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Costa Mesa, CA, United States

Yang Z.,Arizona State University | Lorance E.D.,Vanguard University | Bockisch C.,Arizona State University | Williams L.B.,Arizona State University | And 3 more authors.
Journal of Organic Chemistry | Year: 2014

Hydrothermal organic transformations under geochemically relevant conditions can result in complex product mixtures that form via multiple reaction pathways. The hydrothermal decomposition reactions of the model ketone dibenzyl ketone form a mixture of reduction, dehydration, fragmentation, and coupling products that suggest simultaneous and competitive radical and ionic reaction pathways. Here we show how Norrish Type I photocleavage of dibenzyl ketone can be used to independently generate the benzyl radicals previously proposed as the primary intermediates for the pure hydrothermal reaction. Under hydrothermal conditions, the benzyl radicals undergo hydrogen atom abstraction from dibenzyl ketone and para-coupling reactions that are not observed under ambient conditions. The photochemical method allows the primary radical coupling products to be identified, and because these products are generated rapidly, the method also allows the kinetics of the subsequent dehydration and Paal-Knorr cyclization reactions to be measured. In this way, the radical and ionic thermal and hydrothermal reaction pathways can be studied separately. © 2014 American Chemical Society.

Wosinska Z.M.,Arizona State University | Stump F.L.,Arizona State University | Ranjan R.,Arizona State University | Lorance E.D.,Vanguard University | And 6 more authors.
Photochemistry and Photobiology | Year: 2014

Irreversible photooxidation based on N-O bond fragmentation is demonstrated for N-methoxyheterocycles in both the singlet and triplet excited state manifolds. The energetic requirements for bond fragmentation are studied in detail. Bond fragmentation in the excited singlet manifold is possible for ππ* singlet states with energies significantly larger than the N-O bond dissociation energy of ca 55 kcal mol-1. For the nπ* triplet states, N-O bond fragmentation does not occur in the excited state for orbital overlap and energetic reasons. Irreversible photooxidation occurs in the singlet states by bond fragmentation followed by electron transfer. Irreversible photooxidation occurs in the triplet states via bimolecular electron transfer to the donor followed by bond fragmentation. Using these two sensitization schemes, donors can be irreversibly oxidized with oxidation potentials ranging from ca 1.6-2.2 V vs SCE. The corresponding N-ethylheterocycles are characterized as conventional reversible photooxidants in their triplet states. The utility of these sensitizers is demonstrated by irreversibly generating the guanosine radical cation in buffered aqueous solution. The return or reverse electron transfer that occurs in the primary charge-separated pair that is a feature of all photoinduced electron transfer reactions wastes energy and competes with useful chemistry in the charge-separated species. Here, we describe photoinduced electron transfer schemes that made irreversible by using fragmentable sensitizers. The fragmentable sensitizers are N-methoxyheterocycles that cleave a relatively weak N-O bond in either their reduced or excited forms. Sensitization mechanisms in both the singlet and the triplet manifolds are described. Irreversible oxidation of guanosine is demonstrated as an illustrative example. © 2013 The American Society of Photobiology.

Evans D.H.,University of Arizona | Gruhn N.E.,University of Arizona | Jin J.,Albany State University | Li B.,Albany State University | And 7 more authors.
Journal of Organic Chemistry | Year: 2010

"Chemical Equation Presented" The diverse electrochemical and chemical oxidations of dichalcogena-mesocycles are analyzed, broadening our understanding of the chemistry of the corresponding radical cations and dications. 1,5-Diselenocane and 1,5-dithiocane undergo reversible two-electron oxidation with inverted potentials analogous to 1,5-dithiocane. On the other hand, 1,5-selenathiocane and 1,5-tellurathiocane undergo one-electron oxidative dimerization. The X-ray crystal structures of the Se-Se dimer of the 1,5-selenathiocane one-electron oxidized product and the monomeric two-electron oxidized product (dication) of 1,5-tellurathiocane are reported. 1,5-Dithiocanes and 1,5-diselenocanes with group 14 atoms as ring members undergo irreversible oxidation, unlike the reversible two-electron oxidation of the corresponding silicon-containing 1,5-ditellurocanes. These results demonstrate the chemical consequences of the dication stabilities Te+-Te+ > Se+-Se+> S+-S+, as well as Se+-Se+ > Se+-S+ and Te +-Te+ > Te+-S+. © 2010 American Chemical Society.

Kelly S.B.,Vanguard University | Brown L.E.,California State University, Fullerton | Hooker S.P.,Arizona State University | Swan P.D.,Arizona State University | And 3 more authors.
Journal of Strength and Conditioning Research | Year: 2015

Kelly, SB, Brown, LE, Hooker, SP, Swan, PD, Buman, MP, Alvar, BA, and Black, LE. Comparison of concentric and eccentric bench press repetitions to failure. J Strength Cond Res 29(4): 1027-1032, 2015 - Eccentric muscle actions (ECC) are characterized by muscle lengthening, despite actin-myosin crossbridge formation. Muscles acting eccentrically are capable of producing higher levels of force compared with muscles acting concentrically. The purpose of this study was to determine whether ECC bench press yields greater strength than concentric (CON) as determined by 1 repetition maximum (1RM). Additionally, a comparison was made examining differences in the number of repetitions to failure at different relative intensities of 1RM. Thirty healthy men (age 24.63 ± 5.6 years) were tested for 1RM in CON and ECC bench press and the number of repetitions completed at 60, 70, 80, and 90% 1RM. For CON repetitions, the weight was mechanically lowered to the chest, and the participant pressed it up until the elbows were fully extended. The ECC bench press consisted of lowering a barbell from a fully extended elbow position to the chest in a continuous controlled manner for 3 seconds as determined by electronic metronome. Paired t-tests showed that ECC 1RM (115.99 ± 31.08 kg) was significantly (p ≤ 0.05) greater than CON 1RM (93.56 ± 26.56 kg), and the number of repetitions completed at 90% 1RM was significantly (p ≤ 0.05) greater in ECC (7.67 ± 3.24) as compared with CON (4.57 ± 2.21). There were no significant differences in number of completed repetitions during CON and ECC bench press at 60, 70, and 80% 1RM. These data indicate that ECC actions yield increased force capabilities (∼120%) as compared with CON in the bench press and may be less prone to fatigue, especially at higher intensities. These differences suggest a need to develop unique strategies for training eccentrically. © 2015 National Strength and Conditioning Association.

Ranjan R.,Arizona State University | Olson J.,Arizona State University | Singh P.,Arizona State University | Lorance E.D.,Vanguard University | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2015

Sequestering carbon dioxide emissions by the trap and release of CO2 via thermally activated chemical reactions has proven problematic because of the energetic requirements of the release reactions. Here we demonstrate trap and release of carbon dioxide using electrochemical activation, where the reactions in both directions are exergonic and proceed rapidly with low activation barriers. One-electron reduction of 4,4′-bipyridine forms the radical anion, which undergoes rapid covalent bond formation with carbon dioxide to form an adduct. One-electron oxidation of this adduct releases the bipyridine and carbon dioxide. Reversible trap and release of carbon dioxide over multiple cycles is demonstrated in solution at room temperature, and without the requirement for thermal activation. © 2015 American Chemical Society.

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