86 research outputs found
Experimental and computational study of conductivity of multilayer graphene in polypropylene nanocomposites
[EN] We study the electric conductivity of compounds formed by multilayer graphene in polypropylene. Our study makes a comparative analysis between the experimental and computational results. To obtain an experimental measurement of the electronic properties, we deposited multilayer graphene (MLG) nanoparticles over a polypropylene matrix. The deposition was made over several stages, in which we added to the polymer matrix different percentages of MLG nanoparticles using the melt compounding technique, and we studied the conductivities of the nanocomposites by means of electrochemical impedance spectroscopy (EIS). The second part consists of computational calculations, in which we studied the electronic properties of a graphene sheet under a polypropylene molecule with different slabs in the monomer. In both analyses, there is a strong percolation phenomenon with a percolation threshold of around 18% of the MLG nanoparticles. Before the percolation threshold, the charge carriers are constrained in the polypropylene molecule, making the system an insulating material and creating p-type doping. After the percolation threshold, the charge carriers are constrained in the graphene, making the system a conductor material and creating n-type doping with conductivity values of around 20 S m(-1). This phenomenon is a consequence of a change in the mechanism of charge transfer in the interface between the polypropylene molecule and graphene sheet. To describe the charge transfer mechanism, it is necessary to consider the quantum effect. The incorporation of the quantum effects and the percolation phenomenon make it possible for the theoretical conductivity to be close to the conductivity measured experimentally.This research has been supported by the ENE/2015-69203-R project, granted by the Ministerio de Economia y Competitividad (MINECO), Spain. Also, the authors are grateful to UNAM-DGAPA-PAPIIT projects IG 100618 y IG 114818, DGTIC-UNAM for access to the Miztli-UNAM supercomputer LANCAD-UNAM-DGTIC-055, and UNAM-DGAPA for the Postdoctoral grant for Roxana M. del Castillo.Del Castillo, RM.; Del Castillo, LF.; Calles, AG.; CompaƱ Moreno, V. (2018). Experimental and computational study of conductivity of multilayer graphene in polypropylene nanocomposites. Journal of Materials Chemistry C. 6:7232-7241. https://doi.org/10.1039/c8tc01135dS723272416H. G. Karian , Handbook of polypropylene and polypropylene composites , RheTec, Inc. , Whitmore Lake, Michigan , 2nd edn, 2003 , https://books.google.es/books?hl=es&lr=&id=C0nzeNPUpoIC&oi=fnd&pg=PP1&dq=Handbook+of+polypropylene+and+polypropylene+composites&ots=LYqYBYg45n&sig=3gtYXigr8_O8CUJeefBCtGI7QXA#v=onepage&q=Handbook%20of%20polypropylene%20and%20polypropylene%20composites&f=falseRath, T., & Li, Y. (2011). Nanocomposites based on polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene and exfoliated graphite nanoplates: Effect of nanoplatelet loading on morphology and mechanical properties. Composites Part A: Applied Science and Manufacturing, 42(12), 1995-2002. doi:10.1016/j.compositesa.2011.09.002Kim, M.-S., Yan, J., Kang, K.-M., Joo, K.-H., Kang, Y.-J., & Ahn, S.-H. (2013). Soundproofing ability and mechanical properties of polypropylene/exfoliated graphite nanoplatelet/carbon nanotube (PP/xGnP/CNT) composite. International Journal of Precision Engineering and Manufacturing, 14(6), 1087-1092. doi:10.1007/s12541-013-0146-3Zhang, K., Yu, H.-O., Shi, Y.-D., Chen, Y.-F., Zeng, J.-B., Guo, J., ā¦ Wang, M. (2017). Morphological regulation improved electrical conductivity and electromagnetic interference shielding in poly(l-lactide)/poly(Īµ-caprolactone)/carbon nanotube nanocomposites via constructing stereocomplex crystallites. Journal of Materials Chemistry C, 5(11), 2807-2817. doi:10.1039/c7tc00389gMohd Radzuan, N. A., Yusuf Zakaria, M., Sulong, A. B., & Sahari, J. (2017). The effect of milled carbon fibre filler on electrical conductivity in highly conductive polymer composites. Composites Part B: Engineering, 110, 153-160. doi:10.1016/j.compositesb.2016.11.021Li, Q., Yao, F.