that both the apo- and metallated derivatives of H21(31-mer) form two-stranded a-helical coiled coils in aqueous solution. Further characterization of these derivatives by EPR spin-label experiments helped to determine its three-dimensional backbone structure. In these studies, a Cys-21 mutant of the 31-mer coiled coil, H21/C21(31-mer), was prepared and labeled with a thiol-specific nltroxide spin label (MTSL = l-oxyl-2,2,5,5-tetramethyl-A -pyrroline-3-methyl-methanethiosulfonate) at position 21 of the peptide sequence which is the site of metal substitution in the ET heterodimer. Comparison of the low-temperature, dipolar-broadened spectrum of the spin-labeled dimer with those of magnetically dilute peptide samples yielded a backbone-to-backbone distance that was nearly identical to that of the GCN4 homodimer. Based on these results, computer modeling studies provided an estimate of the metal-to-metal distance in the ET heterodimer of m-m > 25 A. The electron-transfo properties of this system are now being studied by a combination of laser flash-quench and pulse radiolysis techniques. 

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