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Zhou HP, Ye X, Huang W, Wu MQ, Mao LN, Yu B, Xu S, Levchenko I, Bazaka K. Wearable, Flexible, Disposable Plasma-Reduced Graphene Oxide Stress Sensors for Monitoring Activities in Austere Environments. ACS Appl Mater Interfaces 2019; 11:15122-15132. [PMID: 30869857 DOI: 10.1021/acsami.8b22673] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In austere environments, for example, in outer space, on surfaces of extra-terrestrial bodies (Moon, Mars, etc.), or under water, technologies that can enable continuous, reliable, and authentic monitoring of movement of human operators and devices can be critical. We report here the production and human body test of wearable, flexible graphene oxide stress sensors suitable for real-time monitoring of body parameters, state and position of humans, and automatic equipment. These sensors have excellent sensitivity and signal strength across a wide strain range, alleviating the need for additional instrumentation for signal processing and amplification. Their low cost makes them virtually disposable, which may benefit such applications as smart clothing. The sensors were fabricated by a concomitant reduction and N-doping of graphene oxide on polydimethylsiloxane in N2-H2 plasma. The direct bias and other plasma parameters have a significant effect on the reduction and properties of graphene oxide sensors, as shown by optical emission, Raman and X-ray photoelectron spectroscopies, and X-ray diffraction. Optical emission showed different excitation and ionization processes involving atomic and molecular species in the N2-H2 discharge. The photoelectron spectroscopy has confirmed the graphene reduction and introduction of nitrogen doping into the reduced graphene oxide. The bias efficiently controls plasma-induced electric fields, and plasma-related effects determine the N-doping levels. The reduced graphene oxides demonstrate excellent tensile properties, which make them suitable for efficient but cheap stress sensors. This eco-friendly, fast, room-temperature method shows a great potential for fabrication of efficient, flexible sensors.
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Affiliation(s)
| | | | | | | | | | - B Yu
- College of Nanoscale Science and Engineering (CNSE) , State University of New York , Albany , New York 12203 , United States
| | - S Xu
- Plasma Sources and Application Center/Space Propulsion Centre Singapore, NIE, and Institute of Advanced Studies , Nanyang Technological University , 637616 , Singapore
| | - I Levchenko
- Plasma Sources and Application Center/Space Propulsion Centre Singapore, NIE, and Institute of Advanced Studies , Nanyang Technological University , 637616 , Singapore
| | - K Bazaka
- Plasma Sources and Application Center/Space Propulsion Centre Singapore, NIE, and Institute of Advanced Studies , Nanyang Technological University , 637616 , Singapore
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Arutyunov S, Krasheninnikov S, Levchenko I, Orjonikidze R, Sadovskaya N, Kirakosyan L, Kharakh Y. MONITORING OF CHANGES IN PHYSICOCHEMICAL AND CLINICAL CHARACTERISTICS OF THE DENTAL POLYMER MATERIALS USED IN ADDITIVE MANUFACTURING OF DENTAL PROSTHESES. Georgian Med News 2018:37-41. [PMID: 30702067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The use of additive technologies in dentistry is a promising trend; however, the physical and mechanical properties of the materials intended for the fabrication of long-term fixed restorations remain understudied. The aim of this research is to determine the feasibility of the use of long-term fixed provisional restorations made of polymer materials, fabricated using 3D printing. The conformance of the physical and mechanical properties of NextDent C&B Micro Filled Hybrid (ND) and Detax Freeprint temp UV (DX) materials to ISO 1567:1999 standard, stability of their physical and mechanical properties under the conditions of accelerated aging, as well as their resistance to the oral cavity environment were studied. As a result of the performed studies, the DX material turned out to be superior to ND with respect to most characteristics. Clinical observations were conducted on the treatment of chronic generalized periodontitis using the following fixed provisional splints made of various materials: DX, fabricated according to the Slide-And-Separate technology, splints fabricated using the CAD/CAM technology, and adhesive splints reinforced with a GlasSpan fiberglass thread. As a result of the analysis of the OHI-S and PI indices values, the absence of any statistically significant difference between the above-describe treatment methods was determined. The studied materials conform to the requirements of ISO 1567:1999; the materials exhibited different stability under the conditions of accelerated aging, nevertheless, they can be utilized for the fabrication of long-term fixed provisional restorations.
