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At least 1,207 records · Page 67Linked to original sources
PubMed2004

Double-quantum homonuclear correlation magic angle sample spinning nuclear magnetic resonance spectroscopy of dipolar-coupled quadrupolar nuclei.

A double-quantum homonuclear correlation nuclear magnetic resonance experiment for dipolar-coupled half-integer quadrupolar nuclei in solids is presented. The experiment is based on rotary resonance dipolar recoupling and uses bracketed spin-lock pulses to excite double-quantum coherence and later to convert it to the zero-quantum one. A central-transition-selective pi pulse at the beginning of the t1 evolution period differentiates coherence transfer pathways of double-quantum coherences arising from coupled spins and from a single spin, so that the latter can be efficiently filtered out by phase cycling. The experiment was tested on an aluminophosphate molecular sieve AlPO4-14, a material with a variety of aluminum quadrupolar coupling constants, isotropic chemical shifts and homonuclear distances. In a two-dimensional spectrum aluminum dipolar couplings with internuclear distances between 2.9 and 5.5 A were resolved. Although the experiment requires an application of weak radio-frequency fields, frequency offsets did not affect its performance crucially.

Journal Article↗
PubMed1976

The magic number 4 +/- 0: a new look at visual numerosity judgements.

Visual numerosity judgements were made for tachistoscopically presented linear arrays of dots or lines. The interelement interval (which could be specified in spatial frequency terms) was constant for a given array but varied across conditions. A clear limit in the accuracy of numerosity judgements was found to be set at 4 for regularly spaced elements with spatial frequencies below approximately 10 cycles/deg (element and interelement interval of 0-05 deg). This limit in terms of accuracy is accompanied by a fast and almost constant response time for arrays of 4 or less, compared to response times for arrays of more than 4 elements. The limit in accuracy falls to 2 elements rather than 4 for spacing narrower than 0-05 deg alghough with such spacing the elements are still easily resolved. The limit of 4 is found if the stimulus is a bright afterimage, lasting for approximately 60 s. This result suggests that the limit is independent of the time allowed for a single fixation and is a perceptual limit rather than a limit in some memory buffer. 'Numerosity' units are propsoed to account for the results.

Humans↗
PubMed1990

The magic wand: a new stereokinetic anomalous surface.

When a disc with two dots stuck on it a few centimetres apart is set in slow rotatory motion, the two dots appear displaced in depth and rigidly connected to form the two extremities of a rod. The rod appears as a diaphanous transparent object, slightly tinted to the same colour as the dots. Experimental analysis of the phenomenon shows that it is different from previously observed 'moving phantoms', 'motion-induced contours', and 'stereokinetic induced phantoms'. But it shows similarities with all three phenomena: the colour spreading along the apparent rod is facilitated by low illumination and is clearly visible under high illumination with bright colours only; it is seen only when the two dots appear to move with apparent displacement in depth and not when they appear to lie on the plane of the disc. When line-drawn circles instead of full colour dots are used, the anomalous surface of the rod appears to have colourless vitreous transparency. With half-line circles it is clearly visible as an opaque rod of the same colour as the background. When squares or diamonds are used instead of dots, a three-dimensional prism can be observed which has similar appearance to the rod.

Adult↗
PubMed2002

De novo determination of peptide structure with solid-state magic-angle spinning NMR spectroscopy.

The three-dimensional structure of the chemotactic peptide N-formyl-l-Met-l-Leu-l-Phe-OH was determined by using solid-state NMR (SSNMR). The set of SSNMR data consisted of 16 (13)C-(15)N distances and 18 torsion angle constraints (on 10 angles), recorded from uniformly (13)C,(15)N- and (15)N-labeled samples. The peptide's structure was calculated by means of simulated annealing and a newly developed protocol that ensures that all of conformational space, consistent with the structural constraints, is searched completely. The result is a high-quality structure of a molecule that has thus far not been amenable to single-crystal diffraction studies. The extensions of the SSNMR techniques and computational methods to larger systems appear promising.

N-Formylmethionine Leucyl-Phenylalanine↗
PubMed1999

The magical touch: genome targeting in epidermal stem cells induced by tamoxifen application to mouse skin.

Gene knockout technology has provided a powerful tool for functional analyses of genes expressed preferentially in a particular tissue. Given marked similarities between human and mouse skin, such studies with epidermally expressed genes have often provided valuable insights into human genetic skin disorders. Efficient silencing of a specified gene in a temporally regulated and epidermal-specific fashion could extend functional analyses to broadly expressed genes and increase the categories of human skin disorders to which parallels could be drawn. We have generated transgenic mice expressing Cre and a fusion protein between Cre recombinase and the tamoxifen responsive hormone-binding domain of the estrogen receptor (CreER(tam)) under the control of the human keratin 14 (K14) promoter. This promoter is strongly active in dividing cells of epidermis and some other stratified squamous epithelia. With K14-Cre, transgenic embryos recombine genetically introduced loxP sequences efficiently and selectively in the genomes of keratinocytes that reside in embryonic day 14.5 skin, tongue, and esophagus. With K14-CreER(tam), postnatal transgenic mice show no Cre activity until tamoxifen is administered. If orally administered, tamoxifen activates keratinocyte-specific CreER(tam), allowing recombination of loxP sequences in epidermis, tongue, and esophagus. If topically administered, tamoxifen allows recombination in the area of skin where tamoxifen was applied. Finally, we show that epidermal cells harboring a Cre-dependent rearranged genome persist for many months after tamoxifen application, indicating that the epidermal stem cell population has been targeted efficiently. These tools now pave the way for testing the functional role of different somatic mutations that may exist in mosaic disorders of the skin, including squamous and basal cell carcinomas.

Animals↗
PubMed2001

Epitope diversity of N-glycans from bovine peripheral myelin glycoprotein P0 revealed by mass spectrometry and nano probe magic angle spinning 1H NMR spectroscopy.

The carbohydrate structures present on the glycoproteins in the central and peripheral nerve systems are essential in many cell adhesion processes. The P0 glycoprotein, expressed by myelinating Schwann cells, plays an important role during the formation and maintenance of myelin, and it is the most abundant constituent of myelin. Using monoclonal antibodies, the homophilic binding of the P0 glycoprotein was shown to be mediated via the human natural keller cell (HNK)-1 epitope (3-O-SO(3)H-GlcUA(beta1-3)Gal(beta1-4)GlcNAc) present on the N-glycans. We recently described the structure of the N-glycan carrying the HNK-1 epitope, present on bovine peripheral myelin P0 (Voshol, H., van Zuylen, C. W. E. M., Orberger, G., Vliegenthart, J. F. G., and Schachner, M. (1996) J. Biol. Chem. 271, 22957-22960). In this study, we report on the structural characterization of the detectable glycoforms, present on the single N-glycosylation site, using state-of-the-art NMR and mass spectrometry techniques. Even though all structures belong to the hybrid- or biantennary complex-type structures, the variety of epitopes is remarkable. In addition to the 3-O-sulfate present on the HNK-1-carrying structures, most of the glycans contain a 6-O-sulfated N-acetylglucosamine residue. This indicates the activity of a 6-O-sulfo-GlcNAc-transferase, which has not been described before in peripheral nervous tissue. The presence of the disialo-, galactosyl-, and 6-O-sulfosialyl-Lewis X epitopes provides evidence for glycosyltransferase activities not detected until now. The finding of such an epitope diversity triggers questions related to their function and whether events, previously attributed merely to the HNK-1 epitope, could be mediated by the structures described here.

Animals↗
PubMed1966

Magic mountains.

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Hospitals, Chronic Disease↗