Structure and reactivity of cyclic imido derivatives of phosphoric acid

New cyclic 1,3-diazaphospholidine-2,4,5-triones were synthesised and their solvolytic behaviour was studied. Methanolysis of 2-methylamino (24) and 2-dimethylamino (25) derivatives showed evidence of cleavage of both imide P-N bonds. This indicates that the ring opening in these derivatives is much slower than the second P-N cleavage in the ring-opened intermediate (30, scheme 11). On the other hand, methanolysis of 1,3-dimethyl-2-phenoxy-1,3,2-diazaphospholidine-2,4,5-trione (22) yielded the product of the cleavage of only one P-N bond. This product (26, scheme 9) was relatively stable towards further solvolysis. This was taken by Mulliez8 as evidence for the addition-elimination mechanism of solvolysis, since in such a case 22 would experience the usual rate accelerating effect upon the formation of the pv intermediate with trigonal bipyramidal structure. The crystal structures of 24 and 25 were determined in order to investigate the low reactivity of 24 and 25 to solvolysis. This low reactivity correlates with the small size (92.3 and 91.9° respectively) of their endocyclic N-P-N angle. In the case of these two compounds, this suggests that the driving force towards the formation of the pv trigonal bipyramidal intermediate is reduced. Aminolysis of 22 with ammonia and p-anisidine resulted in products which indicate that nucleophilic attack takes place exclusively at the phosphorus atom. In the aminolysis with p-anisidine, both P-0 bond cleavage (displacement of phenol, 43) and ring P-N bond cleavage (44) products were obtained. This can be explained in terms of pseudorotation of the initially formed pv intermediate (22A, scheme 23). The aminolysis of 22 with ammonia yielded exclusively the ring-retained P-OPh bond cleavage product (23). This indicates that pseudorotation of the initially formed pv intermediate (22A, scheme 20) is much faster than endocyclic P-N bond cleavage. Finally,amminolysis of 22 with benzylamine was performed.As reported by Mulliez8, this reaction yielded the product (45) of the initial C-N cleavage, followed by ring closure Acidolysis studies were carried out in anhydrous TFA. These studies indicated that the low reactivity towards nucleophilic attack of 2-amino (23), 2-methylamino (24),2-dimethylamino (25) and 2- p-anisidino (43) derivatives may also be accounted for by the lowered electrophilicity of their phosphorus atom. Finally, within the cyclic 1,3-diazaphospholidine-2,4,5-trione series the reactivity of the various compounds was found to be vastly different, depending on which substituents were present on the exocyclic N atom. Part of the work reported in this thesis has been published; viz.; Phosphoric Carboxylic lmides. Part 6. Structure and Reactivity of 1 ,3,2-diazaphospholidine4,5-diones; Crystal Structure of 1,3-Dimethyl-2-methylamino-1,3,2-diazaphospholidine-2,4,5- trione,Alan T. Hutton, Tomasz A. Modro, Margaret L. Niven, and Sonia Scaillet, J. Chem. Soc. Perkin Trans. II, 17 (1986)

High-resolution 40Ar/39Ar chronostratigraphy of the post-caldera (<20ka) volcanic activity at Pantelleria, Sicily Strait

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A revision of the structure and stratigraphy of pre-Green Tuff ignimbrites at Pantelleria (Strait of Sicily)

