Ayesha Sharmin

Synthesis, structures and reactivity of bis(diphenylphosphino)-methane (dppm)-substituted selenido osmium carbonyl clusters

The unsaturated cluster [(μ-H)Os 3 (CO) 8 {Ph 2 PCH 2 P(Ph)C 6 H 4 }] ( 2 ) reacts with elemental selenium at 110xa0°C to give two triosmium clusters [Os 3 (CO) 7 (μ 3 -Se) 2 (μ-dppm)] ( 3 ), [Os 3 (CO) 7 (μ 3 -CO)(μ 3 -Se)(μ-dppm)] ( 4 ) and the tetraosmium cubane-like cage cluster [Os 4 (CO) 10 (μ 3 -Se) 4 (μ-dppm)] ( 5 ) in 20, 47 and 5% yields, respectively. Treatment of the labile cluster [Os 3 (CO) 10 (MeCN) 2 ] with dppmSe at ambient temperature gives the dinuclear compound [Os 2 (CO) 6 (μ-Se)(μ-dppm)] ( 6 ) along with 3 and 4 in 13, 24 and 4% yields, respectively, while with dppmSe 2 at 80xa0°C it yields 3 and 5 in 27 and 7% yields, respectively, by oxidative transfer of selenium atoms to the metal center. The reaction of 3 with Me 3 NO at 80xa0°C leads to loss of 1 mol of CO and formation of the condensation derivative [Os 6 (CO) 12 (μ 3 -Se) 4 (μ-dppm) 2 ] ( 7 ), containing a central 64-electron butterfly core, in 75% yield. Compound 7 reacts with CO at 98xa0°C to regenerate 4 by cleavage of the three unsupported metalue5f8metal bonds. In the disubstituted square-pyramidal selenido cluster, 3 , the dppm ligand bridges two bonded osmium atoms whereas in 7 both the dppm ligands bridge the open osmium–osmium edges. Treatment of 3 with PPh 3 in the presence of Me 3 NO at room temperature gives the phosphine-substituted compound [Os 3 (CO) 6 (μ 3 -Se) 2 (μ-dppm)(PPh 3 )] ( 8 ) and the dimer 6 in 26 and 20% yields, respectively. The structure of 8 is comparable with that of 3 from which it is derived by replacing one equatorial carbonyl group with the PPh 3 ligand. The molecular structures of the complexes 3 , 4 , 6 , 7 and 8 have been fully elucidated by single-crystal X-ray diffraction studies.

Tuning photophysical properties with ancillary ligands in Ru(II) mono-diimine complexes

The series of complexes [XRu(CO)(L-L)(L)2][PF6] (X = H, TFA, Cl; L-L = 2,2-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4-dicarboxylic-2,2-bipyridyl; L2 = 2PPh3, Ph2 PC2H4PPh2, Ph2PCH═CHPPh2) have been synthesized from the starting complex K[Ru(CO)3(TFA)3] (TFA = CF3CO2) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF6. In the case of L-L = phenanthroline and L2 = 2PPh3, the neutral complex Ru(Ph3P)(CO)(1,10-phenanthroline)( TFA)2 is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L2 = 2PPh3 and X = Cl and for L-L = 2,2-bipyridyl, L2 = 2PPh3 and X = H. All the complexes were characterized in solution by a combination of 1H and 31P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 μs are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.

Ruthenium and osmium carbonyl clusters incorporating stannylene and stannyl ligands.

The reaction of [Ru(3)(CO)(12)] with Ph(3)SnSPh in refluxing benzene furnished the bimetallic Ru-Sn compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-SnPh(2))(SnPh(3))(2)] which consists of a SnPh(2) stannylene bonded to three Ru atoms to give a planar tetra-metal core, with two peripheral SnPh(3) ligands. The stannylene ligand forms a very short bond to one Ru atom [Sn-Ru 2.538(1) A] and very long bonds to the other two [Sn-Ru 3.074(1) A]. The germanium compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-GePh(2))(GePh(3))(2)] was obtained from the reaction of [Ru(3)(CO)(12)] with Ph(3)GeSPh and has a similar structure to that of as evidenced by spectroscopic data. Treatment of [Os(3)(CO)(10)(MeCN)(2)] with Ph(3)SnSPh in refluxing benzene yielded the bimetallic Os-Sn compound [Os(3)(CO)(9)(mu-SPh)(mu(3)-SnPh(2))(MeCN)(eta(1)-C(6)H(5))] . Cluster has a superficially similar planar metal core, but with a different bonding mode with respect to that of . The Ph(2)Sn group is bonded most closely to Os(2) and Os(3) [2.786 and 2.748 A respectively] with a significantly longer bond to Os(1), 2.998 A indicating a weak back-donation to the Sn. The reaction of the bridging dppm compound [Ru(3)(CO)(10)(mu-dppm)] with Ph(3)SnSPh afforded [Ru(3)(CO)(6)(mu-dppm)(mu(3)-S)(mu(3)-SPh)(SnPh(3))] . Compound contains an open triangle of Ru atoms simultaneously capped by a sulfido and a PhS ligand on opposite sides of the cluster with a dppm ligand bridging one of the Ru-Ru edges and a Ph(3)Sn group occupying an axial position on the Ru atom not bridged by the dppm ligand.

