Synthesis,photophysical and electrochemical properties,and biological labeling studies of cyclometalated iridium(III) bis(pyridylbenzaldehyde) complexes: novel luminescent cross-linkers for biomolecules

We report the synthesis, characterization, photophysical, and electrochemical properties of a series of luminescent cyclometalated iridium(III) complexes containing two aldehyde functional groups [Ir(pba)(2)(N-N)](PF(6)) (Hpba=4-(2-pyridyl)benzaldehyde; N-N=2,2'-bipyridine, bpy (1), 1,10-phenanthroline, phen (2), 3,4,7,8-tetramethyl-1,10-phenanthroline, 3,4,7,8-Me(4)-phen (3), 4,7-diphenyl-1,10-phenanthroline, 4,7-Ph(2)-phen (4)). The X-ray crystal structure of complex 1 has been investigated. Upon photoexcitation, complexes 1-4 exhibit intense and long-lived emission in fluid solutions at 298 K and in low-temperature glass. The luminescence is assigned to a triplet intra-ligand ((3)IL) excited state associated with the pba(-) ligand, probably with mixing of some triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir)-->pi*(pba(-))) character. Since each of these complexes possesses two aldehyde groups, which can react with the primary amine groups of biomolecules to form stable secondary amines after reductive amination, we have investigated the possibility of these complexes as novel luminescent cross-linkers for biological substrates. L-Alanine has been labeled with complexes 1-4 to give the luminescent bioconjugates 1-(Ala)(2)-4-(Ala)(2). These conjugates show strong photoluminescence with long emission lifetimes under ambient conditions. On the basis of the emission energy trend, the excited state of these luminescent bioconjugates is likely to bear a high parentage of (3)MLCT (dpi(Ir)-->pi*(N-N)) character. In addition, the glycoprotein avidin (Av) has also been conjugated with complexes 1-4 to give the bioconjugates 1-Av-4-Av. Upon photoexcitation, these bioconjugates also display intense and long-lived (3)MLCT (dpi(Ir)-->pi*(N-N)) emission in aqueous buffer at 298 K. Furthermore, a heterogeneous competitive assay for biotin has been developed using 2-Av and biotinylated microspheres. We have shown that complexes 1-4 represent a new class of multicolor luminescent cross-linkers for biomolecular species.     

Studies on the Diastereoselective Preparation of Bis-cyclopropanes

The identification of two natural products, FR-900848 and U-106305, has stimulated interest concerning the relationship between configurational isomerism, conformational isomerism, and biological activity of polycyclopropanes. Efforts to investigate the relationship between configurational and conformational isomerism through molecular modeling suggest that significantly different three-dimensional structures will result from unique primary structures. Any effort to address these issues demands that stereoselective methods for the preparation of polycyclopropanes be developed. We have investigated the application of zinc-carbenoid cyclopropanation in the presence of chiral dioxaboralanes to the preparation of eight stereochemically unique bicyclopropanes. The trans-vinylcyclopropane starting materials demonstrated very little substrate-induced stereoselectivity, while the cis-vinylcyclopropane demonstrates modest to excellent stereocontrol. A model for the substrate-based stereocontrol is proposed. We also used the spectroscopic data gathered in this investigation to probe the substrate-mediated stereocontrol in the rhodium(II)-catalyzed cyclopropanation of vinylcyclopropanes with ethyl diazoacetate.     

Nature of monster sawteeth and their relationship to Alfven instabilities in tokamaks

A correlation is explored between the presence of energetic particle modes (EPM) and long-period sawtooth oscillations in tokamak plasmas heated by rf waves. The eventual crash of these sawteeth is explained in terms of the loss of the stabilizing fast particles due to the EPM. The absence of long-period sawteeth in high q(a) discharges is explained in terms of ion loss due to toroidal Alfven eigenmodes.     

Coherent acoustic phonon oscillations in semiconductor multiple quantum wells with piezoelectric fields

Large coherent acoustic phonon oscillations were demonstrated using InGaN/GaN multiple quantum wells with piezoelectric fields. With UV femtosecond pulse excitation, photogenerated carriers screened the piezoelectric field and initiated the displacive coherent phonon oscillations. The specific phonon frequency was selected by the coupling between the periodic carrier distribution and the corresponding acoustic phonon mode. The induced acoustic phonon oscillation resulted in piezoelectric field modulation and then caused absorption variation through the quantum confined Franz-Keldysh effect. The wave vector uncertainty due to the finite sample width was found to determine the observed dephasing time.     

Zinc-mediated chain extension of beta-keto phosphonates

A variety of beta-keto phosphonates can be converted to gamma-keto phosphonates through reaction with ethyl(iodomethyl)zinc. The presence of alpha-alkyl substituents, Lewis basic functionality, and modestly acidic NH-protons are accommodated in substrates of this reaction. Chain extension of beta-keto phosphonates that contained olefinic functionality proceeded more quickly than cyclopropanation; however, it was not possible to effect the chain extension to the exclusion of cyclopropane formation. A primary reason for this imperfect chemoselectivity appears to be the slow chain extension of beta-keto phosphonates. Nevertheless, the simplicity, the scope, and efficiency of this method serve to make it an attractive alternative to the established methods for gamma-keto phosphonate formation.     

Quaternized wood as sorbent for reactive dyes

Various species of local wood modified with N-(3-chloro-2-hydroxypropyl)-trimethylammonium chloride showed sorption enhancement for hydrolyzed Reactive Blue 2 (HRB) compared to the untreated samples. The enthalpy of sorption of HRB on Simpoh (Dillenia suffruticosa) was found to be endothermic. Maximum sorption capacity calculated from the Langmuir isotherm was 250.0 mg/g. Under continuous flow conditions HRB could be successfully removed. Dye removal was a function of bed depth and flow rate. However, the bed depth service time model of Bohart and Adams was not applicable in the HRB-quaternized wood system. The modified wood was applied to a sample of industrial textile effluent, and it was found to be able to remove the color successfully under batch conditions.     

Differential phase contrast in optical coherence tomography

We report on a modification of optical coherence tomography (OCT) that allows one to measure small phase differences between beams traversing adjacent areas of a specimen. The sample beam of a polarization-sensitive low-coherence interferometer is split by a Wollaston prism into two components that traverse the object along closely spaced paths. After reflection at the various sample surfaces, the beams are recombined at the Wollaston prism. Any phase difference encountered between the two beams is converted into a change of polarization state of the recombined beam. This change is measured, and the resulting signals are converted to differential phase-contrast OCT images. The first images obtained from simple test objects allowed us to determine path-difference gradients with a resolution of the order of 5 x 10(-5) .