New Methods for Improved Characterization of Silica Nanoparticle-Based Drug Delivery Systems

The incorporation of silica nanoparticles into drug delivery vehicles, and other nanotech platforms, has experienced rapid and significant growth over the past decade. However, as these nanoparticle-based systems become more and more complex, the methods used to analyze these systems have evolved at a comparatively much slower pace, resulting in the need for researchers to expand their toolbox and devise new strategies to characterize these materials. This article describes how X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were recently employed in the analysis of two separate drug delivery systems which contain organic compounds covalently attached to the surfaces of silica nanoparticles. These techniques provided a deluge of qualitative and quantitative information about these drug delivery systems, and have several clear advantages over more common characterization procedures such as Fourier transform infrared spectroscopy (FT-IR) and solid state nuclear magnetic resonance (SSNMR). Thus, XPS and ToF-SIMS should be an integral component of the standard characterization protocol for any nanoparticle-based assembliesparticularly silica-based drug delivery systemsas this field of research continues to develop

A Neutral Naphthalene Diimide [2]Rotaxane

A neutral donor–acceptor [2]rotaxane, which has been synthesized using click chemistry, has had its solid-state structure and superstructure elucidated by X-ray crystallography. Both dynamic ¹H NMR spectroscopy and electrochemical investigations have been employed in an attempt to shed light on both geometrical reorganization and redox-switching processes that are occurring or can be induced within the [2]rotaxane

Redox Switchable Daisy Chain Rotaxanes Driven by Radical–Radical Interactions

We report the one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable ‘daisy chain’ rotaxane switches based on a derivative of the so-called ‘blue box’ (BB⁴⁺) tetracationic cyclophane cyclobis­(paraquat-<i>p</i>-phenylene). These mechanically interlocked molecules are prepared by stoppering kinetically the solution-state assemblies of a self-complementary monomer comprising a BB⁴⁺ ring appended with viologen (V²⁺) and 1,5-dioxynaphthalene (DNP) recognition units using click chemistry. Six daisy chains are isolated from a single reaction: two monomers (which are not formally ‘chains’), two dimers, and two trimers, each pair of which contains a cyclic and an acyclic isomer. The products have been characterized in detail by high-field ¹H NMR spectroscopy in CD₃CNmade possible in large part by the high symmetry of the novel BB⁴⁺ functionalityand the energies associated with certain aspects of their dynamics in solution are quantified. Cyclic voltammetry and spectroelectrochemistry have been used to elucidate the electrochemical switching mechanism of the major cyclic daisy chain products, which relies on spin-pairing interactions between V^•+ and BB^2(•+) radical cations under reductive conditions. These daisy chains are of particular interest as electrochemically addressable molecular switches because, in contrast with more conventional bistable catenanes and rotaxanes, the mechanical movement of the ring between recognition units is accompanied by significant changes in molecular dimensions. Whereas the self-complexed cyclic monomerknown as a [<i>c</i>1]­daisy chain or molecular ‘ouroboros’conveys sphincter-like constriction and dilation of its ultramacrocyclic cavity, the cyclic dimer ([<i>c</i>2]­daisy chain) expresses muscle-like contraction and expansion along its molecular length

Modelling lubrication in gear pairs

The lubrication regime in gear pairs is usually elasto-hydrodynamic, i.e. solid deformations due to the fluid pressure are not negligible. It is well known that lubrication in gear pairs depends upon a number of kinematical parameters, so that it is a non stationary EHD problem. Moreover, it depends upon the dynamic response (i.e. the dynamic load) of the gear pair [1-5]. The problem of finding the dynamic response in gear systems, especially spur gears, has been studied by many research works. Most of them consider as the main source of vibration the time variation of the number of teeth pairs that are in contact at the same time. This fluctuation makes the transmission more stiff, when two pair of teeth are in contact, more deformable when only one pair is in contact. This behaviour can cause oscillations of the gears, and eventually detachment of the teeth in contact, with impacts and noise. The purpose of the present work is to investigate the effect of the varying rotational velocity of the gear pair on the film thickness and the contact pressure distribution. The lubrication regime in spur gear pairs is investigated using an EHL lubrication model. The solver described by Venner and Lubrecht [6] is adapted to the specific transient problem. Different test cases at different speeds are presented, in order to point out the role of the dynamic coupling on the lubricated contact

Internalization of Carbon Nano-onions by Hippocampal Cells Preserves Neuronal Circuit Function and Recognition Memory

