Understanding the Influence of the Electronic Structure on the Crystal Structure of a TTF-PTM Radical Dyad

The understanding of the crystal structure of organic compounds, and its relationship to their physical properties, have become essential to design new advanced molecular materials. In this context, we present a computational study devoted to rationalize the different crystal packing displayed by two closely related organic systems based on the TTF-PTM dyad (TTF = tetrathiafulvalene, PTM = polychlorotriphenylmethane) with almost the same molecular structure but a different electronic one. The radical species (<b>1</b>), with an enhanced electronic donor–acceptor character, exhibits a herringbone packing, whereas the nonradical protonated analogue (<b>2</b>) is organized forming dimers. The stability of the possible polymorphs is analyzed in terms of the cohesion energy of the unit cell, intermolecular interactions between pairs, and molecular flexibility of the dyad molecules. It is observed that the higher electron delocalization in radical compound <b>1</b> has a direct influence on the geometry of the molecule, which seems to dictate its preferential crystal structure

Artificial 3D Culture Systems for T Cell Expansion

Adoptive cell therapy, i.e., the extraction, manipulation, and administration of ex vivo generated autologous T cells to patients, is an emerging alternative to regular procedures in cancer treatment. Nevertheless, these personalized treatments require laborious and expensive laboratory procedures that should be alleviated to enable their incorporation into the clinics. With the objective to improve the ex vivo expansion of large amount of specific T cells, we propose the use of three-dimensional (3D) structures during their activation with artificial antigen-presenting cells, thus resembling the natural environment of the secondary lymphoid organs. Thus, the activation, proliferation, and differentiation of T cells have been analyzed when cultured in the presence of two 3D systems, Matrigel and a 3D polystyrene scaffold, showing an increase in cell proliferation compared to standard suspension systems

A New Microcrystalline Phytosterol Polymorph Generated Using CO₂‑Expanded Solvents

Phytosterols have been receiving increasing attention due to their demonstrated health benefits. Micronization of phytosterol particles is desirable to enhance their physiological efficacy. Utilization of the environmentally friendly compressed fluid-based technology, called Depressurization of an Expanded Liquid Organic Solution (DELOS) was investigated to micronize a phytosterol mixture. A new polymorph of β-sitosterol, which was more crystalline than the native form, was obtained from the DELOS process regardless of the process conditions. In addition, particle size was reduced by an order of magnitude. The crystal structure of the new polymorph was determined from X-ray powder diffraction data. The proposed crystal structure for β-sitosterol, which contains a number of nearly isosteric vicariant molecules of lower molecular weight (mostly campesterol and campestanol, accounting in a crystalline solid-solution for nearly 10% of the molecular mixture) allows the presence of small cavities, in which some residual solvent molecules are temporarily trapped. Further structural analysis of the new and native polymorphs were performed by laser diffractometry, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray powder diffraction. Findings of the study provide a route to obtain nutraceutical products that might show enhanced functional properties

Highly Fluorescent Silicon Nanocrystals Stabilized in Water Using Quatsomes

Fluorescent silicon (Si) nanocrystals (2.8 nm diameter) were incorporated into surfactant assemblies of cetyltrimethylammonium bromide (CTAB) and cholesterol, called quatsomes. In water, the quatsome-Si nanocrystal assemblies remain fluorescent and well-dispersed for weeks. In contrast to Si nanocrystals, alkanethiol-capped gold (Au) nanocrystals do not form stable dispersions in water with quatsomes. Cryogenic transmission electron microscopy (cryo-TEM) confirmed that the Si nanocrystal-quatsome structures do not change over the course of several weeks. The long-term stability of the Si nanocrystal-quatsome assemblies, their fluorescence, and biocompatibility makes them attractive candidates for medical applications

Stimuli-Responsive Functionalization Strategies to Spatially and Temporally Control Surface Properties: Michael vs Diels–Alder Type Additions

Stimuli-responsive self-assembled monolayers (SAMs) are used to confer switchable physical, chemical, or biological properties to surfaces through the application of external stimuli. To obtain spatially and temporally tunable surfaces, we present microcontact printed SAMs of a hydroquinone molecule that are used as a dynamic interface to immobilize different functional molecules either via Diels–Alder or Michael thiol addition reactions upon the application of a low potential. In spite of the use of such reactions and the potential applicability of the resulting surfaces in different fields ranging from sensing to biomedicine through data storage or cleanup, a direct comparison of the two functionalization strategies on a surface has not yet been performed. Although the Michael thiol addition requires molecules that are commercial or easy to synthesize in comparison with the cyclopentadiene derivatives needed for the Diels–Alder reaction, the latter reaction produces more homogeneous coverages under similar experimental conditions

