^(23)Na relaxometry: An overview of theory and applications

^(23)Na is a nuclear magnetic resonance(NMR)-active isotope with a nuclear spin quantum number of 3/2.^(23)Na relaxation phenomenon is at the core of ^(23)Na NMR measurement and analysis.Due to the dominance of quadrupolar interaction,the relaxation behavior of ^(23)Na is physically and mathematically more complex than that of a typical spin-1/2 isotope.In this review,we overview the semi-classical Redfield theory for deriving the formulations of ^(23)Na relaxation.We show that the relaxation behaviors of ^(23)Na can be quantitatively described by constructing the spectral density functions based on the second-order perturbation theory.In addition,we summarize the applications of ^(23)Na relaxometry in different research fields,including biomedicine,sodium ion batteries,and quantum information processing.Because sodium is an essential element in our body,food and industrial materials,the research on sodium by ^(23)Na NMR emerges as important future directions.The theoretical and practical understandings on ^(23)Na relaxation are the step stones for mastering advanced ^(23)Na NMR techniques.

Editorial

Porous media are ubiquitous and characterized by a wide range of distinct morphological and topographical properties,often difficult to access by conventional methods.As a unique technology,magnetic resonance has been applied extensively for several decades to non-invasively characterize the structure,interactions and dynamics of fluids in porous media,as well as these media themselves.It does this via spectroscopy,relaxometry,diffusion,or imaging modalities.This special issue is dedicated to an editorial and a selection of outstanding talks/posters presented at the 15th International Bologna Conference Magnetic Resonance in Porous Media(MRPM15).

Progress in electrolytes for rechargeable Li-based batteries and beyond

Owing to almost unmatched volumetric energy density, Li-based batteries have dominated the portable electronic industry for the past 20 years. Not only will that continue, but they are also now powering plug-in hybrid electric vehicles and zero-emission vehicles. There is impressive progress in the exploration of electrode materials for lithium-based batteries because the electrodes(mainly the cathode) are the limiting factors in terms of overall capacity inside a battery. However, more and more interests have been focused on the electrolytes, which determines the current(power) density, the time stability, the reliability of a battery and the formation of solid electrolyte interface. This review will introduce five types of electrolytes for room temperature Li-based batteries including 1) non-aqueous electrolytes, 2) aqueous solutions, 3)ionic liquids, 4) polymer electrolytes, and 5) hybrid electrolytes. Besides, electrolytes beyond lithium-based systems such as sodium-, magnesium-, calcium-, zinc-and aluminum-based batteries will also be briefly discussed.

Tuning the solution structure of electrolyte for optimal solid-electrolyte-interphase formation in high-voltage lithium metal batteries

The continuous reduction of electrolytes by Li metal leads to a poor lifespan of lithium metal batteries(LMBs). Low Coulombic efficiency(CE) and safety concern due to dendrite growth are the challenging issues for LMB electrolyte design. Novel electrolytes such as highly concentrated electrolytes(HCEs) have been proposed for improving interphase stability. However, this strategy is currently limited for high cost due to the use of a large amount of lithium salts as well as their high viscosity, reduced ion mobility, and poor wettability. In this work, we propose a new type of electrolyte having a moderate concentration. The electrolyte has the advantage of HCEs as the anion is preferentially reduced to form inorganic solidelectrolyte-interphase(SEI). Such optimization has been confirmed through combined spectroscopic and electrochemical characterizations and supported with the first-principle molecular dynamics simulation. We have shown the intrinsic connections between solution structure and their electrochemical stability. The 2.0 M LiDFOB/PC electrolyte, as predicted by our characterizations and simulations, allows stable charge–discharge of LNMO|Li cells at 5C for more than 1500 cycles. The 2.0 M electrolyte generates a dense layer of SEI containing fluoro-oxoborates, Li_(3)BO_(3), LiF, Li_(2)CO_(3), and some organic species effectively passivating the lithium metal, as confirmed by electron microscopy, X-ray photoelectron spectroscopy,and solid-state nuclear magnetic resonance.

Quasi-solid electrolyte membranes with percolated metal–organic frameworks for practical lithium-metal batteries

High-energy Li-metal batteries (LMBs) suffer from short cycle life and safety issues due to severe parasitic reactions and dendrite growth of Li metal anode (LMA) in liquid electrolytes [1–3].It is generally believed that replacing liquid electrolytes with solidstate electrolytes (SSEs) would be a feasible approach for practical LMBs [4,5]. Conventional SSEs including ceramic and polymer electrolytes have been studied for decades.

Consideration of transmembrane water exchange in pharmacokinetic model significantly improves the accuracy of DCE-MRI in estimating cellular density:A pilot study in glioblastoma multiforme

Transmembrane water exchange(TWE)including transcytolemmal water exchange and transvascular water exchange is involved in many in vivo measurements and makes different contributions to the measuring results.In this study,we focus on the potential influence of TWE on the cell density parameter,intracellular water mole fraction pi,derived by dynamic contrast enhanced-magnetic resonance imaging(DCE-MRI)which has been reported as a technique to characterize perfusion and vascularization of tissues,but its accuracy in measuring cell density(or interstitial space)has been questioned.Sixteen patients with glioblastoma multiforme(GBM)were enrolled since GBM shows strong intratumor heterogeneity in both cell density and TWE.All the subjects were collected with DCE-MRI and apparent diffusion coefficient(ADC)map.The latter was considered as a valid surrogate of cell density.Extended Tofts(eTofts)model considering TWE as infinitely large variables and shutter-speed model(SSM)considering TWE as finite ones were used to fit DCE-MRI data.Monte Carlo(MC)and finite difference(FD)methods were used to simulate the influence of TWE on DCE-MRI-derived pi and ADC,respectively.The eTofts model shows a significant overestimation of pi in comparison with SSM in GBM(P<0.001),which is in accordance with MC simulations,and this overestimation shows dependence on the intra-to-extracellular water exchange rate constant(kio).Significant negative correlations between ADC and SSM-derived pi were found in both voxel-wise analyses(t-test P<0.001,average r=-0.74)and inter-subject comparisons(r=-0.63,P=0.009).But no consistent voxel-wise correlations(P>0.05)and a weaker inter-subject negative correlation(r=-0.56,P=0.02)were found between ADC and eTofts-derived pi.Further experimental and FD results revealed that kio made a limited contribution to ADC values in the physiological kio range in GBM,supporting ADC as a valid biomarker of cell density.These results suggest that the DCE-MRI pharmacokinetic shutter-speed model could significantly improve its accuracy in cell density estimation because of the considering transmembrane water exchange.

