Iron(III) Catecholates for Cellular Imaging and Photocytotoxicity in Red Light

Iron(III) complexes [Fe( L )( L′ )(NO₃)]—in which L is phenyl‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 1 ), (anthracen‐9‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 2 ), (pyreny‐1‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 3 – 5 ), and L′ is catecholate ( 1 – 3 ), 4‐tert‐butyl catecholate ( 4 ), and 4‐(2‐aminoethyl)‐benzene‐1,2‐diolate ( 5 )—were synthesized and their photocytotoxic properties examined. The five electron‐paramagnetic complexes displayed a Fe^III/Fe^II redox couple near ?0.4 V versus a saturated calomel electrode (SCE) in DMF/0.1 m tetrabutylammonium perchlorate (TBAP). They showed unprecedented photocytotoxicity in red light (600–720 nm) to give IC₅₀≈15 μM in various cell lines by means of apoptosis to generate reactive oxygen species. They were ingested in the nucleus of HeLa and HaCaT cells in 4 h, thereby interacting favorably with calf thymus (ct)‐DNA and photocleaving pUC19 DNA in red light of 785 nm to form hydroxyl radicals.     

Double-strand DNA cleavage from photodecarboxylation of (micro-oxo)diiron(III) L-histidine complex in visible light

The oxo-bridged diiron(III) complex [{Fe(L-his)(dpq)}(2)(micro-O)](2+) having L-histidine (L-his) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) bound to Fe(III) exemplifies an iron-based model photonuclease that shows visible light-induced DNA double-strand cleavage in a photodecarboxylation pathway and models iron-bleomycin activity.     

Methods to array photonic crystal microcavities for high throughput high sensitivity biosensing on a silicon-chip based platform

We experimentally demonstrate a method to create large-scale chip-integrated photonic crystal sensor microarrays by combining the optical power splitting characteristics of multi-mode interference (MMI) power splitters and transmission drop resonance characteristics of multiple photonic crystal microcavities arrayed along the length of the same photonic crystal waveguide. L13 photonic crystal microcavities are employed which show high Q values (~9300) in the bio-ambient phosphate buffered saline (PBS) as well as high sensitivity, experimentally demonstrated to ~98 atto-grams. Two different probe antibodies were specifically detected simultaneously with a control sample, in the same experiment.     

Photo-induced DNA cleavage activity and remarkable photocytotoxicity of lanthanide(III) complexes of a polypyridyl ligand

Lanthanide(III) complexes [Ln(pyphen)(acac)(2)(NO(3))] (1, 2), [Ln(pydppz)(acac)(2)(NO(3))] (3, 4) and [La(pydppz)(anacac)(2)(NO(3))] (5), where Ln is La(III) (in 1, 3, 5) and Gd(III) (in 2, 4), pyphen is 6-(2-pyridyl)-1,10-phenanthroline, pydppz is 6-(2-pyridyl)-dipyrido[3,2-a:2',3'-c]phenazine, anacac is anthracenylacetylacetonate and acac is acetylacetonate, were prepared, characterized and their DNA photocleavage activity and photocytotoxicity studied. The crystal structure of complex 2 displays a GdO(6)N(3) coordination. The pydppz complexes 3-5 show an electronic spectral band at ~390 nm in DMF. The La(III) complexes are diamagnetic, while the Gd(III) complexes are paramagnetic with seven unpaired electrons. The molar conductivity data suggest 1 : 1 electrolytic nature of the complexes in aqueous DMF. They are avid binders to calf thymus DNA giving K(b) in the range of 5.4 × 10(4)-1.2 × 10(6) M(-1). Complexes 3-5 efficiently cleave supercoiled DNA to its nicked circular form in UV-A light of 365 nm via formation of singlet oxygen ((1)O(2)) and hydroxyl radical (HO˙) species. Complexes 3-5 also exhibit significant photocytotoxic effect in HeLa cancer cells giving respective IC(50) value of 0.16(±0.01), 0.15(±0.01) and 0.26±(0.02) μM in UV-A light of 365 nm, while they are less toxic in dark with an IC(50) value of >3 μM. The presence of an additional pyridyl group makes the pydppz complexes more photocytotoxic than their dppz analogues. FACS analysis of the HeLa cells treated with complex 4 shows apoptosis as the major pathway of cell death. Nuclear localization of complex 5 having an anthracenyl moiety as a fluorophore is evidenced from the confocal microscopic studies.     

Effect of ionic solutes on the hydrogen bond network dynamics of water: power spectral analysis of aqueous NaCl solutions

To understand the modifications of the hydrogen bond network of water by ionic solutes, power spectra as well as static distributions of the potential energies of tagged solvent molecules and solute ions have been computed from molecular dynamics simulations of aqueous NaCl solutions. The key power spectral features of interest are the presence of high-frequency peaks due to localized vibrational modes, the existence of a multiple time scale or 1/falpha frequency regime characteristic of networked liquids, and the frequency of crossover from 1/falpha type behavior to white noise. Hydrophilic solutes, such as the sodium cation and the chloride anion, are shown to mirror the multiple time scale behavior of the hydrogen bond network fluctuations, unlike hydrophobic solutes which display essentially white noise spectra. While the power spectra associated with tagged H2O molecules are not very sensitive to concentration in the intermediate frequency 1/falpha regime, the crossover to white noise is shifted to lower frequencies on going from pure solvent to aqueous alkali halide solutions. This suggests that new and relatively slow time scales enter the picture, possibly associated with processes such as migration of water molecules from the hydration shell to the bulk or conversion of contact ion pairs into solvent-separated ion pairs which translate into variations in equilibrium transport properties of salt solutions with concentration. For anions, cations, and solvent molecules, the trends in the alpha exponents of the multiple time scale region and the self-diffusivities are found to be strongly correlated.     

Diffusivity, excess entropy, and the potential-energy landscape of monatomic liquids

The connection between thermodynamic, transport, and potential-energy landscape features is studied for liquids with Lennard-Jones-type pair interactions using both microcanonical molecular-dynamics and isothermal-isobaric ensemble Monte Carlo simulations. Instantaneous normal-mode and saddle-point analyses of two variants of the monatomic Lennard-Jones liquid have been performed. The diffusivity is shown to depend linearly on several key properties of instantaneous and saddle configurations-the energy, the fraction of negative curvature directions, and the mean, maximum, and minimum eigenvalues of the Hessian. Since the Dzugutov scaling relationship also holds for such systems [Nature (London) 381, 137 (1996)], the exponential of the excess entropy, within the two-particle approximation, displays the same linear dependence on energy landscape properties as the diffusivity.     

Silicon nano-membrane based photonic crystal microcavities for high sensitivity bio-sensing

We experimentally demonstrated photonic crystal microcavity based resonant sensors coupled to photonic crystal waveguides in silicon nano-membrane on insulator for chemical and bio-sensing. Linear L-type microcavities are considered. In contrast to cavities with small mode volumes, but low quality factors for bio-sensing, we showed increasing the length of the microcavity enhances the quality factor of the resonance by an order of magnitude and increases the resonance wavelength shift while retaining compact device characteristics. Q~26760 and sensitivity down to 15 ng/ml and ~110 pg/mm2 in bio-sensing was experimentally demonstrated on silicon-on-insulator devices.