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NMR spectroscopy is a powerful tool to investigate molecular structure and dynamics. The poor sensitivity of this technique, however, limits its ability to tackle questions requiring dilute samples. Low-concentration photo-chemically induced dynamic nuclear polarization (LC-photo-CIDNP) is an optically-enhanced NMR technology capable of addressing the above challenge by increasing the detection limit of aromatic amino acids in solution up to 1,000-fold, either in isolation or within proteins. Here, we show that the absence of NMR-active nuclei close to a magnetically active site of interest (e.g., the structurally diagnostic H(α)-C(α) pair of amino acids) is expected to significantly increase LC-photo-CIDNP hyperpolarization. Then, we exploit the spin-diluted tryptophan isotopolog Trp-α-(13)C-β,β,2,4,5,6,7-d(7) and take advantage of the above prediction to experimentally achieve a ca 4-fold enhancement in NMR sensitivity over regular LC-photo-CIDNP. This advance enables the rapid (within seconds) detection of 20 nM concentrations or the molecule of interest, corresponding to a remarkable 3 ng detection limit. Finally, the above Trp isotopolog is amenable to incorporation within proteins and is readily detectable at 1 μM concentration in complex cell-like media, including E. coli cell-free extracts.

Magnetic resonance techniques are successfully utilized in a broad range of scientific disciplines and in a number of practical applications, with medical MRI being the most widely-known example. Currently, both fundamental and applied magnetic resonance are enjoying a major boost owing to the dramatic signal enhancement provided by the rapidly-developing field of spin hyperpolarization. Such techniques are able to enhance signal intensities in magnetic resonance by several orders of magnitude, and thus to largely overcome its major disadvantage of relatively low sensitivity compared to other analytical techniques. This provides new impetus for existing applications, and, even more importantly, this opens the gates to numerous novel and exciting possibilities in the broad fields of fundamental and applied magnetic resonance. There are many different techniques that fall under the umbrella term “hyperpolarization”. Existing reviews cover the various subfields, but they are mostly addressed separately, and are seldom perceived as integral parts of the same field. In this review we attempt to unify the many methods that are used to hyperpolarize nuclear spins into one picture. Specifically, before delving into the individual techniques, we provide a detailed analysis of the underlying principles of spin hyperpolarization. We attempt to uncover and classify the origins of hyperpolarization; to establish its sources and the specific mechanisms that enable the flow of polarization from a source to the target nuclear spins. After outlining the inner workings of hyperpolarization, we give a more detailed analysis of individual hyperpolarization techniques: the mechanisms by which they work, fundamental and technical requirements, characteristic applications, unresolved issues and possible future directions. While a substantial progress has been achieved in the field of spin hyperpolarization in recent years, the continuing growth of activity indicates that this is just the beginning. It is unlikely that fundamentally new sources of hyperpolarization will be uncovered in the near future, but we expect the field to flourish as new ways to improve and utilize current hyperpolarization techniques are identified and implemented. There is great scope for cross-fertilization between known methods, and developments in one area (e.g., prolonging polarization lifetimes, or creating more efficient excitation-detection schemes) can have a very broad impact across the entire field of hyperpolarization. We hope this review will facilitate this process, since advances in hyperpolarization will help to overcome existing challenges in magnetic resonance and enable novel applications.

Interlaminar failure caused by scratches is a common damage mode in automotive coatings and is considered the potential trigger for irreversible destruction, i.e., plowing. This work strives to numerically investigate the mechanisms responsible for the complex scratch behavior of an automotive coating system, considering the interfacial failure. A finite element model is developed by incorporating a large deformation cohesive zone model for scratch-induced debonding simulation, where the mass scaling technique is utilized to minimize computational burden while ensuring accuracy. The delamination phenomenon of the automotive coating is reproduced, and its effects on scratch damage behavior are analyzed. Accordingly, it is revealed that the interlaminar delamination would produce significant stress redistribution, which leads to brittle and ductile damage of the coating and consequently affects the formation of plowing. Eventually, parametric studies on the effects of interfacial properties are performed. They demonstrate that the shear strength and shear fracture energy dominate scratch-induced delamination.

