Ionic liquids (ILs) have attracted considerable attention in several sectors (from energy storage to catalysis, from drug delivery to separation media) owing to their attractive properties, such as ...high thermal stability, wide electrochemical window, and high ionic conductivity. However, their high viscosity and surface tension compared to conventional organic solvents can lead to unfavorable transport properties. To circumvent undesired kinetics effects limiting mass transfer, the discretization of ILs into small droplets has been proposed as a method to increase the effective surface area and the rates of mass transfer. In the present review paper, we summarize the different methods developed so far for encapsulating ILs in organic or inorganic shells and highlight characteristic features of each approach, while outlining potential applications. The remarkable tunability of ILs, which derives from the high number of anions and cations currently available as well as their permutations, combines with the possibility of tailoring the composition, size, dispersity, and properties (
e.g.
, mechanical, transport) of the shell to provide a toolbox for rationally designing encapsulated ILs for next-generation applications, including carbon capture, energy storage devices, waste handling, and microreactors. We conclude this review with an outlook on potential applications that could benefit from the possibility of encapsulating ILs in organic and inorganic shells.
Encapsulated ionic liquids (ILs) are candidate materials for several applications owing to the attractive properties of ILs combined with the enhanced mass transfer rate obtained through the discretization of ILs in small capsules.
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•Imidazolium-based ionic liquids (ILs) were encapsulated in methacrylate polymer microcapsules.•Polymer-encapsulated ILs were dispersed in non-polar oils at concentration that exceeds ...their solubility limit.•Polymer-encapsulated ILs led to a reduction of friction in steel/steel sliding contacts.•Encapsulated imidazolium-based IL does not tribochemically react at steel surfaces.
While ionic liquids (ILs) have attracted much attention as potential next-generation lubricant additives, their implementation in oil formulations has been hindered by their limited solubility in hydrocarbon fluids and corrosivity. Here, we encapsulate an oil-insoluble IL that has been studied in lubrication science, namely 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (HMIMTFSI), within poly(ethylene glycol dimethacrylate-buytl methacrylate copolymer) (poly(EGDM-c-BMA)) microshells using a mini-emulsion polymerization process. The synthesized poly(EGDM-c-BMA)-encapsulated HMIMTFSI microparticles are shown to be dispersible in a non-polar, synthetic oil (i.e., poly-α-olefin). Tribological experiments indicated that the microcapsules act as an additive reservoir that reduces friction by releasing the encapsulated IL at the sliding interface following the mechanical rupture of the polymer shell. X-ray photoelectron spectroscopy (XPS) measurements provided evidence that HMIMTFSI does not tribochemically react on steel surfaces to create a reaction layer, thus suggesting that this IL reduces friction by generating a solid-like, layered structure upon nanoconfinement at sliding asperities, as proposed by previous nanoscale studies. The results of this work do not only provide new insights into the lubrication mechanism of ILs when used as additives in base oils in general, but also establish a new, broadly-applicable framework based on polymer encapsulation for utilizing ILs or other compounds with limited solubility as additives for oil formulations.
While ionic liquids (ILs) have gained wide interest as potential alternative lubricants able to meet the requirements of next-generation tribological systems owing to their unique physico-chemical ...properties and promising lubricating behavior, our understanding of the mechanisms by which ILs reduce friction and/or wear is still elusive. Here, we combine macroscale tribological experiments with surface-analytical measurements to shed light on the lubrication mechanisms of a class of halogen-free ILs, namely tetraalkylammonium orthoborate ILs, at steel/steel sliding contacts. The tribological results indicate an improvement of the friction-reducing properties of these ILs as the length of the alkyl chains attached to ammonium cations increases. X-ray photoelectron spectroscopy analyses provide further evidence for the dependence of the lubrication mechanism of tetraalkylammonium orthoborate ILs on the IL structure. In the case of tetraalkylammonium orthoborate ILs with asymmetric ammonium cations containing a long alkyl chain, no sacrificial tribofilms were formed on steel surfaces, thus suggesting that the friction-reducing ability of these ILs originates from their propensity to undergo a pressure-induced morphological change at the sliding interface that leads to the generation of a lubricious, solid-like layered structure. Conversely, the higher friction response observed in tribological tests performed with tetraalkylammonium orthoborate ILs containing more symmetric ammonium cations and short alkyl chains is proposed to be due to the inability of this IL to create a transient interfacial layer owing to the reduced van der Waals interactions between the cationic alkyl chains. The resulting hard/hard contact between the sliding surfaces is proposed to lead to the cleavage of boron-oxygen bonds in the presence of water to form species that then adsorb onto the steel surface, including trivalent borate esters and oxalic acid from the decomposition of orthoborate anions, as well as tertiary amines from the degradation of alkylammonium cations induced by hydroxides released during the orthoborate decomposition reaction. The results of this work not only establish links between the molecular structure of a class of halogen-free ILs, their lubricating performance, and lubrication mechanism, but also provide evidence for the existence of multiple mechanisms underpinning the promising lubricating properties of ILs in general.
