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Results for “Biological Resolution”

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At least 163 records · Page 9Linked to original sources
PubMed1999

Resolution of a CPzI precursor, synthesis and biological evaluation of (+) and (-)-N-Boc-CPzI: a further validation of the relationship between chemical solvolytic stability and cytotoxicity.

The chemical resolution, using N-tosyl-L-proline as a chiral auxiliary, of a racemate of the pyrazole analog (+/-)-N-Boc-CPzI of the left hand segment (CPI) of the antitumor agent CC-1065, and the cytotoxic evaluation of both enantiomers are described. The reported results further validate the direct relationship between chemical solvolytic stability of the cyclopropane ring and cytotoxicity proposed by Boger and coworkers.

Animals↗
PubMed1978

Radiation damage relative to transmission electron microscopy of biological specimens at low temperature: a review.

When biological specimens are irradiated by the electron beam in the electron microscope, the specimen structure is damaged as a result of molecular excitation, ionization, and subsequent chemical reactions. The radiation damage that occurs in the normal process of electron microscopy is known to present severe limitations for imaging high resolution detail in biological specimens. The question of radiation damage at low temperatures has therefore been investigated with the view in mind of reducing somewhat the rate at which damage occurs. The radiation damage protection found for small molecule (anhydrous) organic compounds is generally rather limited or even non-existent. However, large molecular, hydrated materials show as much as a 10-fold reduction at low temperature in the rate at which radiation damage occurs, relative to the damage rate at room temperature. In the case of hydrated specimens, therefore, low temperature electron microscopy offers an important advantage as part of the overall effort required in obtaining high resolution images of complex biological structures.

Catalase↗
PubMed1976

Identification of biological molecules in situ at high resolution via the fluorescence excited by a scanning electron beam.

Proteins, nucleic acids, and fluorescein-conjugated antibody are shown to be identifidable in situ via the fluorescence excited by the focused electron beam of a canning electron microscope. A molecular species is identified by its characteristic fluorescence spectrum and by a characteristic alteration of the spectrum with time under the electron beam. Primary protein fluorescence is relatively rapidly destroyed by the beam, but protein photoproduct fluorescence is more rugged and will in some cases permit detection of small numbers of protein molecules. Nucleic acid fluorescence is extremely long-lived and will permit detection of small numbers of nucleic acid residues. The theoretical resolution limit for localization of a particular molecular species -- about 20 A--is determined by the known maximum distance for molecular excitation by fast electrons. Drect extapolation from an observed resolution of 900 A in the localization of nucleic acid using a low-efficiency detector leads to an experimental resolution limit of less than 60 A. Fluorescence is strongly quenched by residual water in the specimen. Similar quenching is produced by some macromolecular associations and so may serve to localize such associations.

Animals↗
PubMed2002

Photoacoustic tomography of biological tissues with high cross-section resolution: reconstruction and experiment.

A modified back-projection approach deduced from an exact reconstruction solution was applied to our photoacoustic tomography of the optical absorption in biological tissues. Pulses from a Ti:sapphire laser (4.7 ns FWHM at 789.2 nm) were employed to generate a distribution of photoacoustic sources in a sample. The sources were detected by a wide-band nonfocused ultrasonic transducer at different positions around the imaging cross section perpendicular to the axis of the laser irradiation. Reconstructed images of phantoms made from chicken breast tissue agreed well with the structures of the samples. The resolution in the imaging cross section was experimentally demonstrated to be better than 60 microm when a 10 MHz transducer (140% bandwidth at -60 dB) was employed, which was nearly diffraction limited by the detectable photoacoustic waves of the highest frequency.

Acoustics↗
PubMed1989

Crystal dissolution of biological and ceramic apatites.

