Application of time-resolved infrared spectroscopy to electronic structure in metal-to-ligand charge-transfer excited states

Infrared data in the nu(CO) region (1800-2150 cm(-1), in acetonitrile at 298 K) are reported for the ground (nu(gs)) and polypyridyl-based, metal-to-ligand charge-transfer (MLCT) excited (nu(es)) states of cis-[Os(pp)2(CO)(L)](n)(+) (pp = 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy); L = PPh3, CH(3)CN, pyridine, Cl, or H) and fac-[Re(pp)(CO)3(4-Etpy)](+) (pp = phen, bpy, 4,4'-(CH3)2bpy, 4,4'-(CH3O)2bpy, or 4,4'-(CO2Et)2bpy; 4-Etpy = 4-ethylpyridine). Systematic variations in nu(gs), nu(es), and Delta(nu) (Delta(nu) = nu(es) - nu(gs)) are observed with the excited-to-ground-state energy gap (E(0)) derived by a Franck-Condon analysis of emission spectra. These variations can be explained qualitatively by invoking a series of electronic interactions. Variations in dpi(M)-pi(CO) back-bonding are important in the ground state. In the excited state, the important interactions are (1) loss of back-bonding and sigma(M-CO) bond polarization, (2) pi(pp*-)-pi(CO) mixing, which provides the orbital basis for mixing pi(CO)- and pi(4,4'-X(2)bpy)-based MLCT excited states, and (3) dpi(M)-pi(pp) mixing, which provides the orbital basis for mixing pipi- and pi(4,4'-X(2)bpy*-)-based MLCT states. The results of density functional theory (DFT) calculations on the ground and excited states of fac-[Re(I)(bpy)(CO)3(4-Etpy)](+) provide assignments for the nu(CO) modes in the MLCT excited state. They also support the importance of pi(4,4'-X2bpy*-)-pi(CO) mixing, provide an explanation for the relative intensities of the A'(2) and A' ' excited-state bands, and provide an explanation for the large excited-to-ground-state nu(CO) shift for the A'(2) mode and its relative insensitivity to variations in X.     

Zur Charakterisierung von Eigenschaften der versteiften dreizähnigen Aminophosphanliganden N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin und N,N-Bis(diphenylphosphino)-2-aminopyridin mit Metallen der Chromgruppe

Inhaltsübersicht. Edukte von Typ M(CO)₆ (M = Cr, Mo,W), N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin (PNP) und Trimethylaminoxid setzen sich bei Raumtemperatur nicht zu dem bekannten Verbindungstyp mer-M(CO)₃PNP, sondern zu Verbindungen der beiden Typen M(CO)₄(PNP=O) mit zweizähnig koordinierten Liganden PNP=O und M(CO)₅(NMe₃) um. Die zu Vergleichszwecken untersuchte Oxidation eines koordinierten PNP-Liganden von mer-Mo(CO)₃(PNP) in Tetramethylbenzollösung ergibt mit Luftsauerstoff bei 180°C eine Reaktion unter Spaltung der P–N-Bindung zur cubanartigen Verbindung Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄ (Ausbeute 48%). In einem Glaseinschlußrohr reagiert der ambidente N,N-Bis(diphenyIphosphino)-2-nminopyridin-Ligand (NPP) mit den Hexacarbonylen M(CO)₆ in Toluollösung bei 140°C zu Verbindungen des Typs M(CO)₄(NPP) mit zweizähniger Verknüpfung des NPP-Liganden. Hierbei bilden die beiden P-Donoratome am Aminstickstoffatom einen MP₂N-Chelatvierring an Stelle des ebenfalls möglichen P, N_py-Chelatfünfrings. Der analoge Chelatvierring entsteht gleichfalls bei einer Ligandensubstitutions-reaktion zwischen Verbindungen des Zweikernkomplextyps MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W; M = Mo, M′ = W) bzw. \V(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃) und NPP. Er bildet sich außerdem bei der Thermolyse von Mo(CO)₄(NPP) zu Mo₂(CO)₆(μ-PPh₂)₂(NPP). Die Identifizierung erfolgt im Falle der Verbindungen Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O_4′ Mo₂(CO)₆(μ-PPh₂)₂(NPP) und W(CO)₄(μ-PPh₂)₂IrH(CO)(NPP) durch Einkristall-Röntgenstrukturanalysen. Alle isolierten Produkte werden durch spektroskopische Messungen insbesondere ³¹P-NMR-Daten charakterisiert. Characterization of Properties of the Rigid Tridentate Chelate Ligand N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine and N,N-Bis(diphenylphosphino)-2-aminopyridine with Transition Metals of the Chromium Group Hexacarbonyls M(CO)₆ (M = Cr, Mo, W), N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine (PNP) and trimethylamine oxide gave products of two types M(CO)₄(PNP=O) having a bidentate ligand PNP=O and M(CO)₅(NMe₃) instead of the desired mer-M(CO)₃PNP. For the purpose of a comparison, aerial oxidation of mer-Mo(CO)₃PNP in tetramethyl benzene solution at 180°C was examined which resulted a P–N bond rupture under formation of the cubane-like product Mo₄(μ₃-O)₄(μ-Ph₂PO₂C₄O₄){yield 48%). In sealed glass tubes the ambidentate ligand N,N-bis(diphenylphosphino)-2-aminopyridine (NPP) was reacted with the hexacarbonyls M(CO)₆ in toluene solution at 140°C to products of the type M(CO)₄NPP with NPP as bidentate ligand. Under this reaction conditions the four-membered chelate ring of the type MP₂N was formed with the two P donor atoms attached to the amine N atom instead of the possible competitive five-membered chelate ring formation with a P and pyridyl nitrogen. The analogous four-membered chelate ring was formed in ligand substitution reactions between the substance NPP and each of the dinuclear coordination compounds MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W, M = Mo, M′ = W) including W(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃); Mo₂(CO)6(μ-PPh₂)₂(NPP) was obtained via thermolysis of Mo(CO)₄(PNP=O). The given structural identification of the compounds Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄, Mo₂(CO)₆ (μ-PPh₂)₂(NPP) and W(CO)₄(μ-PPh₂)₂IrH(CO) (NPP) was done by single-crystal X-ray analysis. All seperated products have been characterized by means of spectroscopic measurements especially ³¹P n.m.r. data.     

