Pyrene 3-cyclodextrin

Anigbogu et al. [158] studied the effects of methanol, r-butyl alcohol (TBA), and cyclopentanol (CP) on anthracene and pyrene retention on a C)8 column (A = 255 nm) using 50% to 70% methanol in water containing 3 mM ) -cyclodextrin and 1% TBA or CP. On the basis of retention effects, the authors speculate that TBA and CP assist in the formation of a cyclodextrin/pyrene complex and conclude that TBA and CP may be effectively used as mobile phase modifiers in these fiised-ring systems. Schuette and Warner [159] conducted a similar study on the effects of N pentanol on or y-cyclodextrin/PAH complexes. A solution of 0.1 M 1-pentanol with 5mM y- or j -cyclodextrin increased the fluorescence emission intensity markedly in Ihe 430-490 nm range. Chromatographic selectivity and efficiency were enhanced and the detection limits were lowered by nearly an order of magnitude. 

Although not studied in my work on cyclodextrins, pyrene 3 has been included in this chapter because it has a very different polarity-sensitive response than the anilinonaphthalene sulfonates described above. Instead of showing an overall increase in intensity in less polar media, pyrene exhibits a change in the relative intensity of two resolved vibronic bands, namely the first and third [72]. Thus, the value of /m/Zi changes according to the local polarity. For example, 7ni/ 7i = 1.68 in cyclohexane compared to 0.63 in water [72]. 

Sodiiun dodecylsulfate, cetyltrimethylam-monium chloride, sodium cholate, -cyclodextrin dansylated amino acids and polycyclic aromatic hydrocarbons > 45-fold 1% in water the greatest enhancement of fluorescence is that of sodium cholate on pyrene [263]... 

Figure 2. (a) Room-temperature phosphorescence spectrum of benzo(e)pyrene on 80% a-cyclodextrin-NaCl in the presence of ben2o(a)pyrene. = 284 nm. (h) Room-temperature phosphorescence spectrum of benzo(e)pyrene on 80% a-cyclodextrin—NaCl. X - 284 nm. 

Figure 3. Three-dimensional plot of the room-temperature fluorescence of a mixture of 500 ng each of benzo(a)pyrene and benzo(e)pyrene on 80% q-cyclodextrin-NaCl. Numbers along dashed lines show the approximate wavelengths (nm) represented by these lines. The excitation wavelength was varied from 250 nm (front spectrum) to 370 nm (back spectrum) at 2-nm increments. Benzo(a)pyrene emitted from approximately 380 nm to 540 nm, and benzo(e)pyrene emitted from 365 nm to 505 nm.

Hossain, M. A., Mihara, H. and Ueno, A. (2003). Novel peptides bearing pyrene and coumarin units with or without beta-cyclodextrin in their side chains exhibit intramolecular fluorescence resonance energy transfer. J. Am. Chem. Soc. 125, 11178-11179. 

Only the silica-based stationary phases with covalently bonded alkyl chain, cyano and propylamino ligands have found practical applications in HPLC. Besides these common ligands, the experimental use of naphthalene, pyrene and nitroaromatic as ligands has also been reported. Silica-based stationary phases with covalently bonded cyclodextrins or cyclodextrin derivatives have been frequently employed in the separation and quantitative determination of isomer pairs. 

Incomplete coverage of the surface of such a fifth-generation POPAM dendrimer exposes hydrophobic areas of adamantyl units remaining uncomplexed by cyclodextrins on the dendritic outer shell [38]. Pyrenes were used as neutral fluorescence probes to examine whether this might lead to aggregation in water driven by the hydrophobic effect [39a]. Their inclusion in the dendrimer/cyclo-dextrin aggregate leads to changes in fluorescence intensity and in the vibrational fine structure. Formation of excimers was also observed. 

It has been estimated that the internal cavity of 8-cyclodextrin is optimal for the inclusion of unsubstituted pyrene [42]. The axis of the included solute is located parallel to that of the cyclodextrin cavity. In the case of benzo(a)pyrene, no complex can be formed with either a- or 8-cyclodextrin [43]. However, a strong complex can be prepared using y-cyclodextrin, with the long axis of the included solute lying along the direction of the cavity axis. 

As with most discoveries, these ideas then passed through a lull before takeoff. Then the Chicago-New York axis of Yang and Turro in the USA investigated the first example (6) in the host-guest mould [10]. Their focus was on the demonstration of exciplex emission of (6) in aqueous solution due to protection by an encapsulating /J-cyclodextrin. Ever since Weller s experiments, exciplex emissions had been observed to fall off rapidly in intensity as solvent polarity was increased [4], A formally related example due to Tazuke from 1982 must, however, be pointed out, where a hydrophobic polymer microdomain in mixed and neat aqueous solution allows exciplex emission from pyrene and dimethyl-aniline pendants [11], The importance of (6) in the present context stems from the correlation of pH-dependent emissions from the naphthalene moiety and from the exciplex. Co-occurrence of externally switchable photophysics and supramolecular phenomena would later become common in the research literature [12]. 

