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At least 19 recordsLinked to original sources
PubMed1977

Method for obtaining a high resolution protein map starting from a low resolution map.

A method is described for estimating the phases of high resolution single-crystal diffraction data from proteins, by using as a starting point a set of low resolution phases (about 3 A) derived by multiple isomorphous replacement (or other) methods. The method consists in refining by least-squares the positions and thermal parameters of a set of dummy atoms placed in the initial low resolution electron density map, so as to minimize the discrepancy between the calculated scattering intensities and the scattering intensities observed in the high resolution data set. Phases calculated from these refined atomic positions are used to extend the resolution and to improve the quality of the electron density map. The success of the method depends on a new least-squares algorithm that has a radius of convergence of about 0.75 A. This large radius of convergence, together with the severe restrictions placed on the initial positions of the dummy atoms by the requirement that they lie within limited regions of the isomorphous electron density map, and the constraint imposed by the polymeric nature of a polypeptide chain account for the success of the method. The method has been successfully used to phase the structure factors of 2-zinc insulin at a resolution of 2 A and 1.5 A, starting from a set of isomorphous phases at 3-A resolution.

Insulin↗
PubMedDate not supplied

Scatter, spatial resolution, and quantitative recovery in high resolution SPECT.

The potential use of single photon emission CT (SPECT) for quantification depends on its physical performance characteristics. We investigated the performance of a high resolution four-head brain SPECT scanner (Neuro-Spect; Summit/Hitachi). With an attenuation coefficient of 0.11 cm-1 and the Chang correction method, the calibration factor of the scanner was 515 (cpm/ml)/(microCi/ml) and showed only a minimal but systematic dependence on object size. Without scatter, the resolution was 4.7 mm (full width at half-maximum); in a scatter medium, the resolution was 5.3-10.0 mm with high resolution collimation and 7.7-18.8 mm with general purpose collimation, depending on filtering. A recovery coefficient of close to 100% was measured in the center of spheres with a size of at least 20 mm placed in a cylindrical water-filled phantom. In lesions of this size, scatter was 20%. We conclude from our measurements that the investigated high resolution SPECT offers significant improvements in resolution, scatter, and recovery, which will improve both the quality of brain studies and the measurement of quantitative parameters such as the cortex/white matter ratio.

Brain↗
PubMed2026

Advanced High-Resolution and Super-Resolution Microscopy Techniques for Investigating Chromatin Structure and Epigenetics.

Fluorescence microscopy has emerged as an indispensable tool for investigating chromatin structure and epigenetic states. This technique not only enables super-resolution imaging to unveil detailed localizations and structures but also offers precise quantitative capabilities for comparing variations across multiple conditions. In this chapter, we present a comprehensive guide to immunofluorescence methods, detailing two primary fixation protocols. Additionally, we describe the application of super-resolution spinning disc microscopy, emphasizing its utility in detecting nuclear and epigenetic markers.

Chromatin↗
PubMed1975

Gas chromatographic resolution of enantiomeric amphetamines and related amines. II. Effects of cyclic structures on diastereomer and enantiomer resolution.

Proline and other cyclic amino acids were used as acylated acid chlorides for the resolution of enantiomers of amphentamine and related amines as diastereomers by gas chromatography. Variation of ring size or incorporation of a heteroatom into the ring of the cyclic resolving agent changed retention times and separation factors, depending on the racemic amine derivatized. Separations were achieved on a short, packed Carbowax 20M column. Because N-trifluoroacetyl L-prolyl chloride has proved especially effective for derivatization of amine enantiomers to give diastereomers which often may be resolved by gas chromatography, the proline ring was incorporated into a new optically active stationary phase. For the enantiomeric derivatives examined, the new proline ester phase gave separations essentially equivalent to those obtained on the commercially available phase, carbonyl bis-(L-valine isopropyl ester). The fact that resolution was achieved on the new phase is evidence that, as has been previously suggested, the ester carbonyls of this type of phase are the significant sites of interaction with the antipodes undergoing separation.

Acylation↗
PubMedDate not supplied

Application of real-time mass spectrometric techniques to environmental organic geochemistry. I. Computerized high resolution mass spectrometry and gas chromatography-low resolution mass spectrometry.

LOGOS (Smith et al. 1971), an integrated mass spectrometer/computer system, has been employed in a series of experiments which illustrate the utility of the automated techniques of real-time mass spectrometry in the study of organic compounds in the environment. These techniques are shown to be particularly useful in resolving complex mixtures of organic compounds encountered in environmental studies. Complete high resolution mass spectrometry, particularly when used in conjunction with combined gas chromatography/mass spectrometry, and auxiliary techniques such as stable isotopic labeling are described to illustrate the type and scope of information that may be obtained. Illustrative samples include extracts of air- and waterborne particulates, extracts of water-soluble organic material, and a DDT metabolite from sewage sludge.

Air↗
PubMed1989

[Application of Pirkle-type chiral column to the resolution of enantiomeric drugs: resolution and identification of alpha-naphthyl isocyanate derivatives of alprenolol and some other beta-blockers].

alpha-Naphthyl isocyanate (NI) as a derivatizing agent to separate several beta-blockers was described. This procedure is simple, rapid and gives good resolution. Experiments with NI derivatives of alprenolol showed that the isocyanate group reacted with the amino group on the analyte to form urea under mild conditions and with the hydroxyl group to form carbamate under relatively vigorous conditions. The results also indicated that the derivatized reactions is 1:1 between NT and analytes.

