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Host-guest complexation of dapoxyl sodium sulphonate (DSS), an intramolecular charge transfer dye with water-soluble and non-toxic macrocycle γ-cyclodextrin (γ-CD), has been investigated in a wide pH range. Steady-state absorption, fluorescence and time-resolved fluorescence measurements confirm the positioning of DSS into the hydrophobic cavity of γ-CD. A large fluorescence enhancement ca. 30 times, due to 1 : 2 complex formation and host-assisted guest-protonation have been utilised for developing a method for the utilisation of CD based drug-delivery applications. A simple fluorescence-displacement based approach is implemented at physiological pH for the assessment of binding strength of pharmaceutically useful small drug molecules (ibuprofen, paracetamol, methyl salicylate, salicylic acid, aspirin, and piroxicam) and six important antibiotic drugs (resazurin, thiamphenicol, chloramphenicol, ampicillin, kanamycin, and sorbic acid) with γ-CD.

A nitrobenzoxadiazole-based fluoroprobe (NBD-Bu) is designed to probe cellular metabolic activity in cancer and normal cells. NBD-Bu shows a significant fluorescence enhancement upon selective binding to the transport protein serum albumin in PBS buffer at ambient conditions. Encouraged by this finding, the site- specificity of NBD-Bu has been explored through a competitive displacement assay in the presence of site-specific markers such as warfarin and ibuprofen. Notably, even at micromolar concentrations, the probe possesses the ability to displace the site marker drug ibuprofen, efficiently. Subsequently, high-resolution fluorescence imaging results consolidated the potential of NBD-Bu for detection of abnormal cellular metabolic activity. [ABSTRACT FROM AUTHOR]

The potential of cucurbiturils, water-soluble macrocyclic host molecules composed of glycoluril units, for tuning the properties of fluorescent dyes and advancing new applications is illustrated. Cucurbit[7]uril (CB7), which presents a particularly attractive derivative due to its intermediary size and high water solubility, has been shown to display a variety of advantageous effects on fluorescent dyes, which include increased fluorescence intensity and brightness, enhanced photostability, protection towards fluorescence quenchers, solubilization, and deaggregation. Particularly noteworthy is the prolongation of the fluorescence lifetimes of different dyes, which can be traced back to the low polarizability of the host cavity. In addition, the host serves as cation receptor, which causes a considerable shift of protonation equilibria and assists the protonation of fluorescent dyes. The latter effect can be exploited in the design of protolytic fluorophore displacement assays. The perspective of cucurbiturils as stabilizers for laser dyes, enhancement agents in time-resolved fluorescence (TRF) assays, contrast agents for fluorescence lifetime imaging (FLIM), and dyes for fluorescent collectors for solar cells is mentioned. Original experimental results for the effect of CB7 on the fluorescence properties of three dyes (Macrolex Yellow 10 GN, Dapoxyl, and 4-(dimethylamino)benzonitrile) are presented. [ABSTRACT FROM AUTHOR]

Abstract: Steady state and time resolved fluorescence measurements have been performed to assess the role of ionic strength and presence of surfactants in the dynamic quenching of 6-methoxyquinoline by halides. The results of quenching by potassium chloride are mainly presented in this paper. The pH dependence of the Stern–Volmer constant has been rationalized in the light of the difference in ionic strengths. The concentration dependent quenching/enhancement of fluorescence by the surfactant, sodium dodecyl sulphate has been observed and explained by considering an equilibrium between free and bound fluorophores and modification of critical micellar concentration of SDS by salts. The concentration of the surfactant has been found to affect the quenching/enhancement of fluorescence by chlorides. Thus, ionic strength and the presence of surfactants are found to be two factors which can affect the sensitivity of the fluorescent probe towards chlorides. [Copyright &y& Elsevier]

Abstract: The interaction of the fluorophore Lucifer yellow with micelles has been monitored using steady state and time resolved fluorescence techniques. Contrary to the popular belief that the fluorophore is too polar to associate with the stern layer or hydrophobic core of micelles, we have observed that it binds with the micelles of the positively charged surfactant cetyl trimethyl ammonium bromide and that such interaction causes an decrease in the rates of its non-radiative processes. This phenomenon cannot be explained solely in the light of a reduced polarity, as we have demonstrated that the photophysics of Lucifer yellow is complex and intramolecular charge transfer does not seem to be the only excited state process that is operative. [Copyright &y& Elsevier]

A pH dependent encapsulation of dapoxyl sodium sulfonate (DSS), a charge transfer (CT) dye, with α- and β-cyclodextrin (CD), macrocyclic molecules made up with sugar units, has been performed using steady-state and time-resolved fluorescence measurements; both confirm the formation of an efficient inclusion complex with both non-protonated and protonated form of DSS. Moreover, the fluorescence intensity is affected due to modulation of acid-dissociation constant by CD encapsulation as a consequence of preferential binding affinities with different prototopic forms of DSS. In particular, we observed that the relocation of DSS from water into the less polar hydrophobic cavity of CD causes huge fluorescence enhancement in water. Our investigation reveals that the micro-polarity inside β-CD cavity is akin to methanol–water (1:1) mixtures. [ABSTRACT FROM AUTHOR]