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4. Pigment Lasers

Author

Lee, Jae Dong, Lee, Jong Kook, Oh, Min Jin Maya, Lee, Jae Dong, Lee, Jong Kook, and Oh, Min Jin Maya

Published
2020
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34. Novel Gating Mechanism of Polyamine Block in the Strong Inward Rectifier K Channel Kir2.1

Author

Lee, Jong-Kook, John, Scott A, and Weiss, James N

Subjects
Medical Physiology, Biomedical and Clinical Sciences, Animals, Biogenic Polyamines, Indoleacetic Acids, Ion Channel Gating, Membrane Potentials, Mutation, Oocytes, Patch-Clamp Techniques, Polyamines, Potassium Channel Blockers, Potassium Channels, Potassium Channels, Inwardly Rectifying, Reverse Transcriptase Polymerase Chain Reaction, Spider Venoms, Wasp Venoms, Xenopus laevis, spider venom toxin, polyamine, inward rectification, K channels, Physiology, Biochemistry and cell biology, Zoology, Medical physiology
Abstract

Inward rectifying K channels are essential for maintaining resting membrane potential and regulating excitability in many cell types. Previous studies have attributed the rectification properties of strong inward rectifiers such as Kir2.1 to voltage-dependent binding of intracellular polyamines or Mg to the pore (direct open channel block), thereby preventing outward passage of K ions. We have studied interactions between polyamines and the polyamine toxins philanthotoxin and argiotoxin on inward rectification in Kir2.1. We present evidence that high affinity polyamine block is not consistent with direct open channel block, but instead involves polyamines binding to another region of the channel (intrinsic gate) to form a blocking complex that occludes the pore. This interaction defines a novel mechanism of ion channel closure.

Published
1999

43. Suppressing antiferromagnetic coupling in rare-earth free ferromagnetic MnBi-Cu permanent magnet.

Author

Choi, Minyeong, Hong, Yang-Ki, Won, Hoyun, Mankey, Gary J., Yeo, Chang-Dong, Lee, Woncheol, Jung, Myung-Hwa, Lee, Taegyu, and Lee, Jong-Kook

Subjects
PERMANENT magnets, MAGNETIC anisotropy, CURIE temperature, PHASE transitions, COPPER surfaces, DENSITY functional theory, MANGANESE, MAGNETOCALORIC effects
Abstract

Rare-earth free, ferromagnetic MnBi shows a positive temperature coefficient of coercivity from room temperature to 400 K and energy product (BH)max of 17.7 MGOe at 300 K. However, MnBi undergoes a first-order structural phase transformation from a ferromagnetic low-temperature phase (LTP) to a paramagnetic high-temperature phase at 613 K below the Curie temperature (Tc) of 716 K. The transformation is attributed to Mn diffusion into the interstitial site of LTP MnBi unit cell. Interstitial Mn antiferromagnetically couples with the Mn at lattice 2a site, lowering the magnetization. Cu-occupied bipyramidal sites are investigated as a possible means to suppress Mn diffusion into the bipyramidal sites using first-principles calculations based on the density functional theory. Saturation magnetization, magnetocrystalline anisotropy constant (K), and Tc of (Mn0.5Bi0.5)100−xCux (x = 0–33) are reported. The magnetocrystalline anisotropy changes to the out-of-plane direction (x = 13) from the in-plane direction (x = 0.0). Tc decreases gradually to 578 K at x = 33 from 716 K at x = 0.0. The calculations show a slightly lower (BH)max of 15.6 MGOe while it is expected that Cu-occupied interstitial sites will significantly suppress Mn diffusion and raise the temperature of the phase transformation. [ABSTRACT FROM AUTHOR]

Published
2021
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