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Results for “Biological Resolution”

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At least 91 records · Page 5Linked to original sources
PubMed1999

Resolution, molecular structure and biological activities of the D- and L-enantiomers of potent anti-implantation agent, DL-2-[4-(2-piperidinoethoxy)phenyl]-3-phenyl-2H-1-benzopyran.

Compound 1 (DL-2-[4-(2-piperidinoethoxy)phenyl]-3-phenyl-2H-1-benzopyran, CDRI 85/287) a potent anti-estrogen and anti-implantation agent has been successfully resolved into its pure D- and L-enantiomers. Biological studies showed L-enantiomer to be the active form, exhibiting a fivefold higher receptor affinity for the rat uterine cytosolic estrogen receptor, 100% contraceptive efficacy at 1.3 mg/kg dose in single day schedule and 89% inhibition of estradiol induced increase of uterine weight at its contraceptive dose. The absolute stereochemistry determined by X-ray crystallographic analysis showed that the L-enantiomer has 2R configuration at its asymmetric centre.

Animals↗
PubMed1993

Imaging of reconstituted biological channels at molecular resolution by atomic force microscopy.

Using atomic force microscopy (AFM), we obtained high-resolution surface images of the bacterial outer membrane channels Escherichia coli OmpF porin and Bordetella pertussis porin that were reconstituted in artificial bilayer membranes as two-dimensional crystalline arrays. These porins were chosen because they are among the most extensively studied proteins of this type and are known for their well-defined crystalline nature in the native membrane. Such reconstituted membrane proteins are ideal specimens to assess the suitability and resolution of AFM for imaging biomembranes and associated proteins. Although OmpF porin often showed a mixed pattern of rectangular and hexagonal arrays with approximately 8.4 x 9.8- and approximately 7.2-nm-spacings, respectively, B. pertussis porin showed mostly a rectangular pattern with an approximately 7.9 x 13.8-nm spacing. The packing patterns of the E. coli OmpF porin in the membrane are very close to those found in electron-microscopic studies. When B. pertussis porin was imaged in a buffer solution, its trimeric subunits were apparently resolved, and the surface of each monomer revealed beadlike structures. This is the first report of such a high-resolution structural analysis of B. pertussis porin by any imaging method. We also imaged the lipid bilayer itself as an internal control for imaging and to further ascertain the resolution. Individual polar head groups of bilayer lipid molecules were resolved, suggesting the intrinsic resolution of AFM for bioimaging.

Bordetella pertussis↗
PubMed2002

Optical scanning holography as a technique for high-resolution three-dimensional biological microscopy.

The applicability of optical scanning holography (OSH) to the field of microscopic imaging for biological applications is assessed. A generalized mathematical description of OSH that takes into account polarization effects, high numerical apertures, and generalized illumination wave fronts is presented. This description is used to show that the proposed single-beam scanning technique relaxes the restrictions under which OSH functions correctly compared with the conventional double-beam scanning method. It is also shown that, although in general OSH is restricted to thin samples, this condition can be relaxed in nonrefracting fluorescence samples, which are of importance in biological microscopy.

Holography↗
PubMed1976

The effects of biological motion on CT resolution.

A variety of periodic and aperiodic psyiologic motions affect the quality of CT images. This study was initiated to estimate what an optimal scan period should be in the design of CT units. Ultrashort scan periods were experimentally similated in the heart and liver to approximate the parameters of future technology.

Animals↗
PubMed1995

Use of high-resolution cytometry in predicting the biologic behavior of T1 adenocarcinoma of the lung.

Touch preparations from 60 cases of T1 adenocarcinoma were analyzed using a high-resolution, automated image cytometer. These cases were divided according to pathologic stage: stage I, 31; stage II, 3; stage III, 19; and stage IV, 7. For each nucleus 57 features were analyzed, and using a linear combination of three texture features describing the DNA distribution in the cell nucleus (TARL, ODMAX and FAREA1), aggressive cancer cells belonging to stage III/IV could be identified. The best discrimination between the stages was achieved when the frequency of aggressive cancer cells was 48%; the correct classification rate was 77%. Using this criterion, 22 of 27 patients (81%) who died of cancer within five years after surgery were correctly predicted. These results suggest that high-resolution cytometry may be of value in predicting the biologic behavior of adenocarcinoma cases, especially in stage I/II.

Adenocarcinoma↗
PubMed1978

High resolution scanning electron microscopy in biology: artefacts caused by the nature and mode of application of the coating material.

Results of high resolution secondary electron observations of the haemocyanin molecule from the marine whelk Buccinum undatum are given. The choice of metal used for surface coating of the sample (gold, gold--palladium or carbon/gold--palldium) and the mode of application of this metal (thermal vacuum evaporation or diode sputtering) were both found to be of utmost importance when working at high magnifications in the scanning electron microscope. Sputter coating with gold gives poor results because of a granular and cracked appearance of the surface film. The haemocyanin molecules were difficult to recognize in these preparations. Best results were obtained by a thermal vacuum evaporation of gold--palladium. It is suggested that the inferior results seen after sputter coating may be due to the high temperatures wihch the specimen experiences during the sputtering, even when cooling of the specimen stage is carried out. Other specimens (diatom valves and latex spheres) were also studied at high magnification giving the same results as the haemocyanin molecules.

