scholarly journals Physical and Topological Properties of Circular DNA

1966 ◽  
Vol 49 (6) ◽  
pp. 103-125 ◽  
Author(s):  
Jerome Vinograd ◽  
Jacob Lebowitz'
Keyword(s):  
Room Temperature ◽  
Melting Behavior ◽  
Neutral Salt ◽  
Winding Number ◽  
Complementary Strand ◽  
Circular Dna ◽  
Tumor Viruses ◽  
Weakly Closed ◽  
A Site ◽  
Melting Experiments

Several types of circular DNA molecules are now known. These are classified as single-stranded rings, covalently closed duplex rings, and weakly bonded duplex rings containing an interruption in one or both strands. Single rings are exemplified by the viral DNA from ϕX174 bacteriophage. Duplex rings appear to exist in a twisted configuration in neutral salt solutions at room temperature. Examples of such molecules are the DNA's from the papova group of tumor viruses and certain intracellular forms of ϕX and λ-DNA. These DNA's have several common properties which derive from the topological requirement that the winding number in such molecules is invariant. They sediment abnormally rapidly in alkaline (denaturing) solvents because of the topological barrier to unwinding. For the same basic reason these DNA's are thermodynamically more stable than the strand separable DNA's in thermal and alkaline melting experiments. The introduction of one single strand scission has a profound effect on the properties of closed circular duplex DNA's. In neutral solutions a scission appears to generate a swivel in the complementary strand at a site in the helix opposite to the scission. The twists are then released and a slower sedimenting, weakly closed circular duplex is formed. Such circular duplexes exhibit normal melting behavior, and in alkali dissociate to form circular and linear single strands which sediment at different velocities. Weakly closed circular duplexes containing an interruption in each strand are formed by intramolecular cyclization of viral λ-DNA. A third kind of weakly closed circular duplex is formed by reannealing single strands derived from circularly permuted T2 DNA. These reconstituted duplexes again contain an interruption in each strand though not necessarily regularly spaced with respect to each other.

Melting behavior of a covalently closed, single-stranded, circular DNA

Biochemistry ◽  
1989 ◽  
Vol 28 (1) ◽  
pp. 268-273 ◽  
Author(s):  
Dorothy A. Erie ◽  
Roger A. Jones ◽  
Wilma K. Olson ◽  
Navin K. Sinha ◽  
Kenneth J. Breslauer
Keyword(s):  
Melting Behavior ◽  
Circular Dna

Phase Diagram of the W-doped Pb(Zn1/3Nb2/3)O3–BaTiO3– PbTiO3 System Around a Morphotropic Phase Boundary Composition

2002 ◽  
Vol 17 (5) ◽  
pp. 1085-1091 ◽  
Author(s):  
W. Z. Zhu ◽  
M. Yan ◽  
A. L. Kholkin ◽  
P. Q. Mantas ◽  
J. L. Baptista
Keyword(s):  
High Temperature ◽  
Phase Boundary ◽  
Morphotropic Phase Boundary ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electrical Neutrality ◽  
Phase Boundary Composition ◽  
A Site ◽  
Successive Phase

The morphotropic phase boundary (MPB) composition that is characterized by the coexistence of rhombohedral and tetragonal phases in the Pb(Zn1/3Nb2/3)O3–BaTiO3– PbTiO3 system was modified by W-doping at the B site of a perovskite structural block. To maintain the electrical neutrality, creation of A-site vacancies was intentionally introduced in the formulation of the examined compositions. Incorporation of W ions was revealed to stabilize the tetragonal phase against the rhombohedral one, shifting the MPB toward the PZN-rich end at room temperature. High-temperature x-ray diffraction examination in combination with dielectric measurements discloses two successive phase transitions as a sample is cooled from high temperature, namely, paraelectric cubic to ferroelectric rhombohedral followed by ferroelectric rhombohedral to ferroelectric tetragonal. W addition appears to suppress the first transition while promoting the second one.

A-site K-doping to enhance room-temperature TCR of polycrystalline La0.8Sr0.2-K MnO3 ceramics

2020 ◽  
Vol 847 ◽  
pp. 156417
Author(s):  
Hongjiang Li ◽  
Kaili Chu ◽  
Xingrui Pu ◽  
Shuai Zhang ◽  
Gang Dong ◽  
...  
Keyword(s):  
Room Temperature ◽  
A Site

scholarly journals Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface

2020 ◽  
Vol 6 (33) ◽  
pp. eaba4924 ◽  
Author(s):  
Gong Chen ◽  
Arantzazu Mascaraque ◽  
Hongying Jia ◽  
Bernd Zimmermann ◽  
MacCallum Robertson ◽  
...  
Keyword(s):  
Room Temperature ◽  
Ferromagnetic Layer ◽  
Spin Orbit Coupling ◽  
Winding Number ◽  
Large Magnitude ◽  
Chemisorbed Oxygen ◽  
Magnetic Layers ◽  
Oxygen Coverage ◽  
Opening Up ◽  
Moriya Interaction

