Charge State Dynamics During Excitation and Depletion of the Nitrogen Vacancy Center in Diamond

The charge state dynamics of the nitrogen-vacancy (NV) center in diamond play a key role in a wide range of applications, yet remain imperfectly understood. Using single ps-pulses and pulse pairs, we quantitatively investigate the charge dynamics associated with excitation and fluorescence depletion of a single NV center. Our pulsed excitation approach permits significant modeling simplifications, and allows us to extract relative rates of excitation, stimulated emission, ionization, and recombination under 531 nm and 766 nm illumination. By varying the duration between paired pulses, we can also investigate ionization and recombination out of metastable states. Our results are directly applicable to experiments employing stimulated emission-depletion imaging, and can be used to predict optimal operating regimes where excitation and stimulated emission are maximized relative to charge-state-switching processes

Involvement of gut microbial fermentation in the metabolic alterations occurring in n-3 polyunsaturated fatty acids-depleted mice

<p>Abstract</p> <p>Backround</p> <p>Western diet is characterized by an insufficient n-3 polyunsaturated fatty acid (PUFA) consumption which is known to promote the pathogenesis of several diseases. We have previously observed that mice fed with a diet poor in n-3 PUFA for two generations exhibit hepatic steatosis together with a decrease in body weight. The gut microbiota contributes to the regulation of host energy metabolism, due to symbiotic relationship with fermentable nutrients provided in the diet. In this study, we have tested the hypothesis that perturbations of the gut microbiota contribute to the metabolic alterations occurring in mice fed a diet poor in n-3 PUFA for two generations (n-3/- mice).</p> <p>Methods</p> <p>C57Bl/6J mice fed with a control or an n-3 PUFA depleted diet for two generations were supplemented with prebiotic (inulin-type Fructooligosaccharides, FOS, 0.20 g/day/mice) during 24 days.</p> <p>Results</p> <p>n-3/-mice exhibited a marked drop in caecum weight, a decrease in lactobacilli and an increase in bifidobacteria in the caecal content as compared to control mice (n-3/+ mice). Dietary supplementation with FOS for 24 days was sufficient to increase caecal weight and bifidobacteria count in both n-3/+ and n-3/-mice. Moreover, FOS increased lactobacilli content in n-3/-mice, whereas it decreased their level in n-3/+ mice. Interestingly, FOS treatment promoted body weight gain in n-3/-mice by increasing energy efficiency. In addition, FOS treatment decreased fasting glycemia and lowered the higher expression of key factors involved in the fatty acid catabolism observed in the liver of n-3/-mice, without lessening steatosis.</p> <p>Conclusions</p> <p>the changes in the gut microbiota composition induced by FOS are different depending on the type of diet. We show that FOS may promote lactobacilli and counteract the catabolic status induced by n-3 PUFA depletion in mice, thereby contributing to restore efficient fat storage.</p

Nutritional Deficiencies and Phospholipid Metabolism

Phospholipids are important components of the cell membranes of all living species. They contribute to the physicochemical properties of the membrane and thus influence the conformation and function of membrane-bound proteins, such as receptors, ion channels, and transporters and also influence cell function by serving as precursors for prostaglandins and other signaling molecules and modulating gene expression through the transcription activation. The components of the diet are determinant for cell functionality. In this review, the effects of macro and micronutrients deficiency on the quality, quantity and metabolism of different phospholipids and their distribution in cells of different organs is presented. Alterations in the amount of both saturated and polyunsaturated fatty acids, vitamins A, E and folate, and other micronutrients, such as zinc and magnesium, are discussed. In all cases we observe alterations in the pattern of phospholipids, the more affected ones being phosphatidylcholine, phosphatidylethanolamine and sphingomyelin. The deficiency of certain nutrients, such as essential fatty acids, fat-soluble vitamins and some metals may contribute to a variety of diseases that can be irreversible even after replacement with normal amount of the nutrients. Usually, the sequelae are more important when the deficiency is present at an early age

Alpha-tocopherol acquisition by plasma lipoproteins and changes in lipoprotein profile after cardiac surgery