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Affiliation(s)
- S Arutyunov
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - S Krasheninnikov
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - I Levchenko
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - R Orjonikidze
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - N Sadovskaya
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - L Kirakosyan
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
| | - Y Kharakh
- Moscow State University of Medicine and Dentistry named after A.I. Evdokimov, Ministry of Healthcare of Russia, Department of propaedeutics of dental diseases; National Research Center "Kurchatov Institute", Laboratory of Polymer Materials; Karpov Institute of Physical Chemistry, Center for Shared Use; Tbilisi State Medical University, Georgia
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3
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Bazaka K, Baranov O, Cvelbar U, Podgornik B, Wang Y, Huang S, Xu L, Lim JWM, Levchenko I, Xu S. Oxygen plasmas: a sharp chisel and handy trowel for nanofabrication. Nanoscale 2018; 10:17494-17511. [PMID: 30226508 DOI: 10.1039/c8nr06502k] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Although extremely chemically reactive, oxygen plasmas feature certain properties that make them attractive not only for material removal via etching and sputtering, but also for driving and sustaining nucleation and growth of various nanostructures in plasma bulk and on plasma-exposed surfaces. In this minireview, a number of representative examples is used to demonstrate key mechanisms and unique capabilities of oxygen plasmas and how these can be used in present-day nano-fabrication. In addition to modification and functionalisation processes typical for oxygen plasmas, their ability to catalyse the growth of complex nanoarchitectures is emphasized. Two types of technologies based on oxygen plasmas, namely surface treatment without a change in the size and shape of surface features, as well as direct growth of oxide structures, are used to better illustrate the capabilities of oxygen plasmas as a powerful process environment. Future applications and possible challenges for the use of oxygen plasmas in nanofabrication are discussed.
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Affiliation(s)
- K Bazaka
- School of Chemistry, Physics, Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia.
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4
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Baranov O, Xu S, Ostrikov K, Wang BB, Cvelbar U, Bazaka K, Levchenko I. Towards universal plasma-enabled platform for the advanced nanofabrication: plasma physics level approach. ACTA ACUST UNITED AC 2018. [DOI: 10.1007/s41614-018-0016-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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5
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Levchenko I, Xu S, Teel G, Mariotti D, Walker MLR, Keidar M. Recent progress and perspectives of space electric propulsion systems based on smart nanomaterials. Nat Commun 2018; 9:879. [PMID: 29491411 PMCID: PMC5830404 DOI: 10.1038/s41467-017-02269-7] [Citation(s) in RCA: 140] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 11/16/2017] [Indexed: 11/23/2022] Open
Abstract
Drastic miniaturization of electronics and ingression of next-generation nanomaterials into space technology have provoked a renaissance in interplanetary flights and near-Earth space exploration using small unmanned satellites and systems. As the next stage, the NASA's 2015 Nanotechnology Roadmap initiative called for new design paradigms that integrate nanotechnology and conceptually new materials to build advanced, deep-space-capable, adaptive spacecraft. This review examines the cutting edge and discusses the opportunities for integration of nanomaterials into the most advanced types of electric propulsion devices that take advantage of their unique features and boost their efficiency and service life. Finally, we propose a concept of an adaptive thruster.
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Affiliation(s)
- I Levchenko
- Plasma Sources and Applications Centre, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616, Singapore.
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology (QUT), Brisbane, QLD, 4000, Australia.
| | - S Xu
- Plasma Sources and Applications Centre, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore, 637616, Singapore
| | - G Teel
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC, 20052, USA
| | - D Mariotti
- Nanotechnology and Integrated Bio-Engineering Centre (NIBEC), Ulster University, Newtownabbey, BT37 0QB, UK
| | - M L R Walker
- School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0150, USA
| | - M Keidar
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC, 20052, USA
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6
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Taba P, Schmutzhard E, Forsberg P, Lutsar I, Ljøstad U, Mygland Å, Levchenko I, Strle F, Steiner I. EAN consensus review on prevention, diagnosis and management of tick‐borne encephalitis. Eur J Neurol 2017; 24:1214-e61. [DOI: 10.1111/ene.13356] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 06/01/2017] [Indexed: 12/30/2022]
Affiliation(s)
- P. Taba
- Department of Neurology and Neurosurgery University of Tartu Tartu Estonia
| | - E. Schmutzhard
- Department of Neurology Medical University Innsbruck Innsbruck Austria
| | - P. Forsberg
- Department of Clinical and Experimental Medicine and Department of Infectious Diseases Linköping University Linköping Sweden
| | - I. Lutsar
- Department of Microbiology University of Tartu Tartu Estonia
| | - U. Ljøstad
- Department of Neurology Sørlandet Hospital Kristiansand Norway
- Department of Clinical Medicine University of Bergen Bergen Norway
| | - Å. Mygland
- Department of Neurology Sørlandet Hospital Kristiansand Norway
- Department of Clinical Medicine University of Bergen Bergen Norway
| | - I. Levchenko
- Institute of Neurology Psychiatry and Narcology of the National Academy of Medical Sciences of Ukraine Kharkiv Ukraine
| | - F. Strle
- Department of Infectious Diseases University Medical Centre Ljubljana Ljubljana Slovenia
| | - I. Steiner
- Department of Neurology Rabin Medical Center Petach Tikva Israel
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7
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Marvi Z, Xu S, Foroutan G, Ostrikov K, Levchenko I. Plasma-deposited hydrogenated amorphous silicon films: multiscale modelling reveals key processes. RSC Adv 2017. [DOI: 10.1039/c7ra00478h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Physical and chemical mechanisms and role of plasma in the synthesis of hydrogenated amorphous silicon were studied numerically to reveal the key growth processes and, hence, to ensure a higher level of control over the film structure and properties.
