Interactions between 4-thiothymidine and water-soluble cyclodextrins: Evidence for supramolecular structures in aqueous solutions

Abstract

SummarySince several years the inclusion of organic compounds (guests) within the hydrophobic cavity (host) of cyclodextrins (CDs) has been the subject of many investigations. Interestingly, the formation of inclusion complexes could affect the properties of the guest molecules and, for example, the influence of the delivery system can be a method to improve/change the photochemical behavior of the guest. In particular, very recent studies have shown the protective role of CDs preventing the degradation of the encapsulated guest. Starting from this consideration, in this work, only the structure and complexation mode of the inclusion complexes involving 4-thiothymidine (S4TdR, a known photosensitizer) and five CDs, namely 2-hydroxypropyl-α-cyclodextrin (2-HP-α-CD), 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD), 2-hydroxypropyl-γ-cyclodextrin (2-HP-γ-CD), heptakis-(2,6-di-O-methyl)-β-cyclodextrin (DIMEB CD) and heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB CD) were investigated by different spectroscopic techniques (UV–vis, FTIR–ATR, 1H NMR) and cyclic voltammetry analysis (CV). This work is necessary for a prospective research on the photoreactivity of S4TdR in aqueous environment and in the presence of CDs to prevent its degradation under irradiation. UV–vis, FTIR–ATR and CV measurements suggested the formation of supramolecular structures involving the employed CDs and mainly the pyrimidine ring of S4TdR. 1H NMR analyses confirmed such indication, unveiling the presence of inclusion complexes. The strongest and deepest interactions were suggested when TRIMEB and DIMEB CDs were studied. The S4TdR affinity towards CDs was also evaluated by using the Benesi–Hildebrand (B–H) equation at 25 °C employing CV and 1H NMR methods. The stoichiometry of the interaction was also inferred and it appears to be 1:1 for all examined CDs.

A New Approach for Improving the Antibacterial and Tumor Cytotoxic Activities of Pipemidic Acid by Including It in Trimethyl-β-cyclodextrin

“…The FT-IR spectrum of TRIMEB showed prominent absorption bands at 2933 cm −1 (symmetric and asymmetric C–H stretching), 1158 cm −1 (for C–O stretching vibrations), and 1016 cm −1 near the region 1076–1022 cm −1 (C–O–C stretching vibrations), that are in good agreement with the values reported by Rizzi et al [28]. The band at 3300 cm −1 (–OH stretching vibrations) characteristic of β-CD [29] was not observed due to the methylation of the –OH moieties.…”

A comprehensive investigation of dye–chitosan blended films for green chemistry applications

“…Probably, unlike DB, for these samples, the dye was present on the surface of the chitosan films, confirming the shielding effect observed in the case of DB–chitosan film. Moreover, in these cases, the DY bands located at 1389 cm −1 and 1420 cm −1 shifted to 1375 cm −1 and 1410 cm −1 , respectively, suggesting the presence of hydrogen bonds and Van der Waals forces involving mainly the NN and CN moieties . Regarding the signals for the amide I and II bands, no important variations were observed.…”

Differential Metal Ion Sensing by an Antipyrine Derivative in Aqueous and β-Cyclodextrin Media: Selectivity Tuning by β-Cyclodextrin

“…A spectral titration of 1 (kept at a constant concentration) against incremental addition of β-CD solutions of progressively increasing concentration showed a hypochromic shift of the absorption spectral band at 310 nm. β-CD mobilizes the electrons of the bound molecule of 1 , and the excitable electrons are partially shielded, leading to the marked changes in the spectrum . The shift of the wavelength of the absorption band was not appreciable enough, providing indirect evidence that the 1 –β-CD complex was not a tight-fit one.…”

“…β-CD mobilizes the electrons of the bound molecule of 1, and the excitable electrons are partially shielded, leading to the marked changes in the spectrum. 36 The shift of the wavelength of the absorption band was not appreciable enough, providing indirect evidence that the 1−β-CD complex was not a tightfit one. Despite providing first evidence of the notable occurrence of associative interaction, the absorbance data could not be used for determination of the binding constant and the stoichiometry of the 1−β-CD complex, as their spectral changes were small (Figure 1A).…”