Noteworthy Chemistry

October 20, 2014

Which rivers are best for generating salinity gradient energy? Salinity gradients where rivers meet the sea are a potentially rich source of renewable energy. Theoretically, this energy source could provide as much as 28,000 TWh of electricity annually, more than enough to cover the 20,000 TWh consumed worldwide in 2011.

With the objective of converting this theoretical salinity gradient energy (SGE) figure to a practical yield, O. Alvarez-Silva*, C. Winter, and A. F. Osorio of the National University of Colombia (Medellín) and the University of Bremen (Germany) examined site-specific potentials (SSPs) that are based on the local salinity structures of specific river mouths and energy losses incurred during water transport to the generating station. The figure shows a cutaway view of a river mouth; increasing salinity levels are shown as darker shades of blue.

Cutaway view of a river mouth showing salinity gradient

Previous SGE estimates were based on average salinity differences between various rivers and the oceans into which they flow, but more realistic estimates must include spatial and temporal salinity variations at specific locations. Large mixing zones are impractical because of the excessive distance between freshwater and saltwater intake points and the associated energy loss during transport of the water to the power plant. The maximum SSP values were observed when the freshwater and saltwater intake ports were <2 km apart.

The tidal range (vertical difference between high and low tides) poses the greatest limitation to harnessing SGE at river mouths. It outweighs the influence of the average river depth and the amount of water discharged. River mouths with a mean tidal range of >1.2 m were deemed unsuitable for use as SGE sources. Deep river mouths, including fjords, may be an exception to this limit because tidal mixing may cause less perturbation of the stratified salinity.

Other significant factors include water pretreatment to reduce fouling and clogging, the energy consumption of the power plants themselves, and the effects of extracting large quantities of fresh and saline water on the natural mixing and circulation patterns in the river mouth. (Environ. Sci. Technol. Lett. DOI: 10.1021/ez500239n; Nancy McGuire)

[To learn how salinity gradient energy works, go to—Ed.]

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Make strong, low-viscosity thermoplastics "supramolecularly". From a manufacturing perspective, it is desirable to design thermoplastics for ease of processing without sacrificing mechanics and thermal stability. One way to achieve this goal is synthetic, architectural tailoring of supramolecular thermoplastics.

F. Tournilhac and co-workers at EPSCI Paris Tech explored the oligomeric condensation of alternating amorphous (soft) and crystalline (stiff) supramolecular fragments. The amorphous sections consisted of C36 derivatives of vegetable oils; diamide units formed the crystalline portions. Assembly of the blocks and dispersity of the thermoplastics were controlled by the ratio of the two components.

Formation of the alternating amorphous–crystalline architecture led to a microphase-segregated structure with varying levels of order, including crystallizable diamide units and supramolecular end groups. These supramolecular multiblocks exhibited melting transition temperatures between 147 and 164 ºC that were balanced by low melt viscosities between 0.2 and 0.8 Pas. The authors attribute these properties to the crystalline character of the multiblock morphology, high oligomer content, and minimal intermolecular hydrogen bonding.

The authors also demonstrated that the assemblies can be reprocessed with preservation of mechanics and rheology. Comparisons with polyurethane technology suggest that these materials may be usable as adhesives and composites. (J. Am. Chem. Soc. DOI: 10.1021/ja505956z; LaShanda Korley)

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Quorum sensing inhibitors limit bacterial pathogenicity. Quorum sensing (QS) is an evolutionarily conserved cell-to-cell bacterial communication system. It is integral for developing and maintaining infections. Pseudomonas aeruginosa, a Gram-negative bacterium that can cause life-threatening infections, has three discrete QS systems, all of which are needed for complete pathogenicity in mammals.

One of these virulence pathways is controlled by MvfR, a transcriptional regulator of pathogenic genes. MvfR is essential for acute and chronic infections but not for cell viability and growth. This makes MvfR a promising drug target because bacteria often evolve to resist antibiotic drugs that are directed at viability and growth targets.

L. Rahme and colleagues at Harvard Medical School, Massachusetts General Hospital, and Shriners Hospitals for Children (all in Boston) and INRS-Armand Frappier Institute (Laval, QU) used high-throughput screenings and functional assays to identify compounds that inhibit MvfR activity without affecting cell growth or viability. Eight of the 17 hits had a benzamide–benzimidazole structural backbone. Unexpectedly, this backbone is unrelated to MvfR ligands, and the chemical family previously was not known to inhibit MvfR activity.

By using structure–activity relationship analysis, the authors identified the substituents that increase MvfR inhibition, silence the QS communication system, and block P. aeruginosa virulence. One of the compounds is highly potent M64 (1; see figure), a QS inhibitor (QSI) that targets MvfR and likely prevents it from activating downstream promoters. M64 disrupts MvfR-dependent cell-to-cell communication, dramatically inhibits P. aeruginosa pathogenicity in vitro and in vivo and reduces bacterial persistence.

