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PubMed2004

Luminescence quenching of a phosphorescent conjugated polyelectrolyte.

The photophysical and luminescence quenching properties of a platinum(II) acetylide-based conjugated polyelectrolyte, Pt-p, which features carboxylic acid solubilizing groups are reported. The Pt-acetylide polymer is water soluble, and it exhibits phosphorescence from a triplet pi,pi exciton based on the conjugated backbone. The phosphorescence from Pt-p is quenched by viologens with different charges (MV(+), MV(2+), and MV(4+)), and in each case the quenching is dominated by a dynamic (diffusional) mechanism. Comparison of the Stern-Volmer quenching properties of Pt-p with those of a structurally analogous fluorescent organic polyelectrolyte leads to the conclusion that the amplified quenching effect, which is commonly observed for fluorescent conjugated polyelectrolytes, is not important for the platinum acetylide phosphorescent conjugated polyelectrolyte.

Journal Article↗

PubMed2005

Phosphorescent oxygen sensor with dendritic protection and two-photon absorbing antenna.

Imaging oxygen in 3D with submicron spatial resolution can be made possible by combining phosphorescence quenching technique with multiphoton laser scanning microscopy. Because Pt and Pd porphyrin-based phosphorescent dyes, traditionally used as phosphors in biological oxygen measurements, exhibit extremely low two-photon absorption (2PA) cross-sections, we designed a nanosensor for oxygen, in which a 2P absorbing antenna is coupled to a metalloporphyrin core via intramolecular energy transfer (ET) with the purpose of amplifying the 2PA induced phosphorescence of the metalloporphyrin. The central component of the device is a polyfunctionalized Pt porphyrin, whose triplet state emission at ambient temperatures is strong, occurs in the near infrared and is sensitive to O2. The 2PA chromophores are chosen in such a way that their absorption is maximal in the near infrared (NIR) window of tissue (e.g., 700-900 nm), while their fluorescence is overlapped with the absorption band(s) of the core metalloporphyrin, ensuring an efficient antenna-core resonance ET. The metalloporphyrin-antenna construct is embedded inside the protecting dendritic jacket, which isolates the core from interactions with biological macromolecules, controls diffusion of oxygen and makes the entire sensor water-soluble. Several Pt porphyrin-coumarin based sensors were synthesized and their photophyics studied to evaluate the proposed design.

Absorption↗

PubMed2005

A heteronuclear bidentate Lewis acid as a phosphorescent fluoride sensor.

Reaction of dimesityl-1,8-naphthalenediylborate (1) with C6F5HgCl results in the formation of a B/Hg heteronuclear bidentate Lewis acid (2), which complexes fluoride to afford [2-mu2-F]-. Structural and photophysical studies carried out in solution and in the solid state indicate that 2 is a highly selective and sensitive phosphorescent fluoride sensor. The proximity of the two Lewis acidic sites enforced by the 1,8-naphthalenediyl backbone promotes fluoride anion chelation and is, therefore, responsible for the high binding constant. The interplay of conjugative and spin-orbit coupling effects mediated by the boron and mercury atoms, respectively, results in the phosphorescent signaling of fluoride binding. Remarkably, fluoride binding occurs in partially aqueous solutions and results in a drastic change of the phosphorescence observed when the solutions are frozen.

Journal Article↗

PubMed1998

Determination of nafronyl in pharmaceutical preparations by means of stopped-flow micellar-stabilized room temperature phosphorescence.

The stopped-flow mixing technique was applied to micellar-stabilized room temperature phosphorimetry by measuring the fast appearance of the phosphorescent signal yielded by nafronyl in the presence of sodium dodecyl sulfate and thallium nitrate. This mixing system diminishes the time required for the deoxygenation of micellar medium by sodium sulfite, allowing a kinetic curve that levels off within only 5 s to be obtained. Phosphorescence enhancers thallium(I) nitrate, sodium dodecyl sulfate and sodium sulfite were optimized to obtain maximum sensitivity and selectivity. A pH value of 10.5 was selected as adequate for phosphorescence development. Two rapid, straightforward and automatic methods were proposed using the slope and amplitude of the kinetic curve, which are directly proportional to the nafronyl concentration, as analytical parameters. Calibration graphs were linear for the concentration range from 30 to 600 ng ml-1. Praxilene, the only commercial formulation containing nafronyl, was analysed by both proposed methodologies. Suitable recovery values were obtained.

