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[reaction: see text] Reaction of various aromatic aldehydes with 2,2'-dipyridyl ketone and ammonium acetate in hot acetic acid provides ready access to a series of substituted 1-pyridylimidazo[1,5-a]pyridines, a class of ligands possessing an N,N-bidentate feature, in good yields.
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Polyimide XU-218 films containing approximately 5 wt pct of Eu(III), Gd(III), Tb(III), and Er(III) were prepared, and the effects of complexing each of the metals with the following four ligands were investigated: N-phenylphthalamate (NPPA), 2,4-pentanedionate (AcAc), 1,3-diphenyl 1,3-propanedionate (DBM), and a new hexa-aza-macrocyclic (MAC) ligand. The tris-chelated complexes of the mononegative ligands NPPA, AcAc, and DBM produced transparent, flexible films, which had magnetic and spectral properties very similar to those of the parent lanthanide complexes, while complexes of MAC showed problems due to the presence of lattice water and yielded dark brittle films. AcAc caused little or no effect on the glass transition temperature (Tg), while NPPA and DBM complexes lowered Tg to 269-290 C, and MAC indicated moisture by inflexion at 95-100 C with a true Tg at 320 C. All lanthanide-containing films were paramagnetic.
The combination of density functional theory (DFT) frequencies and infrared (IR) intensities and experimental spectra is a very powerful tool in the identification of molecules and ions. The computed and measured isotopic ratios make the identification much more secure than frequencies and intensities alone. This will be illustrated using several examples, such as Mn(CO)n and Mn(CO)n-. The accuracy of DFT metal-ligand bond energies will also be discussed.
The structure of trans-bis(acetato-O)bis (4-methylpyridine-N)copper(II), (Cu(C2H3O2)2(C6H7N)2), reported herein, represents a monomeric parent acetate complex with a distorted square-planar arrangement of acetate and 4-methylpyridine ligands around the Cu atom with the following distances and angles: Cu-N = 2.027(4) and Cu-O(1) = 1.950 (3) A; O(1)-Cu-N = 89.1 (2) and O(1)-Cu-N' = 90.0(2)deg. The Cu atom resides on a center of inversion. the most important dihedral angles are the angle between the 4-methylpyridine plane and the acetate plane (O(1), O(2), C(21), and C(22)), 78.2 deg, and the angle between the 4-methylpyridine ring and the coordination plane (Cu, N, O(1)), 31.6 deg.
The use and fabrication of metallo-organic films are discussed. Metallo-organic compounds are ones in which a metal is linked to a long chain carbon ligand through a hetero atom such as O, S, N, P or As. Films formed by the thermal decomposition of these metallo-organics are called MOD films. In order that the products of decomposition contain only CO2, H2O, and in rare cases nitrogen compounds, and to avoid S containing products, the use of a set of metallo-organic compounds for ink fabrication where the linking hetero atom was oxygen was pioneered. These links were made from commercially available carboxylates, or synthesized from commonly available reagents. The processing is described and the molecular design criteria are given. The particular carboxylates or amine carboxylates selected were the octoates or neodecanoates, and they are described.
The successive H2O binding energies of Na(H2O)n(+) are in excellent agreement with experiment and are rather insensitive to electron correlation since the bonding is predominantly electrostatic. A point-charge model shows that changes in the successive binding energies are due primarily to ligand-ligand repulsion. Vibrational frequencies and IR intensities are determined for Na(H2O)n(+) (n = 1-4) at the self-consistent-field and second-order Moller-Plesset levels of theory to facilitate experimental study of these ions.
The structure of trans-bis(acetato-O)bis(4-methyl- pyridine-N)copper(II), (Cu(C2H302)(sub 2)(C6H7N)(sub 2)), re- ported herein, represents a monomeric parent acetate complex with a distorted square-planar arrangement of acetate and 4-methylpyridine ligands around the Cu atom with the following distances and angles: Cu-N = 2.027 (4) and Cu-O1 = 1.950 (3) A; O1-Cu-N = 89.1 (2) and O1 -Cu-N' = 90.9 (2)deg. The Cu atom resides on a center of inversion. The most important dihedral angles are the angle between the 4-methylpyridine plane and the acetate plane (O1, O2, C21 and C22), 78.2 deg and the angle between the 4-methylpyridine ring and the coordination plane (Cu, N, O1), 31.6 deg.
