A Transient-Directing-Group Strategy Enables Enantioselective Reductive Heck Hydroarylation of Alkenes

Metal-coordinating directing groups have seen extensive use in the field of transition-metal-catalyzed alkene functionalization; however, their waste-generating installation and removal steps limit the efficiency and practicality of reactions that rely on their use. Inspired by developments in asymmetric organocatalysis, where reactions rely on reversible covalent interactions between an organic substrate and a chiral mediator, we have developed a transient-directing-group approach to reductive Heck hydroarylation of alkenyl benzaldehyde substrates that proceeds under mild conditions. Highly stereoselective migratory insertion is facilitated by in situ formation of an imine from catalytic amounts of a commercially available amino acid additive. Computational studies reveal an unusual mode of enantioinduction by the remote chiral center in the transient directing group.     

A systematic review on distributed denial of service attack defense mechanisms in programmable networks

Design flaws and vulnerabilities inherent to network protocols, devices, and services make Distributed Denial of Service (DDoS) a persisting threat in the cyberspace, despite decades of research efforts in the area. The historical vertical integration of traditional IP networks limited the solution space, forcing researchers to tweak network protocols while maintaining global compatibility and proper service to legitimate flows. The advent of Software-Defined Networking (SDN) and advances in Programmable Data Planes (PDP) changed the state of affairs and brought novel possibilities to deal with such attacks. In summary, the ability of bringing together network intelligence to a control plane, and offloading flow processing tasks to the forwarding plane, opened up interesting opportunities for network security researchers unlike ever. In this article, we dive into recent research that relies on SDN and PDP to detect, mitigate, and prevent DDoS attacks. Our literature review takes into account the SDN layered view as defined in RFC7426 and focuses on the data, control, and application planes. We follow a systematic methodology to capture related articles and organize them into a taxonomy of DDoS defense mechanisms focusing on three facets: activity level, deployment location, and cooperation degree. From the analysis of existing work, we also highlight key research gaps that may foster future research in the field.     

Coffee adulterant quantification by derivative thermogravimetry and chemometrics analysis

Journal of Thermal Analysis and Calorimetry - Coffee quality is determined by analyzing its chemical, physical, sensory and hygienic-sanitary characteristics. It is a product consumed worldwide...     

Effects of the addition of mango residue on solution combustion synthesis of iron oxides

Journal of Thermal Analysis and Calorimetry - The effects of the addition of mango residue on the combustion of iron nitrate–urea mixtures are presented herein. The process was performed...     

Interfacial processes at single-crystal β-Sn electrodes in organic carbonate electrolytes

In situ atomic force microscopy (AFM) and spectroscopic ellipsometry were used to study the mechanism of organic carbonate electrolytes decomposition and surface layer (re)formation at β-Sn(001) and (100) single crystal electrodes. Interfacial phenomena were investigated at potentials above 0.8 V vs. Li/Li⁺, i.e. where no Sn–Li alloying takes place. The Sn(001) electrode tends to form a protective surface layer of electrolyte reduction products during the first cathodic CV scan, which effectively inhibits further reduction of the electrolyte upon cycling. In contrast, the Sn(100) electrode produces a thick, inhomogeneous and unstable surface layer. The observed significant difference of Sn reactivity toward the electrolyte as a function of Sn surface crystalline orientation suggests radically different reaction paths, reduction products, and properties of the surface film.     

Facile synthesis and coupling of functionalized isomeric biquinolines

A simple route toward functionalized biquinolines, namely 8,5′-dibromo-5,8′-biquinoline 1 and 5,5′-dibromo-8,8′-biquinoline 2, was developed using Skraup syntheses. Both the dibromo compounds undergo facile Suzuki coupling to afford fluorene-coupled products 3 and 4, respectively, an important transformation in designing conjugated materials based on these cores. X-ray structural analyses of 1 and 4 provide insight into the mode of packing within materials containing these units.     

On the vibrationally averaged structure and vibrational expectation values

Analytical expressions for population transfer and spin polarization are deduced for a two-level system in which the levels converge linearly or exponentially from a finite separation. The asymptotic populations and polarizations are discussed for rapid and slow approach trajectories and, in the exponential case, a simple closed form exact to second order in the perturbation for all rates of approach is discussed.     

Improvement of bioactive metabolite production in microbial cultures—A systems approach by OSMAC and deconvolution-based 1HNMR quantification

Traditionally, the screening of metabolites in microbial matrices is performed by monocultures. Nonetheless, the absence of biotic and abiotic interactions generally observed in nature still limit the chemical diversity and leads to “poorer” chemical profiles. Nowadays, several methods have been developed to determine the conditions under which cryptic genes are activated, in an attempt to induce these silenced biosynthetic pathways. Among those, the one strain, many compounds (OSMAC) strategy has been applied to enhance metabolic production by a systematic variation of growth parameters. The complexity of the chemical profiles from OSMAC experiments has required increasingly robust and accurate techniques. In this sense, deconvolution-based ¹HNMR quantification have emerged as a promising methodology to decrease complexity and provide a comprehensive perspective for metabolomics studies. Our present work shows an integrated strategy for the increased production and rapid quantification of compounds from microbial sources. Specifically, an OSMAC design of experiments (DoE) was used to optimize the microbial production of bioactive fusaric acid, cytochalasin D and 3-nitropropionic acid, and Global Spectral Deconvolution (GSD)-based ¹HNMR quantification was carried out for their measurement. The results showed that OSMAC increased the production of the metabolites by up to 33% and that GSD was able to extract accurate NMR integrals even in heavily coalescence spectral regions. Moreover, GSD-¹HNMR quantification was reproducible for all species and exhibited validated results that were more selective and accurate than comparative methods. Overall, this strategy up-regulated important metabolites using a reduced number of experiments and provided fast analyte monitor directly in raw extracts.     

Comparison between Highly Complex Location Models and GAMLSS

This paper presents a discussion regarding regression models, especially those belonging to the location class. Our main motivation is that, with simple distributions having simple interpretations, in some cases, one gets better results than the ones obtained with overly complex distributions. For instance, with the reverse Gumbel (RG) distribution, it is possible to explain response variables by making use of the generalized additive models for location, scale, and shape (GAMLSS) framework, which allows the fitting of several parameters (characteristics) of the probabilistic distributions, like mean, mode, variance, and others. Three real data applications are used to compare several location models against the RG under the GAMLSS framework. The intention is to show that the use of a simple distribution (e.g., RG) based on a more sophisticated regression structure may be preferable than using a more complex location model.