The role of uranium–arene bonding in H2O reduction catalysis

International audienceThe reactivity of uranium compounds towards small molecules typically occurs through stoichiometric rather than catalytic processes. Examples of uranium catalysts reacting with water are particularly scarce, because stable uranyl groups form that preclude the recovery of the uranium compound. Recently, however, an arene-anchored, electron-rich uranium complex has been shown to facilitate the electrocatalytic formation of H-2 from H2O. Here, we present the precise role of uranium-arene delta bonding in intermediates of the catalytic cycle, as well as details of the atypical two-electron oxidative addition of H2O to the trivalent uranium catalyst. Both aspects were explored by synthesizing mid- and high-valent uranium-oxo intermediates and by performing comparative studies with a structurally related complex that cannot engage in d bonding. The redox activity of the arene anchor and a covalent delta-bonding interaction with the uranium ion during H2 formation were supported by density functional theory analysis. Detailed insight into this catalytic system may inspire the design of ligands for new uranium catalysts

Cryopreservation of coconut (Cocos nucifera L.) zygotic embryos does not induce morphological, cytological or molecular changes in recovered seedlings

The present study aimed at exploring the fidelity of coconut (Cocos nucifera L.) plants recovered from cryopreservation. Zygotic embryos from various different cultivars were cryopreserved following four successive steps, namely: rapid dehydration, rapid freezing, rapid thawing and in vitro recovery followed by acclimatization. At the end of the acclimatization period, the seedlings were compared to counterparts of the same age, which were produced from non-cryopreserved embryos. Both series were submitted to morphological, cytological and molecular comparisons. No significant differences in terms of growth rates could be measured. In addition, no morphological variation could be detected through the measurement of shoot elongation rates, production of opened leaves, and the number and total length of primary roots. Karyotype analysis revealed the same chromosome number (2n = 32) in all studied cultivars independently of cryopreservation. No significant differences could be observed between control and cryopreserved material concerning the type of chromosomes, the length of the long and short arms, the arm length ratio and the centromeric index. However, idiogram analysis did show a greater number of black banding on chromosomes isolated from cryopreserved material. Genetic and epigenetic fidelity was assessed through microsatellite (SSR) analysis and global DNA methylation rates; no significant differences would be observed between genomic DNAs isolated from seedlings originating from cryopreserved embryos and respective controls. In conclusion, our results suggest that the method of cryopreservation under study did not induce gross morphological, genetic or epigenetic changes, thus suggesting that it is an appropriate method to efficiently preserve coconut germplasm

A consensus document on bowel preparation before colonoscopy: Prepared by a Task Force from the American Society of Colon and Rectal Surgeons (ASCRS), the American Society for Gastrointestinal Endoscopy (ASGE), and the Society of American Gastrointestinal

Colonoscopy is the most commonly used technique for inspection of the colonic mucosa. The safety and effectiveness of colonoscopy in identifying important colonic pathology is directly impacted by the quality of the bowel preparation performed in anticipation of the procedure. Physicians favor preparations associated with the best patient compliance to achieve the best results. Patients favor preparations that are low in volume, palatable, have easy to complete regimens, and are reimbursed by health insurance or are inexpensive. Both patients and physicians favor preparations that are safe to administer in light of existing comorbid conditions and those that will not interact with previously prescribed medications. Aqueous NaP solutions, NaP tablets, and PEG solutions, especially low-volume solutions, are all accepted and well tolerated by the majority of patients undergoing bowel preparation for colonoscopy. Physicians are advised to select a preparation for each patient based on the safety profile of the agent, NaP or PEG, in light of the overall health of the patient, their comorbid conditions, and currently prescribed medications. In certain circumstances, such as bowel preparation in children and some elderly patients, patients with renal insufficiency, and those with hypertension who are receiving ACE inhibitors or ARBs, it may be advisable to adhere to PEG-based solutions because of the risks of occult physiologic disturbances that may potentially contraindicate the use of NaP-based regimens. A variety of other preparations, none of which seem as popular because of inferior efficacy and/or patient acceptance, remain available for use in other circumstances in which bowel preparation is necessary. Many adjuncts to bowel preparation have been proposed but remain largely inefficacious and therefore cannot be recommended for routine use