Dendrimers in catalysis

Dendrimers are well-defined hyperbranched macromolecules, with the larger ones having characteristic globular structures. These novel materials have been investigated intensively in recent decades, and among other potential applications, they are suitable as soluble supports for homogeneous transition metal complex catalysts. These catalysts offer the advantage of easy separation from products and recycling as well as the potential advantages of unique catalytic properties, including high activity, selectivity, and stability. In this chapter, the current state of research in dendrimer catalysis is reviewed, with emphasis on the importance of the location of the catalyst in the dendritic framework (e.g., at the core or at the periphery). Several approaches to the separation of dendrimer catalysts are evaluated, and unique dendritic effects in catalysis are discussed

Synthesis, characterization and aggregation behavior of block copolymers containing a polyisocyanopeptide segment

Contains fulltext : 57175.pdf (publisher's version ) (Closed access)Following up on previous preliminary communications the synthesis of a series of block copolymers by applying amine end-capped polymers as initiators for the nickel(II) catalyzed polymerization of isocyanides is reported. Using a polystyrene derivative as the initiator, superamphiphiles containing a hydrophobic polystyrene tail and a charged helical polyisocyanide headgroup were prepared. Under proper conditions these superamphiphiles self-assembled in water to give a variety of aggregate morphologies, among which are superhelical architectures. Initiators derived from carbosilane dendritic wedges gave block copolymers with a unique combination of structural elements, i.e. a flexible dendritic block and a rigid polyisocyanide block. Block copolymers derived from the 3rd generation dendrimers form welldefined micellar aggregates in the presence of Ag+ ions. These aggregates have been used to construct nanoarrays of metallic silver. (C) 2004 Elsevier Ltd. All rights reserved

Effect of placebo versus prophylactic postoperative amoxicillin on post-(adeno) tonsillectomy morbidity in Tanzanian children: a two-centre, double-blind randomized controlled non-inferiority trial

Introduction: to date in Africa, there is limited evidence regarding the role of prophylactic antibiotics to prevent post (adeno) tonsillectomy ((A)TE) morbidity in children. As (A)TE is the most performed surgery in the pediatric population, the use of prophylactic antibiotics is likely a major factor in the development of AMR. In Tanzania, as in many other settings with limited resources antibiotics are misused and overprescribed. Potential reasons include limited stewardship and widespread use of postsurgical prophylactic antibiotics. Misuse of antibiotics might contribute significantly to the development of antimicrobial resistance (AMR). Methods: a two-centre, double-blinded randomized controlled non-inferiority trial. Subjects included children from 2-14 years of age with recurrent chronic tonsillitis and/or obstructive sleep apnoea due to adenotonsillar hypertrophy who were electively scheduled for (A)TE in two tertiary hospitals. Participants were randomly allocated to receive either placebo or amoxicillin for five days postoperatively. Primary outcome was non-inferiority of placebo compared with amoxicillin for postoperative haemorrhage (margin 5%; at 14 days) postoperative fever (margin 5%; at 7 days), and pain (margin 1 point; at 7 days). Secondary outcomes included the times required for resumption of normal diet and normal activities, and microbial recolonization of the tonsillar beds. Data were analysed according to intention-to-treat principle. Follow-up was 14 days. Results: between March 13, 2019 and September 20, 2019 270 children were enrolled. All children were randomly assigned to receive placebo (n = 136) or amoxicillin (n = 134). By 14(t) (h)day post-operatively, total of 8 children were lost to follow-up in each arm. No major postoperative haemorrhage was registered. By 14(th) day post-operatively, 22 (17.5%) children in the amoxicillin arm and 19 (14.8%) children in the placebo arm had reported minor haemorrhage (risk difference (RD) -2.6% (95%CI -10.2 - 5.0); pnon-inferiority = 0.045). By 7(th) day post operatively, 8 (6.3%) children in amoxicillin arm and 4 (3.1%) children in placebo arm reported fever during the first week (RD -3.2% (95%CI -7.6 - 1.2); pnon-inferiority = 0.001). By 7(th) day post operatively, mean pain score (mean (SD)) was 3.25 (1.53) in the amoxicillin arm and 3.56 (1.68) in the placebo arm (mean difference 0.31, (95% CI -0.02 - 0.65); pnon-inferiority < 0.001). No statistically significant differences between the two groups were found in any of the secondary outcomes. Findings shows, placebo is non-inferior to amoxicillin for post-operative morbidities in Tanzanian children undergoing (A)TE. Conclusion: it is recommended that antibiotics should only be used when clinically necessary to treat a specific infection. Unnecessary use of antibiotics contributes to the development of antimicrobial resistance. Trial Registration: Pan African Clinical Trials Registry PACTR201905466349317. Retrospectively registered on 15 May 2019

Carbosilane Dendrimeric Carbodiimides: Site Isolation as a Lactamization Tool

The convergent syntheses of three generations of carbosilane dendrimeric carbodiimides are described. The wedge-type building blocks were synthesized in a divergent way, starting from allyl chloride and a repetitive sequence of hydrosilylation with HSiCl3 and a Grignard reaction with allylmagnesium bromide. Hydrogenation of the terminal double bonds led to inert and stable wedges. The chloride substitutent at the focal point was transformed into several functional groups that eventually led to dendrimeric structures with a carbodiimide core. The extent of the site isolation effect of the dendrimers was studied with dilution experiments monitored by FT-IR spectroscopy on the corresponding dendrimeric ureas. These studies showed that only the first generation self-aggregates via hydrogen bonding, while the second and the third do not, implying isolation of core-bound moieties. The dendrimeric carbodiimides mediated lactamization reactions to obtain homodiketopiperazines.