QS inhibitor M64

Because QS is integral throughout eubacteria and archaebacteria, QSI compounds based on M64 and other small molecules identified in this study may be able to fight a wide range of pathogenic bacteria without engendering antibiotic resistance. (PLOS Pathogens DOI: 10.1371/journal.ppat.1004321; Abigail Druck Shudofsky)

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Conduct bioassays with a printer and a DVD drive. Point-of-care (bedside) testing can deliver immediate medical results for patients. Expanded point-of-care tests and assays, however, require inexpensive materials and widely available diagnostic devices. One example is disc-based bioassays that are made possible by the low cost and high capacity of CD and DVD recorders.

X. Li, H.-Z. Yu, and coauthors at Taiyuan University of Technology (China) and Simon Fraser University (Burnaby, BC) took this technique to the next stage by using inkjet printing. The combination of a conventional printer and a DVD/Blu-Ray optical drive can significantly improve disc-based bioassays.

Inkjet printer–DVD/Blu-Ray optical drive combination for bioassays

The researchers first used amide coupling to immobilize an amine-PEG3-biotin probe onto the polycarbonate surface of a DVD-R disc. They then introduced nanogold–streptavidin for target binding. The entire process was automated by using free PrintCD software, which allows customized pattern design on disc surfaces. The quantities of solutions were precisely controlled by the continuous ink supply systems of the printer. The biotin–streptavidin binding assays could be characterized from DVD error distribution conducted with free disc-quality diagnostic software.

The authors demonstrated the full automation of a disc-based bioassay for point-of-care testing by using common, inexpensive computer peripherals. This principle also may be applicable to other biological or medical assays. (Anal. Chem. DOI: 10.1021/ac501870w; Xin Su)

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Monitor intracellular pH changes in real time. The biological functions of subcellular organelles are pH-dependent. Real-time pH measurements in live cells are important for understanding physiological and pathological processes and developing intracellular drug-delivery systems.

Fluorescein isothiocyanate (FITC) can be used to monitor pH changes because its fluorescence is pH-sensitive. Its utility for live-cell imaging, however, is limited by its rapid release from, and self-quenching inside, cellular compartments.

C. He, K. Lu, and W. Lin* at the University of Chicago developed fluorescent pH sensors by covalently conjugating FITC to UiO nanoscale metal–organic frameworks (UiO NMOFs). (UiO stands for the University in Oslo, where these zirconium-containing MOFs were developed.) The resulting F-UiO NMOFs with high fluorescein loadings exhibited the structural stability, fluorescence efficiency, pH sensitivity, and cellular uptake that the authors were looking for.

Live-cell imaging studies showed that the F-UiO NMOFs undergo endocytosis and intracellular trafficking processes, which are the basis of a reliable, accurate method for real-time visualization and monitoring of intracellular pH changes. (J. Am. Chem. Soc. DOI: 10.1021/ja507333c; Ben Zhong Tang)

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Large-scale directed ortho-metalation produces liquid crystal precursors. Liquid crystals are useful materials in the electronic industry. Fluorinated aryl groups are important substructures in many liquid crystals because fluorine atoms provide product properties such as low viscosity, large dielectric anisotropy, and good miscibility.

R. Hua and coauthors at Chengzhi Yonghua Display Materials (Shijiazhuang, China) and Tsinghua University (Beijing) report the multikilogram production of several fluorinated intermediates for liquid crystals that uses directed ortho-metalation of the arene followed by the reaction of the lithiated arene with an electrophile (see figure).

General process for producing ortho-substituted fluoroarenes

The key factor in the production methods is strict temperature control to avoid side reactions; all reaction temperatures should be <70 ºC. The authors’ first reaction sequence used n-butyllithium (n-BuLi) as the lithiating agent, followed by reaction with an organoborate to obtain boronic acids, which were than treated with hydrogen peroxide to produce phenols. Then, using molecular iodine, carbon dioxide, dimethylformamide (DMF), and cyclohexanone as electrophiles, they synthesized aryl iodides, carboxylic acids, aldehydes, and tertiary alcohols, respectively. Acid dehydration of the alcohols can be used to make olefinic compounds.

The reactions were performed in batches that ranged from 3 to 10 kg. In the case of the DMF, the authors substituted freshly prepared lithium diisopropylamide for n-BuLi. This study provides a general method for producing fluorinated aryls intermediates for liquid crystal production on the kilogram scale (Org. Process Res. Dev. DOI: 10.1021/op500133p; José C. Barros).

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