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Affiliation(s)
- Z. Marvi
- Plasma Sources and Applications Centre
- NIE
- Nanyang Technological University
- 637616 Singapore
- Physics Department
| | - S. Xu
- Plasma Sources and Applications Centre
- NIE
- Nanyang Technological University
- 637616 Singapore
| | - G. Foroutan
- Physics Department
- Faculty of Science
- Sahand University of Technology
- Tabriz
- Iran
| | - K. Ostrikov
- CSIRO-QUT Joint Sustainable Materials and Devices Laboratory
- CSIRO
- Lindfield
- Australia
- School of Chemistry
| | - I. Levchenko
- Plasma Sources and Applications Centre
- NIE
- Nanyang Technological University
- 637616 Singapore
- School of Chemistry
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8
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Wang BB, Gao D, Levchenko I, Ostrikov K, Keidar M, Zhu MK, Zheng K, Gao B. Self-organized graphene-like boron nitride containing nanoflakes on copper by low-temperature N2 + H2 plasma. RSC Adv 2016. [DOI: 10.1039/c6ra17940a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A simple and efficient method for synthesizing complex graphene-inspired BNCO nanoflakes by plasma-enhanced hot filament chemical vapour deposition using B4C as a precursor and N2/H2 reactive gases is reported.
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Affiliation(s)
- B. B. Wang
- College of Chemistry and Chemical Engineering
- Chongqing University of Technology
- Chongqing 400054
- P. R. China
| | - D. Gao
- Institute of Microstructure and Properties of Advanced Materials
- Beijing University of Technology
- Beijing 100124
- P. R. China
| | - I. Levchenko
- School of Chemistry, Physics and Mechanical Engineering
- Queensland University of Technology
- Brisbane
- Australia
| | - K. Ostrikov
- Institute for Future Environments
- School of Chemistry, Physics and Mechanical Engineering
- Queensland University of Technology
- Brisbane
- Australia
| | - M. Keidar
- Mechanical and Aerospace Engineering
- The George Washington University
- Washington DC 20052
- USA
| | - M. K. Zhu
- College of Materials Science and Engineering
- Beijing University of Technology
- Beijing 100124
- P. R. China
| | - K. Zheng
- Institute of Microstructure and Properties of Advanced Materials
- Beijing University of Technology
- Beijing 100124
- P. R. China
| | - B. Gao
- College of Computer Science
- Chongqing University
- Chongqing 400044
- P. R. China
- Chongqing Municipal Education Examinations Authority
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9
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Levchenko I, Mai-Prochnow A, Yick S, Bilek MMM, Kondyurin A, Han ZJ, Fang J, Cvelbar U, Mariotti D, Ostrikov K. Hybrid Carbon-Based Nanostructured Platforms for the Advanced Bioreactors. J Nanosci Nanotechnol 2015; 15:10074-10090. [PMID: 26682454 DOI: 10.1166/jnn.2015.11686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Mankind faces several global challenges such as chronic and acute hunger, global poverty, energy deficiency and environment conservation. Common biotechnologies based on batch, fluidbed and other similar processes are now extensively used for the production of a wide range of products such as antibiotics, biofuels, cultured and fermented food products. Unfortunately, these processes suffer from low efficiency, high energy demand, low controllability and rapid biocatalyst degradation by microbiological attack, and thus still are not capable of seriously addressing the global hunger and energy deficiency challenges. Moreover, sustainable future technologies require minimizing the environmental impact of toxic by-products by implementing the "life produces organic matter, organic matter sustains life" principle. Nanostructure-based biotechnology is one of the most promising approaches that can help to solve these challenges. In this work we briefly review the unique features of the carbon-based nanostructured platforms, with some attention paid to other nanomaterials. We discuss the main building blocks and processes to design and fabricate novel platforms, with a focus on dense arrays of the vertically-aligned nanostructures, mainly carbon nanotubes and graphene. Advantages and disadvantages of these systems are considered.
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10
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Levchenko I, Cvelbar U, Modic M, Filipič G, Zhong XX, Mozetič M, Ostrikov K. Nanoherding: Plasma-Chemical Synthesis and Electric-Charge-Driven Self Organization of SiO2 Nanodots. J Phys Chem Lett 2013; 4:681-686. [PMID: 26281886 DOI: 10.1021/jz400092m] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others.
