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Time-resolved near-IR phosphorescence spectroscopy was employed to determine the lifetime of singlet oxygen in Y-zeolites and porous silica and it was found to depend strongly on the alumina content of the zeolite.
A novel molecularly imprinted polymer (MIP) of high interest for room temperature phosphorescence (RTP) sensing systems is described; the synthesized MIP contains iodine as internal heavy atom in the polymeric structure and its applicability for RTP sensing of fluoranthene at microg L(-1) levels is demonstrated.
The first Eu3+ chelate-based phosphorescence probe specific for singlet oxygen has been designed, synthesized and characterized. The probe is highly sensitive, selective and water soluble for time-resolved luminescence detection of singlet oxygen with a detection limit of 2.8 nM.
A newly synthesized 8-quinolinol platinum(II) chelate derivative gelates various organic solvents, and the gel formed shows unique thermo- and solvatochromism of visible and phosphorescent colour in response to a sol-gel phase transition and possesses an attractive ability to inhibit dioxygen quenching of excited triplet states.
A new metal cation probe bearing a central Ir(III) element and 1-aza-15-crown-5-ether substituted pyridyl pyrazolate as the chelate was synthesized. The octahedral molecular structure of was confirmed using single crystal X-ray diffraction analyses. Subsequent photophysical study showed yellow-green emission at approximately 560 nm in both fluid solution and solid state at room temperature. Remarkable differentiation in spectral properties upon metal cation (e.g. Ca2+) complexation makes complex a highly sensitive phosphorescence probe.
Excited state potential energy hypersurfaces of 7H-furo[3,2-g][1]benzopyran-7-one (psoralen) have been explored employing (time-dependent) Kohn-Sham density functional theory. At selected points, we have determined electronic excitation energies and electric dipole (transition) moments utilizing a combined density functional/multireference configuration interaction method. Spin-orbit coupling has been taken into account employing an efficient, non-empirical spin-orbit mean-field Hamiltonian. Franck-Condon factors have been computed for vibrational modes with large displacements in the respective Dushinsky transformations. The simulated band spectra closely resemble experimental band shapes and thus validate the theoretically determined nuclear structures at the S(0), S(1), and T(1) minima. In the S(1) (pi(HOMO)-->pi*(LUMO)) state, the lactone bond of the pyrone ring is significantly elongated. From excited vibrational levels of the S(1) state a conical intersection between a (pi-->sigma*) excited state and the electronic ground state may be energetically accessible. Fast non-radiative decay via this relaxation pathway could explain the low fluorescence quantum yield of psoralen. The T(1) (pi(HOMO-1)-->pi*(LUMO)) exhibits a diradicaloid electronic structure with a broken C(5)-C(6) double bond in the pyrone ring. A variational multireference spin-orbit configuration interaction procedure yields a phosphorescence lifetime of 3 s, in excellent agreement with experimental estimates.
A simple, direct and rapid analytical methodology for the detection of aflatoxin producing Aspergillus spp. strains based on the measurement of room temperature phosphorescence from aflatoxins is presented here.
Multireference complete active space self-consistent-field (CASSCF) and multireference CASSF second-order perturbation theory (MSCASPT2) calculations were performed on the ground state and a number of low-lying excited singlet and triplet states of chlorobenzene. The dual phosphorescence observed experimentally is clearly explained by the MSCASPT2 potential-energy curves. Experimental findings regarding the dissociation channels of chlorobenzene at 193, 248, and 266 nm are clarified from extensive theoretical information including all low-energy potential-energy curves.
Quenched and sensitized room temperature phosphorescence techniques have been used for the detection of PCNs and PCBs after liquid chromatographic separation. The usefulness of these techniques to fingerprinting of commercial Aroclor and Halowax mixtures in complex matrices has been shown. The complementary nature of these detection modes yield valuable information in addition to UV detection. a signal inverter is proposed for linearization of the quenched RTPL signals. In this way linear calibration plots over more than two orders can be obtained. Detection limits are generally in the low nanogram or subnanogram concentration region. The application of RTPL detection techniques to the analysis of commercial PCN and PCB mixtures in surface water and urine is demonstrated. Pre-columns can be used to advantage for pre-concentration and clean-up of this type of samples.
