Collisional quenching of OD A 2Σ+ by H2: experimental and theoretical studies of the state-resolved OD X 2Π product distribution and branching fraction

We report joint experimental and theoretical studies of outcomes resulting from the nonreactive quenching of electronically excited OD?A (2)Σ(+) by H(2). The experiments utilize a pump-probe technique to detect the OD?X (2)Π product state distribution under single collision conditions. The OD?X (2)Π products are observed primarily in their lowest vibrational state (v(") = 0) with substantially less population in v(") = 1. The OD?X (2)Π products are generated with a high degree of rotational excitation, peaking at N(") = 21 with an average rotational energy of 4600 cm(-1), and a strong propensity for populating the Π(A(')) Λ-doublet component indicative of alignment of the half-filled pπ orbital in the plane of OD rotation. Branching fraction measurements show that the nonreactive channel accounts for less than 20% of quenching outcomes. Complementary classical trajectory calculations of the postquenching dynamics are initiated from representative points along seams of conical intersections between the ground and excited-state potentials of OD(A (2)Σ(+),X (2)Π) + H(2). Diabatic modeling of the initial momenta in the dynamical calculations captures the key experimental trends: OD?X (2)Π products released primarily in their ground vibrational state with extensive rotational excitation and a branching ratio that strongly favors reactive quenching. The OD?A (2)Σ(+) + H(2) results are also compared with previous studies on the quenching of OH?A (2)Σ(+) + H(2); the two experimental studies show remarkably similar rotational energy distributions for the OH and OD?X (2)Π radical products.     

Cytotoxicity analysis of water disinfection byproducts with a micro-pillar microfluidic device

Water disinfection byproducts (DBPs) are a class of chemicals that are produced when chemical disinfectants react with organic materials in untreated water. Cytotoxicity and genotoxicity of DBPs have been systematically evaluated to compile a comparative, quantitative database of in vitro mammalian cell toxicity of DBPs. However, one of the most challenging limitations for current DBP cytotoxicity assessment assays is sample availability. Although our current cytotoxicity assay using a 96-well microplate has been designed to reduce sample consumption, further minimization of the size of the test system would allow us to explore various possibilities for point-of-care applications. We have developed a microfluidic device with micro-pillars that shows high uniformity in distribution of cells across all chambers with low cell count. We compare the performance between the 96-well microplate and the microfluidic device by running 72-hour standalone-on-chip cell culture and cytotoxicity analysis experiments, using dimethyl sulfoxide (DMSO) and ethanol as model toxic agents, and bromoacetic acid (BAA) as a representative DBP. The results show close agreement between the two systems. The measured LC(50) values for the 96-well microplate and the microfluidic device are 1.54% v/v and 1.27% v/v for DMSO, 1.44% v/v and 2.92% v/v for ethanol, and 17.6 μM and 8.20 μM for BAA, respectively. The micro-pillar microfluidic device offers a great reduction in sample consumption while maintaining the accuracy of the cytotoxicity analyses of water disinfection byproducts.     

Manganese(III) acetate mediated oxidative radical cyclizations. Toward vicinal all-carbon quaternary stereocenters

Manganese(III) acetate mediated oxidative radical cyclizations have been used to synthesize a range of densely functionalized and sterically congested cyclopentane-lactones. A number of the resulting lactones contain vicinal all-carbon quaternary stereocenters adjacent to a tertiary benzylic stereocenter and are formed with high levels of stereocontrol.     

Cationic zinc enolates as highly active catalysts for acrylate polymerization

Unprecedented cationic zinc enolates have been generated by a novel activation route involving the amido to imino ligand transformation with B(C6F5)3, structurally characterized, and utilized as highly active catalysts for the production of high molecular weight polyacrylates at ambient temperature.     

Exponential Rates of Convergence in the Ergodic Theorem: A Constructive Approach

We prove that, once an algorithm of perfect simulation for a stationary and ergodic random field F taking values in S^\mathbbZdS^{\mathbb{Z}^{d}}, S a bounded subset of R ⁿ , is provided, the speed of convergence in the mean ergodic theorem occurs exponentially fast for F. Applications from (non-equilibrium) statistical mechanics and interacting particle systems are presented.     

Alkene Carboboration Enabled by Synergistic Catalysis

A synergistic Pd/Cu system for the coupling of alkenes, (Bpin)₂ (pin=pinacolate), and aryl/vinyl bromides is disclosed. This method allows for the catalytic generation of secondary Csp³?Cu nucleophiles in situ and subsequent Pd‐catalyzed cross‐coupling.     

Optical Resolution of Dibenzo[a,g]fluorenol via Glycosylation

A simple optical resolution of dibenzo[a,g]fluorenol has been accomplished via borontrifluoride‐mediated Ferrier rearrangement reaction.     

Design and preliminary test results of Daya Bay RPC modules

Resistive Plate Chamber (RPC) modules will be used as one part of the cosmic muon veto system in the Daya Bay reactor neutrino experiment. A total of 189 RPC modules will cover the three water pools in the experiment. To achieve track reconstruction and high efficiency, each module consists of 4 layers, each of which contains two sizes of bare chambers. The placement of bare chambers is reversed in different layers to reduce the overlapping dead areas. The module efficiency and patch efficiency were studied both in simulation and test of the data analysis. 143 modules have been constructed and tested. The preliminary study shows that the module and patch 3 out of 4 layers efficiency reaches about 98%.     

Noninvasive monitoring of photocatalytic degradation of X‐ray contrast media using Raman spectrometry

The photocatalytic degradation of the X‐ray contrast agents iohexol and diatrizoate are monitored by in situ Raman spectrometry measurements in aqueous solution with a TiO₂ photocatalyst. Spectral features and changes are interpreted with the use of density functional theory calculations. While we observe similar results to those published previously, significant changes seen in the Raman spectrum allow us to better identify the mechanisms without the need for deductive approaches or complicated sample preparation. Diatrizoate spectra are consistent with hydroxyl radical attack leading to the loss of CO₂. Iohexol is more difficult to interpret, representing a current challenge to the use of Raman spectrometry for real‐time monitoring of photocatalytic degradation experiments. We explore internal standards that can be added to gauge overall degradation rates to some extent. Potential extensions of the work are described, particularly in terms of increased rate of data acquisition and more general application. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of ultra‐high molecular weight polymers by controlled production of initiating radicals

This study demonstrates that the gradual and slow production of initiating radicals (i.e., hydroxyl radicals here) is the key point for the synthesis of ultra‐high molecular weight (UHMW) polymers via controlled radical polymerization. Hydrogen peroxide (H₂O₂) and ferrous iron (Fe²⁺) react via Fenton redox chemistry to initiate RAFT polymerization. This work presents two enzymatic‐mediated (i.e., Bio‐Fenton‐RAFT and Semi Bio‐Fenton‐RAFT) and one syringe pump‐driven Fenton‐RAFT polymerization processes in which the initiating radicals are carefully and gradually dosed into the reaction solution. The “livingness” of the synthesized UHMW polymers is demonstrated by chain extension and aminolysis experiments. Zimm plots obtained from static light scattering (SLS) technique are used to characterize the UHMW polymers. This Fenton‐RAFT polymerization provides access to polymers of unprecedented UHMW (M_w ~ 20 × 10⁶ g mol^?1) with potential in diverse applications. The UHMW polymers made via the controlled Fenton‐RAFT polymerization by using a syringe pump shows that it is possible to produce such materials through an easy‐to‐set up and scalable process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1922–1930