The 10 most-cited articles in The Journal of Physical Chemistry, 2017

In the light of the recent discovery that carbon-rich borocarbonitrides show electrocatalytic activity for generating hydrogen from water, we have synthesized nanocomposites by covalently cross-linking BC₇N with MoS₂ sheets to explore whether the HER activity can be significantly enhanced. In order to cross-link BC₇N and MoS₂ sheets, we have exploited the presence of different functional groups on the surfaces of BN (NH₂) and graphene (COOH) domains of the borocarbonitride, as quantitatively determined by FLOSS. We have thus obtained two nanocomposites differing in the location of the cross-linking and these are designated as BN/BCN–MoS₂ and G/BCN–MoS₂, depending on which domains in the borocarbonitride participate in cross-linking. These nanocomposites were characterized by various spectroscopic methods including fluorescence labeling and their electrochemical and photochemical HER activity investigated. The composite where the graphene domains are cross-linked to MoS₂ nanosheets, G/BCN–MoS₂ (1:2), exhibits outstanding electrochemical HER activity with an onset potential of −30 mV…

Changes in protein stability are commonly reported as changes in the melting temperature, ΔTM, or as changes in unfolding free energy at a particular temperature, ΔΔG°. Using data for 866 mutants from 16 proteins, we examine the relationship between ΔΔG° and ΔTM. A linear relationship is observed for each protein. The slopes of the plots of ΔTM vs ΔΔG° for different proteins scale as N–¹, where N is the number of residues in the protein. Thus, a given change in ΔG° causes a much larger change in TM for a small protein relative to the effect observed for a large protein. The analysis suggests that reasonable estimates of ΔΔG° for a mutant can be obtained by interpolating measured values of TM. The relationship between ΔΔG° and ΔTM has implications for the design and interpretation of high-throughput assays of protein–ligand binding. So-called thermal shift assays rely upon the increase in stability which results from ligand binding to the folded state. Quantitative relationships are derived which show that the observed thermal shift, ΔTM, scales as N–¹. Hence, thermal shift assays…

All-inorganic cesium lead halide (CsPbX₃; X = Cl, Br, and I) perovskite nanocubes (NCs) exhibit fascinating optical and optoelectronic properties. Postsynthesis anion exchange by mixing NCs with reactive anion species has emerged as a unique strategy to control their composition and band gap. For example, we started with CsPbBr₃ NCs with intense green emission, and then anion exchange with iodide ions yields CsPb(Br/I)₃ mixed halides and CsPbI₃ with emission color systematically varying in the green-red region. However, the internal structure of the anion-exchanged perovskite NCs is not probed. It is believed that the NCs possess a homogeneous alloyed composition, but X-ray diffraction pattern could not give evidence for such alloy formation, because the crystal structure also varies with anion composition. Here, we elucidate the internal heterostructure of anion-exchanged NCs using variable energy hard X-ray photoelectron spectroscopy. The results show that, in contrast to a homogeneous alloy, there is a significant inhomogeneity in the composition across the radius of NCs. The…

A new algorithm is developed to quantify the free-volume hole distribution and its evolution in coarse-grained molecular dynamics simulations of polymeric networks. This is achieved by analyzing the geometry of the network rather than a voxelized image of the structure to accurately and efficiently find and quantify free-volume hole distributions within large scale simulations of polymer networks. The free-volume holes are quantified by fitting the largest ellipsoids and spheres in the free-volumes between polymer chains. The free-volume hole distributions calculated from this algorithm are shown to be in excellent agreement with those measured from positron annihilation lifetime spectroscopy (PALS) experiments at different temperature and pressures. Based on the results predicted using this algorithm, an evolution model is proposed for the thermal behavior of an individual free-volume hole. This model is calibrated such that the average radius of free-volumes holes mimics the one predicted from the simulations. The model is then employed to predict the glass-transition temperature…

We report the thermal conductivity in the range from 7 to 300 K for methylammonium lead triiodide (MAPbI₃) perovskite in different stages of environmental degradation. The results showed that thermal conductivity of the degraded perovskite pellet quickly approached that of lead iodide rather than pure MAPbI₃, even while X-ray diffraction data of the degraded perovskite showed mostly peaks of the perovskite phase, alongside minor peaks from impurity phases belonging to the precursors and to an intermediate phase. For reference, a sample of pure lead iodide was also prepared and analyzed in the same way, and to our knowledge, thermal conductivity for lead iodide in the 7–300 K temperature range has not yet been published. The combination of thermal conductivity and materials characterization provides more detailed knowledge of the composition and structural changes of aged MAPbI₃ perovskite. Moreover, we demonstrate that a thermal percolation threshold can be achieved through mild aging while preserving most of the MAPbI₃ crystal structure.

In this article, we study the dewetting phenomenon of a polymer and carbon dioxide (CO₂) mixture on a planar surface by combining density functional theory and the string method. It is found that dewetting is a first-order discontinuous phase transition. When the pressure is lower than the completely dewetting pressure (Pd), CO₂ stabilizes the polymer films. The density fluctuation of the polymer decreases significantly with the inclusion of CO₂. When the pressure is above Pd, the polymer film is depleted far away from the surface, leaving a thick layer of pure CO₂ in the region near the surface. Pd is proportional to the surface energy strength. The CO₂ molecules enhance the density fluctuation of the polymer during the dewetting process. The polymer-rich phase at the triple point dewets to a CO₂-rich vapor film, as the CO₂-rich liquid film near the surface is metastable. These results have promising application in the industry of fabricating polymer films and antifouling polymers on attractive surfaces.