Hexafunctionalized borromeates using olefin cross metathesis

Employing well-established template-directed protocols, which depend upon dynamic covalent, coordinative, and noncovalent chemistry for their efficient outputs, we have synthesized, in a convergent manner, Borromeates composed of three identical macrocycles which present, diagonally in pairs, six exo-bidentate bipyridyl ligands and six endo-diiminopyridyl ligands, each carrying either pentenyloxy or p-tolylpentenyloxy substituents on their 4-positions, to six zinc(II) ions.     

Nanoscale potentiometry

Potentiometric sensors share unique characteristics that set them apart from other electrochemical sensors. Potentiometric nanoelectrodes have been reported and successfully used for many decades, and we review these developments. Current research chiefly focuses on nanoscale films at the outer or the inner side of the membrane, with outer layers for increasing biocompatibility, expanding the sensor response, or improving the limit of detection (LOD). Inner layers are mainly used for stabilizing the response and eliminating inner aqueous contacts or undesired nanoscale layers of water. We also discuss the ultimate detectability of ions with such sensors and the power of coupling the ultra-low LODs of ion-selective electrodes with nanoparticle labels to give attractive bioassays that can compete with state-of-the-art electrochemical detection.     

Nanoscale proteomics

Efforts to develop a liquid chromatography (LC)/mass spectrometry (MS) technology for ultra-sensitive proteomics studies (i.e., nanoscale proteomics) are described. The approach combines high-efficiency nanoscale LC (separation peak capacity of 10³; 15-m-i.d. packed capillaries with flow rates of 20 nL min^–1, the optimal separation linear velocity) with advanced MS, including high-sensitivity and high-resolution Fourier transform ion cyclotron resonance MS, to perform both single-stage MS and tandem MS (MS/MS) proteomic analyses. The technology enables broad protein identification from nanogram-size proteomics samples and allows the characterization of more abundant proteins from sub-picogram-size samples. Protein identification in such studies using MS is demonstrated from <75 zeptomole of a protein. The average proteome measurement throughput is ~50 proteins h^–1 using MS/MS during separations, presently requiring approximately 3 h sample^–1. Greater throughput (~300 proteins h^–1) and improved detection limits providing more comprehensive proteome coverage can be obtained by using the accurate mass and time tag approach developed in our laboratory. This approach provides a dynamic range of at least 10⁶ for protein relative abundances and an improved basis for quantitation. These capabilities lay the foundation for studies from single or limited numbers of cells.     

Nanoscale metal-organic materials

Metal-organic materials are found to be a fascinating novel class of functional nanomaterials. The limitless combinations between inorganic and organic building blocks enable researchers to synthesize 0- and 1-D metal-organic discrete nanostructures with varied compositions, morphologies and sizes, fabricate 2-D metal-organic thin films and membranes, and even structure them on surfaces at the nanometre length scale. In this tutorial review, the synthetic methodologies for preparing these miniaturized materials as well as their potential properties and future applications are discussed. This review wants to offer a panoramic view of this embryonic class of nanoscale materials that will be of interest to a cross-section of researchers working in chemistry, physics, medicine, nanotechnology, materials chemistry, etc., in the next years.     

Nanoscale intermittent contact-scanning electrochemical microscopy

A major theme in scanning electrochemical microscopy (SECM) is a methodology for nanoscale imaging with distance control and positional feedback of the tip. We report the expansion of intermittent contact (IC)-SECM to the nanoscale, using disk-type Pt nanoelectrodes prepared using the laser-puller sealing method. The Pt was exposed using a focused ion beam milling procedure to cut the end of the electrode to a well-defined glass sheath radius, which could also be used to reshape the tips to reduce the size of the glass sheath. This produced nanoelectrodes that were slightly recessed, which was optimal for IC-SECM on the nanoscale, as it served to protect the active part of the tip. A combination of finite element method simulations, steady-state voltammetry and scanning electron microscopy for the measurement of critical dimensions, was used to estimate Pt recession depth. With this knowledge, the tip-substrate alignment could be further estimated by tip approach curve measurements. IC-SECM has been implemented by using a piezo-bender actuator for the detection of damping of the oscillation amplitude of the tip, when IC occurs, which was used as a tip-position feedback mechanism. The piezo-bender actuator improves significantly on the performance of our previous setup for IC-SECM, as the force acting on the sample due to the tip is greatly reduced, allowing studies with more delicate tips. The capability of IC-SECM is illustrated with studies of a model electrode (metal/glass) substrate.     

