scholarly journals Similarity of the Structure of DNA from a Variety of Sources

1959 ◽  
Vol 5 (3) ◽  
pp. 397-404 ◽  
Author(s):  
L. D. Hamilton ◽  
R. K. Barclay ◽  
M. H. F. Wilkins ◽  
G. L. Brown ◽  
H. R. Wilson ◽  
...  
Keyword(s):  
Double Helix ◽  
Genetic Material ◽  
Paracentrotus Lividus ◽  
Helical Structure ◽  
X Ray Diffraction ◽  
Nitrogen Base ◽  
X Ray ◽  
Calf Thymus ◽  
Wide Range ◽  
Helical Configuration

DNA's from diverse cells of different species and from diverse tissues give the same x-ray diffraction pattern. The presently observable structure of DNA appears, then, to be the same in all cells. Thus, DNA in the resting state—the stored genetic material, from sperm of Paracentrotus lividus, Arbacia lixula, and salmon and from T2 and T7 bacteriophage—gives a pattern indistinguishable from DNA from very rapidly dividing cells, e.g., human acute leukemic leukocytes, human leukemic myeloid cells, mouse sarcoma 180, and bacteria—E. coli and pneumococci—during their logarithmic growth. The same x-ray patterns are given by DNA's from more slowly dividing tissues, e.g. calf liver, calf thymus, and human normal and leukemic lymphatic tissue. DNA from chicken erythrocytes—a DNA presumably metabolically inert—gives a similar picture. DNA's from several sources with a wide range in nitrogen base ratios, prepared independently by different workers using various methods, have given final products in varying yield; these all gave the same x-ray pattern, suggesting that all DNA is in the double-helical configuration. Finally, separation of the DNA molecule into a number of fractions with a varying adenine + thymine:guanine + cytosine ratio, but a constant adenine:thymine and guanine:cytosine ratio, each giving the same x-ray pattern as the original whole molecule, suggests that DNA cannot exist in significant amounts in forms other than the double-helix. X-ray diffraction photographs of sperm heads, extracted nucleoprotamine, calf thymus nuclei and extracted nucleohistone, and of chicken erythrocyte nuclei, are not all as well defined as those given by extracted DNA, but it is clear from the general characteristics of the pattern that much of the DNA bound to protein in these nuclei has the usual helical configuration, and that the double-helical structure of DNA exists in the cell and is not an artifact.

scholarly journals Maurice Hugh Frederick Wilkins. 15 December 1916 — 5 October 2004

2006 ◽  
Vol 52 ◽  
pp. 455-478
Author(s):  
Struther Arnott ◽  
T.W.B. Kibble ◽  
Tim Shallice
Keyword(s):  
Secondary Structure ◽  
Nucleic Acids ◽  
Double Helix ◽  
Genetic Material ◽  
Research Programme ◽  
Dna Structure ◽  
X Ray Diffraction ◽  
Symmetrical Structure ◽  
X Ray ◽  
The Third

Maurice Hugh Frederick Wilkins was the ‘Third man of the double helix’ according to the publishers who were allowed to foist this title on his late–written autobiography. Certainly it is for his role in the discovery of the duplex secondary structure of DNA that he will be remembered. It might be argued that he was the first man, rather than the third, for it was his successful revival of X–ray diffraction studies of DNA and their earliest product in 1950, a pattern of a well–oriented and polycrystalline DNA of unprecedented quality, that allowed him to conclude almost immediately that the basic framework of the genetic material was simple and symmetrical, and that the symmetrical structure took the form of a helix. This same pattern, displayed at a conference in Naples six months later, was the major inspiration for the involvement of J. D. Watson (ForMemRS 1981) in modelling DNA structure in collaboration with F. H. C. Crick (FRS 1959). Crick was a personal friend of Maurice's and was more involved with studies of proteins until the progress of Maurice's research programme and Watson's enthusiastic presence in Cambridge convinced him to put nucleic acids first. The carefully crafted citation for the 1960 Lasker Award, which these three men shared in 1960, put Maurice's name first and accurately referred to ‘… the painstaking x–ray diffraction studies of Wilkins that provided a most important clue that was pursued in an ingenious fashion and to a logical conclusion by Crick and Watson…’. Maurice's diffraction studies of DNA were not only the alpha but also the omega of the double helix because it was left to him to remedy a major flaw in the original (1953) Watson–Crick conjecture.

scholarly journals Multidimensional Ln-Aminophthalate Photoluminescent Coordination Polymers

