The Phenomenon of Self-Induced Diastereomeric Anisochrony and Its Implications in NMR Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is an analytical technique largely applied in the analysis of discrimination processes involving enantiomeric substrates and chiral agents, which can interact with the analyte either via covalent bonding or via formation of diastereomeric solvates. However, enantiodiscrimination has been observed, in some cases, even in the absence of any additional chiral selector. The reasons behind this phenomenon must be found in the capability of some chiral substrates to interact with themselves by forming diastereomeric solvates in solution that can generate nonequivalences in the NMR spectra of enantiomerically enriched mixtures. As a result, differentiation of enantiomers is observed, thus allowing the quantification of the enantiomeric composition of the mixture under investigation. The tendency of certain substrates to self-aggregate and to generate diastereomeric adducts in solution can be defined as Self-Induced Diastereomeric Anisochrony (SIDA), but other acronyms have been used to refer to this phenomenon. In the present work, an overview of SIDA processes investigated via NMR spectroscopy will be provided, with a particular emphasis on the nature of the substrates involved, on the interaction mechanisms at the basis of the phenomenon, and on theoretical treatments proposed in the literature to explain them

An inquiry concerning the Self-Induced Diastereomeric Anisochrony (SIDA) in ester derivatives of dipeptides: NMR investigations and analytical, thermodynamic, and conformational perspectives

The Self-Induced Diastereomeric Anisochrony (SIDA) allows to determine the enantiomeric excess by NMR spectroscopy in a scalemate without the use of a chiral auxiliary. Due to the interactions among enantiomers, diastereomeric complexes may be formed, some peaks may be split, and NMR nonequivalence arise. Several ester derivatives of dipeptides have been studied in order to verify whether they exhibit the SIDA phenomenon or not. These dipeptides were investigated in different solvents so to give the highest possible nonequivalences. Those dipeptides that showed self-discrimination capabilities were then subjected to thermodynamic studies (determination of self-association constants and determination of enthalpy and entropy of self-association), to Diffusion Ordered SpectroscopY (DOSY) experiments and to mono- and bi-dimensional Nuclear Overhauser Effects (NOE) experiments. These measurements allowed to gain insight into the thermodynamic of self-discrimination processes and into the stereochemical arrangements of the supramolecular aggregates responsible for the SIDA phenomenon

Marcadores de DNA na caracterização de germoplasma de feijão macassar (Vigna Unguiculata (L.) Walp.)

O presente estudo descreve os resultados obtidos a partir da aplicação da metodologia de DAF (DNA Amplification Fingerprinting; Impressão Digital da Amplificação do DNA) na discriminação de alguns acessos de feijão macassar (Vigna unguiculata (L.) Walp.) depositados em bancos de germoplasma. O estudo avaliou um total de 30 genótipos, incluindo 28 acessos de feijão macassar, um acesso de V. angularis (Willd.) Ohwi et Ohashi e um acesso de V. umbellata (Thumb.) Ohwi et Ohashi. Nove primers aleatórios (todos decâmeros) foram usados na análise, gerando em média 7,8 bandas e 5,2 bandas polimorficas por primer. A matriz de dados resultante incluiu 69 bandas analisadas com um total de 1342 caracteres. O dendrograma gerado pela análise UPGMA agrupou os acessos de caupi e das duas espécies restantes, revelando também alguns grupamentos a nível intraespecífico. As implicações da presente análise e as futuras perspectivas para o melhoramento do caupi no Brasil são discutidas no presente estudo

Synthesis and Solubility Properties of Methanofullerenes Containing Primary Ammonium Ion Functionalities

The synthesis of novel methanofullerene derivatives bearing a primary ammonium ion functionality is described. They are obtained by a Bingel cyclopropanation reaction on C-60 with malonate esters, bearing both a solubilizing poly(oxyethylene) chain and an aliphatic chain ending with a BOC-protected amine. After removal of the protecting group, a counterion exchange methodology allows for the introduction of a perfluorinated anion, bringing the overall solubility of these derivatives to 98 mg/mL in an organic CH2Cl2 solution

A near-infrared mechanically switchable elastomeric film as a dynamic cell culture substrate

Commercial static cell culture substrates can usually not change their physical properties over time, resulting in a limited representation of the variation in biomechanical cues in vivo. To overcome this limitation, approaches incorporating gold nanoparticles to act as transducers to external stimuli have been employed. In this work, gold nanorods were embedded in an elastomeric matrix and used as photothermal transducers to fabricate biocompatible light-responsive substrates. The nanocomposite films analysed by lock-in thermography and nanoindentation show a homogeneous heat distribution and a greater stiffness when irradiated with NIR light. After irradiation, the initial stiffness values were recovered. In vitro experiments performed during NIR irradiation with NIH-3T3 fibroblasts demonstrated that these films were biocompatible and cells remained viable. Cells cultured on the light stiffened nanocomposite exhibited a greater proliferation rate and stronger focal adhesion clustering, indicating increased cell-surface binding strength

Particle surfaces to study macrophage adherence, migration, and clearance

Nanoparticle adsorption to substrates pose a unique challenge to understand uptake mechanisms as it involves the organization of complex cytoskeletal components by cells to perform endocytosis/phagocytosis. In particular, it is not well‐understood from a cell mechanics perspective how the adhesion of particles on substrate will influence the ease of material clearance. By using a particle model, key contributing factors underlying cell adhesion on nonporous silica particle surfaces, migration and engulfment, are simulated and studied. Following a 24 h incubation period, monocyte‐ derived macrophages and A549 epithelial cells are able to adhere and remove particles in their local vicinity through induction of adhesive pulling arise from cell traction forces and phagocytic/endocytic mechanisms, in a size‐dependent manner. It is observed that such particle‐decorated surfaces can be used to address the influence of surface topography on cell behavior. Substrates which presented 480 nm silica particles are able to induce greater development and maturation of focal adhesions, which play an important role in cellular mechanoregulation. Moreover, under a chemotactic influence, in the presence of 30% fetal bovine serum, macrophages are able to uptake the particles and be directed to translocate along a concentration gradient, indicating that local mechanical effects do not substantially impair normal physiological functions