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Interfacial Catalysis at Oil/Water Interfaces
Published in Alexander G. Vdlkdv, Interfacial Catalysis, 2002
In this connection, Raguse et al. [53] reported the formation of t-BLMs with an ionic reservoir. Self-assembled monolayers of reservoir-forming lipids were first adsorbed on to the gold surface by using gold-sulfur interactions, followed by formation of the t-BLM. The properties of the t-BLM were investigated by impedance spectroscopy. The capacitance of the t-BLM indicated the formation of bilayer membranes of comparable thickness to a solvent-free c-BLM. Also, the ionic sealing ability was comparable to those of classical BLMs. The function of the ionic reservoir was investigated using the potassium-specific ionophore valinomycin. Increasing the size of the reservoir by increasing the length of the hydrophilic region of the reservoir lipid or laterally spacing the reservoir lipid resulted in an improved ionic reservoir. Imposition of a d.c. bias voltage during the measurement of the impedance spectrum affected the conductivity of the t-BLM.
Dielectrophoresis of complex bioparticles
Published in Michael Pycraft Hughes, Nanoelectromechanics in Engineering and Biology, 2018
As seen in Figure 5.12, the spectrum of particles treated with valinomycin is different from the other results in that it exhibits a sharp rise in crossover frequency from 8 MHz in low conductivity media to in excess of 20 MHz at higher conductivities. Valinomycin is a K+ ionophore, that is, it acts to transport potassium ions across the membrane. This leads to equilibrium of K+ ions on either side of the membrane, with other ions contained within the virion being retained. The gradient of the slope of the dielectrophoretic spectrum is therefore due to the interior conductivity following the exterior conductivity, with an extra component corresponding to the non-K+ ions. The model indicates that if the internal baseline conductivity is 40 mS m–1, then the best-fit model matches the response if the membrane relative permittivity is increased to 26. This is a high value for a lipid membrane but may reflect the action of the ionophores suspended within the membrane. All other parameters are within the ranges indicated for fresh viruses. Furthermore, there is a high transmembrane conductivity component σmem of 18 mS m–1, indicative of the large effect of ion transport across the membrane by the ionophore. Such an effect could be mistaken for an unusually high value of Ksi though the low data point at higher conductivity would count against this theory.
Electrochemical Methods
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
A liquid membrane electrode has an ion-exchange material within a solid polymeric membrane. This material exchanges the analyte ion across the membrane, which creates the potential. Calcium and nitrate ions, among others, are measured by liquid membrane electrodes. Other electrodes of similar construction use a neutral molecule which has an affinity for the ion to be determined. For instance, valinomycin has an affinity for potassium ions, and is incorporated in a suitable solvent behind a polymeric membrane to form a potassium selective electrode.
Optimization of fermentation medium and conditions for enhancing valinomycin production by Streptomyces sp. ZJUT-IFE-354
Published in Preparative Biochemistry & Biotechnology, 2023
Dong Zhang, Yingling Bao, Zhi Ma, Jiawei Zhou, Hanchi Chen, Yuele Lu, Linjiang Zhu, Xiaolong Chen
Valinomycin is a cyclododecadepsipeptide composed of a triplicate repeating sequence of the tetramer D-α-hydroxyisovaleric acid -D-valine -L-lactate -L-valine.[1] It showed broad-spectrum bioactivities such as antiviral,[1–3] antitumor,[4] antifungal,[5,6] and insecticidal activities.[7] For example, valinomycin showed antiviral activity against nineteen viruses, including five human coronaviruses HCoV-229E, HCoV-OC43, HCoVNL63, SARS-CoV, and MERS-CoV. Valinomycin was considered as the most potent antiviral agent against SARS-CoV with the half-effective concentrations for the inhibition of virus replication value of 0.85 µM among nearly 10,000 antiviral compounds.[3] Of note, valinomycin may be a potential antiviral agent against SARS-CoV-2,[1,8] resulting in millions of confirmed death cases worldwide. Moreover, valinomycin exhibited strongly in vitro antifungal activity against Sclerotinia sclerotiorum with EC50 and EC95 values of 0.056 ± 0.012 and 0.121 ± 0.023 µg/mL, which were respectively 10.696- and 30.960-fold lower than that those of the commercial agent carbendazim.[6] On the other hand, valinomycin can be used to prepare ion-selective electrodes due to the property of transporting K+ selectively.[9–11] Therefore, the improvement of valinomycin production technology attracts a new interest.