Selective Examination of Plasma Membrane–Associated Photosensitizers Using Total Internal Reflection Fluorescence Spectroscopy: Correlation between Photobleaching and Photodynamic Efficacy of Protoporphyrin IX

Fluorescence spectra, fluorescence decay kinetics, photobleaching kinetics and photodynamic efficacy of protoporphyrin IX (PP) were investigated in endothelial cells in vitro after different incubation times. Fluorescence spectra and photobleaching kinetics were determined during total internal reflection (TIR) illumination or epiillumination. Because penetration depth of the excitation light during TIR illumination was limited to about 100 nm, plasma membrane-associated PP was almost selectively examined. Spectra obtained by TIR fluorescence spectroscopy (FS) showed a very low background, where-as spectra obtained by epi-illumination exhibited considerable background by autofluorescence and scattered light. For photobleaching kinetics during TIR illumination after 1 h or 24 h incubation, a biexponential fluorescence decrease was observed with a rapidly and a slowly bleaching portion. After 1 h incubation, the rapidly bleaching portion was the predominant fraction, whereas after 24 h incubation comparable relative amounts of the rapidly and slowly bleaching portion were determined. The rapidly and slowly bleaching portion were assigned to PP monomers and aggregated species in close vicinity to the plasma membrane. Fluorescence decay measurements after epi-illumination support the decrease of PP monomers within the whole cell with increasing incubation time. In contrast to TIR illumination, photobleaching of PP during epi-illumination was characterized by slow monoexponential fluorescence decrease after 1 h or 24 h incubation. Photodynamic efficacy of PP using epi-illumination was found to depend strongly on incubation time. Considerable cell inactivation was determined for short incubation times (1 h or 3 h), whereas photodynamic efficacy was diminished for longer incubation times. Reduced photodynamic efficacy after long incubation times was assigned to the lower amount of photodynamically active monomers determined close to the plasma membrane as well as within the whole cell. In conclusion, TIRFS measurements are suggested to be an appropriate tool for the examination of the plasma membrane-associated photosensitizer fraction in living cells.     

On a Definitizable Analog of the Trigonometric Moment Problem Generating an Indefinite Toeplitz Form

We prove the existence of an integro-polynomial representation for a sequence of numbers such that there exists a difference operator mapping this sequence to a sequence that generates the solvable trigonometric moment problem. A similar result related to the power moment problem was given in [12].     

Synthesis, spectroscopic and electrochemical characterization, and DFT study of seventeen C70(CF3)n derivatives (n=2, 4, 6, 8, 10, 12)

Eight new C70(CF3)n derivatives (n=2, 6, 10, 12) have been synthesized and characterized by UV/Vis and 19F NMR spectroscopy, cyclic voltammetry, and quantum chemical calculations at the DFT level of theory. Nine previously known derivatives of C70(CF3)n with n=2-12 were also studied by cyclic voltammetry (and seven of them by UV/Vis spectroscopy for the first time). Most of the 17 compounds exhibited two or three reversible reductions at scan rates from 20 mV s(-1) up to 5.0 V s(-1). In general, reduction potentials for the 0/- couple are shifted anodically relative to the C70 0/-) couple. However, the 0/- E1/2 values for a given composition are strongly dependent on the addition pattern of the CF3 groups. The data show that the addition pattern is as important, if not more important in some cases, than the number of substituents, n, in determining E1/2 values. An analysis of the DFT-predicted LUMOs indicates that addition patterns that have non-terminal double bonds in pentagons result in derivatives that are strong electron acceptors.     

Heteronuclear NMR investigation on the structure and dynamics of the chromophore binding pocket of the cyanobacterial phytochrome Cph1

Structural changes of the chromophore in phytochrome proteins associated with its photocycle are still not fully understood. We use heteronuclear NMR to investigate the conformation and dynamics of the chromophore in the binding pocket of the cyanobacterial phytochrome Cph1. On the basis of distance information obtained from three-dimensional nuclear Overhauser enhancement (3D-NOESY) spectra using the photochemically intact photosensory module of Cph1 we demonstrate that the chromophore is in the ZZZssa form in the P(r) (red absorbing form) state and the ZZEssa form in the P(fr) (far-red absorbing form) state of the protein. While ZZZssa for the P(r) state is in agreement with a recently determined X-ray structure, no comparable information for the P(fr) state of photochemically intact phytochrome has been available up to now. In addition, the chromophore in the binding pocket of Cph1 exhibits a notable mobility, which is distinctly different in the two photostates.     