The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction that stabilizes chiral spin textures. It is induced by inversion symmetry breaking in noncentrosymmetric lattices or at interfaces. Recently, interfacial DMI has been found in magnetic layers adjacent to transition metals due to the spin-orbit coupling and at interfaces with graphene due to the Rashba effect. We report direct observation of strong DMI induced by chemisorption of oxygen on a ferromagnetic layer at room temperature. The sign of this DMI and its unexpectedly large magnitude—despite the low atomic number of oxygen—are derived by examining the oxygen coverage–dependent evolution of magnetic chirality. We find that DMI at the oxygen/ferromagnet interface is comparable to those at ferromagnet/transition metal interfaces; it has enabled direct tailoring of skyrmion’s winding number at room temperature via oxygen chemisorption. This result extends the understanding of the DMI, opening up opportunities for the chemisorption-related design of spin-orbitronic devices.

COMPARISON OF PROPERTIES OF PLZT SYSTEM WITH DIFFERENT FORMULATIONS

2006 ◽  
Vol 20 (29) ◽  
pp. 1883-1892
Author(s):  
S. K. PANDEY ◽  
O. P. THAKUR ◽  
ANSHU GOYAL ◽  
D. S. RAWAL ◽  
CHANDRA PRAKASH ◽  
...  
Keyword(s):  
Lead Zirconate Titanate ◽  
Room Temperature ◽  
Piezoelectric Properties ◽  
Lead Zirconate ◽  
Rhombohedral Structure ◽  
X Ray Diffraction ◽  
Sem Study ◽  
A Site ◽  
Single Phase Formation ◽  
Diffuse Phase

We report the comparison of structural, dielectric, ferroelectric and piezoelectric properties of lanthanum-modified lead zirconate titanate (PLZT) ceramics with the substitution of 7 and 8 mol% La 3+ content in PZT (65/35) by three different formulations. The three formulations are (i) cation compensated at A-site, (ii) valency compensated at A-site and (iii) all sites (A and B) compensated. Samples were prepared by solid-state reaction route. X-ray diffraction (XRD) study shows single-phase formation with rhombohedral structure in all the samples. Scanning electron microscopy (SEM) study shows variation in grain size with different formulations. Dielectric studies for all the PLZT samples have been carried out as a function of temperature (room temperature to 350°C) at few selected frequencies (0.1, 1, 10 and 100 kHz) showing characteristics of diffuse phase transition (DPT). Dielectric properties of the poled and unpoled samples at room temperature have also been compared. All these compositions show well-defined ferroelectric behavior with significant change in the coercive field (Ec). Maximum piezoelectric properties have been obtained for the PLZT system with 8 mol% La 3+ prepared by formulation (i).

scholarly journals Domains A and B in the Rb pocket interact to form a transcriptional repressor motif.

1996 ◽  
Vol 16 (9) ◽  
pp. 4862-4868 ◽  
Author(s):  
K N Chow ◽  
D C Dean
Keyword(s):  
Cell Cycle ◽  
Transcription Factors ◽  
Transcriptional Repressor ◽  
Inhibitory Effect ◽  
Binding Assays ◽  
Adenovirus E1a ◽  
Tumor Viruses ◽  
A Site ◽  
Repressor Activity

The retinoblastoma protein (Rb) is a tumor suppressor that regulates progression from the G1 phase to the S phase of the cell cycle. Previously, we found that Rb is a transcriptional repressor that is selectively targeted to promoters through an interaction with the E2F family of cell cycle transcription factors--when Rb is tethered to a promoter through E2F, it not only blocks E2F activity, it also binds surrounding transcription factors, preventing their interaction with the basal transcription complex, thus resulting in a dominant inhibitory effect on transcription of cell cycle genes. Here we examine the repressor motif of Rb. The two domains in the Rb pocket, A and B, which are conserved across species and in the Rb-related proteins p107 and p130, are both required for repressor activity. The nonconserved spacer separating A and B is not required. Although neither A nor B alone had any repressor activity, surprisingly, repressor activity was observed when the domains were coexpressed on separate proteins. Transfection assays suggest that one domain can recruit the other to the promoter to form a repressor motif that can both interact with E2F and have a dominant inhibitory effect on transcription. Using coimmunoprecipitation and in vitro binding assays, we show that A and B interact directly and that mutations which disrupt this interaction inhibit repressor activity. The Rb pocket was originally defined as the binding site for oncoproteins from DNA tumor viruses such as adenovirus E1a. We present evidence that E1a interacts with a site formed by the interaction of A and B and that this interaction with A and B induces or stabilizes the A-B interaction.

