Effect of Solvents and pH on β-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

Nanorod formation of cyclodextrin-covered sudan dyes through supramolecular self-assembly

“…One-dimensional 1 H NMR spectra for SDIII, SDIV and CDs were recorded on a Bruker Avance 400 MHz spectrometer (Germany) using DMSO-d6 (99.9%) as a solvent. The DSC were recorded using Mettler Toledo DSC1 fitted with STR e software (Mettler Toledo, Switzerland), and the temperature scanning range was from 25 C to 250 C with a heating rate of 10 C/min. PXRD spectra were recorded with a Bruker D8 advance diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) and the pattern was measured in the 2u angle range between 5 and 80 with a scan rate of 5 /min.…”

“…The small increase in the absorption with the addition of both CDs has been attributed to the improved dissolution of the guest molecules through the detergent action of CDs. [24][25][26][27][28] Emission spectra monitored at two different excitation wavelengths (350 and 510 nm) are displayed in Figures 3 and 4. The emission spectra at λ exc $ 350 nm are different than that at λ exc $ 510 nm.…”

“…Thus, the polarity and viscosity variations may not play an important role in both dyes. [24][25][26][27][28] The binding constant for the 1:1 and 1:2 inclusion complex formations were calculated using Benesi-Hildebrand equation. [30] It apparently explains that SDIII and SDIV form 1:2 inclusion complexes with both CDs.…”

“…[24][25][26][27] However, in SDIII:CD complexes the phenyl rings (C, D) are partially present in one of the CD cavity and naphthol ring is (D ring only) partially encapsulated in another CD cavity, whereas the hydroxy group is present out side of the CD cavity. The above discussions imply that both dyes form similar types of 1:2 inclusion complexes with a-CD and b-CD which led to the self-assembly of nanostructures.…”

“…In all solvents, when compared to sudan I (SDI) and sudan II (SDII) [24][25][26][27] $ 620, 561 nm). The large red shift and broad absorption and emission spectra suggest intramolecular hydrogen bond (IHB) or intramolecular proton transfer (IPT) present in sudan dye molecules.…”