Differential Shift Research Articles

Homonuclear J-coupling spectroscopy using J-synchronized echo detection

In the strong coupling regime with J-coupling much larger than chemical shift differences, J-coupling spectroscopy enables spectral identification of molecules even when conventional NMR fails. While this classically required the presence of a heteronucleus, we recently showed that J-coupling spectra can be acquired in many homonuclear systems using spin-lock induced crossing (SLIC). Here, we present an alternative method using a spin echo train in lieu of a spin-locking SLIC pulse, which has a number of advantages. In particular, spin echo acquisition within the pulse train enables simultaneous collection of time and frequency data. The resulting 2D spectrum can be used to study dynamic spin evolution, and the time domain data can be averaged to create a 1D J-coupling spectrum with increased signal-to-noise ratio.

Niche and geographical expansions of North American trees and tall shrubs in Europe

AbstractAimWe examine how the climatic niches of North American tree and tall‐shrub species change after their introduction to Europe and how these shifts affect their potential geographical distributions in the new range. We ask whether patterns of niche shifts differ among species confined to different biomes in North America and whether the expansions of species' climatic niches and potential distribution ranges are related to their residence time in Europe and native range size.LocationNorth America and Europe.TaxonVascular plants (trees and shrubs).MethodsWe used principal component analysis to quantify post‐introduction shifts in climatic niches of 59 species native to North America and alien to Europe. We modelled the expansions of their potential geographical ranges using Maxent. Differences in niche shifts and geographical expansion among species introduced from different biomes were tested using the Kruskal–Wallis test. Spearman correlation was used to relate niche and geographical expansions to residence time and native range size.ResultsAlien trees and tall shrubs introduced from North America to Europe exhibited greater niche stability and unfilling than niche expansion, except for the species from Coastal Plain forests. The latter species showed the largest niche and geographical expansions. Species with a small native range in North America introduced to Europe long ago were more likely to expand to new climatic conditions and geographical areas.Main conclusionsWe show that (i) most North American tree and tall‐shrub species introduced to Europe still do not occupy all areas with suitable climatic conditions in their secondary distribution range, but species from Coastal Plain forests tend to expand into areas with climates not found in their native ranges; (ii) the potential of the studied species to spread in Europe depends on the climatic conditions in the biome of origin, the size of their native range and the time since the first introduction.

Methods for Determination of Absolute Configurations of Chiral Diols by THENA Ester and NMR Shift Difference

AbstractDetermination of the absolute configuration of chiral secondary diols by chiral derivatizing agent (CDA) and NMR shift difference is of great challenge due to the complication from the interference of the aromatic anisotropic shielding effect of the two CDAs in close proximity. In this work, tetrahydro-1,4-epoxynaphthalene-1-carboxylic acid (THENA) was introduced as an alternative CDA for diols to overcome such complexity. Since the deshielding effect of THENA is weaker than the shielding effect of other CDAs, THENA would allow the direct analysis of the chemical shift difference in determining the absolute configuration of the chiral diols. In addition, an analytical method based on Riguera’s model could also be used to confirm the assignment. With a good agreement between the assigned configuration based on both analytical models, the absolute configuration of the chiral diols could be assigned with reliability.

Angular shift of Autler–Townes doublet from multi-photon ionization of molecules by circularly polarized laser pulses

We theoretically study the Autler–Townes (AT) splitting of a molecule in a circularly polarized laser pulse by solving the time-dependent Schrödinger equation. We find that the AT doublet in the photoelectron momentum distribution reveals different angular shifts with respect to the molecular axis direction. Using an improved strong-field approximation method, we reproduce the difference of the angular shifts for the AT doublet, which originates from the interference of the electron wave packets released from the ground and excited states of the molecule. By tracing the time evolution of the electron density distribution along the molecular axis, we find that electron delocalization on the two nuclei of the molecule plays a significant role in the formation of photoelectron angular distribution for the AT doublet, which corresponds to a phase jump of π for the phase difference between the ground and excited states.

