Miles Koppang | University of South Dakota (original) (raw)

Papers by Miles Koppang

Journal of the American Chemical Society, Nov 1, 1985

Chemischer Informationsdienst, Jul 29, 1986

Beilstein Journal of Organic Chemistry, Dec 8, 2006

Background Better understanding of the transannular influence of a substituent on the redox-poten... more Background Better understanding of the transannular influence of a substituent on the redox-potentials of bicyclo[2.2.2]octane-derived quinones will help in the design of new compounds with controlled biological activity. However, attempts to directly relate the reduction potentials of substituted triptycene-quinones to the electronic effects of substituents are often unsuccessful. Results First and second redox-potentials of a series of bicyclic quinones are compared to computed energies of their LUMO, LUMO+1, and energies of reduction. Transannular influence of substituent on the redox-potentials is rationalized in terms of MO theory. Acetoxy-substituents in the 5,8-positions of the triptycene-quinone system selectively destabilize the product of the two-electron reduction. Conclusion We have shown that first redox-potentials of substituted bicyclic quinones correlate with their calculated LUMO energies and the energies of reduction. The second redox-potentials correlate with calculated LUMO+1 energies. As opposed to the LUMO orbitals, the LUMO+1 orbital coefficients are weighted significantly on the non-quinone part of the bicyclic system. This accounts for: (1) significantly larger substituent effect on the second redox-potentials, than on the first redox-potentials; (2) lack of stability of the product of two electron reduction of 5,8-diacetoxy-9,10-dihydro-9,10-[1,2]benzenoanthracene-1,4-dione 5.

Journal of the American Chemical Society, May 1, 1984

The electrochemical reduction of diphenyl ether to its unstable radical anion was observed at-2.9... more The electrochemical reduction of diphenyl ether to its unstable radical anion was observed at-2.95 V vs. SCE in dry N,N-dimethylformamide. Kinetic studies by cyclic voltammetry and homogeneous redox catalysis techniques resulted in a first-order rate constant of 4 X lo5 s-' for the decomposition of the radical anion of diphenyl ether. Controlled-potential electrolysis of diphenyl ether resulted in carbon-oxygen bond cleavage with quantitative formation of phenol and benzene. Electroreduction of diphenyl ether in the presence of D 2 0 produced 15% monodeuterium incorporation on benzene. The intermediacy of the phenyl radical in the cleavage pathway was tested by deploying an intramolecular radical trap, an e(3-butenyl) substituent, on diphenyl ether. Electrochemcial reduction of 0-(3-butenyl)phenoxybenzene (1) in the absence of and in the presence of D 2 0 confirmed the presence of the 0-(3-butenyl)phenyl radical in the cleavage mechanism of the radical anion. Electroreduction of 1 in the presence of sodium isopropylate, a hydrogen atom donor, changed the product distribution ratio of l-methylindan-(3-butenyl)benzene. The rate constant of the intramolecular cyclization reaction of the 0-(3-butenyl)phenyl radical was estimated to be 1.5 X lo8 s-I H+

Analytical Chemistry, Jul 21, 2000

Standard electrochemical data for high-quality, borondoped diamond thin-film electrodes are prese... more Standard electrochemical data for high-quality, borondoped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 10 19 B/cm 3 range, and the boron-doping level of the USU films was ∼5 × 10 20 B/cm-3 based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN) 6 3-/4-, Ru(NH 3) 6 3+/2+ , IrCl 6 2-/3-, methyl viologen, dopamine, ascorbic acid, Fe 3+/2+ , and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k o app , observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH 3) 6 3+/2+ , IrCl 6 2-/3-, methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k o app in the 10-2-10-1 cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN) 6 3-/4undergoes electron transfer that is extremely sensitive to the surface chemistry with k o app in the range of 10-2-10-1 cm/s at the hydrogenterminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe 3+/2+ undergoes slow electron transfer at the hydrogen-terminated surface with k o app near 10-5 cm/s. The rate of electron transfer at sp 2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other Boron-doped diamond thin-film electrodes possess important properties, particularly for electroanalysis. 1-9 In recent years, several groups have made progress understanding the factors that influence the electrochemical response of these materials including those of Fujishima (Japan), Pleskov (Russia), Tenne (Israel), Angus and Miller (U.S.A.), and Compton (England). While interesting and, in some cases, unique behavior of diamond

Electroanalysis, Sep 29, 2015

E p ox shifted negativea nd the i p ox increased withi ncreasing solution pH. i p ox also increas... more E p ox shifted negativea nd the i p ox increased withi ncreasing solution pH. i p ox also increased with increasing boron doping level or surface boron site density.F IA-EC analysis revealed ar eproducible response for the aliphatic polyamines in ab inarys olvent (7/93%)a cetonitrile/ borate buffer, pH 11.2. Optimums ignal-to-background ratios for the aliphatic polyamines were seen at potentials between 650 and 670 mV.