Novel PTM–TEMPO Biradical for Fast Dissolution Dynamic Nuclear Polarization

The synthesis and characterization of a novel trityl-TEMPO biradical and the investigation of its properties as Dynamic Nuclear Polarization (DNP) polarizing agent are reported. Comparison with a structurally related monoradical (PTM–TEMPE) or mixtures of the two monoradical components reveals that the biradical has a much higher polarization efficiency and a faster polarization buildup. This offers the possibility of faster recycling further contributing to its efficiency as a polarizing agent

Highly Reduced Double-Decker Single-Molecule Magnets Exhibiting Slow Magnetic Relaxation

F₆₄Pc₂Ln (<b>1</b>_<b>Ln</b>, Ln = Tb or Lu) represent the first halogenated phthalocyanine double-decker lanthanide complexes, and <b>1</b>_<b>Tb</b> exhibits single-molecule magnet properties as revealed by solid-state magnetometry. The fluorine substituents of the phthalocyanine rings have a dramatic effect on the redox properties of the F₆₄Pc₂Ln complexes, namely, a stabilization of their reduced states. Electrochemical and spectroelectrochemical measurements demonstrate that the <b>1</b>_<b>Tb</b>^{<b>–/2–</b>} and <b>1</b>_<b>Tb</b>^{<b>2–/3–</b>} couples exhibit redox reversibility and that the <b>1</b>_<b>Tb</b>^<b>–</b>, <b>1</b>_<b>Tb</b>^<b>2–</b> and <b>1</b>_<b>Tb</b>^<b>3–</b> species may be prepared by bulk electrolysis in acetone. Low-temperature MCD studies reveal for the first time magnetization hystereses for the super-reduced dianionic and trianionic states of Pc₂Ln

Self-Assembly of an Organic Radical Thin Film and Its Memory Function Investigated Using a Liquid-Metal Electrode

In this work, the deposition of a persistent organic radical by thermal evaporation on Au, Pt, and graphene is performed. The impact of the deposition parameters and the nature of the substrate on the molecular organization within the deposited film are investigated. The nonplanarity of the molecule and the role of the molecule–molecule and molecule–substrate interactions are discussed. UV photoelectron spectroscopy experiments demonstrate that the radical character, and hence its magnetic and redox properties, is preserved on the three surfaces. The optimized films are electrically characterized by top-contacting the film/substrate system using a liquid metal that permits achievement of a soft contact avoiding damaging the layer. The hysteretic current versus voltage curves obtained from the electrical characterization point to the potential applicability of the studied system as an organic memory. Moreover, the demonstrated feasibility of using a liquid metal is an appealing approach toward the preparation of flexible devices

Fluorenyl-Loaded Quatsome Nanostructured Fluorescent Probes

Delivery of hydrophobic materials in biological systems, for example, contrast agents or drugs, is an obdurate challenge, severely restricting the use of materials with otherwise advantageous properties. The synthesis and characterization of a highly stable and water-soluble nanovesicle, referred to as a quatsome (QS, vesicle prepared from cholesterol and amphiphilic quaternary amines), that allowed the nanostructuration of a nonwater soluble fluorene-based probe are reported. Photophysical properties of fluorenyl–quatsome nanovesicles were investigated via ultraviolet–visible absorption and fluorescence spectroscopy in various solvents. Colloidal stability and morphology of the nanostructured fluorescent probes were studied via cryogenic transmission electronic microscopy, revealing a “patchy” quatsome vascular morphology. As an example of the utility of these fluorescent nanoprobes, examination of cellular distribution was evaluated in HCT 116 (an epithelial colorectal carcinoma cell line) and COS-7 (an African green monkey kidney cell line) cell lines, demonstrating the selective localization of <b>C-QS</b> and <b>M-QS</b> vesicles in lysosomes with high Pearson’s colocalization coefficient, where <b>C-QS</b> and <b>M-QS</b> refer to quatsomes prepared with hexadecyltrimethylammonium bromide or tetradecyldimethylbenzylammonium chloride, respectively. Further experiments demonstrated their use in time-dependent lysosomal tracking

Synthesis and Structural Characterization of a Dendrimer Model Compound Based on a Cyclotriphosphazene Core with TEMPO Radicals as Substituents

The synthesis of the 3Gc₀T zero generation dendrimer with a cyclotriphosphazene core functionalized with nitroxyl radicals in its six branches has been performed. The radical units have been used as probes to determine the orientation of the six branches in solution experimentally by Electron Paramagnetic Resonance (EPR) spectroscopy compared with the structure obtained in the solid state by X-ray diffraction. The orientation of the dendrimer branches is the same in solution as in the solid state