Infrared hole burning of crown ether 18-c-6 ammonium ion complexes

Crystals of the complexes of 18-crown-6 with a number of ammonium salts (bromide, chloride, two forms of iodide, nitrate) and with amminetrifluoroboron have been prepared, analyzed with X-ray diffraction, and then investigated by infrared hole burning. The complexes all have similar hydrogen-bonding arrangements between the crown ether ring and the ammonium nitrogen. Hole burning of the infrared bands at low temperature identifies the N-D hydrogen bonds of the compounds that have been doped with a small amount of deuterium. The patterns of N-D bands from different complexes are often quite overlapped, with a few notable exceptions. The hole burning reveals a wide variety of phenomena, including monotonic decay and kinetic interchange among the holes and antiholes, a variety similar to that observed in previous hole-burning experiments.     

Pairing heterocyclic cations with closo-dodecafluorododecaborate (2−): Synthesis of binary heterocyclium(1+) salts and a Ag4(heterocycle)8 salt of B12F12

Eight binary salts that pair triazolium(1+), imidazolium(1+), pyrimidinium(1+), or purinium(1+) cations with the icosahedral closo-dodecafluorododecaborate(2−) anion (B₁₂F₁₂²⁻) were synthesized using open-air benchtop metathesis reactions in water or acetonitrile. The scale of the reactions varied from just milligrams to nearly one gram of the K₂B₁₂F₁₂ starting material. Other reaction conditions, the scope of the reaction, and the solubilities for the new salts are discussed. Five [heterocyclium]₂[B₁₂F₁₂] salts, which were obtained in yields ranging from 84% to 99%, displayed significantly higher densities than the corresponding previously reported analogous [heterocyclium]₂[B₁₂H₁₂] and [heterocyclium][CB₁₁H₁₂] salts. A ninth high-density salt consisted of B₁₂F₁₂²⁻ paired with a complex Ag₄(triazole)₈⁴⁺ cation. The structures of eight of the nine new compounds were determined by single-crystal X-ray diffraction analysis. The density of five [heterocyclium]₂[B₁₂F₁₂] salts was found to increase approximately linearly as the distance between the five-membered-ring heterocyclium(1+) cation centroids decreased. This work demonstrates additional flexibility for the rational design of ionic structures with predictable properties, which will ultimately permit the tailoring of ingredient-response behavior.     

The antibiotic CJ-15,801 is an antimetabolite that hijacks and then inhibits CoA biosynthesis

The natural product CJ-15,801 is an inhibitor of Staphylococcus aureus, but not other bacteria. Its close structural resemblance to pantothenic acid, the vitamin precursor of coenzyme A (CoA), and its Michael acceptor moiety suggest that it irreversibly inhibits an enzyme involved in CoA biosynthesis or utilization. However, its mode of action and the basis for its specificity have not been elucidated to date. We demonstrate that CJ-15,801 is transformed by the uniquely selective S. aureus pantothenate kinase, the first CoA biosynthetic enzyme, into a substrate for the next enzyme, phosphopantothenoylcysteine synthetase, which is inhibited through formation of a tight-binding structural mimic of its native reaction intermediate. These findings reveal CJ-15,801 as a vitamin biosynthetic pathway antimetabolite with a mechanism similar to that of the sulfonamide antibiotics and highlight CoA biosynthesis as a viable antimicrobial drug target.     

A buckybowl with a lot of potential: C5-C20H5(CF3)5

Lots of potential: a trifluoromethylated corannulene, C(5)-C(20)H(5)(CF(3))(5), has been prepared and characterized spectroscopically and by X-ray crystallography. The structure exhibits a highly ordered bowl stacking that is unusual for corannulenes with acyclic substituents. The first reduction of C(5)-C(20)H(5)(CF(3))(5) is anodically shifted by 0.95 V, making it the strongest corannulene-based electron acceptor to date.