Robust Interfacial Tribofilms by Borate- and Polymer-Coated ZnO Nanoparticles Leading to Improved Wear Protection under a Boundary Lubrication Regime.

This work reports on the development of borate- and methacrylate-polymer-coated zinc oxide nanoparticles (ZnOBM) via a plasma polymerization technique to replace the harmful conventional antiwear additive zinc dialkyl dithiophosphate (ZDDP) in automotive lubricants. Here, the tribochemistry across the interfaces formed between sliding ferrous surfaces and coated and uncoated ZnO nanoparticles is thoroughly studied from the perspective of elucidating the tribofilm formation, wear, and friction performance of a novel ZnOBM-based nanolubricant. Tribological tests conducted under a boundary lubrication regime revealed that oil formulations containing only ZnOBM nanoadditives and a mixture of ZnOBM with a low amount of ZDDP (350 ppm of P) significantly improve wear performance (up to 95%) compared to the base oil. Electrical contact resistance results acquired in situ during tribological tests demonstrated that lubricants containing ZnOBM nanoparticles at sliding interfaces undergo tribochemical reactions to form stable tribofilms that reduce friction and wear. Atomic force microscopy (AFM), X-ray absorption near-edge spectroscopy (XANES), and X-ray photoelectron spectroscopy (XPS) analysis revealed that ZnOBM nanoparticles, by themselves, form patchy interfacial tribofilms containing iron borate, boron oxide, and zinc oxide and lead to superior tribological performance. Interestingly, ZnOBM nanoparticles interact synergistically with ZDDP to form a hierarchical interface of boron-doped tribofilms, with zinc-iron polyphosphates at the surface and iron oxide, zinc and iron sulfides in the bulk. These encouraging results suggest the potential effective use of the ZnOBM nanoparticles to significantly reduce harmful levels of ZDDP (350 ppm) in the engine oil without compromising the antifriction and antiwear performance and to develop eco-friendly high-performance lubricant additives.

Overcoming Fundamental Limitations in Adsorbent Design: Alkene Adsorption by Non-porous Copper(I) Complexes.

Purifying alkenes from alkanes requires cryogenic distillation. This consumes energy equivalent to countries of ca. 5 million people. Replacing distillation with adsorption processes would significantly increase energy efficiency. Trade-offs between kinetics, selectivity, capacity, and heat of adsorption have prevented production of an optimal adsorbent. We report adsorbents that overcome these trade-offs. [Cu-Br]3 and [Cu-H]3 are air-stable trinuclear complexes that undergo reversible solid-state inter-molecular rearrangements to produce dinuclear [Cu-Br⋅(alkene)]2 and [Cu-H⋅(alkene)]2 . The reversible solid-state rearrangement, confirmed in situ using powder X-ray diffraction, allows adsorbent design trade-offs to be overcome, coupling low heat of adsorption (-10 to -17 kJ mol-1alkene ), high alkene:alkane selectivity (47; 29), and uptake capacity (>2.5 molalkene mol-1Cu3 ). Most remarkably, [Cu-H]3 displays fast uptake and regenerates capacity within 10 minutes.

Affinity mesh screen materials for selective extraction and analysis of antibiotics using transmission mode desorption electrospray ionization mass spectrometry.

The extraction of active compounds from natural sources has shown to be an effective approach to drug discovery. However, the isolation and identification of natural products from complex extracts can be an arduous task. A novel approach to drug discovery is presented through the use of polymer screens functionalized with an l-lysine-d-alanine-d-alanine (Kaa) peptide to create new affinity capture mesh screen materials. The Kaa sequence is a well-characterized specific binding site for antibiotics that inhibit cell wall synthesis in Gram-positive bacteria. The detailed synthesis and characterization of these novel screen materials are presented in this work. Polypropylene mesh screens were first coated with a poly(acrylic acid) film by pulsed plasma polymerization. The synthesized Kaa peptide was then covalently attached to carboxylic acid groups through a condensation reaction. An analysis of captured compounds was performed in a rapid fashion with transmission-mode desorption electrospray ionization (TM-DESI) mass spectrometry. A proof of principle was demonstrated to show the ability of the novel affinity capture materials to select for a macrocyclic antibiotic, vancomycin, over a negative control compound, spectinomycin. With further development, this method may provide a rapid screening technique for new antibacterial compounds, for example, those extracted from natural product sources having a limited supply. Here, we show that the screen can capture vancomycin preferentially over spectinomycin in a spiked extract of tea leaves.

pH- and concentration-programmable electrodialytic buffer generator.

We have presented in a companion paper a suppressor-based electrodialytic buffer generator (EBG) that can produce programmable pH gradients. Here we demonstrate a three-electrode EBG. In this three-compartment flow-through device, the central compartment is separated from the outer compartments with a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM), respectively. One platinum electrode is disposed in each compartment. The flows through each compartment are independent. With appropriate solutions in each compartment, independent potentials are applied to the CEM and AEM electrodes with respect to the grounded central electrode. The CEM current and the AEM current can be independently manipulated to generate buffers with variable concentration and pH in the central compartment. Both the CEM and AEM currents can be positive or negative. For the CEM, a positive current (i(cat)(in)) indicates that cations are coming in from the CEM channel to the center. A negative current (i(cat)(out)) takes cations out of the center to the CEM channel. Similarly for the AEM, currents governing anion transport into the center channel from the AEM channel (AEM electrode negative) or the reverse (AEM electrode positive) are respectively denoted by i(an)(in) or i(an)(out). Most examples herein involve inward ion transport, referred to as the additive mode. Depending on whether i(cat)(in) i(an)(in), H(+)/O(2) and OH(-)/H(2) are respectively produced at the central electrode to maintain electroneutrality. Any gas formed is subsequently removed by a gas removal device. The pH of the central channel effluent is related to the ratio of the currents through the two membranes, while the generated concentration is controlled by the absolute value of the currents. The buffer concentration and pH can be varied in a controlled predictable manner. A pH span of 3-12 was attained and a phosphate buffer concentration up to 140 mM was generated. We demonstrate a variety of combined pH/concentration gradients from a mixture of ethylenediamine, citrate, and phosphate by manipulating i(cat)(in), which controls introduction of the ethylenediammonium ion, and i(an)(in), which controls the introduction of citrate and phosphate ions. We also demonstrate an additive-subtractive mode of operation where both inward and outward currents are used to add one type of ion while removing another type of ion to reproducibly generate pH/concentration gradients.

Manipulation of protein charge states through continuous flow-extractive desorption electrospray ionization: a new ambient ionization technique.

Manipulation of protein charge states in electrospray ionization-mass spectrometry (ESI-MS) has implications for the study of intact proteins, protein-protein interactions, post-translational modifications, and protein sequencing. Control of these protein charge states is often difficult to achieve with conventional methods of analysis. A novel ambient ionization configuration, continuous flow-extractive desorption electrospray ionization (CF-EDESI), is presented as a means to control the charge state distribution of proteins. A key feature of the CF-EDESI technique is the continuous flow needle, which is a hypodermic needle presented orthogonal to the electrospray source and delivers a solvent flow containing analytes for extractive desorption ionization. With this source design, the successful manipulation of cytochrome c and lysozyme charge states with the use of different additives, such as acetic acid and sulfolane, was demonstrated. Results were compared to data obtained with conventional electrospray ionization. Good agreement with previously reported studies of cytochrome c unfolding/folding studies, performed by conventional ESI-MS, is evident. In addition to the protein analysis presented, the CF-EDESI-MS technique should be applicable for analyzing atypical analyte and solvent systems by mass spectrometry while maintaining optimal electrospray source conditions.