Humans↗

PubMed2005

Highly sensitive and selective room-temperature phosphorescence determination of thiabendazole by the supramolecular interaction of thiabendazole/beta-cyclodextrin/triton X-100.

A strong and stable room temperature phosphorescence (RTP) signal (lambda(ex)/lambda(em) = 298/481 nm) resulting from a 1:1:1 beta-cyclodextrin (beta-CD)/thiabendazole (TBZ)/triton X-100 (TX-100) supramolecular ternary inclusion complex was induced by KI as a heavy atom perturber. Based on the heavy-atom induced RTP, a new phosphorescence method for TBZ determination was established. The analytical curve of TBZ gave a linear range of 20-820 ng mL(-1) with a detection limit and relative standard deviation of 2.1 ng mL(-1) and 1.9%, respectively. The interference of 46 coexisting substances was studied. Compared with the method using a chemical oxygen scavenger, this method is simpler as deoxygenation of the solution is not required. The detection limit and the heavy-atom concentration of the proposed method were decreased about 8 and 4 times, respectively. The lifetime of the phosphorescence was prolonged 9 times and the pH range was greatly broadened. The proposed method has been successfully applied to the determination of TBZ in tap water, lake water and pineapples.

Anti-Infective Agents↗

PubMed2006

Lifetime determination of fluorescence and phosphorescence of a series of oligofluorenes.

The photoluminescence (PL) properties of oligofluorenes with 2-ethylhexyl group in 9, 9' position in solution and as thin films were investigated by time-resolved techniques at both room temperature and 77 K. The fluorescence lifetimes of the oligomers decrease with chain length. The lifetimes tau follow the relation tau=386+808(1/n) (ps) where n is the number of fluorene units in the oligomer. Concentration and laser excitation energy dependences of PL spectra of the oligofluorenes are also given. Phosphorescence was observed for oligofluorenes in the frozen matrix of MTHF at 77 K. The lifetime of phosphorescence increases with increasing molecular length. Similar emission bands were observed for oligofluorenes with a central ketogroup. A lifetime analysis clearly reveals that the "green emission" of the oligomers free of ketogroups results from a phosphorescence with lifetime tau of 3 ms while the green emission from the keto-oligomer is a fluorescence from a charge transfer pi-pi* level of tau=8 ns.

Journal Article↗

PubMed2006

Application of density functional theory for studies of excited states and phosphorescence of platinum(II) acetylides.

The electronic states of different conformations of platinum acetylides Pt(PH3)2(C[triple bond]C-Ph)2 and Pt(PH3)2(C[triple bond]C-PhC[triple bond]C-Ph)2 (PE1 and PE2) were calculated with density functional theory (DFT) using effective core potential basis sets. Time dependent DFT calculations of UV absorption spectra showed strong dependence of the intense absorption band maxima on mutual orientation of the phenyl rings with respect to the P-Pt-P axis. Geometry optimization of the first excited triplet state (T1) indicates broken symmetry structure with the excitation being localized in one ligand. This splits the two substitution ligands into a nondistorted aromatic ring with the C[triple bond]C-Ph bonds for one side and into a quinoid structure with a cumulenic C=C=C link on the other side. Quadratic response (QR) calculations of spin-orbit coupling and phosphorescence radiative lifetime (tauR) indicated a good agreement with experimental tauR values reported for solid PE1 and PE2 and PE2 capped with dendrimers in tetrahydrofuran solutions. The QR calculations reproduced an increase of tauR upon prolongation of pi chain of ligands and concommittant redshift of the phosphorescence. Moreover, it is shown how the phosphorescence borrows intensity from sigma-->pi* transitions localized at the C[triple bond]C-Pt-P fragments and that there is no intensity borrowing from delocalized pi-->pi* transitions.

Journal Article↗

PubMed1978

Ligands containing heavy atoms: perturbation of phosphorescence of a tryptophan residue in the binding site of wheat germ agglutinin.

