Ultrafast Single-Molecule Fluorescence Measured by Femtosecond Double-Pulse Excitation Photon Antibunching.

Most measurements of fluorescence lifetimes on the single-molecule level are carried out using avalanche photon diodes (APDs). These single-photon counters are inherently slow, and their response shows a strong dependence on photon energy, which can make reconvolution of the instrument response function (IRF) challenging. An ultrafast time resolution in single-molecule fluorescence is crucial, e.g., in determining donor lifetimes in donor-acceptor couples which undergo energy transfer, or in plasmonic antenna structures, where the radiative rate and non-radiative rates are enhanced. We introduce a femtosecond double-excitation (FeDEx) photon correlation technique, which measures the degree of photon antibunching as a function of time delay between two excitation pulses. In this boxcar integration, the time resolution of fluorescence transients is limited solely by the laser pulse length and is independent of the detector IRF. The versatility of the technique is demonstrated with a custom-made donor-acceptor complex with one donor and two acceptors and with single dye molecules positioned accurately between two gold nanoparticles using DNA origami. The latter structures show ∼75-fold radiative-rate enhancement and fluorescence lifetimes down to 19 ps, which is measured without the need for any reconvolution. With the potential of measuring subpicosecond fluorescence lifetimes, plasmonic antenna structures can now be optimized further.

Anomalous Linear Dichroism in Bent Chromophores of π-conjugated Polymers: Departure from the Franck-Condon Principle.

We examine the influence of bending of π-conjugated chromophores on photoluminescence (PL) by spectrally resolving the depolarization of fluorescence on the single-molecule level. The effect of excited-state mixing mediated by molecular vibrations is manifested in the departure from the usual achromatic linear dichroism of fluorescence, with the polarization anisotropy decreasing in the vibronic progression. Bent chromophores reveal an overall increase in vibronic PL intensity with polarization orthogonal to the molecular long axis. This manifestation of the Renner-Herzberg-Teller (RHT) effect illustrates the breakdown of the Franck-Condon principle in macromolecules used in organic electronics, providing information on the orientation of transition-dipole moments and the origin of spectral broadening. While some of the spectral signatures of the RHT effect appear similar to those of H aggregation in molecular dimers, discrimination between the two phenomena is straightforward since H aggregation does not induce anomalous linear dichroism.

Donor Preconditioning After the Onset of Brain Death With Dopamine Derivate n-Octanoyl Dopamine Improves Early Posttransplant Graft Function in the Rat.

Heart transplantation is the therapy of choice for end-stage heart failure. However, hemodynamic instability, which has been demonstrated in brain-dead donors (BDD), could also affect the posttransplant graft function. We tested the hypothesis that treatment of the BDD with the dopamine derivate n-octanoyl-dopamine (NOD) improves donor cardiac and graft function after transplantation. Donor rats were given a continuous intravenous infusion of either NOD (0.882 mg/kg/h, BDD+NOD, n = 6) or a physiological saline vehicle (BDD, n = 9) for 5 h after the induction of brain death by inflation of a subdural balloon catheter. Controls were sham-operated (n = 9). In BDD, decreased left-ventricular contractility (ejection fraction; maximum rate of rise of left-ventricular pressure; preload recruitable stroke work), relaxation (maximum rate of fall of left-ventricular pressure; Tau), and increased end-diastolic stiffness were significantly improved after the NOD treatment. Following the transplantation, the NOD-treatment of BDD improved impaired systolic function and ventricular relaxation. Additionally, after transplantation increased interleukin-6, tumor necrosis factor TNF-α, NF-kappaB-p65, and nuclear factor (NF)-kappaB-p105 gene expression, and increased caspase-3, TNF-α and NF-kappaB protein expression could be significantly downregulated by the NOD treatment compared to BDD. BDD postconditioning with NOD through downregulation of the pro-apoptotic factor caspase-3, pro-inflammatory cytokines, and NF-kappaB may protect the heart against the myocardial injuries associated with brain death and ischemia/reperfusion.

Interactions between π-conjugated chromophores in a giant molecular spoked wheel.

We discuss the intriguing photophysics of a giant molecular spoked wheel of π-conjugated arylene-alkynylene chromophores on the single-molecule level. This "molecular mesoscopic" structure, C1878H2682, shows fast switching between the 12 identical chromophores since the fluorescence is unpolarised but only one chromophore emits at a time.

Longevity loss among cured tuberculosis patients and the potential value of prevention.

