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Biomedical subjects

P Bertani

Publications and source records attributed to P Bertani.

7 recordsLinked to original sources
PubMed2001

Optically active ortho-metalated half-sandwich ruthenium complexes: solid-state NMR as a convenient tool to analyze mixtures of diastereomers.

Bulk solid samples of various ratios of the cyclometalated arene ruthenium diastereomers (S)Ru- and (R)Ru-[(eta(6)-C6H6)Ru(C6H4-2-(R)-CH(Me)NMe2)PMe2Ph](+)PF6(-) (3a/3b), of which the configurational stability at the metal center has been established by classical solution techniques, have been analyzed by the 13C cross-polarization magic angle spinning (CP-MAS) and 31P MAS NMR. The spectra obtained allowed us to detect both isomers and to estimate their respective proportions by 31P spectra. This technique was applied to a bulk solid sample of the diastereomers (S)Ru- and (R)Ru-[(eta(6)-C6H6)Ru(C6H4-2-(R)-CH(Me)NMe2)NCMe](+)PF6(-) (1a/1b), which were shown to be configurationally labile by classical solution experiments. Detection of isomer 1a only in the resulting 13C CP-MAS NMR spectrum demonstrated that there has been epimerization of 1b to 1a during crystallization, thus confirming the configurational lability at the metal center.

Journal Article↗
PubMed1999

19F/29Si distance determination in fluoride-containing octadecasil by Hartmann-Hahn cross-polarization under fast magic-angle spinning.

19F/29Si Hartmann-Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated 29Si-19F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si-F internuclear distance, r = 2.62 +/- 0.05 A, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69 +/- 0.04 A recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of approximately 14 kHz is shown to be necessary for an effective suppression of 19F-19F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account.

Fluorides↗
PubMed1991

Identification of membrane anchorage domains of the HIV-1 gp160 envelope glycoprotein precursor.

The gp41 transmembrane protein of human immunodeficiency virus type 1 (HIV-1) contains a hydrophobic membrane-spanning domain that serves to anchor the gp120-gp41 complex on the surface of infected cells and virions. To study the requirements for membrane anchorage, conservative amino acid substitutions in three residues at a time were made within this hydrophobic gp41 region. The complete gp160 precursor as well as the gp120 exterior envelope glycoprotein were exported into the supernatant of expressing cells for two mutants with amino acid substitutions in residues 687-689 and 697-699. The soluble gp160 molecules exhibited a binding ability for CD4 on the surface of SupT1 cells that was 33-36% that of the soluble gp120 glycoproteins. These results implicate residues 687-689 and 697-699 as important components of the stop-transfer signal that anchors the gp160 envelope glycoprotein precursor in the membrane. The data also suggest that characteristics in addition to hydrophobicity are required for stop-transfer signals.

Amino Acid Sequence↗