A solid-state NMR study of the formation of molecular sieve SAPO-34

This work examined the formation of a catalytically important microporous material, SAPO-34, in the presence of HF under hydrothermal synthesis conditions. The local environments of P, Al, F and Si atoms in several solid phases obtained at different stages of crystallization were characterized by several solid-state NMR techniques including ³¹P, ²⁷Al, ¹⁹F and ²⁹Si MAS, ²⁷Al triple-quantum MAS, ³¹P{²⁷Al} transfer of populations in double-resonance, ²⁷Al{³¹P} rotational-echo double-resonance (REDOR), ²⁷Al→³¹P heteronuclear correlation spectroscopy, ³¹P{¹⁹F} and ²⁷Al{¹⁹F} REDOR as well as ¹H→³¹P cross polarization. The NMR results provide the new insights into the formation of SAPO-34.     

Combined 17O NMR and 11B-31P double resonance NMR studies of sodium borophosphate glasses

17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B-31P heteronuclear correlation (HETCOR) NMR and 11B{31P} rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS. The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: P-O-P, Na...O-P, P-O-B, B-O-B, Na...O-B. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that P-O-B links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B{31P} REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that B-O-P bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B-31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups.     

Time displacement rotational echo double resonance: heteronuclear dipolar recoupling with suppression of homonuclear interaction under fast magic-angle spinning

We have developed a novel variant of REDOR which is applicable to multiple-spin systems without proton decoupling. The pulse sequence is constructed based on a systematic time displacement of the pi pulses of the conventional REDOR sequence. This so-called time displacement REDOR (td-REDOR) is insensitive to the effect of homonuclear dipole-dipole interaction when the higher order effects are negligible. The validity of td-REDOR has been verified experimentally by the P-31{C-13} measurements on glyphosate at a spinning frequency of 25 kHz. The experimental dephasing curve is in favorable agreement with the simulation data without considering the homonuclear dipole-dipole interactions.     

Characterization of local environments in crystalline borophosphates using single and double resonance NMR

(11)B and (31)P magic-angle spinning as well as (11)B{(31)P} and (31)P{(11)B} rotational echo double resonance (REDOR) NMR have been applied to characterize the local environments in the crystalline borophosphates K(3)[BP(3)O(9)(OH)(3)], NH(4)[ZnBP(2)O(8)] and Rb(3)[B(2)P(3)O(11)(OH)(2)]. Dipolar second moment values extracted from the REDOR curves at short evolution times (DeltaS/S(0) < or = 0.2) are in reasonable agreement with those calculated from the internuclear distances in the corresponding crystal structures. In particular, the method is found to be useful for distinguishing between boron and phosphorus local environments with different numbers of B-O-P connectivities, making REDOR a well-suited tool for medium-range order investigations in glasses.     

REDOR with a relative full-echo reference

REDOR and REDOR-like 13C[19F] and 2H[19F] NMR experiments have been performed on lyophilized whole cells of Staphylococcus aureus. The bacteria were grown to maturity on media containing L-[13C(3)]alanine or L-[methyl-d(3)]alanine, and then complexed with the 4-fluorobiphenyl derivative of chloroeremomycin, an analogue of the widely used antibiotic, vancomycin. The position of the 19F of the drug bound in the bacterial cell wall was determined relative to L-alanine 13C and 2H labels in the peptidoglycan peptide stem that was closest to the fluorinated biphenyl moiety of the drug. These determinations were made by dipolar recoupling methods that do not require an absolute measurement of the REDOR full echo (the signal observed without rotor-synchronized dephasing pulses) of the labels in the peptide stem.     

Double-quantum filtered rotational-echo double resonance

The homonuclear scalar coupling of a directly bonded 13C-13C pair has been used to create a double-quantum filter (DQF) to remove the natural-abundance 13C background in 13C{15N} rotational-echo double-resonance (REDOR) experiments. The DQF scalar and REDOR dipolar evolution periods are coincident which is important for sensitivity in the event of weak 13C-15N dipolar coupling. Calculated and observed 13C{15N} DQF-REDOR dephasings were in agreement for a test sample of mixed recrystallized labeled alanines. Glycine metabolism in a single uniform-15N soybean leaf labeled for 6 min by 13CO2 was measured quantitatively by 13C{15N} DQF-REDOR with no background interferences.     

