Separation and indirect detection of small-chain peptides using chromophoric mobile phase additives

Ruthenium(II) 1,10-phenanthroline, Ru(phen)3(2+), and ruthenium(II) 2,2'-bipyridyl, Ru(bipy)3(2+), salts were evaluated as mobile phase additives for the liquid chromatographic separation of small-chain peptides on a polystyrene-divinylbenzene copolymeric (Hamilton PRP-1) stationary phase. In a basic mobile phase peptides are anions, and retention, resolution and detection occur because of the interactions between the stationary phase, the RuII complex and the peptide anion. Since the RuII complex concentration changes in the analyte band relative to the background eluent RuII complex concentration, the peptide can be detected by indirect photometric detection using the wavelength where the RuII complex absorbs. Peptide analyte peaks may be positive or negative depending on the counter-anion and its concentration. Small-chain peptides that do not contain chromophoric side-chains are detected without derivatization at about 0.1 nmol injected at a 3:1 signal-to-noise ratio. Factors that affect retention, resolution and indirect photometric detection are the RuII complex, its mobile phase concentration, mobile phase pH and solvent composition, and the type and concentration of the mobile phase counter-anion and/or buffer anion.     

Anion-exchange separation and determination of bisphosphonates and related analytes by post-column indirect fluorescence detection

Bisphosphonic acids and their salts can be detected after their liquid chromatographic separation by post-column indirect fluorescence detection (IFD). After separation the analyte is combined with the highly fluorescent Al³⁺–morin (2′,3,4′,5,7-pentahydroxyflavone) solution and fluorescence decreases because of the formation of the nonfluorescent Al³⁺–bisphosphonate complex. The decrease in fluorescence is proportional to the amount of bisphosphonate present. Separation of the multivalent anionic bisphosphonate analytes from other anions and sample matrix is achieved on a strong base anion-exchange column with a strong, basic eluent. The post-column reaction variables, which influence IFD, are identified and optimized for the detection of the bisphosphonates after separation on the anion exchanger. The method is selective, since only a few anions will undergo a reaction with the Al³⁺–morin solution, and sensitive, detection limit for difluoromethylene bisphosphonate, F₂MDP, is 4 ng for S/N=3. The separation–IFD method can be applied to the determination of bisphosphonates, such as F₂MDP, ethane-1-hydroxy-1,1-bisphosphonic acid, dichloromethylene bisphosphonic acid, 4-amino-1-hydroxybutane-1,1-bisphosphonic acid, in biological samples. The separation–IFD method is also applicable to the detection of inositol phosphate anions.     

Heterogeneous binding of dioxygen: EPR and DFT evidence for side-on nickel(II)-superoxo adduct with unprecedented magnetic structure hosted in MFI zeolite

This article reports on the activation of dioxygen on nickel(I) dispersed inside the nanopores of the ZSM-5 zeolite, which can be regarded as a heterogeneous mimetic system (zeozyme) for Ni-bearing enzymes. The side-on η(2)-coordination of the resulting nickel-bound superoxo adduct was ascertained by detailed analysis of the EPR spectra of both (16)O(2) and (17)O(2) species supported by computer simulations of the spectra and relativistic DFT calculations of the EPR signatures. Molecular analysis of the g and A((17)O) tensors (g(xx) = 2.0635, g(yy) = 2.0884, g(zz) = 2.1675; |A(xx)| ≈ 1.0 mT, |A(yy)| = 5.67 mT, |A(zz)| ≈ 1.3 mT) and quantum chemical modeling revealed an unusual electronic and magnetic structure of the observed adduct (with g(zz)(g(max)) > g(yy)(g(mid)) > g(xx)(g(min)) and the largest O-17 hyperfine splitting along the g(mid) direction) in comparison to the known homogeneous and enzymatic nickel-superoxo systems. It is best described as a mixed metalloradical with two supporting oxygen donor ligands and even triangular spin-density redistribution within the η(2)-{NiO(2)}(11) magnetophore. The semioccupied molecular orbital (SOMO) is constituted by highly covalent δ overlap between the out-of-plane 2p(π(g)*) MO of dioxygen and the 3d(x(2)(-y(2))) MO of nickel. By means of the extended transition state-natural orbitals for the chemical valence approach (ETS-NOCV), three distinct orbital channels (associated with σ, π, and δ overlap) of congruent and incongruent charge and spin density flows within the η(2)-{NiO(2)}(11) unit, contributing jointly to activation of the attached dioxygen, were identified. Their individual energetic relevance was quantified, which allowed for explaining the oxygen binding mechanism with unprecedented accuracy. The nature and structure sensitivity of the g tensor was rationalized in terms of the contributions due to the magnetic field-induced couplings of the relevant molecular orbitals that control the g-tensor anisotropy. The calculated O-17 hyperfine coupling constants correspond well with the experimental parameters, supporting assignment of the adduct. To the best of our knowledge, the η(2)-{NiO(2)}(11) superoxo adducts have not been observed yet for digonal mononuclear nickel(I) centers supported by oxygen donor ligands.     