Information on the structure of binding sites of wheat germ agglutinin was obtained on the basis of fluorescence and phosphorescence changes of tryptophan residues induced by the binding of several thiomercuribenzoate derivatives of glycosides. The thiomercuribenzoate derivatives bind selectively to wheat germ agglutinin in the same way as the corresponding sugars. Using the thiomercuribenzoate of di-N-acetyl-beta-chitobiose, it was found that: (i) the fluorescence of tryptophan residues was drastically quenched at both 298 and 77 K; (ii) the phosphorescence intensity was strongly enhanced at 77 K; (iii) the phosphorescence lifetime was markedly decreased. A similar effect was observed with the thiomercuribenzoate of N-acetyl-beta-D-glucosamine. These changes were completely reversed upon addition of 1-O-methyl-di-N-acetyl-beta-chitobioside. The thiomercuribenzoate of beta-D-glucose had no effect at all, and the thiomercuribenzoate of tri-N-acetyl-beta-chitotriose had a limited effect. These results are interpreted as a specific heavy atom effect due to a close contact between one tryptophan residue of the protein and the heavy atom of the bound ligand. They are consistent with the view that: (i) binding sites of wheat germ agglutinin may be divided in three subsites, A, B, and C; (ii) a tryptophan residue is in the binding site at subsite C; and (iii) this residue and the ligand are in close contact. This new method, using the enhancement of spin-orbit coupling due to the selective perturbation induced in a tryptophan residue by a ligand containing a heavy atom, has proved to be suitable for locating the tryptophan residue in the binding site of wheat germ agglutinin and can probably be extended to other sugar-binding proteins.

Binding Sites↗

PubMed1995

Conformational changes of the mitochondrial F1-ATPase epsilon-subunit induced by nucleotide binding as observed by phosphorescence spectroscopy.

Changes in conformation of the epsilon-subunit of the bovine heart mitochondrial F1-ATPase complex as a result of nucleotide binding have been demonstrated from the phosphorescence emission of tryptophan. The triplet state lifetime shows that whereas nucleoside triphosphate binding to the enzyme in the presence of Mg2+ increases the flexibility of the protein structure surrounding the chromophore, nucleoside diphosphate acts in an opposite manner, enhancing the rigidity of this region of the macromolecule. Such changes in dynamic structure of the epsilon-subunit are evident at high ligand concentration added to both the nucleotide-depleted F1 (Nd-F1) and the F1 preparation containing the three tightly bound nucleotides (F1(2,1)). Since the effects observed are similar in both the F1 forms, the binding to the low affinity sites must be responsible for the conformational changes induced in the epsilon-subunit. This is partially supported by the observation that the Trp lifetime is not significantly affected by adding an equimolar concentration of adenine nucleotide to Nd-F1. The effects on protein structure of nucleotide binding to either catalytic or noncatalytic sites have been distinguished by studying the phosphorescence emission of the F1 complex prepared with the three noncatalytic sites filled and the three catalytic sites vacant (F1(3,0)). Phosphorescence lifetime measurements on this F1 form demonstrate that the binding of Mg-NTP to catalytic sites induces a slight enhancement of the rigidity of the epsilon-subunit. This implies that the binding to the vacant noncatalytic site of F1(2,1) must exert the opposite and larger effect of enhancing the flexibility of the protein structure observed in both Nd-F1 and F1(2,1). The observation that enhanced flexibility of the protein occurs upon addition of adenine nucleotides to F1(2,1) in the absence of Mg2+ provides direct support for this suggestion. The connection between changes in structure and the possible functional role of the epsilon-subunit is discussed.

Adenine Nucleotides↗

PubMed2003

Tryptophan phosphorescence spectroscopy reveals that a domain in the NAD(H)-binding component (dI) of transhydrogenase from Rhodospirillum rubrum has an extremely rigid and conformationally homogeneous protein core.

The characteristics of tryptophan phosphorescence from the NAD(H)-binding component (dI) component of Rhodospirillum rubrum transhydrogenase are described. This enzyme couples hydride transfer between NAD(H) and NADP(H) to proton translocation across a membrane and is only active as a dimer. Tryptophan phosphorescence spectroscopy is a sensitive technique for the detection of protein conformational changes and was used here to characterize dI under mechanistically relevant conditions. Our results indicate that the single tryptophan in dI, Trp-72, is embedded in a rigid, compact, and homogeneous protein matrix that efficiently suppresses collisional quenching processes and results in the longest triplet lifetime for Trp ever reported in a protein at ambient temperature (2.9 s). The protein matrix surrounding Trp-72 is extraordinarily rigid up to 50 degrees C. In all previous studies on Trp-containing proteins, changes in structure were reflected in a different triplet lifetime. In dI, the lifetime of Trp-72 phosphorescence was barely affected by protein dimerization, cofactor binding, complexation with the NADP(H)-binding component (dIII), or by the introduction of two amino acid substitutions at the hydride-transfer site. It is suggested that the rigidity and structural invariance of the protein domain (dI.1) housing this Trp residue are important to the mechanism of transhydrogenase: movement of dI.1 affects the width of a cleft which, in turn, regulates the positioning of bound nucleotides ready for hydride transfer. The unique protein core in dI may be a paradigm for the design of compact and stable de novo proteins.

