Synthesis and structural characterization of [PhE(BNMe2)2]2 (E = P or As): Six-Membered P2B4 and As2B4 Rings with Unusual Structures

The reaction of either Li₂PPh or Li₂AsPh with the diborane(4) derivative B₂(NMe₂)₂Br₂ affords the compounds [PhP(BNMe₂)₂]₂ ( 1 ) or [PhAs(BNMe₂)₂]₂ ( 2 ) in good yield. Both 1 and 2 have cyclic structures featuring non-planar P₂B₄ or As₂B₄ six-membered rings which have chair configurations. Although all four borons in each ring have planar coordination, the two phosphorus or arsenic centers have different degrees of pyramidalization. Bond distances within the rings indicate that the B? B, B? P or B? As bonds are single, whereas the exo-B? N bond lengths are consistent with significant π-bonding. The ring structures of 1 and 2 are in sharp contrast to the related boron-nitrogen species (t-BuN)₂N₄Me₄ which has a nido-N₂B₄ framework. The attempted synthesis of the nitrogen analogue of 1 or 2 by using a similar approach did not result in the isolation of [PhN(BNMe₂)₂]₂, instead the tetramino diborane(4) species [B(NMe₂)NHPh]₂ ( 3 ), which has a structure similar to other tetramine diborane(4) compounds, was isolated.     

Gromov hyperbolicity of planar graphs

We prove that under appropriate assumptions adding or removing an infinite amount of edges to a given planar graph preserves its non-hyperbolicity, a result which is shown to be false in general. In particular, we make a conjecture that every tessellation graph of ?² with convex tiles is non-hyperbolic; it is shown that in order to prove this conjecture it suffices to consider tessellation graphs of ?² such that every tile is a triangle and a partial answer to this question is given. A weaker version of this conjecture stating that every tessellation graph of ?² with rectangular tiles is non-hyperbolic is given and partially answered. If this conjecture were true, many tessellation graphs of ?² with tiles which are parallelograms would be non-hyperbolic.     

Oil-in-water lecithin-based microemulsions as a potential delivery system for amphotericin B

In this work the structural features of microemulsions (MEs) containing the pharmaceutical biocompatible Soya phosphatidylcholine/Tween 20 (1:1) as surfactant (S), Captextrade mark 200 as oil phase (O), and phosphate buffer 10mM, pH 7.2 as aqueous phase (W) were studied. Systems obtained with different proportions of the components were described by pseudo-ternary phase diagrams in order to characterize the microemulsions studied here. MEs were prepared with and without the polyene antifungal drug amphotericin B (AmB). The maximum AmB incorporation into the ME system was dependent on both the oil phase and surfactant proportions with 6.80 and 5.7mg/mL in high contents, respectively. The incorporation of AmB into the ME systems significantly increased the profile of the droplet size of the ME for all ranges of surfactant proportions used in the formulations. The microstructures of the system were characterized by dynamic light scattering (DLS) and rheological behavior. The DLS results showed that the size of the oil droplets increases 4.6-fold when AmB is incorporated into the ME system. In all cases the increase in the proportion of the oil phase of the ME leads to a slight increase in the diameter of the oil droplets of the system. Furthermore, for both the AmB-loaded and AmB-unloaded MEs, the size of the oil droplets decrease significantly with the increase of the S proportion in the formulations, demonstrating the efficiency of the surfactant in stabilizing the ME. Depending on the ME composition, an anti-thixotropic behavior was found. The maximum increases of the consistency index caused by the increase of the oil phase of the ME were of 17- and 25-times for the drug-loaded and drug-unloaded MEs, respectively. However, the observed effect for the drug-loaded ME was about 4.6 times higher than that for the drug-unloaded one, demonstrating the strong effect of the drug on the rheological characteristics of the ME system. Therefore, it is possible to conclude that the investigated ME can be used as a very promising vehicle for AmB.     

