TGF-β1 induction of the adenine nucleotide translocator 1 in astrocytes occurs through Smads and Sp1 transcription factors

Background  

The adenine nucleotide translocator 1 (Ant1) is an inner mitochondrial membrane protein involved with energy mobilization during oxidative phosphorylation. We recently showed that rodent Ant1 is upregulated by transforming growth factor-beta (TGF-β) in reactive astrocytes following CNS injury. In the present study, we describe the molecular mechanisms by which TGF-β1 regulates Ant1 gene expression in cultured primary rodent astrocytes.     

Bis­[1,3‐bis­(tri­methyl­silyl)­allyl]­cobalt(II), a stable electron‐deficient allyl complex

The title compound, bis­[(1,2,3‐η)‐(2E)‐1,3‐bis­(tri­methyl­silyl)­prop‐2‐enyl]­cobalt(II), [Co(C₉H₂₁Si₂)₂], is a homoleptic allyl complex with η³‐bound ligands. The Co—C distances range from 1.996 (3) to 2.096 (3) Å and the allyl ligands adopt staggered, nearly parallel, arrangements around the Co atom. The tri­methyl­silyl groups are in syn–anti conformations; the steric shielding they provide to the metal is probably responsible for the thermal stability of the compound.     

Silyl-substituted alkylidenes: preparation of the novel complexes and mechanistic studies of their formation from reactions of alkylidenes with silanes and silyl-to-alkylidyne migration

Alkylidene complexes (Me₃SiCH₂)₃Ta(PMe₃)=CHSiMe₃ (1) and Me₃SiCH₂Ta(PMe₃)₂(=CHSiMe₃)₂ (3a) were found to react with phenylsilanes H₂SiR′Ph (R′=Me, Ph) and (PhSiH₂)₂CH₂ to give disilyl-substituted alkylidenes (Me₃SiCH₂)₃Ta=C(SiMe₃)(SiHR′Ph) (2) and novel metallasilacyclobutadiene and metalladisilacyclohexadiene complexes. Silyl-substituted alkylidene complex (Bu^tCH₂)₂W(=O)[=C(Bu^t)(SiPh₂Bu^t)] (5a) was prepared from the reaction of O₂ with an equilibrium mixture (Bu^tCH₂)W(=CHBu^t)₂(SiPh₂Bu^t) (4b) (Bu^tCH₂)₂W(CBu^t)(SiPh₂Bu^t) (4a). Our recent studies of the preparation of these complexes and mechanistic pathways in the formation of these silyl-substituted alkylidene complexes are summarized.     

Complexities in the ring-opening polymerization of lactide by chiral salen aluminum initiators

The preparation of (R, R)- and (S, S)-salen Al(OR) complexes, where R = Et, CH2(i)Pr, CH2(t)Bu, and CH2CH(S)MeCl, are reported, along with their reactions with rac-lactide (salen = N, N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino). Rapid, reversible coordination of LA to the salen metal complex is observed, and it is shown that the relative rates of alcohol/alkoxide exchange are comparable to the NMR time scale while the rate of chain transfer involving (R, R)-salenAl(O-R-R) and (S, S)-salenAl(O-S-R) is much faster than the initial rate of ring opening of the LA monomer. For a primary [Al-OR] moiety, the ring opening of rac-LA is much faster than the ring-opening polymerization/enchainment of LA, and in the initial ring-opening event, the diastereoselectivity is dependent on the solvent, the chirality of the salen ligand, and the OR group. Irrespective of the initiator group OR or the solvent, the system moves to a pseudostatic equilibrium concentration of L- and D-LA which is dependent on the nature of the chirality of the salen ligand. Further studies show that the relative rate of trans-esterification is slower than the rate of LA enchainment and that the rate of epimerization is the slowest reaction in the system. Adventitious water leads to loss of catalytic activity and formation of the inert oxo-bridged compound [(salen)Al]2(mu-O) which has been structurally characterized.     

Trimethylsilylated allyl complexes of nickel. The stabilized bis(pi-allyl)nickel complex [eta3-1,3-(SiMe3)2C3H3]2Ni and its mono(pi-allyl)NiX (X=Br, I) derivatives

Reaction of 2 equiv of K[1,3-(SiMe3)2C3H3] with NiBr2(dme) in THF at -78 degrees C produces the orange pi-allyl complex [1,3-(SiMe3)2C3H3]2Ni (1). Unlike the pyrophoric (C3H5)2Ni, the trimethylsilylated derivative only slowly decomposes in air (from hours to days). Both eclipsed (1a) and staggered (1b) conformations are found in solution; the eclipsed form irreversibly converts to the thermodynamically more stable staggered conformation when heated above 85 degrees C. Single-crystal X-ray structures obtained for both 1a and 1b confirm that the allyl ligands are bound in a trihapto manner to the metals and that trimethylsilyl substituents are in syn, anti arrangements. Density functional theory calculations performed on the bis(allyl)nickel complexes indicate that the substituents exert little effect on the basic metal-ligand geometries. Trimethylphosphine is converted to tetramethyltetraphosphane, (MeP)4, on reaction with 1. In toluene, 3-bromo-1,3-bis(trimethylsilyl)propene reacts with (COD)2Ni to produce the dimeric purple complex {[1,3-(SiMe3)2C3H3]NiBr}2 (2a). Both NMR and X-ray crystallographic data establish that the allyl ligands are staggered and that the trimethylsilyl substituents are in a syn, syn conformation. NMR data indicate that the reaction of one equivalent of 1 with Br2 in benzene produces an analogous complex (2b) with the allyl ligand substituents in a syn, anti configuration. When 1 equiv of 1 is treated with I2 in hexanes, the dark red dimeric complex {[1,3-(SiMe3)2C3H3]NiI}2 (3) is formed. Its X-ray crystal structure demonstrates that both eclipsed (3a) and staggered (3b) allyl conformation are present. The trimethylsilyl groups on the allyl ligands are in syn, anti arrangements in the two forms.