Quantum and Classical Molecular Dynamics of Ionic Liquid Electrolytes for Na/Li‐based Batteries: Molecular Origins of the Conductivity Behavior

Compositional effects on the charge‐transport properties of electrolytes for batteries based on room‐temperature ionic liquids (RTILs) are well‐known. However, further understanding is required about the molecular origins of these effects, in particular regarding the replacement of Li by Na. In this work, we investigate the use of RTILs in batteries, by means of both classical molecular dynamics (MD), which provides information about structure and molecular transport, and ab initio molecular dynamics (AIMD), which provides information about structure. The focus has been placed on the effect of adding either Na⁺ or Li⁺ to 1‐methyl‐1‐butyl‐pyrrolidinium [C₄PYR]⁺ bis(trifluoromethanesulfonyl)imide [Tf₂N]^?. Radial distribution functions show excellent agreement between MD and AIMD, which ensures the validity of the force fields used in the MD. This is corroborated by the MD results for the density, the diffusion coefficients, and the total conductivity of the electrolytes, which reproduce remarkably well the experimental observations for all studied Na/Li concentrations. By extracting partial conductivities, it is demonstrated that the main contribution to the conductivity is that of [C₄PYR]⁺ and [Tf₂N]^?. However, addition of Na⁺/Li⁺, although not significant on its own, produces a dramatic decrease in the partial conductivities of the RTIL ions. The origin of this indirect effect can be traced to the modification of the microscopic structure of the liquid as observed from the radial distribution functions, owing to the formation of [Na(Tf₂N)_n]^(n?1)? and [Li(Tf₂N)_n]^(n?1)? clusters at high concentrations. This formation hinders the motion of the large ions, hence reducing the total conductivity. We demonstrate that this clustering effect is common to both Li and Na, showing that both ions behave in a similar manner at a microscopic level in spite of their distinct ionic radii. This is an interesting finding for extending Li‐ion and Li‐air technologies to their potentially cheaper Na‐based counterparts.     

In vitro investigation of Brazilian Cerrado plant extract activity against Plasmodium falciparum,Trypanosoma cruzi and T. brucei gambiense

The threatened Brazilian Cerrado biome is an important biodiversity hotspot but still few explored that constitutes a potential reservoir of molecules to treat infectious diseases. We selected eight Cerrado plant species for screening against the erythrocytic stages of Plasmodium falciparum, human intracellular stages of Trypanosoma cruzi and bloodstream forms of T. brucei gambiense, and for their cytotoxicity upon the rat L6-myoblast cell line. Bioassays were performed with 37 hexane, ethyl acetate and ethanol extracts prepared from different plant organs. Activities against parasites were observed for 24 extracts: 9 with anti-P. falciparum, 4 with anti-T. cruzi and 11 with anti-T. brucei gambiense activities. High anti-protozoal activity (IC₅₀ values < 10 μg/mL) without obvious cytotoxicity to L6 cells was observed for eight extracts from plants: Connarus suberosus, Blepharocalyx salicifolius, Psidium laruotteanum and Myrsine guianensis. Overall, studies of plant extracts will contribute to increase the biodiversity knowledge essential for Cerrado conservation and sustainable development.     

Solution and Solid‐State Analysis of Binding of 13‐Substituted Berberine Analogues to Human Telomeric G‐quadruplexes

The interaction between 13‐phenylalkyl and 13‐diphenylalkyl berberine derivatives ( NAX ) and human telomeric DNA G4 structures has been investigated by both spectroscopic and crystallographic methods. NAX042 and NAX053 are the best compounds improving the performance of the natural precursor berberine. This finding is in agreement with the X‐ray diffraction result for the NAX053 ‐Tel12 adduct, showing the ligand which interacts via π‐stacking, sandwiched at the interface of two symmetry‐related quadruplex units, with its benzhydryl group contributing to the overall stability of the adduct by means of additional π‐stacking interactions with the DNA residues. The berberine derivatives were also investigated for their cytotoxic activity towards a panel of human cancer cell lines. Compounds NAX042 and NAX053 affect the viability of cancer cell lines in a dose‐dependent manner.     