BACKGROUND: Evidence of substantial, quantifiable and preventable burdens of mortality hazard even after anti-tuberculosis treatment and cure would be a compelling, concrete, and useful measure of the value of prevention. METHODS: We compared years of potential life lost between a cohort of 3 933 cured tuberculosis (TB) patients and 9 166 persons with latent tuberculous infection. We constructed a regression model to predict the expected years of potential life lost in each cohort and for demographic subgroups. RESULTS: Among decedents, a history of fully treated TB is associated with a predicted average 3.6 more years of potential life loss than a comparable population without active TB. Greater longevity losses were predicted among those identified as White and Hispanic than among Black and Asian counterparts. CONCLUSION: We found significant differences in predicted longevity of treated TB survivors relative to a similar group without active TB. These excess losses are substantial: a total of 14 158 life-years or the equivalent of more than 188 75-year lifespans. These findings illustrate an important opportunity cost associated with each preventable TB case - an average of 3.6 potential years of life. We conclude that substantial preventable mortality burdens remain despite adequate anti-tuberculosis treatment, a compelling rationale for more widespread and systematic use of prevention.

Carnosine treatment in combination with ACE inhibition in diabetic rats.

In humans, we reported an association of a certain allele of carnosinase gene with reduced carnosinase activity and absence of nephropathy in diabetic patients. CN1 degrades histidine dipeptides such as carnosine and anserine. Further, we and others showed that treatment with carnosine improves renal function and wound healing in diabetic mice and rats. We now investigated the effects of carnosine treatment alone and in combination with ACE inhibition, a clinically established nephroprotective drug in diabetic nephropathy. Male Sprague-Dawley rats were injected i.v. with streptozotocin (STZ) to induce diabetes. After 4 weeks, rats were unilaterally nephrectomized and randomized for 24 weeks of treatment with carnosine, lisinopril or both. Renal CN1 protein concentrations were increased under diabetic conditions which correlated with decreased anserine levels. Carnosine treatment normalized CN1 abundance and reduced glucosuria, blood concentrations of glycosylated hemoglobin (HbA1c), carboxyl-methyl lysine (CML), N-acetylglucosamine (GlcNac; all p<0.05 vs. non-treated STZ rats), reduced cataract formation (p<0.05) and urinary albumin excretion (p<0.05), preserved podocyte number (p<0.05) and normalized the increased renal tissue CN1 protein concentration. Treatment with lisinopril had no effect on HbA1C, glucosuria, cataract formation and CN1 concentration, but reduced albumin excretion rate more effectively than carnosine treatment (p<0.05). Treatment with both carnosine and lisinopril combined the effects of single treatment, albeit without additive effect on podocyte number or albuminuria. Increased CN1 amount resulted in decreased anserine levels in the kidney. Both carnosine and lisinopril exert distinct beneficial effects in a standard model of diabetic nephropathy. Both drugs administered together combine the respective effects of single treatment, albeit without exerting additive nephroprotection.

The carbon monoxide releasing molecule (CORM-3) inhibits expression of vascular cell adhesion molecule-1 and E-selectin independently of haem oxygenase-1 expression.

BACKGROUND AND PURPOSE: Although carbon monoxide (CO) can modulate inflammatory processes, the influence of CO on adhesion molecules is less clear. This might be due to the limited amount of CO generated by haem degradation. We therefore tested the ability of a CO releasing molecule (CORM-3), used in supra-physiological concentrations, to modulate the expression of vascular cell adhesion molecule (VCAM)-1 and E-selectin on endothelial cells and the mechanism(s) involved. EXPERIMENTAL APPROACH: Human umbilical vein endothelial cells (HUVECs) were stimulated with tumour necrosis factor (TNF)-alpha in the presence or absence of CORM-3. The influence of CORM-3 on VCAM-1 and E-selectin expression and the nuclear factor (NF)-kappaB pathway was assessed by flow cytometry, Western blotting and electrophoretic mobility shift assay. KEY RESULTS: CORM-3 inhibited the expression of VCAM-1 and E-selectin on TNF-alpha-stimulated HUVEC. VCAM-1 expression was also inhibited when CORM-3 was added 24 h after TNF-alpha stimulation or when TNF-alpha was removed. This was paralleled by deactivation of NF-kappaB and a reduction in VCAM-1 mRNA. Although TNF-alpha removal was more effective in this regard, VCAM-1 protein was down-regulated more rapidly when CORM-3 was added. CORM-3 induced haem oxygenase-1 (HO-1) in a dose- and time-dependent manner, mediated by the transcription factor, Nrf2. CORM-3 was still able to down-regulate VCAM-1 expression in HUVEC transfected with siRNA for HO-1 or Nrf2. CONCLUSIONS AND IMPLICATIONS: Down-regulation of VCAM and E-selectin expression induced by CORM-3 was independent of HO-1 up-regulation and was predominantly due to inhibition of sustained NF-kappaB activation.