Detailed analyses of intramolecular structures are possible. Comparison of NMR and fluorescence data shows meso- and racemic diastereoisomers are found from 2,4-di(2-pyrenyl)pentane 24 jhe polarization of monomer and excimer of 4,9, disubstituted pyrenes have been measured in nematic liquid crystals 25 Quenching of pyrene fluorescence by alcohols in cyclodextrin inclusion complexes has also been studied in detail 26 Solvent effects on the photophysical properties of pyrene-3-carboxylic acid has been used to measure the pJJ, in different solvents 27 Geminate recombination in excited state proton transfer reactions has been studied with... 

Patonay, G. Warner, I.M. Investigation of induced circular dichroism of benzo(a)pyrene cyclodextrin complexes. J. Inclusion Phenom. Mol. Recognit. Chem. 1991, 11 (4), 313-322. 

Hashimoto, S. Thomas, J.K. Fluorescence study of pyrene and naphthalene in cyclodextrin-amphiphile complex systems. J. Am. Chem. Soc. 1985, 107 (16), 4655-4662. 

Fig. 18 Representation of the incorporation of pentane, benzene, and pyrene into a, p, and y cyclodextrins.

Other studies on pyrene involve heavy atom quenching, association in Y"Cyclodextrins and the use of the excimer... 

Nakajima A. A study of the system of pyrene and p-cyclodextrin in aqueous solution utilizing the intensity enhancement phenomenon, Spectrochim Acta A 1983 39 913-5. 

PHN, ACE, PYR, CHY, B[a]P, and benzo[e]pyrene were separated in a 50 mM borate buffer (pH 9) containing a mixture of 20 mM neutral methyl-(3-cyclodextrin (M(3CD) and 25 mM anionic sulfobutylether-(3-cyclodextrin (SB(3CD) at 30 kV and 30°C. " B[a]P and benzo[e]pyrene were successfully resolved with the other compounds in under 11 min in a 50-cm effective length of capillary without micelles in the mobile phase. The system was also less sensitive to temperature and separation potential. LIE detection with excitation at 325 nm at 2.5 mW from a He/Cd laser coupled to an optical fiber allowed for detection limits in the sub ppb range. The method described above was applied to the analysis of contaminated soil that had been extracted by supercritical CO2 for 20 min at 120°C and collected in methanol/DCM. ° Of the 16 EPA PAH mixtures, eleven compounds were detectable in the low ppb range. Ten of the eleven detectable compounds were measured in the soil extract. When compared to RP-HPLC, CE values were slightly lower but only six compounds were detected by HPLC-FLD. No direct relationship between PAH molecular size, polarity, or volatility with migration order was observed and B[b]F/B[k]F isomers were readily separated. 

Sequential complexation was confirmed in reference 97, where it was reported that P-CD addition decreases the R value and increases the intensity of the two vibronic bands. Solutions of P-CD containing 13 always exhibited a biexponential decay the shortest, t, = 130 ns, has the same lifetime of 13 in water, the largest, Tj = 300 ns, indicates that 13 experiences a hydrophobic environment. The ratio of the preexponentials /42Mi grew monotonically with [/ -CD]. The data are consistent with a sequential complexation, as in the complexation of 13 with a-CD. In the 1 1 complex, the included pyrene has the same lifetime as 13 in water because a substantial portion of the molecule is still exposed to the solvent when 13 is encapsulated by two cyclodextrins, it experiences a low-polarity microenvironment and its lifetime consequently increases. In the same paper, the complexing ability of a polymer-supported P-CD of the general formula... 

Enhancement of pyrene fluorescence was reported for the /5-CD-13 complex, owing to the addition of tert-butylamine or n-propylamine for amine concentration lower than 0.1 M. The addition of amines also caused a marked decrease in R from 1.42 for 13 in the presence of 10 M / -CD to 0.75 for the solution in which 10 M / -CD, 13, and 0.1 M amine were present simultaneously [128]. Further increase of the amine concentration led to fluorescence quenching and to an increase of R. The authors inferred that at low amine concentration pyrene is included in a low-polarity environment NMR measurements indicated that the aliphatic chain of the amine was included in the cavity of the cyclodextrin together with pyrene. At high concentrations, amines (mainly tert-butyl-) compete with pyrene for inclusion in the cavity. 

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