Stable Tb Research Articles

Luminescent Lanthanide Complexes with Stereocontrolled Tris(2-pyridylmethyl)amine Ligands: Chirality Effects on Lanthanide Complexation and Luminescence Properties

A series of tris(2-pyridylmethyl)amines including one and two asymmetric centers were synthesized in a stereo-controlled fashion as potential ligands of lanthanide cations. The reaction of chiral pyridylethyl methanesulfonates and bis(pyridylmethyl)amines occurred via an S(N)2 mechanism with complete inversion of asymmetric centers and gave the stereocontrolled tris(2-pyridylmethyl)amines, the stereochemical purity of which was ascertained by GPC, NMR, X-ray, and polarimetry experiments. They formed stable Tb(3+) and Eu(3+) complexes having 1:1, 1:2, and 1:3 stoichiometry (metal:ligand) in CH(3)CN solutions. NMR and UV titration experiments revealed that their complexation behaviors were rarely influenced by ligand chirality but significantly affected by the nature of the counteranion and the concentration ratio of metal to ligand. The Tb(3+) and Eu(3+) complexes with these tripodal ligands exhibited characteristic luminescence spectra upon excitation for pyridine chromophores (260 nm), the intensities of which were largely dependent on the ligand chirality. The meso isomer of the disubstituted tripods particularly exhibited the enhanced terbium luminescence ca. three times more than its diastereomer and un- and monosubstituted tripods. Direct excitation at the lanthanide center had similar chirality effects on the luminescence profiles, indicating that the stereochemistry of the employed ligand largely influenced the lanthanide emitting processes. Since the ligand chirality finely modified the local coordination environments around the lanthanide center, the use of stereocontrolled ligands is applicable in design of the luminescent lanthanide complexes.

Is thermoregulation really unimportant for tropical reptiles? Comparative study of four sympatric snake species from Africa

Most of the studies concerning the thermal and reproductive relationships of snakes have been conducted in temperate regions, whereas very few data are available for African tropical species. In the present study, aspects of the comparative thermal and reproductive ecology of four sympatric freshwater snakes from tropical Africa (the colubrids Natriciteres fuliginoides, N. variegata, Afronatrix anoscopus, and Grayia smythii) are studied with emphasis on exploring whether their thermal ecology relations with reproduction biology may indicate a substantial influence of thermoregulation on their life-history traits (as shown in several studies from temperate-zone reptiles), or whether thermoregulatory biology is less important in tropical reptiles (as suggested in some recent experimental studies). The present study showed that, with minor species-specific differences, thermoregulation certainly has some relevance for the activity and life-history attributes of the studied species, as (i) the females tended to show body temperatures inversely related to their size (snout‐vent length), and (ii) gravid specimens tended to maintain higher body temperatures than non-gravid specimens. However, other sets of our data (e.g., the high and constant Tb exhibited during night-time) strongly indicate that these four species of tropical water snakes can maintain high and stable Tb with little overt thermoregulatory behaviour. As is the rule in most of the other snake species studied to date, the maternal size of the females strongly influenced the number of eggs produced, and testifies that reproductive biology models linking reproductive performance to thermal ecology, highlighted in other snakes from temperate and cool regions, may well apply at least to some extent also to these Afrotropical species. © 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Development of thermoregulation in the sugar glider Petaurus breviceps (Marsupialia: Petauridae)

AbstractYoung, relatively undeveloped sugar gliders Petaurus breviceps have been observed to be left alone in the nest while the mother forages and may be subject to considerable thermal or energetic stress. As no information is available on the development of thermoregulation in this species, which begins reproduction in winter, we measured resting metabolic rate (RMR), body temperature (Tb) and thermal conductance over a range of ambient temperatures (Ta) in 10 sugar gliders from c. 55 days of age until they had grown to adult size. Sugar gliders were unable to maintain a stable Tb over a Ta range of 30–15 °C until the age of 95–100 days, although they raised RMR somewhat as Ta decreased. Further growth resulted in a steady decrease in mass‐specific RMR, an increase in Tb and a substantial decrease in thermal conductance. Our study shows that young gliders below the age of 100 days rely largely on heat produced by adults to maintain a high Tb, but are well able to cope with regular falls in Tb of > 10 °C and a concomitant decrease of RMR. This thermal tolerance and reduction in energy expenditure should allow the mother to forage and replenish her own body fuels while her offspring are left alone in the nest.