Alpha-tocopherol, the most abundant form of vitamin E in man, is transported in the circulation by plasma lipoproteins. It plays important roles, not only in preventing lipid peroxidation, but also in modulating several cell functions such as cell signaling and gene expression. While chylomicrons transport dietary alpha-tocopherol after intestinal absorption, LDL and HDL are the major carriers of alpha-tocopherol in fasting plasma and largely contribute to its delivery to cells and tissues. Exchanges of alpha-tocopherol occur between plasma lipoproteins. In addition, alpha-tocopherol transfers have also been observed, in both directions, between plasma lipoproteins and artificial chylomicrons such as intravenous lipid emulsion particles used in parenteral nutrition. In acute conditions, intravenous supply of vitamin E via lipid emulsions, which bypasses the intestinal tract, may offer some advantages over oral administration to rapidly increase alpha-tocopherol plasma concentration. However, many questions remain unanswered regarding kinetics and factors facilitating vitamin E exchanges between lipid emulsions and plasma lipoproteins. The first part of this work aimed at characterizing alpha-tocopherol transfers between alpha-tocopherol rich emulsion particles and plasma lipoproteins as well as the potential for plasma proteins to modulate such transfers. An in vitro model of incubation was used in which emulsion triglyceride concentration was relatively low and lipoprotein levels comparable to those commonly found in the circulation. Results indicate a high capacity for LDL and HDL to acquire extra-amounts of alpha-tocopherol by rapid mass transfers from alpha-tocopherol-rich emulsion particles. Data further shows that, at a fixed alpha-tocopherol concentration provided by emulsion particles, the limiting factor for alpha-tocopherol enrichment is not the capacity of plasma lipoproteins to accommodate extra-amounts of alpha-tocopherol but the facilitating effect of plasma proteins on alpha-tocopherol transfer, the duration of the incubation and possibly the competition between different acceptor particles. Two lipid transfer proteins, PLTP and CETP, appear to largely mediate facilitation of alpha-tocopherol transfer; however, other plasma proteins may be involved. Data further shows that alpha-tocopherol enriched LDL and HDL can readily transfer newly acquired alpha-tocopherol to cells, without any regulation by plasma proteins.Short-term prophylactic vitamin E supplementation has been suggested to be beneficial in some patients in acute conditions who present reduced plasma vitamin E concentrations in association with important changes in plasma lipids and severe oxidative stress. However, it was not clear whether low plasma vitamin E concentration in critically ill patients is related to changes in the composition of plasma lipoproteins or to a decrease in the number of alpha-tocopherol carriers. In the second part of this work, two clinical studies were conducted to analyze changes of lipoprotein concentration and composition in relation to inflammatory reaction and oxidative stress in selected subgroups of critically ill patients, namely patients undergoing cardiac surgery with different procedures. Important changes in LDL and HDL lipid content were observed, some of which contrast with previous observations made in critically ill septic patients. The reduced plasma level of alpha-tocopherol measured after cardiac surgery is entirely due to a reduced number of circulating LDL and HDL particles. Data suggests that such reduced number in alpha-tocopherol carriers post-surgery may impede the delivery of alpha-tocopherol to cells in conditions of increased requirements due to oxidative stress. Avoidance of extracorporeal circulation during cardiac surgery does not reduce inflammation-related changes in plasma lipids but largely prevents oxidative stress. This data on changes occurring in plasma lipoproteins may help to better define strategies against pro-inflammatory changes or oxidative stress. If further studies would confirm a clinical benefit with evidence-based rationale, alpha-tocopherol enriched lipid emulsions may be used to guarantee a sufficient alpha-tocopherol supply in acute conditions associated with fewer alpha-tocopherol transporters and increased requirements due to high risk of oxidative tissue injury.Doctorat en Sciences biomédicales et pharmaceutiquesinfo:eu-repo/semantics/nonPublishe

Alpha-tocopherol acquisition by plasma lipoproteins and changes in lipoprotein profile after cardiac surgery

