Lithium-ion batteries (LIBs) containing silicon negative electrodes have been the subject of much recent investigation because of the extremely large gravimetric and volumetric capacity of silicon. The crystalline-to-amorphous phase transition that occurs on electrochemical Li insertion into crystalline Si, during the first discharge, hinders attempts to link structure in these systems with electrochemical performance. We apply a combination of static, in situ and magic angle sample spinning, ex situ (7)Li nuclear magnetic resonance (NMR) studies to investigate the changes in local structure that occur in an actual working LIB. The first discharge occurs via the formation of isolated Si atoms and smaller Si-Si clusters embedded in a Li matrix; the latter are broken apart at the end of the discharge, forming isolated Si atoms. A spontaneous reaction of the lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge and potential capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder.

Lithium metal has the highest volumetric and gravimetric energy density of all negative-electrode materials when used as an electrode material in a lithium rechargeable battery. However, the formation of lithium dendrites and/or 'moss' on the metal electrode surface can lead to short circuits following several electrochemical charge-discharge cycles, particularly at high rates, rendering this class of batteries potentially unsafe and unusable owing to the risk of fire and explosion. Many recent investigations have focused on the development of methods to prevent moss/dendrite formation. In parallel, it is important to quantify Li-moss formation, to identify the conditions under which it forms. Although optical and electron microscopy can visually monitor the morphology of the lithium-electrode surface and hence the moss formation, such methods are not well suited for quantitative studies. Here we report the use of in situ NMR spectroscopy, to provide time-resolved, quantitative information about the nature of the metallic lithium deposited on lithium-metal electrodes.

The acquisition of ideal powder line shapes remains a recurring challenge in solid-state wideline nuclear magnetic resonance (NMR). Certain species, particularly quadrupolar spins in sites associated with large electric field gradients, are difficult to excite uniformly and with good efficiencies. This paper discusses some of the opportunities that arise upon departing from standard spin-echo excitation approaches and switching to echo sequences that use low-power, frequency-swept radio frequency (rf) pulses instead. The reduced powers demanded by such swept rf fields allow one to excite spins in different crystallites efficiently and with orientation-independent pulse angles, while the large bandwidths of interest that are needed by the measurement can be covered, thanks to the use of broadband frequency sweeps. The fact that the spins' evolution and ensuing dephasing starts at the beginning of such rf manipulation calls for the use of spin-echo sequences; a number of alternatives capable of providing the desired line shapes both in the frequency and in the time domains are introduced and experimentally demonstrated. Sensitivity- and lineshape-wise these experiments are competitive vis-a-vis current implementations of wideline quadrupolar NMR based on hard rf pulses; additional opportunities that may derive from these ideas are also briefly discussed.

The synthesis of life saving drug molecules in a cost-effective and environmentally benign pathway is of paramount significance. We present an environment friendly protocol to prepare core moieties of top selling drug molecules such as boscalid and telmisartan using Suzuki−Miyaura coupling conditions. In contrast to the traditional synthesis of these pharmaceutically important molecules, we have accomplished a graphite oxide (GO) supported palladium nanoparticles (PdNPs) based catalyst which quantitatively produced these core biaryl moieties of top selling drug molecules in a recyclable way. The catalytic activity remained unchanged even after 16 successive catalytic cycles without incorporating any palladium metal impurity in the pharmaceutically significant organic products. A detailed study including IR spectroscopy, solid state NMR spectroscopy, X-ray photoelectron spectroscopy, and DFT calculation was employed to understand the role of solid support on the nondecaying recycling ability of the catalyst during the Suzuki−Miyaura coupling reaction. The study indicates a strong chemical interaction of the different functionalities present in the GO, with the palladium centers which is primarily responsible for such sustained catalytic activity during the consecutive Suzuki−Miyaura coupling cycles.

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Polymer-based nanosystems have been extensively explored either as therapeutic agents or bioimaging probes in the cancer diagnosis. However, very few systems are successful in combining both therapy and imaging. Herein, a new class of norbornene based copolymer, Nor-Dox-Cob-Btn is proposed as potential theranostics agent for tumor diagonosis. The copolymer (Nor-Dox-Cob-Btn) with doxorubicin, cobalt carbonyl complex, and biotin as pendent functionalized group is synthesized, using ring opening metathesis polymerization (ROMP). The cell viability, drug release, NMR relaxation, NMR 1-D image and Epi fluorescence microscopy studies on Nor-Dox-Cob-Btn nanocarrier are thoroughly studied. The effect of nanocarrier on transverse relaxation (T 2 ) of water molecule and NMR 1-D image suggest that the nanocarrier has the potential application in magnetic resonance imaging agent. The T 2 -weighted MRI agent, along with biotin receptor assisted pH responsive doxorubicin release from Nor-Dox-Cob-Btn, prompts us to envision this newly developed polymer for future application in theranostics. ■ INTRODUCTIONDoxorubicin is a well-known frontline anticancer drug, however due to cardiotoxic effect of doxorubicin, it is always necessary to protect this drug from other healthy cells and tissues inside body. 1 There are several different models available to guide this drug more precisely into the tumor cells, for example, polymer, nanoparticle, liposome. 3 However, polymer based delivery vehicle emerged as a superior over all other existing systems due to its pharmacokinetics and biodistribution profiles via the enhanced permeability as well as retention (EPR) effect. 4 These systems also help to maintain the therapeutic concentration over long periods of time. 2−4 There are mainly two approaches to deliver drugs site-specifically to the tumor cells, namely, covalent and non covalent approaches. 5,8 Drugs encapsulated inside the polymeric aggregates can be placed inside the body for using it localized delivery following the burst mechanism. 3,5,6,8 On contrast, in stimuli responsive covalently attached drug (e.g., pH sensitive, light sensitive, etc.) to the polymeric system gives the sustained release of drug to the tumor cells over long period. 11 There are several reports available in literature based on the pH sensitivity linker, for example hydrazone, ester, and amide, in which hydrazone linker is the most commonly used for the sustained release. 11 The medical application of polymeric nanocarrier has enormous potential to improve the therapeutic efficacy, particularly in cancer therapy. The attachment of folate or biotin functionality to the same polymeric prodrug makes the system more site-specific via receptor mediated drug delivery. 5,7,9 This also improves the survival rates of healthy tissues and cells. The attachment of magnetic particles helps the drug-carrier system further, as this magnetic particle can be utilized as MR imaging agent. 11 Magnetic as well as drug containing polymersomes have a great potential for both ...

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Thermoresponsive polymers exhibit coil-globule transition in aqueous solution where the polymer undergoes transition from the coil-like morphology to a globular form with the change of temperature. Such transitions also reflect changes in the solvent dynamics captured by various spectroscopic methods. In this work, we construct a phenomenological model to capture the dynamics of the NMR relaxation of water molecules of an aqueous solution of thermoresponsive polymers that are known to form hydrogen bonds with the solvent water molecules. The model relies on the behavior of the polymer-solvent hydrogen bonds and the sharing of rotational kinetic energy of water molecules in the vicinity of the polymer chain and the bulk. This is shown to provide a direct estimate of the fractional change of the polymer-water hydrogen bonds across lower critical solution temperature from NMR relaxation data of solvent water along with a reliable estimate of the transition temperature. In addition, it also provides a measure of the dispersion of the strengths of these hydrogen bonds. We exemplify the validity of this model by successfully fitting the experimental data to show that the extracted parameters provide significant insights into the role played by the hydrogen bonds in the process. The possible extension of this model to solvents that form no hydrogen bonds with the polymers is also discussed.