Asymptotic behaviour of low density solutions to the generalized Becker-Döring equations

The asymptotic behaviour of solutions to the generalized Becker-D?ring equations is studied. It is proved that solutions converge strongly to a unique equilibrium if the initial density is sufficiently small. Received July 19, 1996     

New methodology for uranium analysis in swipe samples for nuclear safeguards purposes

Environmental swipe sampling for safeguards purpose has been used by International Atomic Energy Agency since 1997, being a powerful tool to detect undeclared materials and activities. This work describes a new methodology for swipe samples analysis based on ultrasound-assisted acid leaching and compares it with traditional total digestion bulk analysis. The proposed method requires few preparation steps, decreasing the risk of contamination, reduced amounts of reagents and a good option to extract uranium from swipe sample. In a real case study, the swipe samples were collected in a conversion plant at IPEN/CNEN, Brazil. The measurements were carried out by ICP-MS and the results showed relative error lower than 0.96 % for uranium isotopic ratios for the certified reference material (NBS U200). The uncertainties were estimated by following the ISO GUM, with a confidence level of 95 %. The uncertainties percentage for n(²³⁵U)/n(²³⁸U) ratio of the samples ranged from 2.5 to 4.3 %. The values of uranium isotopic ratio obtained for each method demonstrate the viability of using the methodology proposed in this work.     

An ILS-biased randomization algorithm for the two-dimensional loading HFVRP with sequential loading and items rotation

This paper discusses the Two-dimensional Loading Vehicle Routing Problem with Heterogeneous Fleet, Sequential Loading, and Item Rotation (2L-HFVRP-SR). Despite the fact that the 2L-HFVRP-SR can be found in many real-life situations related to the transportation of voluminous items, where heterogeneity of fleets, two-dimensional packing restrictions, sequential loading, and items rotation have to be considered, this rich version of vehicle routing-and-packing problem has been rarely analysed in the literature. Accordingly, this paper contributes to filling the gap by presenting a relatively simple-to-implement algorithm which is able to provide state-of-the-art solutions for such a complex problem in relatively short computational times. The proposed algorithm integrates inside an Iterated Local Search framework, biased-randomized versions of both vehicle routing and packing heuristics. The efficiency of the proposed algorithm is validated throughout an extensive set of computational tests.     

Ultrasound-Assisted Synthesis of 4-Alkoxy-2-methylquinolines: An Efficient Method toward Antitubercular Drug Candidates

Tuberculosis (TB) has been described as a global health crisis since the second half of the 1990s. Mycobacterium tuberculosis (Mtb), the etiologic agent of TB in humans, is a very successful pathogen, being the main cause of death in the population among infectious agents. In 2019, it was estimated that around 10 million individuals were contaminated by this bacillus and about 1.2 million succumbed to the disease. In recent years, our research group has reported the design and synthesis of quinoline derivatives as drug candidates for the treatment of TB. These compounds have demonstrated potent and selective growth inhibition of drug-susceptible and drug-resistant Mtb strains. Herein, a new synthetic approach was established providing efficient and rapid access (15 min) to a series of 4-alkoxy-6-methoxy-2-methylquinolines using ultrasound energy. The new synthetic protocol provides a simple procedure utilizing an open vessel system that affords the target products at satisfactory yields (45–84%) and elevated purities (≥95%). The methodology allows the evaluation of a larger number of molecules in assays against the bacillus, facilitating the determination of the structure–activity relationship with a reduced environmental cost.     

Combination preconditioning of saddle point systems for positive definiteness

Amongst recent contributions to preconditioning methods for saddle point systems, standard iterative methods in nonstandard inner products have been usefully employed. Krzy?anowski (Numerical Linear Algebra with Applications 2011; 18 :123–140) identified a two‐parameter family of preconditioners in this context and Stoll and Wathen (SIAM Journal on Matrix Analysis and Applications 2008; 30 :582–608) introduced combination preconditioning, where two preconditioners, self‐adjoint with respect to different inner products, can lead to further preconditioners and associated bilinear forms or inner products. Preconditioners that render the preconditioned saddle point matrix nonsymmetric but self‐adjoint with respect to a nonstandard inner product always allow a MINRES‐type method (‐PMINRES) to be applied in the relevant inner product. If the preconditioned matrix is also positive definite with respect to the inner product, a more efficient CG‐like method (‐PCG) can be reliably used. We establish eigenvalue expressions for Krzy?anowski preconditioners and show that for a specific choice of parameters, although the Krzy?anowski preconditioned saddle point matrix is self‐adjoint with respect to an inner product, it is never positive definite. We provide explicit expressions for the combination of certain preconditioners and prove the rather counterintuitive result that the combination of two specific preconditioners for which only ‐PMINRES can be reliably used leads to a preconditioner for which, for certain parameter choices, ‐PCG is reliably applicable. That is, combining two indefinite preconditioners can lead to a positive definite preconditioner. This combination preconditioner outperforms either of the two preconditioners from which it is formed for a number of test problems. Copyright © 2012 John Wiley & Sons, Ltd.