Synthesis and properties of a redox-switchable calix[6]arene-based molecular lasso

A self-complexing lasso-like molecule has been synthesised as the first example of a calix[6]arene-based [1]pseudorotaxane. This artificial molecular lasso can be switched between self-threaded and dethreaded structures by redox stimulation.

Interfacial aggregation of Janus rods in binary polymer blends and their effect on phase separation

Janus particles interfacially self-assemble into different structures when incorporated into multiphase systems. Dissipative particle dynamics simulations are employed herein to investigate the interplay between aggregation mechanisms and phase separation in polymer blends. Shorter rods with a standing configuration become increasingly "caged" or trapped in larger aggregates as weight fraction increases, which is reflected in the way that their diffusion is coupled to their aggregation rates. Janus rods of higher aspect ratios that are tilted at the interface aggregate side-by-side and are able to hinder phase separation kinetics. This is due to a combination of individual Janus rod conformations at the interface, their intrinsic aggregation mechanisms, aggregate fractal dimension, and aggregation rates, and can also be traced back to the scaling of the diffusion coefficient of aggregates with their size. Findings presented provide insight into the mechanisms governing two dimensionally growing colloidal aggregates at fluid interfaces, more specifically, those associated with Janus particles, and shed light on the potential of these systems in paving the way for designing new functional materials.

Electrochemically Triggered Co-Conformational Switching in a [2]catenane Comprising a Non-Symmetric Calix[6]arene Wheel and a Two-Station Oriented Macrocycle

Catenanes with desymmetrized ring components can undergo co-conformational rearrangements upon external stimulation and can form the basis for the development of molecular rotary motors. We describe the design, synthesis and properties of a [2]catenane consisting of a macrocycle-the 'track' ring-endowed with two distinct recognition sites (a bipyridinium and an ammonium) for a calix[6]arene-the 'shuttle' ring. By exploiting the ability of the calixarene to thread appropriate non-symmetric axles with directional selectivity, we assembled an oriented pseudorotaxane and converted it into the corresponding oriented catenane by intramolecular ring closing metathesis. Cyclic voltammetric experiments indicate that the calixarene wheel initially surrounds the bipyridinium site, moves away from it when it is reduced, and returns in the original position upon reoxidation. A comparison with appropriate model compounds shows that the presence of the ammonium station is necessary for the calixarene to leave the reduced bipyridinium site.

Efficient active-template synthesis of calix[6]arene-based oriented pseudorotaxanes and rotaxanes

A substrate can modify its chemical features, including a change of its reactivity, as a consequence of non-covalent interactions upon inclusion within a molecular host. Since the rise of supramolecular chemistry, this phenomenon has stimulated the ingenuity of scientists to emulate the function of enzymes by designing supramolecular systems in which the energetics and selectivity of reactions can be manipulated through programmed host-guest interactions and/or steric confinement. In this paper we investigate how the engulfment of a positively charged pyridinium-based guest inside the π-rich cavity of a tris-(N-phenylureido)calix[6]arene host affects its reactivity towards a S_N2 reaction. We found that the alkylation of complexed substrates leads to the formation of pseudorotaxanes and rotaxanes with faster kinetics and higher yields with respect to the standard procedures exploited so far. More importantly, the strategy described here expands the range of efficient synthetic routes for the formation of mechanically interlocked species with a strict control of the mutual orientation of their non-symmetric molecular components.

Plugging a Bipyridinium Axle into Multichromophoric Calix[6]arene Wheels Bearing Naphthyl Units at Different Rims

Tris-(N-phenylureido)-calix[6]arene derivatives are heteroditopic non-symmetric molecular hosts that can form pseudorotaxane complexes with 4,4'-bipyridinium-type guests. Owing to the unique structural features and recognition properties of the calix[6]arene wheel, these systems are of interest for the design and synthesis of novel molecular devices and machines. We envisaged that the incorporation of photoactive units in the calixarene skeleton could lead to the development of systems the working modes of which can be governed and monitored by means of light-activated processes. Here, we report on the synthesis, structural characterization, and spectroscopic, photophysical, and electrochemical investigation of two calix[6]arene wheels decorated with three naphthyl groups anchored to either the upper or lower rim of the phenylureido calixarene platform. We found that the naphthyl units interact mutually and with the calixarene skeleton in a different fashion in the two compounds, which thus exhibit a markedly distinct photophysical behavior. For both hosts, the inclusion of a 4,4'-bipyridinium guest activates energy- and/or electron-transfer processes that lead to non-trivial luminescence changes.

Covalent capture of oriented calix[6]arene rotaxanes by a metal-free active template approach

A rotaxane with predetermined orientation of its nonsymmetric components is obtained by a rim-selective active template effect exerted by a calix[6]arene.