Nanoscale Inhomogeneities in Thermoresponsive Polymers

This article highlights the occurrence and nature of nanoscale inhomogeneities in thermoresponsive polymers and focuses on different experimental techniques for their observation and characterization. Such inhomogeneities can be regarded as nanoscopic domains of collapsed polymer segments (or of a small number of unimers), which provide a nonpolar, hydrophobic interior. Continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy on amphiphilic reporter molecules (spin probes) as an intrinsically local technique is particularly emphasized. In combination with different ensemble‐averaging methods, it provides a holistic understanding of the often inhomogeneous nanoscale processes during the temperature‐induced collapse of a thermoresponsive polymer.     

Stick-Slip Mechanisms at the Nanoscale

When two surfaces slide past each other, energy is mainly dissipated by stick-slip events. Macroscopic stick-slip is usually explained by asperities that come in and out of contact. Herein, we probe stick-slip at the nanoscale at interfaces and polymer coated interfaces by pulling single polymers covalently attached to an AFM cantilever tip laterally over solid substrates in liquid environment. We find two different stick mechanisms, namely desorption stick (DS) and cooperative stick (CS). While DS-slip resembles the velocity dependence of macroscopic stick-slip, CS-slip shows an increase in friction with velocity. For various reasons we anticipate that both stick mechanisms are necessary for a molecular understanding of stick-slip at the interface and interphase.     

Nanoscale characterization of zein self-assembly

Zein, a major protein of corn, is rich in α-helical structure. It has an amphiphilic character and is capable of self-assembly. Zein can self-assemble into various mesostructures that may find applications in food, agricultural, and biomedical engineering. Understanding the mechanism of zein self-assembly at the nanoscale is important for further development of zein structures. In this work, high-resolution transmission electron microscopy (TEM) images revealed nanosize zein stripes, rings, and discs containing a 0.35 nm periodicity, which is characteristic of β-sheet. TEM images were interpreted in terms of the transformation of original α-helices into β-sheet conformation after evaporation-induced self-assembly (EISA). The presence of β-sheet was also detected by circular dichroism (CD) spectroscopy. Zein β-sheets self-assembled into stripes, which curled into rings. Rings formed discs and eventually spheres. The formation of zein nanostructures was believed to be the result of β-sheet orientation, alignment, and packing.     

Nanoscale Wetting of Single Viruses

The epidemic spread of many viral infections is mediated by the environmental conditions and influenced by the ambient humidity. Single virus particles have been mainly visualized by atomic force microscopy (AFM) in liquid conditions, where the effect of the relative humidity on virus topography and surface cannot be systematically assessed. In this work, we employed multi-frequency AFM, simultaneously with standard topography imaging, to study the nanoscale wetting of individual Tobacco Mosaic virions (TMV) from ambient relative humidity to water condensation (RH > 100%). We recorded amplitude and phase vs. distance curves (APD curves) on top of single virions at various RH and converted them into force vs. distance curves. The high sensitivity of multifrequency AFM to visualize condensed water and sub-micrometer droplets, filling gaps between individual TMV particles at RH > 100%, is demonstrated. Dynamic force spectroscopy allows detecting a thin water layer of thickness ~1 nm, adsorbed on the outer surface of single TMV particles at RH < 60%.     

