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At least 397 records · Page 22Linked to original sources
PubMed1993

Tandem mass spectral decompositions of protonated N-acyloligoalanines and N-acyloligoglycines as models for those of the protonated free oligopeptides.

The intensities of the y-type and b-type ions in the tandem mass spectra of the [M + 1]+ ions of acylated oligomers of alanine and glycine give evidence that these ions are not structurally similar to the [M + 1]+ ions of the free oligomers. For example, the intensities do not follow statistical or linear free energy relationships as would be expected if they were homologous. Instead there are sharp differences in intensities: the y3 ions are considerably more intense than expected, and the b2 ions are less intense. The ions whose intensities differ sharply seem to involve cleavage where the amount of stabilization of a product of cyclization changes when the terminal nitrogen is acylated.

Acylation↗
PubMed1987

Proton relaxation time of immature brain. II. In vivo measurement of proton relaxation time (T1 and T2) in pediatric brain by MRI.

T1 and T2 of brain tissue were measured in vivo in children by means of an NMR imaging system (resistive magnet 0.15 T). The subjects were 47 children aged from 2 weeks to 15 years. The sites measured were the basal ganglia (thalamus, caudate nucleus and putamen), internal capsule, cerebral cortex and white matter. T1 and T2 in the infant cases were prolonged significantly compared with those in the older children. The prolongation in the white matter was particularly remarkable. In infants approximately 1 year of age, T1 of cerebral cortex already showed no significant changes as compared with T1 in cases aged 15 years. On the other hand, T2 was prolonged significantly up to 3 years of age.

Adolescent↗
PubMed2004

Half protons or doubly charged protons? The history of metastable ions.

The history of metastable ions is intertwined with that of ions formed by collision-induced dissociation (CID), and frequently the genesis of the two ion types cannot be strictly separated. Originally, metastable ions were considered a curiosity or even a nuisance, being responsible for "humps" in the base line of the recorded mass spectra. In their heyday metastable ions were recognized as having importance for establishing fragmentation sequences and for distinguishing between isomeric ion structures. Today, in many respects the utility of metastable ions has been superseded by a systematic application of CID techniques; yet the evaluation of their shape is still of importance for questions of reaction energies and ion thermochemistry.

Journal Article↗
PubMed1999

In vivo lactate editing in single voxel proton spectroscopy and proton spectroscopic imaging by homonuclear polarisation transfer.

Volume-selective lactate editing has been performed successfully in vitro and in vivo in the brain on a clinical scanner using a PRESS-based single voxel 1H spectroscopy and a 1H spectroscopic imaging sequence. The PRESS sequence was made sensitive to homonuclear polarisation by replacing the standard 180 degree refocusing pulses with 90 degree pulses. Two acquisitions were made at a total echo time around 2/J (J is the coupling constant for CH and CH3 spins in lactate approximately 7 Hz) whose individual echo times differed by 5.5 ms. Subtraction of one signal from the other yielded the lactate resonance alone. The technique is an effective method of separating the overlapping signals of lactate and lipids. Furthermore this editing method can be performed without state of the art MRI scanner hardware.

Brain↗