Spectroscopic studies of inclusion complex of beta-cyclodextrin and benzidine diammonium dipicrate

Formation of inclusion complex between benzidine diammonium dipicrate and beta-cyclodextrin with stoichiometry 1:2 (guest-host) has been established by UV, (1)H NMR, (13)C NMR, IR spectra and powder X-ray diffractometry. (1)H NMR studies are used to confirm the inclusion and to provide information on the geometry of dipicrate inside the cavity of beta-cyclodextrin.

Fluorescence enhancement of 1-napthol-5-sulfonate by forming inclusion complex with beta-cyclodextrin in aqueous solution

Fluorescence enhancement of 1-naphthol-5-sulfonate (1N5S) upon inclusion in beta-cyclodextrin is studied by spectrophotometry and spectrofluorimetery techniques. The spectral shifts were only observed in the emission spectra in different solvents and were found to be directly correlated to the solvent's hydrogen-bond donor strength (alpha). Spectral changes in the absorption spectra upon the addition of beta-cyclodextrin to 1N5S in aqueous medium were too small to allow for the determination of the binding constant. On the other hand; fluorescence measurements show that the emission of both the anionic and neutral forms of 1N5S increase upon the addition of beta-cyclodextrin with an increase in the quantum yield by about 60%. Fluorescence measurements show 1:1 inclusion of 1N5S in the beta-cyclodextrin cavity with an association constant of 88+/-10M(-1). (1)H NMR studies are used to confirm the inclusion and to provide information on the geometry of 1N5S inside the cavity of beta-cyclodextrin.

Spectroscopic studies on the inclusion complex of 2-naphthol-6-sulfonate with beta-cyclodextrin

The photophysical properties of 2-naphthol-6-sulfonate (2-NOH-6-S) in various solvents and in aqueous beta-cyclodextrin solution have been investigated. The fluorescence quantum yields in non-aqueous solvents are approximately 0.20+/-0.02, while in water the yield is higher. The fluorescence quantum yield in water was found to depend on the pH value of the medium and increases as the pH increase up to a pH value of 4.0 where it comes to be constant. Absorption and fluorescence measurements show 1:1 inclusion of 2-NOH-6-S in the beta-cyclodextrin cavity. The association constant of 2-NOH-6-S-beta-cyclodextrin complex based on fluorescence measurements was calculated using Benesi-Hildbrand relationship and found to be 330+/-30M(-1). (1)H NMR studies are used to confirm the inclusion and to provide information on the geometry of 2-NOH-6-S inside the cavity of beta-cyclodextrin.

Secondary assembly of bile salts mediated by β-cyclodextrin–terbium(III) complex

A fluorescent cyclodextrin-Tb(III) complex is successfully synthesized and can include bile salts in its hydrophobic cavities. Therefore, it can efficiently induce the secondary assembly of small bile salt primary micelles to large micelle aggregates, and the aggregation process can be easily observed by transmission electron microscopy (TEM) and fluorescence microscopy.

Inclusion complexes of ketosteroids with beta-cyclodextrin

Inclusion complexes of several steroid derivatives with beta-cyclodextrin (7) were studied in dimethylsulfoxide solution. The investigated molecules were ketosteroids with different functional groups on the skeleton: 3beta-acetoxypregn-5-en-20-one (1), 3beta-acetoxypregna-5,16-dien-20-one (2), 3beta-acetoxyandrost-5-en-17-one (3), 3beta-hydroxyandrost-5-en-17-one (4), 5alpha-androstane-3,17-dione (5) and 17beta-hydroxyandrost-4-en-3-one (6). Complex formation was monitored by two-dimensional ROESY experiments through the detection of intermolecular dipolar interactions. In case of inclusion complex formation, the steroid molecule penetrates the cavity of the cyclodextrin and dipole-dipole interactions (ROEs) can be detected between the glucose H-3 and H-5 protons inside the cyclodextrin cavity and the steroid skeletal protons. Intermolecular interactions were detected in all six cases. However, ROESY experiments provided data indicating only partial immersion (A and B ring of the steroid skeleton) in case of 1, 2 and 6. On the contrary, compounds 3 and 5, showing the most correlation rich spectra, seem to fully immerse in the beta-cyclodextrin cavity.

Influencing the binding selectivity of self-assembled cyclodextrin monolayers on gold through their architecture

Cyclodextrin derivatives modified with seven thioether moieties (1) or with one thiol moiety (2) bind to gold. Monolayers on gold of 1 or mixed monolayers of 2 and mercaptoundecanol were characterized by electrochemistry, wettability, and atomic force microscopy (AFM). Monolayers of 1 are well-ordered, but the order in the mixed monolayers depends on the ratio of 2 to mercaptoundecanol. With sufficient alkyl chains to fill the space under the cyclodextrin moiety of 2, the monolayers are densely packed. Guest recognition at these monolayers in water was studied by surface plasmon resonance (SPR) spectroscopy. For simple organic guests, monolayers of 1 showed the same selectivity and binding strength as beta-cyclodextrin in solution: however, the selectivity towards steroidal bile salts differs from solution. The mixed monolayers of 2, in which the cyclodextrin is less substituted and has more flexibility, bind steroidal guests (6a-6e) with the same selectivity as beta-cyclodextrin in solution.

Inclusion complexation of the sunscreen agent 2-ethylhexyl-p-dimethylaminobenzoate with hydroxypropyl-beta-cyclodextrin: effect on photostability

The interaction between the UV filter, 2-ethylhexyl-p-dimethylaminobenzoate, and unmodified and modified alpha-, beta- or gamma-cyclodextrins was studied in water by phase-solubility analysis. Of the cyclodextrins available, only hydroxypropyl-beta-cyclodextrin caused a marked increase in the aqueous solubility of 2-ethylhexyl-p-dimethylaminobenzoate. The data from the solubility study indicated the formation of a 1:1 (sunscreen-cyclodextrin) complex. The inclusion of the sunscreen agent into the hydroxypropyl-beta-cyclodextrin cavity was confirmed by thermal analysis and by nuclear magnetic resonance spectroscopy. Irradiation-induced degradation of 2-ethylhexyl-p-dimethylaminobenzoate was reduced by complexation with hydroxypropyl-beta-cyclodextrin, this effect being more pronounced in solution (the extent of degradation was 25.5% for the complex compared with 54.6% for free 2-ethylhexyl-p-dimethylaminobenzoate) than in the emulsion vehicle (the extent of degradation was 25.1% for the complex compared with 33.4% for free 2-ethylhexyl-p-dimethylaminobenzoate). Although photodegradation of the sunscreen agent is significantly reduced by formation of the inclusion complex it is important to design a suitable vehicle. Inclusion of 2-ethylhexyl-p-dimethylaminobenzoate-DMAB into the hydroxypropyl-beta-cyclodextrin cavity limits interaction of the UV filter with the skin reducing the side-effects of the formulation.