Neptunium(iv)-hydroxamate complexes: their speciation, and kinetics and mechanism of hydrolysis.

Simple hydroxamic acids such as acteohydroxamic acid (AHA) have been identified as suitable reagents for the control of Pu and Np in advanced separation processes for nuclear fuel reprocessing such as the Advanced PUREX or UREX based recycle processes, due to their ability to strip the tetravalent form of Pu and Np from tri-butyl phosphate into nitric acid. However, both free and metal bound hydroxamates are known to undergo acid catalysed hydrolysis at low pH, the kinetics of which must be characterised before implementation of PUREX/UREX based reprocessing flowsheets. In support of this implementation, a comprehensive thermodynamic and kinetic model that describes both the complex speciation and hydrolysis of AHA in the presence of Np(iv) has been developed. The model has two unique features: (i) in the case of the hydrolysis reaction kinetics, the model includes the hydrolysis of not only free AHA but also both the mono- and bishydroxamato-Np(iv) complexes; (ii) for the associated speciation calculations, the model explicitly includes the ionic strength dependence of not only the mono- and bishydroxamato-Np(iv) complexes but also the mono- and bisnitrato neptunium(iv) and monohydroxoneptunium(iv) complexes. For the latter three species, respective SIT coefficients of Δε1,NO3 = -0.13 ± 0.03 kg mol-1, , Δε2,NO3 = -0.37 ± 0.13 kg mol-1, Δε1,OH = -0.36 kg mol-1 and log10 K01,OH = -1.23 were also determined. Using experimental data from a series of kinetic studies on the Np(iv)-AHA system, this model has been used to determine the rate constants for hydrolysis of mono- and bis-acetohydroxamatoneptunium(iv) at 25 °C for the first time. These were found to be 3.5 × 10-5 ± 2.5 × 10-5 dm3 mol-1 s-1 and 1.9 × 10-3 ± 1.3 × 10-3 dm3 mol-1 s-1, respectively. Comparison of these values with the rate constants for hydrolysis of free AHA indicates that complexation of AHA with Np(iv) increases the rate of hydroxamate hydrolysis - an observation that we attribute to the electron withdrawing effect of the metal centre within the Np(iv)-AHA complex increasing the susceptibility of the AHA carbonyl carbon to nucleophilic attack, the accepted first step in its mechanism of hydrolysis.

[Multifocal tuberculosis. Apropos of 49 cases in the midwest region. GERICCO (Group for Epidemiology and Research in Clinical Infections of the Central West of France), 1991-1993]. / Tuberculose multifocale. A propos de 49 cas dans la région Centre-Ouest (Géricco, 1991-1993).

Diffuse or multifocal tuberculosis (TB) accounts for 9% to 10% of cases of extrapulmonary TB and carries a poor prognosis with a mortality rate of 16% to 25%. Forty-nine cases of multifocal TB defined as involvement of two extrapulmonary sites with or without pulmonary TB were reviewed. Mean patient age (+/- SD) was 50 +/- 18 years. Twenty-three per cent of patients were immigrants. A history of TB and contact with a TB patient were found in 23% and 18% of cases, respectively. Of the 52% of immunocompromised patients, 38% were HIV-positive. The skin tuberculin test was positive in 67% of cases. Mean time from symptom onset to admission was 80 +/- 77 days (median, 58 days). The 49 patients had a total of 128 TB foci. Six patients had positive blood cultures. The tubercle bacillus was recovered from the extrapulmonary sites in 88% of cases. Mean treatment duration was nine months. Recovery from the TB was achieved in 64% of cases. The overall mortality rate was 47%, and 33% of patients died as the direct result of TB. Most deaths occurred in immunocompromised patients. A high index of suspicion for multifocal TB should be maintained in immunocompromised patients, even those who test negative for the HIV.

[Extrapulmonary tuberculosis in the central western region. Retrospective study of 217 cases (Gericco 1991-1993)]. / Tuberculose extrapulmonaire dans la région centre-ouest. Etude rétrospective de 217 cas (Gericco 1991-1993).

OBJECTIVES: To analyze the epidemiological, clinical and diagnostic characteristics of extrapulmonary tuberculosis in western France observed from 1991 to 1993 in different patients populations (HIV+ infected patients, immunosuppressed non-HIV infected patients, non-immunosuppressed patients) and according to various localizations (lymph nodes, bone and joints, genital organs, nervous system and meninges, miliary disease). METHODS: This retrospective study included 217 cases of extrapulmonary tuberculosis diagnosed from 1991 to 1993 in western France by GERICCO (Groupe d'Epidémiologie et de Recherche en Infectiologie Clinique du Centre-Ouest). Demographic, clinical, biological, microbiological and radiographic characteristics as well as clinical course on specific therapy were assessed. RESULTS: Extrapulmonary tuberculosis generally occurred most often in immunosuppressed patients but 34% of cases were observed in people without any underlying disease or risk factors. Delay to diagnosis was especially long in the non-immunosuppressed patients (mean = 96 days) but shorter in the HIV-infected patients (mean = 59 days). It was shorter in case of nervous system involvement (mean = 52 days) or military disease (mean = 80 days) than in bone and joints (mean = 120 days) and lymph nodes (mean = 102 days). Microbiologically proven tuberculosis represented only 75% of cases despite numerous investigations. Overall prognosis was good except in nervous system and meninges localizations. Failures were mainly due to death in immunosuppressed patients. CONCLUSION: Extrapulmonary tuberculosis remains frequent even in patients lacking risk factors. In 50% of cases, confirmation of diagnosis takes more than one month. In case of doubt, clinicians should not wait for laboratory results before implementing empirical specific therapy.