Si-C(sp3) bond activation through oxidative addition at a Rh(i) centre.

An easy, direct and room temperature silicon-carbon bond activation is reported. The reaction of [RhCl(coe)2]2 with the silane Si(Me)2(o-C6H4SMe)2 in the presence of an halide extractor provokes a Si-CH3 bond cleavage yielding a cationic silyl-methyl-Rh(iii). In contrast, if the reaction is performed using the Rh(i) bis-alkene dimers, [RhCl(cod)]2 or [RhCl(nbd)]2, the Si-CH3 bond activation does not occur.

Optimising the acquisition and retention of heat acclimation.

Heat acclimation (HA) often starts in a moderately hot environment to prevent thermal overload and stops immediately prior to athletic activities. The aims of this study were (1) to establish whether acclimation to a moderately hot climate is sufficient to provide full acclimation for extreme heat and (2) to investigate the physiological responses to heat stress during the HA decay period. 15 male subjects exercised for 9 consecutive days at 26° C Wet Bulb Globe Temperature (WBGT) and 3 days at 32° C WBGT on a cycle ergometer for up to 2 h per day and repeated the exercise 3, 7 and 18 days later in 26° C WBGT. Rectal temperature (T (re)) and heart rate (HR) were measured during 60 min of steady state exercise (∼45% of maximum oxygen uptake). During days 1-9, end-exercise T (re) was reduced from 38.7±0.1 to a plateau of 38.2±0.1° C (p<0.05), HR was reduced from 156±10 to 131±11 bpm (p<0.05). No changes in HR and T (re) occurred during the 3 days in the very hot environment. However, T (re) during rest and exercise were significantly lower by 0.4-0.5° C after HA compared with day 9, suggesting that heat acclimation did not decay but resulted in further favourable adaptations.

Ambient temperature and the pituitary hormone responses to exercise in humans.

Pituitary hormones have an important role during exercise yet relatively little is known about the stimulus for their release. Body temperature progressively increases during prolonged steady-state exercise in the heat and we have investigated the role that this may play in the release of prolactin, growth hormone and cortisol (as an indicator of adrenocorticotropic hormone) into the circulation. Fit young male subjects exercised at 73% V(O2,max) until volitional fatigue at 20 degrees C and at 35 degrees C (30% relative humidity at both temperatures). Rectal temperature and mean skin temperature were monitored and blood samples analysed for lactate, glucose, cortisol, growth hormone and prolactin concentrations. During the first 20 min, core temperature rose continuously and to a similar extent at both temperatures, while mean skin temperature was approximately 4 degrees C lower during exercise in the cool. Blood glucose concentration was essentially constant throughout the period of exercise while lactate concentration increased in the first 10 min and then remained constant with very similar changes in the two exercise conditions. Prolactin and growth hormone concentrations both increased during the exercise period while the concentration of cortisol declined slightly before rising slightly over the 40 min period. Prolactin release was significantly greater when exercise was carried out in the heat while there was no difference in the release of growth hormone or cortisol in the two conditions. When plotted as a function of rectal temperature, growth hormone concentration showed a linear relationship which was the same at ambient temperatures of 35 degrees C and 20 degrees C. Prolactin concentration had a curvilinear relationship with rectal temperature and this differed markedly at the two ambient temperatures. Cortisol concentration showed no dependence on any measure of body temperature. Our results are consistent with some aspect of body temperature being a stimulus for growth hormone and prolactin secretion; however, the precise mechanism clearly differs between the two hormones and we suggest that skin temperature modulates prolactin release, but does not affect the release of growth hormone.

[(PPh3)Ag(CB11H6Y6)] (Y = H, Br): highly active, selective and recyclable Lewis acids for a hetero-Diels-Alder reaction.

The complex [(PPh3)Ag(CB11H6Br6)] 1 is an effective and selective catalyst (0.1 mol% loading) for a hetero-Diels-Alder reaction, which shows a marked dependence on the presence of trace amounts of water, while addition of Ag[Y] [Y = CB11H12, CB11H6Br6, O3SCF3] to a phosphine functionalized support gives an efficient and recyclable Lewis acid catalyst for this transformation.

Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise.

