Igor Kozin

Fiber-loop ring-down spectroscopy

Pulsed, visible and near-infrared laser light is coupled into an optical fiber, which is wound into a loop using a fiber splice connector. The light pulses traveling through the fiber-loop are detected using a photomultiplier detector. It is found that once the light is coupled into the fiber it experiences very little loss and the light pulses do a large number of round trips before their intensity is below the detection threshold. Measurements of the loss-per-pass and of the ring-down time allow for characterization of the different loss mechanisms of the light pulses in the fiber and splice connector. This method resembles “cavity ring-down absorption spectroscopy” and is well suited to characterize low-loss processes in fiber optic transmission independent from power fluctuations of the light source. It is demonstrated that by measuring the ring-down times one can accurately determine the absolute transmission of an optical fiber and of the fiber connector. In addition it is demonstrated that the tech...

Kinetics of mixed function oxygenase induction and retene excretion in retene—exposed rainbow trout (Oncorhynchus mykiss)

The polycyclic aromatic hydrocarbon 7-isopropyl-1-methylphenanthrene (retene) induces mixed function oxygenase (MFO) activity of fish. Bile levels of retene and its metabolite(s) were measured in relation to exposure time, exposure concentration, and induction of MFO activity. Synchronous fluorescence spectrometry provided a rapid means of measuring the amount of retene present in the bile of exposed fish, whereas conventional fluorescence spectrometry was used to quantify the amount of retene metabolites. Based on bile analysis, increased retene exposure resulted in an increased uptake of retene and a curvilinear increase in hepatic MFO activity. Retene was present in the bile within 6 h of initial exposure. However, retene metabolite(s) only appeared in the bile after MFO induction had occurred, 12 h after exposure had commenced, suggesting that MFO activity is required for metabolism. Transfer of fish to clean water after 48 h of exposure resulted in a rapid decrease in the presence of retene and its metabolite(s) in the bile, with a calculated half-life of about 14 h. In vitro additions of retene directly to the ethoxyresorufin O-deethylase assay demonstrated that retene is capable of acting as a competitive inhibitor. Thus, retene contamination of postmitochondrial supernatant (S9 fraction) could result in false-negative results in the MFO assay. The MFO activity in extrahepatic tissues (gills, heart, and kidney) was not significantly induced with retene exposure. Thus, the major site of retene metabolism seems to be in the liver. These results confirm that retene is rapidly taken up, metabolized, and excreted by rainbow trout, and that retene metabolism and excretion are linked to hepatic MFO induction.

Fiber Bragg grating photoacoustic detector for liquid chromatography

Fiber Bragg Gratings (FBGs) are known to be sensitive acoustic transducers and have previously been used for the photoacoustic detection of small solid samples. Here, we demonstrate the use of an FBG as an on-line detector for liquid chromatography. The FBG was inserted into a silica capillary and the photoacoustic response from the effluent was generated by a 10 ns pulsed laser. The acoustic pulse was quantified by the FBG through a characteristic change in the reflection spectrum. Good repeatability and linear response were obtained over three orders of magnitude (R(2) > 0.99), and the limit of detection of Coumarin 440 was determined to be 5 microM. The technique was successfully coupled to high performance liquid chromatography and applied to on-line analysis of a three-compound solution. Photoacoustic detection in liquid chromatography using FBGs is a label-free method, which can be applied to the detection of any chromogenic compound irrespective of its fluorogenic properties. It is a simple, inexpensive, and inherently micron-sized technique, insensitive to electromagnetic interference.

Spiro-BODIPYs with a Diaryl Chelate: Impact on Aggregation and Luminescence

Spiro-BODIPYs with a diaryl chelate unit have been found to form J-aggregates in methanol-water solvent mixture and brightly emissive in the solid state. The diaryl chelate unit has a significant impact on J-aggregates and fluorescence of BODIPYs. Crystal structural analysis reveals that the spiro-structures facilitate J-stacking in the solid state.

New red–orange phosphorescent/electroluminescent cycloplatinated complexes of 2,6-bis(2′-indolyl)pyridine

Three novel cyclometalated complexes of 2,6-bis(2′-indolyl)pyridine (H2BIP), Pd(BIP)(Py) (Py = pyridine) (1), Pt(BIP)(SMe2) (2) and Pt(BIP)(Py) (3) have been synthesized and characterized structurally. The Pd and Pt centers in these compounds are four-coordinate with a square planar geometry. The BIP ligand acts as a tridentate chelate to the metal center, and the dimethyl sulfide and the pyridine ligand bind to the metal center as terminal ligands. Compound 1 has no luminescence. Compounds 2 and 3 display bright orange luminescence either at 77 K in a frozen CH2Cl2 solution or at ambient temperature in a polymer matrix (e.g. poly(carbonate) or PVK). The emission maxima for 2 and 3 in the frozen CH2Cl2 solution are at λ = 572 and 589 nm, respectively. The emission spectra of 2 and 3 in the polymer matrix are very similar with λmax = 585 nm. The luminescence of 2 and 3 is phosphorescent as supported by the emission lifetimes of 2 (94(1) μs in CH2Cl2 at 77 K, 22.1(1) μs in poly(carbonate) at 298 K) and 3 (44(1) μs in CH2Cl2 at 77 K, 19(1) μs in poly(carbonate) at 298 K). Based on the luminescence properties of the free ligand and the results of molecular orbital calculations, we propose that the luminescence of 2 and 3 is most likely due to a π → π* transition with a significant dπ orbital contribution from the Pt(II) center to the π level. Electroluminescent devices using compound 3 as the emitter and PVK as the host and hole transport material have been fabricated successfully.