High resolution transmission electron microscopy (Hr TEM) studies on biological and synthetic calcium phosphate have provided information on the dissolution process at the crystal level. The purpose of this study was to investigate the dissolution of ceramic hydroxyapatite (HA) after implantation using Hr TEM. Recovered HA ceramic implanted in bony and nonbony sites in animals and in periodontal pockets in humans were used for the study. For comparison, sections of human fluorotic enamel with caries and sections of shark enameloid previously exposed to 0.1 HCl were similarly investigated. Hr TEM studies demonstrated that in both the biological and ceramic apatites, the lattice and atomic defects were the starting points in the dissolution process. However, significant differences in the process of dissolution were observed: (1) biological apatite crystals showed preferential core dissolution whereas ceramic apatite crystals showed nonspecific dissolution at the cores and at the surfaces; (2) the dissolution of biological apatites appeared to consistently extend along the crystal's c-axis whereas dissolution of the ceramic HA did not appear to be correlated with the crystal's c-axis. The observed differences in crystal dissolution between biological and ceramic apatites may be attributed to the following: (1) the unique crystal/protein interaction present with biological apatites but absent in ceramic HA; (2) differences in defect distribution between biological and ceramic apatites which are due to the differences in the original of these defects; and (3) the longer morphological c-axis of biological apatites compared with that of ceramic apatites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Prospects for using an IVEM with a FEG for imaging macromolecules towards atomic resolution.

Specimen preparation and imaging techniques for biological macromolecules have been improved to the point where attention to the electron-optical imaging conditions becomes a significant factor for achieving high resolution. A field emission gun (FEG) can provide an illumination source with a better spatial and temporal coherence suitable for imaging near atomic resolution. Our computational analysis of carbon film images taken between Scherzer focus and 1.1 microns underfocus (20x Scherzer focus) with the Hitachi 200 kV microscope with a cold field emission gun shows detectable contrast beyond 3.5 A resolution. In biological imaging, a large defocus is often used to optimize the low-resolution contrast in order to facilitate the subsequent steps in computer reconstruction. An intermediate-voltage electron microscope (IVEM) would optimize the contrast at high resolution by reducing the temporal coherent effects. In theory, the IVEM would give a greater depth of field so that large macromolecular assemblies such as viruses and cellular structures can be interpreted and reconstructed reliably using the projection approximation. These experimental and theoretical considerations provide a rationale for designing a future IVEM with a FEG suitable for biological macromolecule imaging close to atomic resolution.

Fourier Analysis↗
PubMed2000

Structure determination of biological macromolecules in solution using nuclear magnetic resonance spectroscopy.

A detailed understanding of the function of a biological macromolecule requires knowledge of its three-dimensional structure. Most atomic-resolution structures of biological macromolecules have been solved either by X-ray diffraction in single crystals or by nuclear magnetic resonance (NMR) in solution. This review surveys the method of NMR structure determination. First, a brief introduction to NMR and its basic concepts is presented. The main part of the article deals with the individual steps necessary for an NMR structure determination. At the end, the discussion turns to considerations on the influence of the molecular size of the macromolecules on the structure determination by NMR. New techniques are discussed that greatly enhance the possibilities of applying NMR to large molecular systems.

Humans↗
PubMed1999

Electrostatically balanced subnanometer imaging of biological specimens by atomic force microscope.

To achieve high-resolution topographs of native biological macromolecules in aqueous solution with the atomic force microscope (AFM) interactions between AFM tip and sample need to be considered. Short-range forces produce the submolecular information of high-resolution topographs. In contrast, no significant high-resolution information is provided by the long-range electrostatic double-layer force. However, this force can be adjusted by pH and electrolytes to distribute the force applied to the AFM tip over a large sample area. As demonstrated on fragile biological samples, adjustment of the electrolyte solution results in a local reduction of both vertical and lateral forces between the AFM tip and proteinous substructures. Under such electrostatically balanced conditions, the deformation of the native protein is minimized and the sample surface can be reproducibly contoured at a lateral resolution of 0.6 nm.

Bacterial Proteins↗
PubMed1983

A high-resolution electron microscope study of synthetic and biological carbonated apatites.

A series of synthetic carbonated apatites and human dental enamels characterized by chemical analysis, infrared spectroscopy, and X-ray diffraction was studied using high-resolution transmission electron microscopy. Steps on the surfaces of apatite crystals, often only a few unit cells high and occasionally one unit cell high, were observed by their Fresnel diffraction contrast. Highly substituted synthetic carbonated apatites appeared to have more irregular and finer-textured surface features than materials with less carbonate substitution. The surface features of enamel apatite crystal were also irregular, but surface steps were less frequently aligned in crystallographic directions. Complex strain fields due to radiation damage centers were observed in some crystals and the fine structure of dislocations and grain boundaries in synthetic apatites was resolved at high magnification. Experimental lattice-image contrasts, in favorable circumstances, could be matched to computer-simulated images and were found to contain detail at near atomic resolution, around 2.0-2.5 A.

Adult↗