Guanidine based amino acid derived task specific ionic liquids as noncorrosive lubricant additives for tribological performance

Strong Bases and beyond: The Prominent Contribution of Neutral Push-Pull Organic Molecules towards Superbases in the Gas Phase

In this review, the principles of gas-phase proton basicity measurements and theoretical calculations are recalled as a reminder of how the basicity PA/GB scale, based on Brønsted-Lowry theory, was constructed in the gas-phase (PA-proton affinity and/or GB-gas-phase basicity in the enthalpy and Gibbs energy scale, respectively). The origins of exceptionally strong gas-phase basicity of some organic nitrogen bases containing N-sp3 (amines), N-sp2 (imines, amidines, guanidines, polyguanides, phosphazenes), and N-sp (nitriles) are rationalized. In particular, the role of push-pull nitrogen bases in the development of the gas-phase basicity in the superbasicity region is emphasized. Some reasons for the difficulties in measurements for poly-functional nitrogen bases are highlighted. Various structural phenomena being in relation with gas-phase acid-base equilibria that should be considered in quantum-chemical calculations of PA/GB parameters are discussed. The preparation methods for strong organic push-pull bases containing a N-sp2 site of protonation are briefly reviewed. Finally, recent trends in research on neutral organic superbases, leaning toward catalytic and other remarkable applications, are underlined.

Synthesis of Polymer-Grafted Carbon Dots Serving as Multifunctional Lubricant Additives with Excellent Tribological Performance and Additional Rust Resistance Function for Steel/Steel Contact

Poly(bis(2-ethylhexyl) phosphoric) methacrylic anhydride-grafted carbon dots (CD-g-PEPMA) have been controllably synthesized and used as multifunctional lubricant additives of poly(ethylene glycol) (PEG200). The polymers on the surfaces of CD-g-PEPMA not only endow them with particularly excellent dispersion stability but also enhance their adsorbability on the steel surface and embedded stability between the rubbing surfaces. Hence, CD-g-PEPMA as an additive showed outstanding rust resistance and tribological performance. Among CD-g-PEPMA-X (X represents the polymerization time), CD-g-PEPMA-2 (X = 2 h) exhibited the best tribological performance. At the optimum c of 2.0 wt %, CD-g-PEPMA-2 reduced the coefficient of friction and wear volume of PEG200 by 60.1 and 74.0%, respectively. The striking friction-reducing and antiwear functions of CD-g-PEPMA as additives can be attributed to the synergistic lubrication effect of carbon cores and polymers. The rolling, polishing, and mending effects of carbon cores combined with the favorable adsorbability and reactivity of polymers on steel surfaces synergistically induced the formation of boundary lubrication films on wear track surfaces. The films are composed of tribochemical reaction products such as Fe2(CO3)3, Fe3C, and FePO4 embedded with carbon cores, tremendously reducing the friction and wear of the friction pair. The research results can provide substantial theoretical guidance and data support for designing and developing high-efficiency polymer-CD integrative multifunctional nanoadditives toward PEG.

Metabolism-Triggered Colorimetric Sensor Array for Fingerprinting and Antibiotic Susceptibility Testing of Bacteria

The rapid identification and antibiotic susceptibility testing (AST) of bacteria would help us to accurately identify the infectious sources as well as guide the use of antibiotics, which are crucial for improving the survival rate and antimicrobial resistance. Herein, a colorimetric sensor array for bacteria fingerprinting was constructed with d-amino acid (d-AA)-modified gold nanoparticles (AuNPs) as probes (Au/d-AA). Bacteria can metabolize the d-AA, triggering the aggregation of AuNPs. Making use of different metabolic capabilities of bacteria toward different d-AA, eight kinds of bacteria including antibiotic-resistant bacteria and strains of the same bacterial species are successfully differentiated via learning the response patterns. Meanwhile, the sensor array also performs well in quantitative analysis of single bacterium and differentiation of bacteria mixtures. More interestingly, a rapid colorimetric AST approach has been developed based on the Au/d-AA nanoprobes by monitoring the d-AA metabolic activity of bacteria toward various antibiotic treatments. In this regard, the outlined work here would promote clinical practicability and facilitate antibiotic stewardship.

Tribological properties of a series of carbon dots modified by ionic liquids with various anion species: experimental findings and density functional theory calculations

A series of carbon dots modified by ionic liquids with various anion species (CDs-ILs-X) were facilely synthesized by a one-pot pyrolysis method and subsequent anion exchange processes, where X- represented the anions of hexafluorophosphate (PF6-), bis(trifluorosulfonyl) imide (NTf2-), bis(salicylato) borate (BScB-) and oleate (OL-). Their tribological properties as lubricant additives of polyethylene glycol (PEG200) were investigated under the ball-on-plate reciprocating mode and steel/steel contact. The maximum friction coefficient and wear volume reductions of PEG200 triggered by CDs-ILs-PF6, CDs-ILs-NTf2, CDs-ILs-BScB and CDs-ILs-OL were up to 42.5% and 71.8%, 40.5% and 74.0%, 40.5% and 72.8%, and 52.2% and 79.5%, respectively. The excellent friction-reducing and anti-wear properties of CDs-ILs-X could be attributed to the formed boundary lubrication films composed of tribochemical products and CDs on the rubbing surfaces. The density functional theory calculations well explained the specific effects of anion species on the tribological performances of CDs-ILs-X. The strongest absorption stability and lowest steric hindrance of OL- made the CDs-ILs-OL form the densest boundary lubrication films on the sliding interfaces, and hence the CDs-ILs-OL exhibited the best tribological performance. The CDs-ILs-OL are promising lubricant additives to PEG owing to their high-performance, low cost and environmental friendliness.