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Affiliation(s)
- I Levchenko
- ‡CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield, NSW 2070, Australia
- §The University of Sydney, Sydney, NSW 2006, Australia
| | - U Cvelbar
- †Jozef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - M Modic
- †Jozef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - G Filipič
- †Jozef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - X X Zhong
- ∥Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
| | - M Mozetič
- †Jozef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - K Ostrikov
- ‡CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield, NSW 2070, Australia
- §The University of Sydney, Sydney, NSW 2006, Australia
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11
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Yajadda MMA, Farrant DI, Levchenko I, Müller KH, Ostrikov K. Demonstration of nonlinear absorption in Au semi-continuous film by electrical measurement. Opt Express 2011; 19:17167-17172. [PMID: 21935079 DOI: 10.1364/oe.19.017167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have demonstrated the nonlinear absorption at 532 nm wavelength in an Au semi-continuous film (SF) resulting from smearing of the Fermi distribution and diffusion of conduction electrons into the substrate. The Au SF was irradiated by a pulsed laser with 8 ns pulse width at 532 nm in near resonance with the interband transition of the Au. We determined the temperature increase in the SF for different intensities by electrical measurement. We calculated the temperature increase by using a 1D heat transport equation; comparing the results of the calculation with measured values for the temperature increase, revealed the nonlinear absorption in the Au SF. We employed this deviation from linear behaviour to determine the nonlinear absorption coefficient.
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Affiliation(s)
- M M A Yajadda
- School of Physics, The University of Sydney, Sydney, NSW 2006, Australia.
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12
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Han ZJ, Yick S, Levchenko I, Tam E, Yajadda MMA, Kumar S, Martin PJ, Furman S, Ostrikov K. Controlled synthesis of a large fraction of metallic single-walled carbon nanotube and semiconducting carbon nanowire networks. Nanoscale 2011; 3:3214-3220. [PMID: 21701743 DOI: 10.1039/c1nr10327j] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Controlled synthesis of both single-walled carbon nanotube and carbon nanowire networks using the same CVD reactor and Fe/Al(2)O(3) catalyst by slightly altering the hydrogenation and temperature conditions is demonstrated. Structural, bonding and electrical characterization using SEM, TEM, Raman spectroscopy, and temperature-dependent resistivity measurements suggest that the nanotubes are of a high quality and a large fraction (well above the common 33% and possibly up to 75%) of them are metallic. On the other hand, the carbon nanowires are amorphous and semiconducting and feature a controlled sp(2)/sp(3) ratio. The growth mechanism which is based on the catalyst nanoisland analysis by AFM and takes into account the hydrogenation and temperature control effects explains the observed switch-over of the nanostructure growth modes. These results are important to achieve the ultimate control of chirality, structure, and conductivity of one-dimensional all-carbon networks.
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Affiliation(s)
- Z J Han
- Plasma Nanoscience Centre Australia (PNCA), CSIRO Materials Science and Engineering, Lindfield, New South Wales, 2070, Australia
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13
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Volotskova O, Levchenko I, Shashurin A, Raitses Y, Ostrikov K, Keidar M. Single-step synthesis and magnetic separation of graphene and carbon nanotubes in arc discharge plasmas. Nanoscale 2010; 2:2281-5. [PMID: 20714656 DOI: 10.1039/c0nr00416b] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The unique properties of graphene and carbon nanotubes made them the most promising nanomaterials attracting enormous attention, due to the prospects for applications in various nanodevices, from nanoelectronics to sensors and energy conversion devices. Here we report on a novel deterministic, single-step approach to simultaneous production and magnetic separation of graphene flakes and carbon nanotubes in an arc discharge by splitting the high-temperature growth and low-temperature separation zones using a non-uniform magnetic field and tailor-designed catalyst alloy, and depositing nanotubes and graphene in different areas. Our results are very relevant to the development of commercially-viable, single-step production of bulk amounts of high-quality graphene.
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Affiliation(s)
- O Volotskova
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, USA
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14
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Abstract
The formation of arrays of vertically aligned nanotips on a moderately heated (up to 500 degrees C) Si surface exposed to reactive low-temperature radio frequency (RF) Ar+H(2) plasmas is studied. It is demonstrated that the nanotip surface density, aspect ratio and height dispersion strongly depend on the substrate temperature, discharge power, and gas composition. It is shown that nanotips with aspect ratios from 2.0 to 4.0 can only be produced at a higher RF power density (41.7 mW cm(-3)) and a hydrogen content of about 60%, and that larger aspect ratios can be achieved at substrate temperatures of about 300 degrees C. The use of higher (up to 500 degrees C) temperatures leads to a decrease of the aspect ratio but promotes the formation of more uniform arrays with the height dispersion decreasing to 1.5. At lower (approximately 20 mW cm(-3)) RF power density, only semispherical nanodots can be produced. Based on these experimental results, a nanotip formation scenario is proposed suggesting that sputtering, etching, hydrogen termination, and atom/radical re-deposition are the main concurrent mechanisms for the nanostructure formation. Numerical calculations of the ion flux distribution and hydrogen termination profiles can be used to predict the nanotip shapes and are in a good agreement with the experimental results. This approach can be applied to describe the kinetics of low-temperature formation of other nanoscale materials by plasma treatment.