-Z., Liu, Y., Zhang, G., Wang, H., & Wang, Q. (2018). High-Temperature Dielectric Materials for Electrical Energy Storage. Annual Review of Materials Research, 48(1), 219-243. doi:10.1146/annurev-matsci-070317-124435Qiao, Y., Yin, X., Zhu, T., Li, H., & Tang, C. (2018). Dielectric polymers with novel chemistry, compositions and architectures. Progress in Polymer Science, 80, 153-162. doi:10.1016/j.progpolymsci.2018.01.003Rosehr, A., & Luinstra, G. A. (2017). Polypropylene composites with finely dispersed multi-walled carbon nanotubes covered with an aluminum oxide shell. Polymer, 120, 164-175. doi:10.1016/j.polymer.2017.05.045Bolotin, K. I., Sikes, K. J., Jiang, Z., Klima, M., Fudenberg, G., Hone, J., ā¦ Stormer, H. L. (2008). Ultrahigh electron mobility in suspended graphene. Solid State Communications, 146(9-10), 351-355. doi:10.1016/j.ssc.2008.02.024Banszerus, L., Schmitz, M., Engels, S., Goldsche, M., Watanabe, K., Taniguchi, T., ā¦ Stampfer, C. (2016). Ballistic Transport Exceeding 28 Ī¼m in CVD Grown Graphene. Nano Letters, 16(2), 1387-1391. doi:10.1021/acs.nanolett.5b04840TerrĆ©s, B., Chizhova, L. A., Libisch, F., Peiro, J., Jƶrger, D., Engels, S., ā¦ Stampfer, C. (2016). Size quantization of Dirac fermions in graphene constrictions. Nature Communications, 7(1). doi:10.1038/ncomms11528Zhang, H.-B., Zheng, W.-G., Yan, Q., Yang, Y., Wang, J.-W., Lu, Z.-H., ā¦ Yu, Z.-Z. (2010). Electrically conductive polyethylene terephthalate/graphene nanocomposites prepared by melt compounding. Polymer, 51(5), 1191-1196. doi:10.1016/j.polymer.2010.01.027Chung, D. D. L. (2015). A review of exfoliated graphite. Journal of Materials Science, 51(1), 554-568. doi:10.1007/s10853-015-9284-6T. Bayerl , A.Benedito , A.Gallegos , G. B.Mitschang and B.Galindo , Melting of Polymer-Polymer Composites by Particulate Heating Promoters and Electromagnetic Radiation , in Synthetic Polymer-Polymer Composites , ed. D. Bhattacharyya and S. Fakirov , Carl HanserVerlag GmbH & Co. KG , 2012 , ch. 24, pp. 39ā64 10.3139/9781569905258.002Harper, J., Price, D., & Zhang, J. (2005). Use of Fillers to Enable the Microwave Processing of Polyethylene. Journal of Microwave Power and Electromagnetic Energy, 40(4), 219-227. doi:10.1080/08327823.2005.11688543Galindo, B., Benedito, A., Gimenez, E., & CompaƱ, V. (2016). Comparative study between the microwave heating efficiency of carbon nanotubes versus multilayer graphene in polypropylene nanocomposites. Composites Part B: Engineering, 98, 330-338. doi:10.1016/j.compositesb.2016.04.082Asadi, K., Kronemeijer, A. J., Cramer, T., Jan Anton Koster, L., Blom, P. W. M., & de Leeuw, D. M. (2013). Polaron hopping mediated by nuclear tunnelling in semiconducting polymers at high carrier density. Nature Communications, 4(1). doi:10.1038/ncomms2708Fan, Z., Gong, F., Nguyen, S. T., & Duong, H. M. (2015). Advanced multifunctional graphene aerogel ā Poly (methyl methacrylate) composites: Experiments and modeling. Carbon, 81, 396-404. doi:10.1016/j.carbon.2014.09.072Zabihi, Z., & Araghi, H. (2016). Monte Carlo simulations of effective electrical conductivity of graphene/poly(methyl methacrylate) nanocomposite: Landauer-Buttiker approach. Synthetic Metals, 217, 87-93. doi:10.1016/j.synthmet.2016.03.024Xia, X., Zhong, Z., & Weng, G. J. (2017). MaxwellāWagnerāSillars mechanism in the frequency dependence of electrical conductivity and dielectric permittivity of graphene-polymer nanocomposites. Mechanics of Materials, 109, 42-50. doi:10.1016/j.mechmat.2017.03.014F. M. Bickelhaupt and E. J.Baerends , KohnāSham Density Functional Theory: Predicting and Understanding Chemistry . in Reviews in Computational Chemistry , 2007 , ed. K. B. Lipkowitz and B. Boyd Donald , John Wiley & Sons, Inc. , vol. 15, pp. 1ā89 10.1002/9780470125922.ch1/summaryPerdew, J. P., Burke, K., & Ernzerhof, M. (1996). Generalized Gradient Approximation Made Simple. Physical Review Letters, 77(18), 3865-3868. doi:10.1103/physrevlett.77.3865Methfessel, M., & Paxton, A. T. (1989). High-precision sampling for Brillouin-zone integration in metals. Physical Review B, 40(6), 3616-3621. doi:10.1103/physrevb.40.3616Monkhorst, H. J., & Pack, J. D. (1976). Special points for Brillouin-zone integrations. Physical Review B, 13(12), 5188-5192. doi:10.1103/physrevb.13.5188Files: C.pbe-van_ak.UPF, H.pbe-van_ak.UPF, N.pbe-van_ak.UPF, and O.pbe-van_ak.UPF, http://www.quantum-espresso.orgVanderbilt, D. (1990). Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Physical Review B, 41(11), 7892-7895. doi:10.1103/physrevb.41.7892SĆørensen, T. S., & CompaƱ, V. (1995). Complex permittivity of a conducting, dielectric layer containing arbitrary binary NernstāPlanck electrolytes with applications to polymer films and cellulose acetate membranes. J. Chem. Soc., Faraday Trans., 91(23), 4235-4250. doi:10.1039/ft9959104235DrĆ¼schler, M., Huber, B., & Roling, B. (2011). On Capacitive Processes at the Interface between 1-Ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate and Au(111). The Journal of Physical Chemistry C, 115(14), 6802-6808. doi:10.1021/jp200395jSerghei, A., Tress, M., Sangoro, J. R., & Kremer, F. (2009). Electrode polarization and charge transport at solid interfaces. Physical Review B, 80(18). doi:10.1103/physrevb.80.184301F. Kremer and A.Schoenhals , Broadban Dielectric Spectroscopy , Springer , Berlin , 2003Coelho, R. (1983). Sur la relaxation dāune charge dāespace. Revue de Physique AppliquĆ©e, 18(3), 137-146. doi:10.1051/rphysap:01983001803013700Macdonald, J. R. (1953). Theory of ac Space-Charge Polarization Effects in Photoconductors, Semiconductors, and Electrolytes. Physical Review, 92(1), 4-17. doi:10.1103/physrev.92.4Klein, R. J., Zhang, S., Dou, S., Jones, B. H., Colby, R. H., & Runt, J. (2006). Modeling electrode polarization in dielectric spectroscopy: Ion mobility and mobile ion concentration of single-ion polymer electrolytes. The Journal of Chemical Physics, 124(14), 144903. doi:10.1063/1.2186638Greenhoe, B. M., Hassan, M. K., Wiggins, J. S., & Mauritz, K. A. (2016). Universal power law behavior of the AC conductivity versus frequency of agglomerate morphologies in conductive carbon nanotube-reinforced epoxy networks. Journal of Polymer Science Part B: Polymer Physics, 54(19), 1918-1923. doi:10.1002/polb.24121Novoselov, K. S. (2004). Electric Field Effect in Atomically Thin Carbon Films. Science, 306(5696), 666-669. doi:10.1126/science.1102896Del Castillo, R. M., & Sansores, L. E. (2015). Study of the electronic structure of Ag, Au, Pt and Pd clusters adsorption on graphene and their effect on conductivity. The European Physical Journal B, 88(10). doi:10.1140/epjb/e2015-60001-2Galpaya, D., Wang, M., Liu, M., Motta, N., Waclawik, E., & Yan, C. (2012). Recent Advances in Fabrication and Characterization of Graphene-Polymer Nanocomposites. Graphene, 01(02), 30-49. doi:10.4236/graphene.2012.12005I. Zvyagin . Charge Transport via Delocalized States in Disordered Materials . in Charge Transport in Disordered Solids with Applications in Electronics , ed. S. Baranovsky , John Wiley & Sons, Inc. , 2006 , pp. 1ā48 10.1002/0470095067.ch1/summaryLeenaerts, O., Partoens, B., & Peeters, F. M. (2009). Adsorption of small molecules on graphene. Microelectronics Journal, 40(4-5), 860-862. doi:10.1016/j.mejo.2008.11.022Hashemi, R., & Weng, G. J. (2016). A theoretical treatment of graphene nanocomposites with percolation threshold, tunneling-assisted conductivity and microcapacitor effect in AC and DC electrical settings. Carbon, 96, 474-490. doi:10.1016/j.carbon.2015.09.103Xia, X., Wang, Y., Zhong, Z., & Weng, G. J. (2017). A frequency-dependent theory of electrical conductivity and dielectric permittivity for graphene-polymer nanocomposites. Carbon, 111, 221-230. doi:10.1016/j.carbon.2016.09.078The determination of the elastic field of an ellipsoidal inclusion, and related problems. (1957). Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 241(1226), 376-396. doi:10.1098/rspa.1957.0133Trotta, S., Marmo, F., & Rosati, L. (2017). Evaluation of the Eshelby tensor for polygonal inclusions. Composites Part B: Engineering, 115, 170-181. doi:10.1016/j.compositesb.2016.10.018L. D. Landau , E. M.Lifshitz and L. P.Pitaevskii , Electrodynamics of Continuous Media , Pergamon Press , New York , 3rd edn, 1984Wang, Y., Weng, G. J., Meguid, S. A., & Hamouda, A. M. (2014). A continuum model with a percolation threshold and tunneling-assisted interfacial conductivity for carbon nanotube-based nanocomposites. Journal of Applied Physics, 115(19), 193706. doi:10.1063/1.4878195Wang, Y., Shan, J. W., & Weng, G. J. (2015). Percolation threshold and electrical conductivity of graphene-based nanocomposites with filler agglomeration and interfacial tunneling. Journal of Applied Physics, 118(6), 065101. doi:10.1063/1.4928293Wehling, T. O., Yuan, S., Lichtenstein, A. I., Geim, A. K., & Katsnelson, M. I. (2010). Resonant Scattering by Realistic Impurities in Graphene. Physical Review Letters, 105(5). doi:10.1103/physrevlett.105.056802Stauber, T., Peres, N. M. R., & Guinea, F. (2007). Electronic transport in graphene: A semiclassical approach including midgap states. Physical Review B, 76(20). doi:10.1103/physrevb.76.205423R. M. Del Castillo and L. E.Sansores . Adsorption of Metal Clusters on Graphene and Their Effect on the Electrical Conductivity , in Graphene Materials ā Advanced Applications , ed. G. Z. Kyzas and A. C. Mitropoulos , INTECH , 2017 , https://www.intechopen.com/books/graphene-materials-advanced-applications/adsorption-of-metal-clusters-on-graphene-and-their-effect-on-the-electrical-conductivit
