Investigation of hydrothermal routes to mixed-metal cerium titanium oxides and metal oxidation state assignment using XANES

The reaction between TiF(3) or TiO(2) and Ce(3+) in sodium hydroxide solutions yields highly crystalline NaCeTi(2)O(6) at room temperature and under mild hydrothermal conditions (T < or = 240 degrees C). There is no evidence for the formation of ternary Ce-Ti-O materials by this method, and the use of bases other than NaOH always produces poorly crystalline materials. The material NaCeTi(2)O(6) has a distorted perovskite structure with sodium and cerium ions randomly occupying the A sites: Pnma, a = 5.4517(8) A, b = 7.7292(6) A, c =5.4573(3) A. XANES spectroscopy at the Ti K edge and Ce L(III) edge, with reference to crystalline model compounds, reveals that cerium is found solely as Ce(III) and titanium as Ti(IV) in NaCeTi(2)O(6). Isomorphous substitution of Ce(3+) by Nd(3+) or Ti(4+) by V(4+) is found to be very facile under hydrothermal conditions (at a temperature of 240 degrees C), by addition of appropriate amounts of metal salts to the hydrothermal reaction mixtures. The series NaCe(1-x)Nd(x)Ti2O6 (0 < or = x < or = 1) and NaCeTi(2-x)V(x)O6 (0 相似文献   

A convenient and rapid synthesis of potassium penicilliantes using EEDQ

N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ, 1) has been utilized as a coupling reagent to attach sterically unhindered acids to the potassium salt of 6-aminopenicillanic acid ( 4 ) at room temperature. The excellent yields and rapidity of the reaction illustrate the convenience of utilizing 1 as the coupling reagent to directly prepare the potassium salt of certain penicillins.     

The use of an immobilized enzyme nylon tube reactor incorporating a four enzyme system for creatinine analysis

A single immobilized enzyme nylon tube reactor was produced incorporating a four enzyme system for the analysis of creatinine. The enzyme activity ratios in the coupling solution used to prepare the reactor were found to be of extreme importance in governing the activity of the latter. The reactor was incorporated into a continuous flow analysis system used to assay creatinine in urine samples and the results were correlated with a manual technique employing the same enzyme system in solution. The precision, correlation, high specificity, simplicity, and speed of the analysis were concluded to be factors in favor of the method's suitability for urine creatinine determinations.     

Reactivity of ionic liquids

Ionic liquids are becoming widely used in synthetic organic chemistry and yet relatively little attention has been paid to the intrinsic reactivity of these low temperature molten salts. Clues to the non-innocent nature of many ionic liquids are contained in the reports of altered reactivity of dissolved substrates, unexpected catalytic activity and unforeseen by-product formation. In this review, we focus on the reactivity of ionic liquids, as opposed to reactivity in ionic liquids (although discussion of the latter is often included where it aids understanding of the former).     

Cathodic reduction of nicotinamide adenine dinucleotide and other adenine-containing compounds in acidic media

Both nicotinamide adenine dinucleotide (NAD⁺) and acid-hydrated NADH, as well as adenine, adenosine, adenosine mono-, di-, and tri-phosphate and adenosine diphosphoribose, undergo four-electron reductions of the protonated adenine ring in acidic media. The values of αn_a (transfer coefficient times the number of electrons involved in the rate-determining step), n (total number of electron transferred), and p (number of protons involved in the rate-determining step) agree well with values previously reported for adenine. Cathodic stripping voltammetry of an adsorbed film can be applied to these compounds. Rapid scan rates are required to eliminate the slow desorption step at ?1.1 V vs. SCE for some of these compounds. Hydration of the nicotinamide ring of NADH appears to inhibit this desorption step, but does not appear to be related directly to the electroactivity of the hydration product.     

Callipeltoside a: total synthesis,assignment of the absolute and relative configuration,and evaluation of synthetic analogues

The total synthesis of the novel antitumor agent callipeltoside A, as well as several analogues, is accomplished and allows assignment of the stereochemistry not previously established. A convergent strategy is employed wherein the target is dissected into three units-the core macrolactone, the sugar callipeltose, and a cyclopropyl bearing chain. The strategy for the synthesis of the macrolactone derives from employment of diastereoselective aldol reactions that emanate from an 11 carbon piece. The stereochemistry of the latter derives from the chiral pool and two asymmetric reactions-a ketone reduction using CBS-oxazaborolidine and a Pd catalyzed asymmetric allylic alkylation (AAA). The novelty of the latter protocol is its control of regioselectivity as well as absolute configuration. The trisubstituted olefin is generated using an alkene-alkyne coupling to create a trisubustituted olefin with complete control of geometry. The excellent chemo- and regioselectivity highlights the synthetic potential of this new ruthenium catalyzed process. The macrolactonization employs in situ formation of an acylketene generated by the thermolysis of a m-dioxolenone. Two strategies evolved for attachment of the side chain-one based upon olefination and a second upon olefin metathesis. The higher efficiency of the latter makes it the method of choice. A novel one pot olefin metathesis-Takai olefination protocol that should be broadly applicable is developed. The sugar is attached by a glycosylation by employing the O-trichloroacetimidate. This route provided both C-13 epimers of the macrolactone by using either enantiomeric ligand in the Pd AAA reaction. It also provided both trans-chlorocyclopropane diastereomers of callipeltoside A which allows the C-20 and C-21 configuration to be established as S and R, respectively. The convergent nature of the synthesis in which the largest piece, the macrolatone, require only 16 linear steps imparts utility to this strategy for the establishment of the structure-activity relationship. Initial biological testing demonstrates the irrelevance of the chloro substituent and the necessity of the sugar.     

