k e d s t r u c t u r e f r om t h e o n e e n d t o t h e o t h e r . T h e v a n d e r W a a l s i n t e r a c t i o n s a r e t h e m a i n s o u r c e o f t h e s t a b i l i z a t i o n o f t h e s e p o l y r o t a x a n e s . H y d r o g e n b o n d s b e tw e e n s u c c e s s i v e -CD s s l i g h t l y f a v o r h e a d -t o -h e a d , t a i l -t o -t a i l s e q u e n c e s o v e r h e a d -t o -t a i l s e q u e n c e s . T h e -CD s i n p o l y r o t a x a n e s a r e m o r e s ymm e t r i c a n d l e s s d i s t o r t e d t h a n t h e i s o l a t e d -CD s . T h e PEG i n t h e p o l y r o t a x a n e i s m o r e e x t e n d e d t h a n a n u n p e r t u r b e d c h a i n , b e c a u s e i t h a s a l a r g e r p o p u l a t i o n o ft r a n s s t a t e s a t i n t e r n a l b o n d s .

PNIPAM hydrogels functionalized with gold nanoparticles were prepared by making use of catechol redox chemistry. For this purpose catechol groups were introduced in the PNIPAM network during the cross-linking polymerization process (PNIPAM–catecholx hydrogel). These groups act as reducing agents of HAuCl4, which enables the functionalization of the PNIPAM with gold nanoparticles (PNIPAM–catecholx@Au hydrogel). The rheological study shows that catechol groups reinforce the hydrogel structure. A stronger effect was observed after the functionalization of the hydrogel with gold nanoparticles. This influence could be easily observed since the variation of G′ with the MBA mole fraction was fitted to a power-law expression G′ ∼ x MBA a , with a = 1.6 for PNIPAMx hydrogels, a = 2.3 for PNIMPAM–catecholx hydrogels and a = 3.2 for PNIMPAM–catecholx@Au hydrogels. The capability of the PNIPAM–catecholx@Au hydrogel to act as a tunable catalyst was demonstrated with a model reduction reaction. The half-lifetime at 25 °C was 10.5 min; however, at 38 °C the half-lifetime was 133 min.

Steady-state fluorescence has been used to study the inclusion complexes of 2-methylnaphthoate (MN) with α- and β-cyclodextrins (CDs). Emission spectra of MN show two bands that are very sensitive to the CD concentration and temperature. The stoichiometry and formation constants of these complexes were investigated by obtaining the ratio of the two bands. Results showed identical stoichiometry (1:1) for both MN/α-CD and MN/β-CD complexes. However, the estimated formation constants were quite different. The thermodynamic parameters Δ H and Δ S were obtained from vant'Hoff plots. Results showed that MN/α-CD complexation is accompanied by an high enthalpy change, while MN/β-CD complexation is mainly en tropically favored. Anisotropy measurements were used to interpret the different signs of Δ S upon inclusion for both complexes. In addition, 2-methylnaphthoate seems to be a good probe for estimating microenvironmental polarity. Effective dielectric constants of inner α- and β-CD cavities were evaluated.

Steady-state fluorescence and molecular mechanics calculation were used to study the inclusion complexes of 2-methylnaphthoate (MN) with γ-cyclodextrin (γ-CD). The stoichiometry (1:1) and binding constants (213 ± 96 M-1 at 25 °C) were extracted from an analysis of the ratio of the intensity of two emission bands that were sensitive to the polarity of the medium. Extrapolation of this ratio to a high concentration of γ-CD permits the estimation of the polarity of the inner cavity, which seems to be only slightly hydrophobic, with a dielectric constant near 74. The ΔH and ΔS for formation of the complex were obtained and compared with previous results for similar complexes of MN with two smaller CDs. Molecular mechanics calculations were applied to study the complex in vacuo and in the presence of water as a solvent. Complexation is mainly due to nonbonded van der Waals interactions of MN with γ-CD. Calculations show that MN penetrates completely into the cavity of γ-CD.