Simultaneous adiabatic spin-locking cross polarization in solid-state NMR of paramagnetic complexes

Continuous-wave irradiations cross polarization and its variations had not been a popular choice for sensitivity enhancement in paramagnetic solids due to the large spectral broadening and the effect of fast relaxation on both the source and target spins. Furthermore, with the application of very-fast sample spinning, which is the prerequisite for high-resolution purposes, polarization transfer over a large bandwidth is further degraded. In this work, we report a wideband sensitivity enhancement in paramagnetic solid with our recently developed technique, simultaneous adiabatic spin-locking cross polarization, SADIS CP. Experiments were demonstrated with Cu(II)(d,l-alanine)₂ · H₂O under high-static field of 14.1 T and very-fast sample spinning of 31 kHz.     

New fluorous ponytailed 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridinium halide salts

It is possible that fluorous compounds could be utilized as directing forces in crystal engineering for applications in materials chemistry or catalysis. Although numerous fluorous compounds have been used for various applications, their structures in the solid state remains a lively matter for debate. The reaction of 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridine with HX (X = I or Cl) yielded new fluorous ponytailed pyridinium halide salts, namely 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridinium iodide, C₈H₉F₃NO⁺·I⁻, (1), and 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridinium chloride, C₈H₉F₃NO⁺·Cl⁻, (2), which were characterized by IR spectroscopy, multinuclei (¹H, ¹³C and ¹⁹F) NMR spectroscopy and single‐crystal X‐ray diffraction. Structure analysis showed that there are two types of hydrogen bonds, namely N—H…X and C—H…X. The iodide anion in salt (1) is hydrogen bonded to three 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridinium cations in the crystal packing, while the chloride ion in salt (2) is involved in six hydrogen bonds to five 4‐[(2,2,2‐trifluoroethoxy)methyl]pyridinium cations, which is attributed to the smaller size and reduced polarizability of the chloride ion compared to the iodide ion. In the IR spectra, the pyridinium N—H stretching band for salt (1) exhibited a blue shift compared with that of salt (2).     

Synthesis and structures of diindeno-fused 1,12-diphenylbenzo[c]phenanthrene and 1,14-diphenyl[5]helicene bearing severe helical twists

Diindeno-fused 1,12-diphenylbenzo[c]phenanthrene 15 and 1,14-diphenyl[5]helicene 20 were prepared in a four-step synthetic sequence from 2,7-naphthalenedicarboxylic acid and 3,6-phenanthrenedicarboxylic acid, respectively. The X-ray structures of 15 and 20 show that the fused ring systems possess severe helical twists. The rotational barriers of the phenyl substituents were determined by the analysis of temperature-dependent 1H NMR spectra. [structure: see text]     

Optimizing after-glow luminescent parameters of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>, by sol–gel method and combustion process

Strontium aluminates are viewed as a promising persistent luminescent materials. There are many researches on strontium aluminates, including SrAl₂O₄, Sr₄Al₁₄O₂₅. Between these two phases, Sr₄Al₁₄O₂₅ shows much better properties than SrAl₂O₄. The traditional way to synthesize Sr₄Al₁₄O₂₅ is the solid state reaction. However, it exists few problems, especially non-homogeneous product. As a result, there are two methods chosen to make homogeneous precursor. One is sol–gel method, the other is combustion with Urea as a fuel. Boric acid is added as a flux in both method. In this study, combustion process is found to be a better way for synthesizing Sr₄Al₁₄O₂₅. We change the temperature, synthetic method. The samples are finely grinded and used for XRD analysis, photoluminescence measurement, and after-glow decay curve to figure out the optimizing luminescent parameters.     

Effect of conjugated linoleic acid immobilization on the hemocompatibility of cellulose acetate membrane

Conjugated linoleic acid (CLA) was covalently immobilized onto cellulose acetate (CA) membranes. The effects of CLA immobilization on the blood coagulation, platelet aggregation, and oxidative stress were evaluated using human blood. The resulting CLA grafting CA membranes were characterized with X-ray photoelectronic spectroscopy (XPS). The complete blood count (CBC) and coagulation time (CT) was evaluated in vitro for the hemocompatibility. Human serum albumin (HSA) and human plasma fibrinogen (HPF) was evaluated for the protein affinity. The production of reactive oxygen species (ROS) was measured by chemiluminescence (CL) method to evaluate the oxidative stress. The results showed that the CLA-immobilizing CA membrane could keep the CBC values more stable than unmodified CA membrane. The CLA-immobilized CA membranes also showed longer CT and less adsorption of plasma proteins. CLA-immobilized CA membrane could keep the CL counts of hydrogen peroxide and superoxide values more stable than unmodified CA membrane. These results suggest that a CLA-immobilized CA membrane could offer protection for patients against oxidative stress and would be helpful for reducing the dosage of anticoagulant during hemodialysis.     

Regioselective Baeyer-Villiger lactonization of 2-substituted pyrrolidin-4-one. Synthesis of statine

Nine 2-substituted pyrrolidin-4-ones 4a-i were obtained via a series of functional group transformation of known prolinol 5 by facile six kinds of methodologies. The target structure of 1,3-amino alcohols 2a-i was constructed in the regioselective Baeyer-Villiger lactonization of ketones 4a-i and reduction of the resulting 4-substituted tetrahydro-1,3-oxazin-6-ones 3a-i. A new and straightforward synthesis of (3S,4S)-statine (6) has been established starting from trans-(2S,4R)-4-hydroxyproline (1).     

The resource allocation problem for demand forecasting and performance measurement

We consider a retailer investing in two monitoring functions for unobservable demand and salesperson’s effort. We show that improving effort monitoring is more effective. Moreover, demand monitoring may be less preferable when it becomes relatively cheaper and balancing these two may be worse when they become more complementary.     

Compact optical function generator

We demonstrate the use of a nonlinear photonic crystal to generate a harmonic comb and an ultrabroad-band acousto-optic modulator for the field amplitudes and phases of the comb to succeed in synthesizing femtosecond and subfemtosecond optical field waveforms. Nonsinusoidal fields of various shapes are synthesized and verified using shaper-assisted linear cross-correlation. The compact all-solid-state system could lead to the realization of a portable arbitrary optical waveform synthesizer that is analogous in many aspects to an RF function generator.     

Photothermal-assisted fabrication of iron fluoride-graphene composite paper cathodes for high-energy lithium-ion batteries

A facile route that combines co-assembly and photothermal reduction was developed to synthesize free-standing, flexible FeF(3)-graphene papers. The papers contain well-dispersed FeF(3) nanoparticles and open diffusion channels in a porous, electrically conducting network of graphene sheets, and demonstrate promising applications as cathodes in high-energy density Li-ion batteries.