Utility of membrane preconcentration-capillary electrophoresis-mass spectrometry in overcoming limited sample loading for analysis of biologically derived drug metabolites, peptides, and proteins

The limited loading of capillary electrophoresis (CE) leads to relatively poor concentration limits of detection. In this work a unique method for analyte preconcentration with capillary electrophoresis-mass spectrometry (CE-MS) is described. A cartridge containing an impregnated membrane is installed at the inlet of the CE capillary, and we term this approach membrane preconcentration capillary electrophoresis-mass spectrometry (mPC-CE-MS). The analysis of in vivo derived metabolites, peptides, and proteins is described showing the wide applicability of the technology in the analysis of numerous compound classes ranging in molecular weight from 200–60,000 u. In particular, we describe the direct mPC-CE-MS analysis of urine obtained from a patient receiving the neuroleptic drug haloperidol. Three metabolites were found in the urine, and two of them are implicated in the Parkinsonian-like side effects caused by taking this drug. The technique is also applied to the analysis of major histocompatibility complex class I peptides obtained from EG-7 cells. Furthermore, the clinical potential of this approach is described by the direct analysis of urine from a patient suffering from multiple myeloma, as well as aqueous humor derived from a patient undergoing surgery. Finally we show that the use of mPC-ME-MS in conjunction with either analyte stacking (small organic molecules such as metabolites) or moving-boundary transient isotachophoresis (peptides and proteins) after analytes have been eluted from the adsorptive membrane affords optimal performance and no compromise in CE mass spectrometry performance.     

In-situ study of the catalytic oxidation of CO on a Pt(1 1 0) surface using ambient pressure X-ray photoelectron spectroscopy

CO and O₂ co-adsorption and the catalytic oxidation of CO on a Pt(1 1 0) surface under various pressures of CO and O₂ (up to 250 mTorr) are studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and mass spectrometry. There is no surface oxide formation on Pt under our reaction conditions. CO oxidation in this pressure (<500 mTorr), O₂ to CO ratio (<10), and temperature (150 °C) regime is consistent with the Langmuir-Hinshelwood reaction mechanism. Our findings provide in-situ surface chemical composition data of the catalytic oxidation of CO on Pt(1 1 0) at total pressures below 1 Torr.     

Sensitized Lanthanide‐Ion Luminescence with Aryl‐Substituted N‐(2‐Nitrophenyl)acetamide‐Derived Chromophores

The syntheses of the two tetraazamacrocyclic ligands L1 and L2 bearing a [(methoxy‐2‐nitrophenyl)amino]carbonyl chromophore, i.e., an N‐(methoxy‐2‐nitrophenyl)acetamide moiety, together with their corresponding lanthanide‐ion complexes are described. A combined spectroscopic (UV/VIS, ¹H‐NMR), structural (X‐ray), and theoretical (DFT) investigation revealed that the absorption properties of the chromophores were dictated by the extent of electronic delocalisation, which in turn was determined by the position of the MeO substituent at the aromatic ring. X‐Ray crystallographic studies showed that when attached to the macrocycle, both isomeric forms of the N‐(methoxy‐2‐nitrophenyl)acetamide unit can participate in coordination, via the C?O, to an encapsulated potassium cation. Luminescence measurements confirmed that such a binding mode also exists in solution for the corresponding lanthanide complexes (q ca. ≤1), with the para‐MeO derivative allowing longer wavelength sensitization (λ_ex 330 nm).     

In situ growth of polymer electrolytes on lithium ion electrode surfaces

Polyacrylonitrile (PAN) films were grown on glassy carbon, nickel foam and MnO₂ substrates by cathodic electropolymerisation of acrylonitrile in acetonitrile with tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. The electronic barrier properties of the films were confirmed by impedance spectroscopy of carbon |PAN| Hg cells while the ionic resistance of the films varied from 200 kΩ cm² in the dry state to 1.4 Ω cm² when plasticised with 1 M LiPF₆ in propylene carbonate. A galvanic cell was prepared by successive electrodepositions of MnO₂ and PAN on a carbon substrate, using liquid lithium amalgam as the top contact. The cell showed a stable open circuit potential and behaved normally under the galvanostatic intermittent titration technique (GITT).     

Redox Economy in Organic Synthesis

Stimulus package for organic synthesis : The economy of step and atom usage has been widely reviewed and acknowledged as being useful frameworks to evaluate the efficiency of synthesis. This Review brings to attention another form of economy which should be considered in the planning and evaluation of a multistep synthesis: redox economy. Several guidelines and examples are included to illustrate the logic of this approach and to stimulate the design of syntheses.

     

Stereodivergent Synthesis of 17‐α and 17‐β‐Aryl Steroids: Application and Biological Evaluation of D‐Ring Cortistatin Analogues

One stereocenter makes all the difference : The synthesis and biological evaluation of 17‐epi‐cortistatin A is reported from a common intermediate used to procure natural cortistatin A. The synthesis features a unique stereocontrolled Raney‐Ni reduction process that can be employed to reliably produce both α‐ and β‐configured D‐ring aryl steroids. Biological evaluations of these “cortalogs” are reported for the first time.

     

A Rhenium Tricarbonyl 4′‐Oxo‐terpy Trimer as a Luminescent Molecular Vessel with a Removable Silver Stopper

Shining metal cups : A luminescent tube of triangular cross‐section and stoppered by a silver ion (see picture: Re yellow, N blue, O red) is formed in two steps from commercial materials. The silver ion can be removed to give a tube, and both species are potential hosts for small ions and molecules; a change in luminescence is triggered by the encapsulation of silver.

     

Branch-and-reduce algorithm for convex programs with additional multiplicative constraints

This article presents a branch-and-reduce algorithm for globally solving for the first time a convex minimization problem (P) with p?1$p?1$ additional multiplicative constraints. In each of these p   additional constraints, the product of two convex functions is constrained to be less than or equal to a positive number. The algorithm works by globally solving a 2p$2p$-dimensional master problem (MP) equivalent to problem (P). During a typical stage k of the algorithm, a point is found that minimizes the objective function of problem (MP) over a nonconvex set F^k$F^k$ that contains the portion of the boundary of the feasible region of the problem where a global optimal solution lies. If this point is feasible in problem (MP), the algorithm terminates. Otherwise, the algorithm continues by branching and creating a new, reduced nonconvex set F^k+1$F^{k+1}$ that is a strict subset of F^k$F^k$. To implement the algorithm, all that is required is the ability to solve standard convex programming problems and to implement simple algebraic steps. Convergence properties of the algorithm are given, and results of some computational experiments are reported.