Terahertz metasurfaces based on bound states in the continuum (BIC) for high-sensitivity refractive index sensing

Terahertz metasurface has attracted much attention in the field of label-free refractive index sensing due to its special fingerprint spectrum. Combining the special electromagnetic response of the metasurface and the ultra-high Q property of the quasi-BIC, a novel high-sensitivity THz sensor is proposed based on symmetry-protected BIC. The breaking of the mirror symmetry means that the resulting dipole displacement excites the surface resonance, and the BIC state is verified by satisfying the quality factor of the inverse square law. It is verified that the oblique incident wave vector can excite the BIC to the quasi-BIC. And the two different asymmetric parameters (displacement S and incident angle θ) of generating quasi-BIC can influence or even counteract each other. In order to increase the accuracy of the detection results, two different sensing parameters are used to detect the same analyte at the same time. The sensitivity of frequency shift difference and amplitude difference is as high as 11.17 GHz/RIU and 0.1766 /RIU, respectively. This work not only provides new ideas for the design of high-sensitivity sensors, but also has potential applications in the field of low-concentration sensing.

19F magnetic resonance probes for detecting formaldehyde

Herein we report two separate 19F magnetic resonance (MR) probes responsive towards formaldehyde. Both agents were synthesized in a single step via aminoallylation of either 4-fluorobenzaldehyde (1FA) or 4-(trifluoromethyl)benzaldehyde (3FA) with ammonia and allylboronic acid pinacol ester. Condensation of the resulting homoallylic amines 1FA and 3FA with formaldehyde, followed by a 2-aza-Cope rearrangement and subsequent hydrolysis affords 4-fluorobenzaldehyde and 4-(trifluoromethyl)benzaldehyde, respectively. In the case of 1FA, this transformation is evidenced by a concomitant downfield shift in the 19F MR signal from −115 ppm to −103 ppm. Further, this transformation is selective towards formaldehyde over other reactive carbonyl species. While 3FA exhibits similar selectivity towards formaldehyde, this more sensitive probe is limited by the small chemical shift difference (0.7 ppm) following its activation.

Determining the atom number from detection noise in a one-dimensional optical lattice clock

In this paper, we demonstrate in situ synchronous frequency comparison between distinct regions in a one-dimensional optical lattice. The synchronous comparison instability is well below the Dick limit and agrees with the limit induced by atomic detection noise. The absolute atom number is extracted from the synchronous comparison instability with an uncertainty below 3%. Surpassing the performance of absorption imaging, this method provides a way to directly and precisely determine the absolute atom number from detection noise. Taking advantage of the inhomogeneous density distribution over the whole lattice, the density shift can also be conveniently measured by this synchronous frequency comparison method. Inconsistent with the expectation of the linear relationship between density shift and atom number difference, nonlinearity is observed, indicating that the assumption of an identical density shift coefficient over the whole lattice is not always safe.

31 P MRSI at 7 T enables high-resolution volumetric mapping of the intracellular magnesium ion content in human lower leg muscles.

The non-invasive determination of the free magnesium ion concentration ([Mg2+free ]) using 31 P MRSI in vivo is of interest in research on various pathologies, e.g. diabetes. The purpose of this study was to demonstrate the potential of 31 P MRSI at 7 T to enable volumetric, high-resolution mapping of [Mg2+free ]. 3D 31 P MRSI datasets from the lower leg of three healthy volunteers were acquired at B0 = 7 T with a nominal spatial resolution of (8× 8× 16)mm3 in 56 min. Volumetric [Mg2+free ] maps were calculated based on the quantified local chemical shift difference between the α- and β-resonance of adenosine triphosphate (ATP) considering also local pH values. Mean [Mg2+free ] values from three different muscle groups were compared. To demonstrate the potential of reducing the measurement time, the analysis was repeated on the acquired MRSI data retrospectively reconstructed with fewer averages. The generated [Mg2+free ] maps revealed local differences, and mean [Mg2+free ] values of (1.08 ± 0.03)mM were found in the tibialis anterior, (0.91 ± 0.04)mM in the soleus and (0.98 ± 0.03)mM in the gastrocnemius medialis. The time-reduced 28-min scan resulted in comparable [Mg2+free ] maps, and mean values being in agreement with the values from the 56-min scan. 31 P MRSI at 7 T enables volumetric, high-resolution mapping of free magnesium ion content in human lower leg muscles. The measurement time of the 31 P MRSI acquisition can be reduced to 28 min, opening the potential to apply volumetric [Mg2+free ] mapping for the investigation of pathologies with altered magnesium homeostasis.