Graphical Abstract
To measure coexpression of matrix metalloproteinase (MMP)-2, MMP-7, and MMP-9 genes by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) in benign and malignant phases ...of colorectal carcinogenesis.
Matrix metalloproteinases degrade and remodel the extracellular matrix and have been implicated in facilitating carcinoma cells to invade and metastasize. MMP-2, MMP-7, and MMP-9 have been shown to be overexpressed in various carcinomas; however, simultaneous examination of these enzymes in human normal mucosa, adenoma, and carcinoma has not been performed to date.
Between January 1, 1998, and June 15, 2000, 40 patients underwent colectomy and harvest and snap-freezing of normal mucosa, adenoma, and carcinoma. Five patients had adenoma and carcinoma in the same specimen; 35 had either adenoma (n = 6) or carcinoma (n = 29). Taqman qRT-PCR methodology was used to measure MMP gene copy number and normalized to beta-actin RNA expression.
The mean age was 62 +/- 4 years, with 22 men and 18 women. One fifth of the adenomas exhibited severe dysplasia. MMP-7 gene expression was significantly increased in adenomas (43 times normal mucosa) but did not increase further in carcinomas (50 times normal mucosa). MMP-2 and MMP-9 were not different in adenomas (1.8 and 1.4 times normal mucosa, respectively) but were elevated in carcinomas (2.2 and 1.8 times normal mucosa, respectively). There was no correlation between size or dysplasia in adenomas or AJCC stage in carcinomas and MMP gene expression.
Overexpression of MMP-7 is an early event in the adenoma-to-carcinoma pathway, and expression does not appear to increase further in carcinomas. MMP-2 and MMP-9 appear to be primarily overexpressed in carcinomas. This may be one mechanism by which adenoma cells gain the ability to invade and carcinoma cells to metastasize.
Small‐scale actuators and propellers have benefited from advances in materials and manufacturing to become more lifelike. Inspired by animal species, multi‐generational chemically powered artificial ...propellers that carry small versions of themselves and deliver them “on‐the‐fly” are described. The released replicas are capable of autonomous propulsion and propelling immediately after detachment. Release occurs without human involvement and relies solely on sacrificial layers separating the carriers and replicas. These layers are composed of transient natural polymers, which dissolve under the swimming conditions to release the confined replicas. Judicious selection of the responsive transient materials, layer thickness, and solution conditions (e.g., pH), leads to programmable delivery of the replicas. Finally, the ability of the same carrier propellers to carry and transport multiple generations of propellers and deliver them at predetermined times is demonstrated.
Multi‐generational chemically powered artificial propellers that carry small versions of themselves and deliver them “on‐the‐fly” are described. Autonomous release relies solely on transient natural polymers. Control of the layer thickness and solution conditions leads to programmable delivery of the propellers. Finally, the ability of the carrier propellers to transport and release multiple generations of propellers at predetermined times is demonstrated.
Silicon-containing diamond-like carbon (DLC) is a class of thin-film materials with excellent mechanical properties, high thermal stability, and good tribological performance over a wide range of ...environmental conditions. While non-alloyed/non-doped DLCs also exhibit good biocompatibility and bioinertness, our understanding of the effect of silicon in DLCs on biomolecules/DLC interactions is still elusive. Here, we evaluated the structural, mechanical, and tribological properties of Si-containing DLC coatings with silicon content fraction of 11% and 16%. Tribological tests, performed by sliding a stainless steel pin on the coatings in water, indicated a low friction response (steady-state coefficient of friction <0.11), while quartz crystal microbalance experiments indicated no adsorption of a model biomolecule, namely adenosine triphosphate (ATP), on Si-containing DLCs. Near-edge X-ray absorption fine structure spectromicroscopy analyses performed after tribological experiments provided evidence for an increase in the fraction of silanol surface terminal groups formed in the worn region upon sliding in water without any significant sp3-to-sp2 rehybridization of carbon atoms. The fraction of surface hydroxyl groups in the worn region increases with the silicon content in Si-containing DLC, which leads to a decrease in friction. This tribologically-induced change in surface termination did not lead to the adsorption of ATP upon incubation of tribotested samples in ATP solutions for several hours. These findings open the path for the use of Si-containing DLC in applications requiring good tribological properties in aqueous solution and an excellent resistance to biomolecule surface adsorption that is maintained even after tribologically-induced variations in surface termination.
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•Si-containing DLC coatings with Si fraction between 11% and 16% were grown.•Increasing Si in DLC decreases friction in water.•Sliding in water leads to an increase in silanol surface terminal groups.•No adsorption of ATP occurs on Si-DLCs independently of the surface termination.
One of the key issues in international climate negotiations is the formulation of targets for emissions reduction for all countries based on the principle of ＂common but differentiated ...responsibilities＂. This formulation depends primarily on the quantitative attribution of the responsibilities of developed and developing countries for historical climate change. Using the Commuity Earth System Model（CESM）, we estimate the responsibilities of developed countries and developing countries for climatic change from 1850 to 2005 using their carbon dioxide, methane and nitrous oxide emissions. The results indicate that developed countries contribute approximately 53%–61%, and developing countries approximately 39%–47%, to the increase in global air temperature, upper oceanic warming, sea-ice reduction in the NH, and permafrost degradation. In addition, the spatial heterogeneity of these changes from 1850 to 2005 is primarily attributed to the emissions of greenhouse gases（GHGs）in developed countries. Although uncertainties remain in the climate model and the external forcings used, GHG emissions in developed countries are the major contributor to the observed climate system changes in the 20 th century.