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Affiliation(s)
- I Levchenko
- Plasma Nanoscience Centre Australia (PNCA), CSIRO Materials Science and Engineering, PO Box 218, Lindfield NSW 2070, Australia
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15
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Abstract
The paper presents results of comparative investigation of carbon nanotubes growth processes in dense low-temperature plasma and on substrate surface. Hybrid/Monte-Carlo numerical simulations were used to demonstrate the differences in the ion fluxes, growth rates and kinetics of adsorbed atoms re-distribution on substrate and nanotubes surfaces. We show that the plasma parameters significantly affect the nanotubes growth kinetics. We demonstrate that the growth rates of the nanotubes in plasma and on surface can differ by three orders, and the specific fluxes to the nanotube in the plasma can exceed the flux to surface-grown nanotube by six orders. We also show that the metal catalyst used for the nanotubes production on surface and in arc is a subject to very different conditions and this may be a key factor for the nanotube growth mode. The obtained dependencies for the ion fluxes to the nanotubes and nanotubes growth rates on the plasma parameters may be useful for selection of the production methods.
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Affiliation(s)
- I Levchenko
- School of Physics, The University of Sydney, Sydney NSW 2006, Australia
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16
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Rider AE, Ostrikov K, Levchenko I. Tailoring the composition of self-assembled Si(1-x)C(x) quantum dots: simulation of plasma/ion-related controls. Nanotechnology 2008; 19:355705. [PMID: 21828859 DOI: 10.1088/0957-4484/19/35/355705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Precise control of composition and internal structure is essential for a variety of novel technological applications which require highly tailored binary quantum dots (QDs) with predictable optoelectronic and mechanical properties. The delicate balancing act between incoming flux and substrate temperature required for the growth of compositionally graded (Si(1-x)C(x); x varies throughout the internal structure), core-multishell (discrete shells of Si and C or combinations thereof) and selected composition (x set) QDs on low-temperature plasma/ion-flux-exposed Si(100) surfaces is investigated via a hybrid numerical simulation. Incident Si and C ions lead to localized substrate heating and a reduction in surface diffusion activation energy. It is shown that by incorporating ions in the influx, a steady-state composition is reached more quickly (for selected composition QDs) and the composition gradient of a Si(1-x)C(x) QD may be fine tuned; additionally (with other deposition conditions remaining the same), larger QDs are obtained on average. It is suggested that ionizing a portion of the influx is another way to control the average size of the QDs, and ultimately, their internal structure. Advantages that can be gained by utilizing plasma/ion-related controls to facilitate the growth of highly tailored, compositionally controlled quantum dots are discussed as well.
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Affiliation(s)
- A E Rider
- Plasma Nanoscience, School of Physics, The University of Sydney, Sydney, NSW 2006, Australia
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17
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Levchenko I, Ostrikov K. Carbon saturation of arrays of Ni catalyst nanoparticles of different size and pattern uniformity on a silicon substrate. Nanotechnology 2008; 19:335703. [PMID: 21730629 DOI: 10.1088/0957-4484/19/33/335703] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The kinetics of saturation of Ni catalyst nanoparticle patterns of the three different degrees of order, used as a model for the growth of carbon nanotips on Si, is investigated numerically using a complex model that involves surface diffusion and ion motion equations. It is revealed that Ni catalyst patterns of different degrees of order, with Ni nanoparticle sizes up to 12.5 nm, exhibit different kinetics of saturation with carbon on the Si surface. It is shown that in the cases examined (surface coverage in the range of 1-50%, highly disordered Ni patterns) the relative pattern saturation factor calculated as the ratio of average incubation times for the processes conducted in the neutral and ionized gas environments reaches 14 and 3.4 for Ni nanoparticles of 2.5 and 12.5 nm, respectively. In the highly ordered Ni patterns, the relative pattern saturation factor reaches 3 for nanoparticles of 2.5 nm and 2.1 for nanoparticles of 12.5 nm. Thus, more simultaneous saturation of Ni catalyst nanoparticles of sizes in the range up to 12.5 nm, deposited on the Si substrate, can be achieved in the low-temperature plasma environment than with the neutral gas-based process.
