High-frequency investigation on nonradiative single-mode dielectric resonators

High-frequency investigations of the recently proposed nonradiative single-mode dielectric resonators are presented. In particular, the TE₀₁₁ mode of high-density polyethylene and single-crystal quartz discs has been experimentally characterized, by means of a simple setup, in a frequency interval around 190 GHz. The obtained unloaded merit factors of 1400 for polyethylene and 2480 for single-crystal quartz lead to magnetic field conversion factors of 15 G/W^1/2 and 49 G/W^1/2, respectively. In the latter case, the obtained value represents the state of the art among the room temperature conversion efficiencies. The close agreement with the theoretical predictions demonstrates that the performances of the proposed resonators are only limited by intrinsic factors, as finite conductivity of metallic mirrors and dielectric losses of the employed materials. Ideal performances are then expected in suitably realized nonradiative resonators, also in the high-frequency regime.     

A practical synthesis of the F-ring of halichondrin B via ozonolytic desymmetrization of a C(2)-symmetric dihydroxycyclohexene

C(2)-symmetric dihydroxycyclohexene 1 was desymmetrized via a one-pot Criegee ozonolysis/acylation protocol to afford acetal-lactone 2. Installation of the allyl side chain on the convex face of the bicyclic system and subsequent reduction provided the desired tetrahydrofuran 4 with the correct relative and absolute stereochemistries. Simple functional group manipulations led to the desired F-ring module 3 of halichondrin B.     

High-field, multifrequency EPR spectroscopy using whispering gallery dielectric resonators

High-field/high frequency EPR spectroscopy measurements are shown. Experiments were carried out at 240- and 316-GHz frequencies. The employed apparatus uses a novel combination of far infrared molecular lasers and of probehead exploiting dielectric resonators working in the whispering gallery modes. This approach constitutes a relatively simple method of multifrequency EPR spectroscopy and opens appealing perspectives in high-sensitivity EPR spectroscopy up to the THz regime.     

Rigid and Compact Binuclear Bis-hydrated Gd-complexes as High Relaxivity MRI Agents

The first binuclear Gd-complex of the 12-membered pyridine-based polyaminocarboxylate macrocyclic ligand PCTA was synthesized by C−C connection of the pyridine units through two different synthetic procedures. A dimeric AAZTA-ligand was also synthesized with the aim to compare the relaxometric results or the two ditopic Gd-complexes. Thus, the ¹H relaxometric study on [Gd₂PCTA₂(H₂O)₄] and on [Gd₂AAZTA₂(H₂O)₄]²⁻ highlighted the remarkable rigidity and compactness of the two binuclear complexes, which results in molar relaxivities (per Gd), at 1.5 T and 298 K of ca. 12–12.6 mM⁻¹ s⁻¹ with an increase of ca. 80 % at 1.5 T and 298 K (+70 % at 310 K) with respect to the corresponding mononuclear complexes.     

Organocatalytic Asymmetric Conjugate Additions to Cyclopent‐1‐enecarbaldehyde: A Critical Assessment of Organocatalytic Approaches towards the Telaprevir Bicyclic Core

In the context of a programme directed at the manufacture of telaprevir, eight possible approaches to its bicyclic α‐amino acid core, based on organocatalytic enantioselective conjugate additions to cyclopent‐1‐enecarbaldehyde, were identified and preliminarily explored. Four reactions, delivering advanced intermediates en route to the target amino acid, were selected for a thorough optimisation. Three of this reactions involved iminium ion catalysis with a prolinol catalyst (addition of nitromethane, nitroacetate and acetamidomalonate) and one was based on a Cinchona‐derived phase‐transfer catalyst (addition of glycine imines). A careful choice of additives allowed lowering of the catalyst loading to 0.5 mol % in some cases. The preparation of intermediates that would give access to the core of telaprevir in good yields and enantioselectivities by exploiting readily available substrates and catalysts, highlights the potential of organocatalytic technology for a cost‐effective preparation of pharmaceuticals.     

New catalysts for Suzuki-Miyaura coupling reactions of heteroatom-substituted heteroaryl chlorides

The new air-stable PdCl2[PR2(Ph-R')]2 complexes, readily prepared from commercial reagents, exhibit unique efficiency as catalysts for the Suzuki-Miyaura coupling reactions of a variety of heteroatom-substituted heteroaryl chlorides with a diverse range of aryl/heteroaryl boronic acids. The coupling reactions catalyzed by the new complexes exhibit high product yields (88-99%) and high catalyst turnover numbers (up to 10,000 TON).     

