Structural and Mechanistic Aspects of Copper Catalyzed Atom Transfer Radical Addition Reactions in the Presence of Reducing Agents

The focus of this dissertation was to improve the atom transfer radical addition (ATRA) by decreasing the amount of copper catalyst needed to achieve good yields of the monoadduct. This is a fundamental organic reaction in which an alkyl halide is added to the carbon-carbon double bond of an alkene via a free radical mechanism. Previously, ATRA required between 5 and 30 mol% of a copper catalyst relative to alkene in order to achieve good yields of the desired monoadduct due to the accumulation of copper(II) as a result of unavoidable radical termination reactions. The solution to this problem was found for the mechanistically similar atom transfer radical polymerization where the addition of a reducing agent served to continuously regenerate copper(I) in situ, allowing for the significant decrease in the amount of copper catalyst. We utilized tris(2-pyridylmethyl)amine (TPMA) as a complexing ligand, due to its high activity in ATRA. Free radial initiator, 2, 2\u27-azobis(isobutyronitrile), was used as a reducing agent and were able to show that polyhalogenated methanes could be efficiently added across a variety of alkenes. Very low catalyst loadings were required for alkenes that do not readily undergo free radical polymerization such as α-olefins. However, significantly higher concentrations of copper catalyst were required for highly active alkenes such as styrene and methyl acrylate. In order to achieve better control of monoadduct formation in these systems, we utilized low temperature free radical initiator 2, 2\u27-azobis(4-methoxy-2, 4-dimethyl-valeronitrile), which was successful in providing good control over ATRA of methyl acrylate, methyl methacrylate, vinyl acetate and styrene with very low catalyst loadings. To better understand the correlation between the structure of the copper complex and its activity in ATRA, copper complexes with the TPMA ligand were isolated and characterized with a variety of anions and auxiliary ligands. We observed that copper(I) TPMA complexes contained coordinated halide anions, which raised questions as to how coordinatively saturated complexes such as these could have such a high activity in an inner sphere electron transfer process such as ATRA. It was determined that ATRA with copper TPMA complexes most likely operates by partial ligand dissociation

Propofol inhibits prokaryotic voltage-gated Na+ channels by promoting activation-coupled inactivation

Propofol is widely used in the clinic for the induction and maintenance of general anesthesia. As with most general anesthetics, however, our understanding of its mechanism of action remains incomplete. Local and general anesthetics largely inhibit voltage-gated Na+ channels (Navs) by inducing an apparent stabilization of the inactivated state, associated in some instances with pore block. To determine the biophysical and molecular basis of propofol action in Navs, we investigated NaChBac and NavMs, two prokaryotic Navs with distinct voltage dependencies and gating kinetics, by whole-cell patch clamp electrophysiology in the absence and presence of propofol at clinically relevant concentrations (2-10 μM). In both Navs, propofol induced a hyperpolarizing shift of the pre-pulse inactivation curve without any significant effects on recovery from inactivation at strongly hyperpolarized voltages, demonstrating that propofol does not stabilize the inactivated state. Moreover, there was no evidence of fast or slow pore block by propofol in a non-inactivating NaChBac mutant (T220A). Propofol also induced hyperpolarizing shifts of the conductance-voltage relationships with negligible effects on the time constants of deactivation at hyperpolarized voltages, indicating that propofol does not stabilize the open state. Instead, propofol decreases the time constants of macroscopic activation and inactivation. Adopting a kinetic scheme of Nav gating that assumes preferential closed-state recovery from inactivation, a 1.7-fold acceleration of the rate constant of activation and a 1.4-fold acceleration of the rate constant of inactivation were sufficient to reproduce experimental observations with computer simulations. In addition, molecular dynamics simulations and molecular docking suggest that propofol binding involves interactions with gating machinery in the S4-S5 linker and external pore regions. Our findings show that propofol is primarily a positive gating modulator of prokaryotic Navs, which ultimately inhibits the channels by promoting activation-coupled inactivation. © 2018 Yang et al

Perioperative Neurocognitive Disorder: State of the Preclinical Science.