Alpha-tocopherol, the most abundant form of vitamin E in man, is transported in the circulation by plasma lipoproteins. It plays important roles, not only in preventing lipid peroxidation, but also in modulating several cell functions such as cell signaling and gene expression. While chylomicrons transport dietary alpha-tocopherol after intestinal absorption, LDL and HDL are the major carriers of alpha-tocopherol in fasting plasma and largely contribute to its delivery to cells and tissues. Exchanges of alpha-tocopherol occur between plasma lipoproteins. In addition, alpha-tocopherol transfers have also been observed, in both directions, between plasma lipoproteins and artificial chylomicrons such as intravenous lipid emulsion particles used in parenteral nutrition. In acute conditions, intravenous supply of vitamin E via lipid emulsions, which bypasses the intestinal tract, may offer some advantages over oral administration to rapidly increase alpha-tocopherol plasma concentration. However, many questions remain unanswered regarding kinetics and factors facilitating vitamin E exchanges between lipid emulsions and plasma lipoproteins. The first part of this work aimed at characterizing alpha-tocopherol transfers between alpha-tocopherol rich emulsion particles and plasma lipoproteins as well as the potential for plasma proteins to modulate such transfers. An in vitro model of incubation was used in which emulsion triglyceride concentration was relatively low and lipoprotein levels comparable to those commonly found in the circulation. Results indicate a high capacity for LDL and HDL to acquire extra-amounts of alpha-tocopherol by rapid mass transfers from alpha-tocopherol-rich emulsion particles. Data further shows that, at a fixed alpha-tocopherol concentration provided by emulsion particles, the limiting factor for alpha-tocopherol enrichment is not the capacity of plasma lipoproteins to accommodate extra-amounts of alpha-tocopherol but the facilitating effect of plasma proteins on alpha-tocopherol transfer, the duration of the incubation and possibly the competition between different acceptor particles. Two lipid transfer proteins, PLTP and CETP, appear to largely mediate facilitation of alpha-tocopherol transfer; however, other plasma proteins may be involved. Data further shows that alpha-tocopherol enriched LDL and HDL can readily transfer newly acquired alpha-tocopherol to cells, without any regulation by plasma proteins.Short-term prophylactic vitamin E supplementation has been suggested to be beneficial in some patients in acute conditions who present reduced plasma vitamin E concentrations in association with important changes in plasma lipids and severe oxidative stress. However, it was not clear whether low plasma vitamin E concentration in critically ill patients is related to changes in the composition of plasma lipoproteins or to a decrease in the number of alpha-tocopherol carriers. In the second part of this work, two clinical studies were conducted to analyze changes of lipoprotein concentration and composition in relation to inflammatory reaction and oxidative stress in selected subgroups of critically ill patients, namely patients undergoing cardiac surgery with different procedures. Important changes in LDL and HDL lipid content were observed, some of which contrast with previous observations made in critically ill septic patients. The reduced plasma level of alpha-tocopherol measured after cardiac surgery is entirely due to a reduced number of circulating LDL and HDL particles. Data suggests that such reduced number in alpha-tocopherol carriers post-surgery may impede the delivery of alpha-tocopherol to cells in conditions of increased requirements due to oxidative stress. Avoidance of extracorporeal circulation during cardiac surgery does not reduce inflammation-related changes in plasma lipids but largely prevents oxidative stress. This data on changes occurring in plasma lipoproteins may help to better define strategies against pro-inflammatory changes or oxidative stress. If further studies would confirm a clinical benefit with evidence-based rationale, alpha-tocopherol enriched lipid emulsions may be used to guarantee a sufficient alpha-tocopherol supply in acute conditions associated with fewer alpha-tocopherol transporters and increased requirements due to high risk of oxidative tissue injury.Doctorat en Sciences biomédicales et pharmaceutiquesinfo:eu-repo/semantics/nonPublishe

Charge state dynamics during excitation and depletion of the nitrogen vacancy center in Diamond