Cue selection in the perception of pitch in music and speech

Spectral shape affects pitch perception; sounds with more high energy harmonics sound higher than sounds with low energy in higher harmonics. Flatter spectral slope corresponds to "tenser" voices while steeper spectral slope correlates to "breathier" voices in speech. In string instruments, the spectral slope differentiates sul ponticello and sul tasto. Listeners were found to integrate spectral slope cues in pitch perception in speech; however, work on music focused on cross-instrument differences, glossing over cue integration within instruments with fixed-formant frequencies. Furthermore, spectral cues and F0 co-vary in human pitch production, but are largely independent in instrumental music. It remains unclear whether music processing is as integrative as speech processing. In this study, listeners were given either speech or violin stimuli with identical pitch contour pairs, and were asked to decide whether the second contour was higher or lower in pitch compared to the first. The spectral slope of each sound was manipulated to include all combinations of “breathier”/“sul tasto” and “tenser”/“sul ponticello” sounding pairs. Results show that listeners integrate spectral slope cues in pitch perception in speech and violin stimuli similarly, with similar categoricity and shift. Overall, listeners with higher musicality have more categorical responses but no differences in shift.

Isotopic Substitution Reveals the Importance of Aluminate Diffusion Dynamics in Gibbsite (Al(OH)3) Crystallization from Alkaline Aqueous Solution

Understanding molecular-scale factors governing the precipitation of aluminum hydroxides, such as gibbsite, under alkaline conditions is important for the formation of laterite deposits, as well as aluminum processing. However, mechanisms enabling tetrahedral aluminate ions to assemble into octahedral sites of the gibbsite lattice remain unclear. Formation of oligomeric complexes has been hypothesized as a critical intermediate step. Here, we report a study of gibbsite solubility in highly alkaline solutions using deuterium substitution to probe equilibrium and kinetic factors that could affect oligomeric intermediate formation, including the reactivity and the diffusivity of aluminate ions. When substituting sodium hydroxide with sodium deuteroxide, solution analysis shows a nearly 40% and 50% increase in gibbsite solubility in 2.4 and 3.3 mol·kg–1 total sodium solutions, respectively. Raman spectroscopy indicated that monomeric aluminate ions are the predominant species in solution irrespective of deuteration. However, both 27Al and 23Na nuclear magnetic resonance (NMR) spectroscopy revealed significant differences in chemical shifts in deuterated solutions, and analysis of 1H, 23Na, and 27Al diffusion coefficients with pulsed-field gradient, stimulated echo NMR spectroscopy shows a decrease in ion diffusivity with increasing total deuterium in solution, consistent with the notion of increasing strength in the hydrogen/deuterium bonding network. Because the relative change in 1H diffusion coefficients are commensurate with the difference in apparent solubility constants, there is evidence for an oligomeric intermediate whose steady-state concentration is maintained by the collision frequency of aluminate ions.

Natural History and Morphology of Crotalus ehecatl (Serpentes: Viperidae)

The Tehuantepec Isthmus rattlesnake (Crotalus ehecatl) is a poorly known species endemic to Mexico. We describe its diet, morphological variation, life history traits and activity patterns based on data from field encounters, museum specimens, and published data. Its diet consists almost exclusively of mammals, with no detected ontogenetic shift or sexual differences in prey type, and with feeding happening mainly in the rainy season. As the first detailed study on the feeding ecology of C. ehecatl, it adds six new prey species and suggests a homogeneous diet among age classes and sexes, but not among seasons. Crotalus ehecatl does not present sexual dimorphism in snout-vent length, head length or total length, but males have significantly longer tails than females, possess fewer ventral scales, more subcaudal and anterior intersupraocular scales. Crotalus ehecatl showed a unimodal activity pattern with peak activity in the summer, with crepuscular and nocturnal activity during the warmer months, and diurnal activity during the cooler months. The timing of C. ehecatl reproductive events, is similar to other rattlesnakes from temperate and tropical zones. Additional studies on this and related species would help to understand how the ecology of Neotropical rattlesnakes differs from rattlesnakes of more temperate zones.

Bound nucleotide can control the dynamic architecture of monomeric actin

Polymerization of actin into cytoskeletal filaments is coupled to its bound adenine nucleotides. The mechanism by which nucleotide modulates actin functions has not been evident from analyses of ATP- and ADP-bound crystal structures of the actin monomer. We report that NMR chemical shift differences between the two forms are globally distributed. Furthermore, microsecond–millisecond motions are spread throughout the molecule in the ATP form, but largely confined to subdomains 1 and 2, and the nucleotide binding site in the ADP form. Through these motions, the ATP- and ADP-bound forms sample different high-energy conformations. A deafness-causing, fast-nucleating actin mutant populates the high-energy conformer of ATP-actin more than the wild-type protein, suggesting that this conformer may be on the pathway to nucleation. Together, the data suggest a model in which differential sampling of a nucleation-compatible form of the actin monomer may contribute to control of actin filament dynamics by nucleotide.

