Rezik A. Agbaria

Fluorescence of metal-ligand complexes of mono- and di-substituted naphthalene derivatives.

In this work, metal ion complexes for several naphthalene derivatives have been investigated. Different working pH values were chosen: 2.5 for complexes with Zr(IV), 4.0 for complexes with Fe(III), 5.0 for complexes with Al(III), and 7.5 for complexes with Cu(II). A stoichiometry of 1:1 for all complexes except two has been established by use of the Benesi–Hildebrand method and the stability constants have been calculated. All complexes between naphthalene derivatives and Cu(II) and Fe(III) show fluorescence quenching. In the case of Al(III), all complexes provided enhanced fluorescence. For Zr(IV), only the complex with 3-hydroxy-2-naphthoic acid provided enhanced fluorescence. The value of the stability constants as a function of the substituents of naphthalene derivatives has been analyzed. One can conclude that Cu(II) showed the largest binding affinity for the mono-substituted derivatives. However, Al(III) and Zr(IV) produced greater selectivity for the di-substituted derivatives. Iron(III) showed no specific binding with any of the naphthalene derivatives.

Extraction of volatile PAHs from air by use of solid cyclodextrin

An approach for extraction of polycyclic aromatic hydrocarbons (PAHs) from air using solid cyclodextrin is presented. A comparison study in which β-cyclodextrin is replaced by α-cyclodextrin provides evidence that β-cyclodextrin extracts vapor phase PAHs by formation of inclusion complexes rather than by association or adsorption interactions. Thus, solid cyclodextrin complexes with vapor phase PAHs and thereby reduces their volatilities. The gas-solid interaction of the PAHs with β-cyclodextrin and the effect of β-cyclodextrin on the volatilities of these compounds are discussed. Fluorescence and absorbance spectroscopies are used to examine the variables that affect the formation of the PAH complexes with the solid cyclodextrin. The use of this system for improved ambient air sampling is proposed.

Influence of organized media on the absorption and fluorescence spectra of auramine-O dye

The spectral characteristics of the aqueous solutions of Auramine O dye in the presence of organized media have been examined. The absorbance and fluorescence of the dye are significantly enhanced in cyclodextrins and surfactants. The dye forms a predominant 1:1 complex with beta-CD, whereas a 1:2 complex is formed with alpha-CD. The dissociation constants of the complexes have been determined by use of a non-linear regression method. Premicellar solutions of the sodium dodecyl sulphate exert maximum influence on the fluorescence and absorbance spectra of the dye. The microviscosity in cyclodextrins and micelles of SDS and Brij-78 have been estimated from fluorescence measurements.

Complexation Studies of Water-soluble Calixarenes and Auramine O Dye

Abstract The dye, Auramine O, whose fluorescence is sensitive to its microenvironment, is used to study the complexation properties of the host molecules, calix[6]arene sulfonates. Complexation between the dye and the sulfonated calixarenes has been characterized by use of absorption and steady state fluorescence measurements. A comparison study of the calixarenes and the monomers suggests that the observed shifts of the absorption and the fluorescence of Auramine O are due to complex formation. In addition, the fluorescence of Auramine O is enhanced as a result of its association with calixarenes. Fluorescence intensities in the absence and presence of calixarenes are employed to calculate formation constants of the inclusion complexes. The stoichiometric ratio for both SCX6/AuO and SCX6-C5H11/AuO is 1:1. The formation constants for these complexes are estimated to be 1.24 × 104 M−1 and 1.53 × 104 M−1, respectively.

Phase transition pattern of 2,5-diphenyloxazole/γ-cyclodextrin (PPO/γ-CD) self-assembly aggregates

Abstract The molecule 2,5-diphenyloxazole (PPO) organizes into non-covalently bonded self-assembled aggregates of guest-host complexes with γ-cyclodextrin (γ-CD) in aqueous solutions. This structure is held together by weak interactions between the PPO and the γ-CD molecules. Therefore a small activation energy allows deterioration of these self-assembled aggregates. In this study, we report the effect of temperature and pH on this unique ensemble of aggregates. We report a phase transition pattern in which the structure disassembles from long to short (i.e. basic unit) aggregates. The relative fluorescence intensities of the excimer and monomer of PPO have been used to study this transition. Earlier investigations reported that these self-assembled aggregates were destroyed by an increase in temperature up to 80°C. In this study, we examined the effect of temperature on this structure and found a phase transition pattern of the temperature-dependent structure. Both the intensity and polarization of the steady state fluorescence reveal similar values of the critical temperature at 46±8°C and 49±7°C for the monomer and excimer fluorescence respectively. In addition, earlier studies proposed that hydrogen bonding between the guest and host molecules may play an active role in stabilizing the linear beads. We examined this hypothesis by changing the pH to an acidic or basic medium. A change in the aggregates was observed at approximately pH 12, which is the pKa value of γ-CD. For the pH range 10–13, a phase transition is centered at about pH 12.

Fluorescence Characterization of the Cyclodextrin/Pyrene Complex Interaction with Chiral Alcohols and Diols

The chiral properties of cyclodextrins (CDs) facilitate the formation of diastereomeric complexes with a number of pesticides and pharmaceuticals which are also frequently composed of one or more chiral centers. The roles of chirality and structural volume in CD binding to a homologous series of linear, chiral alcohols and diols are evaluated by comparing the trend in the pyrene fluorescence I/III band ratio and the hydrophobicity for the CD/pyrene complex with CD/pyrene complexes incorporating achiral alcohols. Stronger hydrophobicity is observed for complexes capped by chiral alcohols relative to complexes formed with a similar achiral counterpart, suggesting the importance of the alcohol chiral center. Furthermore, the diols induce a more hydrophobic environment than their alcohol counterparts with the β-CD/pyrene complex, while the converse is the case for the γ-CD systems. The systems involving γ-CD were also compared by use of pyrene fluorescence lifetime measurements.