In order to elucidate the biochemical roles of imidazol-containing dipeptides, we have studied quenching of singlet molecular oxygen (1O2) by carnosine (beta-alanyl-L-histidine), its structural components (L-histidine, imidazole, and beta-alanine), and related natural free-radical scavengers-L-anserine (beta-alanyl-1-methyl-histidine), ergothioneine (2-thiol-L-histidine-betaine), and taurine (2-aminoethanesulfonic acid) in aqueous (D2O, pD 7) solutions by using monitoring of 1O2-phosphorescence (1270-nm). The rate constants of 1O2 quenching (Kq) by carnosine, anserine, and ergothioneine were shown to be similar [(3 +/- 1) x 10(7) M-1s-1]. Their values resembled those of free-L-histidine [Kq = (4 +/- 1) x 10(7) M-1s-1] and imidazole [Kq = (2 +/- 1) x 10(7) M-1s-1]. Non-aromatic amino acids-taurine and beta-alanine-showed very low quenching activities (Kq < 3 x 10(3) M-1c-1). The Kq values did not correlate with the literature data on abilities of the tested compounds to stimulate muscle working capacities and inhibit myeloperoxidase-catalyzed oxygenation. Thus, the dipeptides can be used as potent water-soluble protectors against 1O2 attack whereas their natural biochemical functions are most probably determined by the processes of different nature.
Changes in cerebral blood flow (CBF) using laser-Doppler and microvascular O2 oxygen tension using oxygen-dependent phosphorescence quenching in the rat somatosensory cortex were obtained during electrical forepaw stimulation. The signal-averaged CBF response resulting from electrical forepaw stimulation consisted of an initial peak (t = 3.1 +/- 0.8 seconds after onset of stimulation), followed by a plateau phase that was maintained throughout the length of the stimulus. In contrast, microvascular O2 tension changes were delayed, reached a plateau level (t = 23.5 +/- 1.7 seconds after the onset of stimulation) that remained for the length of the stimulus and for several seconds after stimulus termination, and then returned to baseline. Using Fick's equation and these dynamic measurements, changes in the calculated cerebral metabolic rate of oxygen (CMRO2) during functional stimulation were determined. The calculated CMRO2 response initially was comparable with the CBF, but with protracted stimulation, CMRO2 changes were approximately one-third that of CBF changes. These results suggest that a complex relation exists, with comparable changes in CBF and CMRO2 initially occurring after stimulation but excessive changes in CBF compared with CMRO2 arising with protracted stimulation.
In vitro [UV absorption, fluorescence, phosphorescence, and nuclear magnetic resonance (NMR)] spectroscopic studies on the normal human lens demonstrate age-related changes which can be correlated with biochemical and photobiologic mechanisms occurring during our lifetime. Chronic cumulative UV exposure results in an age-related increase of photochemically induced chromophores and in color of the lens nucleus. This enables the lens to filter the incident UV radiation, thereby protecting the underlying aging retina from UV photodamage. We have measured the age-related increase in lens fluorescence in vivo on more than 300 normal subjects (1st to 9th decade) by UV slitlamp densitography. These data show a good correlation with the in vitro lens fluorescence studies reported previously and demonstrate that molecular photodamage can be monitored in the lens. In vitro NMR (human and animal lenses) and in vivo experiments currently in progress are rapidly elucidating the physicochemical basis for transparency and the development of light scattering areas. Surface scanning NMR can monitor organophosphate metabolism in the ocular lens in vivo as well as in vitro. These studies demonstrate the feasibility of using biophysical methods (optical spectroscopy and NMR analyses) to delineate age-related parameters in the lens, in vivo as well as in vitro.
Using the highly localized current of electrons tunneling through a double barrier scanning tunneling microscope junction, we excite luminescence from a selected C60 molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C60 molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale.
The rotational mobility of the membrane-bound acetylcholine receptor from Torpedo marmorata has been studied by phosphorescence anisotropy techniques using eosin-5'-isothiocyanate and eosin-5'-iodoacetamide derivatives of the alpha-neurotoxin of Bungarus multicinctus (alpha-bungarotoxin). Normal membranes, those depleted of nonreceptor peripheral peptides by alkaline treatment, as well as membranes subjected to various chemical modifications of the thiol groups, have been characterized. Rotational correlation times (10--26 mus) compatible with the motion of individual 9-S monomeric receptor species of Mr 250 000 were observed upon reduction of the membranes with dithiothreitol or by raising the temperature to 39 degrees C in the case of alkaline-treated membranes. Membranes prepared throughout in N-ethylmaleimide, which yield upon detergent solubilization a predominant 13-S dimeric species and which are not depleted of the nonreceptor v-peptide (Mr 43 000) by alkaline treatment, are relatively more 'rigid' than normal membranes and do not show the anisotropy components characteristic of the monomeric receptor. The influence of the v-peptide on the structural stability of the receptor oligomeric forms and the thiol-dependent interconversions are thus reflected in the time-dependent spectroscopic measurements.
