Cryptococcal meningitis associated HIV infection in the Donka national hospital in Conakry (Guinea)

Background Cryptococcal meningitis (CM) is an infection of the brain parenchyma and subarachnoid space by the encapsulated saprophyte yeast organisms such as Cryptococcus neoformans. Over the last twenty years, HIV has created a large and severely immune compromisized population in whom C. neoformans is a dangerous opportunistic infection. In Guinea, the prevalence of CM is unknown. We hypothesized that the occurrence of CM correlates with AIDS/ HIV prevalence.Method This retrospective observational study was carried out at the national Hospital of Conakry (Guinea) between 2001 and 2002. We describe here the epidemiological and clinical and biological characteristics of CM disease in our national hospital.Results Our data show that, 28.6 % of HIV patients with neurological symptoms had Cryptococcus neoformans in their CSF by using Indian ink staining. The median age was 36±3 years and sex ratio (M/F) was 1.8. The major complaints were fever and cephalgia, giddiness while the major complications were altered consciousness and hemiplegia. CSF was clear with low level of glucose and higher level of albumin. The means of lymphocytes in CSF was 8±2/mm3.Conclusion This data therefore becomes relevant in not only focusing of neurological symptoms associated with HIV to be toxoplasmosis but the possibility of C neoformans in these patients; particularly when they present symptoms such as headaches, giddiness and sniff neck etc. This can easily be carried out with Indian ink staining technique

Studies of optical, magnetical and photo-induced properties of spin transition materials‎ : effects of metal dilution

De nombreux travaux ont été dédiés ces dernières années aux matériaux à transition de spin qui présentent des potentialités pour le stockage de l'information en raison de leurs propriétés physiques commutables : métastabilité thermique et optique. Ce travail est relatif au mécanisme photo-induit dans les systèmes à transition de spin et, plus précisément, à l'étude des effets de dilution sur la température LIESST. L'objectif principal est de mieux cerner les paramètres qui gouvernent T(LIESST). Diverses études expérimentales ont été réalisées sur des composés mononucléaires 0D, polymériques 1D et polynucléaires. L'analyse de l'ensemble des propriétés photomagnétiques a permis de montrer que T(LIESST) est indépendant de la dilution et suggère que cette grandeur est gérée par la molécule et dépend très peu des interactions intermoléculaires.In the last few years, many studies have been dedicated to spin-crossover compounds because of their potential application in data-storage systems. In such systems, optical switching is particularly promising.This work deals with the photo-induced phenomenon encountered in spin crossover systems, more specifically, the effects of metal dilution on the LIESST temperature. The main objective is to better define the parameters that govern T (LIESST). Various experimental studies were performed on mononuclear 0D compounds, polymeric 1D systems and polynuclear systems. The analysis of all photomagnetic properties has shown that T(LIESST) is not affected by the dilution and suggests that this parameter is govern at the molecular scale and depends very few of intermolecular interactions

Etude des propriétés optiques, magnétiques et photo-induites dans les matériaux à transition de spin : effets de la dilution de l'ion métallique

In the last few years, many studies have been dedicated to spin-crossover compounds because of their potential application in data-storage systems. In such systems, optical switching is particularly promising.This work deals with the photo-induced phenomenon encountered in spin crossover systems, more specifically, the effects of metal dilution on the LIESST temperature. The main objective is to better define the parameters that govern T (LIESST). Various experimental studies were performed on mononuclear 0D compounds, polymeric 1D systems and polynuclear systems. The analysis of all photomagnetic properties has shown that T(LIESST) is not affected by the dilution and suggests that this parameter is govern at the molecular scale and depends very few of intermolecular interactions.De nombreux travaux ont été dédiés ces dernières années aux matériaux à transition de spin qui présentent des potentialités pour le stockage de l'information en raison de leurs propriétés physiques commutables : métastabilité thermique et optique. Ce travail est relatif au mécanisme photo-induit dans les systèmes à transition de spin et, plus précisément, à l'étude des effets de dilution sur la température LIESST. L'objectif principal est de mieux cerner les paramètres qui gouvernent T(LIESST). Diverses études expérimentales ont été réalisées sur des composés mononucléaires 0D, polymériques 1D et polynucléaires. L'analyse de l'ensemble des propriétés photomagnétiques a permis de montrer que T(LIESST) est indépendant de la dilution et suggère que cette grandeur est gérée par la molécule et dépend très peu des interactions intermoléculaires

Studies of optical, magnetical and photo-induced properties of spin transition materials‎ : effects of metal dilution