13C NMR investigations and order parameters of rod-like molecules with terminal phenyl and thiophene rings in mesogenic core✰

Rod-like mesogens with the rigid core constituted by a combination of phenyl and thiophene moieties reveal interesting orientational ordering behavior. In this article, four rod-like mesogens constructed with a terminal alkoxy chain on only one side of the mesogenic core with the other end terminated with either a phenyl or thiophene ring have been investigated using 13C NMR spectroscopy. The mesogen with the terphenyl moiety in the core exhibited polymesomorphism with nematic, smectic C, and smectic I mesophases with very high clearing temperatures. The replacement of terphenyl with terthiophene moiety resulted in suppression of polymesomorphism, with only nematic mesophase being observed. Mesogens with single terminal thiophene connected to two phenyl rings in the core also showed only the nematic mesophase for both the possibilities of linking the core to the thiophene ring at the 2- and 3- positions. One- and two- dimensional 13C NMR spectra have been obtained in the mesophases from which the alignment induced chemical shifts of the ring carbons and 13C-1H dipolar couplings, as well as the local order parameters, have been obtained. The considerable difference in 13C chemical shifts and the 13C-1H dipolar couplings of thiophene ring with change in position of the linking unit is attributed to the difference in the order parameters of the thiophene moiety between the two cases. The data obtained on the ordering of phenyl and thiophene rings in the core units offered information into the effect of replacing the phenyl ring with the thiophene ring. So also, the change of position of the link to the thiophene moiety provided important insights into the orientational behavior in the liquid crystalline phase and on the molecular structure.

Review of Ponsonnet (2020): Difference and Repetition in Language Shift to a Creole. The Expression of Emotions

Review of Ponsonnet (2020): Difference and Repetition in Language Shift to a Creole. The Expression of Emotions

Effect of substrate and substrate temperature on the deposition of MoS2 by radio frequency magnetron sputtering

Radio frequency magnetron sputtering is considered as one of the efficient methods to develop large area homogeneous 2D MoS2 on quartz substrates. The application of MoS2 in products, such as transistors, solar cells, photodetectors, chemical sensors, valleytronics, and spintronic devices demands the deposition on a wide variety of substrates. Here, we are examining whether a one step preparation method of sputtering of the molybdenum metal in a sulfur sufficient environment will provide a universal strategy to develop 2D MoS2 on any substrates. The dependence of the deposition on substrate temperature is also studied. On all of the substrates we used (quartz, c-plane sapphire, p-type silicon, and silicon dioxide), uniform coating of 2D MoS2 was confirmed with the presence of E12g and A1g, the Raman signature peaks. Both the Raman shift difference A1g–E12g and atomic force microscopy helped in determining the varying thicknesses of the samples. Hexalayer to bilayer MoS2 were formed when the substrate temperature was increased from 600 to 800 °C, confirming that a higher substrate temperature is needed for producing thinner samples. Absorbance spectra of the samples sputtered on quartz displayed the A, B and convoluted C and D excitonic peaks of 2H-MoS2. Only the samples prepared at higher substrate temperatures yielded a photoluminescence spectrum indicating the formation of trilayer and bilayer MoS2. Optical images and AFM measurements revealed a uniform coating over the entire substrate area. Thus, the one step method of simultaneous sputtering and evaporation proved to be a universal method for developing MoS2 thin films on any kind of substrates.

Alpine plants are on the move: Quantifying distribution shifts of Australian alpine plants through time

