Alternative CHCA-based matrices for the analysis of low molecular weight compounds by UV-MALDI-tandem mass spectrometry

Analysis of low molecular weight compounds (LMWC) in complex matrices by vacuum matrix-assisted laser desorption/ionization (MALDI) often suffers from matrix interferences, which can severely degrade limits of quantitation. It is, therefore, useful to have available a range of suitable matrices, which exhibit complementary regions of interference. Two newly synthesized α-cyanocinnamic acid derivatives are reported here; (E)-2-cyano-3-(naphthalen-2-yl)acrylic acid (NpCCA) and (2E)-3-(anthracen-9-yl)-2-cyanoprop-2enoic acid (AnCCA). Along with the commonly used α-cyano-4-hydroxycinnamic acid (CHCA), and the recently developed 4-chloro-α-cyanocinnamic acid (Cl-CCA) matrices, these constitute a chemically similar series of matrices covering a range of molecular weights, and with correspondingly differing ranges of spectral interference. Their performance was compared by measuring the signal-to-noise ratios (S/N) of 47 analytes, mostly pharmaceuticals, with the different matrices using the selected reaction monitoring (SRM) mode on a triple quadrupole instrument equipped with a vacuum MALDI source. AnCCA, NpCCA and Cl-CCA were found to offer better signal-to-noise ratios in SRM mode than CHCA, but Cl-CCA yielded the best results for 60% of the compounds tested. To better understand the relative performance of this matrix series, the proton affinities (PAs) were measured using the kinetic method. Their relative values were: AnCCA > CHCA > NpCCA > Cl-CCA. This ordering is consistent with the performance data. The synthesis of the new matrices is straightforward and they provide (1) tunability of matrix background interfering ions and (2) enhanced analyte response for certain classes of compounds.     

Tetradentate N2S2 vanadyl(IV) coordination complexes: synthesis, characterization, and reactivity studies

The versatile N(2)S(2) tetradentate ligands (bme-daco)(2-), (bme-dach)(2-), and (ema)(4-) are known to accommodate many divalent transition-metal ions (M = Ni(II), Pd(II), Pt(II), Pb(II), Zn(II), Cd(II), Cu(II), and Fe(II)) while maintaining reactivity at the S-thiolate sites of the respective N(2)S(2)M complexes. The vanadyl ion, of interest for its pharmacological possibilities and its spin-label reporter properties for bioinorganic studies, also shows an affinity for such mixed nitrogen/sulfur-donor environments. Thus, (V≡O)(2+) analogues of a well-characterized series of N(2)S(2)Ni complexes have been prepared as mimics of possible N(2)S(2)(V≡O) formed from in vivo binding sites of the tripeptide motif, Cys-X-Cys. The nucleophilicity of the S-thiolate in these systems is explored with alkylating agents. IR [ν(VO)], electronic spectral, and electron paramagnetic resonance measurements are presented. X-ray diffraction studies of (bme-daco)(V≡O), (bme-dach)(V≡O), and [Et(4)N](2)[(ema)(V≡O)] further characterize the vanadyl complexes. A comparison of the spectral properties with the product of vanadyl interaction with the CGC tripeptide, the biological analogue of the tetraanionic N(2)S(2) ligand, is given.     

Terahertz, infrared and Raman vibrational assignments of [FeFe]-hydrogenase model compounds

Using Raman, terahertz (THz), and mid-infrared (IR) spectroscopies, the vibrational spectra of two chromophore models of hydrogen-producing [FeFe]-hydrogenase, Fe₂(μ-S₂C₃H₆)(CO)₆ and Fe₂(μ-S₂C₂H₄)(CO)₆, have been assigned. The combination of absorption and scattering techniques, along with DFT calculations, allows for assignments to be made without traditional isotopic substitution methods.     

Triangulable Leibniz Algebras

A converse to Lie's theorem for Leibniz algebras is found and generalized. The result is used to find cases in which the generalized property, called triangulable, is 2-recognizable; that is, if all 2-generated subalgebras are triangulable, then the algebra is also. Triangulability joins solvability, supersolvability, strong solvability, and nilpotentcy as a 2-recognizable property for classes of Leibniz algebras.     

Cell mechanics using atomic force microscopy-based single-cell compression

We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.     

Accessing Ambiphilic Phosphine Boronates through C−H Borylation by an Unforeseen Cationic Iridium Complex

Ambiphilic molecules, which contain a Lewis base and Lewis acid, are of great interest based on their unique ability to activate small molecules. Phosphine boronates are one class of these substrates that have interesting catalytic activity. Direct access to these phosphine boronates is described through the iridium‐catalyzed C?H borylation of phosphines. An unconventional cationic iridium catalyst was identified as optimal for a range of phosphines, providing good yields and selectivity across a diverse class of phosphine boronates (isolated as the borane‐protected phosphine). A complimentary catalyst system (quinoline‐based silane ligand with [(COD)IrOMe]₂) was optimal for biphenyl‐based phosphines. Selective polyborylation was also shown providing bis‐ and tris‐borylated phosphines. Deprotection of the phosphine boronate provided free ambiphilic phosphine boronates, which do not have detectable interactions between the phosphorus and boron atoms in solution or the solid state.     

Postprecipitation of zinc with homogeneously precipitated copper sulfide

The postprecipitation of zinc ion onto copper sulfide which has been precipitated from homogeneous solution using thioacetamide has been investigated under various conditions. The zinc carried increases with increasing time, increasing concentration of zinc, increasing digestion temperature, increasing thioacetamide added, and decreasing acid concentration. On the basis of these and several other special observations, it is believed that the postprecipitation is a result of adsorption of bisulfide ion on the surface of the copper sulfide, this adsorbed layer then reacting with the zinc ion.     

Stirring up trouble: Multi-scale mixing measures for steady scalar sources

The mixing efficiency of a flow advecting a passive scalar sustained by steady sources and sinks is naturally defined in terms of the suppression of bulk scalar variance in the presence of stirring, relative to the variance in the absence of stirring. These variances can be weighted at various spatial scales, leading to a family of multi-scale mixing measures and efficiencies. We derive a priori estimates on these efficiencies from the advection-diffusion partial differential equation, focusing on a broad class of statistically homogeneous and isotropic incompressible flows. The analysis produces bounds on the mixing efficiencies in terms of the Péclet number, a measure of the strength of the stirring relative to molecular diffusion. We show by example that the estimates are sharp for particular source, sink and flow combinations. In general the high-Péclet-number behavior of the bounds (scaling exponents as well as prefactors) depends on the structure and smoothness properties of, and length scales in, the scalar source and sink distribution. The fundamental model of the stirring of a monochromatic source/sink combination by the random sine flow is investigated in detail via direct numerical simulation and analysis. The large-scale mixing efficiency follows the upper bound scaling (within a logarithm) at high Péclet number but the intermediate and small-scale efficiencies are qualitatively less than optimal. The Péclet number scaling exponents of the efficiencies observed in the simulations are deduced theoretically from the asymptotic solution of an internal layer problem arising in a quasi-static model.