Nanoscale highly filled epoxy nanocomposite

A new technique has been developed to prepare a highly filled epoxy-montmorillonite (MMT) nanocomposite using an organically modified MMT. Composites with clay content up to 70 wt.% exhibit unusual transparency, which is related to the spatial distribution of the mineral nanodomains. Dispersion of the layered silicate within the crosslinked epoxy matrix was verified using X-ray diffraction pattern, revealing layer spacings of 30 and 70 Å. Examination of these materials by scanning electron microscopy and transmission electron microscopy showed that intercalates have wholly layered morphology at all scales, oriented parallel to the surface of the specimen and have good wetting to the silicate surface by the epoxy matrix. Silicate lamellae intercalated with epoxy resin assembled into a cluster of about 50-120 nm thickness. These clusters assembled into superclusters with an average thickness of 300 nm. Studies by the Vickers hardness test of an epoxy-MMT nanocomposite containing 60 wt.% MMT indicated that the diamond pyramid hardness was 10-29 kg/mm².     

Nanoscale mixing of soft solids

Assessing the state of mixing on the molecular scale in soft solids is challenging. Concentrated solutions of micelles formed by self-assembly of polystyrene-block-poly(ethylene-alt-propylene) (PS-PEP) diblock copolymers in squalane (C(30)H(62)) adopt a body-centered cubic (bcc) lattice, with glassy PS cores. Utilizing small-angle neutron scattering (SANS) and isotopic labeling ((1)H and (2)H (D) polystyrene blocks) in a contrast-matching solvent (a mixture of squalane and perdeuterated squalane), we demonstrate quantitatively the remarkable fact that a commercial mixer can create completely random mixtures of micelles with either normal, PS(H), or deuterium-labeled, PS(D), cores on a well-defined bcc lattice. The resulting SANS intensity is quantitatively modeled by the form factor of a single spherical core. These results demonstrate both the possibility of achieving complete nanoscale mixing in a soft solid and the use of SANS to quantify the randomness.     

Nanoscale Borromean links for real

Borohydride reduction of a Borromean Ring (BR) complex containing six zinc(II) ions and 12 imine bonds has resulted in its demetallation, producing a neutral BR compound and also its free macrocycle, following cleavage of at least one of the imine bonds in the ethanolic reaction mixture.     

Adhesion between Nanoscale Rough Surfaces

In this investigation, the adhesion between particles and plates with root-mean-square, rms, surface roughness of 0.17-10.5 nm was measured by atomic force microscopy. Measurements obtained with particles both larger and smaller than the surface asperities are presented. Results indicate adhesion force decreases sharply with increasing surface roughness in the nanometer scale (<2 nm), followed by a gradual and slow decrease with further increase in roughness. Existing models were found to significantly underestimate adhesion force. Hence, a new model based on a geometry that considers both the height and breadth of asperities yielding an increased asperity radius compared to previous approaches, as detailed in Part I of this series, is applied using both van der Waals and elastic deformation/work of adhesion based approaches. For the system studied in this investigation, the adhesion forces predicted by the proposed model are considerably more accurate than those predicted by past models. Copyright 2000 Academic Press.     

Nanoscale Structure in Short-Chain Ionic Liquids

The temperature (T) and cationic chain length (n) evolution of the nanoscale structure of the sub-layering-threshold members of a model family of room temperature ionic liquids (RTILs) is investigated by x-ray scattering. The measured curves are computer-resolved into individual Teubner-Strey-like lineshapes. The polar-apolar layering is found to start at . Opposite n-trends are found at for the spacings and correlation lengths associated with the diffraction patterns’ two main peaks, and assigned to a shift of balance between the two main interactions, Coulomb and van der Waals, and to increasing packing constraints due to the addition of methylenes. The spacings’ thermal expansion coefficients are found to deviate from the macroscopically-measured values, and to anomalously decrease with increasing temperature. Finally, the reduced temperature scale, , ( melting temperature), is demonstrated to render the observed trends significantly more systematic than those on a conventional T scale.