bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Structures, Anisotropic Growth, and Optical Properties: Controlled Synthesis of Lanthanide Orthophosphate One‐Dimensional Nanomaterials
Authors: Yan Ruoxue , Sun Xiaoming , Wang Xun , Peng Qing , Li Yadong 
Published: February 2005

AbstractThe fundamental understanding of the relationship between crystal structure and the dynamic processes of anisotropic growth on the nanoscale, and exploration of the key factors governing the evolution of physical properties in functional nanomaterials, have become two of the most urgent and challenging issues in the fabrication and exploitation of functional nanomaterials with designed properties and the development of nanoscale devices. Herein, we show how structural and kinetic factors govern the tendency for anisotropic growth of such materials under hydrothermal conditions, and how the crystal structure and morphology influence the optical properties of Ln3+‐doped nanocrystals. The synthesis of phase‐pure and single‐crystalline monoclinic, hexagonal, and tetragonal one‐dimensional LnPO4 nanostructures of different aspect ratios by means of kinetically controlled hydrothermal growth processes is demonstrated. It is shown that the tendency for anisotropic growth under hydrothermal conditions can be enhanced simply by modifying the chemical potentials of species in the reaction solution through the use of carefully selected chelating ligands. A systematic study of the photoluminescence of various Eu3+‐doped lanthanide phosphates has revealed that the optical properties of these nanophosphors are strongly dependent on their crystal structures and morphologies.
Pseudorotation Barriers of Biological Oxyphosphoranes: A Challenge for Simulations of Ribozyme Catalysis
Authors: López Carlos Silva , Faza Olalla Nieto , de Lera Angel R. , York Darrin M. 
Published: February 2005

AbstractPseudorotation reactions of biologically relevant oxyphosphoranes were studied by using density functional and continuum solvation methods. A series of 16 pseudorotation reactions involving acyclic and cyclic oxyphosphoranes in neutral and monoanionic (singly deprotonated) forms were studied, in addition to pseudorotation of PF5. The effect of solvent was treated by using three different solvation models for comparison. The barriers to pseudorotation ranged from 1.5 to 8.1 kcal mol−1 and were influenced systematically by charge state, apicophilicity of ligands, intramolecular hydrogen bonding, cyclic structure and solvation. Barriers to pseudorotation for monoanionic phosphoranes occur with the anionic oxo ligand as the pivotal atom, and are generally lower than for neutral phosphoranes. The OCH3 groups were observed to be more apicophilic than OH groups, and hence pseudorotations that involve axial OCH3/equatorial OH exchange had higher reaction and activation free energy values. Solvent generally lowered barriers relative to the gas‐phase reactions. These results, together with isotope 18O exchange experiments, support the assertion that dianionic phosphoranes are not sufficiently long‐lived to undergo pseudorotation. Comparison of the density functional results with those from several semiempirical quantum models highlight a challenge for new‐generation hybrid quantum mechanical/molecular mechanical potentials for non‐enzymatic and enzymatic phosphoryl transfer reactions: the reliable modeling of pseudorotation processes.
Benzoyl Transfer Reactivities of Racemic 2,4‐Di‐O‐acyl‐myo‐inosityl 1,3,5‐Orthoesters in the Solid State: Molecular Packing and Intermolecular Interactions Correlate with the Ease of the Reaction
Authors: Sarmah Manash P. , Gonnade Rajesh G. , Shashidhar Mysore S. , Bhadbhade Mohan M. 
Published: February 2005

