Effect of temperature on the conformation of dibenzotropone adsorbed on montmorillonites

Abstract

The nature of the adsorption complex formed between dibenzotropone (OBT) and montmorillonite at elevated temperatures is strongly dependent on the interlayer cations. This was shown by electronic and IR spectra, by X-ray diffraction, and by study of the effects of gradual heating of the samples on these analyses. All samples exhibited significant red shifts of the electronic spectra of DBT into the visible range. These red shifts are attributed to two factors, both contributing to the enhancement of the tropylium planar character of DBT: hydrogen-bonding of acidic interlayer water to the carbonyl group, imparting positive charge to the tropone ring; and ~r interactions between the aromatic moiety and the oxygen planes. The position of the maximum was temperature-dependent for Cu-, Ni-, AI-and Fe-montmorillonites, for which heating (100 ~ under vacuum increased the red shift. The organic molecule assumes a planar conformation and is oriented parallel to the clay layers. IR spectra confirming this conformational orientation of DBT are discussed.The basal spacings of the DBT montmorillonite associations depend on the number of water and DBT sheets present in the interlayers. Layers with one or two sheets of DBT and with up to two sheets of water could be distinguished, leading to a maximum spacing of 20.4 ~.Adsorbent-adsorbate interactions induce spectral changes as compared to solution measurements [1, 2]. These spectral changes, which may include shifts in adsorption bands, changes in extinction coefficients, changes in band shape and the appearance or disappearance of bands, are a direct result of (a) the non-symmetry of the adsorbate environment as compared to a symmetrical solvation shell, resulting in adsorbate conformational changes and (b) chemical and physical irregularities and inhomogeneities of the surface, giving rise to special adsorbate-surroundings interactions not usually found in solution [3].Adsorption of organic cationic dyes by montmorillonite generally causes distinct shifts of the absorption maxima in the visible spectrum (metachromasy). Bergmann and O'Konski [4] attributed such shifts to dye-dye interactions on the surface of montmorillonite, a reaction similar to the aggregation of dye molecules in aqueous solutions. In these dye clusters ~ interactions between parallel aromatic moieties result in shifts in the electronic spectrum. Yariv and Lurie [5] showed, however, that spectra! shifts also occur with dye-montmorillonite complexes in which only mono-

The Dibenzosuberenone Scaffold as a Privileged Substructure: From Synthesis to Application

“…c-Met inhibitors are a class of small molecules that mediate the activation of several signaling pathways implicated in aggressive cancer phenotypes. The Katz group reported that certain 5H-benzo [4,5]cyclohepta[1,2-b]pyridin-5ones possess potent c-Met tyrosine kinase inhibitors both in vitro and in vivo. 278 MK-2461 (529) was the most potent compound and was efficacious in mouse tumor xenograft experiments.…”

“…The Grauer group evaluated the effect of temperature on the conformation of 1 adsorbed on montmorillonites. 5 The IR spectra of complexes show that two factors contributed to the enhancement of the tropylium planar character of 5-dibenzosuberenone (1): hydrogen-bonding of acidic interlayer water to the carbonyl group, imparting positive charge to the tropone ring, and π interactions between the aromatic moiety and the oxygen planes. They also reported that 5-dibenzosuberenone (1) absorbed on dry silica gel exhibits a very large red shift in its electronic spectrum due to the formation of the planar aromatic tropylium cation 5 ( Figure 2).…”