Adrenergic beta-Antagonists↗
PubMed1990

Enantiomer resolution by using capillary zone electrophoresis: resolution of racemic tryptophan and determination of the enantiomer composition of commercial pharmaceutical epinephrine.

The enantiomers of D- and L-tryptophan were separated by capillary electrophoresis, using alpha-cyclodextrin as a chiral active component in the background electrolyte. The separation of (-) and (+) epinephrine was achieved by supplementing the background electrolyte with Heptakis (2,6-di-O-methyl-beta-cyclodextrin). As a practical application of the method, the quantitative analysis of (-) and (+) enantiomers in commercial pharmaceutical solutions of adrenaline is shown.

Cyclodextrins↗
PubMed1979

Psychophysical frequency resolution in the cat as determined by simultaneous masking and its relation to auditory-nerve resolution.

Critical bandwidths were measured behaviorally at 1 and 2 kHz by simultaneous masking in four cats. Three methods were used. They were (i) the masking of a tone by noise of variable bandwidth, (ii) the masking of a narrow-band signal by two tones, and (iii) the masking of a tone by noise of rippled spectrum. The three methods agreed closely and gave a mean critical bandwidth of 410 Hz at 1 kHz and 690 Hz at 2 kHz. These values were about three times as great as the electrophysiologically-determined effective bandwidths of single fibers of the auditory nerve at the same frequencies, both as measured in other animals, and in one of the animals that had been tested behaviorally as well. Psychophysical tuning curves were also determined behaviorally; in contrast, they agreed closely with auditory-nerve fibers in both bandwidth and slope. The results suggest that the critical band as measured by simultaneous masking is not a close relation of the frequency-threshold curve of auditory-nerve fibers, but that the psychophysical tuning curve possibly may be. Possible reasons and implications are discussed.

Animals↗
PubMed1992

Sensitivity, resolution and image quality with a multi-head SPECT camera.

This investigation sought to determine which collimation factors were most important in providing superior image quality with a three-headed SPECT device. The relationship between sensitivity, resolution and SPECT image quality was studied. Two different sets of parallel-hole collimators were used. The ultrahigh-resolution collimators have higher spatial resolution (8.9 versus 11.0 mm), but only 55% of the sensitivity of the high-resolution collimators. A phantom with hot rods was imaged with both collimator sets. Observers compared images with the ultrahigh-resolution collimators to images of varying counts with the high-resolution collimators and determined which high-resolution images matched the ultrahigh-resolution images in image quality. Eleven patient studies were acquired with both collimator sets for equal time, and observers chose which image set they preferred. Transverse images of brain and liver studies were simulated with varying resolution and counts and subjectively compared. The phantom study indicated that the improvement in resolution led to image quality comparable to increasing the number of counts by a factor of 2.5 to 3.4. The clinical studies showed that the ultrahigh-resolution collimators were preferred in a large majority of the cases. These trends were also seen in the simulation study. These results confirm that higher resolution collimators should be used with multihead SPECT devices. The improvement in resolution more than compensates for the loss in sensitivity, leading to an overall improvement in image quality.

Brain↗
PubMed1991

Optimization of resolution in capillary zone electrophoresis: combined effect of applied voltage and buffer concentration.

Expressions are formulated for the prediction of solute migration time and resolution as a function applied voltage and buffer concentration in capillary zone electrophoresis. The resolution equation assumes that solute diffusion is the only operative zone-broadening mechanism. A resolution surface in applied voltage and buffer concentration space is presented featuring isochrones that are used to predict the behavior of resolution under constant analysis time. In the resolution-voltage planes the resolution increases continuously with increasing voltage. At the high-voltage border, the resolution decreases continuously with increasing concentration, however, at the low-voltage border the resolution passes through a shallow maximum as the buffer concentration is increased. At constant analysis time, resolution is optimized by simultaneously increasing the voltage and the buffer concentration. In comparison, this theoretical approach, which predicts resolution from solute migration times only, gives values that are consistently about 40-50% higher than experimentally determined resolution.

Acetates↗
PubMedDate not supplied

Contrast, resolution, and detectability in MR imaging.

With the introduction of fast scan techniques and high field imagers, the ability to achieve very high resolution MR images in reasonable imaging times is now possible. Increased resolution allows for better detection of small, high contrast pathological features, but at some cost. Increasing resolution leads to a nonrecoverable decrease in signal-to-noise ratio per pixel and a loss of low contrast detectability for constant imaging time. This article examines the tradeoffs between image resolution, signal-to-noise ratio, and low contrast detectability in MR imaging. Contrast detail curves are presented for images collected in a constant imaging time, with constant field of view and bandwidth but at different resolutions, and these are compared with theoretical curves. The problem of measuring contrast levels in magnitude images, with different resolutions and receiver attenuation values, is discussed and a definition that accommodates these parameters developed. In addition, a clinical example is shown demonstrating a decrease in soft tissue differentiation with increasing resolution, again for fixed imaging time. The results indicate that moving to high resolution imaging matrices requires consideration be given to the sacrifice in low contrast detectability that occurs. Most importantly, it is shown that filtering a high resolution image to a lower resolution image, through nearest neighbor averaging, does not regain the detectability lost in initially collecting the high resolution image.

Brain↗