AbstractRacemic 2,4‐di‐O‐acyl‐myo‐inosityl 1,3,5‐orthoesters undergo transesterification catalyzed by sodium carbonate with varying ease of reaction in the solid state; reactions in solution and melt do not show such varied differences. An interesting crystal of a 1:1 molecular complex of highly reactive racemic 2,4‐di‐O‐benzoyl‐myo‐inosityl 1,3,5‐orthoformate and its orthoacetate analogue exhibited better reactivity than the latter component alone. Single‐crystal X‐ray structures of the reactants have been correlated with the observed differences in the acyl‐transfer efficiencies in the solid state. Although each of the derivatives helically self‐assembles around the crystallographic 21 axis linked through OH⋅⋅⋅O hydrogen bonding, the pre‐organization of the reactive groups (CO [El] and OH [Nu]), CH⋅⋅⋅O and the CH⋅⋅⋅π interactions are significantly more favourable for the reactive derivatives than the less reactive ones. Bond‐length distributions also showed differences; the OC bond of the axial benzoyl group, which gets cleaved during the reaction, is longer (1.345–1.361 Å) relative to the chemically equivalent OC bond of the equatorial benzoyl group (1.316–1.344 Å) in the reactive derivatives. These bond‐length differences are not significant in the less reactive derivatives. The overall molecular organization is different too; the strikingly discrete helices, which may be viewed as “reaction tunnels” and are held by interhelical interactions, are clearly evident in the reactive derivatives in comparison with the less reactive ones.
Nonenzymatic Glucose Detection by Using a Three‐Dimensionally Ordered, Macroporous Platinum Template
Authors: Song Yan‐Yan , Zhang Dai , Gao Wei , Xia Xing‐Hua 
Published: February 2005

AbstractA three‐dimensionally ordered, macroporous, inverse‐opal platinum film was synthesized electrochemically by the inverted colloidal‐crystal template technique. The inverse‐opal film that contains platinum nanoparticles showed improved electrocatalytic activity toward glucose oxidation with respect to the directly deposited platinum; this improvement is due to the interconnected porous structure and the greatly enhanced effective surface area. In addition, the inverse‐opal Pt‐film electrode responds more sensitively to glucose than to common interfering species of ascorbic acid, uric acid, and p‐acetamidophenol due to their different electrochemical reaction mechanisms. Results showed that the ordered macroporous materials with enhanced selectivity and sensitivity are promising for fabrication of nonenzymatic glucose biosensors.
Acidity Trends in α,β‐Unsaturated Sulfur, Selenium, and Tellurium Derivatives: Comparison with C‐, Si‐, Ge‐, Sn‐, N‐, P‐, As‐, and Sb‐Containing Analogues
Authors: Guillemin Jean‐Claude , Riague El Hassan , Gal Jean‐François , Maria Pierre‐Charles , Mó Otilia , Yáñez Manuel 
Published: February 2005

AbstractThe gas‐phase acidity of CH3CH2XH (X=S, Se, Te), CH2CHXH (X=S, Se, Te) and PhXH (X=S, Se) compounds was measured by means of Fourier transform ion cyclotron resonance mass spectrometry. To analyze the role that unsaturation plays on the intrinsic acidity of these systems, a parallel theoretical study, in the framework of the G2 and the G2(MP2) theories, was carried out for all ethyl, ethenyl (vinyl), ethynyl, and phenyl O‐, S‐, Se‐, and Te‐containing derivatives. Unsaturated compounds are stronger acids than their saturated analogues, because of the strong π‐electron donor ability of the heteroatoms that contributes to a large stabilization of the unsaturated anions. Ethynyl derivatives are stronger acids than vinyl compounds, while phenyl derivatives have an intrinsic acidity intermediate between that of the corresponding vinyl and ethynyl analogues. The CH2CHXH vinyl compounds (enol‐like) behave systematically as slightly stronger acids than their CH3C(H)X (keto‐like) tautomers. Vinyl derivatives are stronger acids than ethyl compounds, because the anion stabilization attributable to unsaturation is greater than that undergone in the neutral compounds. Conversely, the enhanced acidity of the ethynyl derivatives with respect to the vinyl compounds is due to two concomitant effects, the stabilization of the anion and the destabilization of the neutral compound. The acidities of ethyl, vinyl, and ethynyl derivatives containing heteroatoms of Groups 14, 15, and 16 of the periodic table are closely related, and reflect the differences in electronegativity of the CH3CH2, CH2CH, and CHC groups.
Titanium Imido Complexes of Cyclooctatetraenyl Ligands
Authors: Dunn Simon C. , Hazari Nilay , Jones Nicholas M. , Moody Aidan G. , Blake Alexander J. , Cowley Andrew R. , Green Jennifer C. , Mountford Philip 
Published: February 2005