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1786
Author(s):  
Carla Queirós ◽  
Chen Sun ◽  
Ana M. G. Silva ◽  
Baltazar de Castro ◽  
Juan Cabanillas-Gonzalez ◽  
...  
Keyword(s):  
Water Content ◽  
Coordination Polymers ◽  
Metal Ion ◽  
Low Cost ◽  
Microwave Assisted Synthesis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach. One- and two-dimensional (1D and 2D) LnCPs were prepared from 5-aminoisophthalic acid and Sm3+/Tb3+ using hydrothermal and/or microwave-assisted synthesis. The unprecedented LnCPs were characterized by single-crystal X-ray diffraction (SCRXD), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), and their photoluminescence (PL) properties were studied in the solid state, at room temperature, using the CPs as powders and encapsulated in poly(methyl methacrylate (PMMA) films, envisaging the potential preparation of devices for sensing. The materials revealed interesting PL properties that depend on the dimensionality, metal ion, co-ligand used and water content.

2D X-ray diffraction and molecular modelling of the crystalline structure of polyesters under uniaxial stress

2021 ◽  
pp. 096739112199822
Author(s):  
Ahmed I Abou-Kandil ◽  
Gerhard Goldbeck
Keyword(s):  
Crystalline Structure ◽  
Molecular Modelling ◽  
Three Dimensional ◽  
Uniaxial Stress ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Modelling Techniques ◽  
Diffraction Patterns

Studying the crystalline structure of uniaxially and biaxially drawn polyesters is of great importance due to their wide range of applications. In this study, we shed some light on the behaviour of PET and PEN under uniaxial stress using experimental and molecular modelling techniques. Comparing experiment with modelling provides insights into polymer crystallisation with extended chains. Experimental x-ray diffraction patterns are reproduced by means of models of chains sliding along the c-axis leading to some loss of three-dimensional order, i.e. moving away from the condition of perfect register of the fully extended chains in triclinic crystals of both PET and PEN. This will help us understand the mechanism of polymer crystallisation under uniaxial stress and the appearance of mesophases in some cases as discussed herein.

scholarly journals Theoretical study of the properties of X-ray diffraction moiré fringes. II. Illustration of angularly integrated moiré images

2019 ◽  
Vol 75 (4) ◽  
pp. 610-623
Author(s):  
Jun-ichi Yoshimura
Keyword(s):  
Incident Wave ◽  
Angular Width ◽  
X Ray Diffraction ◽  
Experimental Conditions ◽  
Acta Cryst ◽  
Low Contrast ◽  
X Ray ◽  
Moiré Fringes ◽  
Wide Range ◽  
Fringe Patterns

Using a theory of X-ray diffraction moiré fringes developed in a previous paper, labelled Part I [Yoshimura (2015). Acta Cryst. A71, 368–381], the X-ray moiré images of a silicon bicrystal having a weak curvature strain and an interspacing gap, assumed to be integrated for an incident-wave angular width, are simulation-computed over a wide range of crystal thicknesses and incident-wave angular width, likely under practical experimental conditions. Along with the simulated moiré images, the graphs of characteristic quantities on the moiré images are presented for a full understanding of them. The treated moiré images are all of rotation moiré. Mo Kα1 radiation and the 220 reflection were assumed in the simulation. The results of this simulation show that fringe patterns, which are significantly modified from simple straight fringes of rotation moiré, appear in some ranges of crystal thicknesses and incident-wave angular width, due to a combined effect of Pendellösung oscillation and an added phase difference from the interspacing gap, under the presence of a curvature strain. The moiré fringes which slope to the perpendicular direction to the diffraction vector in spite of the assumed condition of rotation moiré, and fringe patterns where low-contrast bands are produced with a sharp bend of fringes arising along the bands are examples of the modified fringe pattern. This simulation study provides a wide theoretical survey of the type of bicrystal moiré image produced under a particular condition.

scholarly journals Charge Compensation in Europium-Doped Hafnia Nanoparticles: Solvothermal Synthesis and Colloidal Dispersion

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1042
Author(s):  
Xavier H. Guichard ◽  
Francesco Bernasconi ◽  
Alessandro Lauria
Keyword(s):  
Low Temperature ◽  
Hafnium Oxide ◽  
Aqueous Media ◽  
Charge Compensation ◽  
Colloidal Dispersion ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Direct Formation ◽  
Enhanced Luminescence