A luminescence-based probe for sensitive detection of hydrogen peroxide in seconds

Here, we present a fast and simple hydrogen peroxide assay that is based on time-resolved fluorescence. The emission intensity of a complex consisting of terbium ions (Tb³⁺) and phthalic acid (PA) in HEPES buffer is quenched in the presence of H₂O₂ and this quenching is concentration-dependent. The novel PATb assay detects hydrogen peroxide at a pH range from 7.5 to 8.5 and with a detection limit of 150 nmol L⁻¹ at pH 8.5. The total assay time is less than 1 min. The linear range of the assay can be adapted by a pH adjustment of the aqueous buffer and covers a concentration range from 310 nmol L⁻¹ to 2.56 mmol L⁻¹ in total which encompasses four orders of magnitude. The assay is compatible with high concentrations of all 47 tested inorganic and organic compounds. The PATb assay was applied to quantify H₂O₂ in polluted river water samples. In conclusion, this fast and easy-to-use assay detects H₂O₂ with high sensitivity and precision.     

Luminescence of ruthenium halide complexes containing a hemilabile phosphine pyrenyl ether ligand

A series of Ru(II) complexes, tcc-RuX2(POC4Pyr-P,O)2 (X = Cl (3), Br (4), I (5)), containing the hemilabile phosphine pyrenyl ether ligand 4-{2-(diphenylphosphino)phenoxy}butylpyrene (POC4Pyr (1)) are reported. The synthesis and spectroscopic properties of both the ligand, POC4pyr (1), and ligand oxide, P(=O)OC4pyr 2, and the solid-state structure of 1 are reported. Complexes 3-5 react rapidly with CO to give complexes ttt-RuX2(CO)2(POC4pyr-P)2 (X = Cl (6), Br (7), I (8)). No pyrene excimer emission is detected from 3-5; however, different intensities of excimer emission are observed for 6-8. The intensity of excimer emission decreases through the series, with 6 showing the most intense response. The emission is solely due to intramolecular pyrene excimers at low concentrations (< or =10(-4) M). Comparison of the UV-vis and steady-state fluorescence spectra shows overlap between the low energy d-d absorption of 7 and 8 with excimer emission (480 nm), suggesting nonradiative energy transfer may be occurring. Once excess CO is removed, complexes 6-8 isomerize to cis-dicarbonyl complexes cct-RuX2(CO)2(POC4Pyr-P)2 (X = Cl (9), Br (10), I (11)). The intensity of excimer emission from 9-11 increases with respect to the excimer emission observed for 6-8, with 9 showing a significant increase in excimer intensity.     

Scaffold Effects on Osteogenic Differentiation of Equine Mesenchymal Stem Cells: An In Vitro Comparative Study

The in vitro viability, osteogenic differentiation, and mineralization of four different equine mesenchymal stem cells (MSCs) from bone marrow, periosteum, muscle, and adipose tissue are compared, when they are cultured with different collagen‐based scaffolds or with fibrin glue. The results indicate that bone marrow cells are the best source of MSCs for osteogenic differentiation, and that an electrochemically aggregated collagen gives the highest cell viability and best osteogenic differentiation among the four kinds of scaffolds studied.

     

Synthesis of 5,5′-Disubstituted Bimorpholines

A general method for the synthesis of 5,5′-disubstituted bimorpholines is proposed. According to the method, methyl-substituted and benzyl-substituted compounds were synthesized, starting from tartaric ester acetal. Target compounds were obtained in good yield and high enantiomeric purity.