AbstractReaction of [Ti(NR)Cl2(py)3] (R=tBu or 2,6‐iPr2C6H3) with K2[COT] (COT=C8H8) or Li2[COT′′] (COT′′=1,4‐C8H6(SiMe3)2) gave the monomeric complexes [Ti(NR)(η8‐COT)] or [Ti(NR)(η8‐COT′′)], respectively. The pseudo‐two coordinate, ′pogo stick′ geometry for these complexes is unique in both early transition‐metal and cyclooctatetraenyl ligand chemistry. In contrast, reaction of [Ti(N‐2,6‐Me2C6H3)Cl2(py)3] with K2[COT] gave the μ‐imido‐bridged dimer [Ti2(μ‐N‐2,6‐Me2C6H3)2(η8‐COT)2]. It appears that as the steric bulk of the imido and C8 ring substituents are decreased, dimerisation becomes more favourable. Aryl imido COT complexes were also prepared by imido ligand exchange reactions between anilines and [Ti(NtBu)(η8‐COT)] or [Ti(NtBu)(η8‐COT′′)]. The complexes [Ti(NtBu)(η8‐COT)], [Ti(N‐2,6‐iPr2C6H3)2(η8‐COT)] and [Ti2(μ‐N‐2,6‐Me2C6H3)2(η8‐COT)2] have been crystallographically characterised. The electronic structures of both the monomeric and dimeric complexes have been investigated by using density functional theory (DFT) calculations and gas‐phase photoelectron spectroscopy. The most striking aspect of the bonding is that binding to the imido nitrogen atom is primarily through σ and π interactions, whereas that to the COT or COT′′ ring is almost exclusively through δ symmetry orbitals. A DFT‐based comparison between the bonding in [Ti(NtBu)(η8‐COT)] and the bonding in the previously reported late transition‐metal ′pogo‐stick′ complexes [Os(NtBu)(η6‐C6Me6)], [Ir(NtBu)(η5‐C5Me5)] and [Ni(NO)(η5‐C5H5)] has also been undertaken.
One‐Dimensional Polymers Based on [{CpMo(CO)2}2(μ,η2‐P2)]: Solid‐State Conformation Analysis by NMR Spectroscopy and DFT Calculations
Authors: Scheer Manfred , Gregoriades Laurence , Bai Junfeng , Sierka Marek , Brunklaus Gunther , Eckert Hellmut 
Published: February 2005

AbstractReaction of the complex [{CpMo(CO)2}2(μ,η2‐P2)] (1) with CuI halides leads to the quantitative formation of the novel one‐dimensional linear polymers [CuX{Cp2Mo2(CO)4(μ,η2:η1:η1‐P2)}]∞ (X=Cl (4), Br (5), I (6)). The same products 4 and 5 were obtained when 1 was treated with CuCl2 and CuBr2, respectively. The solid‐state structures are compared and their remarkable influence on the respective 31P magic angle spinning (MAS) NMR spectra is interpreted with the help of density functional theory (DFT) calculations on the model compounds [{(CuX)2{Cp2Cr2(CO)4(μ,η2:η1:η1‐P2)}2}3] (X=Cl (4 a), Br (5 a)) in which the molybdenum atoms are replaced by their lighter homologue chromium.
Pentafluorophenyl–Phenyl Interactions in Biphenyl‐DNA
Authors: Zahn Alain , Brotschi Christine , Leumann Christian J. 
Published: February 2005

