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J M Barr

Publications and source records attributed to J M Barr.

8 recordsLinked to original sources
PubMed2002

Influence of a ring substituent on the tendency to form H(2)O adducts to Ag(+) complexes with phenylalanine analogues in an ion trap mass spectrometer.

In a previous report we showed that certain binary Ag(+)-amino acid complexes formed adduct ions by the attachment of a single water and methanol molecule when stored in an ion trap mass spectrometer: complexes with aliphatic amino acids and with 4-fluorophenylalanine formed the adduct ions whereas complexes with phenylalanine and tryptophan did not. In this study we compared the tendency of the Ag(+) complexes derived from phenylalanine, 4-fluorophenylalanine, 4-hydroxyphenylalanine (tyrosine), 4-bromophenylalanine, 4-nitrophenylalanine and aminocyclohexanepropionic acid to form water adducts when stored, without further activation, in the ion trap for times ranging from 1 to 500 ms. Because the donation of pi electron density to the Ag(+) ion is a likely determining factor in complex reactivity, our aim in the present study was to determine qualitatively the influence of para-position substituents on the aromatic ring on the formation of the water adducts. Our results show that the reactivity of the complexes is influenced significantly by the presence of the various substituents. Decreases in [M + Ag](+) ion abundance, and increases in adduct ion abundance, both measured as a function of storage time, follow the trend -NO(2) > -Br > -F > -OH > -H. The complex of Ag(+) with 4-nitrophenylalanine was nearly as reactive towards water as the Ag(+) complex with aminocyclohexanepropionic acid, the last being an amino acid devoid of pi character in the ring system. Collision induced dissociation of the [M + Ag](+) species derived from the amino acids produces, among other products, Ag(+) complexes with a para-substituted phenylacetaldehyde: complexes that also form adduct species when stored in the ion trap. The trends in adduct ion formation exhibited by the aldehyde-Ag(+) complex ions were similar to those observed for the precursor complexes of Ag(+) and the amino acids, confirming the influence of the ring substituent.

Cations, Divalent↗
PubMed2002

Formation of [b(n) + 17 + Ag]+ product ions from Ag+ cationized native and acetylated peptides.

We compared the tandem mass spectra of a range of native and acetylated Ag(+) cationized peptides to determine the influence of the derivatization step on the abundance of the [b(n) + 17 + Ag](+) product ions. Using tripeptides, the smallest for which the mechanisms to generate [b(2) - 1 + Ag](+) and [b(2) + 17 + Ag](+) products are both operative, we found that in most cases acetylation causes an increase in the abundance of the C-terminal rearrangement ion, [b(2) + 17 + Ag](+), relative to the rival N-terminal rearrangement ion, [b(2) - 1 + Ag](+). The presence of a free amino group to bind to the metal ion significantly influences the relative abundances of the product ions. We propose a mechanism for the formation of the [b(n) + 17 + Ag](+) that is based on the formation of a five-membered oxazolidin-5-one and tetrahedral carbon intermediate that may collapse to a peptide upon release of CO and an imine, aided by the fact that the ring formed during C-terminal rearrangement is both a hemiacylal and hemiaminal. We also identified an influence of amino acid sequence on the relative abundances of the [b(n) + 17 + Ag](+) and [b(n) - 1 + Ag](+) product ions, whereby bulky substituents located on the alpha-carbon of the amino acid to the C-terminal side of the cleavage site apparently promote the formation of the [b(n) + 17 + Ag](+) product over [b(n) - 1 + Ag](+) when the amino acid to the N-terminal side of the cleavage site is glycine. The latter ion is the favored product, however, when the bulky group is positioned on the alpha-carbon of the amino acid to the N-terminal side of the cleavage site.

Journal Article↗
PubMed2002

Multi-stage tandem mass spectrometry of metal cationized leucine enkephalin and leucine enkephalin amide.

