Computational Study of the Migration of Rhenium from One Enantioface of an Olefin to the Other Facilitated by (C-H)center dot center dot center dot Re Interactions

The migration of a metal atom in a metal olefin complex from one pi face of the olefin to the opposite pi face has been rarely documented. Gladysz and co-workers showed that such a movement is indeed possible in monosubstituted chiral Re olefin complexes, resulting in diastereomerization. Interestingly, this isomerization occurred without dissociation, and on the basis of kinetic isotope effects, the involvement of a trans C-H bond was indicated. Either oxidative addition or an agostic interaction of the vinylic C-H(D) bond with the metal could account for the experimentally observed kinetic isotope effect. In this study we compute the free energy of activation for the migration of Re from one enantioface of the olefin to the other through various pathways. On the basis of DFT calculations at the B3LYP level we show that a trans (C-H)center dot center dot center dot Re interaction and trans C-H oxidative addition provide a nondissociative path for the diastereomerization. The trans (C-H)center dot center dot center dot Re interaction path is computed to be more favorable by 2.3 kcal mol(-1) than the oxidative addition path. While direct experimental evidence was not able to discount the migration of the metal through the formation of a eta(2)-arene complex (conducted tour mechanism), computational results at the B3LYP level show that it is energetically more expensive. Surprisingly, a similar analysis carried out at the M06 level computes a lower energy path for the conducted tour mechanism and is not consistent with the experimental isotope effects observed. Metal-(C-H) interactions and oxidative additions of the metal into C-H bonds are closely separated in energy and might contribute to unusual fluxional processes such as this diastereomerization.

Coded Illumination for Motion-blur Free Imaging of Cells on Cell-phone Based Imaging Flow Cytometer

Cell-phone based imaging flow cytometry can be realized by flowing cells through the microfluidic devices, and capturing their images with an optically enhanced camera of the cell-phone. Throughput in flow cytometers is usually enhanced by increasing the flow rate of cells. However, maximum frame rate of camera system limits the achievable flow rate. Beyond this, the images become highly blurred due to motion-smear. We propose to address this issue with coded illumination, which enables recovery of high-fidelity images of cells far beyond their motion-blur limit. This paper presents simulation results of deblurring the synthetically generated cell/bead images under such coded illumination.

A rhodamine-based `turn-on' Al3+ ion-selective reporter and the resultant complex as a secondary sensor for F- ion are applicable to living cell staining

A newly designed fluorescent aluminum(III) complex (L'-Al; 2) of a structurally characterized non-fluorescent rhodamine Schiff base (L) has been isolated in pure form and characterized using spectroscopic and physico-chemical methods with theoretical density functional theory (DFT) support. On addition of Al(III) ions to a solution of L in HEPES buffer (1 mM, pH 7.4; EtOH-water, 1 : 3 v/v) at 25 degrees C, the systematic increase in chelation-enhanced fluorescence (CHEF) enables the detection of Al(III) ions as low as 60 nM with high selectivity, unaffected by the presence of competitive ions. Interestingly, the Al(III) complex (L'-Al; 2) is specifically able to detect fluoride ions by quenching the fluorescence in the presence of large amounts of other anions in the HEPES buffer (1 mM, pH 7.4) at 25 degrees C. On the basis of our experimental and theoretical findings, the addition of Al3+ ions to a solution of L helps to generate a new fluorescence peak at 590 nm, due to the selective binding of Al3+ ions with L in a 1 : 1 ratio with a binding constant (K) of 8.13 x 10(4) M-1. The Schiff base L shows no cytotoxic effect, and it can therefore be employed for determining the intracellular concentration of Al3+ and F-ions by 2 in living cells using fluorescence microscopy.

Specific detection of the cleavage activity of mycobacterial enzymes using a quantum dot based DNA nanosensor

We present a quantum dot based DNA nanosensor specifically targeting the cleavage step in the reaction cycle of the essential DNA-modifying enzyme, mycobacterial topoisomerase I. The design takes advantages of the unique photophysical properties of quantum dots to generate visible fluorescence recovery upon specific cleavage by mycobacterial topoisomerase I. This report, for the first time, demonstrates the possibility to quantify the cleavage activity of the mycobacterial enzyme without the pre-processing sample purification or post-processing signal amplification. The cleavage induced signal response has also proven reliable in biological matrices, such as whole cell extracts prepared from Escherichia coli and human Caco-2 cells. It is expected that the assay may contribute to the clinical diagnostics of bacterial diseases, as well as the evaluation of treatment outcomes.