Companies’ disclosing information of targeted poverty alleviation in China has become a referee for investors to judge the morality of the corporate management and influenced the decision-making of...

The degree of hydrophobicity and net charge per residue are physical properties that enable the discrimination of folded from intrinsically disordered proteins (IDPs) solely on the basis of amino acid sequence. Here, we improve upon the existing classification of proteins and IDPs based on the parameters mentioned above by adopting the scale of nonpolar content of Rose et al. and by taking amino acid side-chain acidity and basicity into account. The resulting algorithm, denoted here as net charge nonpolar or NECNOP, enables the facile prediction of the folded and disordered status of proteins under physiologically relevant conditions with >95% accuracy, based on amino-acid sequence alone. The NECNOP approach displays a much-enhanced performance for proteins with >140 residues, suggesting that small proteins are more likely to have irregular charge and hydrophobicity features. NECNOP analysis of the entire Escherichia coli proteome identifies specific net charge and nonpolar regions peculiar to soluble, integral membrane, and non-integral membrane proteins. Surprisingly, protein net charge and hydrophobicity are found to converge to specific values as chain length increases, across the E. coli proteome. In addition, NECNOP plots enable the straightforward identification of protein sequences corresponding to prion proteins and promise to serve as a powerful predictive tool for the design of large proteins. In summary, NECNOP plots are a straightforward approach that improves our understanding of the relation between the amino acid sequence and three-dimensional structure of proteins as a function of molecular mass.

Due to the potential applications of superhydrophobic surfaces in water-repelling and anti-icing, it is of great interest to study the impacting and freezing processes of water droplets on superhydrophobic surfaces. In this study, the process of a water droplet impacting the PDMS-decorated superhydrophobic aluminum alloy (denoted as Al-PDMS) surface was studied, and the influences of a water droplet falling height and volume were systemically investigated with a high-speed camera. The results indicate that the impacting process can be categorized into four states, which are mainly affected by the dropping height. The bouncing processes of water droplets on horizontal superhydrophobic surfaces are studied by defining spreading factor α and rebounding factor β. Furthermore, the effect of the inclination angle φ of the superhydrophobic plate on the impacting behavior was investigated. The freezing processes of water droplets on superhydrophobic surfaces were also studied. The results showed that the delayed-icing time decreases with decreasing test plate temperature. Additionally, the volume and height of the frozen portion of the water droplets during freezing were investigated, and the movement characteristic of the freezing front was analyzed.

Solution-state NMR typically requires 100 μM to 1 mM samples. This limitation prevents applications to mass-limited and aggregation-prone target molecules. Photochemically induced dynamic nuclear polarization was adapted to data collection on low-concentration samples by radiofrequency gating, enabling rapid 1D NMR spectral acquisition on aromatic amino acids and proteins bearing aromatic residues at nanomolar concentration, i.e., a full order of magnitude below other hyperpolarization techniques in liquids. Both backbone H(1)-C(13) and side-chain resonances were enhanced, enabling secondary and tertiary structure analysis of proteins with remarkable spectral editing, via the (13)C PREPRINT pulse sequence. Laser-enhanced 2D NMR spectra of 5 μM proteins at 600 MHz display 30-fold better S/N than conventional 2D data collected at 900 MHz. Sensitivity enhancements achieved with this technology, denoted as low-concentration photo-CIDNP (LC-photo-CIDNP), depend only weakly on laser intensity, highlighting the opportunity of safer and more cost-effective hypersensitive NMR applications employing low-power laser sources.

Isotopologs are powerful tools for investigating biological systems. We report a biosynthetic-cascade synthesis of Trp isotopologs starting from indole, glycine, and formaldehyde using the enzymes l-threonine aldolase and an engineered β-subunit of tryptophan synthase. This modular route to Trp isotopologs is simple and inexpensive, enabling facile access to these compounds.