In vivo stability and oral bioavailability of an oligodeoxynucleotide phosphorothioate containing segments of 2′-
O-methyloligoribonucleotide phosphorothioates at both the 3′- and 5′-ends (hybrid ...oligonucleotide) were studied. A 25-mer
35S-labeled hybrid oligonucleotide was administered to rats by gavage at a dose of 50 mg/kg body weight. HPLC analysis revealed that this hybrid oligonucleotide was stable in the gastrointestinal tract for up to 6 hr following oral administration. Radioactivity associated with the hybrid oligonucleotide was detectable in portal venous plasma, systemic plasma, various tissues, and urine. Intact hybrid oligonucleotide was detected, by HPLC analysis, in portal venous plasma, systemic plasma, and various tissues. The majority of the radioactivity in urine was associated with degradative products with lower molecular weights, but the intact form was also detected. In summary, the hybrid oligonucleotide was absorbed intact through the gastrointestinal tract, indicating the possibility of oral administration of oligonucleotides, a finding that may be important in the development of antisense oligonucleotides as therapeutic agents.
Human pharmacokinetics of an antisense oligodeoxynucleotide phosphorothioate (GEM 91) developed as an anti—human immunodeficiency virus (HIV) agent was carried out in this study. 35S‐Labeled GEM 91 ...was administered to six HIV‐infected individuals by means of 2‐hour intravenous infusions at a dose of 0.1 mg/kg. Plasma disappearance curves for GEM 91—derived radioactivity could be described by the sum of two exponentials, with half‐life values of 0.18 ± 0.04 and 26.71 ± 1.67 hours. The radioactivity in plasma was further evaluated by polyacrylamide gel electrophoresis, showing the presence of both intact GEM 91 and lower molecular weight metabolites. Urinary excretion represented the major pathway of elimination, with 49.15% ± 6.80% of the administered dose excreted within 24 hours and 70.37% ± 6.72% over 96 hours after dosing. The radioactivity in urine was associated with lower molecular weight metabolites. No drug‐related toxicity was observed.
Clinical Pharmacology & Therapeutics (1995) 58, 44–53; doi: 10.1016/0009‐9236(95)90071‐3
Catabolism of 5-fluorouracil (5-FU) is primarily regulated by DPD. Inactivation of DPD using eniluracil is advantageous in that it renders 5-FU orally bioavailable with more predictable ...pharmacokinetics and blocks one of the major potential mechanisms of 5-FU chemoresistance. The purpose of this study was to initially document inactivation of DPD by eniluracil in primary and metastatic colorectal cancer (CRC) and then to assess the time-course of the regeneration of DPD activity in peripheral blood (and where possible, additional tissues).
Of 28 patients entered, 23 were randomized to preoperative oral eniluracil (20 mg orally twice daily) or placebo prior to definitive resection of primary or metastatic CRC. Three patients were replaced, two because they had no residual tumor on pathologic evaluation and one for not taking the study drug. Patients received eniluracil 48, 36, 24 and approximately 12 h prior to surgical resection. In a second part of the study to document tissue regeneration of DPD, the additional five patients received eniluracil 144, 132, 120 and 108 h prior to surgical resection. DPD activity was measured in normal tissues, tumors and peripheral blood mononuclear cells (PBMC). Serum eniluracil and plasma uracil concentrations were determined before and through 28 days after eniluracil dosing. Data are presented as means+/-SEM, and significance defined as P<0.05.
Eniluracil inactivated DPD below the level of detection in primary and metastatic CRC as well as in normal tissues (0.0 pmol/min per mg protein) compared to primary tumor, metastatic tumor, PBMC, normal mucosa, and normal liver of patients receiving placebo (57+/-12, 119+/-19, 157+/-22, 77+/-12, 243+/-24 pmol/min/mg protein, respectively; P<0.05). At the time of surgery, serum eniluracil and uracil concentrations were 207+/-36 ng/ml and 2700+/-170 ng/ml in drug-treated patients. Within 6 days following treatment with eniluracil, serum eniluracil and uracil concentrations were undetectable, while DPD activity in PBMC had returned to baseline. The second group of patients (n=5) were given eniluracil 8 and 7 days prior to surgery to evaluate DPD regeneration in normal tissues and primary CRC tissue. In samples of these tissues, collected 6 days after the last eniluracil dose, DPD activity approached baseline in normal mucosa, normal liver and primary tumor (28+/-12, 94+/-23 and 20+/-8 pmol/min per mg protein, respectively).
These results demonstrate that oral administration of eniluracil inactivated DPD below the level of detection in normal tissues as well as in primary and metastatic CRC. After discontinuation of eniluracil, DPD rapidly returned toward baseline within 6 days in PBMC, normal intestinal mucosa and normal liver.
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