Ana Mirela Neculai

Structure of the unphosphorylated STAT5a dimer

STAT proteins have the function of signaling from the cell membrane into the nucleus, where they regulate gene transcription. Latent mammalian STAT proteins can form dimers in the cytoplasm even before receptor-mediated activation by specific tyrosine phosphorylation. Here we describe the 3.21-Å crystal structure of an unphosphorylated STAT5a homodimer lacking the N-terminal domain as well as the C-terminal transactivation domain. The overall structure of this fragment is very similar to phosphorylated STATs. However, important differences exist in the dimerization mode. Although the interface between phosphorylated STATs is mediated by their Src-homology 2 domains, the unphosphorylated STAT5a fragment dimerizes in a completely different manner via interactions between their β-barrel and four-helix bundle domains. The STAT4 N-terminal domain dimer can be docked onto this STAT5a core fragment dimer based on shape and charge complementarities. The separation of the dimeric arrangement, taking place upon activation and nuclear translocation of STAT5a, is demonstrated by fluorescence resonance energy transfer experiments in living cells.

Synthesis and structure of monomeric and solvent-free LPrX2 compounds supported by a new β-diketiminato ligand [L = Et2NCH2CH2NC(Me)CHC(Me)NCH2CH2NEt2, X = Cl, Br, BH4]

Abstract Trivalent praseodymium complexes with a new β-diketiminato ligand, possessing two pendant arms, LPrX2, (X=Cl (3), Br (4), BH4 (5)), have been prepared by the reactions of the lithium salt of the ligand with the corresponding halides. X-ray structural and elemental analysis showed that 3, 4, and 5 are neutral, monomeric and solvent-free complexes. These complexes adopt a pseudo-octahedral geometry with the two X (X=Cl, Br, BH4) arranged in the trans positions.

Vanadium complexes incorporating the β-diketiminato ligand L. Syntheses and structures of LV(OSO2CF3)2 and LVPPh2

The reaction of LLi (where L = N,N′-bis(2-diethylaminoethyl)-2,4-pentanediimine-ate(-1)) with VCl3·3THF yielded LVCl2, which was characterized by EI-MS and elemental analysis. Subsequent reactions of LVCl2 with AgOSO2CF3 and KPPh2 afforded two new complexes, LV(OSO2CF3)2 and LVPPh2 which were characterized by 19F, 31P NMR spectroscopy, EI-MS, elemental analysis, and single crystal X-ray structural analysis.

Synthesis and structure of a new fluorinated β-ketoiminato ligand and its lithium derivative

Abstract The preparation and characterization of a new fluorinated β-ketoiminato ligand and its lithium salt of composition [(Et2NCH2CH2NC(CF3)CHC(CF3)OLi)2] are described. The crystal structure of the latter was determined. The use of a Meerwein salt as a new route for obtaining fluorinated β-ketoiminato ligands is also investigated.