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Affiliation(s)
- I Levchenko
- Plasma Nanoscience, School of Physics, The University of Sydney, Sydney NSW 2006, Australia
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Flynn JM, Levchenko I, Seidel M, Wickner SH, Sauer RT, Baker TA. Overlapping recognition determinants within the ssrA degradation tag allow modulation of proteolysis. Proc Natl Acad Sci U S A 2001; 98:10584-9. [PMID: 11535833 PMCID: PMC58509 DOI: 10.1073/pnas.191375298] [Citation(s) in RCA: 224] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ssrA tag, an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP. Mutational analysis of the ssrA tag reveals independent, but overlapping determinants for its interactions with ClpX, ClpA, and SspB, a specificity-enhancing factor for ClpX. ClpX interacts with residues 9-11 at the C terminus of the tag, whereas ClpA recognizes positions 8-10 in addition to residues 1-2 at the N terminus. SspB interacts with residues 1-4 and 7, N-terminal to the ClpX-binding determinants, but overlapping the ClpA determinants. As a result, SspB and ClpX work together to recognize ssrA-tagged substrates efficiently, whereas SspB inhibits recognition of these substrates by ClpA. Thus, dissection of the recognition signals within the ssrA tag provides insight into how multiple proteins function in concert to modulate proteolysis.
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Affiliation(s)
- J M Flynn
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Kim YI, Levchenko I, Fraczkowska K, Woodruff RV, Sauer RT, Baker TA. Molecular determinants of complex formation between Clp/Hsp100 ATPases and the ClpP peptidase. Nat Struct Biol 2001; 8:230-3. [PMID: 11224567 DOI: 10.1038/84967] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Clp/Hsp100 ATPases are hexameric protein machines that catalyze the unfolding, disassembly and disaggregation of specific protein substrates in bacteria, plants and animals. Many family members also interact with peptidases to form ATP-dependent proteases. In Escherichia coli, for instance, the ClpXP protease is assembled from the ClpX ATPase and the ClpP peptidase. Here, we have used multiple sequence alignments to identify a tripeptide 'IGF' in E. coli ClpX that is essential for ClpP recognition. Mutations in this IGF sequence, which appears to be part of a surface loop, disrupt ClpXP complex formation and prevent protease function but have no effect on other ClpX activities. Homologous tripeptides are found only in a subset of Clp/Hsp100 ATPases and are a good predictor of family members that have a ClpP partner. Mapping of the IGF loop onto a homolog of known structure suggests a model for ClpX-ClpP docking.
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Affiliation(s)
- Y I Kim
- Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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Abstract
Events that stall bacterial protein synthesis activate the ssrA-tagging machinery, resulting in resumption of translation and addition of an 11-residue peptide to the carboxyl terminus of the nascent chain. This ssrA-encoded peptide tag marks the incomplete protein for degradation by the energy-dependent ClpXP protease. Here, a ribosome-associated protein, SspB, was found to bind specifically to ssrA-tagged proteins and to enhance recognition of these proteins by ClpXP. Cells with an sspB mutation are defective in degrading ssrA-tagged proteins, demonstrating that SspB is a specificity-enhancing factor for ClpXP that controls substrate choice.
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Affiliation(s)
- I Levchenko
- Department of Biology and Howard Hughes Medical Institute, Building 68, Room 523, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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Levchenko I, Smith CK, Walsh NP, Sauer RT, Baker TA. PDZ-like domains mediate binding specificity in the Clp/Hsp100 family of chaperones and protease regulatory subunits. Cell 1997; 91:939-47. [PMID: 9428517 DOI: 10.1016/s0092-8674(00)80485-7] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
ClpX, a molecular chaperone and the regulatory subunit of the ClpXP protease, is shown to contain tandem modular domains that bind to the C-terminal sequences of target proteins in a manner that parallels functional specificity. Nuclear magnetic resonance studies show that these C-terminal sequences are displayed as disordered peptides on the surface of otherwise folded proteins. The ClpX substrate-binding domains are homologous to sequences in other Clp/Hsp100 proteins and are related more distantly to PDZ domains, which also mediate C-terminal specific protein-protein interactions. Conservation of these binding domains indicates that the mode of substrate recognition characterized here for ClpX will be a conserved feature among Clp/Hsp100 family members and a distinguishing characteristic between this chaperone family and the Hsp70 chaperones.
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Affiliation(s)
- I Levchenko
- Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge 02139, USA
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Abstract
The pi protein of plasmid R6K is involved in control of replication. The aim of this study was to use an in vitro replication system dependent on an R6K-derived gamma origin of replication (gamma ori) to compare replication characteristics of wt pi and a hyperactive variant of pi protein (piS87N; Filutowicz et al., 1994b. Cooperative binding of initiator protein to replication origin conferred by single amino acid substitution. Nucleic Acids Res. 22, 4211-4215). The characteristics of in vitro replication from gamma ori reported in this investigation are as follows: (i) piS87N is considerably more active in comparison to wt pi. (ii) Replication proceeds through Cairns-type intermediates and the initiation site and directionality of the fork movement are similar in the presence of both proteins. (iii) Replication forks emanate unidirectionally in the vicinity of the cluster of seven 22-bp direct repeats within gamma ori. (iv) Replication dependent on wt pi, but not piS87N, is stimulated up to 1.5-fold by rifampicin.