The purpose of this article is to provide a succinct summary of the different experimental approaches that have been used in preclinical postoperative cognitive dysfunction research, and an overview of the knowledge that has accrued. This is not intended to be a comprehensive review, but rather is intended to highlight how the many different approaches have contributed to our understanding of postoperative cognitive dysfunction, and to identify knowledge gaps to be filled by further research. The authors have organized this report by the level of experimental and systems complexity, starting with molecular and cellular approaches, then moving to intact invertebrates and vertebrate animal models. In addition, the authors' goal is to improve the quality and consistency of postoperative cognitive dysfunction and perioperative neurocognitive disorder research by promoting optimal study design, enhanced transparency, and "best practices" in experimental design and reporting to increase the likelihood of corroborating results. Thus, the authors conclude with general guidelines for designing, conducting and reporting perioperative neurocognitive disorder rodent research

Diazepam and Meperidine on Arterial Blood Gases in Healthy Volunteers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97157/1/j.1552-4604.1974.tb01414.x.pd

Stereoselectivity of Isoflurane in Adhesion Molecule Leukocyte Function-Associated Antigen-1

Background: Isoflurane in clinical use is a racemate of S- and R-isoflurane. Previous studies have demonstrated that the effects of S-isoflurane on relevant anesthetic targets might be modestly stronger (less than 2-fold) than R-isoflurane. The X-ray crystallographic structure of the immunological target, leukocyte function-associated antigen-1 (LFA-1) with racemic isoflurane suggested that only S-isoflurane bound specifically to this protein. If so, the use of specific isoflurane enantiomers may have advantage in the surgical settings where a wide range of inflammatory responses is expected to occur. Here, we have further tested the hypothesis that isoflurane enantioselectivity is apparent in solution binding and functional studies. Methods: First, binding of isoflurane enantiomers to LFA-1 was studied using 1-aminoanthracene (1-AMA) displacement assays. The binding site of each enantiomer on LFA-1 was studied using the docking program GLIDE. Functional studies employed the flow-cytometry based ICAM binding assay. Results: Both enantiomers decreased 1-AMA fluorescence signal (at 520 nm), indicating that both competed with 1-AMA and bound to the αL I domain. The docking simulation demonstrated that both enantiomers bound to the LFA-1 “lovastatin site.” ICAM binding assays showed that S-isoflurane inhibited more potently than R-isoflurane, consistent with the result of 1-AMA competition assay. Conclusions: In contrast with the x-ray crystallography, both enantiomers bound to and inhibited LFA-1. S-isoflurane showed slight preference over R-isoflurane

Azi-isoflurane, a Photolabel Analog of the Commonly Used Inhaled General Anesthetic Isoflurane

Volatility and low-affinity hamper an ability to define molecular targets of the inhaled anesthetics. Photolabels have proven to be a useful approach in this regard, although none have closely mimicked contemporary drugs. We report here the synthesis and validation of azi-isoflurane, a compound constructed by adding a diazirinyl moiety to the methyl carbon of the commonly used general anesthetic isoflurane. Azi-isoflurane is slightly more hydrophobic than isoflurane, and more potent in tadpoles. This novel compound inhibits Shaw2 K(+) channel currents similarly to isoflurane and binds to apoferritin with enhanced affinity. Finally, when irradiated at 300 nm, azi-isoflurane adducts to residues known to line isoflurane-binding sites in apoferritin and integrin LFA-1, the only proteins with isoflurane binding sites defined by crystallography. This reagent should allow rapid discovery of isoflurane molecular targets and binding sites within those targets

Cobalt complexes as artificial hydrogenases for the reductive side of water splitting

The generation of H-2 from protons and electrons by complexes of cobalt has an extensive history. During the past decade, interest in this subject has increased as a result of developments in hydrogen generation that are driven electrochemically or photochemically. This article reviews the subject of hydrogen generation using Co complexes as catalysts and discusses the mechanistic implications of the systems studied for making H-2. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. (C) 2013 Elsevier B.V. All rights reserved