Reactivity of Hypervalent Iodine(III) Reagents Bearing Transferable N-Based Groups

Hypervalent iodine reagents have the ability of inverting the polarity of functional groups bound to iodine, a reactivity known as umpolung. This reactivity makes hypervalent iodine compounds highly attractive for the creation of electrophilic synthons of known nucleophiles, resulting in novel synthetic disconnections and the formation of new Nu(nucleophile)−N bond. Electrophilic sources of nitrogen-based groups have been known for many decades and are of great synthetic importance. Traditionally, these reagents are limited to few examples. With the use of hypervalent iodine, the transfer of a wide diversity of nitrogen sources became a possibility. This review compiles the latest reported examples of hypervalent iodine reagents capable of electrophilic transfer of nitrogen-based groups. It showcases the preparation of such reagents, their synthetic utility, and reaction mechanisms involving these group transfer reagents.     

Infrared Spectroscopy Evidence of Weak Interactions in Frustrated Lewis Pairs Formed by Tris(pentafluorophenyl)borane

Frustrated Lewis pairs (FLPs) have been widely investigated as promising catalysts due to their metal-free feature and ability to activate small molecules. Since their discovery, many works have been investigating how these Lewis pairs (intermolecular pairs) are held together in an encounter complex. This prompted several studies based on theoretical investigations, but experimental ones are limited yet. In this communication we show evidence of weak intermolecular interactions between Lewis acids and Lewis bases, distinguishing the Lewis adduct from FLPs, by probing fluorine-carbon vibrational modes using infrared spectroscopy. The main evidence is based on the band shifts occurring in FLPs due to weak hydrogen bonds between the hydrogen atoms of the Lewis base and the fluorine atoms of Lewis acid.     

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint

In the present work, the resonance Raman, UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about approximately 300 nm in diameter) and nanofibers (about approximately 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1, 632 cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609 cm(-1) of PANI fibers is correlated with the extended PANI chain conformation.     

Structure/property relationships for the thermotropic behavior of lysine-based amphiphiles: from hexagonal to smectic phases

Amino acid-derived gemini surfactants arise as a potentially good alternative to the more conventional lipid and synthetic catanionic systems in view of their enhanced interfacial properties, increased chemical stability, and low toxicity. The presence of an amino acid as the polar headgroup allows toxicity reduction, with the simultaneous increase of biodegradability. For these compounds, the establishment of structure/function relationships from the assessment of their basic aggregation properties is therefore of the utmost interest, e.g., in the design of operative self-assembled systems (e.g., liposomes, nanotubes, etc). In this context, the study of the thermal phase behavior of the dry surfactants is a natural, straightforward first step, the more so as thermotropic liquid crystals are also relevant for practical applications. In this work, several lysine-based amphiphiles with a gemini-like configuration have been synthesized, with the amino acid side chain as the spacer group. The molecules are either esters (neutral, with C6-C12 even chains) or sodium carboxylates (anionic, with C6-C12 even chains). Upon increasing the temperature, different crystalline (cr) and liquid-crystalline (lc) phases have been detected and the corresponding thermodynamic and structural parameters determined by a combination of differential scanning calorimetry, polarizing light microscopy and small-angle X-ray scattering. The phase behavior of the amphiphiles is highly dependent on both the chain length and the presence of charge on the headgroup, with significant differences occurring within and between each group of molecules. The C6 and C8 esters form reverse hexagonal cr and lc phases, while C10 and C12 self-assemble into smectic cr and lc structures, with C10 showing also a reverse hexagonal lc phase prior to isotropization. All the carboxylate derivatives form smectic lc phases at high enough temperature prior to isotropization. The rationalization of the phase behavior and phase transition energetics of the compounds has been put forth on the basis of the intermolecular interactions at stake (van der Waals, H-bonding, electrostatic, and packing) and the molecular shape of the amphiphile.