The successive binding energies of up to four H2O and NH3 ligands to Cu(+) are computed at the self-consistent-field and modified coupled-pair functional levels. The most stable structures are those where all ligands are equivalent. Replacing Cu(+) by a point charge gives binding energies that are in good agreement with ab initio and experimental results, and is consistent with bonding that is largely charge dipole in nature. About two-thirds of the large reduction in ligand binding energy between the second and third ligand is due to ligand-ligand repulsion, while one-third is due to increased metal-ligand repulsion resulting from a loss of sd-sigma hybridization. The first and second ligand binding energies increase substantially at the correlated level due to an improved description of sd-sigma hybridization.
Fluorescence spectrum analysis of europic chloride dipyridyl chelates, deriving molecular geometric arrangement and interatomic distances from calculated ligand-field parameters
In long-term space travel, the crew is exposed to microgravity and radiation that invoke potential hazards to the immune system. T cell activation is a critical step in the immune response. Receptor-mediated signaling is inhibited in both microgravity and modeled microgravity (MMG) as reflected by diminished DNA synthesis in peripheral blood lymphocytes and their locomotion through gelled type I collagen. Direct activation of protein kinase C (PKC) bypassing cell surface events using the phorbol ester PMA rescues MMG-inhibited lymphocyte activation and locomotion, whereas the calcium ionophore ionomycin had no rescue effect. Thus calcium-independent PKC isoforms may be affected in MMG-induced locomotion inhibition and rescue. Both calcium-dependent isoforms and calcium-independent PKC isoforms were investigated to assess their expression in lymphocytes in 1 g and MMG culture. Human lymphocytes were cultured and harvested at 24, 48, 72, and 96 h, and serial samples were assessed for locomotion by using type I collagen and expression of PKC isoforms. Expression of PKC-alpha, -delta, and -epsilon was assessed by RT-PCR, flow cytometry, and immunoblotting. Results indicated that PKC isoforms delta and epsilon were downregulated by >50% at the transcriptional and translational levels in MMG-cultured lymphocytes compared with 1-g controls. Events upstream of PKC, such as phosphorylation of phospholipase Cgamma in MMG, revealed accumulation of inactive enzyme. Depressed calcium-independent PKC isoforms may be a consequence of an upstream lesion in the signal transduction pathway. The differential response among calcium-dependent and calcium-independent isoforms may actually result from MMG intrusion events earlier than PKC, but after ligand-receptor interaction.
Single-crystal X-ray structures of four nickel dithiocarbamate complexes, the homoleptic mixed-organic bis-dithiocarbamates Ni[S2CN(isopropyl)(benzyl)]2, Ni[S2CN(ethyl)(n-butyl)]2, and Ni[S2CN(phenyl)(benzyl)]2, as well as the heteroleptic mixed-ligand complex NiCl[P(phenyl)3][(S2CN(phenyl)(benzyl)], were determined. Synthetic, spectroscopic, structural, thermal, and sulfide materials studies are discussed in light of prior literature. The spectroscopic results are routine. A slightly distorted square-planar nickel coordination environment was observed for all four complexes. The organic residues adopt conformations to minimize steric interactions. Steric effects also may determine puckering, if any, about the nickel and nitrogen atoms, both of which are planar or nearly so. A trans-influence affects the Ni-S bond distances. Nitrogen atoms interact with the CS2 carbons with a bond order of about 1.5, and the other substituents on nitrogen display transoid conformations. There are no strong intermolecular interactions, consistent with prior observations of the volatility of nickel dithiocarbamate complexes. Thermogravimetric analysis of the homoleptic species under inert atmosphere is consistent with production of 1:1 nickel sulfide phases. Thermolysis of nickel dithiocarbamates under flowing nitrogen produced hexagonal or -NiS as the major phase; thermolysis under flowing forming gas produced millerite (-NiS) at 300 C, godlevskite (Ni9S8) at 325 and 350 C, and heazlewoodite (Ni3S2) at 400 and 450 C. Failure to exclude oxygen results in production of nickel oxide. Nickel sulfide phases produced seem to be primarily influenced by processing conditions, in agreement with prior literature. Nickel dithiocarbamate complexes demonstrate significant promise to serve as single-source precursors to nickel sulfides, a quite interesting family of materials with numerous potential applications.
