Selective reagents for solvent extraction of metals—I. Quinaldic acids

Alkyl- and alkoxy-substituted quinoline-2-carboxylic acids were synthesized and tested for metal extraction. Zn²⁺ and Cu²⁺ were extracted from aqueous sulphate solutions by reagents containing 8-alkoxy substituents at lower pH values than were Fe²⁺ or Fe³⁺. Reagents without this substituent were unselective in this respect. A possible explanation for the selectivity may be that the 8-substituent influences the coordination geometry of the metal chelates in favour of tetrahedral complexes.     

One-pot functionalization of cellulose nanocrystals with various cationic groups

After successful cationization of cellulose nanocrystals (CNCs) to produce pyridinium-grafted-CNCs, a variety of different cationic CNCs were prepared using a similar procedure, thus unlocking access to a wide variety of cationized cellulose nanocrystals through a simple one-pot reaction. In this study, cationic CNCs were prepared through the use of 4-(1-bromoethyl)benzoic acid or 4-bromomethylbenzoic acid, p-toluenesulfonyl chloride, CNCs, and two different amines, 1-methylimidazole and 4-dimethylaminopyridine. The amines acted as both the base catalyst for the esterification and the nucleophile to form the cationic charge. This method offers a versatile and straightforward route to prepare a variety of different cationic nanocrystals and therefore tailor their interaction with their environment.     

Ru‐Catalyzed Dehydrogenative C−O Bond Formation with Anilines and Phenols

The Ru catalyzed cross‐dehydrogenative C?O bond formation between anilines and phenols is described and discussed. The exclusive C?O versus C?N bond‐formation selectivity, moreover in the absence of chelating–assisting directing groups and while leaving the N?H position untouched, is a remarkable feature of this metal‐catalyzed radical cross‐dehydrogenative coupling.     

Nanotexaphyrin: One‐Pot Synthesis of a Manganese Texaphyrin‐Phospholipid Nanoparticle for Magnetic Resonance Imaging

The discovery and synthesis of novel multifunctional organic building blocks for nanoparticles is challenging. Texaphyrin macrocycles are capable and multifunctional chelators. However, they remain elusive as building blocks for nanoparticles because of the difficulty associated with synthesis of texaphyrin constructs capable of self‐assembly. A novel manganese (Mn)‐texaphyrin‐phospholipid building block is described, along with its one‐pot synthesis and self‐assembly into a Mn‐nanotexaphyrin. This nanoparticle possesses strong resilience to manganese dissociation, structural stability, in vivo bio‐safety, and structure‐dependent T₁ and T₂ relaxivities. Magnetic resonance imaging (MRI) contrast enhanced visualization of lymphatic drainage is demonstrated with respect to proximal lymph nodes on the head and neck VX‐2 tumors of a rabbit. Synthesis of 17 additional metallo‐texaphyrin building blocks suggests that this novel one‐pot synthetic procedure for nanotexaphyrins may lead to a wide range of applications in the field of nanomedicines.     

Uncovering Key Structural Features of an Enantioselective Peptide‐Catalyzed Acylation Utilizing Advanced NMR Techniques

We report on a detailed NMR spectroscopic study of the catalyst‐substrate interaction of a highly enantioselective oligopeptide catalyst that is used for the kinetic resolution of trans‐cycloalkane‐1,2‐diols via monoacylation. The extraordinary selectivity has been rationalized by molecular dynamics as well as density functional theory (DFT) computations. Herein we describe the conformational analysis of the organocatalyst studied by a combination of nuclear Overhauser effect (NOE) and residual dipolar coupling (RDC)‐based methods that resulted in an ensemble of four final conformers. To corroborate the proposed mechanism, we also investigated the catalyst in mixtures with both trans‐cyclohexane‐1,2‐diol enantiomers separately, using advanced NMR methods such as T₁ relaxation time and diffusion‐ordered spectroscopy (DOSY) measurements to probe molecular aggregation. We determined intramolecular distance changes within the catalyst after diol addition from quantitative NOE data. Finally, we developed a pure shift EASY ROESY experiment using PSYCHE homodecoupling to directly observe intermolecular NOE contacts between the trans‐1,2‐diol and the cyclohexyl moiety of the catalyst hidden by spectral overlap in conventional spectra. All experimental NMR data support the results proposed by earlier computations including the proposed key role of dispersion interaction.     

The Influence of Divalent Anions on the Rectification Properties of Nanofluidic Diodes: Insights from Experiments and Theoretical Simulations

During the last decade, the possibility of generating synthetic nanoarchitectures with functionalities comparable to biological entities has sparked the interest of the scientific community related to diverse research fields. In this context, gaining fundamental understanding of the central features that determine the rectifying characteristics of the conical nanopores is of mandatory importance. In this work, we analyze the influence of mono‐ and divalent salts in the ionic current transported by asymmetric nanopores and focus on the delicate interplay between ion exclusion and charge screening effects that govern the functional response of the nanofluidic device. Experiments were performed using KCl and K₂SO₄ as representative species of singly and doubly charged species. Results showed that higher currents and rectification efficiencies are achieved by doubly charged salts. In order to understand the physicochemical processes underlying these effects simulations using the Poisson‐Nernst‐Planck formalism were performed. We consider that our theoretical and experimental account of the effect of divalent anions in the functional response of nanofluidic diodes provides further insights into the critical role of electrostatic interactions (ion exclusion versus charge screening effects) in presetting the ionic selectivity to anions as well as the observed rectification properties of these chemical nanodevices.     

Immobilization/stabilization of lipase fromCandida rugosa

With the aim of fixing the enzyme to the matrix by multiple covalent linkages, lipase from Candida rugosa (formerly cylindracea) has been insolubilized through its amino groups on Sepharose 6B previously activated with 2,3-epoxy-1-propanol. Two main variables that are known to control the number of bonds formed have been tested: the contact time between enzyme and activated support, and the temperature at which the immobilization reaction is carried out. Studies on activity and stability of the different derivatives prepared showed that higher temperatures and longer contact times lead to insolubilized enzymes that are more resistant to inactivation by temperature and the presence of organic solvents. At 50 degrees C and pH 7.2, the insoluble lipase was found to be 140 times more stable than its soluble counterpart.