Complexation of 4‐dimethylaminoazobenzene with various kinds of cyclodextrins: Effects of cyclodextrins on the thermal cis‐to‐trans isomerization

Abstract

On the basis of the change in electronic and induced circular dichroism spectra for complex formation, the complexation of 4-dimethylaminoazobenzene (DAAB) with four kinds of cyclodextrins (α-and β-cyclodextrin (CD), heptakis(2,6-di-O-methyl)-β-cyclodextrin, and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin) was studied in methanol-water and dimethyl sulfoxide-water mixtures. It was found that the trans and cis isomers of DAAB form two different types of complex (inclusion and lid type) with CDs, depending on the kinds of CDs and solvents. Further, we have examined the effect of CDs on the thermal cis-to-trans isomerization of DAAB. The accelerated or decelerated effect on the thermal isomerization was observed upon adding CDs. The effects of CDs on the thermal isomerization are discussed in connection with the complexation of the cis-isomer of DAAB with CDs.

Supramolecular Complexation of Azobenzene Dyes by Cucurbit[7]uril

“…The ammonium tautomer of 3•H + absorbs at 320 nm, and the azonium tautomer absorbs at 500 nm (Figure 6a). 42,45,48 The absorption spectra in Figure 6c illustrate this pH-dependent equilibrium for free 3. In unbuffered water, the dominant peak at 375 nm is assigned to neutral 3, but in pH 1.2 solution, there is virtually no neutral 3; instead, the primary species is 3•H + , which exists as an equilibrium mixture of ammonium and azonium tautomers.…”

“…The spectral behavior of dye 3 in water at different pH has been characterized many times over the years by different research groups using absorption and Raman spectroscopy, as well as 15 N and 13 C NMR. ,,,− The neutral species has an absorption at 375 nm, and upon protonation, 3·H + exists as an equilibrium between ammonium and azonium tautomers, each in a trans azo conformation (Scheme ). The ammonium tautomer of 3·H + absorbs at 320 nm, and the azonium tautomer absorbs at 500 nm (Figure a). ,, The absorption spectra in Figure c illustrate this pH-dependent equilibrium for free 3 . In unbuffered water, the dominant peak at 375 nm is assigned to neutral 3 , but in pH 1.2 solution, there is virtually no neutral 3 ; instead, the primary species is 3·H + , which exists as an equilibrium mixture of ammonium and azonium tautomers.…”

“…It is worth noting that the π → π* and n → π* transitions for neutral 4-( N , N ′-dimethylamino)­azobenzene derivatives, such as 2 , closely overlap, which makes it difficult to produce or observe light-induced interconversion of trans and cis azo conformational isomers . Moreover, the lifetime for any putative cis isomer of the protonated azonium tautomer is very short since the azonium tautomer undergoes facile cis – trans interconversion due to rapid rotation around the protonated azo bond which has partial N–N single bond character. ,− …”

Sensitive detection of a pseudo-polyrotaxane ultrathin film by SPR and QCM-D methods

“…1.2 nm. For the MeAzoPEGn in mixed SAM, these are the most suitable conditions for capturing ␣-CD rings at high density, considering the molecular size of ␣-CD with outer diameter [30,31] …”

Microheterogeneous Catalysis

“…The effects of cyclodextrins on electron transfer processes have been considered above. The effects of these kinds of receptors on biomimetic reactions have been reviewed [ 99 ] as well as studies of cyclodextrin effects on organic reactions [ 100 , 101 , 102 , 103 , 104 , 105 , 106 ], redox reactions [ 107 , 108 , 109 ], ligand substitution reactions [ 110 ], etc. , in such a way that the effects of this kind of catalyst on practically any type of reaction have been studied.…”