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Shin JS, Choi MY, Longtine MS, Nelson DM. Vitamin D effects on pregnancy and the placenta. Placenta 2010; 31:1027-34. [PMID: 20863562 DOI: 10.1016/j.placenta.2010.08.015] [Citation(s) in RCA: 212] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Revised: 08/18/2010] [Accepted: 08/26/2010] [Indexed: 12/19/2022]
Abstract
Vitamin D is a pleiotropic secosteroid hormone important for health and disease prevention. The actions of vitamin D are mediated by the vitamin D receptor that binds the active form of vitamin D [1,25(OH)(2)D] to induce both transcriptional and non-genomic responses. Vitamin D has well known classical functions in calcium uptake and bone metabolism, but more recent work highlights the importance of the nonclassical actions of vitamin D in a variety of cell types. These actions include modulation of the innate and adaptive immune systems and regulation of cell proliferation. Adequate vitamin D intake is essential for maternal and fetal health during pregnancy, and epidemiological data indicate that many pregnant women have sub-optimal vitamin D levels. Notably, vitamin D deficiency correlates with preeclampsia, gestational diabetes mellitus, and bacterial vaginosis, and an increased risk for C-section delivery. Recent work emphasizes the importance of nonclassical roles of vitamin D in pregnancy and the placenta. The placenta produces and responds to vitamin D where vitamin D functions as a modulator of implantation, cytokine production and the immune response to infection. We describe vitamin D metabolism and the cellular responses to vitamin D, and then summarize the role of vitamin D in placental trophoblast, pregnancy and the fetus.
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127
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Kwon HW, Choi MY. Comment on "Dynamical phase transition of a one-dimensional transport process including death". PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:013101. [PMID: 20866671 DOI: 10.1103/physreve.82.013101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Indexed: 05/29/2023]
Abstract
Motivated by the mycologic situation, Dorosz and collaborators considered a modification of the totally asymmetric exclusion process, including the probabilities of injection and of death. In the case of the backward-ordered sequential dynamics with the death probability larger than the critical value, the average particle density in the stationary state was erroneously reported to equal the injection probability. Correcting the error, we find that the average density is given by the death probability rather than the injection probability.
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128
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Cheong SH, Lee KM, Yang YI, Seo JY, Choi MY, Yoon YC. Blind oral endotracheal intubation of rats using a ventilator to verify correct placement. Lab Anim 2010; 44:278-80. [PMID: 20385651 DOI: 10.1258/la.2010.009118] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Endotracheal intubation in rats is challenging due to difficulties visualizing the epiglottis and vocal cords. No visualization of these structures results in repeated intubation attempts which can cause trauma to the oral cavity and/or oesophagus, and death of the animal due to respiratory failure. Here, we describe a simple blind oral tracheal intubation technique in the rat that decreases the frequency of repeated intubations using an intubation device that comprises a 16 G intravenous catheter and a modified 18 G epidural needle, and a rodent ventilator. The epidural needle is bent in such a way that it curves in conformity with the rat's oral airway in order to direct the catheter into the larynx, and the rodent ventilator is used to verify its correct placement. The first attempt success rate of endotracheal intubation using the blind oral tracheal intubation technique with a rodent ventilator was greater than the first attempt success rate using the blind oral tracheal intubation technique without using a rodent ventilator. Although this method is a simple modification of a previously described method of blind oral endotracheal intubation, our method is easy to learn, inexpensive and does not require specialized equipment.