Effective charge compensation of europium in hafnium oxide nanoparticles was achieved at low temperature, allowing high doping incorporation (up to 6 at.%) and enhanced luminescence. The efficiency of the incorporation and charge compensation was confirmed by scanning electron microscope energy dispersive X-ray spectroscopy and powder X-ray diffraction measurements. Despite the known polymorphism of hafnium oxide, when doped to a concentration above 3 at.%, only the pure monoclinic phase was observed up to 6 at.% of europium. Furthermore, the low-temperature solvothermal route allowed the direct formation of stable dispersions of the synthesized material over a wide range of concentrations in aqueous media. The dispersions were studied by diffuse light scattering (DLS) to evaluate their quality and by photoluminescence to investigate the incorporation of the dopants into the lattice.

scholarly journals In situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated Ce(IV)-based Metal-Organic Frameworks with UiO-66 and MIL-140 architectures

2020 ◽  
Author(s):  
Stephen Shearan ◽  
Jannick Jacobsen ◽  
Ferdinando Costantino ◽  
Roberto D’Amato ◽  
Dmitri Novikov ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Metal Organic Frameworks ◽  
Building Blocks ◽  
Nucleation And Growth ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Determining Step ◽  
Wide Range ◽  
Metal Organic

We report on the results of a thorough <i>in situ</i> synchrotron powder X-ray diffraction study of the crystallisation in aqueous medium of two recently discovered perfluorinated Ce(IV)-based metal-organic frameworks (MOFs), analogues of the already well investigated Zr(IV)-based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The two MOFs were originally obtained in pure form in similar conditions, using ammonium cerium nitrate and tetrafluoroterephthalic acid as building blocks, and small variations of the reaction parameters were found to yield mixed phases. Here, we investigate the crystallisation of these compounds <i>in situ</i> in a wide range of conditions, varying parameters such as temperature, amount of the protonation modulator nitric acid (HNO<sub>3</sub>) and amount of the coordination modulator acetic acid (AcOH). When only HNO<sub>3</sub> is present in the reaction environment, F4_MIL-140A(Ce) is obtained as a pure phase. Heating preferentially accelerates nucleation, which becomes rate determining below 57 °C, whereas the modulator influences nucleation and crystal growth to a similar extent. Upon addition of AcOH to the system, alongside HNO<sub>3</sub>, mixed-phased products, consisting of F4_MIL-140A(Ce) and F4_UiO-66(Ce), are obtained. In these conditions, F4_UiO-66(Ce) is always formed faster and no interconversion between the two phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate determining step. An increase in the amount of HNO<sub>3</sub> slows down both nucleation and growth rates for F4_MIL-140A(Ce), whereas nucleation is mainly affected for F4_UiO-66(Ce). In addition, a higher amount HNO<sub>3</sub> favours the formation of F4_MIL-140A(Ce). Similarly, increasing the amount of AcOH leads to slowing down of the nucleation and growth rate, but favours the formation of F4_UiO-66(Ce). The pure F4_UiO-66(Ce) phase could also be obtained when using larger amounts of AcOH in the presence of minimal HNO<sub>3</sub>. Based on these <i>in situ</i> results, a new optimised route to achieving a pure, high quality F4_MIL-140A(Ce) phase in mild conditions (60 °C, 1 h) is also identified.

Single Crystal Wurtzitic Aluminum Nitride Growth on Silicon Using Supersonic Gas Jets

1995 ◽  
Vol 395 ◽  
Author(s):  
S. A. Ustin ◽  
L. Lauhon ◽  
K. A. Brown ◽  
D. Q. Hu ◽  
W. Ho
Keyword(s):  
Aluminum Nitride ◽  
Growth Rates ◽  
High Energy ◽  
X Ray Diffraction ◽  
Rutherford Back Scattering ◽  
X Ray ◽  
Supersonic Molecular Beam ◽  
Supersonic Beams ◽  
Wide Range

ABSTRACTHighly oriented aluminum nitride (0001) films have been grown on Si(001) and Si (111) substrates at temperatures between 550° C and 775° C with dual supersonic molecular beam sources. Triethylaluminum (TEA;[(C2H5)3Al]) and ammonia (NH3) were used as precursors. Hydrogen, helium, and nitrogen were used as seeding gases for the precursors, providing a wide range of possible kinetic energies for the supersonic beams due to the disparate masses of the seed gases. Growth rates of AIN were found to depend strongly on the substrate orientation and the kinetic energy of the incident precursor; a significant increase in growth rate is seen when seeding in hydrogen or helium as opposed to nitrogen. Growth rates were 2–3 times greater on Si(001) than on Si(111). Structural characterization of the films was done by reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD). X-ray rocking curve (XRC) full-width half-maxima (FWHM) were seen as small as 2.5°. Rutherford back scattering (RBS) was used to determine the thickness of the films and their chemical composition. Films were shown to be nitrogen rich, deviating from perfect stoichiometry by 10%–20%. Surface analysis was performed by Auger electron spectroscopy (AES).