Search for narrow baryonium states near the NN threshold

The reactions $\text{p}\text{p}\text{→π}{}^{\mathrm{?}}\text{X}\text{and}\text{p}\text{d}\text{→}\text{pX}$ earch for narrow baryonium states in the mass region between 1.6 and 2.0 GeV/c². No such state has been observed. In the first reaction the upper limit for the production of narrow baryonium states is 8μb/sr for a 3 standard deviation signal with 4 MeV/c² width. In the second reaction this limit is 10 μb/sr. The second reaction is rather insensitive for observation of baryonium states as it is dominated by quasi-free contributions.     

Hyperchange exchange reactions on nuclei

In hypercharge exchange reactions (K^?, π^?) on light nuclei Λ particles with small recoil momentum have been produced. The observed hypernuclear states in _Λ⁹Be, _Λ¹²C and _Λ¹⁶O have simple neutron-hole Λ-particle configurations.     

Hypernuclei with sigma particles

The production of Σ particles in the (K⁻, π⁻) on ⁹Be at 720 MeV/c has been studied at the CERN proton synchrotron (PS). The missing-mass spectrum shows structures in the Σ region, which have been interpreted as belonging to hypernuclei with sigma particles. An upper limit of 8 MeV for the width of these states has been estimated.     

Preparation,stability and acidity of difluoromethylene bis phosphonic acid

Hydrolysis of difluoromethylene phosphonate esters quantitatively yields difluoromethylene $\text{bis}$ phosphonic acid as a dihydrate. $\text{In vacuo}$ drying leads to either the monohydrate or the anhydrous acid. Titration of either the free acid or its disodium salt and computer fit of the data gives all four pKas. The disodium salt and the free acid are thermally stable, and the disodium salt is extremely stable even to strong base.     

Separation and indirect detection of alkyl sulfonates and sulfates

Iron(II) 1,10-phenanthroline, Fe(phen)3(2+), salts are used as mobile phase additives for the liquid chromatographic separation of alkyl sulfonates and sulfates on the reversed-phase PRP-1. As alkyl chain length increases retention increases. For a given chain length an alkyl sulfate is more retained than the corresponding alkyl sulfonate. Major elution variables that affect retention are mobile phase solvent and counteranion concentration. Indirect photometric detection is used to detect alkyl sulfonates and sulfates at 510 nm where Fe(phen)3(2+) salts absorb. Conditions for isocratic and gradient elution of multicomponent mixtures are described. Detection limits depending on analyte approached 0.1 nmol for isocratic elution and 3 nmol for gradient elution.     

Upscaling and Automation: Pushing the Boundaries of Multiscale Modeling through Symbolic Computing

Transport in Porous Media - Macroscopic differential equations that accurately account for microscopic phenomena can be systematically generated using rigorous upscaling methods. However, such...