Ni–Co nanoalloy catalysts have been prepared by a simple solid phase reaction approach and were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), temperature-programmed desorption of H2 (H2-TPD) and X-ray photoelectron spectroscopy (XPS). The Ni–Co nanoalloy catalyst was evaluated for hydrogenation of d-glucose under aqueous phase condition. The results indicated that the Ni–Co nanoalloy catalysts were more active than the single metal Ni or Co nano-catalyst. Moreover, Ni–Co nanoalloy catalyst with the molar ratio of Co/Ni = 1 showed the highest catalytic activity in hydrogenation reaction. It was observed that metallic Ni in Ni–Co nanoalloy was more negatively charged, which was favorable for improving the catalytic activity. In addition, the present catalyst was found to be extended for the efficient hydrogenation of the various biomass platform molecules, which showed comparable activity and selectivity with that of Pd/C catalyst. The XRD, TEM and XPS characterization of the spent nanoalloy catalyst indicated that the slight aggregation, crystallization, and surface oxidation happened in the consecutive catalytic recycles, resulting in the deactivation of catalyst. Finally, the reaction kinetics of d-glucose hydrogenation has been also investigated.

The influence of geographical distance on the decision-making behaviors of economic entities is an interesting topic in new economic geography. To investigate the impact of high-speed railway coverage on firms, we considered high-speed railway coverage in China as a quasi-natural experiment, empirically explored the relation between the staggered coverage of high-speed railways and corporate investment using the data of the stations of Chinese high-speed railways and listed firms from 2009 to 2017and DID regression. Furthermore, grouping tests were conducted according to corporate operational efficiency and financing constraints. In addition, whether the investment of non-SOEs and labor-intensive firms improved due to high-speed railway coverage was analyzed. Results corroborate that the investment in listed firms in cities covered by high-speed railways increases more significantly compared with cities that are not covered. Hence, high-speed railway coverage promoted capital factor liquidity, mitigated financing constraints, and increased corporate investment. Moreover, high-speed railway coverage is more likely to optimize the investment of the groups of firms that have higher asset liquidity, lower financing constraints, intensive labor, or private ownership.The conclusion provides critical insights for the decision-making behaviors of high-speed railway construction and constitutes theoretical basis for the promotion effect of transportation infrastructure construction on corporate investment.

Low-concentration photochemically induced dynamic nuclear polarization (LC-photo-CIDNP) has recently emerged as a powerful technology for the detection of aromatic amino acids and proteins in solution in the low-micromolar to nanomolar concentration range. LC-photo-CIDNP is typically carried out in the presence of high-power lasers, which are costly and maintenance-heavy. Here, we show that LC-photo-CIDNP can be performed with light-emitting diodes (LEDs), which are inexpensive and much less cumbersome than lasers, laser diodes, flash lamps, or other light sources. When nuclear magnetic resonance (NMR) sample concentration is within the low-micromolar to nanomolar range, as in LC-photo-CIDNP, replacement of lasers with LEDs leads to no losses in sensitivity. We also investigate the effect of optical-fiber thickness and compare excitation rate constants of an Ar ion laser (488 nm) and a 466 nm LED, taking LED emission bandwidths into account. In addition, importantly, we develop a novel pulse sequence ((13)C RASPRINT) to perform ultrarapid LC-photo-CIDNP data collection. Remarkably, (13)C RASPRINT leads to 4-fold savings in data collection time. The latter advance relies on the fact that photo-CID nuclear hyperpolarization does not suffer from the longitudinal-relaxation recovery requirements of conventional NMR. Finally, we combine both the above improvements, resulting in facile and rapid (≈16 s–2.5 min) collection of 1 and 2D NMR data on aromatic amino acids and proteins in solution at nanomolar to low micromolar concentration.

Low-concentration photochemically induced dynamic polarization (LC-photo-CIDNP) enables the spectroscopic analysis of biomolecules containing the amino acids Trp and Tyr at sub-micromolar concentration in solution. Typical LC-photo-CIDNP pulse sequences involving (1)H-(13)C correlation, however, perform well in the case of aromatic resonances but display a relatively poor signal-to-noise ratio for (13)C(α) and (13)C(β) resonances. Here, we develop a novel pulse sequence denoted as (13)C perturbation-recovered selective-pulse photo-CINDP enhanced reverse INEPT, or (13)C PRESPRINT, tailored to the LC-photo-CIDNP analysis of (1)H-(13)C(α) pairs. Our method, which is based on full suppression of 1-bond C(α)-C’ scalar-coupling evolution during the constant-time delay, results into a sensitivity improvement by a factor of 2. The enhanced performance of this pulse sequence enabled us to improve the analysis of LC-photo-CIDNP laser-power dependence at very low (200 nM) sample concentration. An improved theoretical model, developed to quantitatively describe this laser-power dependence, shows excellent agreement with our (13)C PRESPRINT experimental data.

