3,425 research outputs found
The effect of proton disorder on the structure of ice-Ih: A theoretical study
No full textA precise and accurate measurement of the crystal structure of ice-Ih is hindered by its disordered H-bond network. In this work, we carried out first-principle calculations to study the effects of H-bond topology on the structure of ice-Ih with emphasis on the molecular geometry of water and the distortion in oxygen lattice. An analytic algorithm based on group and graph theory is employed to enumerate all possible configurations in a given unit cell and to select a set of structures for detailed examinations. In total we have studied more than 60 ice-Ih structures in a hexagonal unit cell of 48 water molecules by quantum-chemical methods and found a significant amount of static distortion in the oxygen positions from their crystallographic positions which is in good agreements with highly significant higher-order terms obtained from both x-ray and neutron-diffraction data. Much debated structural information such as H-O-H angle and O-H bond length is found to be 106.34 +/- 0.36 degrees and 0.9997 +/- 0.0008 A, compared to experimental value of 106.6 +/- 1.5 degrees and 0.986 +/- 0.005 A. Detailed benchmarking calculations were carried out to gauge the influence of using different exchange and correlation functionals, pseudopotentials, and unit-cell sizes. Our results have proven that first-principle methods are useful complementary tools to experiments, especially for cases in which experimental accuracy is limited by intrinsic orientational disorder. (c) 2005 American Institute of Physics
Involvement of HIF-1α-dependent PAI-1 up-regulation in Cyr61/CCN1 induced gastric cancer cell invasion.
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The role of the VEGF-C/VEGFR-3 axis in cancer progression
No full text[[abstract]]Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR-3) (also called VEGFR-3) is activated by its specific ligand, VEGF-C, which promotes cancer progression. The VEGF-C/VEGFR-3 axis is expressed not only by lymphatic endothelial cells but also by a variety of human tumour cells. Activation of the VEGF-C/VEGFR-3 axis in lymphatic endothelial cells can facilitate metastasis by increasing the formation of lymphatic vessels (lymphangiogenesis) within and around tumours. The VEGF-C/VEGFR-3 axis plays a critical role in leukaemic cell proliferation, survival, and resistance to chemotherapy. Moreover, activation of the VEGF-C/VEGFR-3 axis in several types of solid tumours enhances cancer cell mobility and invasion capabilities, promoting cancer cell metastasis. In this review, we discuss the novel function and molecular mechanism of the VEGF-C/VEGFR-3 axis in cancer progression
Anti-HIV tigliane diterpenoids from Reutealis trisperma
No full textLu, Yan, Huang, Ya-Si, Chen, Chin-Ho, Akiyama, Toshiyuki, Morris-Natschke, Susan L., Cheng, Yung-Yi, Chen, Ih-Sheng, Yang, Sheng-Zehn, Chen, Dao-Feng, Lee, Kuo-Hsiung (2020): Anti-HIV tigliane diterpenoids from Reutealis trisperma. Phytochemistry (112360) 174: 1-6, DOI: 10.1016/j.phytochem.2020.112360, URL: http://dx.doi.org/10.1016/j.phytochem.2020.11236
Fig. 2. Key 2D in Anti-HIV tigliane diterpenoids from Reutealis trisperma
No full textFig. 2. Key 2D-NMR correlations of 1–3.Published as part of Lu, Yan, Huang, Ya-Si, Chen, Chin-Ho, Akiyama, Toshiyuki, Morris-Natschke, Susan L., Cheng, Yung-Yi, Chen, Ih-Sheng, Yang, Sheng-Zehn, Chen, Dao-Feng & Lee, Kuo-Hsiung, 2020, Anti-HIV tigliane diterpenoids from Reutealis trisperma, pp. 1-6 in Phytochemistry (112360) 174 on page 2, DOI: 10.1016/j.phytochem.2020.112360, http://zenodo.org/record/829473
Fig. 3. Key 2D in Anti-HIV tigliane diterpenoids from Reutealis trisperma
No full textFig. 3. Key 2D-NMR correlations of 4.Published as part of Lu, Yan, Huang, Ya-Si, Chen, Chin-Ho, Akiyama, Toshiyuki, Morris-Natschke, Susan L., Cheng, Yung-Yi, Chen, Ih-Sheng, Yang, Sheng-Zehn, Chen, Dao-Feng & Lee, Kuo-Hsiung, 2020, Anti-HIV tigliane diterpenoids from Reutealis trisperma, pp. 1-6 in Phytochemistry (112360) 174 on page 3, DOI: 10.1016/j.phytochem.2020.112360, http://zenodo.org/record/829473
Hydrogen bond topology and the ice VII/VIII and Ih/XI proton ordering phase transitions
Full text linkIce Ih, ordinary ice at atmospheric pressure, is a proton-disordered crystal that when cooled under special conditions is believed to transform to ferroelectric proton-ordered ice XI, but this transformation is still subject to controversy. Ice VII, also proton disordered throughout its region of stability, transforms to proton-ordered ice VIII upon cooling. In contrast to the ice Ih/XI transition, the VII/VIII transition and the crystal structure of ice VIII are well characterized. In order to shed some light on the ice Ih proton ordering transition, we present the results of periodic electronic density functional theory calculations and statistical simulations. We are able to describe the small energy differences among the innumerable H-bond configurations possible in a large simulation cell by using an analytic theory to extrapolate from electronic DFT calculations on small unit cells to cells large enough to approximate the thermodynamic limit. We first validate our methods by comparing our predictions to the well-characterized ice VII/VIII proton ordering transition, finding agreement with respect to both the transition temperature and structure of the low-temperature phase. For ice Ih, our results indicate that a proton-ordered phase is attainable at low temperatures, the structure of which is in agreement with the experimentally proposed ferroelectric Cmc2_1 structure. The predicted transition temperature of 98 K is in qualitative agreement with the observed transition at 72 K on KOH-doped ice samples
Analysis of Plasmodium falciparum diversity in natural infections by deep sequencing.
Full text linkMalaria elimination strategies require surveillance of the parasite population for genetic changes that demand a public health response, such as new forms of drug resistance. Here we describe methods for the large-scale analysis of genetic variation in Plasmodium falciparum by deep sequencing of parasite DNA obtained from the blood of patients with malaria, either directly or after short-term culture. Analysis of 86,158 exonic single nucleotide polymorphisms that passed genotyping quality control in 227 samples from Africa, Asia and Oceania provides genome-wide estimates of allele frequency distribution, population structure and linkage disequilibrium. By comparing the genetic diversity of individual infections with that of the local parasite population, we derive a metric of within-host diversity that is related to the level of inbreeding in the population. An open-access web application has been established for the exploration of regional differences in allele frequency and of highly differentiated loci in the P. falciparum genome
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