AbstractAimAlpine plant species’ distributions are thought to have been shifting to higher elevations in response to climate change. By moving upslope, species can occupy cooler and more suitable environments as climate change warms their current ranges. Despite evidence of upslope migration in the northern hemisphere, there is limited evidence for elevational shifts in southern hemisphere plants. Our study aimed to determine if alpine plants in Australia have migrated upslope in the last 2 to 6 decades.LocationKosciuszko National Park, NSW, Australia.MethodsWe collated historic occurrence data for 36 Australian alpine plant species from herbarium specimens and historic field observations and combined these historic data with modern occurrence data collected in the field.ResultsEleven of the thirty‐six species had shifted upslope in mean elevation and four species showed downslope elevational shifts. The rate of change for upslope shifts varied between 4 and 10 m per year and the rate of change for most downslope shifts was between 4 and 8 m per year, with one species shifting downslope at a high rate of 18 m per year. Additionally, some species showed shifts upward in their upper range edge and/or upward or downward shifts in their lower range edge. Five species also showed range contractions in the difference between their lower and upper range edges over time, while two showed range expansions. We found no significant differences in elevational shifts through time among herbaceous dicotyledons, herbaceous monocotyledons and shrubs.Main ConclusionsPlant elevational shifts are occurring rapidly in the Australian alpine zone. This may allow species to persist under climate change. However, if current warming trends continue, several species within the Australian alpine zone will likely run out of suitable habitat within a century.

NMR assignment of non-modified tRNAIle from Escherichia coli

tRNAs are L-shaped RNA molecules of ~ 80 nucleotides that are responsible for decoding the mRNA and for the incorporation of the correct amino acid into the growing peptidyl-chain at the ribosome. They occur in all kingdoms of life and both their functions, and their structure are highly conserved. The L-shaped tertiary structure is based on a cloverleaf-like secondary structure that consists of four base paired stems connected by three to four loops. The anticodon base triplet, which is complementary to the sequence of the mRNA, resides in the anticodon loop whereas the amino acid is attached to the sequence CCA at the 3′-terminus of the molecule. tRNAs exhibit very stable secondary and tertiary structures and contain up to 10% modified nucleotides. However, their structure and function can also be maintained in the absence of nucleotide modifications. Here, we present the assignments of nucleobase resonances of the non-modified 77 nt tRNAIle from the gram-negative bacterium Escherichia coli. We obtained assignments for all imino resonances visible in the spectra of the tRNA as well as for additional exchangeable and non-exchangeable protons and for heteronuclei of the nucleobases. Based on these assignments we could determine the chemical shift differences between modified and non-modified tRNAIle as a first step towards the analysis of the effect of nucleotide modifications on tRNA’s structure and dynamics.

Pulse induced resonance with angular dependent total enhancement of multi-dimensional solid-state NMR correlation spectra

We demonstrate a new resonance condition that obeys the relation Δδ=nνR/2, where Δδ is the chemical shift difference between two homonuclear-coupled spins, νR is the magic-angle spinning speed and n is an integer. This modulation on the rotational resonance recoupling condition is obtained by the application of rotor-synchronous 1H pulses when at least one proton is dipolar-coupled to one of the homonuclear spins. We suggest a new experimental scheme entitled ‘pulse induced resonance with angular dependent total enhancement’ (PIRATE) that can enhance proton-driven spin diffusion by the application of a single 1H pulse every rotor period. Experimental evidence is demonstrated on the two carbon spins of glycine and on the Y21M mutant of fd bacteriophage virus. Numerical simulations reveal the existence of the resonances and report on the important interactions governing these phenomena.

486 Patients Who Die, Then Talk: Outcomes in Patients with Traumatic Extra-Arachnoid Subdural Hematoma

INTRODUCTION: A critical step in the management of TBI patients is evaluating for lesions that require urgent surgical evacuation. Amongst the most common of these surgical lesions are subdural hematomas (SDH). A subset of patients with SDH have purely extra-arachnoid lesions (EASDH). These patients present in similarly grave neurologic condition as the general SDH hematoma population. METHODS: This is a single-center prospective cohort of patients presenting with EASDH from January 2015 to December 2016. The senior author, an neurosurgical trauma subspecialist, made the determination of EASDH versus mixed subarachnoid and SDH based on the patient’s CT scan. Controls from the TRACK-TBI database who had SDH as well as either subarachnoid or other parenchymal injuries were included. RESULTS: A total of 49 patients with EASDH were compared to 246 controls. There were no significant differences in baseline demographics between the groups. A significant difference in midline shift was noted. After controlling for midline shift, EASDH patients had 5.68 greater odds of having a better 2-week GOS-E. The expected two-week mortality, as predicted by the CRASH model, was similar between the two groups, but the EASDH group fared much better than the predicted mortality, at 10%. CONCLUSION: Patients with EASDH represent a unique clinical entity. They are often elderly and have large lesions with significant midline shift. However, patients often have a dramatic improvement.

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid