Pharmaceutical applications on columns packed with sub-2 microm particles

During the last few years, there has been a great interest in the development of fast liquid chromatography. Among the reported approaches, the reduction of the particle size to attain sub-2microm diameter represents a good solution for achieving both increased separation power and faster analysis time. This paper demonstrates the chromatographic performance of such supports using plate-height curves and reveals the possibility for obtaining ultra-fast or highly efficient separations, according to the column geometry and system pressure limitations. The stability of these columns is initially evaluated using a system suitability experiment. The chromatographic performance remains stable in terms of retention, efficiency, and pressure for more than 1700 injections with pressure conditions ranging from 200 to 800 bar. Several fast and ultra-fast pharmaceutical applications are reported. In isocratic mode, a 5- to 10-fold reduction in analysis time is obtained with limited influence on efficiency and resolution. The run time is further reduced by 30-fold with the shorter available columns (i.e., 30 mm length). In gradient mode, the separation of a complex mixture containing an active pharmaceutical compound and related impurities is significantly improved with column length equal to 100 mm, to increase peak capacity and resolution.     

Highly sensitive detection of pharmaceutical compounds in biological fluids using capillary electrophoresis coupled with laser-induced native fluorescence

Insulin administration can increase muscle glycogen by utilising hyperinsulinaemic clamps prior to sports events or during the recovery phases, and increase muscle size by its chalonic action to inhibit protein breakdown. In order to control insulin abuse in equine sports, a method to detect effectively the use of insulins in horses would be required. Besides the readily available human insulin and its synthetic analogues, structurally similar insulins from other species can also be used as doping agents. This study describes a method for the simultaneous detection of bovine, porcine and human insulins, as well as the synthetic analogues Humalog (Lilly) and Novolog (Novo Nordisk) in equine plasma. Insulins were isolated from equine plasma by immunoaffinity purification, followed by centrifugal filtration, and analysed by nano-liquid chromatography-tandem mass spectrometry (LC/MS/MS). Insulin and analogues were detected and confirmed by comparing their retention times and major product ions. All five insulins (human insulin, Humalog, Novolog, bovine insulin and porcine insulin), which are exogenous in the horse, could be detected and confirmed at 0.05ng/mL. This method was successful in confirming the presence of human insulin in plasma collected from horses up to 4h after having been administered a single low dose of recombinant human insulin (Humulin R, Eli Lilly). To our knowledge, this is the first identification of exogenous insulin from post-administration horse plasma samples.     

Optimized liquid chromatography-mass spectrometry approach for the isolation of minor stress biomarkers in plant extracts and their identification by capillary nuclear magnetic resonance

A LC-MS approach is presented for the isolation of minor key plant biomarkers, in view of their characterization by NMR at the microgram scale. Due to the complexity of plant extracts, the purification of metabolites present in low concentrations is critical. The strategy used relies on the optimization of the chromatographic analysis using ultra-performance liquid chromatography-time-of-flight mass spectrometry (UPLC-TOF-MS), thanks to modelling software. The optimized method is then transferred to semi-preparative LC conditions with MS detection. The approach is illustrated by the isolation of wound-induced jasmonate derivatives revealed by a metabolomic study in Arabidopsis thaliana leaves and their subsequent characterization by capillary NMR (CapNMR).     

Pentamethylcyclopentadienyl ruthenium: an efficient catalyst for the redox isomerization of functionalized allylic alcohols into carbonyl compounds

The catalytic activity of the ruthenium(II) complex [RuCp^∗(CH₃CN)₃][PF₆] 1 in the transposition of allylic alcohols into carbonyl compounds, in acetonitrile, is reported. This catalyst has proven to be able to catalyze the transformation of poorly reactive and/or functionalized substrates under smooth conditions.     

Photophysical Insights of Halogenated Dipyrrolonaphthyridine-Diones as Potential Photodynamic Therapy Agents†

We report the synthesis and photophysical characterization of novel halogenated dipyrrolonaphthyridine-diones (X₂–DPNDs, X = Cl, Br, and I), as candidates for photodynamic therapy (PDT) application. Apart from the heavy atom-induced spin-orbit coupling (SOC) dynamics in the investigated X₂–DPNDs, it was found that the position of the halogen atom (relative to the nitrogen of the pyrrole ring) also influenced the triplet excited state behavior. Interestingly, the faster/efficiency sensitization of ³O₂ to ¹O₂ using X₂–DPND correlates with the rate of triplet population, k_ISC >1.6 × 10⁸ s⁻¹ for I₂–DPND vs k_ISC >2.9 × 10⁹ s⁻¹ for Cl₂–DPND and Br₂–DPND (where τ_ISC = 343 ± 3 ps for I₂–DPND and τ_ISC = 5–6 ns for Cl₂–DPND and Br₂–DPND are the lowest time constants/values for ISC). Furthermore, the heavy atom-induced SOC in Cl₂–DPND and Br₂–DPND did not lead to a reduction of the corresponding fluorescence (ca 75% vs 67% for the parent DPND). The attractive photophysical characteristics of Cl₂/Br₂–DPND put them on the landscape as not only promising PDT agents but also as fluorescence probes. The present study is a stepping stone in the development of novel organic photosystems for synergistic photomedicinal applications.     