High resolution three-dimensional visualization and characterization of coronary atherosclerosis in vitro by synchrotron radiation x-ray microtomography and highly localized x-ray diffraction

Human atherosclerotic plaques in both native and bypass arteries have been visualized using microtomography to provide additional information on the nature of coronary artery disease. Plaques contained within arteries removed from three white males aged 51, 55 and 70 are imaged in three-dimensions with monochromatic synchrotron x-ray radiation. Fields of view are 658 x 658 x 517 voxels. with cubic voxels ranging from 12 to 13 microm on a side. X-ray energies range from 11 to 15 keV (bandpass approximately 10 eV). At lower energies, high local absorption tends to generate reconstruction artefacts, while at higher energies the arterial wall is scarcely visible. At all energies, calcifications are clearly visible and differences are observed between plaques in native arteries (lifetime accumulations) versus bypass arteries (plaques developing in the interval between the heart bypass operation and the autopsy). In order to characterize coronary calcification, a microfocused, 50 microm2, 25 keV x-ray beam was used to acquire powder diffraction data from selected calcifications. Also, large calcifications were removed from the native arteries and imaged with 25 keV x-ray energy. Calcifications are composed of hydroxyapatite crystallites and an amorphous phase. In summary, native calcifications are larger and have a higher fraction of hydroxyapatite than calcifications from the bypass arteries.

Spectroscopic study of a representative polar cap of buckminsterfullerene: Cyclopentacorannulene

The spectroscopic properties of corannulene and cyclopentacorannulene are examined by use of absorption and steady-state fluorescence measurements. A red shift in the emission maxima of cyclopentacorannulene is noted with respect to the emission maxima in the corannulene spectrum. Similar differences in the absorption spectra of both molecules are also observed. Reasons for the dissimilarities in the absorption and emission spectra of these molecules are discussed. The fluorescence quantum yields and lifetimes of the molecules measured in organic solvents are reported. The fluorescence quantum yield and lifetime of cyclopentacorannulene are lower than those of corannulene. This difference is attributed to the highly strained and nonplanar structure of cyclopentacorannulene. The effectiveness of nitromethane as a quencher of corannulene and cyclopentacorannulene fluorescence is examined. In contrast to previously reported results, the fluorescence of these molecules is quenched by nitromethane. Fluorescence quenching of the molecules has been attributed to complex formation in the ground state, i.e., static quenching.

Binding of Pyrene to Cyclodextrin Polymers

Polymers containing the three cyclodextrin (CD) molecules, α-CD, β-CD, and γ-CD, linked by epichlorohydrin (α-CDP, β-CDP, and γ-CDP) are highly water-soluble polydisperse mixtures containing CD units joined by repeating glyceryl linkers [-(CH2-CHOH-CH2-) n ]. The average n value is 12-15, and gel filtration chromatography analysis indicates that the two major polymer components have molecular weights (MWs) of <2000 (1 CD/polymer chain) and 9-10,000 (4-5 CDs/polymer chain). We have used fluorescence properties to study the binding of pyrene to the three commercially available CDPs and to dialyzed samples of the CDPs, in which the low-MW (<2000, CDPL) and high-MW (9-10,000, CDPH) components have been separated. The pyrene emission I/III ratios for the three polymers are larger and exhibit a smaller range than the I/III ratios for the CD monomers. Moreover, the I/III ratio for the dialyzed polymers, β-CDPL and β-CDPH, are, within error, the same as that for β-CDP. It has been previously shown that additives, such as pentafluoropropanol (PFP), cause a dramatic decrease in the pyrene I/III ratio in the presence of β-CD. No effect on the pyrene I/III ratio is observed when these additives are added in the presence of the CDPs. The pyrene fluorescence decays in the presence of all three native polymers and the dialyzed β-CDPs are quite similar but different from the pyrene fluorescence decays in the presence of the three CD monomers. Moreover, the pyrene lifetimes show much greater dependence on iodide quencher concentration in the presence of CDPs than in the presence of β-CD and γ-CD. These data suggest that pyrene exists in a more exposed and hydrophilic environment when bound to the CDPs than that observed with the CDs. The agreement of the results for pyrene in the presence of β-CDP, β-CDPH, and β-CDPL would seem to rule out significant cooperative binding from two CD units on a single chain, which has previously been suggested. We conclude that pyrene binding to the CDPs may be largely noninclusional, involving considerable participation of the glyceryl linker units.

Spectroscopic Studies of Water-soluble Sulfonated Calix(6)arene

Fluorescence and absorption studies of water-soluble sulfonated calix[6]arene (SCX6) are reported. Water-soluble calixarenes are potentially useful as host molecules for luminophores, and studies of their spectroscopic characteristics are therefore crucial. The absorption and fluorescence spectra of these molecules in aqueous solution were collected, analyzed, and compared with 4-hydroxybenzene sulfonate at different pHs. A red shift in the absorption spectrum and a change in the fluorescence spectrum of the calixarenes are observed upon an increase in pH from 2.0 to 13.0. Some of these spectroscopic changes are attributed to intramolecular hydrogen bonding between adjacent hydroxyl groups of SCX6 after proton disassociation. The formation of excimers between phenolic groups in the calixarene molecule is proposed. In addition, inner-filter effects of SCX6 are discussed. These inner-filter effects prove to be a disadvantage for the use of SCX6 as a host molecule for complexation studies by use of fluorescence probes whose absorption spectra overlap with those of calixarenes.