Photophysical Studies of Bioconjugated Ruthenium Metal–Ligand Complexes Incorporated in Phospholipid Membrane Bilayers

The luminescent, mono-diimine ruthenium complexes [(H)Ru(CO)(PPh3)2(dcbpy)][PF6] (1) (dcbpy = 4,4-dicarboxy-2,2-bipyridyl) and [(H)Ru(CO)(dppene)(5-amino-1,10-phen)][PF6] (2) (dppene = bis(diphenylphosphino)ethylene; phen = phenanthroline) were conjugated with 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DPPE) and with cholesterol in the case of complex 2. Using standard conjugation techniques, compound 1 gives the bis-lipid derivative [(H)Ru(CO)(PPh3)2(dcbpy-N-DPPE2)][PF6] (3), while 2 provides the monolipid conjugate [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(S)-N-DPPE)][PF6] (4) and the cholesterol derivative [(H)Ru(CO)(dppene)(1,10-phen-5-NHC(O)Ocholesteryl)][PF6] (5). These compounds were characterized by spectroscopic methods, and their photophysical properties were measured in organic solvents. The luminescence of lipid conjugates 3 and 4 is quenched in organic solvents while compound 4 shows a weak, short-lived, blue-shifted emission in aqueous solution. The cholesterol conjugate 5 shows the long-lived, microsecond-time scale emission associated with triplet metal-to-ligand charge-transfer excited states. Incorporation of conjugate 3 in lipid bilayer vesicles restores the luminescence, but with blue shifts (~80 nm) accompanied by nanosecond-time scale lifetimes. In the vesicles conjugate 4 shows a short-lived and blue-shifted emission similar to that observed in solution but with increased intensity. Conjugation of the complex [(H)Ru(CO)(PhP2C2H4C(O)O-N-succinimidyl)2(bpy)][PF6] (6) (bpy = 2,2-bipyridyl) with DPPE gives the phosphine-conjugated complex [(H)Ru(CO)(PhP2C2H4C(O)-N-DPPE)2(bpy)][PF6] (7). Complex 7 also exhibits a short-lived and blue-shifted emission in solution and in vesicles as observed for complexes 3 and 4. We have also conjugated the complex [Ru(bpy)2(5-amino-1,10-phen)][PF6]2 (8) with both cholesterol (9) and DPPE (10). Neither complex 9 nor the previously reported complex 10 exhibited the blue shifts observed for complexes 3 and 4 when incorporated into large unilamellar vesicles (LUVs). The anisotropies of the emissions of complexes 3, 4, and 7 were also measured in LUVs, and those of complex 5 were measured in both glycerol and LUVs. High fundamental anisotropies were observed for complexes 3, 4, and 7.

Structural and functional characterization of the acidic region from the RIZ tumor suppressor.

RIZ (retinoblastoma protein-interacting zinc finger protein), also denoted PRDM2, is a transcriptional regulator and tumor suppressor. It was initially identified because of its ability to interact with another well-established tumor suppressor, the retinoblastoma protein (Rb). A short motif, IRCDE, in the acidic region (AR) of RIZ was reported to play an important role in the interaction with the pocket domain of Rb. The IRCDE motif is similar to a consensus Rb-binding sequence LXCXE (where X denotes any amino acid) that is found in several viral Rb-inactivating oncoproteins. To improve our understanding of the molecular basis of binding of Rb to RIZ, we investigated the interaction between purified recombinant AR and the pocket domain of Rb using nuclear magnetic resonance spectroscopy, isothermal titration calorimetry, and fluorescence anisotropy experiments. We show that AR is intrinsically disordered and that it binds the pocket domain with submicromolar affinity. We also demonstrate that the interaction between AR and the pocket domain is mediated primarily by the short stretch of residues containing the IRCDE motif and that the contribution of other parts of AR to the interaction with the pocket domain is minimal. Overall, our data provide clear evidence that RIZ is one of the few cellular proteins that can interact directly with the LXCXE-binding cleft on Rb.

CCDC 669735: Experimental Crystal Structure Determination

Related Article: A.K.Raha, S.Ghosh, Md.M.Karim, D.A.Tocher, N.Begum, A.Sharmin, E.Rosenberg, S.E.Kabir|2008|J.Organomet.Chem.|693|3613|doi:10.1016/j.jorganchem.2008.08.032