Analytical Chemistry, Feb 10, 1999

ABSTRACT

Chemischer Informationsdienst, Mar 11, 1986

ChemInform Abstract Während die Cyclisierung des aus dem Bromid (I) erzeugten Li-Derivats zu dem ... more ChemInform Abstract Während die Cyclisierung des aus dem Bromid (I) erzeugten Li-Derivats zu dem Indan (III) bei-78 rc C im Gegensatz zu der des aus (I) gebildeten Radikals nicht stattfindet, ist nach Erwärmen auf Raumtemp. und Quenchen mit H2O oder D2O ein bestimmter Anteil an (III) festzustellen. Die Ausb. für die deuterierten und nichtdeuterierten Verbindungen (II) und (III) in Abhängigkeit von Reaktionszeit und-medium sind in einer Tab. zusammengestellt.

Analytical Chemistry, Jul 1, 1996

Microelectrodes have been used to modify locally the electrochemical activity on glassy carbon el... more Microelectrodes have been used to modify locally the electrochemical activity on glassy carbon electrodes. Glassy carbon was electrochemically oxidized to form an oxide layer which is inhibitory toward certain electrontransfer reactions. Activity was restored through the application of hydroxide, which was generated electrochemically at the tip of a microelectrode. With the tip positioned in close proximity to the anodized glassy carbon surface, microdomains of electrochemical activity were created in an otherwise inactive matrix. The distribution of electrochemical activity was characterized using electrochemical feedback at the microelectrode, electrogenerated chemiluminescence imaging, and electrodeposition of silver. Spatially directed activation of the glassy carbon surface was accomplished in the micrometer domain.

Analytical Chemistry, Oct 1, 1997

Journal of Chemical Education, Sep 1, 1992

ABSTRACT A cyclic voltammetric experiment involving the electrodeposition of atomic hydrogen onto... more ABSTRACT A cyclic voltammetric experiment involving the electrodeposition of atomic hydrogen onto a clean polycrystalline platinum surface. Keywords (Audience): Upper-Division Undergraduate

Chemischer Informationsdienst, Nov 26, 1985

ChemInform Abstract The radical anion (II) decomposes with a first order rate constant of 4•105/s... more ChemInform Abstract The radical anion (II) decomposes with a first order rate constant of 4•105/s to give (III) and (IV) quantitatively with current efficiency considerably less than 100%. In the presence of D2O ca. 15% deuterium incorporation occurs. The analogous reaction of (V) provided with an intramolecular radical trap confirms the radical anion cleavage involving phenyl radicals. The addition of Na-isopropylate changes the product ratio (VIII)/(IXb) from 13 to 5 (cyclic voltammetry).

Electroanalysis, Nov 23, 2021

Analysis of amino acids is crucial to protein structure elucidation. Amino acids, amenable to sep... more Analysis of amino acids is crucial to protein structure elucidation. Amino acids, amenable to separation by liquid chromatography (LC), can be detected by sensitive detectors used in liquid chromatograph including absorbance, fluorescence or electrochemical detector when derivatized. Derivatization of amino acids using suitable reagents enhances the separation and detection of amino acids using liquid chromatography. Sanger's reagent (1‐fluoro‐2,4‐dinitrobenzene, DNFB) makes amino acids suitable for absorbance detection. However, little has been done in terms of liquid chromatography with electrochemical detection (LC‐EC) of the DNFB derivatized amino acids. Furthermore, sensor development based on electrochemistry of nitroaromatics has increased dramatically for explosive detection. Since nitroaromatics are electrochemically active, it is essential to determine the reduction pathway. Cyclic voltammetry (CV), rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) experiments have been performed on nitrobenzene (NB) and N‐methyl‐2,4‐dinitroaniline (NMDNA). The results showed that the nitro group was reduced to hydroxylamine in aqueous solutions by addition of four electrons and four protons per nitro group and the hydroxylamine can be reversibly oxidized into a nitroso by removal of two electrons and two protons. Electrochemical detection of the nitro groups is appropriate for dual electrode detection of DNFB labeled amino acids in which reduction can occur on an upstream electrode and corresponding oxidation of the reduction product occurs on the downstream electrode.

Bulletin of the American Physical Society, Apr 12, 2008

DEAP/CLEAN COLLABORATION-The purpose of this project is to investigate the possibility of using u... more DEAP/CLEAN COLLABORATION-The purpose of this project is to investigate the possibility of using underground water as a source for depleted argon which will be the target material for next generation dark matter detectors at deep underground laboratories and to design a machine that would extract argon from underground water. The only source of 39 Ar from old underground water is 39 Ar that is produced from (n,p) reactions with 39 K. An analysis of the soil was conducted to determine the 39 K content and the number of free neutrons due to (α,n) reactions induced by 232 Th and 238 U decay. This was done with atomic absorption spectrometry and a low background counting facility, respectively. The results indicated that the soil contains approximately 2% 39 K and 2 neutrons/y/g/ppm. As a result, 39 Ar is predicted to be about a factor of 70 lower than atmospheric level. In addition, a machine was designed that would be capable of extracting argon from underground water.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.