Single-stranded DNA oligonucleotides have unique, and in some cases sequence-specific molecular interactions with the surface of carbon nanotubes that remain the subject of fundamental study. In this work, we observe and analyze a generic, ionic strength-mediated phase transition exhibited by over 25 distinct oligonucleotides adsorbed to single-walled carbon nanotubes (SWCNTs) in colloidal suspension. The phase transition occurs as monovalent salts are used to modify the ionic strength from 500 mM to 1 mM, causing a reversible reduction in the fluorescence quantum yield by as much as 90%. The phase transition is only observable by fluorescence quenching within a window of pH and in the presence of dissolved O, but occurs independently of this optical quenching. The negatively charged phosphate backbone increases (decreases) the DNA surface coverage on an areal basis at high (low) ionic strength, and is well described by a two-state equilibrium model. The resulting quantitative model is able to describe and link, for the first time, the observed changes in optical properties of DNA-wrapped SWCNTs with ionic strength, pH, adsorbed O, and ascorbic acid. Cytosine nucleobases are shown to alter the adhesion of the DNA to SWCNTs through direct protonation from solution, decreasing the driving force for this phase transition. We show that the phase transition also changes the observed SWCNT corona phase, modulating the recognition of riboflavin. These results provide insight into the unique molecular interactions between DNA and the SWCNT surface, and have implications for molecular sensing, assembly, and nanoparticle separations.

Due to the critical role of stereochemistry in determining properties such as biological activity, as well as growing interest in sustainability, there is a strong impetus to develop catalytic and enantioselective methods for synthesis. Alkylboranes are an important family of target compounds, serving as useful intermediates, as well as endpoints (medicines such as Velcade™), in fields such as pharmaceutical science and organic chemistry. Because C–B bonds can be transformed into a wide variety of C–X bonds (e.g., X = C, N, O, and halogen) with stereochemical fidelity, the ability to generate enantioenriched alkylboranes in which boron is bound to a stereogenic carbon represents an extremely powerful tool in synthesis, providing access to an enormous array of valuable classes of chiral molecules, including alcohols, amines, and alkyl halides. Despite progress in recent years, there is still a need for more versatile methods for the catalytic asymmetric synthesis of enantioenriched alkylboranes. In this report, we describe a novel approach toward this objective, specifically, the use of a chiral nickel catalyst to achieve stereoconvergent couplings of readily available racemic α-haloboranes with organozinc reagents under mild conditions. We demonstrate that this method provides straightforward access to a diverse array of enantioenriched alkylboranes, and we highlight the remarkable utility of these compounds in synthesis.

Materials science has made progress in maximizing or minimizing the thermal conductivity of materials; however, the thermal effusivity—related to the product of conductivity and capacity—has received limited attention, despite its importance in the coupling of thermal energy to the environment. Herein, we design materials that maximize the thermal effusivity by impregnating copper and nickel foams with conformal, chemical-vapor-deposited graphene and octadecane as a phase change material. These materials are ideal for ambient energy harvesting in the form of what we call thermal resonators to generate persistent electrical power from thermal fluctuations over large ranges of frequencies. Theory and experiment demonstrate that the harvestable power for these devices is proportional to the thermal effusivity of the dominant thermal mass. To illustrate, we measure persistent energy harvesting from diurnal frequencies, extracting as high as 350 mV and 1.3 mW from approximately 10 °C diurnal temperature differences.

No abstract

No abstract