Room temperature phosphorescence in cyclodextrins. Analytical applications

Abstract

Surfactants which form micelles and cyclodextrins are two of the most common forms of organized media. Surfactants are known for their ability to self-assemble in water and/or organic solvents and form normal/reverse micelles above the critical micelle concentration (CMC). Micellar solubilization in surfactant solutions has been widely exploited in analytical chemistry. The formation of inclusion compounds, by using cyclodextrins as hosts, has been also frequently used to enhance the analytical responses of analytes by incorporation of guest molecules into the cyclodextrins hydrophobic cavity [1].The first observation of room temperature phosphorescence (RTP), using a microscopically organized media, used sodium dodecylsulfate (SDS) micelles in the presence of tallium [2]. Since then, several media have been investigated to stabilize the triplet-state in fluid solution at room temperature. Normal micelles, mainly sodium dodecylsulfate [3][4][5][6], cetyltrimethylammonium bromide (CTB) [7][8][9] and Triton X-100 [10] micelles, have been used in RTP analytical applications. As an alternative to the use of normal micelles, microemulsions, formed in heptane-SDS-1-pentanol, have been also reported for RTP obtention [11][12][13][14].Cyclodextrins (CDs) can form complexes with phosphors and heavy atom containing additives and these host-guest aggregates serve to populate and stabilize the fragile tripletstate, producing characteristic room temperature phosphorescence. These inclusion complexes induce an intense phosphorescence emission which is partially insensitive to Cyclodextrins are composed of D-glucose residues joined by α(1→4) linkages. α-, β-and γ-CDs, which are made up of six, seven and eight D-glucose residues, are the most common members of a CD family. These CDs are shaped like a truncated cone with a hollow, hydrophobic cavity in which a hydrophobic guest can be incorporated.Molecular encapsulation by means of molecular inclusion complex formation offers a new approach in analytical chemistry. Generally, the inclusion complex involves the spatial entrapment of a single guest molecule in the cavity of the host molecule, without the formation of any covalent bonds. Cyclodextrins, cyclic non-reducing oligosaccharides, have been extensively used to obtain these inclusion complexes. In particular, many studies have focused on the ability of CDs to include guests of varying sizes in different stoichiometric ratios and several analytical applications of these complexes have been reported [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].It is well documented that, depending upon the host CD (i.e. α-, β-or γ-CD) and the size of the guest, different

Fluorescence Studies of the Hydrogen Bonding of Excited‐State Molecules within Supramolecular Host–Guest Inclusion Complexes

“…In this case, interaction with the alcohol shields the BPT guest from the quenching interaction with water, and a very dramatic increase in the S 2 fluorescence results. Hydrogen bonding has also been shown to have significant effects on the properties of triplet states included within CD cavities, using phosphorescence and time-resolved absorbance studies [81][82][83][84][85]. Bohne et al [81][82][83] have shown that triplet xanthone is much more weakly bound in b-CD than is ground-state xanthone, with measured binding constants K of 1100 and 48 M À1 for the ground and triplet states respectively [81].…”

“…They measured the dynamics of triplet xanthone inclusion into b-CD [81] and found a much faster exit rate for the triplet as compared with ground-state xanthone, supporting the idea of hydrogen bonding by the water solvent competing with binding into CDs. Other researchers have shown that inclusion of guests within CDs can lead to strongly enhanced room-temperature phosphorescence (RTP) [84,85]. Hartmann et al showed that the addition of hydrogen bonding substrates such as bulky alcohols or amines significantly enhances the RTP of 1-bromonaphthalene via hydrogen bonding to the CD rim hydroxyls, thus forming a lid on the CD cavity, and providing increased protection of the guest from O 2 quenching [84].…”

“…Hartmann et al showed that the addition of hydrogen bonding substrates such as bulky alcohols or amines significantly enhances the RTP of 1-bromonaphthalene via hydrogen bonding to the CD rim hydroxyls, thus forming a lid on the CD cavity, and providing increased protection of the guest from O 2 quenching [84]. Muñoz de la Peña et al have provided a useful review of the analytical applications of this hydrogen-bonding CDenhanced RTP [85].…”

Determination of Phenylureas Herbicides in Foodstuffs Based on Matrix Solid-Phase Dispersion Extraction and RP-LC with UV Detection

“…However, derivatization is still necessary for thermally unstable PUHs to be determined by GC. Liquid chromatography (LC) provides the advantage of direct analysis of PUHs, and several detectors have been coupled to LC for the determination of PUHs, including fluorescence [5][6][7], MS [8,9], and UV [10][11][12][13][14]. Among those methods, UV detection offers many advantages, such as low cost, and the absence of labeling process.…”

“…In order to determine trace analytes by UV detection method, a sample preparation technique prior to analysis is needed, the most used sample preparation techniques include SPE [3,5,8,[12][13][14], SPME [6,11], LLE [10], LPME [15,16], and DLLME [17]. However, these techniques possess some defects.…”