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Adrian Ponce

Publications and source records attributed to Adrian Ponce.

4 recordsLinked to original sources
PubMed2006

Applications of a rapid endospore viability assay for monitoring UV inactivation and characterizing arctic ice cores.

We have developed a rapid endospore viability assay (EVA) in which endospore germination serves as an indicator for viability and applied it to (i) monitor UV inactivation of endospores as a function of dose and (ii) determine the proportion of viable endospores in arctic ice cores (Greenland Ice Sheet Project 2 [GISP2] cores; 94 m). EVA is based on the detection of dipicolinic acid (DPA), which is released from endospores during germination. DPA concentrations were determined using the terbium ion (Tb3+)-DPA luminescence assay, and germination was induced by L-alanine addition. The concentrations of germinable endospores were determined by comparison to a standard curve. Parallel EVA and phase-contrast microscopy experiments to determine the percentage of germinable spores yielded comparable results (54.3% +/- 3.8% and 48.9% +/- 4.5%, respectively), while only 27.8% +/- 7.6% of spores produced CFU. EVA was applied to monitor the inactivation of spore suspensions as a function of UV dose, yielding reproducible correlations between EVA and CFU inactivation data. The 90% inactivation doses were 2,773 J/m2, 3,947 J/m2, and 1,322 J/m2 for EVA, phase-contrast microscopy, and CFU reduction, respectively. Finally, EVA was applied to quantify germinable and total endospore concentrations in two GISP2 ice cores. The first ice core contained 295 +/- 19 germinable spores/ml and 369 +/- 36 total spores/ml (i.e., the percentage of germinable endospores was 79.9% +/- 9.3%), and the second core contained 131 +/- 4 germinable spores/ml and 162 +/- 17 total spores/ml (i.e., the percentage of germinable endospores was 80.9% +/- 8.8%), whereas only 2 CFU/ml were detected by culturing.

Arctic Regions↗
PubMed1999

pH-Dependent Excited-State Dynamics of [Ru(bpy)(3)](2+)-Modified Amino Acids: Effects of an Amide Linkage and Remote Functional Groups.

The pH-dependent photophysical properties of a series of polypyridyl ruthenium-substituted amino acids were investigated by steady-state and time-resolved luminescence spectroscopy. [H(3)N-DAPA(Rub(2)m)-OH](PF(6))(3) (1), [H(3)N-DABA(Rub(2)m)-OH](PF(6))(3) (2), [H(3)N-Orn(Rub(2)m)-OH](PF(6))(3) (3), and [H(3)N-Lys(Rub(2)m)-OH](PF(6))(3) (4) were obtained by formation of an amide link between the omega-NH(2) group of the respective commercially available amino acid and [Rub(2)(m-OH)](2+) (b = bipyridine, m-OH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid). Due to the absence of significant electronic interactions between the ruthenium chromophore and the amino acid moieties, the energetics and extinction coefficients of the absorption spectra of 1-4 do not change as a function of pH. The luminescence intensities of these complexes, however, show a marked dependence on pH. At low pH (<2), quenching via excited-state protonation of the amide link leads to short lifetimes. In the pH 2-8 range, the lifetimes depend on the amino acid side chain length of the complex. At high pH (>9), lifetimes are approaching that of [Ru(bpy)(3)](2+), suggesting that the amino acid moiety has a negligible effect on nonadiabatic pathways in the excited-state decay of the ruthenium moiety. Our results are discussed with respect to the rapidly growing interest in ruthenium-substituted amino acids as spectroscopic and mechanistic tools in biological systems.

Journal Article↗