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Lee C, Kim DW, Kim J, Yang MH, Choi MY, Kim JS. Copper Ion Selective Membrane Electrode Based on Bis(salphenH2) Derivatives. ACTA ACUST UNITED AC 2010. [DOI: 10.1166/sl.2010.1267] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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130
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Kuyanov-Prozument K, Choi MY, Vilesov AF. Spectrum and infrared intensities of OH-stretching bands of water dimers. J Chem Phys 2010; 132:014304. [DOI: 10.1063/1.3276459] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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131
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Park DK, Lee SJ, Lee JH, Choi MY, Han SW. Effect of polymeric stabilizers on the catalytic activity of Pt nanoparticles synthesized by laser ablation. Chem Phys Lett 2010. [DOI: 10.1016/j.cplett.2009.11.031] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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132
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Choi MY, Miller RE. Imidazole dimer and its water complexes formed in superfluid helium nanodroplets: Infrared spectroscopic studies of free OH vibrational stretching modes. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.07.032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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133
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Lee SJ, Choi MY, Miller RE. Vibrational spectroscopy of xanthine in superfluid helium nanodroplets. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.05.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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134
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Ha T, Chung S, Choi MY. 1/t pressure and fermion behaviour of water in two dimensions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:202101. [PMID: 21825506 DOI: 10.1088/0953-8984/21/20/202101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A variety of metal vacuum systems display the celebrated 1/t pressure, namely power-law dependence on time t, with the exponent close to unity, the origin of which has been a long-standing controversy. Here we propose a chemisorption model for water adsorbates, based on the argument for fermion behaviour of water vapour adsorbed on a stainless-steel surface, and obtain analytically the power-law behaviour of pressure, with an exponent of unity. Further, the model predicts that the pressure should depend on the temperature T according to T(3/2), which is indeed confirmed by our experiment. Our results should help elucidate the unique characteristics of the adsorbed water.
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Skvortsov D, Lee SJ, Choi MY, Vilesov AF. Hydrated HCl Clusters, HCl(H2O)1−3, in Helium Nanodroplets: Studies of Free OH Vibrational Stretching Modes. J Phys Chem A 2009; 113:7360-5. [DOI: 10.1021/jp811497c] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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136
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Wee YM, Kim SC, Koo SK, Kim YH, Jung EJ, Choi MY, Park YH, Park KT, Lim DG, Han DJ. Improved islet yields after purification following the novel endogenous trypsin inhibitor and histidine-tryptophan-ketoglutarate treatment in pigs. Transplant Proc 2008; 40:2585-7. [PMID: 18929808 DOI: 10.1016/j.transproceed.2008.08.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
BACKGROUND Adult porcine islet xenotransplantation into humans is greatly diminished by the difficulty to isolate islets because of their fragility. The goal of this study was to improve the efficacy of islet yields using endogenous trypsin inhibitor and histidine-tryptophan-ketoglutarate (HTK) perfusate. METHOD We compared two porcine islet isolation protocols: Eurocollins solution for in situ pancreas perfusion without use of an endogenous trypsin inhibitor versus HTK solution including endogenous trypsin inhibitor for pancreas perfusion. RESULTS Endogenous trypsin inhibitor and HTK strategies significantly improved total islet yield, recovery, and islet index after purification (P < .05), whereas unpurified islet yield did not increase. An average of 228,000 +/- 95,000 islet equivalents (IEQ) (n = 20) purified islets were obtained in the first group compared with 115,000 +/- 56,000 IEQ (n = 18) in the second group. The average islet index was significantly increased in the first group compared with the second group before and after purification: before: 0.28 versus 0.49 versus after: 0.25 versus 0.4 (P < .05). At this time, islet purity, viability, and stimulation index did not show a significant difference between groups. CONCLUSION Our study showed that endogenous trypsin inhibitor and HTK strategies significantly improved purified islet isolation efficacy because of reduction of islet fragility.
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Koo SK, Kim SC, Wee YM, Kim YH, Jung EJ, Choi MY, Park YH, Park KT, Lim DG, Han DJ. Experimental microencapsulation of porcine and rat pancreatic islet cells with air-driven droplet generator and alginate. Transplant Proc 2008; 40:2578-80. [PMID: 18929806 DOI: 10.1016/j.transproceed.2008.08.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Transplantation of microencapsulated islets is proposed as an ideal therapy for the treatment of type 1 diabetes mellitus without immunosuppression. This strategy is based on the principle that foreign cells are protected from the host immune system by an artificial membrane. The aim of this study was to establish an ideal condition of microencapsulation using an air-driven droplet generator and alginate in vitro. The optimal conditions for islet encapsulation were an alginate inflow rate of 10 mL/h, CO2 flow rate of 2.0 L/min in a concentration of 2% alginate. For 2.5% alginate, the alginate inflow rate of 20 mL/h, CO2 flow rate 3.0 L/min was ideal; alginate inflow rate of 40 mL/h, CO2 flow rate of 4.0 L/min showed good microcapsules at 3% alginate. Viability of encapsulated islets was greater than 90%. In terms of insulin secretion, encapsulated islets secreted insulin in response to glucose in static culture medium. However, there was no normal response to low or high glucose challenge with a stimulation index less than 2.0. Microencapsulation of pig islets was successfully performed with air-driven droplet generator and alginate in vitro. Further studies about biocompatibility and glucose control in vivo may provide a useful tool for treatment of patients with diabetes mellitus.
