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James K Hurst

Publications and source records attributed to James K Hurst.

9 recordsLinked to original sources
PubMed2006

Comparative toxicities of putative phagocyte-generated oxidizing radicals toward a bacterium (Escherichia coli) and a yeast (Saccharomyces cerevisiae).

Toxicities of the radiolytically generated oxidizing radicals HO(*), CO(3)(-)(*), and NO(2)(*) toward suspension cultures of a bacterium (Escherichia coli) and a yeast (Saccharomyces cerevisiae) were examined. As demonstrated by the absence of protection from the membrane-impermeable HO(*) scavenger polyethylene glycol (PEG), externally generated HO(*) was not bactericidal under these conditions; however, partial protection by PEG was observed for S. cerevisiae, indicating the presence of a fungicidal pathway involving external HO(*). For both organisms, conversion of external HO(*) to the secondary radical, CO(3)(-)(*), by reaction with HCO(3)(-) increases their susceptibility to radiolytic killing. In contrast, externally generated NO(2)(*) exhibited toxicity comparable to that of CO(3)(-)(*) toward E. coli, but completely blocked the extracellular toxicity of HO(*) toward S. cerevisiae. Cogeneration of equal fluxes of NO(2)(-)(*) and either HO(*) or CO(3)(-)(*) also essentially eliminated the extracellular microbicidal reactions. This behavior is consistent with expectations based upon relative rates of radical-radical self-coupling and cross-coupling reactions. The different patterns of toxicity observed imply fundamentally different microbicidal mechanisms for the two organisms, wherein the bacterium is susceptible to killing by oxidation of highly reactive targets on its cellular envelope but, despite undergoing similar oxidative insult, the fungus is not.

Antifungal Agents↗
PubMed2006

Spiropyran-based photochromic polymer nanoparticles with optically switchable luminescence.

Polymer nanoparticles of 40-400 nm diameter with spiropyran-merocyanine dyes incorporated into their hydrophobic cavities have been prepared; in contrast to their virtually nonfluorescent character in most environments, the merocyanine forms of the encapsulated dyes are highly fluorescent. Spiro-mero photoisomerization is reversible, allowing the fluorescence to be switched "on" and "off" by alternating UV and visible light. Immobilizing the dye inside hydrophobic pockets of nanoparticles also improves its photostability, rendering it more resistant than the same dyes in solution to fatigue effects arising from photochemical switching. The photophysical characteristics of the encapsulated fluorophores differ dramatically from those of the same species in solution, making nanoparticle-protected hydrophobic fluorophores attractive materials for potential applications such as optical data storage and switching and biological fluorescent labeling. To evaluate the potential for biological tagging, these optically addressable nanoparticles have been delivered into living cells and imaged with a liquid nitrogen-cooled CCD.

Acrylamides↗
PubMed2006

Photoregulated transmembrane charge separation by linked spiropyran-anthraquinone molecules.

Amide-linked spiropyran-anthraquinone (SP-AQ) conjugates were shown to mediate ZnTPPS(4-)-photosensitized transmembrane reduction of occluded Co(bpy)3(3+) within unilamellar phosphatidylcholine vesicles by external EDTA. Overall quantum yields for these reactions were dependent upon the isomeric state of the dye; specifically, 30-35% photoconversion of the closed-ring spiropyran (SP) moiety to the open-ring merocyanine (MC) form caused the quantum yield to decrease by 6-fold in the simple conjugate and 3-fold for an analogue containing a lipophilic 4-dodecylphenoxy substituent on the anthraquinone moiety. Transient spectroscopic and fluorescence quenching measurements revealed that two factors contributed to these photoisomerization-induced changes in quantum yields: increased efficiencies of fluorescence quenching of 1ZnTPPS4- by the merocyanine group and lowered transmembrane diffusion rates of the merocyanine-containing redox carriers. Transient spectrophotometry also revealed the sequential formation and decay of two reaction intermediates, identified as 3ZnTPPS4- and a species with the optical properties of a semiquinone radical. Kinetic profiles for Co(bpy)3(3+) reduction under continuous photolysis in the presence and absence of added ionophores indicated that transmembrane redox mediated by SP-AQ was electroneutral, but reaction by the other quinone-containing mediators was electrogenic. The minimal reaction mechanism suggested from the combined studies is oxidative quenching of vesicle-bound 3ZnTPPS4- by the anthraquinone unit, followed by either H+/e- cotransport by transmembrane diffusion of SP-AQH* or, for the other redox mediators, semiquinone anion-quinone electron exchange leading to net transmembrane electron transfer, with subsequent one-electron reduction of the internal Co(bpy)3(3+). Thermal one-electron reduction of Co(bpy)3(3+) by EDTA is energetically unfavorable; the photosensitized reaction therefore occurs with partial conversion of photonic energy to chemical and transmembrane electrochemical potentials.

2,2'-Dipyridyl↗
PubMed2005

Light-controlled molecular switches modulate nanocrystal fluorescence.

