Redox and spectroscopic orbitals in Ru(II) and Os(II) phenolate complexes

A detailed spectroscopic and electrochemical study of a series of novel phenolate bound complexes, of general formulas [M(L-L)(2)(box)](PF(6)), where M is Os and Ru, L-L is 2,2-bipyridine or 2,2-biquinoline, and box is 2-(2-hydroxyphenyl)benzoxazole, is presented. The objectives of this study were to probe the origin of the LUMOs and HOMOs in these complexes, to elucidate the impact of metal and counter ligand on the electronic properties of the complex, and to identify the extent of orbital mixing in comparison with considerably more frequently studied quinoid complexes. [M(L-L)(2)(box)](PF(6)) complexes exhibit a rich electronic spectroscopy extending into the near infrared region and good photostability, making them potentially useful as solar sensitizers. Electrochemistry and spectroscopy indicate that the first oxidation is metal based and is associated with the M(II)/(III) redox states. A second oxidative wave, which is irreversible at slow scan rates, is associated with the phenolate ligand. The stabilities of the oxidized complexes are assessed using dynamic electrochemistry and discussed from the perspective of metal and counter ligand (LL) identity and follow the order of increasing stability [Ru(biq)(2)(box)](+) < [Ru(bpy)(2)(box)](+) < [Os(bpy)(2)(box)](+). Electronic and resonance Raman spectroscopy indicate that the lowest energy optical transition for the ruthenium complexes is a phenolate (pi) to L-L (pi) interligand charge-transfer transition (ILCT) suggesting the HOMO is phenolate based whereas electrochemical data suggest that the HOMO is metal based. This unusual lack of correlation between redox and spectroscopically assigned orbitals is discussed in terms of metal-ligand orbital mixing which appears to be most significant in the biquinoline based complex.     

Hybridization and Melting Behavior of Peptide Nucleic Acid (PNA) Oligonucleotide Chimeras Conjugated to Gold Nanoparticles

Peptide nucleic acids (PNA) and PNA–DNA chimeras carrying thiol groups were used for surface functionalization of Au nanoparticles. Conjugation of PNA to citrate‐stabilized Au nanoparticles destabilized the nanoparticles causing them to precipitate. Addition of a tail of glutamic acid to the PNA prevented destabilization of the nanoparticles but resulted in loss of interaction with complementary sequences. Importantly, PNA–DNA chimeras gave stable conjugates with Au nanoparticles. The hybridization and melting properties of complexes formed from chimera–nanoparticle conjugates and oligonucleotide–nanoparticle conjugates are described for the first time. Similar to oligonucleotide–nanoparticle conjugates, conjugates with PNA–DNA chimeras gave sharper and more‐defined melting profiles than those obtained with unmodified oligonucleotides. In addition, mismatch discrimination was found to be more efficient than with unmodified oligonucleotides.     

Tracking bacterial infection of macrophages using a novel red-emission pH sensor

The relationship between bacteria and host phagocytic cells is key to the induction of immunity. To visualize and monitor bacterial infection, we developed a novel bacterial membrane permeable pH sensor for the noninvasive monitoring of bacterial entry into murine macrophages. The pH sensor was constructed using 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as an electron-withdrawing group and aniline as an electron-donating group. A piperazine moiety was used as the pH-sensitive group. Because of the strong electron-donating and -withdrawing units conjugated in the sensing moiety M, the fluorophore emitted in the red spectral window, away from the autofluorescence regions of the bacteria. Following the engulfment of sensor-labeled bacteria by macrophages and their subsequent merger with host lysosomes, the resulting low-pH environment enhances the fluorescence intensity of the pH sensors inside the bacteria. Time-lapse analysis of the fluorescent intensity suggested significant heterogeneity of bacterial uptake among macrophages. In addition, qRT-PCR analysis of the bacterial 16 S rRNA gene expression within single macrophage cells suggested that the 16 S rRNA of the bacteria was still intact 120 min after they had been engulfed by macrophages. A toxicity assay showed that the pH sensor has no cytotoxicity towards either E. coli or murine macrophages. The sensor shows good repeatability, a long lifetime, and a fast response to pH changes, and can be used for a variety of bacteria.     

Evaluation of a new polymeric stationary phase with reversed-phase properties for high temperature liquid chromatography

The performance of a polymeric stationary phase with reversed-phase properties (ET-RP1) was evaluated for LC separations at elevated temperature. The most significant observation was that the reduced plate height (h) decreased from 3.4 at 25 °C (optimal flow 0.5 mL/min) to 2.4 at 150 °C (optimal flow 2.5 mL/min) which is comparable to the efficiency obtained with silica-based reversed-phase columns of 4.6 mm ID operated at 0.8 mL/min. The phase showed no deterioration after long use at 150 °C within the pH range 1–9. Catalytic activity originating from the stationary phase material, e.g. as experienced on zirconium columns operated at elevated temperature, was absent. The performance of ET-RP1 is illustrated with the analysis of some pharmaceutical samples by LC and LC–MS. Operation at elevated temperature also allows to reduce the amount of organic modifier or to replace acetonitrile and methanol by the biodegradable ethanol.     

