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The reversible formation of hydrogen bonds is a ubiquitous mechanism for controlling molecular assembly in biological systems. However, achieving predictable reversibility in artificial two-dimensional (2D) materials remains a significant challenge. Here, we use an external electric field (EEF) at the solid/liquid interface to trigger the switching of H-bond-linked 2D networks using a scanning tunneling microscope. Assisted by density functional theory and molecular dynamics simulations, we systematically vary the molecule-to-molecule interactions, i.e., the hydrogen-bonding strength, as well as the molecule-to-substrate interactions to analyze the EEF switching effect. By tuning the building block’s hydrogen-bonding ability (carboxylic acids vs aldehydes) and substrate nature and charge (graphite, graphene/Cu, graphene/SiO2), we induce or freeze the switching properties and control the final polymorphic output in the 2D network. Our results indicate that the switching ability is not inherent to any particular building block but instead relies on a synergistic combination of the relative adsorbate/adsorbate and absorbate/substrate energetic contributions under surface polarization. Furthermore, we describe the dynamics of the switching mechanism based on the rotation of carboxylic groups and proton exchange, which generate the polarizable species that are influenced by the EEF. This work provides insights into the design and control of reversible molecular assembly in 2D materials, with potential applications in a wide range of fields, including sensors and electronics.

Coracoid process fracture with anterior shoulder instability is a rare presentation. With a coracoid body fracture extending to the tip, a biomechanically stronger Latarjet procedure cannot be performed, instead, a weaker procedure like the Bristow procedure can be done. Here we present a 7-year follow-up where a staged procedure of fixation of the coracoid process followed by an open Latarjet procedure utilizing the healed coracoid.

The surface chemistry of 1,6-dibromo-3,8-diiodopyrene (Br2I2Py) is comparatively studied on Au(111) versus Ag(111) surfaces under ultrahigh vacuum conditions by a combination of high-resolution scanning tunneling microscopy (STM) and X-ray spectroscopy. The chemical state of the molecular networks, that is, the dehalogenation and the possible formation of organometallic intermediates, is assessed by X-ray photoelectron spectroscopy. In addition, pyrene tilt angles are quantified by carbon K-edge near edge X-ray absorption fine structure experiments. Upon room-temperature (RT) deposition of Br2I2Py onto Au(111), only partial deiodination was found, and STM revealed the coexistence of ordered arrangements of both intact Br2I2Py molecules and organometallic dimers as well as few larger aggregates. Further annealing to 100 °C triggered full deiodination followed by the formation of organometallic chains of otherwise still brominated molecules. By contrast, on Ag(111), iodine is fully and bromine is partly dissociated upon RT deposition of Br2I2Py. The initially disordered organometallic aggregates can be reorganized into more ordered structures by mild annealing at 125 °C. Yet, the conversion of the organometallic intermediates into well-defined cross-linked quasi 2D covalent networks was neither possible on Au(111) nor on Ag(111). This is attributed to the large steric hindrance in the covalently linked adsorbed state.

Second-term general chemistry is a key gateway course at our institution for a variety of STEM (Science, Technology, Engineering, and Mathematics) majors. Herein, we examine data on DFW% (i.e., % of D and F grades and withdrawals) in our general chemistry courses over roughly a quarter-century period, focusing on sections taught by the authors. The data are discussed in light of changes in curriculum, pedagogy, and assessments, which included introduction of recitation sections, classroom response systems (clickers), and online homework, restructuring of course content into a modular format, followed by a redesign of the course modules along an anchoring concepts scheme, introduction of the flipped classroom, and introduction of regular low-stakes quizzing. We find that the lowest DFW%, roughly 5%, occurs in classrooms combining an active learning pedagogy, core concepts curriculum, and low-stakes assessments with instructor intervention. Trends in the DFW populations are examined for White, non-Hispanic students, first-generation students, and by binary gender. We find that women are increasingly underrepresented in the DFW population, which may reflect the recent incorporation of lower stakes assessments. To the degree that our lowest DFW rates are consistent with that found by other researchers using different but related approaches, these may represent a baseline target for DFW rates in general chemistry II. Finally, while a trend toward lower DFW rates is found for both general chemistry I and II, the follow-on course, organic chemistry I, shows an inverse trend, which emphasizes the need for larger scale reform.

Surface-confined self-assembled molecular networks are commonly described as crystalline structures with short- and long-range order. Few exceptions to this trend are found in the literature reporting on amorphous and glassy networks and discussing the origins of their disordered nature at the atomic scale. Here, we show that an amorphous two-component metal–organic network can be synthesized on a crystalline metal surface at room temperature by vapor deposition of organic molecules and metal atoms. Scanning tunneling microscopy reveals the transformation of a crystalline close-packed organic layer into a disordered porous layer formed through the self-assembly of an organic semiconductor functionalized with two cyano groups upon introduction of iron atoms on Ag(111). In contrast to the commonly observed preference for trigonal crystal symmetry in 2D systems that form glassy networks, our metal–organic network favors rhombic or square tessellation of the surface. Statistical analysis of the network’s morphology reveals that entropy plays a critical part in its stabilization. Phase segregation of the binary mixture of monodisperse metal atoms and organic molecules into spatially separate homogeneously crystalline domains of molecules and metal atoms upon thermal annealing and subsequent cooling is observed. This suggests that the amorphous network is kinetically trapped at room temperature during the preparation process.

The oxidation of substituted benzyl alcohols by bis(2,2'-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Charton's triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 9–16, 1997.

Review: 63 refs.