RADIOLOGIC MANIFESTATIONS OF PULMONARY TUBERCULOSIS

In summary, the following points are reemphasized: 1. The chest film is the mainstay in the radiologic evaluation of suspected or proven pulmonary TB. CT is occasionally useful for clarifying confusing findings but has not been conclusively shown to have a significant impact on patient management. 2. Primary TB is increasingly a disease of adults. 3. Primary TB usually manifests as a parenchymal consolidation in any pulmonary lobe or segment. Distinguishing features from typical bacterial pneumonia include associated adenopathy, lack of systemic toxicity, failure to respond to conventional antibacterial therapy, and recent PPD conversion. 4. Associated ipsilateral hilar and/or mediastinal adenopathy is almost universal in children with primary TB but is less common in adults. Adenopathy without parenchymal disease is an unusual but well-reported manifestation. 5. Many of the so-called unusual manifestations of adult TB are the usual manifestations of primary disease. The terms adult and childhood TB should be discarded. 6. Postprimary TB typically manifests as a heterogeneous, often cavitary opacity in the apical and posterior segments of the upper lobes and the superior segments of the lower lobes. Lymphadenopathy is rare. 7. Activity of postprimary disease cannot be accurately assessed by chest radiography. Radiographic stability for 6 months and negative sputum cultures is the best indicator of inactive disease. The descriptive terms inactive or old TB should be discarded in favor of radiographically stable TB, as viable bacilli may persist despite adequate therapy. 8. Cavitation is the most important radiologic finding in postprimary disease. Cavitation implies a high bacillary burden, high infectivity, and is associated with numerous complications including endobronchial spread, tuberculous empyema, hematogenous dissemination, pulmonary artery pseudoaneurysm, and so forth. 9. Tuberculous pleurisy is more common in primary than postprimary disease. It is a common presenting manifestation in young adults. The effusions are unilateral, large, and self-limited. The pleural fluid usually is a serous exudate with a marked lymphocytosis. Fluid cultures are frequently negative. Correct diagnosis and therapy is important, as untreated patients are at high risk for subsequent pulmonary reactivation. 10. Miliary disease is also more common in primary than postprimary disease; however, its frequency in elderly patients with postprimary TB is increasing. This form, known as late generalized TB, is apt to be misdiagnosed or not diagnosed in life and has a high mortality.

Metabolic adaptations to hypothermia in snipe hatchings (Gallinago media)

1. Physiological adaptation to hypothermia were studied in newly hatched great snipe chicks (Gallinago media) by measuring oxygen uptake (VO2), heart rate (HR), respiratory frequency (RF), and body temperature (Tb) at different ambient temperatures (Ta). 2. Tb of 1-day-old chicks at Ta of 35°C stabilized at about 40°C. At Ta between 20 and 30°C the chicks maintained a Tb about 8°C above Ta. Hatchlings maintained a higher gradient when active than when resting. Below 20°C they were unable to maintain a stable Tb. 3. In resting hatchlings VO2 was similar at Ta between 35 and 20°C (Tb 40–30°C), VO2 range 1.7–2.5 ml·g-1·h-1. Below 20°C, VO2 declined with time. 4. The HR of 1-day-old chicks fell linearly with Tb during cooling. The Q10 of the HR was 1.7 at Tb 38°C and increased to 3.0 at 29°C. The RF showed a slight tendency to decrease with decreasing Tb. 5. It is concluded that the ability to maintain normal dexterity at low Tb is an important aspect of snipe survival strategy. Maintaining a temperature gradient rather than a constant high Tb presumably saves energy. It is suggested that the mechanisms whereby VO2 is maintained at a low Tb may involve isoenzymes and adaptations of the nervous system. However, such adaptations would not seem to affect the pacemaker mechanism as evidenced by the high Q10 of the HR.

Weather, microclimate, and energy costs of thermoregulation for breeding Adélie Penguins.

We measured meteorological conditions and estimated the energy costs of thermoregulation for young and adult Adélie Penguins (Pygoscelis adeliae) at a breeding colony near the Antarctic Peninsula. Air temperatures averaged < 5°C and strong winds were frequent. Operative temperatures (Te) for adults ranged from -8 to 28°C, averaging 5-6°C, for the period from courtship to fledging of chicks. The average energy cost of thermoregulation (Cth) for adult penguins was equivalent to 10-16% of basal metabolism. Cth comprised about 15% of the estimated daily energy budget (DEB) of incubating adults, but only about 1% of the DEB of adults feeding chicks. The Te's for chicks older than 14 days ranged from 0 to 31°C, averaging 8.0 C. The Cth for downy chicks ranged from about 31% of minimal metabolic rate (MMR) in 1 kg chicks to about 10% of MMR in 3 kg chicks. Between initial thermal independence (age 12-14 days) and the cessation of parental feeding (age 35-40 days), chicks use about 10-11% of assimilated energy for thermoregulation. Cth is equivalent to about 17% of the MMR of fledglings during their 2-3 week fast. We observed no indication of thermal stress (i.e., conditions in which birds cannot maintain stable Tb) in adults and no indication of cold stress in any age class. However, on clear, calm days when air temperature exceeds 7-10°C for several hours, downy chicks are vulnerable to lethal hyperthermia.

Thermal Ecology of the Tropical Iguanid Lizard, Leiocephalus schreibersi

-The Hispaniolan lizard, Lezocephalus schreibersi, precisely maintained a narrow range of body temperatures (Tb) (R = 36.7, SE = 0.17 C) that was significantly above concomitant air (Ta) and site (Ts) temperatures throughout all but the last hour of their emergence period. Lizards moved frequently between shade and sun throughout the day. Hourly basking frequency of the population was greatest (80%) when most lizards were emerging from their burrows (0900-0959 h), gradually declined to 35% at midday, then oscillated between 20-40% for the remaining afternoon hours. An hour before the majority of lizards entered their borrows (1700 h), movement markedly decreased and Tb declined to overlap Ts, as lizards appeared to relax thermoregulatory behavior. An important feature of this species' thermoecology is that the elevated and relatively stable Tb of Leiocephalus schreabersi permitted the lizards to be physically active during the entire day; rising ambient temperatures during the day never reached the maintained Tb Of this stenothermic species. In addition, no seasonal effects (November vs. May-June) were detected in the above thermal profile.