De nombreux travaux ont été dédiés ces dernières années aux matériaux à transition de spin qui présentent des potentialités pour le stockage de l'information en raison de leurs propriétés physiques commutables : métastabilité thermique et optique. Ce travail est relatif au mécanisme photo-induit dans les systèmes à transition de spin et, plus précisément, à l'étude des effets de dilution sur la température LIESST. L'objectif principal est de mieux cerner les paramètres qui gouvernent T(LIESST). Diverses études expérimentales ont été réalisées sur des composés mononucléaires 0D, polymériques 1D et polynucléaires. L'analyse de l'ensemble des propriétés photomagnétiques a permis de montrer que T(LIESST) est indépendant de la dilution et suggère que cette grandeur est gérée par la molécule et dépend très peu des interactions intermoléculaires.In the last few years, many studies have been dedicated to spin-crossover compounds because of their potential application in data-storage systems. In such systems, optical switching is particularly promising.This work deals with the photo-induced phenomenon encountered in spin crossover systems, more specifically, the effects of metal dilution on the LIESST temperature. The main objective is to better define the parameters that govern T (LIESST). Various experimental studies were performed on mononuclear 0D compounds, polymeric 1D systems and polynuclear systems. The analysis of all photomagnetic properties has shown that T(LIESST) is not affected by the dilution and suggests that this parameter is govern at the molecular scale and depends very few of intermolecular interactions

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

Light-Induced Excited Spin-State Trapping has been studied since 1982 in solution and 1984 in solid state as it offers a reversible way of photoswitching the electronic configuration of spin crossover systems. Since then, the lifetime of the photo-induced state was deeply investigated through kinetics measurements. In 1998, a fast and easy way to record the limit temperature above which the photo-induced state is erased, denoted T(LIESST), was introduced. This procedure has been widely used in the spin crossover community due to its easiness and its efficiency to provide detailed information on the photo-induced state. Correlations between T(LIESST) and structural parameters have been proposed for instance. However, it intrinsically contains drawbacks that can lead to misinterpretation of behaviours and can lead to an over estimation of its scope. This review aims to present and discuss not only the correct way to measure T(LIESST) but also the essential contributions it has brought and the limits not to be exceeded in its interpretation.Initiative d'excellence de l'Université de BordeauxEtude femtoseconde rayons X et optique de la dynamique ultrarapide de photocommutation de matériaux moléculaires magnétique

The role of ligand design affecting the thermal and light-induced spin transition in mononuclear iron(II) complexes

Molecules are increasingly considered for information processing and sensing applications. Therefore, much research has focused on the improvement of such property changes, especially the ability to observe the switching at room temperature. The relationship between chemical structure and spin state in a transition metal complex has an important bearing on the design of spin crossover materials. Thus, ligand design has been the focus of much attention. It has allowed generation of highly cooperative spin-transition iron (II) complexes to promote hysteretic effects. We present herein the thermal and light-induced magnetic properties of several photoswitchable precursors based on a bidentate ligand (phenanthroline), and a monodentate ligand such as a pyridine or picoline derivative. These results were discussed on the basis of the alkyl-substituted pyridine ligand effects on the magnetic and phtomagnetic properties of mononuclear iron (II) complexes. Interestingly, single crystals were obtained for the 4-cyano-pyridine derivate allowing the X-ray diffraction crystal-structure determination.Advanced Materials by DesignInitiative d'excellence de l'Université de BordeauxEtude femtoseconde rayons X et optique de la dynamique ultrarapide de photocommutation de matériaux moléculaires magnétique

The role of ligand design affecting the thermal and light-induced spin transition in mononuclear iron(II) complexes

Molecules are increasingly considered for information processing and sensing applications. Therefore, much research has focused on the improvement of such property changes, especially the ability to observe the switching at room temperature. The relationship between chemical structure and spin state in a transition metal complex has an important bearing on the design of spin crossover materials. Thus, ligand design has been the focus of much attention. It has allowed generation of highly cooperative spin-transition iron (II) complexes to promote hysteretic effects. We present herein the thermal and light-induced magnetic properties of several photoswitchable precursors based on a bidentate ligand (phenanthroline), and a monodentate ligand such as a pyridine or picoline derivative. These results were discussed on the basis of the alkyl-substituted pyridine ligand effects on the magnetic and phtomagnetic properties of mononuclear iron (II) complexes. Interestingly, single crystals were obtained for the 4-cyano-pyridine derivate allowing the X-ray diffraction crystal-structure determination.Advanced Materials by DesignInitiative d'excellence de l'Université de BordeauxEtude femtoseconde rayons X et optique de la dynamique ultrarapide de photocommutation de matériaux moléculaires magnétique

Observation of the structural and optical multiscale dynamics in a spin-crossover crystals

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