We have examined the multi-stage collision induced dissociation (CID) of metal cationized leucine enkephalin, leucine enkephalin amide, and the N-acetylated versions of the peptides using ion trap mass spectrometry. In accord with earlier studies, the most prominent species observed during the multi-stage CID of alkali metal cationized leucine enkephalin are the [b(n) + 17 + Cat]+ ions. At higher CID stages (i.e. >MS(4)), however, dissociation of the [b2 + 17 + Cat]+ ion, a cationized dipeptide, results in the production of [a(n) -1 + Cat]+ species. The multi-stage CID of Ag+ cationized leucine enkephalin can be initiated with either the [b(n) -1 + Ag]+ or [b(n) + 17 + Ag]+ ions produced at the MS/MS stage. For the former, sequential CID stages cause, in general, the loss of CO, and then the loss of the imine of the C-terminal amino acid, to reveal the amino acid sequence. Similar to the alkali cationized species, CID of [b2 -1 + Ag]+ produces prominent [a(n) -1 + Ag]+ ions. The multi-stage CID of argentinated peptides is reminiscent of fragmentation observed for protonated peptides, in that a series of (b(n)) and (a(n)) type ions are generated in sequential CID stages. The Ag+ cation is similar to the alkali metals, however, in that the [b(n) + 17 + Ag]+ product is produced at the MS/MS and MS3 stages, and that sequential CID stages cause the elimination of amino acid residues primarily from the C-terminus. We found that N-acetylation of the peptide significantly influenced the fragmentation pathways observed, in particular by promoting the formation of more easily interpreted (in the context of unambiguous sequence determination) dissociation spectra from the [b2 + 17 + Li]+, [b2 + 17 + Na]+ and [b2 -1 + Ag]+ precursor ions. Our results suggest, therefore, that N-acetylation may improve the efficacy of multi-stage CID experiments for C-terminal peptide sequencing in the gas phase. For leucine enkephalin amide, only the multi-stage CID of the argentinated peptide allowed the complete amino acid sequence to be determined from the C-terminal side.

Cations↗
PubMed1978

Inflammatory linear verrucose epidermal nevus.

We treated three patients with inflammatory linear verrucose epidermal nevus. The lesions were either verrucose or psoriasiform and all had an inflammatory component. Histologic features included psoriasiform acanthosis with spongiosis and parakeratosis. Features that distinguish this entity and the differential diagnoses are discussed.

Adult↗
PubMedDate not supplied

Understanding pediatric intestinal pseudo-obstruction: implications for nurses.

Pseudo-obstruction is actually a group of disorders resulting in bowel dysmotility in the absence of anatomic obstruction. Because of varied pathologic abnormalities of the GI tract involved in the disorder, pseudo-obstruction has been reported in the literature under different names, including hypoganglionosis, chronic adynamic ileus, pseudo-Hirschprung's disease, visceral neuropathy, visceral myopathy, and megacystis-microcolon-intestinal hypoperistalsis syndrome. Although a rare condition, its effects are severe, disabling, and life-threatening in pediatric clients. Prognosis is inversely correlated with age and is especially poor in those children with symptoms as newborns. Management involves promoting nutrition adequate for growth, treating symptoms, and preventing complications. Total parenteral nutrition is almost always required, and its long-term use is associated with chronic cholestasis and potential hepatic failure. Nurses may encounter pediatric clients with this disorder and their families in many different healthcare arenas, such as in radiology departments, ambulatory care, and acute and home care settings. The purpose of this article is to review current literature on this disease and summarize information useful to nurses.

Child↗
PubMedDate not supplied

Chronic intestinal pseudo-obstruction: pediatric case presentations and review of the literature.

ISSUES AND PURPOSE: Chronic intestinal pseudo-obstruction (CIP) is a rare condition characterized by small bowel dysmotility. Its effects are severe and disabling in pediatric clients. The purpose of this article is to provide an overview of CIP and summarize information useful to pediatric nurses. CONCLUSION: Nursing management of the pediatric client with CIP is challenging, not only in terms of direct care provided to the child, but also in ongoing support and education of the child and family. PRACTICE IMPLICATIONS: Nurses practicing in either inpatient or outpatient settings may encounter children and families dealing with this disorder. Nurses are in a key position to educate others and influence the outcomes of care provided to children with CIP and their families.

Child, Preschool↗