A new room-temperature ionic liquid (RTIL) consisting of a polyoxometalate (POM) anion and tri-block copolymer (P123)-functionalized imidazolium cation was synthesized and utilized as a halogen-free catalyst for esterification. The catalytic system was a homogeneous solution at the beginning of the reaction, but an emulsion formed during the course of the reaction, and a progressive phase separation of the catalyst occurred at 0 °C over the course of 3 h. Dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier transform/infrared spectroscopy (FT/IR) have been used to characterize the properties of the IL during the reaction. The new IL catalyst was found to be highly efficient in the esterification of various alcohols and can be recycled at least seven times.

Two kinds of nickel nanoparticles (NPs) well-dispersed in aqueous phase have been conveniently prepared by reducing nickel(II) salt with hydrazine in the presence of amino group (−NH2) functionalized ionic liquids: 1-(3-aminopropyl)-2,3-dimethylimidazolium bromide ([AMMIM][Br]) and 1-(3-aminopropyl)-2,3-dimethylimidazolium acetate ([AMMIM][AcO]). The Ni(0) particles are composed of smaller ones which assemble in a blackberry-like shape. The Ni nanoparticles stabilized with [AMMIM][AcO] are much larger than those stabilized with [AMMIM][Br], and the former unexpectedly give much higher activity in the selective hydrogenation of citral and nitrobenzene (NB) in aqueous phase. The Ni(0) nanocatalysts dispersed in aqueous phase are stable enough to be reused at least five times without significant loss of catalytic activity and selectivity during the catalytic recycles.

The highly water-soluble palladium nanoparticles (NPs) were synthesized by using the amphiphilic poly(ethylene glycol)-functionalized dicationic imidazolium-based ionic liquid (C(12)Im-PEG IL) as a stabilizing agent. The aqueous dispersed palladium NPs in the range of 1.9 ± 0.3 nm were observed by transmission electron microscopy (TEM). The physicochemical properties of C(12)Im-PEG IL in aqueous phase have been characterized by electrical conductivity, surface tension and dynamic light scattering (DLS) measurements. It was demonstrated that the amphiphilic ionic liquid can form micelles above its critical micelle concentration (CMC) in aqueous solution and the micelles played a crucial role in stabilizing the palladium NPs and thus promoted catalytic hydrogenation. Furthermore, the dicationic ionic liquid can also act as a gemini surfactant and generated emulsion between hydrophobic substrates and the catalytic aqueous phase during the reaction. The aqueous dispersed palladium NPs showed efficient activity for the catalytic hydrogenation of various substrates under very mild conditions and the stabilizing Pd(0) nanoparticles (NPs) can be reused at least eight times with complete conservation of activity.

Nickel nanoparticles (NPs) well-dispersed in the aqueous phase were conveniently prepared by reducing nickel(II) salt with hydrazine in the presence of the functionalized ionic liquid 1-(3-aminopropyl)-2,3-dimethylimidazolium bromide. UV/Vis spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) show the presence of a weak interaction of the functionalized ionic liquid with Ni(II) and Ni(0) complexes. The face-centered cubic structure of the Ni(0) NPs was confirmed by X-ray diffraction (XRD) characterization. Transmission electron microscopy (TEM) images reveal that smaller Ni(0) particles of approximately 6-7 nm average diameter assemble to give larger, blackberry-shaped particles with an average diameter of around 35 nm. The Ni NPs were employed as highly efficient catalysts for the selective hydrogenation of C=C double bonds in the aqueous phase under mild reaction conditions (40-90 degrees C at 1.0-3.0 MPa), and the Ni(0) nanocatalysts in the aqueous phase are stable enough to be reused at least seven times without significant loss of catalytic activity during subsequent reuse cycles.