Direct On-Line Coupling of Capillary HPLC with (1)H NMR Spectroscopy for the Structural Determination of Retinyl Acetate Dimers: 2D NMR Spectroscopy in the Nanoliter Scale

This paper presents the application of directly coupled capillary high-performance liquid chromatography (capillary HPLC) and proton high-field nuclear magnetic resonance spectroscopy (NMR) for structural elucidation of a so-far unknown kitol isomer. One- and two-dimensional continuous- and stopped-flow NMR spectra were recorded in a 180 μm i.d. capillary, corresponding to a detection volume of only 200 nL. Unequivocal structural assignment on the basis of 1D and 2D stopped-flow capillary HPLC-NMR experiments was performed. The kitol isomer mixture was present in a sample of thermally isomerized retinyl acetate and separated on a capillary column.     

Analysis of the (Trimethylsilyl)propionic Acid-β(12-28) Peptide Binding Equilibrium with NMR Spectroscopy

The binding of a small molecule, (trimethylsilyl)propionic acid (TSP), to a 17-residue peptide, β(12-28), is examined using (1)H NMR spectroscopy. β(12-28) (VHHQKLVFFAEDVGSNK) is a central fragment of the 40-42-residue Alzheimer's-associated Aβ peptide. This peptide has been previously shown to form soluble aggregates in low-pH aqueous solution. The TSP resonance is broadened appreciably in solutions containing relatively high concentrations (～2 mM) of the peptide. The changes in TSP line width measured by titration of a peptide solution with TSP indicate a 1:1 binding stoichiometry. If the concentrations of both the peptide and TSP are reduced by 1 order of magnitude, the resonances of both species are sharp, suggesting that TSP binds predominately to the aggregated peptide. Nuclear Overhauser effect experiments indicate that the TSP interacts predominately with the side chains of the aliphatic peptide residues Leu(17) and Val(18). Pulsed-field gradient NMR measurements of TSP and peptide diffusion coefficients provide a more quantitative picture of the TSP-peptide binding equilibrium. The measured diffusion coefficients were used to calculate the fractions of the free and bound TSP. These results substantiate the conclusion that the stoichiometry of the TSP-peptide binding equilibrium is essentially 1:1 and further indicate anticooperative behavior in solutions containing an excess of TSP resulting in a dissociation of the peptide aggregates.     

Laser-Induced Fluorescence Excitation Spectroscopy of the Magnesium Oxide B(1)?(+)-A(1)nu system

Excitation scans of the MgO B(1)?(+)-A(1)? transition were made in a seeded acetylene-air flame. The combustion of magnesium in oxygen and carbon dioxide is well known and is of significant interest for fire safety, solid propellant applications, and recently for use as an in situ resource propellant for planetary exploration of Mars. This spectroscopic study expands the available data on this electronic transition, particularly data at high rotational states that are lacking in the literature. Rotational parameters of the v = 0, 1, and 2 states of B(1)?(+) are derived.     

Realization of the Temperature Scale in the Range from 234.3 K (Hg Triple Point) to 1084.62°C (Cu Freezing Point) in Croatia

This article describes the realization of the International Temperature Scale in the range from 234.3 K (mercury triple point) to 1084.62°C (copper freezing point) at the Laboratory for Process Measurement (LPM), Faculty of Mechanical Engineering and Naval Architecture (FSB), University of Zagreb. The system for the realization of the ITS-90 consists of the sealed fixed-point cells (mercury triple point, water triple point and gallium melting point) and the apparatus designed for the optimal realization of open fixed-point cells which include the gallium melting point, tin freezing point, zinc freezing point, aluminum freezing point, and copper freezing point. The maintenance of the open fixed-point cells is described, including the system for filling the cells with pure argon and for maintaining the pressure during the realization.     

Point-Contact Andreev-Reflection Spectroscopy in the Fe-based Superconductor LaFeAsO1−x F x

Point-contact Andreev-reflection (PCAR) spectroscopy measurements have been performed in the Fe-based superconductor LaFeAsO_1−x F _x in order to investigate the energy gaps. The Andreev spectra show clear and reproducible features that could be related to two nodeless gaps. Their values, as determined by fitting the conductance curves measured in junctions with local T _c =27.3–28.6 K within the two-band BTK model, are Δ ₁=2.75–3.8 meV for the small gap and Δ ₂=7.9–10.2 meV for the larger one, respectively. The absence of zero-bias conductance peaks and considerations regarding the nonperfectly directional current injection in PCAR experiments and the polycrystalline nature of the samples rule out the possibility of nodal gaps in the superconductor. Moreover, the conductance curves show pseudogap-like features coexisting, at low temperature, with superconductivity and disappearing close to the Néel temperature of the parent compound, T _N≈140 K.     

The CUORE Experiment: Bolometric Detectors in 1-Ton Scale Projects

CUORE is the first of a new generation 1-ton scale cryogenic detectors for rare events physics. CUORE, a detector to search neutrinoless Double Beta Decay of ¹³⁰Te, is an array of 988 TeO₂ bolometers that will work at 10 mK. Latest developments on detectors performances are reported together with improvements reached in background reduction. Results of CUORICINO, a single CUORE tower running since 2003, that widely showed the feasibility of the project are also reported and discussed. P. Gorla on behalf of the CUORE collaboration.     

Use of the F − 2 : LiF Colour-centre Laser in Intracavity Laser Spectroscopy

Investigations of the F ^? ₂: LiF colour-centre laser used in intracavity laser (ICL) spectroscopy are reported. A F^? ₂: LiF laser operated at room temperature with a 200 μs pulse duration and 50–200cm^-1 pulse spectral width was used to form to basis of an ICL spectrometer with a threshold absorption sensitivity of 5 × 10 ^-8 cm ^-1 and a spectral resolution of 0·;041 cm^-1. The high sensitivity of the spectrometer enabled the recording in the 8000–9100cm ^-1 region of a variety of previously unrecorded lines of the v ₂ + 2v ₃ band of HDO and the v ₃ band of ¹² CH ₄ and ¹³ CH ₄. The special method for describing the hole enhancement in the laser radiation spectrum due to the absorption lines was used for measuring the half-widths and relative intensities of the H₂O lines.     

π-d Interaction in the Field Induced Superconductor λ-(BETS)2FeCl4: Studied by 77Se NMR

⁷⁷Se NMR measurements have been performed in the normal state of the organic, magnetic field induced superconductor λ(BETS)₂FeCl₄, to examine the interaction between Fe local spins and π conduction electrons. Large, negative Knight shift values were observed at fields lower than the one corresponding to onset of field induced superconductivity. This evidences that the conduction electrons feel a negative internal field coming from the Fe spins through the exchange interaction { } · { }. This suggests that the superconductivity induced by high magnetic fields has its origin in the Jaccarino-Peter compensation mechanism. The estimated value of the exchange interaction J, is 30% smaller than that predicted by the resistivity measurements.     

Properties of Evaporated Si_(1-x)Sn_x and Si_(1_x)Sn_x:H Amorphous Alloys

Amorphous Si_(1-x)Sn_x alloys have been prepared by co-evaporation onto substrates maintained atliquid nitrogen temperature. Their atomic structure is investigated using density measurements,scanning high-energy electron diffraction and Mossbauer spectroscopy. The optical and electricalproperties are reported. Then, a method to hydrogenate the films during the evaporation process isdescribed and applied to the preparation of amorphous semiconductors from pure silicon to pure tin.Finally, multilayers of type Si / Si:H / ... or Si:H / Si:D / ... are studied. The modulation of hydrogen isshown by low-angle neutron scattering and measurements of hydrogen diffusivity are presented.     

Role of the proton tunneling in the phase transition of K3D1−x H x (SO4)2

Dielectric and thermodynamic properties have been investigated for isotopically mixed crystals of K₃D_1–x H_x(SO₄)₂, which are composed of structurally isolated dimeric units SO ₄ ^– ... H-SO ₄ ^– . The critical temperature T_c for the antiferroelectric phase transition decreases with proton concentration (x) and eventually the phase transition vanishes at x_c 0.66 ± 0.04. The x-dependent behavior of T_c, the dielectric constant (T) and the specific heat C(T) are well accounted for by the mean-field theory for the transverse Ising model, indicating an important role of the proton tunneling on the phase transition and related properties. These features are compared with conventional hydrogen-bonded dielectrics with infinite networks of the hydrogen bonds.     

辉光放电a-Si_(1-x)Ge_x:H的光电特性

改变 GDa-Si_(1-x)Ge_x∶H 薄膜中 Ge 的含量,可以获得1.8—0.9eV 的带隙能量范围。对于x>0.3的薄膜,准费米能级的位置接近带隙的中央,电导激活能随 x 值的增加而线性地减小。光敏感性(σ_p/σ_d)在 x 从0变化到1的整个范围内下降4个数量级。实验表明,选择合适的衬底温度(T_s=250～300℃)以及较低的射频功率可以得到质量较好的 a—Si_(1-x)Ge_x∶H 薄膜。     

Measurement of Internal Acyl Migration Reaction Kinetics Using Directly Coupled HPLC-NMR: Application for the Positional Isomers of Synthetic (2-Fluorobenzoyl)-d-glucopyranuronic Acid

Ester glucuronides (1-O-acyl-β-d-glucopyranuronates) of many drugs may undergo internal acyl migration reactions, resulting in the formation of new positional isomers with both α- and β-anomers. We illustrate here a novel approach for the direct investigation of the acyl migration kinetics of ester glucuronides and show the application with respect to the isomers of synthetic (2-fluorobenzoyl)-d-glucopyranuronic acid. Individual isomers were separated from an equilibrium mixture containing the β-1-O-acyl, α- and β-2-O-acyl, α- and β-3-O-acyl, and α- and β-4-O-acyl isomers at pH 7.4 in 20 mM phosphate buffer. The interconverting isomers were separated using reversed-phase HPLC and pumped directly into a dedicated on-line NMR flow probe in a 600 MHz NMR spectrometer. The flow was stopped with each isomer in the NMR flow probe, and sequential NMR spectra were collected at 25 °C, allowing direct measurement of the production of positional isomers from each selectively isolated glucuronide isomer. All of the positional isomers and anomers were characterized, and relative quantities determined, and a kinetic model describing the rearrangement reactions was constructed. The acyl migration reaction kinetics were simulated using a theoretical approach using nine first-order rate constants determined for the acyl migration reactions and six first-order rate constants describing the mutarotation each of the 2-, 3-, and 4-positional isomers. The rate constants (in h(-)(1)) for the rearrangement reactions of the 2-fluorobenzoyl glucuronide isomers were as follows: β-1-O-acyl, 0.29 ± 0.01; α-2-O-acyl, 0.11 ± 0.01; β-2-O-acyl, 0.07 ± 0.01; α-3-O-acyl, 0.10 ± 0.01; β-3-O-acyl, 0.09 ± 0.01; α-4-O-acyl, 0.09 ± 0.01; and β-4-O-acyl, 0.06 ± 0.01. The α- and β-anomerization rates were estimated on the basis of the kinetics model; the anomerization rates of the 4-O-acyl isomers were additionally determined experimentally using directly coupled HPLC-NMR. The fitted anomerization rates for the 4-O-acyl isomer were 0.80 (α → β) and 0.50 h(-)(1) (β → α), whereas the experimentally estimated anomerization rates were 0.89 ± 0.1 and 0.52 ± 0.1 h(-)(1), respectively. The dynamic stop-flow HPLC-NMR approach allows unique kinetic information to be obtained relating to glucuronide reactivity, and this approach will be useful in future structure-reactivity studies on drug ester glucuronides and their properties.     

Emergence of Pairing Interaction in the Hubbard Model in the Strong Coupling Limit

We implement the rotationally-invariant formulation of the two-dimensional Hubbard model, with nearest-neighbors hopping t, which allows for the analytic study of the system in the low-energy limit. Both U(1) and SU(2) gauge transformations are used to factorize the charge and spin contribution to the original electron operator in terms of the corresponding gauge fields. The Hubbard Coulomb energy U-term is then expressed in terms of quantum phase variables conjugate to the local charge and variable spin quantization axis, providing a useful representation of strongly correlated systems. It is shown that these gauge fields play a similar role as phonons in the BCS theory: they act as the “glue” for fermion pairing. By tracing out gauge degrees of freedom the form of paired states is established and the strength of the pairing potential is determined. It is found that the attractive pairing potential in the effective low-energy fermionic action is non-zero in a rather narrow range of U/t.     

NMR Study on a Pnictide Superconductor LaFeAsO1−x H x in a H-Overdoped Regime: Revival of Antiferromagnetic Fluctuations

An electron-doped high-T _c pnictide LaFeAsO_1?x H _x is recently known for having double superconducting (SC) domes in the phase diagram. We have performed nuclear magnetic resonance (NMR) measurements in an H-overdoped regime to investigate the second SC dome on a microscopic level. We unexpectedly discovered that the linewidths of both ⁷⁵As and ¹H spectra broaden at low temperatures for the 58 and 62.5 % H-doped samples, indicating that the antiferromagnetic (AF) ordering returns in the heavily H-doped regime. The finding itself is rare because an excess carrier doping tends to cause Fermi-liquid behavior in strongly correlated electron systems. We demonstrate that the new AF ordering originates from the nesting between electron pockets.     