The nitrogen-vacancy (NV) defect center in diamond shows great promise for many applications in quantum information processing and precision sensing. The NV center naturally occurs in two different charge states (NV0 and NV-), which have very different optical and spin properties. Understanding laser-induced switching between these charge states is essential for taking advantage of the NV center's properties in many contexts. Reducing the amount of optically-induced ionization is often important for increasing SNR and spin-coherence times. On the other hand charge state switching can be taken advantage of through spin-to-charge conversion techniques, enhancing optical spin-state readout of the NV center [1].A method for charge state initialization and readout using yellow (594 nm) laser illumination was used to investigate the ionization and recombination processes from other laser sources. The commonly used CW green (532 nm) laser was found to follow a simple two-level process at low powers while deviation occurred at higher powers, resulting in an unexpected peak in NV- population. This unexpected behaviour was found to be associated with an unknown process relaxing in the dark with a lifetime of 8.8 ± 0.6 µs. A spin-dependence in ionization was also observed due to the reduced ionization rate out of the metastable singlet state in NV- at this wavelength.Pulsed green (531 nm) and red (766 nm) illumination were used to study the charge state dynamics during excitation and depletion processes. Red illumination is known to cause depletion of NV- fluorescence, but it was initially unclear how much of this reduction is due to stimulated emission and how much is from charge state ionization, as both are non-radiative processes. By simultaneously modeling the measured excitation, fluorescence depletion, and charge state switching of the pulsed lasers, we were able to quantitatively extract the relative rates of excitation, ionization, and stimulated emission for the two colors of pulsed laser. The models developed through these measurements were used to calculate the amount of expected spin-polarization after a single excitation then depletion pulse sequence. These results have implications for stimulated emission depletion (STED) microscopy [2], laser threshold magnetometry [3] and spin to charge conversion [1,4].Le centre azote-lacune (ou centre NV) du diamant démontre un potentiel élevé pour un grand nombre d'applications en traitement d'information quantique ainsi que pour la détection haute-précision. Le centre NV se présente naturellement sous deux états de charge distincts (NV0 et NV-) possédant des propriétés optiques et de spin trés différentes. Dans de nombreux contextes, il est essentiel de comprendre le passage d'un état de charge à l'autre induit par illumination laser pour mettre à profit les propriétés du centre NV. Réduire l'ionisation photoinduite est souvent important pour l'augmentation du rapport signal sur bruit ainsi que pour le maintien de la cohérence du spin. De manière alternative, la commutation de niveau de charge peut être exploitée par des techniques de conversion spin/charge, améliorant la mesure optique de l'état de spin du centre NV [1].Une méthode d'initialisation et de mesure du niveau de charge utilisant une illumination par laser jaune (594 nm) a été utilisée pour investiguer les processus d'ionisation et de recombinaison provenant d'autres sources laser. Il a été constaté que le laser vert (532 nm) à ondes continues, couramment utilisé, suit un processus simple à deux paliers à faibles puissances tandis qu'une déviation se produit pour des puissances plus importantes, provoquant un pic inattendu dans la population de NV-. Ce comportement imprévu a été associé à un processus inconnu relaxant dans l'absence d'illumination avec une durée de vie de 8.8 ± 0.6 µs. Une dépendance de l'ionisation par rapport à l'état de spin a aussi été observée dû à un taux d'ionisation réduit de l'état singulet métastable du NV- à cette longueur d'onde.L'illumination en mode pulsé de lasers vert (531 nm) et rouge (766 nm) a été utilisée pour étudier la dynamique des niveaux de charge durant les processus d'excitation et de déplétion. L'illumination rouge peut causer la déplétion de la fluorescence NV- mais il était initialement peu clair à quel point cette réduction était dû à l'émission stimulée ou à l'ionisation du niveau de charge, puisque tous les deux sont des processus non-radiatifs. En modélisant simultanément l'excitation mesurée, la déplétion de la fluorescence et la commutation du niveau de charge induites par les lasers pulsés, il a été possible d'extraire de faç con quantitative les taux relatifs d'excitation, d'ionisation ainsi que d'émission stimulée pour chacune des deux couleurs de laser pulsé. Les modèles développés ainsi ont été utilisés pour calculer la polarisation prévue du spin suite à une excitation simple suivie d'une séquence pulsée de déplétion. Ces résultats ont des implications pour la microscopie à déplétion par émission stimulée (STED) [2], la magnétométrie à seuil d'émission stimulée [3], et la conversion spin/charge [1,4]