Solid-state NMR in the field of drug delivery:State of the art and new perspectives

In the last decades,a variety of nuclear magnetic resonance(NMR)techniques have been applied with success in the field of advanced functional materials,including the important area of drug delivery.In such field,solid-state NMR(SSNMR)is an irreplaceable tool in the arsenal of characterization techniques,offering unique and comprehensive perspectives for the description of chemical structure,spatial connectivity and interfacial phenomena of solid dosage forms.This review focuses on the widespread applications of SSNMR in drug delivery field,an overview of selected case studies is provided,together with possible developments.

Solid-state NMR studies on the organic matrix of bone

Bone is a hierarchical architecture that consists of both inorganic and organic components.The organic components,including collagen and numerous non-collagenous biomolecules,are crucial for maintaining the mechanical strength and physiological functions of bone.The native structures of organic components and especially the mutual interactions between different components are important questions to be addressed.Among different analytical techniques,solid-state nuclear magnetic resonance(SSNMR)spectroscopy is a powerful tool to reveal the chemical and interactional information at an atomic level.Recent advancements of SSNMR technology and experimental protocols have brought great advances in understanding the molecular details in native bones.In this review,we summarize the progresses on the SSNMR studies of various organic components in the bone matrix.In the first part,we review the studies on collagen from four different aspects:(1)waterassociated molecular dynamics;(2)the intrahelical/interhelical interactions in collagen residues;(3)the interactions between collagen and citrate;and(4)the cross-linking between collagen and inorganic surface.In the second part,we review the studies on the non-protein biomolecules including sugar species,citrate,lipids,and nucleic acids.In the end,we propose an outlook of future directions for SSNMR investigations on bones.

Inhibition of furin by bone targeting superparamagnetic iron oxide nanoparticles alleviated breast cancer bone metastasis

Breast cancer bone metastasis poses significant challenge for therapeutic strategies.Inside the metastatic environment,osteoclasts and tumor cells interact synergistically to promote cancer progression.In this study,the proprotein convertase furin is targeted due to its critical roles in both tumor cell invasion and osteoclast function.Importantly,the furin inhibitor is specifically delivered by bone targeting superparamagnetic iron oxide(SPIO)nanoparticles.Our in vitro and in vivo data demonstrate that this system can effectively inhibit both osteoclastic bone resorption and breast cancer invastion,leading to alleviated osteolysis.Therefore,the bone targeting&furin inhibition nanoparticle system is a promising therapeutic and diagnostic strategy for breast cancer bone metastasis.

Efficient quasi-stationary charge transfer from quantum dots to acceptors physically-adsorbed in the ligand monolayer

Alkanoate-coated CdSe/CdS core/shell quantum dots(QDs)with near-unity photoluminescence(PL)quantum yield and monoexponential PL decay dynamics are applied for studying quasi-stationary charge transfer from photo-excited QDs to quinone derivatives physically-adsorbed within the ligand monolayer of a QD.Though PL quenching efficiency due to electron transfer can be up to>80%,transient PL and transient absorption spectra reveal that the charge transfer rate ranges from single-digit nanoseconds to sub-nanoseconds,which is~3 orders of magnitude slower than that of static charge transfer and〜2 orders of magnitude faster than that of collisional charge transfer.The physically-adsorbed acceptors can slowly(500-1,000 min dependent on the size of the quinone derivatives)desorb from the ligand monolayer after removal of the free acceptors.Contrary to collisional charge transfer,the efficiency of quasi-stationary charge transfer increases as the ligand length increases by providing additional adsorption compartments in the elongated hydrocarbon chain region.Because ligand monolayer commonly exists for a typical colloidal nanocrystal,the quasi-stationary charge transfer uncovered here would likely play an important role when colloidal nanocrystals are involved in photocatalysis,photovoltaic devices,and other applications related to photo-excitation.

The instability of a stable metal-organic framework in amino acid solutions

Metal–organic frameworks(MOFs)are being investigated as the potential materials for future drug delivery and gene therapy systems thanks to their tunable functionality and biocompatibility.However,the structure of MOFs could be altered in a biological environment or in a buffer solution.It is of great importance to evaluate the stability of MOFs and understand the degradation processes for the sake of the biomedical applications.In this work,we investigate the stability of UiO-66,a generally-perceived stable MOF,in different amino acid solutions.We find that UiO-66 loses crystallinity in relatively mild basic conditions(when pH≥9)in the presence of amino acids.The instability is more pronounced in the lysine and arginine solutions which have stronger basicity.It can be attributed to the accelerated ligand exchange of UiO-66 under basic conditions.With a combination of techniques,we show that the amino acids can replace the organic linkers and form zirconium-amino acid complexes.Our research reveals one possible mechanism of MOF degradation in biological environment,yet such degradability could be also an important designable property for MOFs in biomedical applications.