Surface Characterization of Ni_(64)P_(20)Fe_(16)Amorphous Alloy by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy

The nature of the native oxides formed on thesurface layer of amorphous alloy Ni_(64)P_(20)Fe_(16)hasbeen studied by X-ray photoelectron spectroscopy(XPS)and Auger electron spectroscopy(AES)withdepth profiling by ion bombardment.There aregreat distinctions in compositions and chemicalstates between the surface layer and the bulk.Themain constituents Ni,P and Fe are lower in the sur-face layer,and they are mostly in oxidized states,whereas C,O and N are enriched in the surface lay-er.The thickness of surface oxide layer isapproximately 20 nm,this layer was assumed to beof great significance to various properties of amor-phous alloy Ni_(64)P_(20)Fe_(16),expecially to the chemicaland catalytic properties.Experiments proved thattransitional element Fe cannot improve oxidationresistance of the amorphous Ni-P system.     

a-Si:H/a-Si_(1-x)C_x:H 多层膜的电学和光学性质

采用等离子体辉光放电单室系统制备的 a-Si:H/a-Si_(1-x)C_x:H 多层膜结构具有低的暗电导和高的光电导特性,且不同于单层膜,有明显的 S-W 效应。随着子层厚度 L 减小,多层膜曝光态(B)的暗电导率σdB 较退火态(A)的σdA 减小快,即光诱导衰退程度增大,而光电导无明显变化。本文还测定了此多层膜结构的光能隙 E_g,得到随子层厚度减小“蓝移”的结果。用一维单量子阱模型作了讨论,实验值与理论计算符合较好。     

Resonance Effect on the Tunneling Reaction: H+H2→H2+H in Solid Hydrogen

The tunneling abstraction reaction: H+H₂H₂+H in -irradiated solid hydrogen has been studied using electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) spectroscopy and gas-chromatography. The rate constant for the tunneling reaction in solid hydrogen was found to decrease with the increase in the concentration of ortho-H₂ molecules in solid hydrogen. We concluded that the decrease in the rate constant is due to the energy level mismatching between reactant species of H+H₂ trapped and product species of H₂+H trapped in the reverse induced by inhomogeneous intermolecular interactions between ortho-H² molecules in solid hydrogen. This result indicates that resonance effects play an important role in tunneling reactions in solids.     

Role of the Structural‐Rheological State of Poly(Meth)Acrylate Solutions in Their Soaking into Capillary‐Porous Bodies

We have investigated the influence of the structuralrheological state of solutions of poly(meth)acryl copolymers on the rate of their capillary rise and the uniformity of the polymer distribution in the bulk of porous bodies — models of monuments of art made of ceramics, terracotta, loessial and lime plaster, and concrete. It has been found that in the region of concentrations corresponding to the transition of poly(meth)acrylate solutions from the viscousNewtonian to the structuralviscous rheological state there is a sharp decrease in the rate of capillary rise of solutions into clay, chalk, and cementsand specimens. A worsening of the uniformity of the polymer distribution over the height of the porous specimens, a decrease in their surface wetting with copolymer solutions, and a decrease in the value of the polymer adsorption on the filler surface are also observed.     

Spin relaxation in normal liquid3He:T 1 in the Fermi liquid (T≪T F) regime

The low-temperature (TT _F) spin relaxation timeT ₁ in normal liquid³He is calculated. First an expression forT ₁ is obtained using the Landau kinetic equation, which is in terms of the perturbations of the scattering amplitudes due to nuclear dipole-dipole interactions. These perturbations are obtained using the induced interaction model, which explicitly includes the effects of many-body correlations arising from the Pauli principle. The results are in good agreement with experiment, as well as with previous calculations.     

a-Si_(1-x)Nx:H 光电导的改善及其原由

氮的掺入能够改善 a-Si∶H 的光电导性。用 ESR 方法难以分析其原因。吸收系数的弱吸收段却能显示出氮造成 a-Si∶H 缺陷态密度的变小。当掺氮量 x(?)0.01时,a-Si_(1-x)N_x 之ημT 值呈最大,在 E_(?)下1.2eV 处缺陷态密度最低,约3.3×10~(15)/cm~3。过量地掺氮则导致缺陷态密度增加,光电导降低。