Seeing the Supracolloidal Assemblies in 3D: Unraveling High-Resolution Structures Using Electron Tomography

The interplay of chromophore-spacer length in light-induced gold nanocluster self-assembly

The light-induced self-assembly of chromophore-tethered precision nanoclusters (NCs) has recently received significant attention due to their facile control over structure, function, and reversibility under ambient conditions. However, the magnitude of assembly depends on the photoswitching efficiency, chemical structure, and proximity of the chromophore to the NC surface. Herein, using azobenzene alkyl monothiol (AMT)-capped gold NCs with two different spacer lengths (denoted as C3-NC and C9-NC), we show that reversible cis ↔ trans isomerization efficiency can be readily tuned to control the self-assembly kinetics of NCs. Irrespective of the chain length, the time required for trans-to-cis (140 s) and cis-to-trans (260 s) isomerization of individual C3-AMT and C9-AMT is identical in dichloromethane solution. When a similar experiment was performed using a solution of C3-NCs and C9-NCs, it resulted in self-assembled disc-like superstructures. Notably, the trans-to-cis photoswitching in C3-NC could reach only 65% even after 460 seconds of irradiation. On the other hand, C9-NC completed this process within 160 seconds of irradiation. The low photoswitching efficiency of the C3-NC analog is due to the short and rigid spacer length of C3-AMT ligands, which are in close proximity to the NC surface, resulting in steric hindrance experienced at the NC-chromophore interface. Importantly, the slow photoswitching in C3-NCs helps isolate and investigate the intermediates of assembly. Using high-resolution electron microscopy, atomic force microscopy, and 3D reconstruction, we show that the discs are made up of densely packed arrays of NCs. The prolonged illumination of C9-NCs results in a chain-like assembly due to the dipolar attraction between the previously assembled superstructures. The efficient photoisomerization of chromophores located away from the nanocluster surface has been identified as the key element to speed up the light-induced assembly in chromophore-tethered nanoclusters. Such information will be useful while developing nanoscale photoswitches for electrochemistry, biosensors, and electronic devices.

Shaping in the Third Direction: Colloidal Photonic Crystals with Quadratic Surfaces Self-Assembled by Hanging-Drop Method

High-quality, 3D-shaped, SiO2 colloidal photonic crystals (ellipsoids, hyperboloids, and others) were fabricated by self-assembly. They possess a quadratic surface and are wide-angle-independent, direction-dependent, diffractive reflection crystals. Their size varies between 1 and 5 mm and can be achieved as mechanical-resistant, free-standing, thick (hundreds of ordered layers) objects. High-quality, 3D-shaped, polystyrene inverse-opal photonic superstructures (highly similar to diatom frustules) were synthesized by using an inside infiltration method as wide-angle-independent, reflective diffraction objects. They possess multiple reflection bands given by their special architecture (a torus on the top of an ellipsoid) and by their different sized holes (384 nm and 264 nm). Our hanging-drop self-assembly approach uses setups which deform the shape of an ordinary spherical drop; thus, the colloidal self-assembly takes place on a non-axisymmetric liquid/air interface. The deformed drop surface is a kind of topological interface which changes its shape in time, remaining as a quality template for the self-assembly process. Three-dimensional-shaped colloidal photonic crystals might be used as devices for future spectrophotometers, aspheric or freeform diffracting mirrors, or metasurfaces for experiments regarding space-time curvature analogy.

Observing atomically precise nanocluster aggregates in solution by mass photometry

We report the first mass photometric characterization of nanoaggregates of atomically precise nanoclusters (NCs) in solution. The differently-sized nanoaggregates of silver-gold alloy NCs, [Ag11-xAux(DPPB)5Cl5O2]2+ [x = 1-5 and DPPB = 1,4-bis(diphenylphosphino)butane], formed in solution, were examined by mass photometry (MP) with a protein calibration. In addition, we conducted MP studies of varying solvent composition to understand the structural evolution of nanoaggregates. The masses of nanoaggregates were correlated to structures of 15 to 50 nm diameter observed in cryo-electron microscopy.

Development of Cholinium-Based API Ionic Liquids with Enhanced Drug Solubility: Biological Evaluation and Interfacial Properties

We report an efficient sustainable two-step anion exchange synthetic procedure for the preparation of choline API ionic liquids (Cho-API-ILs) that contain active pharmaceutical ingredients (APIs) as anions combined with choline-based cations. We have evaluated the in vitro cytotoxicity for the synthesized compounds using three different cells lines, namely, HEK293 (normal kidney cell line), SW480, and HCT 116 (colon carcinoma cells). The solubility of APIs and Cho-API-ILs was evaluated in water/buffer solutions and was found higher for Cho-API-ILs. Further, we have investigated the antimicrobial potential of the pure APIs, ILs, and Cho-API-ILs against clinically relevant microorganisms, and the results demonstrated the promise of Cho-API-ILs as potent antimicrobial agents to treat bacterial infections. Moreover, the aggregation and adsorption properties of the Cho-API-ILs were observed by using a surface tension technique. The aggregation behavior of these Cho-API-ILs was further supported by conductivity and pyrene probe fluorescence. The thermodynamics of aggregation for Cho-API-ILs has been assessed from the temperature dependence of surface tension. The micellar size and their stability have been studied by dynamic light scattering, transmission electron microscopy, and zeta potential. Therefore, the duality in the nature of Cho-API-ILs has been explored with the upgradation of their physical, chemical, and biopharmaceutical properties, which enhance the opportunities for advances in pharmaceutical sciences.