Acrylamide↗

PubMed2005

Substrate-induced conformational changes in the membrane-embedded IIC(mtl)-domain of the mannitol permease from Escherichia coli, EnzymeII(mtl), probed by tryptophan phosphorescence spectroscopy.

Membrane-bound transport proteins are expected to proceed via different conformational states during the translocation of a solute across the membrane. Tryptophan phosphorescence spectroscopy is one of the most sensitive methods used for detecting conformational changes in proteins. We employed this technique to study substrate-induced conformational changes in the mannitol permease, EnzymeII(mtl), of the phosphoenolpyruvate-dependent phosphotransferase system from Escherichia coli. Ten mutants containing a single tryptophan were engineered in the membrane-embedded IIC(mtl)-domain, harboring the mannitol translocation pathway. The mutants were characterized with respect to steady-state and time-resolved phosphorescence, yielding detailed, site-specific information of the Trp microenvironment and protein conformational homogeneity. The study revealed that the Trp environments vary from apolar, unstructured, and flexible sites to buried, highly homogeneous, rigid peptide cores. The most remarkable example of the latter was observed for position 97, because its long sub-second phosphorescence lifetime and highly structured spectra in both glassy and fluid media imply a well defined and rigid core around the probe that is typical of beta-sheet-rich structural motifs. The addition of mannitol had a large impact on most of the Trp positions studied. In the case of position 97, mannitol binding induced partial unfolding of the rigid protein core. On the contrary, for residue positions 126, 133, and 147, both steady-state and time-resolved data showed that mannitol binding induces a more ordered and homogeneous structure around these residues. The observations are discussed in context of the current mechanistic and structural model of EII(mtl).

Amino Acid Motifs↗

PubMed1982

Rotational motion of cytochrome c derivatives bound to membranes measured by fluorescence and phosphorescence anisotropy.

Molecular motion of metal-free and metal-substituted cytochrome c derivatives was examined using the anisotropy of emissions from the singlet and the triplet states. The anisotropy of fluorescence provides a means to study the motion of cytochrome c in the nanosecond time scale, since the fluorescence lifetime of metal-free cytochrome c is around 10 ns. We find that the anisotropy of fluorescence of metal-free cytochrome c when bound to mitochondria does not decay, but when bound to phospholipids has a small component which decays independently of the rotation of the whole molecule. The use of phosphorescence extends the time scale for study into the millisecond regime, since the lifetime of the excited triplet state of zinc cytochrome c, as measured by triplet-triplet absorption and phosphorescence emission is approximately equal to 9 ms for free zinc cytochrome c and 7 ms for mitochondrial membrane-bound zinc cytochrome c at room temperature. The decay of anisotropy of phosphorescence emission of mitochondrial membrane-bound zinc cytochrome c is clearly biphasic; the fast component corresponds to a rotational relaxation time of 300 mus and the slow component with relaxation time of approximately equal to 6 ms. The slow component appears to be due to the rotation of the entire mitochondrion, whereas the fast component was interpreted to be due to the rotation of cytochrome c in a cone about a single axis perpendicular to the plane of the membrane surface.

Animals↗

PubMed1963

Phosphorescence of rat kidneys cooled in liquid nitrogen.

Cut surfaces of rat kidneys exhibit intense, reproducible, and very detailed phosphorescent patterns after they are cooled with liquid nitrogen and then exposed to shortwave ultraviolet radiation. Ligation of the renal blood vessels for a period of 6 to 24 hours destroys most of this phosphorescence, whereas a ligation of the ureter has no effect on kidney phosphorescence.

Animals↗

PubMed1993

Microvessel PO2 measurements by phosphorescence decay method.

A system is described for the in vivo noninvasive measurement of intravascular PO2 at the microscopic level. Under special circumstances the method can also be used to measure interstitial PO2. The PO2 determination is based on the O2-dependent quenching of phosphorescence of palladium-porphyrins bound to albumin. This compound was injected intravenously in the dosage of 30 mg/kg body wt and dissolved in saline to a concentration of 15 mg/ml. The phosphorescence emission was excited by epi-illumination with a strobe xenon arc and measured by a photomultiplier in a well-defined tissue area as small as 15 x 30 microns. A selected portion of the phosphorescence decay was fitted by a single exponential, and the Stern-Volmer equation was used to calculate PO2. Calibration was performed in vitro using saline and blood and was in agreement with previous reports. In vivo observations were made in normal tissue regions from the unanesthetized hamster transparent skin fold chamber preparation. The method allows PO2 determinations, in the range of 0-80 mmHg, in microvessels with diameters of 15-100 microns. Simultaneous transillumination of the tissue also allows measurement of vessel diameter and red blood cell velocity in the same vessels.