Spiropyran dyes were attached to fluorescent core-shell CdSe/ZnS nanocrystals via thiol-containing linkers. Photoisomerization of the dye to its merocyanine form by UV irradiation caused a dramatic loss in the intrinsic nanoparticle fluorescence, which was regained upon reversing the isomerization with visible light. The fluorescence quenching efficiency increased with increasing spectral overlap of fluorescence emission and merocyanine adsorption bands, consistent with FRET as the quenching mechanism. Typically, complete quenching required at least 80 bound dye molecules per particle.

Benzopyrans↗
PubMed2005

Green fluorescent protein-expressing Escherichia coli as a selective probe for HOCl generation within neutrophils.

Escherichia coli were transformed by electroporation to introduce a plasmid harboring a GFP gene-containing vector. The fluorescence of the purified GFP isolated from the transformant was quenched by myeloperoxidase (MPO)-generated HOCl, by peroxynitrous acid (ONOOH) and by enzymatically or radiolytically generated NO(2)(.) but not by other putative neutrophil-generated oxidants. Fluorescence from the bacterium was effectively quenched by HOCl but not peroxynitrite, oxidizing radicals derived from its O-O bond homolysis, or the other oxidants under study. Exposure of serum-opsonized bacteria to human neutrophils resulted in extensive loss of GFP fluorescence; fluorescence microscopy revealed that phagocytosed bacteria were completely quenched but that bacteria remaining in the external media were unquenched. Addition of sodium azide to the medium to inhibit MPO prevented neutrophil-mediated fluorescence quenching. Because the amount of HOCl required to inhibit bacterial fluorescence was an order of magnitude greater than required to inhibit colonial growth, these results imply that sufficient HOCl was formed within the neutrophil phagosome to kill the microbe.

Animals↗
PubMed2004

Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion.

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.

Journal Article↗
PubMed2004

HOCl-mediated cell death and metabolic dysfunction in the yeast Saccharomyces cerevisiae.

The nature of oxidative damage to Saccharomyces cerevisiae caused by levels of HOCl that inhibit cell replication was explored with the intent of identifying the loci of lethal lesions. Functions of cytosolic enzymes and organelles that are highly sensitive to inactivation by HOCl, including aldolase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the mitochondrion, were only marginally affected by exposure of the yeast to levels of HOCl that completely inhibited colony formation. Loss of function in membrane-localized proteins, including the hexose transporters and PMA1 H(+)-ATPase, which is the primary proton pump located within the S. cerevisiae plasma membrane, was also marginal and K(+) leak rates to the extracellular medium increased only slowly with exposure to increasing amounts of HOCl, indicating that the plasma membrane retained its intrinsic impermeability to ions and metabolites. Adenylate phosphorylation levels in fermenting yeast declined in parallel with viability; however, yeast grown on respiratory substrates maintained near-normal phosphorylation levels at HOCl doses several-fold greater than that required for killing. This overall pattern of cellular response to HOCl differs markedly from that previously reported for bacteria, which appear to be killed by inhibition of plasma membrane proteins involved in energy transduction. The absence of significant loss of function in critical oxidant-sensitive cellular components and retention of ATP-synthesizing capabilities in respiring yeast cells exposed to lethal levels of HOCl suggests that toxicity in this case may arise by programmed cell death.

Adenine Nucleotides↗
PubMed2003

Hydroxyl radical formation by O-O bond homolysis in peroxynitrous acid.

Peroxynitrite decay in weakly alkaline media occurs by two concurrent sets of pathways which are distinguished by their reaction products. One set leads to net isomerization to NO(3)(-) and the other set to net decomposition to O(2) plus NO(2)(-). At sufficiently high peroxynitrite concentrations, the decay half-time becomes concentration-independent and approaches a limiting value predicted by a mechanism in which reaction is initiated by unimolecular homolysis of the peroxo O-O bond, i.e., the following reaction: ONOOH --> (*)OH + (*)NO(2). This dynamical behavior excludes alternative postulated mechanisms that ascribe decomposition to bond rearrangement within bimolecular adducts. Nitrate and nitrite product distributions measured at very low peroxynitrite concentrations also correspond to predictions of the homolysis model, contrary to a recent report from another laboratory. Additionally, (1) the rate constant for the reaction ONOO(-) --> (*)NO + (*)O(2)(-), which is critical to the kinetic model, has been confirmed, (2) the apparent volume of activation for ONOOH decay (DeltaV() = 9.7 +/- 1.4 cm(3)/mol) has been shown to be independent of the concentration of added nitrite and identical to most other reported values, and (3) complex patterns of inhibition of O(2) formation by radical scavengers, which are impossible to rationalize by alternative proposed reaction schemes, are shown to be quantitatively in accord with the homolysis model. These observations resolve major disputes over experimental data existing in the literature; despite extensive investigation of these reactions, no verifiable experimental evidence has been advanced that contradicts the homolysis model.

Algorithms↗