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Scanning Electrochemical Microscopy of Living Cells
Published in Allen J. Bard, Michael V. Mirkin, Scanning Electrochemical Microscopy, 2022
Changyue Du, Thilini Suduwella, Isabelle Beaulieu, Steen B. Schougaard, Janine Mauzeroll
Yamada et al. have studied K+ flux at human embryonic kidney 293 cells (HEK293). A nanopipette containing a solution of bis(benzo-15-crown-5) dissolved in 1,6-dichlorohexane is used as an ion-selective electrode (ISE) to probe K+ for shear force-based constant-distance SECM. The SECM image of HEK293 cells revealed that most of the cell surface was impermeable to K+, but several areas with greater K+ flux, than the one of the surrounding areas, were present. This finding suggested the existence of K+ channels, such as K2p or KV channels, in these areas.163
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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
Although the polymerization reaction is necessarily a condensation, its kinetics somewhat resemble those of chain reactions such as the polymerication of olefins, in which chains leading to high molecular weight polymer may occur immediately. Under ultrasound irradiation, polymerization is greatly accelerated, so that it can be carried out at much lower temperatures (60 °C).64 The resulting polymer is of high molecular weight and monomodal. Worsfold62 and others65 have studied the effect of phase-transfer catalysts, for example, ether, on polymer molecular weight distribution. In the absence of catalysts, an induction period is observed, but addition of small amounts of a crown ether (e.g., a 15-crown-5), eliminates the induction period, but does not otherwise change the rate of disappearance of the dichlorosilanes during the early part of the condensation. In the presence of crown ether, the yields of high polymer is increased, and molecular weight distribution is strongly affected, becoming nearly monomodal. The surface area of the sodium also affects the product distribution, but not the maximum rate of disappearance of the monomer.
Nanoscale electrokinetic phenomena
Published in Zhigang Li, Nanofluidics, 2018
Allowing or screening the transport of ions can also be achieved by modifying channels with ion-responsive molecules. Figure 8.35a and b illustrates conical polyimide (PI) nanochannels modified with crown ether molecules to realize selective transport of ions, which are inspired by biological Na+ and K+ channels (Figure 8.35c) (Liu et al., 2015a). Crown ethers have a ring-shape structure and can bind with cations having a size similar to that of the cavity of crown ethers. To discriminate Na+ and K+, whose radii are about 0.98 and 1.38 Å, respectively, two types of crown ethers, 4′-aminobenzo-15-crown-5 (4-AB15C5) and 4′-aminobenzo-18-crown-6 (4-AB18C6), are used to modify PI nanochannels. The radius of 4-AB15C5 cavity is about 0.86–1.1 Å, which fits Na+ well. The cavity radius of 4-AB18C6 is in the range of 1.3–1.6 Å, similar to the size of K+. Therefore, these two crown ether molecules can selectively bind with Na+ or K+ and form stable complexes. If they are immobilized on a PI channel surface, the channel can be converted to a Na+-activated or K+-activated ionic gate.
Crown ethers having side arms: a diverse and versatile supramolecular chemistry
Published in Journal of Coordination Chemistry, 2021
Michael R. Gokel, Michael McKeever, Joseph W. Meisel, Saeedeh Negin, Mohit B. Patel, Shanheng Yin, George W. Gokel
The general toxicity of crown ethers was recognized by Pedersen [48], who is credited with inventing this class of compounds, and by Ts’o [49] who worked with cyclic oligomers of ethylene oxide. However, to put toxicity in perspective, Hendrixson and coworkers surveyed a number of common crowns to determine toxicity in white male mice [50]. They reported LD50 data [51] (in g/kg of body weight) for the “parent” compounds. Their values were 12-crown-4, 3.15 g/kg; 15-crown-5, 1.02 g/kg; and 18-crown-6, 0.70 g/kg. The average weight of a man in the United States is currently 195 lb and of a woman it is 165 lb. This gives an average value for a human of 180 lb, or 81.8 kg. At 0.70 g/kg the lethal dose for 50% of average humans would be 57.7 g. For comparison, we note that LD50 for aspirin to mice is 1.1 g/kg. For a mouse weighing 81.8 kg (not known so far), the amount of aspirin required to reach LD50 would be 90 g or 277 × 325 mg pills. Were the toxic dose 0.70 g/kg, it would still require 176 aspirin pills to kill the enormous mouse. A further comparison is widely prescribed alprazolam (Xanax®), for which LD50 is a little over 300 mg/kg of body weight in rats.
An electrospray ionization mass spectrometric study of beryllium chloride solutions and complexes with crown ether and cryptand macrocyclic ligands
Published in Journal of Coordination Chemistry, 2020
Onyekachi Raymond, William Henderson, Joseph R. Lane, Penelope J. Brothers, Paul G. Plieger
Crown ether complexes of beryllium have been characterized in the solid state and the X-ray structures of beryllium complexes with 12-crown-4 (12C4), 15-crown-5 (15C5) and 18-crown-6 (18C6), Chart 1, have all been reported [22–24]. Ironically, as far as we are aware, corresponding solution-based speciation of beryllium complexation by crown ethers has never been explored either by ESI MS or any other solution-based technique. However, ion extraction studies with the benzo-9-crown-3 ligand and its naphthalene analog reveal good complex formation with beryllium, to the extent that the benzo-9-crown-3 is a component of a beryllium selective membrane electrode [25, 26]. In contrast, a considerable number of studies have used ESI MS to explore the interactions of crown ethers with the neighboring alkali, alkaline earth and other divalent metal ions, supporting the correlation between the size of the cation and the effective radius of the cavity of the crown ether [27]. Therefore, aqueous mixtures of Be2+ and crown ether ligands were examined by ESI MS to identify the representative species occurring in solution, as well as the potential of the crown ethers as beryllium chelators. Closely related to the crown ethers are the cryptand ligands such as cryptand[2.2.2] (Chart 1) which possesses a larger cavity size and as a result may possibly complex a beryllium oxido/hydroxido-bridged species, as reported with other metal centers [28].
Bismuth coordination chemistry: a brief retrospective spanning crystallography to clinical potential
Published in Journal of Coordination Chemistry, 2021
Andrew H. Bond, Robin D. Rogers
In general, complexes without covalent bonds to Bi3+ do not exhibit secondary bonding interactions or lone pair effects. The [Bi(NO3)2(EO5)]+ cation, [Bi(NO3)3(12-crown-4)], and [Bi(NO3)3(OH2)3]·18-crown-6 all exhibit fairly narrow ranges in Bi-O separations [42]. This is consistent with our structural studies of [Pb(NO3)(12-crown-4)2][Pb(NO3)3(12-crown-4)], [PbL2][Pb(NO3)3L]2 (L = 15-crown-5 or benzo-15-crown-5), and [Pb(NO3)2(18-crown-6)] [76] in which stereochemical activity of lone pair electron density was not observed.