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138
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Choi MY, Dong F, Han SW, Miller RE. Nonplanarity of Adenine: Vibrational Transition Moment Angle Studies in Helium Nanodroplets. J Phys Chem A 2008; 112:7185-90. [DOI: 10.1021/jp8012688] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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139
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Kim J, Kang DM, Shin SC, Choi MY, Kim J, Lee SS, Kim JS. Functional polyterthiophene-appended uranyl-salophen complex: Electropolymerization and ion-selective response for monohydrogen phosphate. Anal Chim Acta 2008; 614:85-92. [DOI: 10.1016/j.aca.2008.03.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2007] [Revised: 02/28/2008] [Accepted: 03/05/2008] [Indexed: 10/22/2022]
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140
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Skvortsov D, Sliter R, Choi MY, Vilesov AF. Interchange-tunneling splitting in HCl dimer in helium nanodroplets. J Chem Phys 2008; 128:094308. [DOI: 10.1063/1.2834925] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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141
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Skvortsov D, Choi MY, Vilesov AF. Study of HCl Clusters in Helium Nanodroplets: Experiments and ab Initio Calculations as Stepping Stones from Gas Phase to Bulk. J Phys Chem A 2007; 111:12711-6. [DOI: 10.1021/jp076123o] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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142
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Cho MW, Choi MY. Equalization of synaptic efficacy by synchronous neural activity. PHYSICAL REVIEW LETTERS 2007; 99:208102. [PMID: 18233189 DOI: 10.1103/physrevlett.99.208102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Indexed: 05/25/2023]
Abstract
It is commonly believed that spike timings of a postsynaptic neuron tend to follow those of the presynaptic neuron. Such orthodromic firing may, however, cause a conflict with the functional integrity of complex neuronal networks due to asymmetric temporal Hebbian plasticity. We argue that reversed spike timing in a synapse is a typical phenomenon in the cortex, which has a stabilizing effect on the neuronal network structure. We further demonstrate how the firing causality in a synapse is perturbed by synchronous neural activity and how the equilibrium property of spike-timing dependent plasticity is determined principally by the degree of synchronization. Remarkably, even noise-induced activity and synchrony of neurons can result in equalization of synaptic efficacy.
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143
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Kim YH, Choi MY, Kim YS, Park CH, Lee JH, Chung IY, Yoo JM, Choi WS, Cho GJ, Kang SS. Triamcinolone acetonide protects the rat retina from STZ-induced acute inflammation and early vascular leakage. Life Sci 2007; 81:1167-73. [PMID: 17881007 DOI: 10.1016/j.lfs.2007.08.024] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 08/08/2007] [Accepted: 08/17/2007] [Indexed: 10/22/2022]
Abstract
Streptozotocin (STZ) has been commonly used to induce in vivo and in vitro hyperglycemic diabetes and its toxicity leads to inflammation and vascular injury. Triamcinolone acetonide (TA), as an anti-angiogenic/anti-inflammatory drug, is clinically used to improve the visual acuity in neovascular and edematous ocular diseases. The aim of this study was to investigate the effect of TA on early inflammation and vascular leakage in the retina of STZ-induced hyperglycemic rats. Hyperglycemia was induced in 8-week-old male Sprague-Dawley (SD) rats by a single intraperitoneal injection of STZ (65 mg/kg); only rats with blood glucose levels >13.9 mmol/l 1 day after STZ injection were included in STZ-hyperglycemic group. Sex- and age-matched SD rats injected with buffer were used as the control group. One day before STZ and buffer injection, 2 microl TA (4 mg/ml in saline) and 2 microl saline were intravitreal-injected into the right and the left eyes of rats, respectively. Retinal vascular leakage was measured using the Evans-blue method. Changes in pro-inflammatory target genes, such as tumor necrotic factor (TNF)-alpha, intracellular adhesion molecule (ICAM)-1, and vascular endothelial growth factor (VEGF) were assessed by immunoblottings, immunostaining, and ELISA analyses. Vascular hyperleakage and up-regulation of most pro-inflammatory genes peaked within a few days after STZ injection and had recovered. However, these changes were blocked by TA pretreatment. Our data suggest that TA controls STZ-induced early vascular leakage and temporary pro-inflammatory signals in the rat retina.