Investigation of Amorphous/Crystalline State in Cu-Hf-Al Alloys

2010 ◽  
Vol 649 ◽  
pp. 87-92
Author(s):  
E. Nagy ◽  
Viktória Rontó ◽  
Jenő Sólyom ◽  
András Roósz
Keyword(s):  
Amorphous Alloys ◽  
Great Influence ◽  
Amorphous State ◽  
High Strength ◽  
Al Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
Wide Range ◽  
Different Shapes ◽  
Important Purpose

Cu-Hf-Al alloys are considered to be relatively new ones among Cu-based bulk amorphous alloys. Cu-Hf-Al alloys have high strength in amorphous state and this property makes many applications feasible for the industry. During the production of amorphous alloys the most important purpose is to produce them in the biggest diameter to make them suitable for a wide range of applications. The circumstances of the production process have a great influence on the developing structure. In the present work solidification of Cu-Hf-Al alloys were investigated. The alloys were cast into different shapes with different Al contents with special regard to the appearance of the amorphous/crystalline structure. The appearance and the structure of crystalline phases were determined by X-ray diffraction and X-ray, DSC and metallographic measurements were used to investigate the developing structure.

X-ray Diffraction Study of Amorphous NixZr(100-x)-Alloys Prepared by Melt-Spinning

1991 ◽  
Vol 46 (11) ◽  
pp. 947-950
Author(s):  
W.-M. Kuschke ◽  
P. Lamparter ◽  
S. Steeb
Keyword(s):  
Melt Spinning ◽  
Pair Correlation ◽  
Nickel Concentration ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
X Ray ◽  
Coordination Numbers ◽  
Structure Factors ◽  
Wide Range ◽  
Good Agreement

AbstractAmorphous Ni-Zr-alloys can be prepared by melt-spinning within a wide range of composition. Studies by X-ray diffraction yielded structure factors, pair correlation functions, total coordination numbers and atomic distances in dependence on the nickel concentration in the range of 25 up to 45 atomic percent. The change of the total coordination number and atomic distances turned out to be linear with the composition in this range. This is in good agreement with the linear composition dependence of the superconducting transition temperature, magnetic susceptibility, crystallization temperature, and electrical resistivity in the investigated range of composition.

The petrology of the Mount Padbury mesosiderite and its achondrite enclaves

1966 ◽  
Vol 36 (276) ◽  
pp. 1029-1060 ◽  
Author(s):  
G. J. H. McCall
Keyword(s):  
Microscopic Analysis ◽  
Host Material ◽  
Refractive Indices ◽  
X Ray Diffraction ◽  
Thin Sections ◽  
X Ray ◽  
Wide Range ◽  
Varied Range ◽  
Optical Determination

SummaryThe petrography of the Mount Padbury meteorite, previously briefly recorded, is described in some detail. Both the metalliferous host material of the mesosiderite and the varied range of silicate-rich, virtually metal-free enclaves (including both familiar achondrite material and unfamiliar achondrite material) are described. Eucrite, brecciated eucrite, and a peculiar ‘shocked’ form of eucrite (resembling some terrestrial flaser-gabbros) are the calcium-rich achondrite types represented; hypersthene achondrite (including typical diogenite material and unfamiliar material) and olivine achondrite (granular aggregates of olivine not entirely similar to the unique chassignite and single crystals up to 4 in. in length) are the calcium-poor achondrite types represented. The eucrite displays more or less uniform mineralogy, but the mineral constituents are present in varying proportions, and there is a wide range of textural variations recognized. The silicate grain fragments enclosed in the metallic reticulation to form the mesosiderite host material are, significantly, entirely of minerals seen within the achondrite enclaves—plagioclase, hypersthene, pigeonite, olivine, and tridymite.These results include microscopic analysis of thin sections and polished sections, X-ray diffraction studies, optical determination of refractive indices using mineral grain mounts, and chemical analyses.The wider implications of this new and unique meteorite find are briefly considered.

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