Predicting self-assembly and structure in diluted aqueous solutions of modified mono- and bis-β-cyclodextrins that contain naphthoxy chromophore groups

Abstract

The water diluted solution behaviour of mono-and bis-b-cyclodextrin (mono-and bis-CD) derivatives, whose appended groups and inter-CD linkers contain a naphthoxy chromophore moiety, has been studied using steady-state and time-resolved fluorescence techniques, circular dichroism and molecular modelling.Mono-CD derivatives form non-covalent dimeric tail-to-tail supramolecular structures via the mutual partial penetration, through their primary sides, of axially oriented naphthoxy appended groups and the selfinclusion of the naphthoxy moiety is rather improbable. Non-covalent dimer formation may compete with any guest complexation. Nevertheless, these assemblies can be broken up by decreasing medium polarity or when the appended group is captured by macrorings such as cucurbit[7]urils or native bCDs. Bis-CD derivatives, however, do not exhibit self-association processes which were observed in the monoderivatives. This is because the presence of the bulky naphthoxy group in the spacer keeps the bCD cavities, which are capable of accommodating an external guest, away from each other. The dinaphthoxy group, in the bis-NbCD, was located in a quasi-parallel plane conformation between both CDs.

Reversible Light-Induced Dimerization of Secondary Face Azobenzene-Functionalized β-Cyclodextrin Derivatives

“…This bisignal can be attributed to an exciton coupling (EC), which occurs when two chromophores are close in the space and at least one of them exhibits relatively large molar absorptivity . It must arise from the intermolecular interaction between two azobenzene modules, supporting the formation of a face-to-face 3 - E -isomer dimeric species …”

“… 33 It must arise from the intermolecular interaction between two azobenzene modules, supporting the formation of a face-to-face 3 - E -isomer dimeric species. 34 …”

“…33 It must arise from the intermolecular interaction between two azobenzene modules, supporting the formation of a face-toface 3-E-isomer dimeric species. 34 Photoisomerization of the above 3-E solutions by irradiation at 365 nm resulted in concomitant disappearance of the EC bisignal in the ICD spectra. Instead, rather symmetrical positive and negative bands centered at 325 and 445 nm, ascribable to the 3-Z-isomer π → π* and n → π transitions, were detected (Figure 4, middle panel).…”

Enabling technologies and green processes in cyclodextrin chemistry

“…Recently the preparation of a large number of CD-derivatives by MW-assisted CuAAC regioselective cycloadditions has been described. A selected series of derivatives are depicted in Scheme 10 : CD-acryloyl derivative [ 60 – 61 ], β-CD/dye derivatives [ 31 , 62 – 64 ], CD-ionic liquid hybrids [ 65 – 66 ], CD-based iminosugar conjugates [ 67 ], water-soluble CD homo- and heterodimers [ 68 – 69 ], trimers [ 70 – 71 ] and oligomers [ 72 ] of α-, β- and γ-CD have all been successfully produced. This wide variety of compounds was obtained in good to excellent yield under MW irradiation (from 20 min to 3 h at 75 °C to 100 °C).…”

Dynamic Control of the Self-Assembling Properties of Cyclodextrins by the Interplay of Aromatic and Host-Guest Interactions

“…Most reported examples of CD-aromatic conjugates focus on single position-linked derivatives that keep considerable mobility, which limits accurate three-dimensional definition, however (Gamieldien et al, 2010). Covalently bridging CD building blocks with aromatic tethers has been advantageously exploited for preorganization purposes in some cases (Carmona et al, 2015; Sun et al, 2015; Gallego-Yerga et al, 2018). Alternatively, prototypes featuring a two-point connected aromatic component at either the primary (Yang et al, 2008; Le Gac et al, 2016; Ménand et al, 2016, 2018; Yan et al, 2017) or the secondary rim (Balbuena et al, 2007, 2013) in a monomeric CD derivative have been reported, allowing unprecedented control over the topological and supramolecular attributes.…”