A study was undertaken in man to investigate whether during moderate cold stress, the proportion of carbohydrate (CHO) oxidized is increased, and whether prior prolonged exhaustive exercise compromises thermoregulation. Eight euglycaemic men were cooled by a liquid-conditioned suit (1) after an overnight fast (Con) and (2) approximately 2 h after an exercise protocol in which CHO availability was substantially lowered (Post-Ex). The cooling stimulus lasted 90 min (Cooling) and was preceded by a 30 min thermo-neutral baseline phase (Base). In Con, aural temperature (T(aural)) and the rate of CHO oxidized (CHOox) were not altered from the values at Base during Cooling, whereas the following were increased: the rate of heat production (Hprod, approximately 1.9-fold), thigh electromyographical activity (EMG, approximately 2.5-fold), and the rate of fat oxidized (FATox, approximately 1.7-fold). In Post-Ex, T(aural) did not decrease from the value at Base during Cooling, and compared with Con, EMG, CHOox and the rate of heat loss were not different, whereas Hprod (P < or = 0.01), FATox (P < or = 0.01) and mean skin temperature (P < or = 0.01) were higher, and T(aural) was lower (P < or = 0.05). It is concluded that during moderate cold stress, shivering thermogenesis is supported by an increase in the oxidation of fat, and despite an alteration in the initial thermoregulatory responses to Cooling approximately 2 h after exhaustive exercise, thermoregulation was not impaired.

The influence of cold stress and a 36- h fast on the physiological responses to prolonged intermittent walking in man.

In a previous study, rectal temperature (Tre) was found to be lower, and oxygen consumption (VO2) and the respiratory exchange ratio (R) were higher in a cold (+5 degrees C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent walking at approximately 30% of peak VO2 (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226-R233, 1997). The aim of the present study was to establish whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15 min rest, 45 min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the exercise protocol approximately 120 min after a standard meal (FED/ COLD), whereas in the other the subjects had fasted for 36 h (FASTED/COLD). The first two exercise periods were conducted at a higher intensity (HIGHER, 6 km x h[-1] and 10% incline), than the four subsequent exercise periods (LOW, 5 km x h[-1] and 0% incline). There was no difference in the time endured in FED/ COLD and FASTED/COLD. In FASTED/COLD compared with FED/COLD, R was lower during HIGHER and LOW, and Tre was lower during LOW, whereas there was no difference in VO2, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting exercise performance under these experimental conditions.

Physiological responses to cold stress during prolonged intermittent low- and high-intensity walking.

In a previous study [Am. J. Physiol. 272 (Regulatory Integrative Comp. Physiol. 41): R226-R233, 1997], the physiological responses to 240 min of intermittent low-intensity walking exercise in a cold (+5 degrees C), wet, and windy environment (Cold) may have been influenced by a 120-min preceding phase of intermittent higher-intensity exercise. Furthermore, the physiological responses observed during this latter phase may have been different if it had been more prolonged. To address these questions, active men attempted a 360-min intermittent (15 min of rest, 45 min of exercise) exercise protocol in Cold and a thermoneutral environment (+15 degrees C, Neutral) at a low (0% grade, 5 km/h; Low; n = 14) and a higher (10% grade, 6 km/h; High; n = 10) intensity. During Low, rectal temperature was lower in Cold than in Neutral, whereas O2 consumption, carbohydrate oxidation, plasma norepinephrine and epinephrine, and blood lactate were higher. During High, Cold had a similar but less marked influence on the thermoregulatory responses to exercise than during Low. In conclusion, the physiological responses to Low are similarly influenced by Cold whether or not they are preceded by High. Furthermore, during intermittent exercise up to an intensity of approximately 60% of peak O2 consumption, a cold, wet, and windy environment will influence the physiological responses to exercise and potentially impair performance.

Physiological responses to a cold, wet, and windy environment during prolonged intermittent walking.

The potentially deleterious influence of body cooling on the thermoregulatory and metabolic responses to prolonged walking exercise has not been established. To address this problem, 10 men completed a 6-h intermittent (15 min rest, 45 min exercise) walking protocol in a thermoneutral (+15 degrees C) condition (Neutral) and a cold (+5 degrees C), wet, and windy condition (Cold). The first two exercise periods were conducted at a higher intensity (Higher, 6 km/h and 10% incline) than the subsequent four exercise periods (Lower, 5 km/h and 0% incline). Rectal temperature was lower and heart rate no different in Cold compared with Neutral, whereas the following were higher: oxygen consumption, respiratory exchange ratio, plasma norepinephrine and epinephrine, and blood lactate and glucose. There was no environmental influence on these variables during Higher. In conclusion, heat production during Lower was not sufficient to offset heat loss to the cold environment, and the resulting reduction in rectal temperature and metabolic perturbations may be detrimental if exercise is prolonged.