scholarly journals Ion-Exchange Reaction Of A-Site In A2Ta2O6 Pyrochlore Crystal Structure

2015 ◽  
Vol 60 (2) ◽  
pp. 941-944 ◽  
Author(s):  
M. Matsunami ◽  
T. Hashizume ◽  
A. Saiki
Keyword(s):  
Crystal Structure ◽  
Aqueous Solution ◽  
Ion Exchange ◽  
Room Temperature ◽  
Electrode Materials ◽  
Pyrochlore Structure ◽  
Rechargeable Battery ◽  
Ion Exchange Reaction ◽  
Li Ion ◽  
A Site

Abstract Na+ or K+ ion rechargeable battery is started to garner attention recently in Place of Li+ ion cell. It is important that A+ site ion can move in and out the positive-electrode materials. When K2Ta2O6 powder had a pyrochlore structure was only dipped into NaOH aqueous solution at room temperature, Na2Ta2O6 was obtained. K2Ta2O6 was fabricated from a tantalum sheet by a hydrothermal synthesize with KOH aqueous solution. When Na2Ta2O6 was dipped into KOH aqueous solution, K2Ta2O6 was obtained again. If KTaO3 had a perovskite structure was dipped, Ion-exchange was not observed by XRD. Because a lattice constant of pyrochlore structure of K-Ta-O system is bigger than perovskite, K+ or Na+ ion could shinny through and exchange between Ta5+ and O2− ion site in a pyrochlore structure. K+ or Na+ ion exchange of A2Ta2O6 pyrochlore had reversibility. Therefore, A2Ta2O6 had a pyrochlore structure can be expected such as Na+ ion rechargeable battery element.

The purification from Escherichia coli of a protein relaxing superhelical DNA

1976 ◽  
Vol 54 (4) ◽  
pp. 301-306 ◽  
Author(s):  
M. G. Burrington ◽  
A. R. Morgan
Keyword(s):  
Escherichia Coli ◽  
Sodium Dodecyl ◽  
Gel Filtration ◽  
Rapid Screening ◽  
Intact Protein ◽  
Winding Number ◽  
Circular Dna ◽  
E Coli ◽  
The Individual ◽  
Negative Supercoils

The Escherichia coli omega protein was first described by Wang (Wang, J.C.: J. Mol. Biol. 55, 523–533 (1971)) as having the ability to relax supercoiled covalently-closed circular DNA by changing the topological winding number, α. We have developed a rapid assay for omega activity which has allowed us to purify the protein to homogeneity. It appears to be an αβ-ype subunit protein with a molecular weight of the intact protein of about 80 000 (determined by gel filtration) and of the individual subunits of 56 000 and 31 000 (sodium dodecyl sulfate polyacrylamide gels). We have confirmed Wang's observation that it only partly relaxes negative supercoils, and is not active on positive supercoils. Its characteristics with respect to pH, salts, temperature and chromatography are described. A method for rapid screening of E. coli for omega mutants is described.

scholarly journals Structure and magnetism of the A site scandium perovskite (Sc 0.94 Mn 0.06 )Mn 0.65 Ni 0.35 O 3 synthesized at high pressure

2014 ◽  
Vol 372 (2013) ◽  
pp. 20130012 ◽  
Author(s):  
Chris I. Thomas ◽  
Matthew R. Suchomel ◽  
Giap V. Duong ◽  
Andrew M. Fogg ◽  
John B. Claridge ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Room Temperature ◽  
Magnetic Measurements ◽  
Ambient Pressure ◽  
Oxidation States ◽  
Formula Unit ◽  
Triclinic Structure ◽  
Bond Valence Sum ◽  
A Site

Scandium perovskite (Sc 0.94 Mn 0.06 )Mn 0.65 Ni 0.35 O 3 , synthesized at high pressure and high temperature, has a triclinic structure (space group ) at room temperature and ambient pressure with a √2 a p ×√2 a p ×2 a p structure with α ≈90 ° , β ≈89 ° , γ ≈90 ° . Magnetic measurements show that the material displays Curie–Weiss behaviour above 50 K with C =2.11 emu K mol −1 ( μ eff =4.11 μ B per formula unit) and θ =−95.27 K. Bond valence sum analysis of the crystal structure shows that manganese is present in three different oxidation states (+2, +3, +4), with the +2 oxidation state on the A site resulting in a highly tilted perovskite structure (average tilt 21.2 ° compared with 15.7 ° calculated for LaCaMnNbO 6 ), giving the formula .

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