Inclusive Educational Review of Software Architectural Styles and Patterns for the Students of the College of Information and Computing Sciences of Cagayan State University
A good architectural design has a high contribution to the success of a system. In addition, this
architectural design is useful for the Information Technology (IT) students as their basis of their
software development of their capstone project. The utilization of inappropriate architecture can lead
to disastrous consequences for IT student researchers. A detailed understanding of software
architecture styles is very useful to analyze distributed and complex systems which is the trend of
capstone projects. This paper explores the quality attributes of three architecture styles namely
shared-nothing, broker, and representational state transfer, which are perceived as beneficial to
distributed system architecture that serve as guide to student researchers. This is to provide a picture
of the said three key software architecture styles which could be helpful not only for student
researchers but also for the software developers by adding references to minimize the uncertainty
while selecting the appropriate architectural style for their specific needs. An architectural style must
be chosen correctly to obtain all its benefits in the system. In this paper, the three architectural styles
are compared on the foundation of various quality attributes derived from ISO 9126-1 standard such
as functionality, reliability, usability, efficiency, maintainability, and portability. The results of the
study are useful to guide the student researchers in their capstone project and to reduce the number
of unsuccessful attempts of software development component of their capstone project
Generation of Glucose-Responsive Functional Islets with a Three-Dimensional Structure from Mouse Fetal Pancreatic Cells and iPS Cells In Vitro
Islets of Langerhans are a pancreatic endocrine compartment consisting of insulin-producing Ī² cells together with several other hormone-producing cells. While some insulin-producing cells or immature pancreatic cells have been generated in vitro from ES and iPS cells, islets with proper functions and a three-dimensional (3D) structure have never been successfully produced. To test whether islets can be formed in vitro, we first examined the potential of mouse fetal pancreatic cells. We found that E16.5 pancreatic cells, just before forming islets, were able to develop cell aggregates consisting of Ī² cells surrounded by glucagon-producing Ī± cells, a structure similar to murine adult islets. Moreover, the transplantation of these cells improved blood glucose levels in hyperglycemic mice. These results indicate that functional islets are formed in vitro from fetal pancreatic cells at a specific developmental stage. By adopting these culture conditions to the differentiation of mouse iPS cells, we developed a two-step system to generate islets, i.e. immature pancreatic cells were first produced from iPS cells, and then transferred to culture conditions that allowed the formation of islets from fetal pancreatic cells. The islets exhibited distinct 3D structural features similar to adult pancreatic islets and secreted insulin in response to glucose concentrations. Transplantation of the islets improved blood glucose levels in hyperglycemic mice. In conclusion, the two-step culture system allows the generation of functional islets with a 3D structure from iPS cells
Potential Pathways to Restore Ī²-Cell Mass: Pluripotent Stem Cells, Reprogramming, and Endogenous Regeneration
