1,4,5,8-Naphthalene Tetracarboxylate Dianhydride/g-C\u3csub\u3e3\u3c/sub\u3eN\u3csub\u3e4\u3c/sub\u3e van der Waals Heterojunctions Exhibit Enhanced Photochemical H\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Production and Antimicrobial Activity

Organic semiconductors, including graphitic carbon nitride (g-C3N4, CN), represent an important class of materials for the development of novel antimicrobial or biomedical technologies. Of principal interest is the ability of these materials to catalyze the reduction of elemental oxygen to generate reactive oxygen species (ROS), including hydrogen peroxide (H2O2). Here, we describe the fabrication of photoactive van der Waals heterojunctions incorporating 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) and CN. The composite heterojunction systems were characterized by a combination of physical (TEM, SEM, pXRD), spectroscopic (FT-IR, XPS, DRUV, photoluminescence, TCSPC) and kinetic experiments. Electronic interactions between the two components of the heterojunction increase the rate of photochemical production of H2O2 from elemental oxygen by 410%, relative to samples of pure CN. Mechanistic analysis reveals that interaction of NTCDA with the surface of CN modifies the mechanism of H2O2 formation in the heterojunction photocatalysts. The photochemical production of H2O2 by irradiation of the most active heterojunction composition is sufficient to reduce the viability of E. coli O157:H7, S. aureus and Ps. aeruginosa PAO1 by 99%. Importantly, H2O2 production by the NTCDA/CN heterojunctions suppresses Ps. aeruginosa biofilm formation, even at light exposure doses that had a lesser impact on overall planktonic cell growth

Materials Characterization and Testing of Heat-Reflective Coatings to Mitigate the Urban Heat Island

The Urban Heat Island (UHI) effect—urban areas higher in temperature than rural counterparts—is exacerbated by pavement surfaces. Heat-Reflective Coatings (HRC) are being developed to cool pavements for UHI mitigation. Six HRCs were tested via engineering performance tests, spectroscopy, and microscopy to determine changes in surface temperature and to understand optimal cooling mechanisms of each coating based on microstructure-property-performance architecture. Integrated multimodal characterization approaches were used to: 1. Determine the micro/nano scale heat reflection mechanisms that in each coating material; 2. Compare the heat reflection performance of each coating and rank them by cost effectiveness; 3. Inspire the design and optimization of new cool pavement with specifications and recommendations. During engineering performance tests, coated concrete samples underwent heating and cooling cycles in which the surface, atmospheric, and subsurface temperatures were recorded using an infrared thermal camera, a thermometer and thermocouples, respectively. Results from performance testing clearly demonstrated an overall decrease in surface temperature for coated samples compared to uncoated concrete. Ultraviolet-Near-Infrared and Fourier Transform Infrared spectrometers were used to quantify solar and thermal reflectance and HRCs were found to have significantly higher reflectance in the visible and near-infrared range compared to uncoated concrete. Scanning Electron Microscopy imaging of HRCs revealed the presence of silicon dioxide and titanium dioxide nanoparticles of varying size and morphology. Results of engineering performance testing and multimodal characterization indicate the potential of using HRCs to mitigate the UHI effect by cooling pavement surfaces

Role of electronic structure on nitrate reduction to ammonium: a periodic journey

Electrocatalytic reduction of waste nitrate to ammonium provides a circular process with reduced carbon dioxide emissions compared to current nitrate treatment and ammonia production processes. However, electrocatalysts require a delicate balance between a surfaces’ activity for the competing hydrogen evolution (HER) and nitrate reduction reactions (NO3RR). We measure ammonium Faradaic efficiencies (FEs) of several transition metals (TMs) ranging from 3.6±6.6% (on Ag) to 93.7±0.9% (on Co) in neutral buffered media. A microkinetic model identifies competitive adsorption between nitrate and hydrogen adatoms (H*) as the origin of voltage-dependent nitrate rate order. NO3RR FE is described via competition for electrons with the HER, decreasing sharply for TMs with high work function or hydrogen adsorption energy. Density functional theory calculations indicate Co maximizes ammonium selectivity by: (1) binding intermediate nitrite strongly to enable subsequent reduction; and (2) promoting subsequent nitric oxide dissociation, leading to selective reduction of nitrogen adatoms (N*) to ammonium

Synthesis and Characterization of Next-Generation Adenine-Based Inhibitors of Bacterial MTN

Infectious disease currently accounts for approximately one-third of the annual worldwide mortality and presents a pressing threat to the health and well-being of the global population. The challenge of infectious disease is compounded by a continued emergence of drug resistant and multiple-drug resistant microorganisms which, in turn, underscores the need to develop novel antibiotics that are both selective and safe. One potential target for new antimicrobial therapies is 5’-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTN). This enzyme is unique to microorganisms and plays a central role in processes associated with bacterial quorum sensing including the expression of drug resistance, biofilm formation, and exotoxin production. Here, we describe the use of copper-catalyzed, azo/alkyne click reactions to synthesize a series of non-hydrolyzable small molecule inhibitors (SMIs) from the building block 9-(prop-2-yn-1-yl)-9H-purin-6-amine. The SMIs developed in this study are designed to mimic the transition-state structure of the native substrate and are anticipated to function as competitive inhibitors of the target enzyme. The ability of the SMIs to exert an anti-MTN effect in vitro has been explored