Ruthenium-catalyzed synthesis of allylic alcohols: boronic acid as a hydroxide source

Secondary allylic alcohols were synthesized from linear allylic halides or carbonates using a catalytic amount of a ruthenium complex in the presence of boronic acid. The effects of solvent, base, ruthenium precursor, and boronic acid were fully explored, and the scope of the reaction was extended to various substrates. We also describe a preliminary investigation towards an enantioselective process.     

Non-uniform surface charge distributions in CE: theoretical and experimental approach based on Taylor dispersion

The control of the EOF direction and magnitude remains one of the more challenging issues for the optimization of separations in CE. In this work, we investigated the possibility to use non-uniform surface charge distribution for the modulation of the EOF in CE. Non-uniform zeta potentials were obtained by modifying a section of the capillary surface using adsorption of polyelectrolytes. Three different methods were studied: (i) partial polycation coating on a fused silica capillary, (ii) partial polycation (or polyanion) coating on polyelectrolyte multilayers, and (iii) partial polycation coating on a capillary previously modified with poly(ethylene oxide). The magnitude and the direction of the EOF as a function of the coated capillary length were first studied. The stability of the EOF and the separation performances were also considered taking two dialanine diastereoisomers as model compounds. In partially coated capillaries, the average solvent flow is the sum of two contributions: a non-dispersive electroosmotic contribution related to the capillary surface charge, and a dispersive hydrodynamic contribution that depends on the difference of surface charge between the coated and the non-coated capillary zones. To get a better insight into the influence of the hydrodynamic contribution to the total peak dispersion, the peak variances corresponding to the Taylor dispersion, the injection plug, and the axial diffusion were calculated. This work demonstrates that peak dispersion in a capillary partially coated by the inlet end is different from that obtained when the coating is performed by the outlet end. Experimentally, the combination of a partially coated capillary with a large volume sample stacking preconcentration step can be used for injecting up to 95% of the capillary volume. This approach leads to a preconcentration factor of 60 compared with CZE with classical injection.     

Validation of an ultra-fast UPLC-UV method for the separation of antituberculosis tablets

A simple method using ultra performance LC (UPLC) coupled with UV detection was developed and validated for the determination of antituberculosis drugs in combined dosage form, i. e. isoniazid (ISN), pyrazinamide (PYR) and rifampicin (RIF). Drugs were separated on a short column (2.1 mm x 50 mm) packed with 1.7 mum particles, using an elution gradient procedure. At 30 degrees C, less than 2 min was necessary for the complete separation of the three antituberculosis drugs, while the original USP method was performed in 15 min. Further improvements were obtained with the combination of UPLC and high temperature (up to 90 degrees C), namely HT-UPLC, which allows the application of higher mobile phase flow rates. Therefore, the separation of ISN, PYR and RIF was performed in less than 1 min. After validation (selectivity, trueness, precision and accuracy), both methods (UPLC and HT-UPLC) have proven suitable for the routine quality control analysis of antituberculosis drugs in combined dosage form. Additionally, a large number of samples per day can be analysed due to the short analysis times.     

Approximations of Lovász extensions and their induced interaction index

The Lovász extension of a pseudo-Boolean function f:{0,1}ⁿ→R is defined on each simplex of the standard triangulation of [0,1]ⁿ as the unique affine function that interpolates f at the n+1 vertices of the simplex. Its degree is that of the unique multilinear polynomial that expresses f. In this paper we investigate the least squares approximation problem of an arbitrary Lovász extension by Lovász extensions of (at most) a specified degree. We derive explicit expressions of these approximations. The corresponding approximation problem for pseudo-Boolean functions was investigated by Hammer and Holzman [Approximations of pseudo-Boolean functions; applications to game theory, Z. Oper. Res. 36(1) (1992) 3-21] and then solved explicitly by Grabisch et al. [Equivalent representations of set functions, Math. Oper. Res. 25(2) (2000) 157-178], giving rise to an alternative definition of Banzhaf interaction index. Similarly we introduce a new interaction index from approximations of and we present some of its properties. It turns out that its corresponding power index identifies with the power index introduced by Grabisch and Labreuche [How to improve acts: an alternative representation of the importance of criteria in MCDM, Internat. J. Uncertain. Fuzziness Knowledge-Based Syst. 9(2) (2001) 145-157].     

Damming an electronic energy reservoir: ion-regulated electronic energy shuttling in a [2]rotaxane

We demonstrate the first example of bidirectional reversible electronic energy transfer (REET) between the mechanically bonded components of a rotaxane. Our prototypical system was designed such that photoexcitation of a chromophore in the axle results in temporary storage of electronic energy in a quasi-isoenergetic “reservoir” chromophore in the macrocycle. Over time, the emissive state of the axle is repopulated from this reservoir, resulting in long-lived, delayed luminescence. Importantly, we show that cation binding in the cavity formed by the mechanical bond perturbs the axle chromophore energy levels, modulating the REET process, and ultimately providing a luminescence read-out of cation binding. Modulation of REET processes represents an unexplored mechanism in luminescent molecular sensor development.

Delayed emission due to reversible electronic energy transfer (REET) between chromophores in the axle and macrocycle components of a rotaxane is demonstrated. The REET process can be modulated by metal ion binding in the cavity of the rotaxane.