Currently available Ī²-cell replacement therapies for patients with diabetes, including islet and pancreas transplantation, are largely successful in restoring normal glucose metabolism, but the scarcity of organ donors restricts their more widespread use. To solve this supply problem, several different strategies for achieving Ī²-cell mass restoration are being pursued. These include the generation of Ī² cells from stem cells and their subsequent transplantation, or regeneration-type approaches, such as stimulating endogenous regenerative mechanisms or inducing reprogramming of non-Ī² cells into Ī² cells. Because these strategies would ultimately generate allogeneic or syngeneic Ī² cells in humans, the control of alloimmunity and/or autoimmunity in addition to replacing lost Ī² cells will be of utmost importance. We briefly review the recent literature on these three promising strategies toward Ī²-cell replacement or restoration and point out the major issues impacting their translation to treating human diabetes
Enhanced self-renewal of hematopoietic stem/progenitor cells mediated by the stem cell gene Sall4
<p>Abstract</p> <p>Background</p> <p>Sall4 is a key factor for the maintenance of pluripotency and self-renewal of embryonic stem cells (ESCs). Our previous studies have shown that Sall4 is a robust stimulator for human hematopoietic stem and progenitor cell (HSC/HPC) expansion. The purpose of the current study is to further evaluate how Sall4 may affect HSC/HPC activities in a murine system.</p> <p>Methods</p> <p>Lentiviral vectors expressing Sall4A or Sall4B isoform were used to transduce mouse bone marrow Lin-/Sca1+/c-Kit+ (LSK) cells and HSC/HPC self-renewal and differentiation were evaluated.</p> <p>Results</p> <p>Forced expression of Sall4 isoforms led to sustained <it>ex vivo </it>proliferation of LSK cells. In addition, Sall4 expanded HSC/HPCs exhibited increased <it>in vivo </it>repopulating abilities after bone marrow transplantation. These activities were associated with dramatic upregulation of multiple HSC/HPC regulatory genes including HoxB4, Notch1, Bmi1, Runx1, Meis1 and Nf-ya. Consistently, downregulation of endogenous Sall4 expression led to reduced LSK cell proliferation and accelerated cell differentiation. Moreover, in myeloid progenitor cells (32D), overexpression of Sall4 isoforms inhibited granulocytic differentiation and permitted expansion of undifferentiated cells with defined cytokines, consistent with the known functions of Sall4 in the ES cell system.</p> <p>Conclusion</p> <p>Sall4 is a potent regulator for HSC/HPC self-renewal, likely by increasing self-renewal activity and inhibiting differentiation. Our work provides further support that Sall4 manipulation may be a new model for expanding clinically transplantable stem cells.</p
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Reducing nutrients, organic micropollutants, antibiotic resistance, and toxicity in rural wastewater effluent with subsurface filtration treatment technology
The ability of a sub-surface treatment filtration system to remove nutrients, thirty-nine organic contaminants, metals, and antibiotic resistant gene (ARG)-bearing organisms, and to attenuate acute toxicity of wastewater lagoon effluents, was assessed. Significant removal was observed for nutrients between the conventional primary and secondary sewage lagoons, with further average attenuation of 59% and 50% of ammonia and total phosphorus (TP), respectively, within the filter. Effluent concentrations of ammonia ranged from 0.4 to 2.6mg/L and concentrations of TP from 1 to 4.1mg/L, with decreasing acute toxicity from primary to secondary lagoons, and no toxicity observed in the filtration system based on MicrotoxĀ® assays. Most organic micropollutants were also efficiently removed between the primary and secondary lagoons (e.g., up to 98% for atenolol). However, in general, little attenuation occurred within the filter for estrogenic compounds (e.g., 17Ī±-ethinylestradiol); Ī²-blockers (e.g., metoprolol); antidepressants (e.g., fluoxetine-Prozac); antibacterial agents (e.g., triclosan), non-steroidal anti-inflammatory drugs (e.g., diclofenac); lipid regulators (e.g., clofibric acid); and macrolide (e.g., clarithromycin) and sulfonamide (e.g., sulfamethazine) antibiotics; or metals (Cr, Cu, Fe, Mn, Ni, and Zn). This lack of removal was likely due to a minimal hydraulic residence time within the filter (~6h) under current operating conditions. The lagoon treatment system effectively removed ~99% of sulfonamide resistant bacteria, but the filter both reduced tetracycline-resistant bacteria (~58%) in wastewater and harbored them in the biofilms, as relative abundances of sul and tet genes were greatest there. The filter also harbored nitrifying and denitrifying bacteria, respectively, contributing to N removal. These results suggest that the constructed sub-surface treatment filtration system can provide a low-cost, low-maintenance, and effective means to reduce nutrient loading and improve microbial community structure and function