Animals↗
PubMed1991

Interfacial energies and surface-tension forces involved in the preparation of thin, flat crystals of biological macromolecules for high-resolution electron microscopy.

It is generally agreed that surface-tension forces and the direct interaction between the specimen and either the air-water interface or the water-substrate interface can influence significantly the preparation of biological materials for electron microscopy. Even so, there is relatively little systematic information available that would make it possible to control surface-tension forces and interfacial energies in a quantitative fashion. The main objective in undertaking the present work has been to understand somewhat better the factors that influence the degree of specimen flatness of large, monolayer crystals of biological macromolecules. However, the data obtained in our work should be useful in understanding the preparation of specimens of biological macromolecules in general. Data collection by electron diffraction and electron microscopy at high resolution and high tilt angles requires thin crystals of biological macromolecules that are flat to at least 1 degree, and perhaps less than 0.2 degrees, over areas as large as 1 micron2 or more. In addition to determining empirically by electron diffraction experiments whether sufficiently flat specimens can be prepared on various types of modified or unmodified carbon support films, we have begun to use other techniques to characterize both the surfaces involved and the interaction of our specimen with these surfaces. In the specific case of large, monolayer crystals of bacteriorhodopsin prepared as glucose-embedded specimens on hydrophobic carbon films, it was concluded that the initial interfacial interaction involves adsorption of the specimen to the air-water interface rather than adsorption of the specimen to the substrate. Surface-tension forces at the air-water interface and an apparently repulsive interaction between the specimen and the hydrophobic carbon seem to be major factors influencing the specimen flatness in this case. In the more general case it seems likely that interfacial interactions with either the substrate or the air-water interface can be variously manipulated in the search to find desirable conditions of specimen preparation.

Adsorption↗
PubMed1990

Imaging of protein molecules--towards atomic resolution.

This review discusses some of the recent developments in high resolution imaging of biological molecules. Electron micrographs of unstained biological molecules never show the resolution or contrast that would be predicted. Movements in the specimen caused by radiation damage, and possibly charging of the specimen are the most significant factors in the reduction of image contrast of these radiation-sensitive specimens. Until these limitations are overcome it is unlikely that the structures of biological molecules will be determined to the resolutions to which they are preserved. The causes of contrast loss in images are discussed in a quantitative manner and the use of crystalline paraffin as a model for radiation-sensitive specimens in general is described. Procedures for improving the contrast in images of biological molecules are described, including the new method of spot-scan imaging. Possible future developments, including high resolution imaging of single particles, are discussed.

Microscopy, Electron↗
PubMed1984

The pleated sheet: an unusual negative-staining method for transmission electron microscopy of biological macromolecules.

A novel method for preparing negatively stained specimens is described which appears to improve the routine resolution of biological structure in direct images obtained by transmission electron microscopy. In the new method, which we term the pleated sheet technique, macromolecules are adsorbed to a carbon film by the Valentine procedure (R. Valentine, B. Shapiro, and E. Stadtman (1968) Biochemistry, 7, 2143-2152), and the film then carefully pleated while in contact with a 1% uranyl formate solution to trap stain within the folds of pleats. A grid is placed on the compressed film, and film plus grid retrieved with a Saran Wrap drum. Subsequent dehydration produces a filmed grid containing negatively stained macromolecules within the folds of pleated regions and positively stained macromolecules in single sheet regions. The effect of sandwiching sample and stain between carbon layers is to produce exceedingly uniform negative staining so that stain contours more accurately and more reproducibly reflect true molecular contours. Electron micrographs of IgG and IgA molecules prepared by these methods are exhibited that permit unambiguous comparison of structure imaged in the electron microscope against known structures solved by single-crystal X-ray diffraction. Correlation is excellent; the smallest resolvable element in micrographs is an immunoglobulin domain, whose molecular weight is 12 000.

Animals↗
PubMed1979

Scanning electron microscopy at macromolecular resolution in low energy mode on biological specimens coated with ultra thin metal films.

In this report, conditions for attaining high resolution in scanning electron microscopy with soft biological specimens are described using the currently available high resolution scanning electron microscopes in emission mode of low energy electrons (secondary and charging electrons). Retinal rod outer segments, red blood cells, intestinal mucosa, and ferritin molecules were all used as biological test specimens. From uncoated specimens a new source of signal, referred to as a discharge signal, can provide a high yield of low energy electrons from an excitation area approximately the size of the beam's cross section. Additionally, under these conditions sufficient topographic contrast can be achieved by applying ultra thin metal coatins. A 0.5 nm thick gold film is found sufficient for generating the total signal, whereas increased coating thickness causes additional topographic background signal. However, a 2.0 nm film is needed for imaging surface details with the present instrument. Ultra thin, even, and grainless tantalum films have been found effective in eliminating the charging artifacts caused by external fields, and the decoration artifacts caused by crystal growth as seen in gold films. To improve, in high magnification work on ultra thin coated specimen, signal-to-noise ratio, methods for obtaining saturation of the signal with discharge electrons are shown. The necessity of confirming the information obtained in SEM by independent techniques (TEM of stereo-replicas or ultra thin sections) is discussed.

Animals↗