Search

The hydrothermal reactions of either uranyl nitrate or uranium trioxide with 4-carboxyphenylphosphonic acid and HF/CsOH in the presence of Cs Ba2熫抢 result in the formation of Cs2{(UO2)2(PO3HC6H4CO2H)3(PO3C6H4CO2H)F} (CsUcpp-1), Cs4{(UO2)6(PO3C6H4CO2H)8}(H2O)7(CsUcpp-2), Ba{(UO2)2(PO3C6H4CO2H)2F2}(H2O)2(BaUcpp-1), and Cs3{(UO2)(O3PC6H4CO2)}3(H2O)3·4H2O (CsUcpp-3). All these compounds contain the UO22骈麷 coordinated by five additional donor atoms resulting in a pentagonal bipyramidal coordination environment. CsUcpp-1, CsUcpp-2, and BaUcpp-1were isolated at low pH, whereas CsUcpp-3was synthesized at high pH giving rise to complete elimination of protonation of phosphonic and carboxylic acid moieties. The pH of the reaction is playing a vital role in the formation of the pillared structures in which the carboxylate and phosphonate moieties are coordinated to uranium center in CsUcpp-3, while in the other three compounds, the carboxylate moiety coordinate exclusively to the Cs Ba2熫抢. [ABSTRACT FROM AUTHOR]

The hydrothermal treatment of uranyl nitrate and 1,4-benzenebisphosphonic acid with a variety of aliphatic amines (tetramethylammonium hydroxide, tetraethylammonium hydroxide, and diethyldimethylammonium hydroxide) and small quantities of hydrofluoric acid at 200 °C results in the crystallization of a series of layered uranyl diphosphonate compounds, [(CH3)4N][(UO2)3(O3PC6H4PO3H)2F(H2O)]·0.5H2O (Me4Ubbp), [(CH3CH2)4N]{(UO2)[C6H4(PO3H)(PO3H1.5)]2(H2O)} (Et4Ubbp), and [(CH3CH2)2N(CH3)2][(UO2)3(O3PC6H4PO3H)2F(H2O)] (Et2Me2Ubbp). All these new compounds have layered structures, but the structures of Me4Ubbpand Et2Me2Ubbpare similar in that they both contain UO6F and UO7pentagonal bipyramids within dimers that are bridged by the phosphonate into a three-dimensional structure. The structure of Et4Ubbpcontains a single crystallographically unique UO7unit. The edge-sharing pentagonal bipyramids are linked into chains formulated as {(UO2)[C6H4(PO3H)(PO3H1.5)]2(H2O)}1−. The voids in these structures are filled with the organic templates so that the overall charge balance is maintained. Intense fluorescence was observed from these compounds at room temperature. [ABSTRACT FROM AUTHOR]

Bisphosphines Ph2P(CH2)nPPh2(n= 1, 2, 4, 6) may be easily monobenzylated to generate cationic phosphine/phosphonium ligands [Ph2P(CH2)nPPh2CH2Ph]+. These ligands may be doped into a catalytic reaction involving neutral complexes with labile phosphine ligands, and replacement of a neutral phosphine with a charged analogue renders the resulting complex amenable to electrospray ionisation mass spectrometry (ESI-MS). Examination of olefin hydrogenation with Wilkinson's catalyst, RhCl(PPh3)3, revealed that this approach yielded rapid identification of all off-cycle solution species as well as catalyst poisons. Reactive intermediates could be generated using collision-induced dissociation (CID) of a triphenylphosphine ligand to make three-coordinate RhClP2species, and these react with alkenes in the gas phase to form RhClP2(alkene). The solution speciation and gas phase behaviour revealed by ESI-MS match closely to what is already known about the system from kinetic and NMR studies. [ABSTRACT FROM AUTHOR]

Despite the vast number of techniques developed for the cyclization of small peptides, cyclization efficiency remains problematic in peptides that lack turn-promoting structures. Here we demonstrate the utility of click chemistry as a macrocyclization tool in the solid-phase synthesis of cyclic tetra-, penta-, hexa-, and heptapeptides. On-resin cyclization is completed at room temperature within 6 h, resulting in predominantly monomer with small amounts of cyclomultimer byproducts. [ABSTRACT FROM AUTHOR]

Negative-ion electrospray ionisation mass spectrometry with an anionic phosphine ligand enables detection of key intermediates in the Sonogashira reaction. MS/MS techniques are used to generate a Hammett plot for the key reductive elimination step. [ABSTRACT FROM AUTHOR]

The boric acid flux reactions of uranyl nitrate with sodium, potassium, rubidium, or thallium fluoride result in the formation of a novel family of uranyl(VI) fluoroborate materials. These compounds are Na[(UO2)B5O8(OH)F]·H2O (NaUBOF-1), K[(UO2)B5O8(OH)F] (KUBOF-1), K11[(UO2)6B24O36F22)](H2BO3) (KUBOF-2), Rb[(UO2)B5O8(OH)F] (RbUBOF-1), and Tl[(UO2)B5O8(OH)F] (TlUBOF-1). A new neptunium(VI) fluoroborate that is isotypic with NaUBOF-1, Na[(NpO2)B5O8(OH)F]·H2O (NaNpBOF-1), was synthesized via the boric acid flux reaction of neptunium(VI) nitrate with sodium fluoride. These new actinide fluoroborates share a common structural motif consisting of a linear actinyl (U(Np)O22+) cation surrounded by BO3triangles and BO4tetrahedra to create an U(Np)O8hexagonal bipyramidal environment around uranium or neptunium. The borate anions bridge between actinyl units to create layers. B–F bonds were formed during the reactions to yield BO3F tetrahedral units. The BO3F tetrahedra and additional BO3triangles extend from the actinyl polyborate layers and are directed approximately perpendicular to the layers. A novel actinyl borate layered topology was found in K11[(UO2)6B24O36F22)](H2BO3) (KUBOF-2). Except for K[(UO2)B5O8(OH)F] (KUBOF-1) and K11[(UO2)6B24O36F22)](H2BO3) (KUBOF-2), all of the other actinide fluoroborate phases adopt noncentrosymmetric space groups. Tl[(UO2)B5O8(OH)F] (TlUBOF-1), which can be obtained as a pure phase, displays second-harmonic generation of 532-nm light from 1064-nm light. [ABSTRACT FROM AUTHOR]