Animals↗

PubMed2001

Microvascular and interstitial PO(2) measurements in rat skeletal muscle by phosphorescence quenching.

To clarify the transport of O(2) across the microvessels in skeletal muscle, we designed an intravital laser microscope that utilizes a phosphorescence quenching technique to determine both the microvascular and tissue PO(2). After we injected the phosphorescent probe into systemic blood, phosphorescence excited by a N(2)-dye pulse laser was detected with a photomultiplier over a 10 microm in diameter area. In vitro and in vivo calibrations confirmed that the present method is accurate for PO(2) measurements in the range of 7-90 Torr (r = 0.958) and has a rapid response time. This method was then used to measure the PO(2) of microvessels with different diameters (40-130 microm) and of interstitial spaces in rat cremaster muscle. These measurements showed a significant drop in PO(2) in the arterioles after branching (from 74.6 to 46.6 Torr) and the presence of a large PO(2) gradient at the blood-tissue interface of arterioles (15-20 Torr). These findings suggest that capillaries are not the sole source of oxygen supply to surrounding tissue.

Animals↗

PubMed2004

Oxygen distribution in murine tumors: characterization using oxygen-dependent quenching of phosphorescence.

In the present work, a novel method for detecting hypoxia in tumors, phosphorescence quenching, was used to evaluate tissue and tumor oxygenation. This technique is based on the concept that phosphorescence lifetime and intensity are inversely proportional to the oxygen concentration in the tissue sample. We used the phosphor Oxyphor G2 to evaluate the oxygen profiles in three murine tumor models: K1735 malignant melanoma, RENCA renal cell carcinoma, and Lewis lung carcinoma. Oxygen measurements were obtained both as histograms of oxygen distribution within the sample and as an average oxygen pressure within the tissue sampled; the latter allowing real-time oxygen monitoring. Each of the tumor types examined had a characteristic and consistent oxygen profile. K1735 tumors were all well oxygenated, with a peak oxygen pressure of 37.8 +/- 5.1 Torr; RENCA tumors had intermediate oxygen pressures, with a peak oxygen pressure of 24.8 +/- 17.9 Torr; and LLC tumors were all severely hypoxic, with a peak oxygen pressure of 1.8 +/- 1.1 Torr. These results correlated well with measurements of tumor cell oxygenation measured by nitroimidazole (EF5) binding and were consistent with assessments of tumor blood flow by contrast enhanced ultrasound and tumor histology. The results show that phosphorescence quenching is a reliable, reproducible, and noninvasive method capable of providing real-time determination of oxygen concentrations within tumors.

Animals↗

PubMed1997

Platinum porphyrins as phosphorescent label for time-resolved microscopy.

We investigated phosphorescent metalloporphyrins as potential labels for time-resolved microscopy. On the basis of spectroscopic analysis of their physicochemical properties (quantum yield, molar absorption coefficient, decay times) the best candidates were selected. Next, we synthesized antibody and avidin metalloporphyrin conjugates. The optimal F/P ratio with respect to quantum yield, decay time, and retention of biological activity of these immunoreagents was determined. The reagents were then evaluated by in situ hybridization and immunocytochemical procedures for demonstration of hapten-labeled DNA probes, membrane antigens (CD type), and 28S rRNA. All stained samples exhibited bright phosphorescence that could be selectively detected using time-resolved microscopy, especially when glucose/glucose oxidase was added to the embedding medium to deplete oxygen. Applications of time-resolved detection of phosphorescent porphyrins in strongly autofluorescent material (histological sections) are discussed.

Affinity Labels↗

PubMed2004

Phosphorescence lifetime imaging in turbid media: the inverse problem and experimental image reconstruction.

Three-dimensional phosphorescence lifetime imaging is a novel method for the mapping of oxygen concentration in biological tissues. We present reconstruction techniques for recovering phosphorescent objects in highly scattering media based on the telegraph equation and two regularization methods, i.e., the Tikhonov-Phillips regularization and the maximum entropy method. Theoretical results are experimentally validated, and the reconstructed images of phosphorescent objects rendering oxygen maps in a layer are presented.

Biological Phenomena↗