The phosphorescence properties of Trp109 in alkaline phosphatase from Escherichia coli have been utilized to probe the conformation of the polypeptide following the removal of metal ions, reconstitution with Zn2+ and Cd2+ and phosphorylation. The complete removal of metal ions induces a drastic loosening of the protein structure that extends to the inner core of the macromolecule. While binding of a single metal ion/subunit (A-site occupancy) restores the holoconformer, practically no structuring effect is observed upon B-site occupancy by the second incoming metal ion. An exception to this rule occurs at alkaline pH and when the adjacent subunit in the dimer is metal-free. Under these circumstances a conformation of the subunit more compact than that of the fully saturated dimer manifests some degree of communication across the subunit interface. The binding of more than two metal ions/monomer generally destabilizes the protein, the effect being more pronounced at acid pH. Finally, the binding of inorganic phosphate restores the native-like configuration abolishing any destabilization induced by excess metal ions and acid pH. If the negative cooperativity towards metal binding to A sites in doubly metalated forms at pH 8 is in substantial agreement with 113Cd-NMR data, the equivalence in conformation between Zn2+- and Cd2+-reconstituted alkaline phosphatase emphasizes that no serious structural changes are introduced by the metal replacement.
Random collisions between macromolecules lead to dynamic associations (lengthy encounters) that in principle could affect their conformation and, in the case of enzymes, their binding and catalytic properties. Exploiting the unique sensitivity of the phosphorescence lifetime, tau, of Trp to the internal flexibility of globular proteins we probed the perturbations induced in the structure of the coenzyme-binding domain of alcohol dehydrogenase (LADH) and glyceraldehyde-3-phosphate dehydrogenase (GraPDH) by the presence in solution of other dehydrogenases and of functionally unrelated proteins. With Trp314 of LADH, the results emphasize that while tau is not affected by the concentration of LADH itself, the addition of micromolar quantities of other proteins causes a distinct reduction in it. From the linear increase of 1/tau with protein concentration one obtains values for the apparent second-order Stern-Volmer rate constant that range between 2-200 x 10(3) M-1 s-1, decreasing 2-3-fold when ternary complexes of LADH with NADH or NAD+ and inhibitors are involved. Similar effects were observed with Trp310 of GraPDH except that with sorbitol dehydrogenase as perturbant the increase of 1/tau is hyperbolic and governed by an apparent dissociation constant of about 1 microM. Finally, glycerol-3-phosphate dehydrogenase, the strongest perturber of both LADH and GraPDH, has either no effect on lactic dehydrogenase from pig heart or induces a moderate lengthening of the triplet lifetime of the rabbit muscle enzyme. Because Stern-Volmer behavior is typical also of diffusion-mediated quenching reactions, a parallel investigation with cysteine, cystine and N-acetyl-tryptophanamide demonstrated that among potential, protein-associated, quenching moieties namely, -SH, -S-S- and indole groups, only the latter has rate constants approaching the magnitude of protein perturbants. Since considerable evidence rules out the predominance of such quenching reactions, these findings confirm a subtle form of communication between protein molecules in solution. The lack of specificity and the similar effects between dehydrogenases with right and wrong stereospecificity for direct coenzyme transfer suggests that the perturbations monitored are unrelated to this function.
The quantum yield of formation and kinetic behaviour of O2(1 delta g) in D2O dispersions of small unilamellar vesicles (SUVs) of dipalmitoyl phosphatidylcholine were studied by time-resolved detection of near-IR phosphorescence. At a SUV concentration of 26 nM, O2(1 delta g) is not quenched by the vesicles. It diffuses quickly through the lipid bilayer and a partition equilibrium of O2(1 delta g) between the lipid bilayer and the buffer is attained before decay occurs. In this equilibrium situation O2(1 delta g) is mostly located in the buffer phase, which permits the determination of absolute quantum yields for O2(1 delta g) production, phi delta, by comparison of the luminescence in the dispersions with that in neat D2O. The maximal phi delta values for the sensitizers incorporated in the SUV bilayer were 0.47 +/- 0.09 for the dipyridyl complex of zinc(II) phthalocyanine (ZnPc), 0.35 +/- 0.08 for porphycene, and 0.36 +/- 0.08 for 2,7,12,17-tetra-n-propylporphycene. These values are equal to those in neat organic solvents but lower than those previously obtained in SUVs by using chemical trapping agents. The high degree of organization of the environment around the sensitizers does not influence their efficiency of producing O2(1 delta g). While no concentration dependence is observed for ZnPc (at least up to a local concentration of 20 mM in the bilayer), phi delta for both porphycenes significantly decreases above a local concentration of 4 mM in the bilayer. This result is expected in view of previous observations on the concentration dependence of other photophysical parameters of the porphycenes in such microheterogeneous media.
Thermally stimulated radiophosphorescence has been studied as a means of high-resolution dosimetry. Small grains of CaSO4:Mn phosphor, embedded in a thin Teflon tape, constitute the dosimeter. The light emitted after irradiation is measured with a photomultiplier coupled to the eyepiece of a scanning microscope. With CaSO4:Mn, the phosphorescence at room temperature is sufficient for measurement after doses in excess of 3000 rads. The spatial resolution of the technique is about 0.2 mm. The method has been tested by measuring the dose distributions from a radium needle and a beta-emitting eye applicator.