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144
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Kim YH, Choi MY, Kim YS, Han JM, Lee JH, Park CH, Kang SS, Choi WS, Cho GJ. Protein kinase C delta regulates anti-apoptotic alphaB-crystallin in the retina of type 2 diabetes. Neurobiol Dis 2007; 28:293-303. [PMID: 17904375 DOI: 10.1016/j.nbd.2007.07.017] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2007] [Revised: 07/06/2007] [Accepted: 07/17/2007] [Indexed: 12/22/2022] Open
Abstract
We investigated the relationship between phosphorylation of alphaB-crystallin (alphaBC) and retinal apoptosis in type 2 diabetes. The retinas of male Otsuka Long-Evans Tokushima fatty (OLETF) rats at 24 and 35 weeks were used as an animal model for type 2 diabetes and sex- and age-matched Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In the retinas of 35-week OLETF rats, the interaction between alphaBC and protein kinase C delta (PKC delta) among the PKC isozymes, alphaBC phosphorylation at Ser45 (S45p-alphaBC), TUNEL-positive apoptotic ganglion cells, several apoptotic signs, and co-localization of S45p-alphaBC and TUNEL significantly increased as compared with other groups while the alphaBC-Bax interaction greatly decreased. These changes were abolished by rottlerin treatment, a highly specific PKC delta inhibitor. These results suggest that PKC delta is involved in regulation of anti-apoptotic function of alphaBC in the retina of type 2 diabetes.
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145
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Kim S, Yi J, Choi MY. Magnetization of circular DNA. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:012902. [PMID: 17677517 DOI: 10.1103/physreve.76.012902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2006] [Indexed: 05/16/2023]
Abstract
We investigate the orbital magnetization of DNA molecules in the relaxed circular structure. It is shown that DNA of homogeneous sequence exhibits paramagnetic responses to external magnetic fields and, surprisingly, the magnetism of circular DNA is equivalent to that of linear DNA. This turns out to result from the fact that the electron population is localized largely on one of the strands. More intriguingly, the magnetic susceptibility is observed to depend on the ring topology defined by the linking number. We also consider sequence heterogeneity and find that the magnetization displays characteristic oscillations, the pattern of which depends crucially on the sequence and the base content.
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146
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Kim YH, Chung IY, Choi MY, Kim YS, Lee JH, Park CH, Kang SS, Roh GS, Choi WS, Yoo JM, Cho GJ. Triamcinolone suppresses retinal vascular pathology via a potent interruption of proinflammatory signal-regulated activation of VEGF during a relative hypoxia. Neurobiol Dis 2007; 26:569-76. [PMID: 17434742 DOI: 10.1016/j.nbd.2007.02.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2006] [Revised: 01/31/2007] [Accepted: 02/04/2007] [Indexed: 10/23/2022] Open
Abstract
We examined the effect of triamcinolone acetonide (TA), a corticosteroid, on the relationship between vascular pathophysiology and vascular endothelial growth factor (VEGF) activation in the retina of a rat model of oxygen-induced retinopathy (OIR). OIR was induced by exposure of hyperoxia (80% oxygen) to Sprague-Dawley (SD) rats from P2 to P14 and then returned to normoxic conditions. TA was intravitreal-injected once into the right eye of OIR rats at P15. Effects of TA on vascular pathophysiology or changes of various genes in response to hypoxia and/or proinflammation under hypoxic retina were assessed by the Evans-blue method, fluorescein isothiocyanate-dextran (FITC-D) infusion, immunoblotting, and ELIZA. TA not only reduced retinal neovascularization and vascular leakage in the OIR-rat retina, but also blocked the induction of hypoxia-response proinflammatory genes before it negatively controlled VEGF activation. These findings suggest a potential that TA suppresses retinal neovascular pathophysiology via proinflammation-mediated activation of VEGF during hypoxia.