International audienceAt Pantelleria, peralkaline silicic magmas were erupted across a range of eruptive typologies and magnitudes: pyroclastic flows, Plinian to strombolian pumice fallout and lava flows. In this paper we focus on the intermediate cycle of eruptive activity which is bracketed by ignimbrite units slightly older than the two caldera collapses which marked the volcanological activity of the island. This age interval (180-85 ka) was punctuated by six ignimbrite-forming eruptions (silicic and variably peralkaline) for a cumulative erupted magma volume of approximately 6 km3 dense rock equivalent. Based on new 40Ar/39Ar (Na,K)-feldspar ages and petrographic data, we propose an updated volcanostratigraphic scheme for these welded and rheomorphic ignimbrites that can be summarised as follows: (i) the age of the old ('La Vecchia') caldera collapse is now tightly constrained between 140 and 146 ka and the caldera-forming eruption can be traced to a lithic-rich welded tuff breccia that outcrops in two opposite sectors of the island (south-west and north-east); (ii) four ignimbrite units previously considered unrelated are now merged in two distinct eruptive paroxysmal events at 107 and 85 ka. In particular, the 85 ka eruptive event is comparable in magnitude to the younger (caldera forming) Green Tuff Plinian eruption; (iii) the recurrence patterns of the 107 and 85 ka eruptions, compared to the Green Tuff, allow us to qualitatively assess that the climax in production of low-temperature silicic and peralkaline melt was focused in the age interval 85-45 ka

Increased cardiac autonomic responses to auditory challenges in swaddled infants

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Pacifiers during sleep and sudden infant death

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Discharge from the neonatal intensive care unit with noninvasive respiratory support: an 11-year experience in a tertiary pediatric care center in Belgium.

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Pacifier use modifies infant's cardiac autonomic controls during sleep

Objective: The risk for sudden infant death (SIDS) was postulated to decrease with the use of a pacifier and by conditions increasing parasympathetic tonus during sleep. We evaluated the influence of a pacifier on cardiac autonomic controls in healthy infants. Study design: Thirty-four healthy infants were studied polygraphically during one night: 17 infants regularly used a pacifier during sleep and 17 never used a pacifier. Thumb users or occasional pacifier users were not included in the study. The infants were recorded at a median age of 10 weeks (range 6-18 weeks). Autonomic nervous system (ANS) was evaluated by spectral analysis of the heart rate (HR). The high frequency component of HR spectral analysis reflected parasympathetic tonus and the low frequency on high frequency ratio corresponded to the sympathovagal balance. Results: Most infants (63.6%) lost their pacifier within 30 min of falling asleep. Sucking periods were associated with increases in cardiac sympathovagal balance. During non-sucking periods, in both REM and NREM sleep, infants using a pacifier were characterized by lower sympathetic activity and higher parasympathetic tonus compared with non-pacifier users. Conclusions: The use of pacifiers modifies cardiac autonomic controls during both sucking and non-sucking sleep periods. Non-nutritive sucking could regulate autonomic control in infants. These findings could be relevant to mechanisms implicated in the occurrence of sudden infant deaths during sleep. © 2004 Elsevier Ireland Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Development of cardiopulmonary integration and the role of arousability from sleep.

The recent literature on cardiopulmonary integration in infants is surveyed here, focusing on arousals from sleep. Recent studies reported that the ontogenicity of cardiopulmonary integration cannot be evaluated independently from that of sleep-wake cycles. The issue is of importance for researchers and clinicians evaluating cardiorespiratory characteristics in infants. It also has significant implications in the understanding of clinical conditions, such as parasomnias, obstructive sleep apneas, or some cases of sudden infant death syndrome. The propensity to arouse can be evaluated by exposing the sleeper to awakening challenges. Arousal thresholds are determined by measuring the intensity of the stimulus needed to induce arousals. However, these studies are complicated by factors such as the scoring of the arousal responses. Another difficulty lies in the choice and modality of the arousal stimulus. Noise, gases, light, and nociceptive, mechanical, chemical, or temperature stimuli have all been used to induce arousals. Confounding factors modify the sleeper's responses to a given stimulus. Prenatal drug, alcohol, or cigarette use and the infant's age or, previous sleep deprivation also modify thresholds. Other confounding factors include time of the night, sleep stages, the sleeper's body position, and sleeping conditions. Arousal can also occur spontaneously because of endogenous stimuli. The literature surveyed here also covers such unresolved issues as the clinical significance of aborted arousals, or the mechanisms responsible for the arousal reactions.Journal ArticleReviewinfo:eu-repo/semantics/publishe