AbstractWe prepared and investigated oligonucleotide duplexes of the sequence d(GATGAC(X)nGCTAG)⋅d(CTAGC(Y)nGTCATC), in which X and Y designate biphenyl‐ (bph) and pentafluorobiphenyl‐ (5Fbph) C‐nucleotides, respectively, and n varies from 0–4. These hydrophobic base substitutes are expected to adopt a zipperlike, interstrand stacking motif, in which not only bph/bph or 5Fbph/5Fbph homo pairs, but also 5Fbph/bph mixed pairs can be formed. By performing UV‐melting curve analysis we found that incorporation of a single 5Fbph/5Fbph pair leads to a duplex that is essentially as stable as the unmodified duplex (n=0), and 2.4 K more stable than the duplex with the nonfluorinated bph/bph pair. The Tm of the mixed bph/5Fbph pair was in between the Tm values of the respective homo pairs. Additional, unnatural aromatic pairs increased the Tm by +3.0–4.4 K/couple, irrespective of the nature of the aromatic residue. A thermodynamic analysis using isothermal titration calorimetry (ITC) of a series of duplexes with n=3 revealed lower (less negative) duplex formation enthalpies (ΔH) in the 5Fbph/5Fbph case than in the bph/bph case, and confirmed the higher thermodynamic stability (ΔG) of the fluorinated duplex, suggesting it to be of entropic origin. Our data are compatible with a model in which the stacking of 5Fbph versus bph is dominated by dehydration of the aromatic units upon duplex formation. They do not support a model in which van der Waals dispersive forces (induced dipoles) or electrostatic (quadrupole) interactions play a dominant role.
Betaine‐Induced Assembly of Neutral Infinite Columns and Chains of Linked Silver(I) Polyhedra with Embedded Acetylenediide
Authors: Zhao Xiao‐Li , Wang Quan‐Ming , Mak Thomas C. W. 
Published: February 2005

AbstractTen polymeric silver(I) double salts containing embedded acetylenediide: [(Ag2C2)2(AgCF3CO2)9(L1)3] (1), [(Ag2C2)2(AgCF3CO2)10(L2)3]⋅H2O (2), [(Ag2C2)(AgCF3CO2)4(L3)(H2O)]⋅0.75 H2O (3), [(Ag2C2)1.5(AgCF3CO2)7(L4)2] (4), [(Ag2C2)(AgCF3CO2)7(L5)2(H2O)] (5), [(Ag2C2) (AgC2F5CO2)7(L1)3(H2O)] (6), [(Ag2C2)(AgCF3CO2)7(L1)3(H2O)]⋅2 H2O (7), [(Ag2C2)(AgC2F5CO2)6(L3)2] (8), [(Ag2C2)2(AgC2F5CO2)12(L4)2(H2O)4]⋅H2O (9), and [(Ag2C2)(AgCF3CO2)6(L3)2(H2O)]⋅H2O (10) have been isolated by varying the types of betaines, the perfluorocarboxylate ligands employed, and the reaction conditions. Single‐crystal X‐ray analysis has shown that 1–4 all have a columnar structure composed of fused silver(I) double cages, with C22− species embedded in its stem and an exterior coat comprising anionic and zwitterionic carboxylates. For 5 and 6, single silver(I) cages are linked into a beaded chain through both types of carboxylate ligands. In 7, two different coordination modes of L1 connect the silver(I) polyhedra into a chain. For 8, the μ2‐O,O′ coordination mode of L3 connects the silver(I) double cages into a chain. Compound 9 exhibits a two‐dimensional architecture generated from the cross‐linkage of double cages by C2F5CO2−, L4, and [Ag2(C2F5CO2)2] units. Similar to 9, 10 is also a two‐dimensional structure, which is formed by connecting the chains of linked double cages through [Ag2(CF3CO2)2] bridging.
Cullin‐5 plays multiple roles in cell fate specification and synapse formation during Drosophila development
Authors: Ayyub Champakali , Sen Anindya , Gonsalves Foster , Badrinath Kishan , Bhandari Poonam , Shashidhara L.S. , Krishna Sudhir , Rodrigues Veronica 
Published: February 2005