The interaction between inorganic Li salts (LiTf,LiNTf2) and the surface of alumina particles as studied with solid state nuclear magnetic resonance

The interaction between Li salts {LiTf (Tf = CF₃SO₃) and LiNTf₂ (NTf₂ = N(SO₂CF₃)₂)} with surface modified alumina particles (basic, neutral or acidic) is investigated employing a range of advanced solid state NMR methodologies. Utilizing ⁷Li MAS NMR, a new signal – in addition to the signal of the pure salt – could be identified in the composite samples, increasing with increasing basicity of the alumina surface. Employing ⁷Li–{¹H} CPMAS NMR and ⁷Li–{¹H}–CPMAS–{²⁷Al} REAPDOR NMR spectroscopy, this new signal could be unequivocally assigned to an alumina-surface bound Li species. For the anions, ¹⁹F MAS NMR spectra clearly prove the existence of new anion sites. Employing ¹⁹F–{⁷Li} REDOR spectroscopy and ¹⁹F–{²⁷Al} TRAPDOR NMR spectroscopy, the identified signals could be safely assigned to anions within the pristine Li salt and anions attached to the alumina surface. These results present direct evidence for the anion???alumina surface and cation???alumina surface interaction, suggested by several authors to aid in the interpretation of the effect of the ceramic additive on the ionic conductivity.     

Solid-state NMR studies for the determination of 11B electric field-gradient tensor orientations in P/B Frustrated Lewis Pairs and related systems

A solid state NMR method is described for measuring the angle Θ specifying the orientation of the principal component of the ¹¹B electric field gradient tensor relative to the ¹¹B^…31P internuclear vector of ¹¹B–³¹P spin pairs. It is based on the anisotropic dephasing of ¹¹B spins in the dipolar field of ³¹P nuclei via ¹¹B{³¹P} Rotational Echo DOuble Resonance (REDOR) experiments. The method is applied to four solid borane–phosphane compounds related to Frustrated Lewis Pair (FLP) chemistry. Results determined by numerical line shape simulations are found in excellent agreement with theoretically calculated values using advanced DFT methods. The angle Θ, which can be measured with an estimated precision of ±5°, offers a clear spectroscopic distinction between classical Lewis-acid/base adducts and active Frustrated Lewis pairs (FLPs).     

Observation of four-wave mixing in caesium atoms using a noncycling transition

In this paper the generation of four-wave mixing (FWM) signal using a noncycling transition of caesium atoms is investigated when the pumping laser is locked to the transition $6{\rm S}_{1/2}F=4\to6{\rm P}_{3/2}F'=4$, and meanwhile the probe frequency is scanned across the $6{\rm S}_{1/2}F=4 \to6{\rm P}_{3/2}$ transition. The efficiency of the four-wave mixing signal as a function of the intensity of the pumping beams and the detuning of the pumping beams is also studied. In order to increase the detection efficiency, a repumping laser which is resonant with $6{\rm S}_{1/2} F=3\to 6{\rm P}_{3/2}F'=4$ transition is used. A theoretical model is also introduced, and the theoretical results are in qualitative agreement with experimental ones.     

Phosporus-31 Solid-State NMR in High-Field Gradients: Prospects for Imaging Bone Using the Long Echo-Train Summation Technique (LETS)

Stray-field techniques are reported for ³¹P studies of solids for a variety of compounds including bone, bone meal and calcium hydroxyapatite. Long Hahn echo trains produced by the application of many pulses were used as in the long echo-train summation technique. Double-resonance enhancements of ³¹P by use of both direct and indirect experiments were attempted on a sample of NH₄PF₆:³¹P{¹⁹F} double resonance produced, at most, a 26% increase in the initial level of the ³¹P echo signal.     