Facilitated Intramolecular Conjugate Addition of Amides of 3-(3',6'-Dioxo-2',4'-dimethyl-1',4'-cyclohexadienyl)-3,3-dimethylpropionic Acid. 2. Kinetics of Degradation

The chemical stability studies of amides of 3-(3',6'-dioxo-2',4'-dimethyl-1',4'-cyclohexadienyl)-3,3-dimethylpropionic acid (Qa) [Qop(a-j)] were conducted in order to determine the utility of this redox-sensitive system as a potential prodrug promoiety or redox-sensitive protecting group in organic synthesis. This study showed that quinone propionic amides of aniline derivatives [Qop(a-d)] underwent rapid degradation in mildly acidic conditions (pH 4.5-6.0) to yield degradation products resulting from the intramolecular 1,2- or 1,4- conjugate addition of the amide nitrogen to the quinone ring. This conjugate addition was found to be specific base-catalyzed and independent of the para substituent on the aromatic ring of the amine. The predominant route of degradation yielded a five-membered ring spirolactam. By altering the nature of the amine component of the amide, these degradation reactions were prevented. Amides of Qa other than those of the aniline type [Qop(e-j)] were found to be substantially more stable and were thus proposed as the more suitable candidates for this potential redox-sensitive prodrug system and redox-sensitive protecting group for amines and alcohols in organic synthesis.     

New emissive fac-tricarbonylchlorobis(ligand)rhenium(I) complexes prepared from pyridine/thiophene hybrid ligands

Stille coupling between tributyl-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-stannane and 4-bromopyridine resulted in the preparation of the new pyridine/thiophene hybrid ligand 4-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)-pyridine [4-py-EDOT] (1). Reaction of 1, 4-thiophen-2-yl-pyridine (2), or 4-[2,2^′]bithiophenyl-5-yl-pyridine (3) with ClRe(CO)₅ resulted in the isolation of complexes 4-6, ClRe(L)₂(CO)₃, where L=1, 2, or 3 respectively. The solid-state structure of 4 was determined by X-ray crystallography, which clearly shows the fac arrangement of the three CO ligands and the two 4-py-EDOT ligands arranged cis to one another. The metal complexes 4-6 have been characterized by ¹H and ¹³C NMR, ESI or FAB MS, FTIR, UV-Vis, fluorescence, and elemental analysis.     

Examining the out-of-center distortion in the [NbOF5]2- anion

Out-of-center "primary" electronic distortions are inherent to the oxide fluoride anions of the early d0 transition metals. In the [NbOF5]2- anion, the Nb5+ moves from the center of the octahedron toward the oxide ligand to form a short Nb=O bond and long trans Nb-F bond. The combined results of single-crystal X-ray diffraction and electronic structure calculations indicate that the primary distortion of the [NbOF5]2- anion is affected by the coordination environment that is created by the three-dimensional extended structure. The formation of bonds between an M(L)4(2+) (M = Cd2+, Cu2+; L = 3-aminopyridine, 4-aminopyridine) cation and the oxide and/or trans-fluoride ligands of the [NbOF5]2- anion weakens the pi component of the Nb=O bond. At the same time, hydrogen bond interactions between the equatorial fluorides and the aminopyridine groups both lengthen the equatorial Nb-F bonds and can further reduce the symmetry of the [NbOF5]2- anion. These combined three-dimensional bond network interactions that serve to lengthen the Nb=O bond and thereby decrease the primary distortion of the [NbOF5]2- anion are illustrated in the structures of three new niobium oxide fluoride phases, [4-apyH]2[Cu(4-apy)4(NbOF5)2] (4-apy = 4-aminopyridine), Cd(3-apy)4NbOF5 (3-apy = 3-aminopyridine), and Cu(3-apy)4NbOF5, that were synthesized and characterized using X-ray diffraction. Crystal data for [4-apyH]2[Cu(4-apy)4(NbOF5)2]: tetragonal, space group /4(1)/ acd (No. 142), with a = 20.8745(8) A, c = 17.2929(9) A, and Z= 8. Cd(3-apy)4NbOF5: tetragonal, space group P4(3) (No. 78), with a = 8.4034(4) A, c = 34.933(3) A, and Z = 4. Cu(3-apy)4NbOF5: monoclinic, space group P2(1)/n (No. 14), with a = 8.822(1) A, b = 16.385(3) A, c = 8.902(1) A, beta = 109.270(3) degrees, and Z = 2.