Combined solid-phase extraction and 2D LC–MS for characterization of the neuropeptides in rat-brain tissue

A comprehensive two-dimensional capillary liquid chromatographic (2D LC) method has been established for determination of neuropeptides in rat brain tissue. Rats were exposed to different levels of stress before sacrificing and the aim of this study was to design a powerful separation and detection technique capable of characterizing differences between cerebral neuropeptide expression as a function of stress level. Rat brain samples were homogenized and subjected to clean-up by solid-phase extraction (SPE) on both a reversed-phase (C₁₈) and a weak cation-exchange (CBA) cartridge. The samples were divided in two fractions (A and B) depending on retention on the CBA column. Subsequently, 50 L of the sample were injected on to a strong cation exchanger (SCX) at a mobile phase pH of 3, which enabled preconcentration of positively charged compounds. The trapped compounds were eluted using step gradients of ammonium formate in water–ACN (90:10, v/v). Before enrichment in the second dimension, the eluate from the first dimension was diluted with water containing 0.1% TFA. The compounds eluting from the first dimension were trapped in the second dimension using a dual precolumn system consisting of two short capillary columns packed with Kromasil C₁₈, 10 m particles. Subsequently, the trapped compounds were backflushed on to a 10 cm long, 320 m I.D. analytical column packed with Kromasil C₁₈ 3.5 m particles, on which they were efficiently separated. Detection was performed using an ion-trap mass spectrometer (ITMS) in both the MS and the MS–MS mode. Comparison of base-peak chromatograms (BPC) from MS analysis of stressed and non-stressed rats clearly revealed several differences in neuropeptide expression. The MS–MS data obtained combined with Mascot software were employed for peptide identification.     

Persulfate and perphosphate oxidation of 2-propanol: A relative rate study

A competitive reaction study for two isoelectronic peroxides (peroxodisulfate S₂O and peroxodiphosphate P₂O) interacting with the free radical ·Clpar;CH₃)₂OH is described. The radical formation is initiated by photolysis, the amounts of peroxide remaining analyzed volumetrically. It is found that persulfate reacts with the organic radical over 100 times more rapidly than does perphosphate. Mechanistic consequences in relation to previous work are briefly discussed.     

Sources and mechanisms of wheel/rail noise: state-of-the-art and recent research

A review is presented of wheel/rail research studies, published since 1978. Additionally a study is presented which is focussed on the magnitudes and relative importance of vertical and horizontal forces in the wheel/rail contact zone. In the specific case and the frequency range 50–2000 Hz the vertical force appeared to be 3–10 times larger than the lateral (axial) force. Nevertheless radiation due to axial excitation of the wheel dominates the wayside sound pressure level in several one-third octave frequency bands. Another significant contribution to the wayside A-weighted sound pressure level is attributed to vertical excitation of the rail.     

Multicomponent self-modelling curve resolution in high-performance liquid chromatography by iterative target transformation analysis

Iterative target transformation factor analysis can provide a method for resolving elution profiles consisting of any number of compounds. The results obtained for 3-component resolution are consistent with the results obtained with conventional methods of curve resolution. The same restrictions with regard to overlap and relative signal heights of the compounds seem to apply to the conventional method of curve resolution and the proposed method. The method is tested on data from high-performance liquid chromatography with a diode-array detector obtained for polynuclear aromatic hydrocarbons and for proteins.     

Nanoporous Network Channels from Self‐Assembled Triblock Copolymer Supramolecules

Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.

     

Perpendicular giant magnetoresistance of magnetic multilayers

The theoretical and experimental studies of the giant magnetoresistance effect in metallic magnetic multilayers with measuring current perpendicular to the interface planes are reviewed. Theoretical formalisms of electronic transport in the inhomogeneous electron gas are critically compared with emphasis on the perpendicular magnetoresistance in multilayers. The effects of interface roughness, potential steps at the interfaces, and realistic band structures are addressed. The experimental determination of the perpendicular resistance of metallic multilayers requires either low-resistance measurement techniques or microfabricated samples with enhanced resistances. The experimental methods known at present are discussed and, where possible, compared with each other.     

The mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with coumarilic acid/1,10-phenanthroline

Journal of Thermal Analysis and Calorimetry - The coumarilate (coum?) and 1,10-phenanthroline (phen) mixed ligand complexes of Co(II) (1), Ni(II) (2) Cu(II) (3) and Zn(II) (4) were...     

Computational and NMR Studies on the Complexation of Lithium Ion to 8-Crown-4

Lithium ion selective crown ethers have been the subject of much research for a multitude of applications. Current research is aimed at structurally rigidifying crown ethers, as restructuring of the crown ether ring upon ion binding is energetically unfavorable. In this work, the lithium ion binding ability of the relatively rigid 8-crown-4 was investigated both computationally by density functional theory calculations and experimentally by ¹H and ⁷Li NMR spectroscopy. Although both computational and experimental results showed 8-crown-4 to bind lithium ion, this binding was found to be weak compared to larger crown ethers. The computational analysis revealed that the complexation is driven by enthalpy rather than entropy, illustrating that rigidity is only of nominal importance. To elucidate the origin of the favorable interaction of lithium ion with crown ethers, activation strain analyses and energy decomposition analyses were performed pointing to the favorable interaction being mainly electrostatic in nature. 8-crown-4 presents the smallest crown ether reported to date capable of binding lithium ion, possessing two distinct conformations from which it is able to do so.     

Total Synthesis and Structural Revision of the Antibiotic Tetrapeptide GE81112A

The total synthesis of the naturally occurring antibiotic GE81112A, a densely functionalized tetrapeptide, is reported. Comparison of spectral data with those of the natural product and the lack of biological activity of the synthesized compound led us to revise the published configuration of the 3‐hydroxypipecolic acid moiety. This hypothesis was fully validated by the synthesis of the corresponding epimer.