Fabrication of Nd3+ and Yb3+ doped NIR emitting nano fluorescent probe: A candidate for bioimaging applications.

The intentional design of rare earth doped luminescent architecture exhibits unique optical properties and it can be considered as a promising and potential probe for optical imaging applications. Calcium fluoride (CaF2) nanoparticles doped with optimum concentration of Nd3+ and Yb3+ as sensitizer and activator, respectively, were synthesized by wet precipitation method and characterized by x-ray diffraction (XRD) and photoluminescence. In spite of the fact that the energy transfer takes place from Nd3+ to Yb3+, the luminescence intensity was found to be weak due to the lattice defects generated from the doping of trivalent cations (Nd3+ and Yb3+) for divalent host cations (Ca2+). These defect centres were tailored via charge compensation approach by co-doping Na+ ion and by optimizing its concentration and heat treatment duration. CaF2 doped with 5 mol% Nd3+, 3 mol% Yb3+ and 4 mol% Na+ after heat treatment for 2 h exhibited significantly enhanced emission intensity and life time. The ex vivo fluorescence imaging experiment was done at various thickness of chicken breast tissue. The maximum theoretical depth penetration of the NIR light was calculated and the value is 14 mm. The fabricated phosphor can serve as contrast agent for deep tissue near infrared (NIR) light imaging.

Directing Biosynthesis: Practical Supply of Natural and Unnatural Cyanobactins.

The increasingly rapid accumulation of genomic information is revolutionizing natural products discovery. However, the translation of sequence data to chemical products remains a challenge. Here, we detail methods used to circumvent the supply problem of cyanobactin natural products, both by engineered synthesis in Escherichia coli and by using purified enzymes in vitro. Such methodologies exploit nature's strategies of combinatorial chemistry in the cyanobactin class of RiPP natural products. As a result, it is possible to synthesize a wide variety of natural and unnatural compounds.

Optical characterization of melanin.

The optical properties of melanin have been characterized for a number of laser wavelengths in the visible region. The index of refraction of melanin is measured by the conventional method of minimum deviation using a hollow quartz prism at these wavelengths. The inverse adding doubling method based on the diffusion approximation and radiative transport theory have been employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of inverse adding doubling method have been compared to the Monte Carlo simulation technique.

NIR to NIR upconversion in KYb2F7: RE3+ (RE = Tm, Er) nanoparticles for biological imaging.

Until recently, many contrast agents widely used in biological imaging have absorbed and emitted in the visible region, limiting their usefulness for deeper tissue imaging. In order to push the boundaries of deep tissue imaging with non-ionizing radiation, contrast agents in the near infrared (NIR) regime, which is not strongly absorbed or scattered by most tissues, are being sought after. Upconverting nanoparticles (UCNPs) are attractive candidates since their upconversion emission is tunable with a very narrow bandwidth and they do not photobleach or blink. The upconversion produced by the nanoparticles can be tailored for NIR to NIR by carefully choosing the lanthanide dopants and dopant ratios such as KYb2F7: RE3+ (RE = Tm, Er). Spectroscopic characterization was done by analyzing absorption, fluorescence, and quantum yield data. In order to study the toxicity of the nanoparticles Monkey Retinal Endothelial Cells (MREC) were cultivated in 24 well plates and then treated with nanoparticles at different concentrations in triplicate to obtain the optimal concentration for in vivo experiments. It will be shown that these UCNPs do not elicit a strong toxic response such as quantum dots and some noble metal nanoparticles. 3-D optical slices of nanoparticle treated fibroblast cells were imaged using a confocal microscope where the nucleus and cytoplasm were stained with DAPI and Alexa Fluor respectively. These results presented support the initial assumption, which suggests that KYb2F7: RE3+ would be excellent candidates for NIR contrast agents.

Stokes emission in GdF3:Nd³âº nanoparticles for bioimaging probes.

There is increasing interest in rare earth (RE) doped nanoparticles (NPs) due to their sharp absorption and photoluminescence (PL) in the near infrared (NIR) spectral region. These NIR based nanoparticles (NPs) could allow biological imaging at substantial depths with enhanced contrast and high spatial resolution due to the absence of auto fluorescence in biological samples under infrared excitation. Here, we present the highly efficient infrared photoluminescence in GdF3:Nd(3+) nanoparticles under 800 nm excitation within the hydrodynamic size limitations for bio-applications. The downconversion (Stokes emission) absolute quantum yields (QY) in powder, polymaleic anhydride-alt-1-octadicene (PMAO) coated powder and colloidal solutions have been investigated. QY measurements have revealed that downconversion (Stokes emission) QYs of approximately 5 ± 2 nm sized GdF3:1% Nd(3+) colloidal NPs are 2000 times higher than those of efficient upconversion (UC) particles NaYF4:20% Er/2% Yb of the same size. Furthermore, the utility of these NIR emitting nanoparticles for bioimaging probes has been demonstrated by confocal imaging and spectroscopic study.

Cadmium(II) complexes of (arylazo)imidazoles: synthesis, structure, photochromism, and density functional theory calculation.

Reaction between CdX2 and 1-alkyl-2-(phenylazo)imidazole (RaaiR') has isolated complexes of composition Cd(RaaiR')2X2 in MeOH or MeCN. Crystallization of Cd(RaaiR')2I2 from N,N-dimethylformamide (DMF) has separated [Cd(RaaiR')I2.DMF], while Cd(RaaiR')2X2 (X = Cl and Br) remains unchanged in its composition upon crystallization under identical conditions. The structure has been established by spectral (UV-vis and 1H NMR) data and confirmation in the latter case by a single-crystal X-ray diffraction study of [Cd(TaiMe)I2.DMF] [where TaiMe = 1-methyl-2-(p-tolylazo)imidazole]. UV-light irradiation in a MeCN solution of Cd(RaaiR')2I2 and [Cd(RaaiR')I2.DMF] shows trans-to-cis isomerization of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation. Quantum yields (phit-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi values than their cadmium(II) iodo complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by a controlled-temperature experiment. The effects of the anions (Cl-, Br-, I-, and ClO4-) and the number of coordinated azoimidazoles (RaaiR') [Cd(RaaiR') or Cd(RaaiR')2] on the rate and quantum yields of photochromism are established in this work. A slow rate of photoisomerization of [Cd(RaaiR')4](ClO4)2 compared to Cd(RaaiR')I2 or Cd(RaaiR')2X2 may be associated with the increased mass and rotor volume of the complexes. The rate of isomerization is also dependent on the nature of X and follows the sequence Cd(RaaiR')2Cl2 < Cd(RaaiR')2Br2 < Cd(RaaiR')2I2. It may be related to the size and electronegativity of halide, which reduces the effective molar association in the order of I < Br < Cl and hence the rate. Gaussian 03 calculations of representative complexes and free ligands are used to explain the difference in the rates and quantum yields of photoisomerization.