First record of the Sparkling-tailed Hummingbird (Tilmatura dupontii, Trochilidae) for Sierra de Huautla Biosphere Reserve, Morelos, Mexico

In August, 2005 we observed and photographed one male of Sparkling-Tailed hummingbird (Tilmatura dupontii) foraging on Firerbush shrub flowers (Hamelia patens, Rubiaceae). The present observation is the first record of this species for the Sierra de Huautla Biosphere Reserve, in the south of Morelos, Mexico, ca. 50 km southeast of previous reported observations of the species in Morelo

Electron transfer reactions between excited diarylmethyl and triarylmethyl carbocations and aromatic donors

The excited singlet states of a variety of diarylmethyl and triarylmethyl carbocations were characterized by fluorescence spectroscopy. The dibenzosuberenyl, xanthenyl and 9-phenylxanthenyl cations are strongly fluorescent (\u3a6 = 0.1-0.3) and have fluorescence lifetimes in the 30-40 ns range in 2,2,2-trifluoroethanol. The fluorescence of each of these cations is efficiently quenched by a variety of substituted aromatics (e.g. cumene, anisole, toluene) with rate constants in excess of 10\u2079 M\u207b\ub9 s\u207b\ub9. There is a correlation between the observed rate constants and the oxidation potential of the aromatic quencher which suggests that an electron transfer process occurs to generate a dibenzosuberenyl radical/silane radical cation pair. This hypthesis is confirmed by irradiation of the dibenzosuberenyl cation in the presence of benzyltrimethylsilane. This reaction produces 5-benzyldibenzocycloheptene, which is formed by addition of the benzyl radical produced via cleavage of the silane radical cation to either the dibenzosuberenyl radical or cation. Quenching studies suggest that the efficiency of product formation is controlled by the competition between cage escape and back electron transfer for the initial geminate radical/radical ion pair.NRC publication: Ye

Application of time-resolved diffuse reflectance techniques in studies of reaction intermediates in suspensions of Bacillus subtilis: Photochem.Photobiol.

NRC publication: Ye

Acidities of arenium ions in acetonitrile

NRC publication: Ye

Four-Month Moon and Mars Crew Water Utilization Study Conducted at the Flashline Mars Arctic Research Station, Devon Island, Nunavut

A categorized water usage study was undertaken at the Flashline Mars Arctic Research Station on Devon Island, Nunavut in the High Canadian Arctic. This study was conducted as part of a long duration four-month Mars mission simulation during the summer of 2007. The study determined that the crew of seven averaged 82.07 L/day over the expedition (standard deviation 22.58 L/day). The study also incorporated a Mars Time Study phase which determined that an average of 12.12 L/sol of water was required for each crewmember. Drinking, food preparation, hand/face, oral, dish wash, clothes wash, shower, shaving, cleaning, engineering, science, plant growth and medical water were each individually monitored throughout the detailed study phases. It was determined that implementing the monitoring program itself resulted in an approximate water savings of 1.5 L/day per crewmember. The seven person crew averaged 202 distinct water draws a day (standard deviation 34) with high water use periods focusing around meal times. No statistically significant correlation was established between total water use and EVA or exercise duration. Study results suggest that current crew water utilization estimates for long duration planetary surface stays are more than two times greater than that required

Photodegradation of the lignin model \u3b1-guaiacoxyacetoveratrone, unusual effects of solvent, oxygen, and singlet state participation

\u3b1-Guaiacoxyacetoveratrone, a lignin model compound, has been studied using a combination of laser flash photolysis and steady state quantum yields. Triplet lifetimes range from 175 to 600\u2002ns while the quantum yields of photodegradation vary from 0.06 to 0.6, depending on the solvent. Singlet processes (\u3a6 ~ 0.1), previously unobserved for aromatic ketones, are implicated in the mechanism, and account for most or all of the degradation in aprotic solvents. Key words: photodegradation, \u3b1-guaiacoxyacetoveratrone.Utilisant une combinaison de la photolyse \ue9clair au laser et des rendements quantiques dans l'\ue9tat stationnaire, on a \ue9tudi\ue9 l'\u3b1-guaiacoxyac\ue9tov\ue9ratrone, un compos\ue9 mod\ue8le de la lignine. Les temps de vie des triplets vont de 175 \ue0 600\u2002ns alors que les rendements quantiques de la photod\ue9gradation varient de 0,06 \ue0 0,6, suivant la nature du solvant. Des processus singulets (\u3a6 ~ 0,1), qui n'ont pas \ue9t\ue9 observ\ue9s ant\ue9rieurement avec des c\ue9tones aromatiques, sont impliqu\ue9s dans le m\ue9canisme et ils permettent d'expliquer toutes, ou pratiquement toutes, les d\ue9gradations observ\ue9es dans les solvants aprotiques.The authors were affiliated with NRC Division of Chemistry at time of publicationNRC publication: Ye

2,3,5,6-Tetrakis(Methylene)-1,4-Cyclohexanediyl (1,2,4,5-Tetramethylenebenzene), a Disjoint Non-Kekule Singlet Hydrocarbon Biradical

The title compound 4a, a purple transient whose main UV-vis absorption band occurs near 490 nm (epsilon = 5000 M-1 cm-1), has been generated by irradiation of 2,3,5,6-tetramethylene-7-oxonorbornane (5a). It has been observed directly by immobilization in frozen matrices or in polymer films and by time-resolved spectroscopy following nanosecond later flash photolysis of the ketone precursor 5a. Although the matrix-immobilized irradiated samples containing biradical 4a show a triplet electron spin resonance (ESR) spectrum at low temperature, some other species is the carrier, since the ESR spectrum persists even after complete photobleaching of the UV-vis spectrum characteristic of 4a. The singlet spin state for biradical 4a, predicted by theory, is confirmed not only by the absence of an ESR spectrum assignable to it but also by the appearance of a C-13 cross-polarization magic angle spinning NMR spectrum (delta = 113 ppm) observed when glassy preparations of 5a-2,3-di-(CH2)-C-13 are irradiated. The rates of dimerization of 4a in fluid media, (1.9-3) x 10(10) M-1 s-1, and the rate of capture by O2, 1.86 x 10(7) M-1 s-1, are also consistent with the behavior expected of a singlet biradical