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R S Brown

Publications and source records attributed to R S Brown.

At least 37 records · Page 2Linked to original sources
PubMed2001

La(3+)-catalyzed methanolysis of phosphate diesters. Remarkable rate acceleration of the methanolysis of diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate.

The interaction of La(3+) with diphenyl phosphate, methyl p-nitrophenyl phosphate, and bis(p-nitrophenyl) phosphate (4, 5, and 3) and the ensuing catalysis of methanolysis has been studied in methanol under completely homogeneous conditions of known pH. (31)P NMR shows that phosphates 3 and 4 are each associated with La(3+) as a rapidly interconverting mixture of complexes having 2:1, 1:1 (or 2:2), and 1:2 stoichiometry. At [La(3+)] > 2 x 10(-4) M, the kinetically dominant species in the pH regions of interest are phosphate-bound La(3+) dimers having 2-5 associated methoxides. Potentiometric titration reveals that 4 mM La(3+) alone in MeOH exhibits two apparent pK(a)s at 7.86 and 10.44 consuming 1 and 1.5 CH(3)O(-) per metal, the suggested structures being La(3+) dimers with first two and then five associated methoxides. In the presence of 0.5 equiv of 4 the potentiometric titration reveals strong complexation of 4 to La(3+) and a profile with apparent pK(a)s at 7.8 and 11.1 consuming 1 and 1.5 CH(3)O(-) per metal corresponding to phosphate-bridged La(3+) dimers with first two and then five associated methoxides. Methanolysis of 3-5 is strongly accelerated by La(3+). At pH 8.9 or 11.1, respectively, as little as 5 x 10(-4) M La(OTf)(3) accelerates the methanolysis of 3 or 4 by 10(10)-fold relative to the background reaction. Detailed kinetic studies of the methanolysis of 5 at varying [La(3+)] and pH indicate that both La(3+) monomers and dimers with associated methoxides are reactive species. The rate constants for La(3+) monomer and dimer catalysis of the methanolysis of 5 are dependent on pH, the slopes of the log plots being 0.35 and 0.5, respectively. A scheme is proposed to account for the non-first-order dependence on [CH(3)O(-)] wherein the La(3+)(CH(3)O(-))(x) + 5 <--> La(3+)(CH(3)O(-))(x):5 and (La(3+))(2)(CH(3)O(-))(y) + 5 <--> 5:(La(3+))(2)(CH(3)O(-))(y) equilibria are driven to the left with increasing numbers of associated methoxides and that attack on these complexes, whether by external or metal-associated methoxide, is slower due to the reduced net positive charge on the complex.

Journal Article↗
PubMed2001

Catalysis of the methanolysis of activated amides by divalent and trivalent metal ions. The effect of Zn(2+), Co(2+), and La(3+) on the methanolysis of acetylimidazole and its (NH(3))(5)Co(III) complex.

The metal ions Zn(2+), Co(2+), and La(3+) strongly catalyze the methanolysis of the activated amides acetylimidazole (1) and its ligand-exchange-inert Co(III) complex, (NH(3))(5)Co(III)-AcIm (2). Studies of the kinetics of methanolysis are performed with pH measurement and control, and the metal ions are soluble in the medium throughout the pH regions where ionization of the M(x+)(CH(3)OH)(y) occurs. Zn(2+) and Co(2+) act as Lewis acids toward 1, catalyzing attack of external methoxide on a 1:M(2+) complex at values only 100-fold lower than the diffusion limit, the k(OR) values being 5.6 x 10(7) M(-1) s(-1) and 2.5 x 10(7) M(-1) s(-1), while that for CH(3)O(-) attack on 2 is 4.69 x 10(7) M(-1) s(-1). Since neither Zn(2+) nor Co(2+) promotes the methanolysis of 2, these metals appear to be acting through transient binding to the distal N of 1, which activates the C=O of the complex to external CH(3)O(-) attack. La(3+) catalyzes the methanolysis of both 1 and 2, which occurs by a mechanism that is fundamentally different from that exhibited by Zn(2+) and Co(2+) in that the active species appears to be a bis-methoxy-bridged dimer (La(3+))(2)(CH(3)O(-))(2)(CH(3)OH)(x)() that interacts directly with the C=O unit of the substrate.

Amides↗
PubMed2001

Should patients with chronic hepatitis C who have normal ALT levels be treated?

