Photocrystallographic structure determination of a new geometric isomer of [Ru(NH3)4(H2O)(eta1-OSO)][MeC6H4SO3]2

The structure of a new metastable geometric isomer of [Ru(NH3)4(H2O)(SO2)][MeC6H4SO3]2 in which the SO2 group is coordinated through a single oxygen in an eta1-OSO bonding mode has been determined at 13 K; the new isomer was obtained as a 36% component of the structure within a single crystal upon irradiation using a tungsten lamp.     

Deflected mirage mediation: a phenomenological framework for generalized supersymmetry breaking

We present a general phenomenological framework for dialing between gravity mediation, gauge mediation, and anomaly mediation. The approach is motivated from recent developments in moduli stabilization, which suggest that gravity mediated terms can be effectively loop suppressed and thus comparable to gauge and anomaly mediated terms. The gauginos exhibit a mirage unification behavior at a "deflected" scale, and gluinos are often the lightest colored sparticles. The approach provides a rich setting in which to explore generalized supersymmetry breaking at the CERN Large Hadron Collider.     

State-resolved UV photofragmentation spectrum of the metal dication complex [Zn(pyridine)(4)](2+)

A combined theoretical and experimental study of electronic transitions in the complex [Zn(pyridine)(4)](2+) provides the first example of a state-resolved electronic spectrum to be recorded for a dication complex in the gas phase.     

N,N'-diarylureas: a new family of atropisomers exhibiting highly diastereoselective reactivity

2,6-disubstituted N-aryl ureas rotate slowly about their Ar-N bonds and can exist as separable atropisomers. They also react remarkably diastereoselectively, with the urea axis controlling new stereogenic centers with high fidelity in a variety of nucleophilic and electrophilic addition reactions. The sense of diastereoselectivity in lateral lithiation-electrophilic quench reactions is electrophile-dependent and appears to be the result of stereospecific reaction with one of two interconvertible diastereoisomeric organolithiums.     

Haloing, flocculation, and bridging in colloid-nanoparticle suspensions

Integral equation theory with a hybrid closure approximation is employed to study the equilibrium structure of highly size asymmetric mixtures of spherical colloids and nanoparticles. Nonequilibrium contact aggregation and bridging gel formation is also qualitatively discussed. The effect of size asymmetry, nanoparticle volume fraction and charge, and the spatial range, strength, and functional form of colloid-nanoparticle and colloid-colloid attractions in determining the potential-of-mean force (PMF) between the large spheres is systematically explored. For hard, neutral particles with weak colloid-nanoparticle attraction qualitatively distinct forms of the PMF are predicted: (i) a contact depletion attraction, (ii) a repulsive form associated with thermodynamically stable "nanoparticle haloing," and (iii) repulsive at contact but with a strong and tight bridging minimum. As the interfacial cohesion strengthens and becomes shorter range the PMF acquires a deep and tight bridging minimum. At sufficiently high nanoparticle volume fractions, a repulsive barrier then emerges which can provide kinetic stabilization. The charging of nanoparticles can greatly reduce the volume fractions where significant changes of the PMF occur. For direct and interfacial van der Waals attractions, the large qualitative consequences of changing the absolute magnitude of nanoparticle and colloid diameters at fixed size asymmetry ratio are also studied. The theoretical results are compared with recent experimental and simulation studies. Calculations of the real and Fourier space mixture structure at nonzero colloid volume fractions reveal complex spatial reorganization of the nanoparticles due to many body correlations.     

Quantitative in vitro demonstration of two-photon photodynamic therapy using photofrin and visudyne

Photodynamic therapy (PDT), the combined action of a photosensitizer and light to produce a cytotoxic effect, is an approved therapy for a number of diseases. At present, clinical PDT treatments involve one-photon excitation of the photosensitizer. A major limitation is that damage may be caused to healthy tissues that have absorbed the drug and lie in the beam path. Two-photon excitation may minimize this collateral damage, as the probability of absorption increases with the square of the light intensity, enabling spatial confinement of the photosensitizer activation. A potential application is the treatment of the wet-form of age-related macular degeneration, the foremost cause of central vision loss in the elderly. Herein, the commercial photosensitizers Visudyne and Photofrin are used to demonstrate quantitative in vitro two-photon PDT. A uniform layer of endothelial cells (YPEN-1) was irradiated with a Ti:sapphire laser (300 fs, 865 nm, 90 MHz) using a confocal scanning microscope. Quantification of the two-photon PDT effect was achieved using the permeability stain Hoechst 33258 and a SYTOX Orange viability stain. Visudyne was found to be around seven times more effective as a two-photon photosensitizer than Photofrin under the conditions used, consistent with its higher two-photon absorption cross-section. We also demonstrate for the first time the quadratic intensity dependence of cellular two-photon PDT. This simple in vitro method for quantifying the efficacy of photosensitizers for two-photon excited PDT will be valuable to test specifically designed two-photon photosensitizers before proceeding to in vivo studies in preclinical animal models.     

Evanescent wave excited luminescence from levitated quantum dot modified colloids

Evanescent wave excited luminescence of quantum dot modified polystyrene (QDPS) colloids is investigated to measure potential energy profiles of QDPS colloids electrostatically levitated above a planar glass surface. Luminescence is characterized for three different-sized PS colloids modified with three different-sized QDs using confocal microscopy, emission spectra, flow cytometry, and temporal measurements of levitated and deposited colloids. Colloid-surface potential energy profiles constructed from scattering and luminescence intensity data display excellent agreement with each other, theoretical predictions, and independently measured parameters. QDPS luminescence intensity is indirectly confirmed to have an exponential dependence on height similar to conventional colloidal evanescent wave scattering. Our findings indicate that evanescent wave excited QDPS luminescence could enable total internal reflection microscopy measurements of index-matched hard spheres, multiple specific biomolecular interactions via spectral multiplexing, enhanced morphology-dependent resonance modes, and integrated evanescent wave-video-confocal microscopy experiments not possible with scattering.     

Ground-and Excited-State Characterization of an Electrostatic Complex between Tetrakis-(4-Sulfonatophenyl)porphyrin and 16-Pyrimidinium Crown-4

Abstract— We report the formation of an electrostatic complex between (16-pyrimidinium crown-4)tetranitrate (16PC4) and tetrakis-(4-sulfonatophenyl)porphyrin (4SP) in aqueous solution. Ground-state complex formation results in a red shift of the 4SP visible absorption bands and a decrease in absorbance of the Soret band. The equilibrium constant for complex formation (determined from optical titrations) is found to be (2.0 ± 0.2) × 10⁵ M ⁻¹. In addition, the data fit to an expression describing a 1:1 stoichiometry. Excitation of the complex results in quenching of both the excited singlet and triplet states of the associated porphyrin. The singlet-state lifetime decreases from 10 ns for the free porphyrin to 1.5 ns in the presence of 16PC4 at low solution ionic strengths. In addition, evidence is presented for triplet-state quenching within the complex with k _q= (1.1 ± 0.1) × 10⁴ s⁻¹. The mechanism of quenching is tentatively assigned to electron transfer from either the excited singlet or excited triplet state of the porphyrin to the ground state of the 16PC4.