Computational studies of Cu(II)/Met and Cu(I)/Met binding motifs relevant for the chemistry of Alzheimer's disease

A systematic study of the binding motifs of Cu(II) and Cu(I) to a methionine model peptide, namely, N-formylmethioninamide 1, has been carried out by quantum chemical computations. Geometries of the coordination modes obtained at the B3LYP/6-31G(d) level of theory are discussed in the context of copper coordination by the peptide backbone and the S atom of a methionine residue in peptides with special emphasis on Met35 of the amyloid-beta peptide (Abeta) of Alzheimer's disease. The relative binding free energies in the gas phase, DeltaG(g), are calculated at the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d) level of theory, and the solvation affects are included by means of the COSMO model to obtain the relative binding energies in solution, DeltaG(aq). A free energy of binding, DeltaG(aq) = -19.4 kJ mol(-1), relative to aqueous Cu(II) and the free peptide is found for the most stable Cu(II)/Met complex, 12. The most stable Cu(I)/Met complex, 23, is bound by -15.6 kJ mol(-1) relative to the separated species. The reduction potential relative to the standard hydrogen electrode is estimated to be E degrees (12/23) = 0.41 V. On the basis of these results, the participation of Met35 as a low affinity binding site of Cu(II) in Abeta, and its role in the redox chemistry underlying Alzheimer's disease is discussed.     

Ultra performance liquid chromatography – mass spectrometry studies of formalin‐induced alterations of human brain lipidome

The development of ‘omics’ sciences offers new opportunities for the study of neurodegenerative diseases but increases at the same time the sample demand on brain banks that collect and store valuable human post‐mortem tissue. Our study aims to evaluate in lipidomics the potential of formalin‐fixed tissue compared with the cryopreservation method, considered as the gold standard for biochemical research. Two complementary liquid chromatography/mass spectrometry analytical platforms were used on the basis of hybrid quadrupole time‐of‐flight and triple quadrupole mass spectrometers. Untargeted fingerprinting, semitargeted profiling of specific lipid classes and targeted monitoring of lipid species were performed in formalin‐fixed and cryopreserved samples to provide detailed information at the molecular level on the formalin‐induced alterations of the brain tissue. In vitro incubations of lipid standards were also performed to further describe the degradation processes induced by formaldehyde. Phospholipid compounds were found to be extensively hydrolysed, whilst the sphingolipid ones were preserved. N‐methylation and N‐formylation of amine‐containing phospholipids have also been evidenced. These findings show that the potential detrimental effect of formalin on the analytes of interest must be taken into account when analysing formalin‐fixed samples. Copyright © 2014 John Wiley & Sons, Ltd.     

MALDI imaging mass spectrometry of lipids by adding lithium salts to the matrix solution

Mass spectrometry imaging of lipids using MALDI–TOF/TOF mass spectrometers is of growing interest for chemical mapping of organic compounds at the surface of tissue sections. Many efforts have been devoted to the best matrix choice and deposition technique. Nevertheless, the identification of lipid species desorbed from tissue sections remains problematic. It is now well-known that protonated, sodium- and potassium-cationized lipids are detected from biological samples, thus complicating the data analysis. A new sample preparation method is proposed, involving the use of lithium salts in the matrix solution in order to simplify the mass spectra with only lithium-cationized molecules instead of a mixture of various cationized species. Five different lithium salts were tested. Among them, lithium trifluoroacetate and lithium iodide merged the different lipid adducts into one single lithium-cationized species. An optimized sample preparation protocol demonstrated that the lithium trifluoroacetate salt slightly increased desorption of phosphatidylcholines. Mass spectrometry images acquired on rat brain tissue sections by adding lithium trifluoroacetate showed the best results in terms of image contrast. Moreover, more structurally relevant fragments were generated by tandem mass spectrometry when analyzing lithium-cationized species.     

Novel catalysis of o-nitrophenyl carbonates by p-dimethlaminonopyridine

Transesterification reactions of o-nitrophenyl carbonates have been found to be greatly facilitated by use of p-dialkylaminopyridines as catalysts. A 20-fold rate increase is observed using 0.01 eq. of p-dimethylaminopyridine in place of 2.00 eq of triethylamine. Such rate enhancement is $\text{not}$ observed with p-nitrophenyl carbonates: 2.00 eq of Et₃N causes reaction to occur 8.5 times faster than 0.01 eq of DMAP. DMAP catalyzed reactions of o-nitrophenyl carbonate have been used to prepare aromatic carbonates of 0° in high yields, and avoid the necessity of using 2 equiv. of base.     

Unsteady flow through helicopter rotors

Zusammenfassung Es wird ein Beitrag geliefert zur Stützung der schon früher ge?usserten überzeugung, dass nichtstation?re Str?mungsanteile das Schwingungsverhalten und die aeroelastische Stabilit?t von Helikopter-Drehflügeln wesentlich beeinflussen k?nnen. Die Untersuchung betont besonders den D?mpfungsverlust, welcher sich aus den entlang der Spannweite eines schwebenden Drehflügels schraubenf?rmig abgehenden Wirbeln ergibt. Gem?ss dem Bedürfnis für verbesserte Mittel zur Behandlung nichtstation?rer aerodynamischer Vorg?nge werden zwei neue theoretische Entwicklungen beschrieben und zum Berechnen von Luftkr?ften auf typische schwingende Drehflügel angewendet. Die erste dieser Arbeiten erfasst auf zweidimensionaler Basis das Vorhandensein einer Bodenebene. Es wird angenommen, dass die Wirbel im Abwinde des schwebenden Drehflügels durch die Bodenebene nicht zurückgeworfen, sondern schnell zerstreut werden. Als Resultat zeigt sich, dass die einer spezifischen Schwingungsform entsprechende aerodynamische D?mpfung durch den Einfluss des Bodens, der praktisch etwa zwei Drehflügel-Durchmesser hinaufreicht, im allgemeinen vergr?ssert wird. Die zweite der vorgelegten Theorien betrifft die dreidimensionale Str?mung über ein schwingendes Flügelblatt, welches als tragende Linie und unter Vernachl?ssigung der Krümmung seines Abwindes untersucht wird. Numerische Rechnungen sind ziemlich mühsam, aber mittels Rechenmaschinen ohne weiteres durchführbar. In einem herausgegriffenen typischen Beispiele zeigte sich, dass die Luftkr?fte bedeutend kleiner sind als die von der Streifentheorie angezeigten, dass aber die Phasendifferenz zwischen Anstellwinkel und Luftkr?ften fast unver?ndert bleibt.

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This investigation was performed under USAF Contract AF33(616)-3270 sponsored jointly by the US Army and Dynamics Branch of the Aircraft Laboratory, Wright Air Development Center.