Up to 25% of patients with chronic hepatitis C have persistently normal serum alanine aminotransferase (ALT) levels. Reports from some studies indicate that patients with normal ALT levels are more likely to be female and nondrinkers. Patients with persistently normal aminotransferase levels often have mild disease on liver biopsy with little or no fibrosis, but a small number of patients may have substantial fibrosis or cirrhosis. Treatment with interferon monotherapy has been disappointing. Combination therapy with interferon and ribavirin is controversial, but early clinical results have shown good response rates. Currently, therapy for chronic HCV patients with normal ALT levels should be based upon results from liver biopsy and preferably be done in the context of a clinical trial.

Alanine Transaminase↗
PubMed2001

Trends in testicular carcinoma in England and Wales, 1971-99.

OBJECTIVES: To examine incidence, mortality and survival trends in England and Wales for testicular cancer, using the recently developed national cancer and national mortality databases. METHODS: The directly age-standardized incidence rates for testicular cancer in England and Wales were calculated for the period 1971-97 and age-standardized mortality for years 1971-99. Trends in the data were then assessed, including the influence of social deprivation on testicular cancer incidence and survival. RESULTS: The number of newly diagnosed cases of testicular carcinoma in 1971-97 in England and Wales increased from almost 650 to 1400. The age-standardized rates were 2.9 per 100000 cases in 1971 and 5.4 per 100000 in 1997, an increase of 88% over 26 years. There was a large decrease in mortality since the mid-1970s, with an age-standardized mortality of < 0.5 per 100000 since 1985. For men with testicular carcinoma diagnosed in 1991-93, the 1-year relative survival was almost 98% and 5-year relative survival almost 95%, compared with 82% and 69%, respectively, for men diagnosed during 1971-75. There is a 'deprivation gap' for the 5-year survival of > 6% in favour of the most affluent socio-economic group, with no significant change over recent years. CONCLUSIONS: The incidence of testicular cancer is increasing in England and Wales, consistent with the trend documented in other developed countries. The reduction in mortality has been marked since the mid-1970s, reflecting improved cancer management, in particular the introduction of platinum-based chemotherapy regimens for advanced disease. Survival rates in England and Wales are as good as in other European countries. Further developments in chemotherapy are unlikely to produce such a marked improvement in survival rates again, and minimizing the effect of social status on survival rates should be an important target of future care.

Adolescent↗
PubMed2001

Current trends in colorectal cancer: site, incidence, mortality and survival in England and Wales.

The objective was to examine trends in colorectal cancer (CRC) incidence and mortality in England and Wales over the last 30 years. Age-standardized incidence, mortality and survival rates for CRC, based on data from the National Cancer Intelligence Centre at the Office for National Statistics, were calculated and trends assessed. Between 1971 and 1997 the total number of cases of CRC increased by 42%, from 20,400 to 28,900. The site distribution of CRC between 1971 and 1994 was: rectum 38%, sigmoid 29%, caecum 15%, transverse colon and flexures 10%, ascending colon 5%, and descending colon 3%. Between 1971 and 1997 the direct age-standardized incidence increased by 20% in males and by 5% in females. The direct age-standardized mortality fell by 24% in males and by 37% in females. Age-standardized relative 5-year survival in adults improved from 22%-27% for patients diagnosed during 1971-1975 to over 40% for those diagnosed during the period 1991-1993. In conclusion, the incidence of CRC in England and Wales has been steadily rising. It is more common in males and has increased more rapidly in males than in females. The reasons for these trends remain unclear. Five-year survival has improved substantially, but rates are still below those in comparable countries elsewhere in Europe and in the USA.

Adolescent↗
PubMed2001

First report of an isolated jejunal seminoma: presentation with melaena and iron deficiency anaemia.

We present the case history of a man with isolated seminoma in the jejunum and abnormal testes but no provable malignant testicular disease. Treatment with cisplatin-based chemotherapy led to complete resolution of the jejunal seminoma. The rarity of seminoma involving the small bowel is highlighted. A literature search did not reveal other similar cases of isolated seminoma affecting the jejunum. The possible origins of this tumour are discussed.

Anemia, Iron-Deficiency↗
PubMed2001

Massive mediastinal seminoma post-orchidectomy--late relapse with skip-metastases or new primary?