AbstractWe describe a developmental analysis of Drosophila Cullin‐5 (Cul‐5) identified from the genome sequence on the basis of its high degree of homology to vertebrate and worm sequences. The gene is expressed in a restricted manner in ectodermal cells throughout development suggesting pleiotropic functions. We decided to examine the phenotypes of Cul‐5 aberrations in two well‐studied developmental systems: the neuromuscular junction (NMJ) and the developing sensory organ. Alteration of Cul‐5 levels in motoneurons results in an increase in bouton number at the NMJ. The cells of a sensory organ on the adult notum arise from a single progenitor cell by regulated cell division. Aberrations in Cul‐5 affect different steps in the lineage consistent with a role in cell fate determination, proliferation, and death. Such phenotypes highlight the multiple cellular processes in which Cul‐5 can participate. Developmental Dynamics 232:865–875, 2005. © 2005 Wiley‐Liss, Inc.
Killer cell immunoglobulin‐like receptors (KIR) of the African‐origin sabaeus monkey: evidence for recombination events in the evolution of KIR
Authors: Hershberger Karen L. , Kurian Jessica , Korber Bette T. , Letvin Norman L. 
Published: February 2005

AbstractKiller cell immunoglobulin (Ig)‐like receptors (KIR) were characterized in the West African sabaeus monkey (Chlorocebus sabaeus) to elucidate the mechanism by which diversity evolves in this family of molecules. Complementary DNA encoding four forms of KIR molecules, including KIR3DL, KIR2DL4, KIR2DL5, and KIR3DH forms, were identified in two unrelated sabaeus monkeys. A novel hybrid form showing features found in both KIR2DL5 and KIR3DH was also identified. Both the KIR3DL and KIR3DH forms from the sabaeus monkey were considerably more polymorphic than any KIR form identified in great apes or humans. The polymorphic residues of the three Ig‐like domains were frequently located in structural loops, indicating that point mutations have occurred in these regions. The three Ig‐like domains of the KIR3D forms of six primate species were found to have different patterns of clustering in phylogenetic trees, suggesting that each Ig‐like domain has a distinct phylogenetic history. This variation in relationships suggests that repeated recombination events have occurred between the Ig‐like domains during the evolution of the KIR family in primates. Recombination between individual Ig‐like domains, in addition to point mutations, provides a mechanism for generating the diversity of the KIR genes.
Contribution of stromal cells to the migration, function and retention of plasma cells in human spleen: potential roles of CXCL12, IL‐6 and CD54
Authors: Ellyard Julia I. , Avery Danielle T. , Mackay Charles R. , Tangye Stuart G. 
Published: February 2005

AbstractPlasma cells (PC) localize to discrete areas of secondary lymphoid tissue and bone marrow (BM). The positioning of PC in different sites is believed to be regulated by chemokines and adhesion molecules expressed by accessory cells in the lymphoid tissue microenvironment. However, the mechanisms responsible for the positioning of PC within the red pulp (RP) of human spleen have not been elucidated. Therefore, we examined the contribution of human splenic stromal cells to the migration and function of human PC. Splenic PC expressed the chemokine receptor CXCR4 and responded to its ligand CXCL12. In contrast, PC lacked CXCR5 and CCR7, and consequently exhibited minimal migration towards CXCL13 and CCL21. Splenic stromal cells proved to be a rich source of CXCL12, and could induce the migration of human B cells. Furthermore, they supported Ig production by splenic PC mainly by secreting IL‐6. Lastly, a striking difference between splenic and BM PC was the constitutive expression of CD11a by only splenic PC. Notably, splenic stromal cells expressed high levels of CD54, the counter‐structure of CD11a, and splenic PC were positioned adjacent to stromal cells in the RP. Thus, we propose that stromal cells attract PC to the RP and contribute to their retention and function through the combined expression of CXCL12, CD54 and IL‐6.
Peptide immunization excludes antigen‐specific T cells from splenic lymphoid compartments
Authors: Zhang Lei , Lizzio Elaine F. , Chen Trina , Kozlowski Steven 
Published: February 2005