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Affiliation(s)
- I Levchenko
- Department of Bacteriology, University of Wisconsin-Madison, 53706, USA
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Levchenko I, Yamauchi M, Baker TA. ClpX and MuB interact with overlapping regions of Mu transposase: implications for control of the transposition pathway. Genes Dev 1997; 11:1561-72. [PMID: 9203582 DOI: 10.1101/gad.11.12.1561] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Transposition of phage Mu is catalyzed by an extremely stable transposase-DNA complex. Once recombination is complete, the Escherichia coli ClpX protein, a member of the Clp/Hsp100 chaperone family, initiates disassembly of the complex for phage DNA replication to commence. To understand how the transition between recombination and replication is controlled, we investigated how transposase-DNA complexes are recognized by ClpX. We find that a 10-amino-acid peptide from the carboxy-terminal domain of transposase is required for its recognition by ClpX. This short, positively charged peptide is also sufficient to convert a heterologous protein into a ClpX substrate. The region of transposase that interacts with the transposition activator, MuB protein, is also defined further and found to overlap with that recognized by ClpX. As a consequence, MuB inhibits disassembly of several transposase-DNA complexes that are intermediates in recombination. This ability of MuB to block access to transposase suggests a mechanism for restricting ClpX-mediated remodeling to the proper stage during replicative transposition. We propose that overlap of sequences involved in subunit interactions and those that target a protein for remodeling or destruction may be a useful design for proteins that function in pathways where remodeling or degradation must be regulated.
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Affiliation(s)
- I Levchenko
- Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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Levchenko I, Filutowicz M. Initiator protein pi can bind independently to two domains of the gamma origin core of plasmid R6K: the direct repeats and the A+T-rich segment. Nucleic Acids Res 1996; 24:1936-42. [PMID: 8657577 PMCID: PMC145866 DOI: 10.1093/nar/24.10.1936] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The pi protein of plasmid R6K functions in both replication and transcription. pi autoregulates its own synthesis and is required for replication of the RISK gamma origin. pi performs these functions by binding to specific DNA sites arranged as pairs of 6-10 bp inverted repeats (IRs) or as a cluster of seven tandem 22 bp direct repeats (DRs) which lack symmetry. The sites share the TGAGRG nucleotide motif (where R is A or G). The DRs and IRs flank the central A+T-rich segment of the gamma origin. In this work we carried out DNase I and hydroxyl radical protection experiments on various deletion derivatives of the gamma origin complexed with pi protein. These experiments revealed binding of pi to a novel site embedded within the A+T-rich segment. This interaction manifests primarily by the appearance of the enhanced scissions of DNA by DNase I and hydroxyl radicals. pi interaction with the A+T-rich site is independent of pi binding to the DRs and IRs. We propose that pi protein can recognize distinct families of DNA sequences in the gamma origin.
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Affiliation(s)
- I Levchenko
- Department of Bacteriology, University of Wisconsin, Madison 53706, USA
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Abstract
The plasmid R6K gamma origin consists of two adjacent modules, the enhancer and the core, and requires R6K initiator protein pi for replication. While the core alone can replicate at a low level of wild-type pi protein, we show here that host cells do not stably maintain core plasmids. The presence of the enhancer segment confers stable inheritance on core plasmids without a significant change in average plasmid copy number. Deletions and site-directed mutagenesis indicated that the stability of core plasmids is not mediated by binding sites or consensus sequences in the enhancer for DnaA, pi protein, gyrase, Fis, or Dcm methylase. Proper segregation of core plasmids requires only the R6K stb or stability-related region, which includes the 20-bp segment of the 100-bp enhancer adjacent to the core. The use of the pi 116 mutant protein, which increases plasmid copy number fourfold, does not stabilize core plasmids lacking the enhancer. We also show that at an elevated level of wild-type pi, the gamma-origin plasmid is unstable, even in the presence of the enhancer. We discuss the differences and similarities between the R6K stability system and those found in other plasmids.
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Affiliation(s)
- F Wu
- Department of Bacteriology, University of Wisconsin, Madison 53706, USA
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Abstract
Mu transposition is promoted by an extremely stable complex containing a tetramer of the transposase (MuA) bound to the recombining DNA. Here we purify the Escherichia coli ClpX protein, a member of a family of multimeric ATPases present in prokaryotes and eukaryotes (the Clp family), on the basis of its ability to remove the transposase from the DNA after recombination. Previously, ClpX has been shown to function with the ClpP peptidase in protein turnover. However, neither ClpP nor any other protease is required for disassembly of the transposase. The released MuA is not modified extensively, degraded, or irreversibly denatured, and is able to perform another round of recombination in vitro. We conclude that ClpX catalyzes the ATP-dependent release of MuA by promoting a transient conformational change in the protein and, therefore, can be considered a molecular chaperone. ClpX is important at the transition between the recombination and DNA replication steps of transposition in vitro; this function probably corresponds to the essential contribution of ClpX for Mu growth. Deletion analysis reveals that the sequence at the carboxyl terminus of MuA is important for disassembly by ClpX and can target MuA for degradation by ClpXP in vitro. These data contribute to the emerging picture that members of the Clp family are chaperones specifically suited for disaggregating proteins and are able to function with or without a collaborating protease.