Real-time PCR of single bacterial cells on an array of adhering droplets

Real-time PCR at the single bacterial cell level is an indispensable tool to quantitatively reveal the heterogeneity of isogenetic cells. Conventional PCR platforms that utilize microtiter plates or PCR tubes have been widely used, but their large reaction volumes are not suited for sensitive single-cell analysis. Microfluidic devices provide high density, low volume PCR chambers, but they are usually expensive and require dedicated equipment to manipulate liquid and perform detection. To address these limitations, we developed an inexpensive chip-level device that is compatible with a commercial real-time PCR thermal cycler to perform quantitative PCR for single bacterial cells. The chip contains twelve surface-adhering droplets, defined by hydrophilic patterning, that serve as real-time PCR reaction chambers when they are immersed in oil. A one-step process that premixed reagents with cell medium before loading was applied, so no on-chip liquid manipulation and DNA purification were needed. To validate its application for genetic analysis, Synechocystis PCC 6803 cells were loaded on the chip from 1000 cells to one cell per droplet, and their 16S rRNA gene (two copies per cell) was analyzed on a commercially available ABI StepOne real-time PCR thermal cycler. The result showed that the device is capable of genetic analysis at single bacterial cell level with C(q) standard deviation less than 1.05 cycles. The successful rate of this chip-based operation is more than 85% at the single bacterial cell level.     

Binary-black-hole encounters, gravitational bursts, and maximum final spin

The spin of the final black hole in the coalescence of nonspinning black holes is determined by the "residual" orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. We study the angular momentum radiated, the spin of the final black hole, and the gravitational bursts in a sequence of equal mass encounters. The initial orbital configurations range from those producing an almost direct infall to others leading to numerous orbits before infall, with multiple bursts of radiation. Our sequence consists of orbits with fixed impact parameter. What varies is the initial linear momentum of the black holes. For this sequence, the final black hole of mass M_{h} gets a maximum spin parameter a/M_{h} approximately 0.823, with this maximum occurring for initial orbital angular momentum L/M_{h};{2} approximately 1.176.     

Total pore blocking as an alternative method for the on-column determination of the external porosity of packed and monolithic reversed-phase columns

An alternative method to determine the interstitial void volume and the external porosity inside a packed or a monolithic column was developed. The method is based on the total blocking of the mesopores of a porous support by filling them with a hydrophobic solvent. The strong interaction of the latter with the hydrophobic coating inside the pores keeps the solvent in position during the subsequent measurements. With the pores of the stationary phase material completely inaccessible for any type of polar molecules, the method allows to perform interstitial void measurements using small molecular weight (MW) molecules instead of the large MW molecules that need to be used in inverse size exclusion chromatography (ISEC). These small MW molecules are able to penetrate every corner of the interstitial volume and therefore lead to a very accurate determination of the external porosity. Since only one type of molecules needs to be injected, the often troublesome regression analysis needed in ISEC is omitted as well. In the present contribution, the method has been applied to a packed bed and a monolithic column to investigate the optimal conditions of flow velocity, liquid compositions, and unretained marker selection. The robustness and the repeatability of the method are discussed as well.     

High performance liquid chromatography analysis of wine anthocyanins revisited: Effect of particle size and temperature

The complex anthocyanin fraction of red wines poses a demanding analytical challenge. We have found that anthocyanins are characterised by extremely low optimal chromatographic velocities, and as a consequence generic HPLC methods suffer from limited resolving power. Slow on-column inter-conversion reactions, particularly between carbinol and flavylium species, are shown to occur on the same time scale as chromatographic separation, leading to increased plate heights at normal chromatographic velocities. In order to improve current routine HPLC separations, the use of small (1.7 μm) particles and high temperature liquid chromatography (HTLC) were investigated. 1.7 μm particles provide better efficiency and higher optimal linear velocities, although column lengths of ∼20 cm should be used to avoid the detrimental effects of conversion reactions. More importantly, operation at temperatures up to 50 °C increases the kinetics of inter-conversion reactions, and implies significantly improved efficiency under relatively mild analysis conditions. It is further demonstrated using relevant kinetic data that no on-column thermal degradation of these thermally labile compounds is observed at 50 °C and analysis times of <2 h.