Photophysical and Structural Features of Inclusion Complexes with Fluorescent Dyes

Abstract

The synthesis of a new watersoluble b-cyclodextrin CD-St, with seven steroidic naphthalene chromophores linked to the primary rim, is reported together with the photophysical and structural features of its inclusion complexes with merocyanine and oxazine fluorescent dyes. These complexes were formed in a buffer at pH 10. At this pH the cyclodextrin is 14 times negatively charged since each chromophore bears two carboxylic groups. No excimer emission was detected, as expected from the design principles. Two complexes can be formed with stoichiometries 1:1 and 2:1 (CD:dye) for both dyes. The respective association constants were determined. In the 2:1 complexes, the cyclodextrin secondary rims are facing each other.Such complexes are outstanding artificial antennae with 14 chromophores surrounding an energy acceptor. Comparison was made with another (previously reported) water-soluble b-cyclodextrin CD-NA with seven naphthalene chromophoresÐalso linked to the primary rimÐbut bearing only one carboxylic group each. In fact, CD-NA only forms 1:1 complexes with the same dyes. The difference in complexing ability of CD-NA and CD-St is discussed.

Multichromophoric Cyclodextrins. 8. Dynamics of Homo- and Heterotransfer of Excitation Energy in Inclusion Complexes with Fluorescent Dyes

“…Moreover, the fluorescence emission arising from the dye exceeds the value expected from direct excitation of the dye. In line with the preceding paper, these experiments confirm: (i) the formation of complexes between CD-St and the dyes; (ii) the process of energy transfer occurring from CD-St to the dye.

4 Corrected fluorescence spectra of CD-St/Dye mixtures (λ exc = 320 nm) as a function of the dye concentration.

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“…In the case of Ox 725, the data were first analyzed leaving β and I ∞ as floating parameters. The value found for β was (2.4 ± 0.1) × 10 10 , which is in reasonable agreement with the value of 5 × 10 10 obtained by a more accurate method described in the preceding paper . The asymptotic value I ∞ was found to be very close to zero within experimental error which led us to the important conclusion that the energy transfer efficiency is close to 1.…”

“…For this investigation, excimer formation between antenna chromophores should be avoided because excimers act as energy traps in the excitation energy hopping process, and energy transfer to an acceptor included in the cavity can occur from both monomer and excimer forms of the antenna chromophores. With this in mind, a new water-soluble β-cyclodextrin CD-St was synthesized; the synthesis together with the photophysical and structural features of its inclusion complexes with a merocyanine dye (DCMOH) and an oxazine dye (Oxazine 725) (see Figure ) were reported in the preceding paper of this series . The formation of two complexes, CD-St:Dye and (CD-St) 2 :Dye, was observed and the constants for the following equilibria were found to be 10 4 and 10 7 , respectively; therefore, at micromolar concentrations of CD-St and the dyes, the formation of 1:1 complex can be ignored, and only the 2:1 complex (Figure ) will be considered in the present work.…”

Binding Ability and Assembly Behavior of β-Cyclodextrin Complexes with 2,2‘-Dipyridine and 4,4‘-Dipyridine

“…Macrocyclic sugars called cyclodextrins ( α -, β -, and γ -CDs) could form stable inclusion complexes with a variety of guest molecules, in which the guest molecules are included within the hydrophobic cavity of CDs. − A commonly accepted model for complex formation suggests that the complex is formed when a suitable hydrophobic molecule displaces water from the cavity. , Several recent works reported the solution studies of CD upon complexation with amino acids, , peptides, , dyes, , steroids, − and so on, using different methods such as fluorescence spectrometry, UV−vis spectrometry, and titration microcalorimetry. These studies not only were directed toward an understanding of binding behavior and molecular/chiral recognition of CDs but also provided valuable information on the effects of changes in functionality and chirality of guests.…”

Molecular Recognition Studies on Supramolecular Systems. 32.1 Molecular Recognition of Dyes by Organoselenium-Bridged Bis(β-cyclodextrin)s

“…Extensive studies on molecular recognition by native and modified cyclodextrins as molecular receptors have documented that the truncated corn-shaped hydrophobic cavity of cyclodextrins can selectively bind diverse substrates to form host−guest complexes or supramolecular species, − which provide an excellent model system mimicking the substrate-specific interaction of enzymes − As a new family of cyclodextrin derivatives, bridged cyclodextrin dimers are known to greatly enhance the original molecular binding ability of native cyclodextrins through the cooperative binding of dual hydrophobic cavities located in a close vicinity. Consequently, a number of cyclodextrin dimers have been synthesized to investigate the inclusion complexation behavior which is significantly different from that of the monocyclodextrin counterparts.…”