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Affiliation(s)
- I Levchenko
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge 02139, USA
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Wu F, Levchenko I, Filutowicz M. Binding of DnaA protein to a replication enhancer counteracts the inhibition of plasmid R6K gamma origin replication mediated by elevated levels of R6K pi protein. J Bacteriol 1994; 176:6795-801. [PMID: 7961437 PMCID: PMC197046 DOI: 10.1128/jb.176.22.6795-6801.1994] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Replication of the gamma origin of Escherichia coli plasmid R6K requires pi protein, encoded by the R6K pir gene, and many host factors, including DnaA protein. Pi has dual roles, activating replication at low levels and inhibiting replication at high levels. The inhibitory function of pi is counteracted by integration host factor and a specific sequence of the origin called the enhancer. This 106-bp DNA segment contains a binding site for DnaA protein (DnaA box 1). In this study, we mutated this site to determine if it was required for the enhancer's function. Using gamma origin derivative plasmids with the DnaA box 1 altered or deleted, we show that this site is necessary to protect the origin against levels of wild-type pi protein that would otherwise inhibit replication. To show that the base substitutions in DnaA box 1 weakened the binding of DnaA, we developed a new application of the agarose gel retardation assay. This quick and easy assay has broad applicability, as shown in binding studies with DNA fragments carrying a different segment of the R6K origin, the chromosomal origin (oriC), or the pUC origin. The gel retardation assay suggests a stoichiometry of DnaA binding different from that deduced from other assays.
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Affiliation(s)
- F Wu
- Department of Bacteriology, University of Wisconsin--Madison 53706
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Filutowicz M, York D, Levchenko I. Cooperative binding of initiator protein to replication origin conferred by single amino acid substitution. Nucleic Acids Res 1994; 22:4211-5. [PMID: 7937147 PMCID: PMC331923 DOI: 10.1093/nar/22.20.4211] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The replication initiator protein pi of plasmid R6K binds seven 22 bp direct repeats (DR) in the gamma origin. The pi protein also binds to an inverted repeat (IR) in the operator of its own gene, pir, which lies outside the gamma origin sequences. A genetic system was devised to select for pi protein mutants which discriminate between IR and DR (York et al., Gene (Amst.) 116, 7-12, 1992; York and Filutowicz, J. Biol. Chem. 268, 21854-21861, 1993). From this selection the mutant pi S87N protein was isolated which is deficient in repressing the pir gene's expression because it cannot bind to IR at the pir gene operator. Remarkably, we discovered that pi S87N binds to DR cooperatively under conditions where wt pi binds independently. Moreover, the pi S87N is more active as a replication initiator in vivo when supplied at the same level as wt pi. Quantitative binding assays showed that both wt pi and pi S87N bind a DNA fragment containing a single DR unit with a similar affinity (Kd = 0.3 x 10(-12) M). Thus, cooperativity of pi S87N is most likely achieved through altered interactions between promoters bound at adjacent DR units.
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Affiliation(s)
- M Filutowicz
- Department of Bacteriology, University of Wisconsin, Madison 53706
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Abstract
Replication of plasmid R6K is controlled by the homodimeric initiator protein pi, which binds to seven 22-bp direct repeats (iterons) in the gamma-origin. One of the genetically engineered pi variants (delta C164 pi) contains only the 164 N-terminal amino acids (aa) of the 305-aa pi molecule. This truncated pi polypeptide retains the ability to function as a specific inhibitor of R6K replication in vivo, though it neither drives replication, nor binds to iterons [Greener et al., Mol. Gen. Genet. 224 (1990) 24-32]. In order to define the region of pi responsible for dimerization, we have performed chemical crosslinking experiments with purified delta C164 pi and shown that this polypeptide is dimeric. We did not observe an exchange between protein monomers upon mixing of wild-type pi and delta C164 pi homodimers. However, heterodimers, as well as each type of homodimers, were formed when these polypeptides refolded after guanidine hydrochloride treatment. Thus, both dimerization and dimer stability are determined by the N-terminal domain of pi. We speculate that these properties might depend on the leucine zipper and RGD motifs that have been identified in the two regions of the N-terminal domain of pi.
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Affiliation(s)
- I Levchenko
- Department of Bacteriology, University of Wisconsin, Madison 53706
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Filutowicz M, Dellis S, Levchenko I, Urh M, Wu F, York D. Regulation of replication of an iteron-containing DNA molecule. Prog Nucleic Acid Res Mol Biol 1994; 48:239-73. [PMID: 7938550 DOI: 10.1016/s0079-6603(08)60857-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- M Filutowicz
- Department of Bacteriology, University of Wisconsin-Madison 53706
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