Total versus quantum correlations in a two-mode Gaussian state

In Li and Luo(2007 Phys. Rev. A 76 032327), the inequality(1/2)T≥ Q was identified as a fundamental postulate for a consistent theory of quantum versus classical correlations for arbitrary measures of total T and quantum Q correlations in bipartite quantum states. Besides, Hayden et al(2006 Commun. Math. Phys. 265 95) have conjectured that, in some conditions within systems endowed with infinite-dimensional Hilbert spaces, quantum correlations may dominate not only half of total correlations but total correlations itself. Here, in a two-mode Gaussian state,quantifying T and Q respectively by the quantum mutual information I~G and the entanglement of formation(EoF) ε_F~G, we verify that ε_(F,R)~G,is always less than(1/2) I_R~G when I~G and ε_F~G are defined via the Rényi-2 entropy. While via the von Neumann entropy, ε_(F,V)~G,may even dominate I_V~G itself,which partly consolidates the Hayden conjecture, and partly, provides strong evidence hinting that the origin of this counterintuitive behavior should intrinsically be related to the von Neumann entropy by which the EoF ε_(F,V)~G,is defined, rather than related to the conceptual definition of the EoF ε_F. The obtained results show that—in the special case of mixed two-mode Gaussian states—quantum entanglement can be faithfully quantified by the Gaussian Rényi-2 EoF ε_(F,R)~G,.     

Measuring oxygen-phosphorus distances and the orientation of electric field gradient tensors using 17O-[31P] REDOR in phosphate glasses

Rotational echo double resonance (REDOR) of spin-12 nuclei is an extremely useful tool for the determination of distances in solids as well as of relative orientations of chemical shift and dipole tensors. We present the corresponding version for measuring the relative orientation of electric quadrupole and dipole tensors and demonstrate its applicability for non-bridging oxygens in phosphate glasses using 17O-[31P] REDOR NMR. The orientational information is found in the changes of the second-order quadrupole patterns as a function of the echo delay. Results and numeric simulations are presented for 17O-[31P] REDOR NMR of 17O-enriched sodium phosphate glasses. For non-bridging oxygens, the symmetric quadrupole tensor is found to be aligned along the phosphorus-oxygen bond. The distance between P and the non-bridging oxygen is calculated for two glasses of different compositions.     

Determination of the structure of {31}ne by a fully microscopic framework

We perform the first quantitative analysis of the reaction cross sections of {28-32}Ne by {12}C at 240 MeV/nucleon, using the double-folding model with the Melbourne g matrix and the deformed projectile density calculated by antisymmetrized molecular dynamics. To describe the tail of the last neutron of {31}Ne, we adopt the resonating group method combined with antisymmetrized molecular dynamics. The theoretical prediction excellently reproduces the measured cross sections of {28-32}Ne with no adjustable parameters. The ground state properties of {31}Ne, i.e., strong deformation and a halo structure with spin parity 3/2{-}, are clarified.     

An advanced NMR protocol for the structural characterization of aluminophosphate glasses

In this work a combination of complementary advanced solid-state nuclear magnetic resonance (NMR) strategies is employed to analyse the network organization in aluminophosphate glasses to an unprecedented level of detailed insight. The combined results from MAS, MQMAS and (31)P-{(27)Al}-CP-heteronuclear correlation spectroscopy (HETCOR) NMR experiments allow for a detailed speciation of the different phosphate and aluminate species present in the glass. The interconnection of these local building units to an extended three-dimensional network is explored employing heteronuclear dipolar and scalar NMR approaches to quantify P-O-Al connectivity by (31)P{(27)Al}-heteronuclear multiple quantum coherence (HMQC), -rotational echo adiabatic passage double resonance (REAPDOR) and -HETCOR NMR as well as (27)Al{(31)P}-rotational echo double resonance (REDOR) NMR experiments, complemented by (31)P-2D-J-RESolved MAS NMR experiments to probe P-O-P connectivity utilizing the through bond scalar J-coupling. The combination of the results from the various NMR approaches enables us to not only quantify the phosphate units present in the glass but also to identify their respective structural environments within the three-dimensional network on a medium length scale employing a modified Q notation, Q(n)(m),(AlO)(x), where n denotes the number of connected tetrahedral phosphate, m gives the number of aluminate species connected to a central phosphate unit and x specifies the nature of the bonded aluminate species (i.e. 4, 5 or 6 coordinate aluminium).     

Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds

This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830 nm wavelength with pulse duration of 120 fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability,γ, of Compound 1 is of 1.0 × 10^-31 esu. Due to the charge transfer, the γ of Compound 2 with electron donor and acceptor group is 4.9 × 10^-31 esu, which is a four-time enhancement in comparison with Compound i. The absorption spectra show that the electron push-pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity.     

溶胶凝胶法制备参氟二氧化锡薄膜

利用溶胶凝胶方法，在硅碱玻璃底板上制备的透明低电阻SnO2:F薄膜，是一种低辐射导电薄膜。将SnCl4·5H2O 和 NH4F 溶解在50%乙醇和50%水的溶液中。制备条件为底板温度450℃，喷嘴与底板之间的距离60mm,载气流速8 L/min，制备时间5分钟。制成的SnO2:F薄膜面电阻为2Ω/□，可重复性好。并且文中还定性给出了SnO2:F薄膜其红外反射率与面电阻之间的关系。     

The fluorescence of dye-nucleic acid complexes

Numerous fluorescent compounds, predominantly dyes, are able to form intermolecular complexes with deoxyribonucleic acid (DNA), ribonucleic acid (RNA), nucleoproteins, and various of their synthetic analogues. As a consequence of the binding, fluorescence spectroscopic data, i.e. quantum yield, decay time, and polarization properties, are altered as compared with the free dye. Fluorescence measurements are well suited to gain information on binding processes, steric location of the fluorescent ligands at the nucleic acid template, and energy transfer processes from the nucleic acid bases to complexed compounds. Moreover, conclusions on conformational structures in nucleic acids in vitro and in vivo can be drawn. Finally, they help to study the biological activity of various compounds on a molecular level, including problems involved in chromosomal fluorescence staining.     

Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe11.83Si0.94Al0.23 compounds

Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} compounds has been investigated by means of magnetization measurements. X-ray diffraction shows the prepared compounds to be single phase with the cubic NaZn_{13}-type structure. Substitution of Co for Fe leads to an increase of Curie temperature of the material. The magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} and LaFe_{11.03}Co_{0.80}Si_{0.94}Al_{0.23} compounds are 21.8J/(kg·K) to 16.9J/(kg·K) under a magnetic field change of 0－5T at Curie temperature, respectively. Giant magnetic entropy changes are attributed to the higher magnetization and the rapid change in magnetization at Curie temperature.     

Electronic shot noise in fractal conductors

By solving a master equation in the Sierpiński lattice and in a planar random-resistor network, we determine the scaling with size L of the shot noise power P due to elastic scattering in a fractal conductor. We find a power-law scaling P proportional, variantL;{d_{f}-2-alpha}, with an exponent depending on the fractal dimension d_{f} and the anomalous diffusion exponent alpha. This is the same scaling as the time-averaged current I[over ], which implies that the Fano factor F=P/2eI[over ] is scale-independent. We obtain a value of F=1/3 for anomalous diffusion that is the same as for normal diffusion, even if there is no smallest length scale below which the normal diffusion equation holds. The fact that F remains fixed at 1/3 as one crosses the percolation threshold in a random-resistor network may explain recent measurements of a doping-independent Fano factor in a graphene flake.     

19F/29Si rotational-echo double-resonance and heteronuclear spin counting under fast magic-angle spinning in fluoride-containing octadecasil

19F/29Si rotational-echo double-resonance (REDOR) and theta-REDOR NMR techniques have been applied under fast magic-angle spinning to a powder sample of fluoride-containing octadecasil. Efficient dipolar recoupling was observed and the effect of finite pulse lengths was found to be negligible using standard radiofrequency field strengths. Moreover, the determined internuclear distance of the 19F-29Si spin pairs formed by the silicons in the D4R units (T-1 site) and the fluoride anions is in very good agreement with previous REDOR and Hartmann-Hahn cross-polarization measurements. Numerical simulation of the REDOR dephasing curves at both the T-1 and T-2 sites considering all fluoride anions in the infinite solid lattice clearly confirm the X-ray crystal structure of octadecasil. Heteronuclear spin-counting theta-REDOR experiments are found to be very useful to obtain direct insight into the local network of dipolar interactions. Indeed, while 19F-29Si pair-like behavior is confirmed at the T-1 site, multiple dipolar interactions are clearly evidenced at the T-2 site.