Differentiation of Isomeric Hydroxypyridine <Emphasis Type="Italic">N</Emphasis>-Oxides Using Metal Complexation and Electrospray Ionization Mass Spectrometry

Differentiation between two isomers of hydroxypyridine N-oxide according to the metal cation adducts generated by electrospray ionization (ESI) was investigated for different metal cations, namely Mg (II), Al (III), Ca (II), Sc (III), Fe (III), Co (II), Ni (II), Cu (II), Zn (II), Ga (III), besides the diatomic cation VO(IV). Protonated molecules of the isomeric hydroxypyridine N-oxides as well as the singly/doubly charged adducts formed from neutral or deprotonated ligands and a doubly/triply charged cation were produced in the gas phase using ESI, recording mass spectra with different metal ions for each isomer. While complex formation was successful for 2-hydroxypyridine N-oxide with trivalent ions, in the case of 3-hydroxypyridine N-oxide, only peaks related to the protonated molecule were present. On the other hand, divalent cations formed specific species for each isomer, giving characteristic spectra in every case. Hence, differentiation was possible irrespective of the metal cation utilized. In addition, quantum chemical calculations at the B3LYP/6-31 + G(d,p) level of theory were performed in order to gain insight into the different complexation of calcium(II) with the isomers of hydroxypyridine N-oxide. The relative stability in the gas phase of the neutral complexes of calcium made up of two ligands, as well as the singly charged and doubly charged complexes, was investigated. The results of these calculations improved the understanding of the differences observed in the mass spectra obtained for each isomer.     

Facile syntheses of novel benzo-1,3-dioxolo-, benzothiazolo-, pyrido-, and quinolino-fused 5H-benzo[d]-pyrazolo[5,1-b][1,3]-oxazines and 1H-pyrazoles

A number of novel benzo-1,3-dioxolo-, benzothiazolo-, pyrido-, and quinolino-fused 5H-benzo[d]pyrazolo[5,1-b][1,3]-oxazines and 1H-pyrazoles were synthesized utilizing an easy and effective N,N-bond forming heterocyclization reaction. In so doing, the substrate scope of this heterocyclization reaction, which starts with o-nitroheterocyclic aldehydes, was expanded to provide several unique heterocyclic compounds for biological screening. This work further demonstrates the versatility of this simple, base-mediated, one-pot heterocyclization method in the construction of novel heterocycles.     

Crystallization and characterization of an inflammatory lectin purified from the seeds of Dioclea wilsonii

DwL, a lectin extracted from the seeds of Dioclea wilsonii, is a metalloprotein with strong agglutinating activity against rabbit and ABO erythrocytes, inhibited by glucose and mannose. DwL was purified by affinity chromatography on a Sephadex G-50 column and ion exchange chromatography on a HiTrap SP XL column. SDS-PAGE revealed three electrophoretic bands corresponding to the α (25,634 ± 2 Da), β (12,873 ± 2 Da) and γ (12,779 ± 2 Da) chains. Protein sequencing was done by Tandem Mass Spectrometry. The primary sequence featured 237 amino acids and was highly homologous to other reported Diocleinae lectins. A complete X-ray dataset was collected at 2.0 ? for X-Man-complexed DWL crystals produced by the vapor diffusion method. The crystals were orthorhombic and belonged to the space group I222, with the unit-cell parameters a = 59.6, b = 67.9 and c = 109.0 ?. DWL differed in potency from other ConA-like lectins and was found to induce neutrophil migration in rats, making it particularly useful in structural/functional studies of this class of proteins.     

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd,Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Y, Gd) were investigated by means of powder and single‐crystal X‐ray diffraction (XRD), as well as optical near‐IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero‐phonon lines suggests the existence of two kinds of Yb³⁺ ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y³⁺. A strong temperature dependence of the intensity of Yb–Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb³⁺ is in good agreement with crystallographic ones: R=3.856 Å, R_cryst=3.849 Å.     

Attracting graphs of skew products with non-contracting fiber maps

We study attracting graphs of step skew products from the topological and ergodic points of view where the usual contracting-like assumptions of the fiber dynamics are replaced by weaker merely topological conditions. In this context, we prove the existence of an attracting invariant graph and study its topological properties. We prove the existence of globally attracting measures and we show that (in some specific cases) the rate of convergence to these measures is exponential.

     

Statistical Properties of Unimodal Maps

We consider typical analytic unimodal maps which possess a chaotic attractor. Our main result is an explicit combinatorial formula for the exponents of periodic orbits. Since the exponents of periodic orbits form a complete set of smooth invariants, the smooth structure is completely determined by purely topological data (“typical rigidity”), which is quite unexpected in this setting. It implies in particular that the lamination structure of spaces of analytic unimodal maps (obtained by the partition into topological conjugacy classes, see [ALM]) is not transversely absolutely continuous. As an intermediate step in the proof of the formula, we show that the distribution of the critical orbit is described by the physical measure supported in the chaotic attractor.     

Search for neutral, long-lived particles decaying into two muons in pp[over] collisions at sqrt[s]=1.96 TeV

We present a search for a neutral particle, pair produced in pp[over] collisions at sqrt[s]=1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses approximately 380 pb(-1) of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair-production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4x10(-11) s, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpretation of NuTeV's excess of dimuon events.     

Surface charge estimation on hemispherical dielectric samples from EFM force gradient measurements

A numerical model capable of estimating the surface charge density(σ_S) and the dielectric constant(k_e) of a hemispherical sample from force gradient measurements is proposed. Force gradients are commonly detected by a biased conductive tip during electrostatic force microscopy(EFM) probing but provide limited quantitative assessment of the charge in the sample. The proposed model gives an analytical solution for the force exerted over a biased conical tip. Theoretical numerical results, presented in the form of multitraces of minimum force gradients for fixed bias voltages and tip-sample distances allow the translation of EFM force gradient measurements into functions of σ_S and k_e.     

First observation of F

We measured the excitation function for ¹³O + p elastic scattering to obtain data on the unknown ¹⁴F nucleus. The ground state and several low-lying excited states in ¹⁴F were observed and spin/parity assignments were made. ¹⁴F appears to be much less unstable than was predicted. We compare theoretical predictions for the ¹⁴F level scheme with the experimental results.