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147
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Choi MY, Miller RE. Infrared Laser Spectroscopy of Uracil and Thymine in Helium Nanodroplets: Vibrational Transition Moment Angle Study. J Phys Chem A 2007; 111:2475-9. [PMID: 17388352 DOI: 10.1021/jp0674625] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Vibrational spectra are reported in the N-H stretching region for uracil and thymine monomers in helium nanodroplets. Each monomer shows only a single isomer, the global minimum, in agreement with previous experimental and theoretical studies. The assignment of the infrared vibrational bands in the spectra is aided by the measurement of the corresponding vibrational transition moment angles (VTMAs) and ab initio frequency calculations. The ambiguity in the VTMA assignment of the N3H band for the uracil monomer is explained by the presence of dimer bands, which are overlapped with the monomer band.
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148
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Jeong D, Choi J, Choi MY. Collective oscillations, bicluster motion, and dynamical order in a system of globally coupled rotors with repulsive interactions. Phys Rev E 2007; 74:056106. [PMID: 17279967 DOI: 10.1103/physreve.74.056106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Revised: 07/02/2006] [Indexed: 11/07/2022]
Abstract
We perform extensive numerical simulations on a system of globally coupled rotors with repulsive interactions. By controlling systematically initial conditions, we determine the criterion for the emergence of bicluster motion. It is found that stable bicluster motion emerges at low temperatures, where the initial kinetic energy accounts for less than about 60% of the total energy. Also observed are collective oscillations of the potential energy and the magnetization, which are persistent. With appropriately chosen initial conditions, the system exhibits characteristic motion where biclusters keep forming and disappearing continually. It is argued that such bicluster motion is closely related to the dynamical order suggested recently.
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149
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Jeong D, Shim Y, Choi MY, Kim HJ. Effects of Solute Electronic Polarizability on Solvation in a Room-Temperature Ionic Liquid. J Phys Chem B 2007; 111:4920-5. [PMID: 17253742 DOI: 10.1021/jp067316z] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of solute polarizability on solvation and solute transport in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF(6)-) are investigated via molecular dynamics simulations. A valence-bond description is employed to account for the instantaneous adjustment of the solute electronic charge distribution to the fluctuating solvent environment. It is found that the ultrafast inertial component of solvation dynamics becomes slower as the solute polarizability grows. Moreover, its contribution to overall solvent relaxation becomes reduced with increasing polarizability, especially in the case of nonequilibrium solvation dynamics. Overall, the inclusion of the solute electronic polarizability in the simulations improves the agreement with time-dependent Stokes shift measurements.
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150
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Shim Y, Jeong D, Choi MY, Kim HJ. Rotational dynamics of a diatomic solute in the room-temperature ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate. J Chem Phys 2006; 125:61102. [PMID: 16942266 DOI: 10.1063/1.2232303] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Reorientational time correlation functions C(l)(t)( identical withP(l)[cos theta(t)]) for a diatomic solute in 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI(+)PF(6) (-)) are analyzed via molecular dynamics computer simulations, where <...> denotes an equilibrium ensemble average, P(l) the lth order Legendre polynomial and theta(t) the angle between the solute orientation at time t and its initial direction. Overall results are indicative of heterogeneous dynamics in EMI(+)PF(6) (-). For a small nondipolar solute, C(l)(t) are well-described as stretched exponential functions in wide time ranges. One striking feature is that after rapid initial relaxation, C(2)(t) decays more slowly than C(1)(t). As a result, the correlation time associated with the former is considerably longer than that with the latter. This is ascribed to solvent structural fluctuations, which allow large-amplitude solute rotations. As the solute size grows, relaxation of C(l)(t) approaches exponential decay.
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