AbstractUsing adoptive transfer of TCR‐transgenic T cells, we examined the homing of transgenic T cells to splenic compartments in situ. After systemic immunization with peptide or protein antigen, the location of clonotypic T cells, cytokine production, cell surface markers, and apoptosis were assessed. There were distinct differences in the splenic homing of CD4+ TCR‐transgenic T cells in mice immunized with peptide as compared to mice immunized with whole‐protein antigen. T cells in peptide‐immunized mice were found almost exclusively in the splenic red pulp, but not in the T and B cell zones (white pulp), while the majority of T cells immunized with whole protein were found in the white pulp. Many more Fas ligand‐expressing and apoptotic cells were present after peptide immunization than after whole‐protein immunization. Localization of IL‐4‐, IL‐2‐ and IFN‐γ‐producing cells to the lymphocyte‐containing splenic white pulp was only observed with whole‐protein immunization. The unique homing and increased apoptosis of immune cells post peptide immunization may help explain the ineffectiveness of many peptide vaccines. Linkage of the same peptide epitope to a carrier protein increased white pulp T cell localization and decreased apoptosis, suggesting a strategy to enhance peptide vaccine responses.
The role of TCR stimulation and TGF‐β in controlling the expression of CD94/NKG2A receptors on CD8 T cells
Authors: Gunturi Anasuya , Berg Rance E. , Crossley Emily , Murray Sean , Forman James 
Published: February 2005

AbstractFollowing antigen recognition, murine CD8 T cells express CD94/NKG2A receptors. Our results show that this up‐regulation occurs rapidly in vitro and is accompanied by an ∼8‐fold increase in CD94 and ∼125‐fold increase in NKG2A mRNA. In contrast, only a twofold increase in NKG2C mRNA is noted. The addition of TGF‐β, but not IL‐10, IL‐12 or IL‐15, leads to a further increase in cell membrane expression of these receptors, as well as a ∼6‐fold increase in mRNA for both chains. TGF‐β also increases CD94/NKG2A expression on memory CD8 T cells that are re‐exposed to antigen. The effect of TGF‐β on increasing CD94/NKG2A expression on both naive and memory CD8 T cells occurs only when there is a concurrent stimulation through the TCR. In contrast, TGF‐β does not increase expression of CD94/NKG2A on resting or activated NK cells. We also show by using purified CD8 T cells, that TGF‐β acts directly on these cells. These results implicate a role for both antigen and TGF‐β in increasing expression of inhibitory CD94/NKG2A receptors on CD8 T cells.
MyD88 and TLR2, but not TLR4, are required for host defense against Cryptococcus neoformans
Authors: Biondo Carmelo , Midiri Angelina , Messina Luciano , Tomasello Francesco , Garufi Gabriella , Catania Maria Rosaria , Bombaci Mauro , Beninati Concetta , Teti Giuseppe , Mancuso Giuseppe 
Published: February 2005

AbstractWe investigated here the potential role of Toll‐like receptors (TLR) and the adaptor protein MyD88 in innate immunity responses to Cryptococcus neoformans, a pathogenic encapsulated yeast. Peritoneal macrophages from MyD88–/– or TLR2–/– mice released significantly less TNF‐α, compared with wild‐type controls, after in vitro stimulation with whole yeasts. In contrast, no differences in TNF‐α release were noted between macrophages from C3H/HeJ mice, which have a loss of function mutation in TLR4, relative to C3H/HeN controls. When MyD88‐ or TLR2‐deficient mice were infected with low doses of the H99 serotype A strain, all of the control animals, but none of MyD88–/– and only 38% of the TLR2–/– animals survived, in association with higher fungal burden in the mutant mice. Both MyD88–/– and TLR2–/– animals showed decreased TNF‐α, IL‐12p40 and/or IFN‐γ expression in various organs during infection. No difference in susceptibility to experimental cryptococcosis was found between C3H/HeJ mice and C3H/HeN controls. In conclusion, our data indicate that TLR2 and MyD88, but not TLR4, critically contribute to anti‐cryptococcal defenses through the induction of increased TNF‐α, IL‐12 and IFN‐γ expression.