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Spectinomycin, an aminocyclitol antibiotic, is subject to inactivation by aminoglycoside modifying enzymes (AMEs) through adenylylation or phosphorylation of the 6-hydroxy group position. In this study, the effects of deoxygenation of the 2- and 6-hydroxy group positions on the spectinomycin actinamine ring are probed to evaluate their relationship to ribosomal binding and the antimicrobial activities of spectinomycin, semisynthetic aminomethyl spectinomycins (amSPCs), and spectinamides. To generate these analogs, an improved synthesis of 6-deoxyspectinomycin was developed using the Barton deoxygenation reaction. 6-Dehydrospectinamide was also synthesized from spectinamide 4 to evaluate the H-bond acceptor character on the C-6 position. All the synthesized analogs were tested for antibacterial activity against a panel of Gram (+) and Gram (-) pathogens, plus Mycobacterium tuberculosis. The molecular contribution of the 2- and 6-hydroxy group and the aryl functionalities of all analogs were examined by measuring inhibition of ribosomal translation and molecular dynamics experiments with MM/GBSA analysis. The results of this work indicate that the 6-hydroxy group, which is the primary target of AMEs, is a required motif for antimicrobial activity in current analogs. Removal of the 6-hydroxy group could be partially rescued by offsetting ribosomal binding contributions made by the aryl side chains found in the spectinamide and amSPCs. This study builds on the knowledge of the structure-activity relationships of spectinomycin analogs and is being used to aid the design of next-generation spectinomycins.

The kinetics and mechanisms of phase transitions that occur during lithiation of amorphous silicon thin films were extensively studied using electrochemical techniques and transmission electron microscopy. Measurements of current made while changing applied potentials at a constant rate (cyclic voltammograms) showed peaks that correspond to the formation of two amorphous Li-Si alloys with different stoichiometries. Peaks associated with these phase transitions were also observed in current-time measurements made in potentiostatic experiments. The times at which currents reached maxima were found to be independent of film thickness, suggesting that the phase transitions occur throughout the volume of the films. Analysis of current-time measurements using the Johnson-Mehl-Avrami-Kolmogorov method indicate that the transitions occur through a first-order nucleation and growth process. This conclusion is supported by cross-section transmission electron microscopy in which high-energy electron-beam-induced sputtering of lithium led to contrast between the parent and product phases. In contrast with other studies, the polyamorphic amorphous-to-amorphous first-order phase transitions observed in this study are driven by changes in composition rather than changes in pressure or temperature. The potentiostatic techniques employed in this study can be used to characterize the nature and kinetics of phase transitions that occur in other electrode materials for lithium-ion batteries.

RuO₂ films can serve as high-performance electrodes for thin film lithium-ion batteries due to their large volumetric charge capacity, low rate sensitivity and excellent cyclability. Unlike other electrode materials, RuO₂ films also do not require high temperature processing, making them suitable for integration with low-power CMOS circuits and for fabrication on flexible membranes. To determine the mechanisms through which Li is reversibly stored in RuO₂ films, detailed characterization studies of sputtered thin films were carried out; galvanostatic and potentiostatic intermittent titration and cyclic voltammetry studies were coupled with ex situ selected area electron diffraction, X-ray photoelectron and Raman spectroscopy, optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy and in situ electrochemical impedance spectroscopy. During lithiation, amorphous RuO₂ is transformed to amorphous LixRuO₂ through an alloying reaction and this is followed by a reversible side reaction to form an SEI layer. LixRuO₂ then undergoes a conversion reaction to form a mixture of nanosized Ru and Li₂O crystals, and finally at low voltages Li is inserted into the Ru/Li₂O mixture. These reactions occur in a different sequence during delithiation and a large overpotential is required to reverse the conversion reaction, leading to a large energy loss during cycling. It is argued that this hysteretic behavior is associated with slow diffusive processes required for the conversion reactions. The methodology developed in this study can also be applied to other candidate thin film electrode materials and learnings from studies of thin films can be applied to more complex powder-based electrodes used in bulk batteries.

The mechanisms and kinetics of lithiation and delithiation of amorphous silicon were investigated using potentiostatic techniques and thin films of different thickness, with a focus on the initial lithiation process that occurs in the first cycle. In potentiostatic tests, distinct kinks were observed in the current vs. time curves, and the time at which the kink occurred increased for thicker films. This behavior can be explained using a model in which a sharp interface between an amorphous LixSi phase and Li-saturated amorphous Si propagates through the film. Using this model, the rate-limiting process was determined to be diffusion of Li in the LixSi phase rather than reaction at the lithiation front. The Li diffusivity in the lithiated phase was determined to be in the 10−13 cm2/s range, independent of film thickness above 135 nm. The thin-film potentiostatic technique used in this study should prove useful in investigation of the mechanisms and rate parameters for other phase transitions that occur during lithiation of silicon and for kinetic studies of other electrode materials. ©2018 The Author(s)