Ectopic PDX-1 Expression Directly Reprograms Human Keratinocytes along Pancreatic Insulin-Producing Cells Fate
BACKGROUND: Cellular differentiation and lineage commitment have previously been considered irreversible processes. However, recent studies have indicated that differentiated adult cells can be reprogrammed to pluripotency and, in some cases, directly into alternate committed lineages. However, although pluripotent cells can be induced in numerous somatic cell sources, it was thought that inducing alternate committed lineages is primarily only possible in cells of developmentally related tissues. Here, we challenge this view and analyze whether direct adult cell reprogramming to alternate committed lineages can cross the boundaries of distinct developmental germ layers. METHODOLOGY/PRINCIPAL FINDINGS: We ectopically expressed non-integrating pancreatic differentiation factors in ectoderm-derived human keratinocytes to determine whether these factors could directly induce endoderm-derived pancreatic lineage and Ī²-cell-like function. We found that PDX-1 and to a lesser extent other pancreatic transcription factors, could rapidly and specifically activate pancreatic lineage and Ī²-cell-like functional characteristics in ectoderm-derived human keratinocytes. Human keratinocytes transdifferentiated along the Ī² cell lineage produced processed and secreted insulin in response to elevated glucose concentrations. Using irreversible lineage tracing for KRT-5 promoter activity, we present supporting evidence that insulin-positive cells induced by ectopic PDX-1 expression are generated in ectoderm derived keratinocytes. CONCLUSIONS/SIGNIFICANCE: These findings constitute the first demonstration of human ectoderm cells to endoderm derived pancreatic cells transdifferentiation. The study represents a proof of concept which suggests that transcription factors induced reprogramming is wider and more general developmental process than initially considered. These results expanded the arsenal of adult cells that can be used as a cell source for generating functional endocrine pancreatic cells. Directly reprogramming somatic cells into alternate desired tissues has important implications in developing patient-specific, regenerative medicine approaches
Analysis of nucleoside-binding proteins by ligand-specific elution from dye resin: application to Mycobacterium tuberculosis aldehyde dehydrogenases
We show that Cibacron Blue F3GA dye resin chromatography can be used to identify ligands that specifically interact with proteins from Mycobacterium tuberculosis, and that the identification of these ligands can facilitate structure determination by enhancing the quality of crystals. Four native Mtb proteins of the aldehyde dehydrogenase (ALDH) family were previously shown to be specifically eluted from a Cibacron Blue F3GA dye resin with nucleosides. In this study we characterized the nucleoside-binding specificity of one of these ALDH isozymes (recombinant Mtb Rv0223c) and compared these biochemical results with co-crystallization experiments with different Rv0223c-nucleoside pairings. We found that the strongly interacting ligands (NAD and NADH) aided formation of high-quality crystals, permitting solution of the first Mtb ALDH (Rv0223c) structure. Other nucleoside ligands (AMP, FAD, adenosine, GTP and NADP) exhibited weaker binding to Rv0223c, and produced co-crystals diffracting to lower resolution. Difference electron density maps based on crystals of Rv0223c with various nucleoside ligands show most share the binding site where the natural ligand NAD binds. From the high degree of similarity of sequence and structure compared to human mitochondrial ALDH-2 (BLAST Z-scoreĀ =Ā 53.5 and RMSDĀ =Ā 1.5 Ć
), Rv0223c appears to belong to the ALDH-2 class. An altered oligomerization domain in the Rv0223c structure seems to keep this protein as monomer whereas native human ALDH-2 is a multimer
- ā¦