Autologous Islet Transplantation in Patients Requiring Pancreatectomy: A Broader Spectrum of Indications Beyond Chronic Pancreatitis

Islet autotransplantation (IAT) is usually performed in patients undergoing pancreatic surgery for chronic pancreatitis. In the present series, IAT was offered also to patients undergoing pancreatic surgery for both nonmalignant and malignant diseases, having either completion pancreatectomy as treatment for severe pancreatic fistulas (n = 21) or extensive distal pancreatectomy for neoplasms of the pancreatic neck (n = 19) or pancreatoduodenectomy because of the high risk of pancreatic fistula (n = 32). Fifty-eight of 72 patients who were eligible to this broader spectrum of indication actually received IAT. There was no evidence of a higher-than-expected rate of major complications for pancreatectomy. Forty-five patients receiving IAT were still alive at the time of the last scheduled follow-up (1375 ± 365 days). Eighteen (95%) of 19 and 11 (28%) of 39 patients reached insulin independence after partial or total pancreatectomy, respectively. The metabolic results were dependent on the transplanted islet mass. Thirty-one of 58 patients had malignant diseases of the pancreas or periampullary region, and only three patients developed ex novo liver metastases after IAT (median follow-up 914 ± 382 days). Our data demonstrate the feasibility, efficacy, and safety of IAT for a broader spectrum of clinical indications beyond chronic pancreatitis.

Calix[4]arene-Functionalised Silver Nanoparticles as Hosts for Pyridinium-Loaded Gold Nanoparticles as Guests

A series of lipophilic gold nanoparticles (AuNPs) circa 5 nm in diameter and having a mixed organic layer consisting of 1-dodecanethiol and 1-(11-mercaptoundecyl) pyridinium bromide was synthesised by reacting tetraoctylammonium bromide stabilised AuNPs in toluene with different mixtures of the two thiolate ligands. A bidentate ω-alkylthiolate calix[4]arene derivative was instead used as a functional protecting layer on AgNPs of approximately 3 nm. The functionalised nanoparticles were characterised by transmission electron microscopy (TEM), and by UV/Vis and X-ray photoelectron spectroscopy (XPS). Recognition of the pyridinium moieties loaded on the AuNPs by the calix[4]arene units immobilised on the AgNPs was demonstrated in solution of weakly polar solvents by UV/Vis titrations and DLS measurements. The extent of Au-AgNPs aggregation, shown through the low-energy shift of their surface plasmon bands (SPB), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs. Extensive aggregation between dodecanethiol-capped AuNPs and the Ag calix[4]arene-functionalised NPs was also promoted by the action of a simple N-octyl pyridinium difunctional supramolecular linker. This linker can interdigitate through its long fatty tail in the organic layer of the dodecanethiol-capped AuNPs, and simultaneously interact through its pyridinium moiety with the calix[4]arene units at the surface of the modified AgNPs.

Lorentz microscopy sheds light on the role of dipolar interactions in magnetic hyperthermia

Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.

Islet product characteristics and factors related to successful human islet transplantation from the Collaborative Islet Transplant Registry (CITR) 1999-2010

The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and transplants. This retrospective report analyzed 1017 islet isolation procedures performed for 537 recipients of allogeneic clinical islet transplantation in 1999-2010. This study describes changes in donor and islet isolation variables by era and factors associated with quantity and quality of final islet products. Donor body weight and BMI increased significantly over the period (p<0.001). Islet yield measures have improved with time including islet equivalent (IEQ)/particle ratio and IEQs infused. The average dose of islets infused significantly increased in the era of 2007-2010 when compared to 1999-2002 (445.4±156.8 vs. 421.3±155.4×0(3) IEQ; p<0.05). Islet purity and total number of β cells significantly improved over the study period (p<0.01 and <0.05, respectively). Otherwise, the quality of clinical islets has remained consistently very high through this period, and differs substantially from nonclinical islets. In multivariate analysis of all recipient, donor and islet factors, and medical management factors, the only islet product characteristic that correlated with clinical outcomes was total IEQs infused. This analysis shows improvements in both quantity and some quality criteria of clinical islets produced over 1999-2010, and these parallel improvements in clinical outcomes over the same period.

Liver perfusion changes occurring during pancreatic islet engraftment: a dynamic contrast-enhanced magnetic resonance study

The aim of this study was to investigate liver microvascular adaptation following the intraportal infusion of pancreatic islets (pancreatic islet transplantation [islet-tx]) in diabetic patients using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). DCE-MRI was performed before and 7 days after islet-tx in six diabetic patients. Initial area under curve (AUC60) and volume transfer coefficient (Ktrans) were assessed as markers of liver perfusion. Clinical and metabolic monthly follow-up was performed in all patients, considering fasting C-peptide and β-score as main indices of graft function. High variability in the response of liver microvasculature to islet infusion was observed: two patients showed a significant reduction in liver perfusion after transplantation (pt.2: AUC60 = -23.4%, Ktrans = -31.7%; pt.4: AUC60 = -23.7%, Ktrans = -27.9%); three patients did not show any significant variation of liver perfusion and one patient showed a significant increase (pt.3: AUC60 = +31%, Ktrans = +42.8%). Interestingly, a correlation between DCE-MRI parameters and indices of graft function was observed and, in particular, both patients with DCE-MRI evidence of posttransplantation liver perfusion reduction experienced premature graft failure. Our preliminary study demonstrated that DCE-MRI may identify different adaptive responses of liver microvasculature in patients submitted to islet-tx. These different responses could have an impact on islet engraftment, although reported findings need confirmation from larger studies.