Lewis bases were extracted from a Utah COED syncrude via ligand exchange. Addition of this extract to Jet A at levels as low as 5 ppm N produced deterioration of stability in both JFTOT and accelerated storage tests (7 days at 394 K with 13:1air to fuel ratio). Comparable effects on Jet A stability were obtained by addition of pyridine and quinoline, while pyrrole and indole were less detrimental at the same concentration level. The weight of deposit produced accelerated storage tests was found to be proportional to the concentration of added nitrogen compound. Over the narrow temperature range accessible with the experimental method, Arrhenius plots obtained by assuming specific rate to be proportional to the weight of material deposited in seven days exhibit greater slopes in the presence of those nitrogen compounds producing the greater deposition rates. It is shown that despite variation in appearance the elemental composition and spectral characteristics of the deposits are unaffected by addition of the nitrogen compounds. The linearity of the Arrhenius plots and of a plot of Arrhenius slope versus intercept for all the compounds suggests a constancy of mechanism over the range of temperature and heterocycles studied.
Spectroscopic properties of mixed complexes with two different ligand groups surrounding lanthanide ion, discussing energy transfer and absorption
In long-term space travel, the crew is exposed to microgravity and radiation that invoke potential hazards to the immune system. T cell activation is a critical step in the immune response. Receptor-mediated signaling is inhibited both in microgravity and modeled microgravity (MMG) as reflected in diminished DNA synthess in peripheral blood lymphocytes and their locomotion through gelled type 1 collagen. Direct activation of Protein Kinase C (PKC) bypassing cell surface events using the phorbol ester PMA rescues MMG-inhibited lymphocyte activation and locomotion, whereas calcium ionophore ionomycin had no rescue effect. Thus calcium-independent PKC isoforms may be affected in MMG-induced locomotion inhibition and rescue. Both calcium-dependent isoforms and calcium-independent PKC isoforms were investigated to assess their expression in lymphocytes in 19 and MMG-culture. Human lymphocytes were cultured and harvested at 24, 48, 72 and 96 hours and serial samples assessed for locomotion using type I collagen and expression of PKC isoforms. Expression of PKC-alpha, -delta and -epsilon was assessed by RT-PCR, flow cytometry and immunoblotting. Results indicated that PKC isoforms delta and epsilon were down-regulated by more than 50% at the transcriptional and translational levels in MMG-cultured lymphocytes compared with 19 controls. Events upstream of PKC such as phosphorylation of Phospholipase C(gamma) (PLC-gamma) in MMG, revealed accumulation of inactive enzyme. Depressed Ca++ -independent PKC isoforms may be a consequence of an upstream lesion in the signal transduction pathway. The differential response among calcium-dependent and calcium-independent isoforms may actually result from MMG intrusion events earlier than, but after ligand-receptor interaction. Keywords: Signal transduction, locomotion, immunity
The molecular dynamics of chloride capture from water by the tetraprotonated cryptand SC24 has been studied for the cases of 19 distances between the criptand and the chloride. The chloride capture is found to be characterized by a rapid cooperative change in the conformation of the cryptand when the Cl(-) begins to enter the ligand and just as it encounters the energy barrier. The conformational transition is associated with a shift of three N-H bonds from the pure endo orientation, such that they point toward the chloride.
In vitro selection allows rare functional RNA or DNA molecules to be isolated from pools of over 10(15) different sequences. This approach has been used to identify RNA and DNA ligands for numerous small molecules, and recent three-dimensional structure solutions have revealed the basis for ligand recognition in several cases. By selecting high-affinity and -specificity nucleic acid ligands for proteins, promising new therapeutic and diagnostic reagents have been identified. Selection experiments have also been carried out to identify ribozymes that catalyze a variety of chemical transformations, including RNA cleavage, ligation, and synthesis, as well as alkylation and acyl-transfer reactions and N-glycosidic and peptide bond formation. The existence of such RNA enzymes supports the notion that ribozymes could have directed a primitive metabolism before the evolution of protein synthesis. New in vitro protein selection techniques should allow for a direct comparison of the frequency of ligand binding and catalytic structures in pools of random sequence polynucleotides versus polypeptides.
Stimulated emission and laser action from liquid solutions of gadolinium organic chelates at room temperatures