Phenylene-ethynylene macrocycles as model systems of interchromophoric interactions in pi-conjugated macromolecules.

Unraveling the complex photophysics of macromolecular pi-conjugated systems requires both the development of suitable model systems to access a particular subset of a material's parameter space and the choice of matching spectroscopic techniques. We address the question of the strength of interchromophoric interactions in macromolecular systems by studying the fluorescence depolarization kinetics of a family of prototypical conjugated macrocycles. Shrinking the size of the molecular system decelerates fluorescence depolarization even though the radius of gyration decreases. Although the smaller macrocycles show faster rotational diffusion, the larger compounds exhibit an additional initial depolarization mechanism, attributed to intramolecular interchromophoric energy transfer. Comparison with fragments of the molecule illustrates that the larger macrocycles can be interpreted as bichromophoric systems, whereas the effectively parallel chromophoric elements of the smaller ring are indistinguishable in terms of polarization. The potential role of strong interchromophoric interaction is discussed. The results illustrate a subtle link between interchromophoric arrangement and ultrafast fluorescence depolarization, phenomena, which are often considered in the context of conjugated polymers: chromophoric alignment can potentially counteract the effect of polarization memory loss through energy transfer.

SAMs of shape-persistent macrocycles: structure and binding on HOPG and Au(111).

Self-assembled monolayers of shape-persistent macrocycles have been adsorbed on highly oriented pyrolytic graphite and Au(111) substrates. Their structure and binding characteristics have been investigated by scanning tunneling microscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy experiments. Special functionalization of the macrocycles for the first time has enabled their self-assembling and binding on a metal substrate and opened a new route for new functional nanostructures.

Synthesis, aggregation, and adsorption phenomena of shape-persistent macrocycles with extraannular polyalkyl substituents.

The synthesis of shape-persistent macrocycles based on the phenyl-ethynyl backbone containing various extraannular alkyl side chains is described. Although compound solubility increases with increasing size of the side groups, decreasing the solvent polarity induces aggregation of the rings by nonspecific interactions. This was investigated by proton NMR spectroscopy. The magnitude of aggregation can be varied by using solvent mixtures of different hexane content, supporting the model of a solvophobic effect. From 1,2,4-trichlorobenzene solution the macrocycle 1c adsorbs at the surface of highly oriented pyrolitic graphite (HOPG). The two-dimensional order of the structure was investigated by scanning tunneling microscopy (STM) revealing the formation of a two-dimensional lattice of p1(2)mm symmetry with lattice parameters A = 3.6 nm, B = 5.7 nm, and Gamma = 74 degrees.

Cyanobacterial toxins: removal during drinking water treatment, and human risk assessment.

Cyanobacteria (blue-green algae) produce toxins that may present a hazard for drinking water safety. These toxins (microcystins, nodularins, saxitoxins, anatoxin-a, anatoxin-a(s), cylindrospermopsin) are structurally diverse and their effects range from liver damage, including liver cancer, to neurotoxicity. The occurrence of cyanobacteria and their toxins in water bodies used for the production of drinking water poses a technical challenge for water utility managers. With respect to their removal in water treatment procedures, of the more than 60 microcystin congeners, microcystin-LR (L, L-leucine; R, L-arginine) is the best studied cyanobacterial toxin, whereas information for the other toxins is largely lacking. In response to the growing concern about nonlethal acute and chronic effects of microcystins, the World Health Organization has recently set a new provisional guideline value for microcystin-LR of 1.0 microg/L drinking water. This will lead to further efforts by water suppliers to develop effective treatment procedures to remove these toxins. Of the water treatment procedures discussed in this review, chlorination, possibly micro-/ultrafiltration, but especially ozonation are the most effective in destroying cyanobacteria and in removing microcystins. However, these treatments may not be sufficient during bloom situations or when a high organic load is present, and toxin levels should therefore be monitored during the water treatment process. In order to perform an adequate human risk assessment of microcystin exposure via drinking water, the issue of water treatment byproducts will have to be addressed in the future.