Gel-phase 19F NMR spectral quality for resins commonly used in solid-phase organic synthesis; a study of peptide solid-phase glycosylations

The spectroscopic properties for seven different commercial resins used in solid-phase synthesis were investigated with (19)F NMR spectroscopy. A fluorine-labeled dipeptide was synthesized on each resin, and the resolution of the (19)F resonances in CDCl(3), DMSO-d(6), benzene-d(6) and CD(3)OD were measured with a conventional NMR spectrometer, i.e. without using magic angle spinning. In general, resins containing poly(ethylene glycol) chains (ArgoGel, TentaGel and PEGA) were found to be favorable for the (19)F NMR spectral quality. Three serine containing tri-, penta-, and heptapeptides were then prepared on an ArgoGel resin functionalized with a fluorine-labeled linker. The resin bound peptides were glycosylated utilizing a thiogalactoside glycosyl donor carrying fluorine-labeled protective groups. Monitoring of the glycosylations with gel-phase (19)F NMR spectroscopy allowed each glycopeptide to be formed in similar 80% yield, using a minimal amount of glycosyl donor (3 x 2 equivalents). In addition, it was found that the glycosylation yields were independent of peptide length.     

The critical probability for Voronoi percolation in the hyperbolic plane tends to 1/2

We consider percolation on the Voronoi tessellation generated by a homogeneous Poisson point process on the hyperbolic plane. We show that the critical probability for the existence of an infinite cluster tends to 1/2 as the intensity of the Poisson process tends to infinity. This confirms a conjecture of Benjamini and Schramm [5].     

Time-resolved vibrational spectroscopy

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Time-resolved vibrational spectroscopy     

Boundary and Lens Rigidity of Lorentzian Surfaces

Let be a Lorentzian metric on the plane that agrees with the standard metric outside a compact set and so that there are no conjugate points along any time-like geodesic of . Then and are isometric. Further, if and are two dimensional compact time oriented Lorentzian manifolds with space--like boundaries and so that all time-like geodesics of maximize the distances between their points and and are ``boundary isometric', then there is a conformal diffeomorphism between and and they have the same areas. Similar results hold in higher dimensions under an extra assumption on the volumes of the manifolds.

     

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol mass spectrometry (BAMS). EIP values were determined for a series of amino acid, dipicolinic acid, and peptide aerosol particles to determine what chemical features aid in ionization. The spectra of individual amino acids and dipicolinic acid, as well as mixtures, were examined for extent of fragmentation and the presence of molecular ion dimers, which are indicative of ionization conditions. Standard mixtures yielded information with respect to the significance of secondary ion plume reactions on observed spectra. A greater understanding of how these parameters affect EIP and spectra characteristics of bio-aerosols will aid in the intelligent selection of viable future biomarkers for the identification of bio-terrorism agents.     

Electronic structure of the permanganate ion

The electronic structure of the permanganate ion has been investigated, using a semiquantitative LCAO MO method without empirical parameters. The atomic orbital basis set for the central ion has been varied systematically, and the effect of symmetric changes of bond distances has also been examined. In addition, calculations have been performed in which the regions around the ligands have been made more attractive for electrons, to simulate the presence of cations in solution and in the crystalline state. The electronic absorption spectrum of MnO ₄ ^– has been tentatively assigned, on the basis of predicted band shapes and transition energies.

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Zusammenfassung Die Elektronenstruktur des Permanganations wurde mit einer halbquantitativen LCAO-MO Methode ohne empirische Parameter behandelt. Die Zustandsfunktionen des Zentralatoms wurden variiert und der Einflu\ symmetrische Änderungen der BindungsabstÄnde untersucht. Um die Gegenwart von Kationen in Lösung und im Kristall zu simulieren, wurden daneben auch Rechnungen durchgeführt, bei denen einer stÄrkeren Elektronenanziehung durch die Liganden Rechnung getragen wird. Ferner wurde versucht, das Absorptionsspektrum von MnO ₄ ^– auf Grund der vorausgesagten Bandenform und übergangsenergien zu deuten.

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Résumé La structure électronique de l'ion permanganate est étudiée à l'aide d'une méthode LCAO MO semi-quantitative sans paramètres empiriques. La base d'orbitales atomiques pour l'ion central a été systématiquement variée et l'effet de changements symétriques des longueurs de liaison a été aussi examiné. Pour simuler la présence des cations dans la solution et dans le cristal on a fait des calculs dans lesquels la région autour des ligands était rendue plus attractive pour les électrons. Le spectre d'absorption de MnO ₄ ^–1 est interprété à l'aide des prédictions sur les formes des bandes et les énergies de transition.

     

An alternative preparation of the 2-dimethylaminomethylene-1,3-bis(dimethylimmonio)propane salt from phosphonoacetic acids and some applications in heterocyclic synthesis

An alternative preparation of a 2-iminovinamidinium salt from phosphonoacetic acids is described along with its application to the synthesis of 5-formylpyrimidines and masked 4-formylpyrazoles.     

The Lewis basicity of the [Pt3(μ-CO)3(PR3)3] clusters and the X-ray crystal structure of [{ZnI2}{Pt3(μ-CO)3(PPh(i-Pr)2)3}]

The cluster compounds [Pt₃(μ-CO)₃(PR₃)₃] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX₂, and Group XIII, MX₃, to form cluster compounds of the composition [{MX_n}{Pt₃(μ-CO)₃(PR₃)₃}]. The X-ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt₃(μ-CO)₃(PPh(i-Pr)₂)₃}].