Markov shifts and topological entropy of families of homoclinic tangles

The existence of a homoclinic orbit in dynamical systems implies chaotic behaviour with positive entropy. In this work, we determine explicitly the Markov shifts associated to certain Smale horseshoe homoclinic orbits which allow us to compute a lower bound for the topological entropy that such a system can have. It is done associating a heteroclinic orbit which belongs to the same isotopy class and then determining the Markov partition of the dynamical core of an end periodic mapping.     

Highly Axial Magnetic Anisotropy in a N3O5 Dysprosium(III) Coordination Environment Generated by a Merocyanine Ligand

A spiropyran‐based switchable ligand isomerizes upon reaction with lanthanide(III) precursors to generate complexes with an unusual N₃O₅ coordination sphere. The air‐stable dysprosium(III) complex shows a hysteresis loop at 2 K and a very strong axial magnetic anisotropy generated by the merocyanine phenolate donor.     

Catalytic Activity of Cationic and Neutral Silver(I)–XPhos Complexes with Nitrogen Ligands or Tolylsulfonate for Mannich and Aza‐Diels–Alder Coupling Reactions

Cationic and neutral silver(I)–L complexes (L=Buchwald‐type biaryl phosphanes) with nitrogen co‐ligands or organosulfonate counter ions have been synthesised and characterised through their structural and spectroscopic properties. At room temperature, both cationic and neutral silver(I)–L complexes are extremely active catalysts in the promotion of the single and double A³ coupling of terminal (di)alkynes, pyrrolidine and formaldehyde. In addition, the aza‐Diels–Alder two‐ and three‐component coupling reactions of Danishefsky’s diene with an imine or amine and aldehyde are efficiently catalysed by these cationic or neutral silver(I)–L complexes. The solvent influences the catalytic performance due to limited complex solubility or solvent decomposition and reactivity. The isolation of new silver(I)–L complexes with reagents as ligands lends support to mechanistic proposals for such catalytic processes. The activity, stability and metal–distal arene interaction of these silver(I)–L catalysts have been compared with those of analogous cationic gold(I) and copper(I) complexes.     

Assessment of a high‐order MUSCL method for rotor flows

This work presents the implementation of a high‐order, finite‐volume scheme suitable for rotor flows. The formulation is based on the variable extrapolation MUSCL‐scheme, where high‐order spatial accuracy (up to fourth‐order) is achieved using correction terms obtained through successive differentiation. A variety of results are presented, including 2‐ and 3‐dimensional test cases. Results with the proposed scheme, showed better wake and higher resolution of vortical structures compared with the standard MUSCL, even when coarse meshes were employed. The method was also demonstrated for 3‐dimensional unsteady flows using overset and moving grids for the UH‐60A rotor in forward flight and the Enhanced Rotorcraft Innovative Concept Achievement tiltrotor in aeroplane mode. For medium grids, the present method adds reasonable CPU and memory overheads and offers good accuracy on relatively coarse grids.     

Synthesis,Structure, Reactivity and Catalytic Implications of a Cationic,Acetylide-Bridged Trigold–JohnPhos Species

The cationic complex [(JohnPhos–Au)₃(acetylide)][SbF₆] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide–trigold(I)–JohnPhos system; the trinuclear–acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η¹,η²,η¹ coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)₂] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [Au^IL1][SbF₆] complexes in CH₂Cl₂ at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [Cu^IL1][PF₆] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established.     

Metal Nodes of Metal-Organic Frameworks can Activate Molecular Hydrogen

Hydrogenation of multiple bonds are among the most general and important organic reactions. Typical heterogeneous catalysts are based on transition metal nanoparticles, including noble metals. Data are presented here showing that metal nodes of MIL-101(Cr) and UiO-66 in the absence of occluded metal nanoparticles can promote hydrogenation of polarized X=Y double bonds of nitro and carbonyl groups. The catalytic activity is a function of the composition of the metal node and the organic linker. It is proposed that the reaction mechanism is based on the operation of frustrated Lewis acid/base pairs.     

Electrochemical sensing of heavy metals in biological media: A review

Trace metals are required in the body as they play a significant role in several biochemical processes. Moreover, certain heavy metals are beneficial at appropriate levels. Copper (Cu), for example, is essential for red blood cell formation, bone strength, and infant growth. Despite these fundamental roles, Cu can become toxic at high levels. Other heavy metals such as lead (Pb), cadmium (Cd), manganese (Mn), and mercury (Hg), have been identified to cause acute and chronic health complications. For these reasons, rapid, real-time quantification of such metals in biological media is of interest to improving human health outcomes. Electrochemical methods offer numerous advantages, such as portability, capability to be miniaturized, low cost, and ease-of-use. In this review, we examine recent developments in electrochemical sensing for the detection of heavy metals in biological media. To meet the requirements for inclusion in this review, the electrochemical sensor must have been evaluated in biological media (blood, serum, sweat, saliva, urine, brain tissue/cells). Several applications are explored to examine recent advancements in electrochemical sensing within these matrices. Addressing the challenges through materials, device, and system innovations, it is expected that electrochemical sensing of heavy metals in biological media will facilitate future diagnoses and treatments in healthcare.     

Host-guest Assembly Based on γ-Cyclodextrin-functionalized Multiwalled Carbon Nanotubes for Rutin Electrochemical Sensing

Here, we report multiwalled carbon nanotubes (MWCNTs) functionalized with γ-cyclodextrins (γCD) as a novel electrochemical strategy for Rutin determination, showing superior performance than β-cyclodextrins (βCD) modified MWCNTs, suggesting an adequate environment for host-guest interactions. Under optimized conditions, the sensor showed a linear range of 39–975 nmol L⁻¹ and a limit of detection of 7 nmol L⁻¹. When tested with quercetin, catechin, and caffeine, the platform presented high selectivity with an interference response <10 %. The method was employed to quantify Rutin in spiked pharmaceutical and herbal extracts, providing recovery of 93–98.4 %. Also, HPLC-PDA confirmed the method‘s accuracy.     

Optimization of Experimental Parameters to Explore Small‐Ligand/Aptamer Interactions through Use of 1H NMR Spectroscopy and Molecular Modeling

Aptamers constitute an emerging class of molecules designed and selected to recognize any given target that ranges from small compounds to large biomolecules, and even cells. However, the underlying physicochemical principles that govern the ligand‐binding process still have to be clarified. A major issue when dealing with short oligonucleotides is their intrinsic flexibility that renders their active conformation highly sensitive to experimental conditions. To overcome this problem and determine the best experimental parameters, an approach based on the design‐of‐experiments methodology has been developed. Here, the focus is on DNA aptamers that possess high specificity and affinity for small molecules, L ‐tyrosinamide, and adenosine monophosphate. Factors such as buffer, pH value, ionic strength, Mg²⁺‐ion concentration, and ligand/aptamer ratio have been considered to find the optimal experimental conditions. It was then possible to gain new insight into the conformational features of the two ligands by using ligand‐observed NMR spectroscopic techniques and molecular mechanics.