One area where nanomedicine may offer superior performances and efficacy compared to current strategies is in the diagnosis and treatment of central nervous system (CNS) diseases. However, the application of nanomaterials in such complex arenas is still in its infancy and an optimal vector for the therapy of CNS diseases has not been identified. Graphitic carbon nano-onions (CNOs) represent a class of carbon nanomaterials that shows promising potential for biomedical purposes. To probe the possible applications of graphitic CNOs as a platform for therapeutic and diagnostic interventions on CNS diseases, fluorescently labeled CNOs were stereotaxically injected in vivo in mice hippocampus. Their diffusion within brain tissues and their cellular localization were analyzed ex vivo by confocal microscopy, electron microscopy, and correlative light-electron microscopy techniques. The subsequent fluorescent staining of hippocampal cells populations indicates they efficiently internalize the nanomaterial. Furthermore, the inflammatory potential of the CNOs injection was found comparable to sterile vehicle infusion, and it did not result in manifest neurophysiological and behavioral alterations of hippocampal-mediated functions. These results clearly demonstrate that CNOs can interface effectively with several cell types, which encourages further their development as possible brain disease-targeted diagnostics or therapeutics nanocarriers

γ‑Cyclodextrin Cuprate Sandwich-Type Complexes

Three structures, based on γ-cyclodextrin (γ-CD) and metal ions (Cu²⁺, Li⁺, Na⁺, and Rb⁺), have been prepared in aqueous and alkaline media and characterized structurally by single-crystal X-ray diffraction. Their dimeric assemblies adopt cylindrical channels along the <i>c</i> axes in the crystals. Coordinative and hydrogen bonding between the cylinders and the solvent molecules lead to the formation of two-dimensional sheets, with the identity of the alkali-metal ion strongly influencing the precise nature of the solid-state structures. In the case of the Rb⁺ complex, coordinative bonding involving the Rb⁺ ions leads to the formation of an extended two-dimensional structure. Nonbound solvent molecules can be removed, and gas isotherm analyses confirm the permanent porosity of these new complexes. Carbon dioxide (CO₂) adsorption studies show that the extended structure, obtained upon crystallization of the Rb⁺-based sandwich-type dimers, has the highest CO₂ sequestration ability of the three γ-CD complexes reported

Redox-Controlled Selective Docking in a [2]Catenane Host

The docking by neutral and charged guests selectively in two geometrically different binding pockets in a dynamic [2]­catenane host is demonstrated in the solid state by manipulating its redox chemistry. The change in redox properties, not only alters the affinity of the host toward neutral and charged guests, but it also induces a profound change in the geometry of the host to accommodate them. X-ray crystallography, performed on the two different 1:1 complexes, demonstrates unambiguously the fact that the [2]­catenane host provides a uniquely different binding pocket wherein a methyl viologen dication is stabilized by interacting with a bipyridinium radical cation, despite the presence of Coulombic repulsions

Redox-Controlled Selective Docking in a [2]Catenane Host

The docking by neutral and charged guests selectively in two geometrically different binding pockets in a dynamic [2]­catenane host is demonstrated in the solid state by manipulating its redox chemistry. The change in redox properties, not only alters the affinity of the host toward neutral and charged guests, but it also induces a profound change in the geometry of the host to accommodate them. X-ray crystallography, performed on the two different 1:1 complexes, demonstrates unambiguously the fact that the [2]­catenane host provides a uniquely different binding pocket wherein a methyl viologen dication is stabilized by interacting with a bipyridinium radical cation, despite the presence of Coulombic repulsions

Mixed-Valence Superstructure Assembled from a Mixed-Valence Host–Guest Complex

Herein, we report an unprecedented mixed-valence crystal superstructure that consists of a 2:1 host–guest complex [MV⊂​(CBPQT)₂]^2/3+ [MV = methyl viologen, CBPQT = cyclobis­(paraquat-<i>p</i>-phenylene)]. One electron is distributed statistically between three [MV⊂​(CBPQT)₂]^•+ composed of a total of 15 viologen units. The mixed-valence state is validated by single-crystal X-ray crystallography, which supports an empirical formula of [MV⊂​(CBPQT)₂]₃·​(PF₆)₂ for the body-centered cubic superstructure. Electron paramagnetic resonance provides further evidence of electron delocalization. Quantum chemistry calculations confirm the mixed-valence state in the crystal superstructure. Our findings demonstrate that precise tuning of the redox states in host–guest systems can lead to a promising supramolecular strategy for achieving long-range electron delocalization in solid-state devices

Energetically Demanding Transport in a Supramolecular Assembly

A challenge in contemporary chemistry is the realization of artificial molecular machines that can perform work in solution on their environments. Here, we report on the design and production of a supramolecular flashing energy ratchet capable of processing chemical fuel generated by redox changes to drive a ring in one direction relative to a dumbbell toward an energetically uphill state. The kinetics of the reaction pathway juxtapose a low energy [2]­pseudorotaxane that forms under equilibrium conditions with a high energy, metastable [2]­pseudorotaxane which resides away from equilibrium