A case of a massive, biopsy-proven, advanced seminoma in the mediastinum 12 years after orchidectomy for a malignant right-sided testicular tumour of unknown histology is presented. The highly unusual nature of this presentation is discussed and may represent either late relapse from skip-metastases or metachronous gonadal and extragonadal tumour development. Immunohistochemical staining was unable to distinguish the site of origin of the lesion.

Adult↗
PubMed2001

Function of basonuclin in increasing transcription of the ribosomal RNA genes during mouse oogenesis.

Active protein synthesis during early oogenesis requires accelerated transcription of ribosomal RNA genes (rDNAs). In response to this demand, rDNAs are amplified more than 1000-fold early in Xenopus oogenesis. Here, we report evidence that rDNA is not amplified in mouse oocytes, but these cells may instead employ the zinc-finger protein basonuclin, a putative rDNA transcription factor, to enhance rRNA synthesis. This conclusion is based on observations that basonuclin is localized in the nucleolus in the mouse oocyte early in its growth phase, when rRNA transcription is highly active; and that the binding sites of basonuclin zinc fingers on the human and mouse rDNA promoters are homologous. In a co-transfection assay, basonuclin can elevate transcription from an rDNA promoter, and its zinc-finger domain can inhibit RNA polymerase I transcription, as detected by a run-on assay, in growing mouse oocytes.

Animals↗
PubMed2001

Diabetic neuropathy masquerading as glossodynia.

BACKGROUND: Diabetic neuropathy, or DN, occurs in approximately 50 percent of patients who have type 2 diabetes mellitus, or DM. Oral burning and symptoms consistent with glossodynia (burning mouth syndrome) may occur secondary to DN. CASE DESCRIPTION: A 54-year-old woman reported to a university dental clinic with a chief complaint of oral burning. No clinical signs were evident. Her medical history was positive for type 2 DM. The initial diagnosis was glossodynia, and she was evaluated with relevant blood studies, which indicated that her diabetes was not well-controlled. The patient was referred back to her physician, and her symptoms abated once her diabetic condition was under control. CLINICAL IMPLICATIONS: It is important to consider DN within the differential diagnoses of patients who have symptoms consistent with glossodynia but have no clinical signs. Dentists are invaluable in ascertaining underlying systemic disease considerations in patients with oral symptomatology. Cooperation between dentists and physicians often is helpful and necessary in caring for patients who have uncontrolled type 2 DM and oral symptoms.

Burning Mouth Syndrome↗
PubMed2001

Endoscopic treatment of patients with portal hypertension.

This article discusses endoscopic treatment of patients with sequelae from portal hypertension. The literature on endoscopic therapy for primary and secondary prophylaxis of esophageal varices is reviewed. Therapeutic approaches to less commonly seen entities, such as portal gastropathy and portal colopathy, are discussed.

Endoscopy, Gastrointestinal↗
PubMed2001

Minority dentists.

Explore the source record for details and available documents.

Black or African American↗
PubMed2001

The Microcystis cyanobacteria bloom in the Swan River--February 2000.

In February 2000 the Swan-Canning estuary in Western Australia experienced a record bloom of the toxic cyanobacteria Microcystis aeruginosa. At its height, concentrations of M. aeruginosa reached integrated water column cell counts of 15,000/ml and formed bright green scums in sheltered bays, where counts of 130 million cells/ml were recorded. Due to public health concerns parts of the river were closed from 10 to 22 February 2000. Two unseasonably large summer rain events in early and late January 2000 created conditions for the bloom. Freshwater runoff, estimated at 270 GL, was enough to fill the Swan-Canning estuary five times over and brought with it high levels of nutrients, mainly nitrogen (> 2.0 mg/L TN) and phosphorus (> 0.15 mg/L TP). A number of methods to reduce bloom accumulations were tried, including an attempt to increase the salinity of the surface water above the critical 10 ppt level for Microcystis; using a bentonite clay and poly-aluminium chloride mixture to flocculate and sink the algae; and sucking up scums using oil spill equipment. Over 900 tonnes of M. aeruginosa were removed and safely disposed using sewage treatment facilities. The bloom collapsed when the freshwater flush subsided and seawater intrusion from the Indian Ocean re-established itself, raising the salinities above the tolerance of Microcystis.

Environmental Monitoring↗