A chemical approach to the pharmaceutical optimization of an anti-HIV protein

Chemical protein synthesis is important for dissecting the molecular basis of protein function. Here we advance its scope by demonstrating the significant improvement of the multifaceted pharmaceutical profile of small proteins exclusively via a chemical-based approach. The focus of this work centered on CCL-5 (RANTES) derivatives with potent anti-HIV activity. The overall chemical strategy involved a combination of coded and noncoded amino acid mutagenesis, peptide backbone engineering, and site-specific polymer attachment. The ability to alter specific protein residues, as well as precise control of the position and type of polymer attachment, allows for the exploration of specific molecular designs and resulted in novel CCL-5 analogues with significant differences in their respective biochemical and pharmaceutical properties. Using this approach, the complex-interplay of variables contributing to the noncovalent self-association (aggregation) state, CCR-5 specificity, in vivo elimination half-life, and anti-HIV activity of CCL-5-based protein analogues could be empirically evaluated via total chemical synthesis. This work has led to the identification of potent (sub-nanomolar) anti-HIV proteins with significantly improved pharmaceutical profiles, and illustrates the increasing value of protein chemical synthesis in contemporary therapeutic discovery. These antiviral molecules provide a novel mechanism of action for the development of a new generation of anti-HIV therapeutics which are still desperately needed.     

Construction and validation of a RET TK catalytic domain by homology modeling

RET tyrosine kinase (TK) oncoproteins are potential targets for anticancer therapy. However, the search for novel RET inhibitors has been hampered by the lack of a 3D structure of the receptor. In this study, the "open" and the "closed" structure of the RET TK catalytic domain have been built by homology modeling techniques. The structures were validated by extensive docking studies with practically all the inhibitors reported in the literature and through molecular dynamics simulations of the resulting complexes. All the expected major interactions between the active domain amino acids and the inhibitors have been reproduced in their details. Furthermore, the proposed 3D models are in agreement with the results of available mutation studies. Therefore, these models could be profitably used to filter off from large libraries new potential hit compounds able to target this enzyme.     

Morphology of Compatibilized Ternary Blends

In this work, the evolution of the morphology of polypropylene/polystyrene/poly(methyl metacrylate) (PP/PS/PMMA) blends to which graft copolymers polypropylene-graft-polystyrene (PP-g-PS) of 2 compositions (55/45 and 70/30), polypropylene-graft-poly(methyl metacrylate) (PP-g-PMMA), or styrene-block-(ethylene- co-butadiene)-block-styrene (SEBS) was added has been studied. The ternary blends morphologies were predicted using phenomenological models that predict the morphology of ternary blends as a function of the interfacial tension between the blend components (spreading coefficient and free energy minimization). All blends studied presented a core-shell morphology with PS as shell and PMMA as core. The addition of PP-g-PS or SEBS resulted in a reduction of the size of the PS shell phase and, the addition of PP-g-PMMA did not seem to have any effect on the diameter of PMMA. The difference observed between the different morphologies relied on the number of droplets of core within the shell. All the phenomenological models predictions corroborated the experimental results, except when PP-g-PMMA was added to the blend.     

Approximating piecewise nonlinearities in dynamic systems with sigmoid functions: advantages and limitations

In the industry field, the increasingly stringent requirements of lightweight structures are exposing the ultimately nonlinear nature of mechanical systems. This is extremely true for systems with moving parts and loose fixtures which show piecewise stiffness behaviours. Nevertheless, the numerical solution of systems with ideal piecewise mathematical characteristics is associated with time-consuming procedures and a high computational burden. Smoothing functions can conveniently simplify the mathematical form of such systems, but little research has been carried out to evaluate their effect on the mechanical response of multi-degree-of-freedom systems. To investigate this problem, a slightly damped mechanical two-degree-of-freedom system with soft piecewise constraints is studied via numerical continuation and numerical integration procedures. Sigmoid functions are adopted to approximate the constraints, and the effect of such approximation is explored by comparing the results of the approximate system with the ones of the ideal piecewise counter-part. The numerical results show that the sigmoid functions can correctly catch the very complex dynamics of the proposed system when both the above-mentioned techniques are adopted. Moreover, a reduction in the computational burden, as well as an increase in numerical robustness, is observed in the approximate case.