Photolyse et photo-oxydation d'aldéhydes saturés ramifiés

L’étude cinétique de la photolyse d'aldéhydes saturés à chaîne ramifiée et de son inhibition par le napthalène permet de préciser le comportement de ces molécules dans le domaine de concentration 10–2M – 10–1M ; on peut déduire du mécanisme un procédé simple de mesure du rendement quantique de transition inter-systèmes S1 → T1, l'état excité triplet T1 (nπ*) se désactivant essentiellement par un processus bimoléculaire d'autodésactivation. Le rendement quantique de population du triplet est égal à 0,295, 0,34 et 0,41 respectivement pour l'éthyl-2 butanal, le diméthyl-2,2 propanai et l'isobutanal.L'étude cinétique de la photo-oxydation de ces mêmes aldéhydes, inhibée par le napthalène montre que la durée de vie de l'état triplet n'est pas perturbée par l'oxygène dissous dans le n-heptane. La comparaison entre photolyse et photo-oxydation permet de préciser les processus d'amorçage de la réaction en chaînes d'oxydation

Photolyse et photo-oxydation d'aldéhydes satures normaux

Le niveau triplet T1 (nπ*) d'aldéhydes saturés à chaîne droite se désactive essentiellement par un processus bimoléculaire d'autodésactivation, lorsque la concentration de l'aldéhyde est comprise entre 10–2 et 10–1 M. Le rendement quantique de population du niveau triplet T1 (nπ*) de l’aldéhyde est alors égal à la moitié du rendement quantique de disparition réelle. La photo-oxydation du n-propanal, du n-butanal et du n-hexanal implique un processus d’amorçage des chaînes d'oxydation issu du niveau excité singulet plus efficace que celui issu de l'état excité triplet

Comportement photochimique des acides coumariques et actinométrie à faible densité optique et en faisceau non parallèle

L'isomérisation photochimique cis [math] trans du dianion de l’acide orthocoumarique est un processus primaire sur lequel peut être basée une technique actinométrique très rapide et très sensible. Cette technique s'est avérée particulièrement intéressante pour évaluer le nombre de photons absorbés dans les solutions de très faible densité optique soumises à une irradiation en faisceau non parallèle. Comme exemples d’application, on donne les résultats obtenus sur la photo- oxydation du phénol et de crésols excités à 253,7 nm, en solution très diluée

Side Effect of Dopamine Replacement Therapy and Deep Brain Stimulation in Parkinson’s Disease

International audienc

Dopamine replacement therapy and deep brain stimulation of the subthalamic nuclei induce modulation of emotional processes at different spatial frequencies in Parkinson's disease.

International audienceBackground: Deep brain stimulation of the subthalamic nuclei (STN-DBS) is an effective treatment for the most severe forms of Parkinson's disease (PD) and is intended to suppress these patients' motor symptoms. However, be it in association with Dopamine Replacement Therapy (DRT) or not, STN-DBS may in some cases induce addictive or emotional disorders. Objective: In the current study, we suggest that PD patients suffer from emotional deficits that have not been revealed in previous studies because in those experiments the stimuli were displayed for a time long enough to allow patients to have recourse to perceptual strategies in order to recognize the emotional facial expressions (EFE). Methods: The aim of the current article is to demonstrate the existence of emotional disorders in PD by using a rapid presentation of the visual stimuli (200-ms display time) which curtails their perceptual analysis, and to determine whether STN-DBS, either associated or not associated with DRT, has an impact on the recognition of emotions. Results: The results show that EFE recognition performance depends on both STN-DBS ('on' vs. 'off') and medication ('on' vs. 'off'), but also that these variables have an interactive influence on EFE recognition performance. Moreover, we also reveal how these EFE impairments depend on different spatial frequencies perceptual channels (related to different cortical vs. subcortical neural structures). Conclusions: The effect of PD without therapy seems to be particularly acute for LSF emotional faces, possibly due to a subcortical dysfunction. However, our results indicate that the joint action of STN-DBS and DRT could also disrupt recognition of emotional expressions at the level of occipito-temporal cortical areas (processing HSF visual information) inducing broad global impairment of EFE at the level of HSF visual channels

Side Effect of Dopamine Replacement Therapy and Deep Brain Stimulation in Parkinson’s Disease

International audienc

The combined effect of subthalamic nuclei deep brain stimulation and L-dopa increases emotion recognition in Parkinson's disease.

International audienceDeep brain stimulation of the subthalamic nucleus (DBS) is a widely used surgical technique to suppress motor symptoms in Parkinson's disease (PD), and as such improves patients' quality of life. However, DBS may produce emotional disorders such as a reduced ability to recognize emotional facial expressions (EFE). Previous studies have not considered the fact that DBS and l-dopa medication can have differential, common, or complementary consequences on EFE processing. A thorough way of investigating the effect of DBS and l-dopa medication in greater detail is to compare patients' performances after surgery, with the two therapies either being administered ('on') or not administered ('off'). We therefore used a four-condition (l-dopa 'on'/DBS 'on', l-dopa 'on'/DBS 'off', l-dopa 'off'/DBS 'on', and l-dopa 'off'/DBS 'off') EFE recognition paradigm and compared implanted PD patients to healthy controls. The results confirmed those of previous studies, yielding a significant impairment in the detection of some facial expressions relative to controls. Disgust recognition was impaired when patients were 'off' l-dopa and 'on' DBS, and fear recognition impaired when 'off' of both therapies. More interestingly, the combined effect of both DBS and l-dopa administration seems much more beneficial for EFE recognition than the separate administration of each individual therapy. We discuss the implications of these findings in the light of the inverted U curve function that describes the differential effects of dopamine level on the right orbitofrontal cortex (OFC). We propose that, while l-dopa could "overdose" in dopamine the ventral stream of the OFC, DBS would compensate for this over-activation by decreasing OFC activity, thereby restoring the necessary OFC-amygdala interaction. Another finding is that, when collapsing over all treatment conditions, PD patients recognized more neutral faces than the matched controls, a result that concurs with embodiment theories