Heme−copper oxidases have a crucial role in the energy transduction mechanism, catalyzing the reduction of dioxygen to water. The reduction of dioxygen takes place at the binuclear center, which contains heme a3and CuB. The X-ray crystal structures have revealed that the C6′ of tyrosine 244 (bovine heart numbering) is cross-linked to a nitrogen of histidine 240, a ligand to CuB. The role of the cross-linked tyrosine at the active site still remains unclear. In order to provide insight into the function of the cross-linked tyrosine, we have investigated the spectroscopic and electrochemical properties of chemical analogues of the CuB−His−Tyr site. The analogues, a tridentate histidine−phenol cross-linked ether ligand and the corresponding Cu-containing complex, were previously synthesized in our laboratory (White, K.; et al. Chem. Commun. 2007, 3252−3254). Spectrophotometric titrations of the ligand and the Cu-complex indicate a pKaof the phenolic proton of 8.8 and 7.7, respectively. These results are consistent with the cross-linked tyrosine playing a proton delivery role at the cytochrome coxidase active site. The presence of the phenoxyl radical was investigated at low temperature using electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) difference spectroscopy. UV photolysis of the ligand, without bound copper, generated a narrow g= 2.0047 signal, attributed to the phenoxyl radial. EPR spectra recorded before and after UV photolysis of the Cu-complex showed a g= 2 signal characteristic of oxidized copper, suggesting that the copper is not spin-coupled to the phenoxyl radical. An EPR signal from the phenoxyl radical was not observed in the Cu-complex, either due to spin relaxation of the two unpaired electrons or to masking of the narrow phenoxyl radical signal by the strong copper contribution. Stable isotope (13C) labeling of the phenol ring (C1′) Cu-complex, combined with photoinduced difference FT-IR spectroscopy, revealed bands at 1485 and 1483 cm−1in the 12C-minus-13C-isotope-edited spectra of the ligand and Cu-complex, respectively. These bands are attributed to the radical v7astretching frequency and are shifted to 1468 and 1472 cm−1, respectively, with 13C1′ labeling. These results show that a radical is generated in both the ligand and the Cu-complex and support the unambiguous assignment of a vibrational band to the phenoxyl radical v7astretching mode. These data are discussed with respect to a possible role of the cross-linked tyrosine radical in cytochrome coxidase. [ABSTRACT FROM AUTHOR]

A survey of individual specimens of northern Papua New Guinea derived Cacospongia mycofijiensishas yielded novel sesquiterpenes, aignopsanoic acid A (1), methyl aignopsanoate A (2), and isoaignopsanoic acid A (3). The structures and absolute configurations of 1−3were established using NMR data, X-ray crystallography results, and an analysis of CD properties. Two of these metabolites, 1 and 2, were moderately active against Trypanosoma brucei, the parasite responsible for sleeping sickness. [ABSTRACT FROM AUTHOR]

1,4-Piperazine-2,5-diones derived from 2-amino-7-nitro-4-methoxyindan-2-carboxylic acid were prepared in meso, racemic, and enantiomerically pure forms, crystallized from DMSO or DMF, and the supramolecular organization in the crystals determined by X-ray crystallography. These molecules were designed to bear two strongly dipolar p-nitroanisole groups, aligned in the enantiomeric stereoisomers and opposed in the meso stereoisomer. Consistent with piperazinediones of similar size and shape bearing nonpolar or weakly dipolar arene groups, these compounds engage in R 22(8) hydrogen bonding, most often forming one-dimensional tapes. However, the preference for arene perpendicular edge-to-center interactions seen in the former is replaced by a preference for parallel edge-to-center arene interactions. While the dipoles of parallel edge-to-center associated arenes are often opposed, this is not a requirement in the solid state. [ABSTRACT FROM AUTHOR]

Decomposition of a diazo -ketoamide derived from N-trityl serine imidazolide and N-protected acetanilides provides, instead of the expected 3-acyloxindole product, an enantiomerically pure (EP) -lactam. The amino acid stereocenter is incorporated, the second chiral center is induced, and trityl protection of the -lactam ring is realized for the first time. The desired 3-acyloxindole is obtained from oxindole and Tr-Ser(OBn)-imidazole, the X-ray of which provides the first structural determination of an EP amino acid imidazolide. [ABSTRACT FROM AUTHOR]

We have discovered a metal−organic framework containing cationic inorganic layers. The metal fluoride−organodisulfonate structure, Pb2F2C2H4(SO3)2, was synthesized hydrothermally. The lead fluoride cationic layers are covalently connected by 1,2-ethanedisulfonate chains oriented perpendicular to the layers. The material is thermally stable to ca. 325 °C, above which the material collapses to phase-pure -PbF2. This material is a rare example of the use of organosulfonates as organic linker and the first metal−organic framework to contain lead fluoride connectivity. The existence of extended cationic inorganic moieties embedded within a metal−organic framework material further diversifies the possible structure types of this rapidly growing class of materials. [ABSTRACT FROM AUTHOR]